Nuclear safety and Nuclear accident

Nuclear safety covers the actions taken to prevent nuclear and radiation accidents or to limit their consequences. This covers nuclear power plants as well as all other nuclear facilities, the transportation of nuclear materials, and the use and storage of nuclear materials for medical, power, industry, and military uses. HP Probook 6545B Battery

The nuclear power industry has improved the safety and performance of reactors, and has proposed new (but generally untested) “inherently” safe reactor designs but there is no guarantee that the reactors will be designed, built and operated correctly.[ HP Probook 6540B Battery

1] Mistakes do occur and the designers of reactors at Fukushima in Japan did not anticipate that a tsunami generated by an earthquake would disable the backup systems that were supposed to stabilize the reactor after the earthquake.[2] Catastrophic scenarios involving terrorist attacks are also conceivable.[1] HP Probook 6445B Battery

Nuclear weapon safety, as well as the safety of military research involving nuclear materials, is generally handled by agencies different from those that oversee civilian safety, for various reasons, including secrecy. HP Probook 6440B Battery

Internationally the International Atomic Energy Agency ”works for the safe, secure and peaceful uses of nuclear science and technology.”[citation needed] Many nations utilizing nuclear power have special institutions overseeing and regulating nuclear safety. HP Probook 4710S/CT Battery

Civilian nuclear safety in the U.S. is regulated by the Nuclear Regulatory Commission (NRC). The safety of nuclear plants and materials controlled by the U.S. government for research, weapons production, and those powering naval vessels is not governed by the NRC.[3][4] HP Probook 4710S Battery

In the UK nuclear safety is regulated by the Nuclear Installations Inspectorate (NII) and the Defence Nuclear Safety Regulator (DNSR). HP Probook 4710S Battery

The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) is the Federal Government body that monitors and identifies solar radiation and nuclear radiation risks in Australia. It is the main body dealing with ionizing and non-ionizing radiation[5] and publishes material regarding radiation protection.[6] HP Probook 4515S Battery

Other agencies include:

Canadian Nuclear Safety Commission

Radiological Protection Institute of Ireland

Federal Atomic Energy Agency in Russia

Kernfysische dienst, (NL)

Pakistan Nuclear Regulatory Authority

Bundesamt für Strahlenschutz, (DE)

Atomic Energy Regulatory Board (India). HP Probook 4515S Battery


Nuclear power plants are some of the most sophisticated and complex energy systems ever designed.[7] Any complex system, no matter how well it is designed and engineered, cannot be deemed failure-proof. Stephanie Cooke has reported that: HP Probook 4510S Battery

The reactors themselves were enormously complex machines with an incalculable number of things that could go wrong. When that happened at Three Mile Island in 1979, another fault line in the nuclear world was exposed. HP Probook 4415S BatteryOne malfunction led to another, and then to a series of others, until the core of the reactor itself began to melt, and even the world’s most highly trained nuclear engineers did not know how to respond. The accident revealed serious deficiencies in a system that was meant to protect public health and safety.[8] HP Probook 4416S Battery

A fundamental issue related to complexity is that nuclear power systems have exceedingly long lifetimes. The timeframe involved from the start of construction of a commercial nuclear power station, through to the safe disposal of its last radioactive waste, may be 100 to 150 years.[7]

See also: Design basis accidentHP Probook 4415S Battery

Failure modes of nuclear power plants

There are concerns that a combination of human and mechanical error at a nuclear facility could result in significant harm to people and the environment:[9] HP Probook 4415S Battery

Operating nuclear reactors contain large amounts of radioactive fission products which, if dispersed, can pose a direct radiation hazard, contaminate soil and vegetation, and be ingested by humans and animals. Human exposure at high enough levels can cause both short-term illness and death and longer-term death by cancer and other diseases.[10] HP EliteBook 8730W Battery

Nuclear reactors can fail in a variety of ways. Should the instability of the nuclear material generate unexpected behavior, it may result in an uncontrolled power excursion. Normally, the cooling system in a reactor is designed to be able to handle the excess heat this causes; however, should the reactor also experience a loss-of-coolant accident, then the fuel may melt or cause the vessel it is contained in to overheat and melt. This event is called a nuclear meltdown. HP EliteBook 8730P Battery

Because the heat generated can be tremendous, immense pressure can build up in the reactor vessel, resulting in a steam explosion, which happened at Chernobyl. However, thereactor design used at Chernobyl was unique in many ways. HP EliteBook 8730P Battery

It utilized a positive void coefficient, meaning a cooling failure caused reactor power to rapidly escalate. All reactors built outside the former Soviet Union have had negative void coefficients, a passively safe design. More importantly though, the Chernobyl plant lacked a containment structure. Western reactors have this structure, which acts to contain radiation in the event of a failure. Containment structures are, by design, some of the strongest structures built by mankind. HP EliteBook 8530P Battery

Intentional cause of such failures may be the result of nuclear terrorism.

Hazards of nuclear material

Nuclear material may be hazardous if not properly handled or disposed of. Experiments of near critical mass-sized pieces of nuclear material can pose a risk of a criticality accident.David Hahn, “The Radioactive Boy Scout” who tried to build a nuclear reactor at home, serves as an excellent example of a nuclear experimenter who failed to develop or follow proper safety protocols. Such failures raise the specter of radioactive contamination. HP EliteBook 6930P Battery

Even when properly contained, fission byproducts which are no longer useful generate radioactive waste, which must be properly disposed of. In addition, material exposed to neutron radiation—present in nuclear reactors—may become radioactive in its own right, or become contaminated with nuclear waste. Additionally, toxic or dangerous chemicals may be used as part of the plant’s operation, which must be properly handled and disposed of. HP EliteBook 2740P Tablet Battery

Vulnerability of nuclear plants to attack

Nuclear power plants are generally (although not always) considered “hard” targets. In the U.S., plants are surrounded by a double row of tall fences which are electronically monitored. The plant grounds are patrolled by a sizeable force of armed guards.[11] The NRC’s “Design Basis Threat” criteria for plants is a secret, and so what size of attacking force the plants are able to protect against is unknown. HP Pavilion DV5Z-1100 Battery

However, to scram (make an emergency shutdown) a plant takes less than 5 seconds while unimpeded restart takes hours, severely hampering a terrorist force in a goal to release radioactivity. HP Pavilion DV5Z Battery

Attack from the air is an issue that has been highlighted since the September 11 attacks in the U.S. However, it was in 1972 when three hijackers took control of a domestic passenger flight along the east coast of the U.S. and threatened to crash the plane into a U.S. nuclear weapons plant in Oak Ridge, Tennessee. The plane got as close as 8,000 feet above the site before the hijackers’ demands were metHP Pavilion DV5Z-1000 Battery

The most important barrier against the release of radioactivity in the event of an aircraft strike on a nuclear power plant is the containment building and its missile shield. HP Pavilion G71 Battery

Current NRC Chairman Dale Klein has said “Nuclear power plants are inherently robust structures that our studies show  provide adequate protection in a hypothetical attack by an airplane. The NRC has also taken actions that require nuclear power plant operators to be able to manage large fires or explosions—no matter what has caused them.”[14] HP Pavilion G71 Battery

In addition, supporters point to large studies carried out by the U.S. Electric Power Research Institute that tested the robustness of both reactor and waste fuel storage and found that they should be able to sustain a terrorist attack comparable to the September 11 terrorist attacks in the U.S. Spent fuel is usually housed inside the plant’s “protected zone”[15HP Pavilion G60 Battery

or aspent nuclear fuel shipping cask; stealing it for use in a "dirty bomb" is extremely difficult. Exposure to the intense radiation would almost certainly quickly incapacitate or kill anyone who attempts to do so.[16] HP Pavilion G50 Battery

In September 2010, analysis of the Stuxnet computer worm suggested that it was designed to sabotage a nuclear power plant. Such a cyber attack would bypass the physical safeguards in place and so the exploit demonstrates an important new vulnerability.[17] HP Pavilion G50 Battery

New nuclear technologies

The next nuclear plants to be built will likely be Generation III or III+ designs, and a few such are already in operation in Japan. Generation IV reactors would have even greater improvements in safety. These new designs are expected to be passively safe or nearly so, and perhaps even inherently safe (as in the PBMR designs). HP Pavilion DV6Z-1100 Battery

Some improvements made (not all in all designs) are having three sets of emergency diesel generators and associated emergency core cooling systems rather than just one pair, having quench tanks (large coolant-filled tanks) above the core that open into it automatically, having a double containment (one containment building inside another), etc. HP Pavilion DV6Z Battery

However, safety risks may be the greatest when nuclear systems are the newest, and operators have less experience with them. HP Pavilion DV6T Battery

Nuclear engineer David Lochbaum explained that almost all serious nuclear accidents occurred with what was at the time the most recent technology. He argues that “the problem with new reactors and accidents is twofold: scenarios arise that are impossible to plan for in simulations; and humans make mistakes”.[1HP Pavilion DV6T Battery

8] As one director of a U.S. research laboratory put it, “fabrication, construction, operation, and maintenance of new reactors will face a steep learning curve: advanced technologies will have a heightened risk of accidents and mistakes. The technology may be proven, but people are not”.[18] HP Pavilion DV7 Battery

Safety culture and human errors

One relatively prevalent notion in discussions of nuclear safety is that of safety culture. The International Nuclear Safety Advisory Group, defines the term as “the personal dedication and accountability of all individuals engaged in any activity which has a bearing on the safety of nuclear power plants”.[19] The goal is “to design systems that use human capabilities in appropriate ways, that protect systems from human frailties, and that protect humans from hazards associated with the system”.[19] HP Pavilion DV5T Battery

At the same time, there is some evidence that operational practices are not easy to change. Operators almost never follow instructions and written procedures exactly, and “the violation of rules appears to be quite rational, given the actual workload and timing constraints under which the operators must do their job”. Many attempts to improve nuclear safety culture “were compensated by people adapting to the change in an unpredicted way”.[19] For this reason, training simulators are used. HP Pavilion DV5 Battery

An assessment conducted by the Commissariat à l’Énergie Atomique (CEA) in France concluded that no amount of technical innovation can eliminate the risk of human-induced errors associated with the operation of nuclear power plants. Two types of mistakes were deemed most serious: errors committed during field operations, such as maintenance and testing, that can cause an accident; and human errors made during small accidents that cascade to complete failure.[18] HP Pavilion DV5 Battery


Historically many scientists and engineers have made decisions on behalf of potentially affected populations about whether a particular level of risk and uncertainty is acceptable for them. Many nuclear engineers and scientists that have made such decisions, HP Pavilion DV5 Batteryeven for good reasons relating to long term energy availability, now consider that doing so without informed consent is wrong, and that nuclear power safety and nuclear technologies should be based fundamentally on morality, rather than purely on technical, economic and business considerations.[20] Sony VAIO PCG-7111L Battery

Nuclear and radiation accidents

2011 Fukushima I accidents

See also: Fukushima I nuclear accidents and Timeline of the Fukushima nuclear accidents

The 40-year-old Fukushima I Nuclear Power Plant, built in the 1970s, endured Japan’s worst earthquake on record in March 2011 but had its power and back-up generators knocked out by a 7-meter tsunami that followed.[ Sony VAIO PCG-7111L Battery

21] The designers of the reactors at Fukushima did not anticipate that a tsunami generated by an earthquake would disable the backup systems that were supposed to stabilize the reactor after the earthquake. Nuclear reactors are such “inherently complex, tightly coupled systems that, in rare, emergency situations, cascading interactions will unfold very rapidly in such a way that human operators will be unable to predict and master them”.[22] Sony VAIO PCG-7Z1L Battery

Lacking electricity to pump water needed to cool the atomic core, engineers vented radioactive steam into the atmosphere to release pressure, leading to a series of explosions that blew out concrete walls around the reactors. Radiation readings spiked around Fukushima as the disaster widened, forcing the evacuation of 200,000 people and causing radiation levels to rise on the outskirts of Tokyo, 135 miles (210 kilometers) to the south, with a population of 30 million.[21] Sony VAIO PCG-7Z1L Battery

Back-up diesel generators that might have averted the disaster were positioned in a basement, where they were overwhelmed by waves. The cascade of events at Fukushima had been foretold in a report published in the U.S. several decades ago:[21] Sony VAIO PCG-7132L Battery

The 1990 report by the U.S. Nuclear Regulatory Commission, an independent agency responsible for safety at the country’s power plants, identified earthquake-induced diesel generator failure and power outage leading to failure of cooling systems as one of the “most likely causes” of nuclear accidents from an external event.[21] Sony VAIO PCG-7113L Battery

While the report was cited in a 2004 statement by Japan’s Nuclear and Industrial Safety Agency, it seems adequate measures to address the risk were not taken by Tokyo Electric.Katsuhiko Ishibashi, a seismology professor at Kobe University, has said that Japan’s history of nuclear accidents stems from an overconfidence in plant engineering. In 2006, he resigned from a government panel on nuclear reactor safety, because the review process was rigged and “unscientific”.[21] Sony VAIO PCG-7112L Battery

The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in theUkrainian SSR (now Ukraine). It is considered the worst nuclear power plant accident in history, and it is the only one classified as a level 7 event on the International Nuclear Event Scale. Sony VAIO PCG-8Z2L Battery

The disaster began during a systems test on 26 April 1986 at reactor number four of the Chernobyl plant, which is near the town of Pripyat. There was a sudden power output surge, and when an emergency shutdown was attempted, a more extreme spike in power output occurred, which led to a reactor vessel rupture and a series of explosions. Sony VAIO PCG-8Z2L Battery

This event exposed the graphite moderator components of the reactor to air, causing them to ignite. The resulting fire sent a plume of radioactive fallout into the atmosphere and over an extensive geographical area, including Pripyat. The plume drifted over large parts of the western Soviet Union, Eastern Europe, Western Europe, and Northern Europe. Large areas in Ukraine, Belarus, and Russia were evacuated, and over 336,000 people were resettled. According to official post-Soviet data,[1][2] about 60% of the fallout landed in Belarus. Sony VAIO PCG-8Y1L Battery

The accident raised concerns about the safety of the Soviet nuclear power industry, as well as nuclear power in general, slowing its expansion for a number of years and forcing the Soviet government to become less secretive about its procedures.[3][notes 1] Sony VAIO PCG-6W1L Battery

Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chernobyl accident. More than fifty deaths are directly attributed to the accident, all among the reactor staff and emergency workers. Estimates of the total number of deaths attributable to the accident vary enormously, from possibly 4,000 to close to a million.[4][5] Sony VAIO PCG-6S2L Battery


On 26 April 1986, at 01:23 (UTC+3), reactor four suffered a catastrophic power increase, leading to explosions in its core. This dispersed large quantities of radioactive fuel and core materials into the atmosphere[6]:73 and ignited the combustible graphite moderator. Sony VAIO PCG-6S1L Battery

The burning graphite moderator increased the emission of radioactive particles, carried by the smoke, as the reactor had not been contained by any kind of hard containment vessel. The accident occurred during an experiment scheduled to test a potential safety emergency core coolingfeature, which took place during the normal shutdown procedure. Sony VAIO PCG-6S1L Battery

The attempted experiment

Even when not actively generating power, nuclear power reactors require cooling, typically provided by coolant flow, to remove decay heat.[7] Pressurized water reactors use water flow at high pressure to remove waste heat. Following an emergency shutdown (scram), the core still generates a significant amount of residual heat, which is initially about seven percent of the total thermal output of the plant. If not removed by coolant systems, the heat could lead to core damage.[8][9] Sony VAIO PCG-6S1L Battery

Following an emergency shutdown, reactor cooling is still required to keep the temperature in the reactor core low enough to avoid fuel damage. The reactor that exploded in Chernobyl consisted of about 1,600 individual fuel channels, and each operational channel required a flow of 28 metric tons (28,000 liters (7,400 USgal)) of water per hour.[ Sony Vaio VGN-FW73JGB Battery

]:7 There had been concerns that in the event of a power grid failure, external power would not have been immediately available to run the plant’s cooling water pumps. Chernobyl’s reactors had three backupdiesel generators. Each generator required 15 seconds to start up but took 60–75 seconds[6]:15 to attain full speed and reach the capacity of 5.5 MW required to run one main cooling water pump.[6]:30Sony Vaio VGN-FW73JGB Battery

This one-minute power gap was considered unacceptable, and it had been suggested that the mechanical energy (rotational momentum) of the steam turbine could be used to generate electricity to run the main cooling water pumps while the turbine was still spinning down. In theory, analyses indicated that this residual momentum had the potential to provide power for 45 seconds,[6]: Sony Vaio VGN-FW73JGB Battery

16 which would bridge the power gap between the onset of the external power failure and the full availability of electric power from the emergency diesel generators. This capability still needed to be confirmed experimentally, and previous tests had ended unsuccessfully. An initial test carried out in 1982 showed that the excitation voltage of the turbine-generator was insufficient; it did not maintain the desired magnetic field during the spin-down. Sony VAIO VGN-FW31M Battery

The system was modified, and the test was repeated in 1984 but again proved unsuccessful. In 1985, the tests were attempted a third time but also yielded negative results. The test procedure was to be repeated again in 1986, and it was scheduled to take place during the maintenance shutdown of Reactor Four.[10] Sony VAIO VGN-FW21M Battery

The test focused on the switching sequences of the electrical supplies for the reactor. The test procedure was to begin with an automatic emergency shutdown (SCRAM). No detrimental effect on the safety of the reactor was anticipated, so the test program was not formally coordinated with either the chief designer of the reactor (NIKIET) or the scientific manager. Sony VAIO VGN-FW21Z Battery

Instead, it was approved only by the director of the plant (and even this approval was not consistent with established procedures). According to the test parameters, the thermal output of the reactor should have been no lower than 700 MW at the start of the experiment. If test conditions had been as planned, the procedure would almost certainly have been carried out safely; the eventual disaster resulted from attempts to boost the reactor output once the experiment had been started, which was inconsistent with approved procedure.[11Sony VAIO VGN-FW21I Battery


The Chernobyl power plant had been in operation for two years without the capability to ride through the first 60–75 seconds of a total loss of electric power, thus lacking an important safety feature. Sony VAIO VGN-FW21E Battery

The station managers presumably wished to correct this at the first opportunity, which may explain why they continued the test even when serious problems arose, and why the requisite approval for the test was not sought from the Soviet nuclear oversight regulator (even though there was a representative at the complex of 4 reactors).[ Sony VAIO VGN-FW17W Battery

The experimental procedure was intended to run as follows:

The reactor was to be running at a low power level, between >700 MW & 800 MW.

The steam turbine was to be run up to full speed.

When these conditions were achieved, the steam supply was to be closed off.

The turbines would be allowed to freewheel down. Sony VAIO VGN-FW17/B Battery

Generator performance was to be recorded to determine whether it could provide the bridging power for coolant pumps. Sony VAIO VGN-FW17/B Battery

Conditions prior to the accident

The conditions to run the test were established prior to the day shift of 25 April 1986. The day shift workers had been instructed in advance and were familiar with the established procedures. A special team of electrical engineers was present to test the new voltage regulating system.[ Sony VAIO VGN-FW11S Battery

12] As planned, a gradual reduction in the output of the power unit was begun at 01:06 on 25 April, and the power level had reached 50% of its nominal 3200 MW thermal level by the beginning of the day shift. At this point, another regional power station unexpectedly went off line, and the Kiev electrical grid controller requested that the further reduction of Chernobyl’s output be postponed, as power was needed to satisfy the peak evening demand. The Chernobyl plant director agreed and postponed the test. Sony VAIO VGN-FW11M Battery

At 23:04, the Kiev grid controller allowed the reactor shut-down to resume. This delay had some serious consequences: the day shift had long since departed, the evening shift was also preparing to leave, and the night shift would not take over until midnight, well into the job. According to plan, the test should have been finalized during the day shift, and the night shift would only have had to maintain decay heat cooling systems in an otherwise shut down plant; the night shift had very limited time to prepare for and carry out the experiment. Sony VAIO VGP-BPS13B/Q Battery

Further rapid reduction in the power level from 50% was actually executed during the shift change-over. Alexander Akimov was chief of the night shift, and Leonid Toptunov was the operator responsible for the reactor’s operational regimen, including the movement of the control rods. Toptunov was a young engineer who had worked independently as a senior engineer for approximately three monthsSony VAIO VGP-BPS13A/Q Battery

The test plan called for the power output of reactor 4 to be gradually reduced to a thermal level of 700–1000 MW.[13] The level established in the test program (700 MW) was achieved at 00:05 on April 26; however, because of the natural production of the neutron absorber xenon-135 in the core, reactor power continued to decrease, even without further operator action. As the power reached approximately 500 MW, Top mistakenly inserted the control rods too far, bringing the reactor to an unintended near-shutdown state. The exact circumstances are hard to know, because both Akimov and Toptunov died from radiation sickness. Sony VAIO VGP-BPS13/Q Battery

The reactor power dropped to 30 MW thermal (or less)—an almost completely shut down power level, which was approximately 5 percent of the minimum initial power level established as safe for the test.[11]:73 Control-room personnel consequently made the decision to restore the power and extracted the reactor control rods,[1Sony VAIO VGP-BPS13/Q Battery

] and several minutes elapsed between their extraction and the point that the power output began to increase and subsequently stabilize at 160–200 MW (thermal). This maneuver withdrew the majority of control rods to the rods’ upper limits, but the low value of the operational reactivity margin restricted any further rise of reactor power. Sony VAIO VGP-BPS13/Q Battery

The rapid reduction in the power during the initial shutdown, and the subsequent operation at a level of less than 200 MW led to increased poisoning of the reactor core by the accumulation of xenon-135. This made it necessary to extract additional control rods from the reactor core in order to counteract the poisoning. Sony VAIO VGP-BPS13/Q Battery

The operation of the reactor at the low power level with a small reactivity margin was accompanied by unstable core temperature and coolant flow, and possibly by instability of neutron flux.[15] Various alarms started going off at this point. Sony VAIO VGP-BPS13/Q Battery

The control room received repeated emergency signals regarding the levels in the steam/water separator drums, as well as of relief valves opened to relieve excess steam into a turbine condenser and of large excursions or variations in the flow rate of feed water, and also from the neutron power controller. Sony VAIO VGP-BPS13A/B Battery

In the period between 00:35 and 00:45, emergency alarm signals concerning thermal-hydraulic parameters were apparently ignored, apparently to preserve the reactor power level. Emergency signals from the reactor emergency protection system (EPS-5) triggered a trip which turned off both turbine-generators.[16] Sony VGP-BPS13 Battery

After a while, a more or less stable state at a power level of 200 MW was achieved, and preparation for the experiment continued. As part of the test plan, extra water pumps were activated at 01:05 on 26 April, increasing the water flow. HP Pavilion DM4-1014TX BATTERY

The increased coolant flow rate through the reactor produced an increase in the inlet coolant temperature of the reactor core, which now more closely approached the nucleate boiling temperature of water, reducing the safety margin. The flow exceeded the allowed limit at 01:19. At the same time, the extra water flow lowered the overall core temperature and reduced the existing steam voids in the core.[17HP Pavilion DM4-1013TX BATTERY

] Since water also absorbs neutrons (and the higher density of liquid water makes it a better absorber than steam), turning on additional pumps decreased the reactor power further still. This prompted the operators to remove the manual control rods further to maintain power.[18] HP Pavilion DM4-1010TX BATTERY

All these actions led to an extremely unstable reactor configuration. Nearly all of the control rods were removed, which would limit the value of the safety rods when initially inserted in a scram condition. Further, the reactor coolant had reduced boiling, but had limited margin to boiling, so any power excursion would produce boiling, reducing neutron absorption by the water. The reactor was in an unstable configuration that was clearly outside the safe operating envelope established by the designers. HP Pavilion DM4-1010TX BATTERY

Experiment and explosion

At 1:23:04 a.m. the experiment began. The steam to the turbines was shut off, and a run down of the turbine generator began, together with four (of eight total) Main Circulating Pumps (MCP). The diesel generator started and sequentially picked up loads, which was complete by 01:23:43; during this period the power for these four MCPs was supplied by the coasting down turbine generator. HP Pavilion DM4-1010TX BATTERY

As the momentum of the turbine generator that powered the water pumps decreased, the water flow rate decreased, leading to increased formation of steam voids (bubbles) in the core. Because of the positive void coefficient of the RBMK reactor at low reactor power levels, it was now primed to embark on a positive feedback loop, in which the formation of steam voids reduced the ability of the liquid water coolant to absorb neutrons, which in turn increased the reactor’s power output. Sony VGP-BPS13B/Q Akku,    ,  This caused yet more water to flash into steam, giving yet a further power increase. However, during almost the entire period of the experiment the automatic control system successfully counteracted this positive feedback, continuously inserting control rods into the reactor core to limit the power rise. Sony VGP-BPS13Q Akku

At 1:23:40, as recorded by the SKALA centralized control system, an emergency shutdown or SCRAM of the reactor, which inadvertently triggered the explosion, was initiated. The scram was started when the EPS-5 button (also known as the AZ-5 button) of the reactor emergency protection system was pressed thus fully inserting all control rods, including the manual control rods that had been incautiously withdrawn earlier. Sony VGP-BPS13 AkkuThe reason the EPS-5 button was pressed is not known, whether it was done as an emergency measure or simply as a routine method of shutting down the reactor upon completion of the experiment. There is a view[who?] that the SCRAM may have been ordered as a response to the unexpected rapid power increase, although there is no recorded data convincingly testifying to this.  Sony VGP-BPS13S AkkuSome[who?] have suggested that the button was not pressed but rather that the signal was automatically produced by the emergency protection system; however, the SKALA clearly registered a manual scram signal. , Sony VGP-BPS13B/S AkkuIn spite of this, the question as to when or even whether the EPS-5 button was pressed was the subject of debate. There are assertions[who?] that the pressure was caused by the rapid power acceleration at the start, and allegations that the button was not pressed until the reactor began to self-destruct but others[who?] assert that it happened earlier and in calm conditions.[19]:578 Sony VGP-BPS13A/S Akku [20] For whatever reason, the EPS-5 button was pressed, so the insertion of control rods into the reactor core began. The control rod insertion mechanism operated at a relatively slow speed (0.4 m/s) taking 18–20 seconds for the rods to travel the full approximately 7-meter core length (height).  Sony VGP-BPS13A/B AkkuA bigger problem was a flawed graphite-tip control rod design, which initially displaced coolant before neutron-absorbing material was inserted and the reaction slowed. As a result, the SCRAM actually increased the reaction rate in the lower half of the core. Sony VGP-BPl13 Akku,

A few seconds after the start of the SCRAM, a massive power spike occurred, the core overheated, and seconds later this overheating resulted in the initial explosion. Some of the fuel rods fractured, blocking the control rod columns and causing the control rods to become stuck after being inserted only one-third of the way. Sony VAIO VGN-FZ Series Sony VAIO VGN-FZ Series

Within three seconds the reactor output rose above 530 MW.[6]:31 The subsequent course of events was not registered by instruments: it is known only as a result of mathematical simulation. Apparently, a great rise in power first caused an increase in fuel temperature and massive steam buildup, leading to a rapid increase in steam pressure. Sony VAIO VGN-FZ Series

This destroyed fuel elements and ruptured the channels in which these elements were located.[21] Then, according to some estimations[wSony VAIO VGN-FW31ZJ Akkuho?], the reactor jumped to around 30 GW thermal, ten times the normal operational output. The last reading on the control panel was 33 GW. Sony VAIO VGN-FW32J Akku It was not possible to reconstruct the precise sequence of the processes that led to the destruction of the reactor and the power unit building, but a steam explosion, like the explosion of a steam boiler from excess vapor pressure, appears to have been the next event. Sony VAIO VGN-FW31Z Akku There is a general understanding that it was steam from the wrecked channels entering the reactor inner structure that caused the destruction of the reactor casing, tearing off and lifting by force the 2,000 ton upper plate (to which the entire reactor assembly is fastened). Apparently, this was the first explosion that many[who?] heard.[22]:366 This ruptured further fuel channels—as a result the remaining coolant flashed to steam and escaped the reactor core. The total water loss combined with a high positive void coefficient to increase the reactor power. Sony VAIO VGN-FW31J Akku

A second, more powerful explosion occurred about two or three seconds after the first; evidence indicates that the second explosion resulted from a nuclear excursion.[23] The nuclear excursion dispersed the core and effectively terminated that phase of the event. However, a graphite fire was burning by now, greatly contributing to the spread of radioactive material and the contamination of outlying areas[Sony VAIO VGN-FW31E Akku There were initially several hypotheses about the nature of the second explosion. One view was that "the second explosion was caused by the hydrogen which had been produced either by the overheated steam-zirconium reaction or by the reaction of red-hot graphite with steam that produce hydrogen and carbon monoxide." Sony VAIO VGN-FW31M AkkuAnother hypothesis posits that the second explosion was a thermal explosion of the reactor as a result of the uncontrollable escape of fast neutrons caused by the complete water loss in the reactor core.[25] A third hypothesis was that the explosion was caused, exceptionally, by steam. According to this version, the flow of steam and the steam pressure caused all the destruction following the ejection from the shaft of a substantial part of the graphite and fuel. Sony VAIO VGN-FW21M Akku

According to observers outside Unit 4, burning lumps of material and sparks shot into the air above the reactor. Some of them fell on to the roof of the machine hall and started a fire. About 25 per cent of the red-hot graphite blocks and overheated material from the fuel channels was ejected. …Parts of the graphite blocks and fuel channels were out of the reactor building. …As a result of the damage to the building an airflow through the core was established by the high temperature of the core. The air ignited the hot graphite and started a graphite fire.[6]:32Sony VAIO VGN-FW21Z Akku

However, the ratio of xenon radioisotopes released during the event provides compelling evidence that the second explosion was a nuclear power transient. This nuclear transient released ~0.01 kiloton of TNT equivalent (40 GJ) of energy; the analysis indicates that the nuclear excursion was limited to a small portion of the core.[23] Sony VGP-BPL13 Battery

Contrary to safety regulations, a combustible material (bitumen) had been used in the construction of the roof of the reactor building and the turbine hall. Ejected material ignited at least five fires on the roof of the (still operating) adjacent reactor 3. It was imperative to put those fires out and protect the cooling systems of reactor 3.[6]:42 Inside reactor 3, the chief of the night shift, Yuri Bagdasarov, wanted to shut down the reactor immediately, but chief engineer Nikolai Fomin would not allow this.[wSony VGP-BPS13A/B Batteryhy?] The operators were given respirators and potassium iodide tablets and told to continue working. At 05:00, however, Bagdasarov made his own decision to shut down the reactor, leaving only those operators there who had to work theemergency cooling systems.[6]:44Sony VGP-BPL13 Battery

Radiation levels

The radiation levels in the worst-hit areas of the reactor building have been estimated to be 5.6 roentgens per second (R/s) (1.4 milliamperes per kilogram), equivalent to more than 20,000 roentgens per hour. A lethal dose is around 500 roentgens (0.13 coulombs per kilogram) over 5 hours, so in some areas, unprotected workers received fatal doses within minutes. However, a dosimeter capable of measuring up to 1,000 R/s (0.3 A/kg) was inaccessible because of the explosion, and another one failed when turned on. All remaining dosimeters had limits of 0.001 R/s (0.3 µA/kg) and therefore read “off scale.” Sony VGP-BPS13B/B Battery

Thus, the reactor crew could ascertain only that the radiation levels were somewhere above 0.001 R/s (3.6 R/h, or 0.3 µA/kg), while the true levels were much, much higher in some areas.[6]:42–50 Sony VGP-BPS13/S Battery

Because of the inaccurate low readings, the reactor crew chief Alexander Akimov assumed that the reactor was intact. The evidence of pieces of graphite and reactor fuel lying around the building was ignored, and the readings of another dosimeter brought in by 04:30 were dismissed under the assumption that the new dosimeter must have been defective.[6]:42–50 Akimov stayed with his crew in the reactor building until morning, trying to pump water into the reactor. None of them wore any protective gear. Most, including Akimov, died from radiation exposure within three weeks.[28]:247–48Sony VGP-BPS13A/S Battery

Shortly after the accident, firefighters arrived to try to extinguish the fires. First on the scene was a Chernobyl Power Station firefighter brigade under the command of Lieutenant Volodymyr Pravik, who died on 9 May 1986 of acute radiation sickness. They were not told how dangerously radioactive the smoke and the debris were, and may not even have known that the accident was anything more than a regular electrical fire: “We didn’t know it was the reactor. No one had told us.”[29] Sony VGP-BPS13B/S Battery

Grigorii Khmel, the driver of one of the fire-engines, later described what happened:

We arrived there at 10 or 15 minutes to two in the morning… We saw graphite scattered about. Misha asked: “What is graphite?” I kicked it away. But one of the fighters on the other truck picked it up. “It’s hot,” he said. The pieces of graphite were of different sizes, some big, some small enough to pick up…  Sony VGP-BPS13/Q Battery

We didn’t know much about radiation. Even those who worked there had no idea. There was no water left in the trucks. Misha filled the cistern and we aimed the water at the top. Then those boys who died went up to the roof—Vashchik Kolya and others, and Volodya Pravik… They went up the ladder… and I never saw them again.[30]:54Sony VGP-BPS13A/Q Battery

However, Anatoli Zakharov, a fireman stationed in Chernobyl since 1980, offers a different description:

I remember joking to the others, “There must be an incredible amount of radiation here. We’ll be lucky if we’re all still alive in the morning.”  Sony VGP-BPS13B/Q Battery

Twenty years after the disaster, he claimed the firefighters from the Fire Station No. 2 were aware of the risks.

Of course we knew! If we’d followed regulations, we would never have gone near the reactor. But it was a moral obligation—our duty. We were like kamikaze.[31] Sony VGP-BPS13B/Q Battery

The immediate priority was to extinguish fires on the roof of the station and the area around the building containing Reactor No. 4 to protect No. 3 and keep its core cooling systems intact. The fires were extinguished by 05:00, but many firefighters received high doses of radiation. The fire inside Reactor No. 4 continued to burn until 10 May 1986;  Sony VAIO VGN-FW21Z Battery it is possible that well over half of the graphite burned out.[6]:73 The fire was extinguished by a combined effort of helicopters dropping over 5,000 metric tons of sand, lead, clay, and boron onto the burning reactor and injection of liquid nitrogen. Ukrainian filmmaker Vladimir Shevchenko captured film footage of an Mi-8 helicopter as it collided with a nearby construction crane, causing the helicopter to fall near the damaged reactor building and kill its four-man crew.[32] Sony VAIO VGN-FW21M Battery

From eyewitness accounts of the firefighters involved before they died (as reported on the CBC television series Witness), one described his experience of the radiation as “tasting like metal,” and feeling a sensation similar to that of pins and needles all over his face. (This is similar to the description given by Louis Slotin, a Manhattan Project physicist who died days after a fatal radiation overdose from a criticality accident.)[33] Sony VAIO VGN-FW21M Battery

The explosion and fire threw hot particles of the nuclear fuel and also far more dangerous fission products, radioactive isotopes such as caesium-137, iodine-131, strontium-90 and otherradionuclides, into the air: the residents of the surrounding area observed the radioactive cloud on the night of the explosion. Sony VAIO VGN-FW21M Battery


1:26:03 – fire alarm activated

1:28 – arrival of local firefighters, Pravik’s guard

1:35 – arrival of firefighters from Pripyat, Kibenok’s guardSony VAIO VGN-FW21M Battery

1:40 – arrival of Telyatnikov

2:10 – turbine hall roof fire extinguished

2:30 – main reactor hall roof fires suppressed

3:30 – arrival of Kiev firefighters[34]

4:50 – fires mostly localized

6:35 – all fires extinguished‡[35] Sony VAIO VGN-FZ11M Battery

With the exception of the fire contained inside Reactor 4, which continued to burn for many days.[6]:73

Evacuation of Pripyat

This section may require cleanup to meet Wikipedia’s quality standards. Please improve this section if you can. The talk page may contain suggestions. (April 2009)

The nearby city of Pripyat was not immediately evacuated after the incident. Only after radiation levels set off alarms at the Forsmark Nuclear Power Plant in Sweden,[36] over one thousand kilometers from the Chernobyl Plant, did the Soviet Union admit that an accident had occurred. Nevertheless, authorities attempted to conceal the scale of the disaster. For example, while evacuating the city of Pripyat, Sony VAIO VGN-FZ21E Battery the following warning message was read on local radio: “An accident has occurred at the Chernobyl Nuclear Power Plant. One of the atomic reactors has been damaged. Aid will be given to those affected and a committee of government inquiry has been set up.”[citation needed] Sony VAIO VGN-FZ21E Battery

The government committee was eventually[when?] formed, and tasked to investigating the accident. It was headed by Valeri Legasov, who arrived at Chernobyl in the evening of 26 April. By the time Legasov arrived, two people had already died and 52 were receiving medical attention in a hospital. Sony VAIO VGN-FZ38M Battery By the night of 26–27 April—more than 24 hours after the explosion—Legasov’s committee had ample evidence showing extremely high levels of radiation had caused a number of cases of radiation exposure. Based on the evidence at hand, Legasov’s committee acknowledged the destruction of the reactor and ordered the evacuation of Pripyat.

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The evacuation began at 14:00 on 27 April. In order to expedite the evacuation, the residents were told to bring only what was necessary, as the authorities had said it would only last approximately three days. As a result, most of the residents left their personal belongings, which can still be found today. An exclusion zone of 30 km (19 mi) remains in place today (although its shape has changed and its size has been expanded).

Sony VAIO VGN-NR11Z/T Battery

Steam explosion risk

Two floors of bubbler pools beneath the reactor served as a large water reservoir from the emergency cooling pumps and as a pressure suppression system capable of condensing steam from a (small) broken steam pipe;

Sony VAIO VGN-NR11Z/T Battery

the third floor above them, below the reactor, served as a steam tunnel. The steam released from a broken pipe was supposed to enter the steam tunnel and be led into the pools to bubble through a layer of water. The pools and the basement were flooded because of ruptured cooling water pipes and accumulated fire water. They now constituted a serious steam explosion risk. The smoldering graphite, fuel and other material above, at more than 1200 °C,[38Sony VAIO VGN-NR11M/S Battery] started to burn through the reactor floor and mixed with molten concrete that had lined the reactor, creating corium, a radioactive semi-liquid material comparable to lava.[37][39] If this mixture had melted through the floor into the pool of water, it would have created a massive steam explosionthat would have ejected more radioactive material from the reactor. It became an immediate priority to drain the pool.[40] Sony VAIO VGN-NR11M/S Battery

The bubbler pool could be drained by opening its sluice gates. Volunteers in diving suits entered the radioactive water and managed to open the gates. These were engineers Alexei Ananenko (who knew where the valves were) and Valeri Bezpalov, accompanied by a third man, Boris Baranov, who provided them with light from a lamp, though this lamp failed, leaving them to find the valves by feeling their way along a pipe. Dell Latitude E5400 battery

All of them returned to the surface and according to Ananenko, their colleagues jumped for joy when they heard they had managed to open the valves. Despite their good condition after completion of the task, all of them suffered from radiation sickness, and at least two—Ananenko and Bezpalov—later died.[citation Dell Latitude E5400 battery

needed] Some sources claim incorrectly that they died in the plant.[41] It is likely that intense alpha radiation hydrolyzed the water, generating a low-pHhydrogen peroxide (H2O2) solution akin to an oxidizing acid.[42] Conversion of bubbler pool water to H2O2 is confirmed by the presence in the Chernobyl lavas of studtite andmetastudtite,[43][44] the only minerals that contain peroxide.[45]

Fire brigade pumps were then used to drain the basement. The operation was not completed until 8 May, after 20,000 metric tons of highly radioactive water were pumped out. Dell Latitude E5400 battery

With the bubbler pool gone, a meltdown was less likely to produce a powerful steam explosion. To do so, the molten core would now have to reach the water table below the reactor. To reduce the likelihood of this, it was decided to freeze the earth beneath the reactor, which would also stabilize the foundations. Using oil drilling equipment, injection of liquid nitrogenbegan on 4 May. It was estimated that 25 metric tons of liquid nitrogen per day would be required to keep the soil frozen at −100 °C.[6]:59 This idea[clarification needed] was soon scrapped and the bottom room where the cooling system would have been installed was filled with concrete. Dell Latitude E5500 Battery

Debris removal

The worst of the radioactive debris was collected inside what was left of the reactor, much of it shoveled in by liquidators wearing heavy protective gear (dubbed “bio-robots” by the military); Dell Latitude E5400 Battery

these workers could only spend a maximum of 40 seconds at a time working on the rooftops of the surrounding buildings because of the extremely high doses of radiation given off by the blocks of graphite and other debris. The reactor itself was covered with bags containing sand, lead, and boric acid dropped from helicopters (some 5,000 metric tons during the week following the accident). By December 1986 a large concrete sarcophagus had been erected, to seal off the reactor and its contents.[46] Dell Studio 1737 battery

Many of the vehicles used by the “liquidators” remain parked in a field in the Chernobyl area.[47] Dell Studio 1737 battery


Operator error initially faulted

There were two official explanations of the accident: the first, subsequently acknowledged as erroneous, was published in August 1986 and effectively placed the blame on the power plant operators. To investigate the causes of the accident the IAEA created a group known as the International Nuclear Safety Advisory Group (INSAG), which in its report of 1986, Dell Studio 17 battery

INSAG-1, on the whole also supported this view, based on the data provided by the Soviets and the oral statements of specialists.[48] In this view, the catastrophic accident was caused by gross violations of operating rules and regulations. “During preparation and testing of the turbine generator under run-down conditions using the auxiliary load, personnel disconnected a series of technical protection systems and breached the most important operational safety provisions for conducting a technical exercise.”[49]: Dell Studio 1535 battery

311 The operator error was probably due to their lack of knowledge of nuclear reactor physics and engineering, as well as lack of experience and training. According to these allegations, at the time of the accident the reactor was being operated with many key safety systems turned off, most notably the Emergency Core Cooling System (ECCS), LAR (Local Automatic control system), Dell XPS M1710 battery

and AZ (emergency power reduction system). Personnel had an insufficiently detailed understanding of technical procedures involved with the nuclear reactor, and knowingly ignored regulations to speed test completion.[49] Dell XPS M1310 battery

The developers of the reactor plant considered this combination of events to be impossible and therefore did not allow for the creation of emergency protection systems capable of preventing the combination of events that led to the crisis, Dell XPS m1530 battery

namely the intentional disabling of emergency protection equipment plus the violation of operating procedures. Thus the primary cause of the accident was the extremely improbable combination of rule infringement plus the operational routine allowed by the power station staff.[49]:312Dell XPS M1710 battery

In this analysis of the causes of the accident, deficiencies in the reactor design and in the operating regulations that made the accident possible were set aside and mentioned only casually. Serious critical observations covered only general questions and did not address the specific reasons for the accident. Dell XPS m1330 Battery

The following general picture arose from these observations. Several procedural irregularities also helped to make the accident possible. One was insufficient communication between the safety officers and the operators in charge of the experiment being run that night. The reactor operators disabled safety systems down to the generators, Dell XPS 15  Battery

which the test was really about. The main process computer, SKALA, was running in such a way that the main control computer could not shut down the reactor or even reduce power. Normally the reactor would have started to insert all of the control rods. The computer would have also started the “Emergency Core Protection System” that introduces 24 control rods into the active zone within 2.5 seconds, which is still slow by 1986 standards. All control was transferred from the process computer to the human operators. Dell XPS 13 battery

This view is reflected in numerous publications and also artistic works on the theme of the Chernobyl accident that appeared immediately after the accident,[6] and for a long time remained dominant in the public consciousness and in popular publications. Dell Studio XPS 13 Battery

Operating instructions and design deficiencies found

In 1993 the IAEA Nuclear Safety Advisory Group (INSAG) published an additional report, INSAG-7,[11] which reviewed “that part of the INSAG-1 report in which primary attention is given to the reasons for the accident.” In this later report, most of the accusations against staff for breach of regulations were acknowledged to be erroneous, Dell Latitude E5500 Battery

based on incorrect information obtained in August 1986. This report reflected another view of the reasons for the accident, presented in Appendix I. According to this account, the operators’ actions in turning off theEmergency Core Cooling System, interfering with the settings on the protection equipment, Dell XPS M1530 Batteryand blocking the level and pressure in the separator drum did not contribute to the original cause of the accident and its magnitude, though they may have been a breach of regulations. Turning off the emergency system designed to prevent the two turbine generators from stopping was not a violation of regulations.[11] Dell XPS M1530 Battery

Human factors contributed to the conditions that led to the disaster. These included operating the reactor at a low power level—less than 700 MW—a level documented in the run-down test program, and operating with a small operational reactivity margin (ORM). Operating the reactor at this low power level was not forbidden by regulations, contradicting what Soviet experts asserted in 1986.[11Dell XPS M1530 Battery18 However, regulations did forbid operating the reactor with a small margin of reactivity. However, "... post-accident studies have shown that the way in which the real role of the ORM is reflected in the Operating Procedures and design documentation for the RBMK-1000 is extremely contradictory," and furthermore, "ORM was not treated as an operational safety limit, violation of which could lead to an accident.",[11]:34-25Dell XPS M1530 Battery).

According to the INSAG-7 Report, the chief reasons for the accident lie in the peculiarities of physics and in the construction of the reactor. There are two such reasons:[11]:18Dell Latitude D620 Battery

The reactor had a dangerously large positive void coefficient. The void coefficient is a measurement of how a reactor responds to increased steam formation in the water coolant. Most other reactor designs have a negative coefficient, i.e. they attempt to decrease heat output when the vapor phase in the reactor increases, because if the coolant contains steam bubbles, fewer neutrons are slowed down. Faster neutrons are less likely to split uranium atoms, so the reactor produces less power (a negative feed-back). Dell Latitude D620 Battery

Chernobyl’s RBMK reactor, however, used solid graphite as a neutron moderator to slow down the neutrons, and the water in it, on the contrary, acts like a harmful neutron absorber. Thus neutrons are slowed down even if steam bubbles form in the water. Dell Latitude D520 Battery Furthermore, because steam absorbs neutrons much less readily than water, increasing the intensity of vaporization means that more neutrons are able to split uranium atoms, increasing the reactor’s power output. This makes the RBMK design very unstable at low power levels, and prone to suddenly increasing energy production to a dangerous level. This behavior is counter-intuitive, and this property of the reactor was unknown to the crew. Dell Latitude D620 Battery

A more significant flaw was in the design of the control rods that are inserted into the reactor to slow down the reaction. In the RBMK reactor design, the lower part of each control rod was made of graphite and was 1.3 meters shorter than necessary, and in the space beneath the rods were hollow channels filled with waterHP Pavilion DV5Z Battery. The upper part of the rod—the truly functional part that absorbs the neutrons and thereby halts the reaction—was made of boron carbide. With this design, when the rods are inserted into the reactor from the uppermost position, the graphite parts initially displace some water. Thus for the first few seconds of control rod activation, reactor power output is increased, rather than reduced as desired. This behavior is counter-intuitive and was not known to the reactor operators. Sony VAIO PCG-8Z2L Battery

Other deficiencies besides these were noted in the RBMK-1000 reactor design, as were its non-compliance with accepted standards and with the requirements of nuclear reactor safety.

Both views were heavily lobbied by different groups, including the reactor’s designers, power plant personnel, and the Soviet and Ukrainian governments. HP Pavilion DV5Z Battery According to the IAEA’s 1986 analysis, the main cause of the accident was the operators’ actions. But according to the IAEA’s 1993 revised analysis the main cause was the reactor’s design.[50] One reason there were such contradictory viewpoints and so much debate about the causes of the Chernobyl accident was that the primary data covering the disaster, as registered by the instruments and sensors, were not completely published in the official sources. HP Pavilion DV5Z-1000 Battery

Once again, the human factor had to be considered as a major element in causing the accident. INSAG notes that both the operating regulations and staff handled the disabling of the reactor protection easily enough: HP Pavilion G70 Battery

witness the length of time for which the ECCS was out of service while the reactor was operated at half power. INSAG’s view is that it was the operating crew’s deviation from the test program that was mostly to blame. “Most reprehensibly, unapproved changes in the test procedure were deliberately made on the spot, although the plant was known to be in a very different condition from that intended for the test.” [11]:24HP Pavilion G60 Battery

As in the previously released report INSAG-1, close attention is paid in report INSAG-7 to the inadequate (at the moment of the accident) “culture of safety” at all levels. Deficiency in the safety culture was inherent not only at the operational stage but also, and to no lesser extent, during activities at other stages in the lifetime of nuclear power plants (including design, engineering, construction, HP Pavilion G50 Battery

manufacture and regulation). The poor quality of operating procedures and instructions, and their conflicting character, put a heavy burden on the operating crew, including the Chief Engineer. “The accident can be said to have flowed from a deficient safety culture, not only at the Chernobyl plant, but throughout the Soviet design, operating and regulatory organizations for nuclear power that existed at that time.” [11]:24HP Pavilion G50 Battery


Main article: Chernobyl disaster effects

International spread of radioactive substances

Four hundred times more radioactive material was released than had been by the atomic bombing of Hiroshima. However, compared to the total amount released by nuclear weapons testing during the 1950s and 1960s, the Chernobyl disaster released 1/100 to 1/1000 the radioactivity.[51] The fallout was detected over all of Europe except for the Iberian Peninsula.[52][53][54] HP Pavilion DV6Z-1100 Battery

The initial evidence that a major release of radioactive material was affecting other countries came not from Soviet sources, but from Sweden, where on the morning of 28 April[55] workers at the Forsmark Nuclear Power Plant (approximately 1,100 km (680 mi) from the Chernobyl site) were found to have radioactive particles on their clothes.[ HP Pavilion DV6Z Battery

56] It was Sweden’s search for the source of radioactivity, after they had determined there was no leak at the Swedish plant, that at noon on April 28 led to the first hint of a serious nuclear problem in the western Soviet Union. Hence the evacuation of Pripyat on April 27, 36 hours after the initial explosions, was silently completed before the disaster became known outside the Soviet Union. The rise in radiation levels had at that time already been measured in Finland, but a civil service strike delayed the response and publication.[57] HP Pavilion DV6Z Battery

Contamination from the Chernobyl accident was scattered irregularly depending on weather conditions. Reports from Soviet and Western scientists indicate that Belarus received about 60% of the contamination that fell on the former Soviet Union. HP Pavilion DV7 Battery

However, the 2006 TORCH report stated that half of the volatile particles had landed outside Ukraine, Belarus, and Russia. A large area in Russia south of Bryansk was also contaminated, as were parts of northwestern Ukraine. Studies in surrounding countries indicate that over one million people could have been affected by radiation.[58] HP Pavilion DV6 Battery

Recently published data from a long-term monitoring program (The Korma Report)[59] show a decrease in internal radiation exposure of the inhabitants of a region in Belarus close toGomel. Resettlement may even be possible in prohibited areas provided that people comply with appropriate dietary rules.

HP Pavilion DV5T Battery

In Western Europe, precautionary measures taken in response to the radiation included seemingly arbitrary regulations banning the importation of certain foods but not others. In Francesome officials stated that the Chernobyl accident had no adverse effects.[60] Official figures in southern Bavaria in Germany indicated that some wild plant species contained substantial levels of caesium, which were believed to have been passed onto them by wild boars, a significant number of which had already contained radioactive particles above the allowed level, consuming them. HP Pavilion DV5 Battery

Radioactive release

Like many other releases of radioactivity into the environment, the Chernobyl release was controlled by the physical and chemical properties of the radioactive elements in the core. While the general population often perceives plutonium as a particularly dangerous nuclear fuel, its effects are almost eclipsed by those of its fission products. Particularly dangerous are highly radioactive compounds that accumulate in the food chain, such as some isotopes of iodine and strontium. HP Pavilion DV4T Battery

Two reports on the release of radioisotopes from the site were made available, one by the OSTI and a more detailed report by the OECD, both in 1998.[62][63] At different times after the accident, different isotopes were responsible for the majority of the external dose. The dose that was calculated is that received from external gamma irradiation for a person standing in the open. The dose to a person in a shelter or the internal dose is harder to estimate. HP Pavilion DV4T Battery

The release of radioisotopes from the nuclear fuel was largely controlled by their boiling points, and the majority of the radioactivity present in the core was retained in the reactor.

All of the noble gases, including krypton and xenon, contained within the reactor were released immediately into the atmosphere by the first steam explosion. Sony VAIO VGP-BPS13 Battery

About 1760 PBq of I-131, 55% of the radioactive iodine in the reactor, was released, as a mixture of vapor, solid particles, and organic iodine compounds. Sony VAIO VGP-BPS13A/B Battery

Caesium and tellurium were released in aerosol form.

An early estimate for fuel material released to the environment was 3 t ± 1.5%; this was later revised to 3.5 t ± 0.5%. This corresponds to the atmospheric emission of 6 t of fragmented fuel.[63] Sony VAIO VGP-BPS13B/B Battery

Two sizes of particles were released: small particles of 0.3 to 1.5 micrometers (aerodynamic diameter) and large particles of 10 micrometers. The large particles contained about 80% to 90% of the released nonvolatile radioisotopes zirconium-95, niobium-95, lanthanum-140, cerium-144 and the transuranic elements, including neptunium, plutonium and the minor actinides, embedded in a uranium oxide matrix. Sony VAIO VGP-BPS13B/B Battery

Health of plant workers and local people

In the aftermath of the accident, 237 people suffered from acute radiation sickness, of whom 31 died within the first three months.[64][65] Most of these were fire and rescue workers trying to bring the accident under control, who were not fully aware of how dangerous exposure to theradiation in the smoke was. Sony VAIO VGP-BSP13B/S Battery

Whereas, in the World Health Organization’s 2006 report of the Chernobyl Forum expert group on the 237 emergency workers who were diagnosed with ARS, ARS was identified as the cause of death for 28 of these people within the first few months after the disaster. There were no further deaths identified, in the general population affected by the disaster, as being caused by ARS. Sony VAIO VGP-BSP13B/Q Battery

Of the 72,000 Russian Emergency Workers being studied, 216 non-cancer deaths are attributed to the disaster, between 1991 and 1998. The latency period for solid cancers caused by excess radiation exposure is 10 or more years; thus at the time of the WHO report being undertaken, the rates of solid cancer deaths were no greater than the general population. Some 135,000 people were evacuated from the area, including 50,000 from Pripyat. Sony VAIO VGP-BPS13A/Q Battery

Residual radioactivity in the environment

Rivers, lakes and reservoirs

The Chernobyl nuclear power plant is located next to the Pripyat River, which feeds into the Dnipro River reservoir system, one of the largest surface water systems in Europe. The radioactive contamination of aquatic systems therefore became a major issue in the immediate aftermath of the accident.[66] In the most affected areas of Ukraine, levels of radioactivity (particularly radioiodine: I-131, radiocaesium: Cs-137and radiostrontium: Sr-90) in drinking water caused concern during the weeks and months after the accident. After this initial period, however, radioactivity in rivers and reservoirs was generally below guideline limits for safe drinking water.[66] Sony VAIO VGP-BSP13Q Battery

Bio-accumulation of radioactivity in fish[67] resulted in concentrations (both in western Europe and in the former Soviet Union) that in many cases were significantly above guideline maximum levels for consumption.[66] Guideline maximum levels for radiocaesium in fish vary from country to country but are approximately 1,000 Bq/kg in the European Union.[ Sony VAIO VGN-NR11M/S Battery

68] In the Kiev Reservoir in Ukraine, concentrations in fish were several thousand Bq/kg during the years after the accident.[67] In small ”closed” lakes in Belarus and the Bryansk region of Russia, concentrations in a number of fish species varied from 0.1 to 60 kBq/kg during the period 1990–92.[69] The contamination of fish caused short-term concern in parts of the UK and Germany and in the long term (years rather than months) in the affected areas of Ukraine, Belarus, and Russia as well as in parts of Scandinavia.[66] Sony VAIO VGN-NR11S/S Battery


Groundwater was not badly affected by the Chernobyl accident since radionuclides with short half-lives decayed away long before they could affect groundwater supplies, and longer-lived radionuclides such as radiocaesium and radiostrontium were adsorbed to surface soils before they could transfer to groundwater.[70Sony VAIO VGN-NR11S/S Battery

] However, significant transfers of radionuclides to groundwater have occurred from waste disposal sites in the 30 km (19 mi) exclusion zone around Chernobyl. Although there is a potential for transfer of radionuclides from these disposal sites off-site (i.e. out of the 30 km (19 mi) exclusion zone), the IAEA Chernobyl Report[70] argues that this is not significant in comparison to current levels ofwashout of surface-deposited radioactivity. Sony VAIO VGN-NR11S/S Battery

Flora and fauna

After the disaster, four square kilometers of pine forest in the immediate vicinity of the reactor turned reddish-brown and died, earning the name of the “Red Forest”.[71] Some animals in the worst-hit areas also died or stopped reproducing. Most domestic animals were removed from the exclusion zone, but horses left on an island in the Pripyat River 6 km (4 mi) from the power plant died when their thyroid glands were destroyed by radiation doses of 150–200 Sv.[72] Some cattle on the same island died and those that survived were stunted because of thyroid damage. The next generation appeared to be normal.[72] Sony VAIO PCG-5G3L Battery

A robot sent into the reactor itself has returned with samples of black, melanin-rich radiotrophic fungi that are growing on the reactor’s walls.[73] Sony VAIO PCG-5J1L Battery

Of the 440,350 wild boar killed in the 2010 hunting season in Germany, over 1,000 were found to be contaminated with levels of radiation above the permitted limit of 600 bequerels, due to residual radioactivity from Chernobyl.[74] Sony VAIO PCG-5J2L Battery

The Norwegian Agricultural Authority reported that in 2009 a total of 18,000 livestock in Norway needed to be given uncontaminated feed for a period of time before slaughter in order to ensure that their meat was safe for human consumption. This was due to residual radioactivity from Chernobyl in the plants they graze on in the wild during the summer. The after-effects of Chernobyl were expected to be seen for a further 100 years, although the severity of the impact would decline over that period.[75] Sony VAIO PCG-5K2L Battery

Chernobyl after the disaster

Main article: Chernobyl after the disaster

Recovery process

Recovery projects

The Chernobyl Shelter FundSony VAIO PCG-5K1L Battery

The Chernobyl Shelter Fund was established in 1997 at the Denver 23rd G8 summit to finance the Shelter Implementation Plan (SIP). The plan calls for transforming the site into an ecologically safe condition by means of stabilization of the sarcophagus followed by construction of a New Safe Confinement (NSC). While the original cost estimate for the SIP was US$768 million, the 2006 estimate was $1.2 billion. Sony VAIO PCG-6S1L Battery

The SIP is being managed by a consortium of Bechtel, Battelle, and Electricité de France, and conceptual design for the NSC consists of a movable arch, constructed away from the shelter to avoid high radiation, to be slid over the sarcophagus. The NSC is expected to be completed in 2013, and will be the largest movable structure ever built. Sony VAIO PCG-8Y1L Battery


Span: 270 m (886 ft)

Height: 100 m (330 ft)

Length: 150 m (492 ft) Sony VAIO PCG-8Y2L Battery

The United Nations Development Programme

The United Nations Development Programme has launched in 2003 a specific project called the Chernobyl Recovery and Development Programme (CRDP) for the recovery of the affected areas.[76] Sony VAIO PCG-8Z2L Battery

The programme was initiated in February 2002 based on the recommendations in the report on Human Consequences of the Chernobyl Nuclear Accident. The main goal of the CRDP’s activities is supporting the Government of Ukraine in mitigating long-term social, economic, and ecological consequences of the Chernobyl catastrophe. CRDP works in the four most Chernobyl-affected areas in Ukraine: Kyivska, Zhytomyrska, Chernihivska and Rivnenska. Sony VAIO PCG-8Z1L Battery

The International Project on the Health Effects of the Chernobyl AccidentSony VAIO PCG-8Z2L Battery

The International Project on the Health Effects of the Chernobyl Accident (IPEHCA) was created and received US $20 million, mainly from Japan, in hopes of discovering the main cause of health problems due to 131I radiation. These funds were divided between Ukraine, Belarus, and Russia, the three main affected countries, for further investigation of health effects. As there was significant corruption in former Soviet countries, most of the foreign aid was given to Russia, and no positive outcome from this money has been demonstrated. Sony VAIO PCG-8Z2L Battery

An international assessment of the health effects of the Chernobyl accident is contained in a series of reports by the United Nations Scientific Committee of the Effects of Atomic Radiation (UNSCEAR).[77] UNSCEAR was set up as a collaboration between various UN bodies, including the World Health Organisation, after the atomic bomb attacks on Hiroshima and Nagasaki, to assess the long-term effects of radiation on human health. Sony VAIO VGN-FW11S Battery

UNSCEAR has conducted 20 years of detailed scientific and epidemiological research on the effects of the Chernobyl accident. Apart from the 57 direct deaths in the accident itself, UNSCEAR originally predicted up to 4,000 additional cancer cases due to the accident.[4] However, the latest UNSCEAR reports suggest that these estimates were overstated.[78] In addition, the IAEA states that there has been no increase in the rate of birth defects or abnormalities, or solid cancers (such as lung cancer) corroborating UNSCEAR’s assessments.[79] Sony VAIO VGN-FW21E  Battery

Precisely, UNSCEAR states:

Among the residents of Belaruss 09, the Russian Federation and Ukraine there had been, up to 2002, about 4,000 cases of thyroid cancer reported in children and adolescents who were exposed at the time of the accident, and more cases are to be expected during the next decades. Sony VAIO VGN-FW21M Battery

Notwithstanding problems associated with screening, many of those cancers were most likely caused by radiation exposures shortly after the accident. Apart from this increase, there is no evidence of a major public health impact attributable to radiation exposure 20 years after the accident. There is no scientific evidence of increases in overall cancer incidence or mortality rates or in rates of non-malignant disorders that could be related to radiation exposure. The risk of leukaemia in the general population, Sony VAIO VGN-FW31M Battery

one of the main concerns owing to its short latency time, does not appear to be elevated. Although those most highly exposed individuals are at an increased risk of radiation-associated effects, the great majority of the population is not likely to experience serious health consequences as a result of radiation from the Chernobyl accident. Many other health problems have been noted in the populations that are not related to radiation exposure.[78] Sony VAIO VGN-FW31M Battery

Thyroid cancer is generally treatable.[80] With proper treatment, the five-year survival rate of thyroid cancer is 96%, and 92% after 30 years.[81] Sony VAIO VGN-FW31J Battery

The Chernobyl Forum is a regular meeting of IAEA, other United Nations organizations (FAO, UN-OCHA, UNDP, UNEP, UNSCEAR, WHO, and the World Bank), and the governments of Belarus, Russia, and Ukraine that issues regular scientific assessments of the evidence for health effects of the Chernobyl accident.[8Sony VGN-FW31ZJ battery

2] The Chernobyl Forum concluded that twenty-eightemergency workers died from acute radiation syndrome including beta burns and 15 patients died from thyroid cancer, and it roughly estimated that cancer deaths caused by Chernobyl may reach a total of about 4,000 among the 600,000 people having received the greatest exposures. It also concluded that a greater risk than the long-term effects of radiation exposure is the risk to mental health of exaggerated fears about the effects of radiation:[79] Sony VGN-FW32J battery

The designation of the affected population as “victims” rather than “survivors” has led them to perceive themselves as helpless, weak and lacking control over their future. This, in turn, has led either to over cautious behavior and exaggerated health concerns, or to reckless conduct, such as consumption of mushrooms, berries and game from areas still designated as highly contaminated, overuse of alcohol and tobacco, and unprotected promiscuous sexual activity.[83]

Fred Mettler commented that 20 years later:[84] Sony VGN-FW41M/H battery

The population remains largely unsure of what the effects of radiation actually are and retain a sense of foreboding. A number of adolescents and young adults who have been exposed to modest or small amounts of radiation feel that they are somehow fatally flawed and there is no downside to using illicit drugs or having unprotected sex. To reverse such attitudes and behaviors will likely take years although some youth groups have begun programs that have promise. Sony VGN-FW52JB battery

In addition, disadvantaged children around Chernobyl suffer from health problems that are attributable not only to the Chernobyl accident, but also to the poor state of post-Soviet health systems.[85] Sony VGN-FW73JGB battery

Another study critical of the Chernobyl Forum report was commissioned by Greenpeace, which asserts that “the most recently published figures indicate that in Belarus, Russia and Ukraine alone the accident could have resulted in an estimated 200,000 additional deaths in the period between 1990 and 2004.”[86] The Scientific Secretary of the Chernobyl Forum questioned the choice by the report authors to selectively use non-peer reviewed papers and only those non-peer reviewed papers as their source material while Gregory Härtl (spokesman for the WHO) expressed concern that the conclusions were motivated by ideology.[87] Sony VAIO VGN-FW31Z Battery

The German affiliate of the International Physicians for the Prevention of Nuclear War (IPPNW) argued that more than 10,000 people are today affected by thyroid cancer and 50,000 cases are expected in the future.[88] Sony VAIO VGN-FW31E Battery

A 2009 English translation of an earlier 2007 Russian language publication titled “Chernobyl” presented an analysis of scientific literature and concluded that medical records between 1986, the year of the accident, and 2004 reflect 985,000 deaths as a result of the radioactivity released. The authors suggested that most of the deaths were in Russia, Belarus and Ukraine, but others were spread through the many other countries the radiation from Chernobyl struck.[ Sony VAIO VGN-FW31J Battery

5] The literature analysis draws on over 1,000 published titles and over 5,000 internet and printed publications discussing the consequences of the Chernobyl disaster. The authors contend that those publications and papers were written by leading Eastern European authorities and have largely been downplayed or ignored by the IAEA and UNSCEAR.[89] Author Alexy V. Yablokov was also one of the general editors on the Greenpeace commissioned report also criticizing the Chernobyl Forum finds published one year prior to the Russian language version of this report.[86]

Other health issues linked with the Chernobyl disaster include。Sony VAIO VGN-FW31M Battery

Down syndrome (trisomy 21). In West Berlin, Germany, prevalence of Down syndrome (trisomy 21) peaked 9 months following the main fallout.[11, 12][citation needed] Between 1980 and 1986, the birth prevalence of Down syndrome was quite stable (i.e., 1.35–1.59 per 1,000 live births [27–31 cases]).[citation needed] In 1987, 46 cases were diagnosed (prevalence = 2.11 per 1,000 live births). Most of the excess resulted from a cluster of 12 cases among children born in January 1987.[citation needed] The prevalence of Down syndrome in 1988 was 1.77, and in 1989, it reached pre-Chernobyl values. Sony VAIO VGN-FW21M Battery

The authors[citation needed] noted that the isolated geographical position of West Berlin prior to reunification, the free genetic counseling, and complete coverage of the population through one central cytogenetic laboratory support completeness of case ascertainment; in addition, constant culture preparation and analysis protocols ensure a high quality of data.[ Sony VAIO VGN-FW21Z Battery


Chromosomal aberrations. Reports of structural chromosome aberrations in people exposed to fallout in Belarus and other parts of the former Soviet Union, Austria, and Germany argue against a simple dose-response relationship between degree of exposure and incidence of aberrationsSony VAIO VGN-FW21E Battery

These findings are relevant because a close relationship exists between chromosome changes and congenital malformations. Inasmuch as some types of aberrations are almost specific for ionizing radiation, researchers use aberrations to assess exposure dose. On the basis of current coefficients, however, one cannot assume that calculation of individual exposure doses resulting from fallout would not induce measurable rates of chromosome aberrationsSony VGP-BPS13A/B Battery

Neural tube defects (NTDs) in Turkey. During the embryonic phase of fetal development, the neural tube differentiates into the brain and spinal cord (i.e., collectively forming the central nervous system). Chemical or physical interactions with this process can cause NTDs. Common features of this class of malformations are more or less extended fissures, often accompanied by consecutive dislocation of central nervous system (CNS) tissue. NTDs include spina bifida occulta and aperta, encephalocele, and—in the extreme case—anencephaly. The first evidence in support of a possible association between CNS malformations and fallout from Chernobyl was published by Akar et al.. in 1988.[ Sony VGP-BPS13A/B Battery

he Mustafakemalpasa State Hospital, Bursa region, covers a population of approximately 90,000. Investigators have documented the prevalence of malformations since 1983.[citation needed] The prevalence of NTDs was 1.7 to 9.2 per 1,000 births, but during the first 6 months of 1987 increased to 20 per 1,000 (12 cases). The excess was most pronounced for the subgroup of anencephalics, in which prevalence increased 5-fold (i.e., 10 per 1,000 [6 cases]). In the consecutive months that followed (i.e., July–December 1987), the prevalence decreased again (1.3 per 1,000 for all NTDs, 0.6 per 1,000 for anencephaly), and it reached pre-Chernobyl levels during the first half of 1988 (all NTDs: 0.6 per 1,000; anencephaly: 0.2 per 1,000). This initial report was supported by several similar findings in observational studies from different regions of Turkey.[citation needed] Sony VGP-BSP13/S Battery

In popular culture

See also: Chernobyl disaster in popular culture and Nuclear power debate

The Chernobyl accident attracted a great deal of interest. Because of the distrust that many people (both within and outside the USSR) had in the Soviet authorities, a great deal of debate about the situation at the site occurred in the first world during the early days of the event. Because of defective intelligence based on photographs taken from space, it was thought that unit number three had also suffered a dire accident. Sony VGP-BSP13B/S Battery

Journalists mistrusted many professionals (such as the spokesman from the UK NRPB), and in turn encouraged the public to mistrust them.[90] Sony VGP-BSP13B/S Battery

In Italy, the Chernobyl accident was reflected in the outcome of the 1987 referendum. As a result of that referendum, Italy began phasing out its nuclear power plants in 1988, a decision that was effectively reversed in 2008. Sony VGP-BSP13B/Q Battery

In 1995 Japanese animator Hayao Miyazaki wrote and directed “On Your Mark”, a music video for Japanese pop duo Chage & Aska. This was essentially an animated music video lasting almost seven minutes. The opening scene shows a clean, old-fashioned and apparently deserted small village which is dominated by a huge, asymmetrical version of the Chernobyl “sarcophagus.” In an interview in “Animage” magazine in 1995, Miyazaki compared the sarcophagus in the video to Chernobyl, noting the survival of plant life.[91] Sony VGP-BSP13Q Battery

The video game Call of Duty 4: Modern Warfare features a mission taking place in Pripyat.[92] The “S.T.A.L.K.E.R” series of video games is set in the Chernobyl Exclusion Zone.[93] Sony VAIO VGN-FZ21E Battery

Commemoration of the disaster

The Front Veranda (1986), a lithograph by Susan Dorothea White in the National Gallery of Australia, exemplifies worldwide awareness of the event. Heavy Water: A film for Chernobylwas released by Seventh Art in 2006 to commemorate the disaster through poetry and first-hand accounts.[94] The film secured the Cinequest Award as well as the Rhode Island “best score” award [95] along with a screening at Tate Modern.[96] Sony VAIO VGN-FZ21J Battery

Chernobyl 20

This exhibit presents the stories of 20 people who have each been affected by the disaster, and each person’s account is written on a panel. The 20 individuals whose stories are related in the exhibition are from Belarus, France, Latvia, Russia, Sweden, Ukraine, and the United Kingdom.

Developed by Danish photo-journalist Mads Eskesen, the exhibition is prepared in multiple languages including English, German, Danish, Dutch, Russian, and Ukrainian. Sony VAIO VGN-FZ21M Battery

In Kiev, Ukraine, the exhibition was launched at the “Chernobyl 20 Remembrance for the Future” conference on 23 April 2006. It was then exhibited during 2006 in the United States,Australia, Denmark, the Netherlands, Switzerland, Ukraine, and the United Kingdom. Sony VAIO VGN-FZ21Z Battery

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