Nuclear safety and security

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.

Although there is no way to guarantee that a reactor will always be designed, built and operated safely, the nuclear power industry has improved the safety and performance of reactors, and has proposed safer reactor designs, though many of these designs have yet to be tested at industrial or commercial scales. 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. According to UBS AG, the Fukushima I nuclear accidents have cast doubt on whether even an advanced economy like Japan can master nuclear safety. Catastrophic scenarios involving terrorist attacks are also conceivable.

An interdisciplinary team from MIT have estimated that given the expected growth of nuclear power from 2005 – 2055, at least four serious nuclear accidents would be expected in that period. To date, there have been five serious accidents (core damage) in the world since 1970 (one at Three Mile Island in 1979; one at Chernobyl in 1986; and three at Fukushima-Daiichi in 2011), corresponding to the beginning of the operation of generation II reactors. This leads to on average one serious accident happening every eight years worldwide.

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. There are ongoing concerns about terrorist groups acquiring nuclear bomb-making material.

Overview of nuclear processes and safety issues

As of 2011, nuclear safety considerations occur in a limited number of situations, including:

• Nuclear fission power used in nuclear power stations, and nuclear submarines and ships
• Nuclear weapons
• Fissionable fuels such as uranium and plutonium and their extraction, storage and use
• Radioactive materials used for medical, diagnostic, batteries for some space projects, and research purposes
• Nuclear waste, the radioactive waste residue of nuclear materials
• Nuclear fusion power, a technology under long-term development
• Unplanned entry of nuclear materials into the biosphere and food chain (living plants, animals and humans) if breathed or ingested.

With the exception of thermonuclear weapons and experimental fusion research, all safety issues specific to nuclear power stems from two issues - the toxicity and radioactivity of heavy fissionable materials, waste byproducts, and other radioactive materials, and the risks of unplanned or uncontrolled nuclear fission events.

Nuclear safety therefore covers at minimum: -

• Extraction, transportation, storage, processing, and disposal of fissionable materials
• Safety of nuclear power generators
• Control and safe management of nuclear weapons, nuclear material capable of use as a weapon, and other radioactive materials
• Safe handling, accountability and use in industrial, medical and research contexts
• Disposal of nuclear waste
• Limitations on exposure to radiation

Responsible agencies

File:Iaea-vienna.JPG

IAEA headquarters in Vienna, Austria

Internationally the International Atomic Energy Agency "works with its Member States and multiple partners worldwide to promote safe, secure and peaceful nuclear technologies." Some scientists say that the 2011 Japanese nuclear accidents have revealed that the nuclear industry lacks sufficient oversight, leading to renewed calls to redefine the mandate of the IAEA so that it can better police nuclear power plants worldwide. There are several problems with the IAEA says Najmedin Meshkati of University of Southern California:

It recommends safety standards, but member states are not required to comply; it promotes nuclear energy, but it also monitors nuclear use; it is the sole global organization overseeing the nuclear energy industry, yet it is also weighed down by checking compliance with the Nuclear Non-Proliferation Treaty (NPT).

Many nations utilizing nuclear power have special institutions overseeing and regulating nuclear safety. 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. In the UK nuclear safety is regulated by the Office for Nuclear Regulation (ONR) and the Defence Nuclear Safety Regulator (DNSR). 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 and publishes material regarding radiation protection.

Other agencies include:

• Autorité de sûreté nucléaire
• 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)

Nuclear power plant

Main article: Nuclear power plant

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.

Although there is no way to guarantee that a reactor will always be designed, built and operated safely, the nuclear power industry has improved the safety and performance of reactors, and has proposed safer reactor designs, though many of these designs have yet to be tested at industrial or commercial scales. 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. According to UBS AG, the Fukushima I nuclear accidents have cast doubt on whether even an advanced economy like Japan can master nuclear safety. Catastrophic scenarios involving terrorist attacks are also conceivable.

An interdisciplinary team from MIT have estimated that given the expected growth of nuclear power from 2005 – 2055, at least four serious nuclear accidents would be expected in that period. To date, there have been five serious accidents (core damage) in the world since 1970 (one at Three Mile Island in 1979; one at Chernobyl in 1986; and three at Fukushima-Daiichi in 2011), corresponding to the beginning of the operation of generation II reactors. This leads to on average one serious accident happening every eight years worldwide.

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. There are ongoing concerns about terrorist groups acquiring nuclear bomb-making material.

Overview of nuclear processes and safety issues

As of 2011, nuclear safety considerations occur in a limited number of situations, including:

• Nuclear fission power used in nuclear power stations, and nuclear submarines and ships
• Nuclear weapons
• Fissionable fuels such as uranium and plutonium and their extraction, storage and use
• Radioactive materials used for medical, diagnostic, batteries for some space projects, and research purposes
• Nuclear waste, the radioactive waste residue of nuclear materials
• Nuclear fusion power, a technology under long-term development
• Unplanned entry of nuclear materials into the biosphere and food chain (living plants, animals and humans) if breathed or ingested.

With the exception of thermonuclear weapons and experimental fusion research, all safety issues specific to nuclear power stems from two issues - the toxicity and radioactivity of heavy fissionable materials, waste byproducts, and other radioactive materials, and the risks of unplanned or uncontrolled nuclear fission events.

Nuclear safety therefore covers at minimum: -

• Extraction, transportation, storage, processing, and disposal of fissionable materials
• Safety of nuclear power generators
• Control and safe management of nuclear weapons, nuclear material capable of use as a weapon, and other radioactive materials
• Safe handling, accountability and use in industrial, medical and research contexts
• Disposal of nuclear waste
• Limitations on exposure to radiation

Responsible agencies

File:Iaea-vienna.JPG

IAEA headquarters in Vienna, Austria

Internationally the International Atomic Energy Agency "works with its Member States and multiple partners worldwide to promote safe, secure and peaceful nuclear technologies." Some scientists say that the 2011 Japanese nuclear accidents have revealed that the nuclear industry lacks sufficient oversight, leading to renewed calls to redefine the mandate of the IAEA so that it can better police nuclear power plants worldwide. There are several problems with the IAEA says Najmedin Meshkati of University of Southern California:

It recommends safety standards, but member states are not required to comply; it promotes nuclear energy, but it also monitors nuclear use; it is the sole global organization overseeing the nuclear energy industry, yet it is also weighed down by checking compliance with the Nuclear Non-Proliferation Treaty (NPT).

Many nations utilizing nuclear power have special institutions overseeing and regulating nuclear safety. 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. In the UK nuclear safety is regulated by the Office for Nuclear Regulation (ONR) and the Defence Nuclear Safety Regulator (DNSR). 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 and publishes material regarding radiation protection.

Other agencies include:

• Autorité de sûreté nucléaire
• 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)

Nuclear power plant

Main article: Nuclear power plant

Hazards of nuclear material

Main article: High-level radioactive waste management

Spent nuclear fuel stored underwater and uncapped at the Hanford site in Washington, USA.

The world's nuclear fleet creates about 10,000 metric tons of high-level spent nuclear fuel each year. High-level radioactive waste management concerns management and disposal of highly radioactive materials created during production of nuclear power. The technical issues in accomplishing this are daunting, due to the extremely long periods radioactive wastes remain deadly to living organisms. Of particular concern are two long-lived fission products, Technetium-99 (half-life 220,000 years) and Iodine-129 (half-life 15.7 million years), which dominate spent nuclear fuel radioactivity after a few thousand years. The most troublesome transuranic elements in spent fuel are Neptunium-237 (half-life two million years) and Plutonium-239 (half-life 24,000 years). Consequently, high-level radioactive waste requires sophisticated treatment and management to successfully isolate it from the biosphere. This usually necessitates treatment, followed by a long-term management strategy involving permanent storage, disposal or transformation of the waste into a non-toxic form.

Governments around the world are considering a range of waste management and disposal options, usually involving deep-geologic placement, although there has been limited progress toward implementing long-term waste management solutions. This is partly because the timeframes in question when dealing with radioactive waste range from 10,000 to millions of years, according to studies based on the effect of estimated radiation doses.

Since the fraction of a radioisotope's atoms decaying per unit of time is inversely proportional to its half-life, the relative radioactivity of a quantity of buried human radioactive waste would diminish over time compared to natural radioisotopes (such as the decay chain of 120 trillion tons of thorium and 40 trillion tons of uranium which are at relatively trace concentrations of parts per million each over the crust's 3 * 10¹⁹ ton mass). For instance, over a timeframe of thousands of years, after the most active short half-life radioisotopes decayed, burying U.S. nuclear waste would increase the radioactivity in the top 2000 feet of rock and soil in the United States (10 million km²) by ≈ 1 part in 10 million over the cumulative amount of natural radioisotopes in such a volume, although the vicinity of the site would have a far higher concentration of artificial radioisotopes underground than such an average.

Improvements to nuclear fission technologies

Newer reactor designs intended to provide increased safety have been developed over time. These designs include those that incorporate passive safety and Small Modular Reactors. While these reactor designs "are intended to inspire trust, they may have an unintended effect: creating distrust of older reactors that lack the touted safety features".

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).

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.

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

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”. 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”.

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”.

According to Areva's Southeast Asia and Oceania director, Selena Ng, Japan's Fukushima nuclear disaster is "a huge wake-up call for a nuclear industry that hasn't always been sufficiently transparent about safety issues". She said "There was a sort of complacency before Fukushima and I don't think we can afford to have that complacency now".

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.

According to Mycle Schneider, reactor safety depends above all on a 'culture of security', including the quality of maintenance and training, the competence of the operator and the workforce, and the rigour of regulatory oversight. So a better-designed, newer reactor is not always a safer one, and older reactors are not necessarily more dangerous than newer ones. The 1978 Three Mile Island accident in the United States occurred in a reactor that had started operation only three months earlier, and the Chernobyl disaster occurred after only two years of operation. A serious loss of coolant occurred at the French Civaux-1 reactor in 1998, less than five months after start-up.

However safe a plant is designed to be, it is operated by humans who are prone to errors. Laurent Stricker, a nuclear engineer and chairman of the World Association of Nuclear Operators says that operators must guard against complacency and avoid overconfidence. Experts say that the "largest single internal factor determining the safety of a plant is the culture of security among regulators, operators and the workforce — and creating such a culture is not easy".

Risks

The routine health risks and greenhouse gas emissions from nuclear fission power are small relative to those associated with coal, but there are several "catastrophic risks":

The extreme danger of the radioactive material in power plants and of nuclear technology in and of itself is so well-known that the US government was prompted (at the industry's urging) to enact provisions that protect the nuclear industry from bearing the full burden of such inherently risky nuclear operations. The Price-Anderson Act limits industry's liability in the case of accidents, and the 1982 Nuclear Waste Policy Act charges the federal government with responsibility for permanently storing nuclear waste.

Population density is one critical lens through which other risks have to be assessed, says Laurent Stricker, a nuclear engineer and chairman of the World Association of Nuclear Operators:

The KANUPP plant in Karachi, Pakistan, has the most people — 8.2 million — living within 30 kilometres of a nuclear plant, although it has just one relatively small reactor with an output of 125 megawatts. Next in the league, however, are much larger plants — Taiwan's 1,933-megawatt Kuosheng plant with 5.5 million people within a 30-kilometre radius and the 1,208-megawatt Chin Shan plant with 4.7 million; both zones include the capital city of Taipei.

• International Nuclear Events Scale
• Comparative Risk Assessment
• Statistical Risk Assessment
• Probabilistic risk assessment
  • Severe Accident Risks: An Assessment for Five U.S. Nuclear Power Plants NUREG-1150 1991
  • Calculation of Reactor Accident Consequences CRAC-II 1982
  • Rasmussen Report: Reactor Safety Study WASH-1400 1975
  • The Brookhaven Report: Theoretical Possibilities and Consequences of Major Accidents in Large Nuclear Power Plants WASH-740 1957

The AP1000 has a maximum core damage frequency of 5.09 x 10⁻⁷ per plant per year. The Evolutionary Power Reactor (EPR) has a maximum core damage frequency of 4 x 10⁻⁷ per plant per year. General Electric has recalculated maximum core damage frequencies per year per plant for its nuclear power plant designs:

BWR/4 -- 1 x 10^-5

BWR/6 -- 1 x 10^-6

ABWR -- 2 x 10^-7

ESBWR -- 3 x 10^-8

Black Swan events

Black Swan events are highly unlikely occurrences that have big repercussions. Despite planning, nuclear power will always be vulnerable to black swan events:

A rare event – especially one that has never occurred – is difficult to foresee, expensive to plan for and easy to discount with statistics. Just because something is only supposed to happen every 10,000 years does not mean that it will not happen tomorrow. Over the typical 40-year life of a plant, assumptions can also change, as they did on September 11, 2001, in August 2005 when Hurricane Katrina struck, and in March after Fukushima.

The list of potential black swan events is "damningly diverse":

Nuclear reactors and their spent-fuel pools are targets for terrorists piloting hijacked planes. Reactors may be situated downstream from dams that, should they ever burst, could unleash biblical floods. Some reactors are located close to earthquake faults or shorelines exposed to tsunamis or hurricane storm surges. Any one of these threats could produce the ultimate danger scenario like the ones that emerges at Three Mile Island and Fukushima – a catastrophic coolant failure, the overheating and melting of the radioactive fuel rods, and the deadly release of radioactive material.

Beyond design basis events

As Fukushima showed, external threats — such as earthquakes, tsunamis, fires, flooding, tornadoes and terrorist attacks — are some of the greatest risk factors for a serious nuclear accident. Yet, nuclear plant operators have normally considered these accident sequences (called 'beyond design basis' events) so unlikely that they have not built in complete safeguards.

Forecasting the location of the next earthquake or the size of the next tsunami is an imperfect art. Nuclear plants situated outside known geological danger zones "could pose greater accident threats in the event of an earthquake than those inside, as the former could have weaker protection built in". The Fukushima I plant, for example, was "located in an area designated, on Japan's seismic risk map, as having a relatively low chance of a large earthquake and tsunami; when the 2011 tsunami arrived, it was in excess of anything its engineers had planned for".

Transparency and ethics

According to Stephanie Cooke, it is difficult to know what really goes on inside nuclear power plants because the industry is shrouded in secrecy. Corporations and governments control what information is made available to the public. Cooke says "when information is made available, it is often couched in jargon and incomprehensible prose".

Kennette Benedict has said that nuclear technology and plant operations continue to lack transparency and to be relatively closed to public view:

Despite victories like the creation of the Atomic Energy Commission, and later the Nuclear Regular Commission, the secrecy that began with the Manhattan Project has tended to permeate the civilian nuclear program, as well as the military and defense programs.

In 1986, Soviet officials held off reporting the Chernobyl disaster for several days. The operators of the Fukushima plant, Tokyo Electric Power Co, were also criticised for not quickly disclosing information on radiation leaks from the plant. Russian President Dmitry Medvedev said there must be greater transparency in nuclear emergencies.

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, even 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.

Non-Nuclear Futures: The Case for an Ethical Energy Strategy is a 1975 book by Amory B. Lovins and John H. Price. The main theme of the book is that the most important parts of the nuclear power debate are not technical disputes but relate to personal values, and are the legitimate province of every citizen, whether technically trained or not.

Nuclear and radiation accidents

According to Zia Mian and Alexander Glaser, the "past six decades have shown that nuclear technology does not tolerate error". Nuclear power is perhaps the primary example of what are called ‘high-risk technologies’ with ‘catastrophic potential’, because “no matter how effective conventional safety devices are, there is a form of accident that is inevitable, and such accidents are a ‘normal’ consequence of the system.” In short, there is no escape from system failures.

Accident liability protection

See also: Price-Anderson Nuclear Industries Indemnity Act

Kristin Shrader-Frechette has said "if reactors were safe, nuclear industries would not demand government-guaranteed, accident-liability protection, as a condition for their generating electricity". No private insurance company or even consortium of insurance companies "would shoulder the fearsome liabilities arising from severe nuclear accidents".

2011 Fukushima I accidents

Three of the reactors at Fukushima I overheated, causing meltdowns that eventually led to hydrogen explosions, which released large amounts of radioactive gases into the air.

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

Despite all assurances, a major nuclear accident on the scale of the 1986 Chernobyl disaster happened again in 2011 in Japan, one of the world's most industrially advanced countries. Nuclear Safety Commission Chairman Haruki Madarame told a parliamentary inquiry in February 2012 that "Japan's atomic safety rules are inferior to global standards and left the country unprepared for the Fukushima nuclear disaster last March". There were flaws in, and lax enforcement of, the safety rules governing Japanese nuclear power companies, and this included insufficient protection against tsunamis.

A 2012 report in The Economist said: "The reactors at Fukushima were of an old design. The risks they faced had not been well analysed. The operating company was poorly regulated and did not know what was going on. The operators made mistakes. The representatives of the safety inspectorate fled. Some of the equipment failed. The establishment repeatedly played down the risks and suppressed information about the movement of the radioactive plume, so some people were evacuated from more lightly to more heavily contaminated places".

The designers of the Fukushima I Nuclear Power Plant reactors 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".

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. There was a rise in radiation levels on the outskirts of Tokyo, with a population of 30 million, 135 miles (210 kilometers) to the south.

Back-up diesel generators that might have averted the disaster were positioned in a basement, where they were quickly overwhelmed by waves. The cascade of events at Fukushima had been predicted in a report published in the U.S. several decades ago:

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.

The report was cited in a 2004 statement by Japan’s Nuclear and Industrial Safety Agency, but it seems adequate measures to address the risk were not taken by TEPCO. 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”.

According to the International Atomic Energy Agency, Japan "underestimated the danger of tsunamis and failed to prepare adequate backup systems at the Fukushima Daiichi nuclear plant". This repeated a widely held criticism in Japan that "collusive ties between regulators and industry led to weak oversight and a failure to ensure adequate safety levels at the plant". The IAEA also said that the Fukushima disaster exposed the lack of adequate backup systems at the plant. Once power was completely lost, critical functions like the cooling system shut down. Three of the reactors "quickly overheated, causing meltdowns that eventually led to explosions, which hurled large amounts of radioactive material into the air".

Louise Fréchette and Trevor Findlay have said that more effort is needed to ensure nuclear safety and improve responses to accidents:

The multiple reactor crises at Japan's Fukushima nuclear power plant reinforce the need for strengthening global instruments to ensure nuclear safety worldwide. The fact that a country that has been operating nuclear power reactors for decades should prove so alarmingly improvisational in its response and so unwilling to reveal the facts even to its own people, much less the International Atomic Energy Agency, is a reminder that nuclear safety is a constant work-in-progress.

David Lochbaum, chief nuclear safety officer with the Union of Concerned Scientists, has repeatedly questioned the safety of the Fukushima I Plant's General Electric Mark 1 reactor design, which is used in almost a quarter of the United States' nuclear fleet.

A report from the Japanese Government to the IAEA says the "nuclear fuel in three reactors probably melted through the inner containment vessels, not just the core". The report says the "inadequate" basic reactor design — the Mark-1 model developed by General Electric — included "the venting system for the containment vessels and the location of spent fuel cooling pools high in the buildings, which resulted in leaks of radioactive water that hampered repair work".

Following the Fukushima emergency, the European Union decided that reactors across all 27 member nations should undergo safety tests.

According to UBS AG, the Fukushima I nuclear accidents are likely to hurt the nuclear power industry’s credibility more than the Chernobyl disaster in 1986:

The accident in the former Soviet Union 25 years ago 'affected one reactor in a totalitarian state with no safety culture,' UBS analysts including Per Lekander and Stephen Oldfield wrote in a report today. 'At Fukushima, four reactors have been out of control for weeks -- casting doubt on whether even an advanced economy can master nuclear safety.'

The Fukushima accident exposed some troubling nuclear safety issues:

Despite the resources poured into analyzing crustal movements and having expert committees determine earthquake risk, for instance, researchers never considered the possibility of a magnitude-9 earthquake followed by a massive tsunami. The failure of multiple safety features on nuclear power plants has raised questions about the nation's engineering prowess. Government flip-flopping on acceptable levels of radiation exposure confused the public, and health professionals provided little guidance. Facing a dearth of reliable information on radiation levels, citizens armed themselves with dosimeters, pooled data, and together produced radiological contamination maps far more detailed than anything the government or official scientific sources ever provided.

As of January 2012, questions also linger as to the extent of damage to the Fukushima plant caused by the earthquake even before the tsunami hit. Any evidence of serious quake damage at the plant would "cast new doubt on the safety of other reactors in quake-prone Japan".

Two government advisers have said that "Japan's safety review of nuclear reactors after the Fukushima disaster is based on faulty criteria and many people involved have conflicts of interest". Hiromitsu Ino, Professor Emeritus at the University of Tokyo, says "The whole process being undertaken is exactly the same as that used previous to the Fukushima Dai-Ichi accident, even though the accident showed all these guidelines and categories to be insufficient".

In March 2012, Prime Minister Yoshihiko Noda acknowledged that the Japanese government shared the blame for the Fukushima disaster, saying that officials had been blinded by a false belief in the country's "technological infallibility", and were all too steeped in a "safety myth".

1986 Chernobyl disaster

Main articles: Chernobyl disaster and Chernobyl disaster effects

Map showing Caesium-137 contamination in Belarus, Russia, and Ukraine as of 1996.

The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine. An explosion and fire released large quantities of radioactive contamination into the atmosphere, which spread over much of Western USSR and Europe. It is considered the worst nuclear power plant accident in history, and is one of only two classified as a level 7 event on the International Nuclear Event Scale (the other being the Fukushima Daiichi nuclear disaster). The battle to contain the contamination and avert a greater catastrophe ultimately involved over 500,000 workers and cost an estimated 18 billion rubles, crippling the Soviet economy. The accident raised concerns about the safety of the nuclear power industry, slowing its expansion for a number of years.

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 predicted in 2005 that up to 4,000 additional cancer deaths related to the accident would appear "among the 600 000 persons receiving more significant exposures (liquidators working in 1986–87, evacuees, and residents of the most contaminated areas)". Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chernobyl disaster.

Other accidents

See also: List of civilian nuclear accidents, List of civilian radiation accidents, and List of military nuclear accidents

Serious nuclear and radiation accidents include the Chalk River accidents (1952, 1958 & 2008), Mayak disaster (1957), Windscale fire (1957), SL-1 accident (1961), Soviet submarine K-19 accident (1961), Three Mile Island accident (1979), Church Rock uranium mill spill (1979), Soviet submarine K-431 accident (1985), Goiânia accident (1987), Zaragoza radiotherapy accident (1990), Costa Rica radiotherapy accident (1996), Tokaimura nuclear accident (1999), Sellafield THORP leak (2005), and the Flerus IRE Cobalt-60 spill (2006).

Health impacts

Japan towns, villages, and cities around the Fukushima Daiichi nuclear plant. The 20km and 30km areas had evacuation and sheltering orders, and additional administrative districts that had an evacuation order are highlighted.

See also: Chernobyl disaster effects and Nuclear power debate

In spite of accidents like Chernobyl, studies have shown that nuclear deaths are mostly in uranium mining and that nuclear energy has generated far fewer deaths than the high pollution levels that result from the use of conventional fossil fuels.

Journalist Stephanie Cooke says that it is not useful to make comparisons just in terms of number of deaths, as the way people live afterwards is also relevant, as in the case of the 2011 Japanese nuclear accidents:

You have people in Japan right now that are facing either not returning to their homes forever, or if they do return to their homes, living in a contaminated area for basically ever... It affects millions of people, it affects our land, it affects our atmosphere ... it's affecting future generations ... I don't think any of these great big massive plants that spew pollution into the air are good. But I don't think it's really helpful to make these comparisons just in terms of number of deaths.

The Fukushima accident forced more than 80,000 residents to evacuate from neighborhoods around the plant.

A survey by the Iitate, Fukushima local government obtained responses from some 1,743 people who have evacuated from the village, which lies within the emergency evacuation zone around the crippled Fukushima Daiichi Plant. It shows that many residents are experiencing growing frustration and instability due to the nuclear crisis and an inability to return to the lives they were living before the disaster. Sixty percent of respondents stated that their health and the health of their families had deteriorated after evacuating, while 39.9 percent reported feeling more irritated compared to before the disaster.

Summarizing all responses to questions related to evacuees' current family status, one-third of all surveyed families live apart from their children, while 50.1 percent live away from other family members (including elderly parents) with whom they lived before the disaster. The survey also showed that 34.7 percent of the evacuees have suffered salary cuts of 50 percent or more since the outbreak of the nuclear disaster. A total of 36.8 percent reported a lack of sleep, while 17.9 percent reported smoking or drinking more than before they evacuated.

Developing countries

There are concerns about developing countries "rushing to join the so-called nuclear renaissance without the necessary infrastructure, personnel, regulatory frameworks and safety culture". Some countries with nuclear aspirations, like Nigeria, Kenya, Bangladesh and Venezuela, have no significant industrial experience and will require at least a decade of preparation even before breaking ground at a reactor site.

The speed of the nuclear construction program in China has raised safety concerns. The challenge for the government and nuclear companies is to "keep an eye on a growing army of contractors and subcontractors who may be tempted to cut corners". China is advised to maintain nuclear safeguards in a business culture where quality and safety are sometimes sacrificed in favor of cost-cutting, profits, and corruption. China has asked for international assistance in training more nuclear power plant inspectors.

Nuclear weapons plant security

There are ongoing concerns about terrorist groups acquiring nuclear bomb-making material. The notion of terrorist organizations using nuclear weapons (especially very small ones, such as suitcase nukes) has been a threat in American rhetoric and culture.

Various acts of civil disobedience since 1980 by the peace group Plowshares have shown how nuclear weapons facilities can be penetrated, and the groups actions represent extraordinary breaches of security at nuclear weapons plants in the United States. On July 28, 2012, three members of Plowshares cut through fences at the Y-12 National Security Complex in Oak Ridge, Tennessee, which manufactures US nuclear weapons and stockpiles highly enriched uranium. The group spray-painted protest messages, hung banners, and splashed blood.

The National Nuclear Security Administration has acknowledged the seriousness of the 2012 Plowshares action, which involved the protesters walking into a high-security zone of the plant, calling the security breach "unprecedented." Independent security contractor, WSI, has since had a weeklong "security stand-down," a halt to weapons production, and mandatory refresher training for all security staff.

Non-proliferation policy experts are concerned about the relative ease with which these unarmed, unsophisticated protesters could cut through a fence and walk into the center of the facility. This is further evidence that nuclear security -- the securing of highly enriched uranium and plutonium -- should be a top priority to prevent terrorist groups from acquiring nuclear bomb-making material. These experts have questioned “the use of private contractors to provide security at facilities that manufacture and store the government's most dangerous military material”.

Fusion power

Main articles: Fusion power and Fusion power § Safety and the environment

Fusion power is a developing technology still under research. It relies on fusing rather than fissioning (splitting) atomic nuclei, using very different processes compared to current nuclear power plants. Commercial plants and prototype generators are not anticipated before 2030 - 2050. Fusion has significant safety advantages over current fission methods.

Nuclear fusion uses only tiny amounts of fuel at any time, and requires precisely controlled conditions to generate any net energy. Fusion reaction processes are so delicate that this level of safety is inherent; no elaborate failsafe mechanism is required. The fuel itself is extremely safe at any temperature outside that of a working fusion reactor and only tiny amounts are used. If the reactor were damaged or control impaired, or the fuel supply stops, reactions and heat generation would cease almost immediately. For the same reason, there is also no risk of a thermal runaway or nuclear meltdown, since any significant change will render the reactions unable to produce excess heat. In comparison, a fission reactor is typically loaded with enough fuel for one or several years, enough fuel in a sufficiently small space will always produce thermal runaway or "meltdown", and no additional fuel is necessary to keep the reaction going. In the event of fire, calculations suggest that the total amount of radioactive gases from a typical fusion plant would be so small, about 1 kg, that they would have diluted to legally acceptable limits by the time they blew as far as the plant's perimeter fence.

In general terms, fusion reactors also create less radioactive material than a fission reactor, the material it would create is less damaging biologically, and the radioactivity "falls off" within a time period that is within existing engineering capabilities. The main byproduct is a small amount of helium, which is harmless to life. Of more concern is tritium, which, like other isotopes of hydrogen, is a very light gas, and difficult to retain completely. Although volatile and biologically active, the health risk is lower than most other radioactive contaminants, due to tritium's short half-life (12 years), very low decay energy (~14.95 keV), and the fact that it does not bioaccumulate (instead being cycled out of the body as water, with a biological half-life of 7 to 14 days). However the effect of widespread fusion power may require attention in this area.

Unlike fission reactors, whose used fuel rods and other waste remains highly radioactive for thousands of years, most of the radioactive material in a fusion reactor would be the reactor core itself, which would be dangerous for about 50 years, and low-level waste another 100. Fusion reactors can more easily be designed using "low activation" materials that do not easily become radioactive, such as vanadium or carbon fiber. Although the core of a decommissioned reactor will be considerably more radioactive during those 50 years than fission waste, the relatively short time period makes waste management fairly straightforward. By 300 years it would have the same radioactivity as coal ash.

In some designs, powerful magnets are used. Failure of their support structure could allow the magnets to fly outward. The severity of this event would be similar to any other magnet quench, and can be effectively stopped with a containment building.

The overlap with nuclear weapons technology is limited. Copious neutrons could be used to breed plutonium for an atomic bomb, but not without extensive redesign of the reactor, so that production would be difficult to conceal. The theoretical and computational tools needed for hydrogen bomb design are closely related to those needed for inertial confinement fusion, but have very little in common with the more scientifically developed magnetic confinement fusion. Tritium, if used, is a component of the trigger of hydrogen bombs, but not a major problem in production.

See also

• Lists of nuclear disasters and radioactive incidents
• Deep geological repository
• Design basis accident
• Environmental impact of nuclear power
• International Nuclear Events Scale
• Nuclear accidents in the United States
• Nuclear criticality safety
• Nuclear fuel response to reactor accidents
• Nuclear power debate
• Nuclear power plant emergency response team
• Nuclear power whistleblowers
• Nuclear weapon
• Passive nuclear safety
• Yucca Mountain nuclear waste repository
• Safety code (nuclear reactor)
• World Association of Nuclear Operators

External links

• International Atomic Energy Agency website
• Nuclear Safety Info Resources
• Nuclear Safety Discussion Forums
• The Nuclear Energy Option, online book by Bernard L. Cohen. Emphasis on risk estimates of nuclear.

Hazards of nuclear material

Main article: High-level radioactive waste management

Spent nuclear fuel stored underwater and uncapped at the Hanford site in Washington, USA.

The world's nuclear fleet creates about 10,000 metric tons of high-level spent nuclear fuel each year. High-level radioactive waste management concerns management and disposal of highly radioactive materials created during production of nuclear power. The technical issues in accomplishing this are daunting, due to the extremely long periods radioactive wastes remain deadly to living organisms. Of particular concern are two long-lived fission products, Technetium-99 (half-life 220,000 years) and Iodine-129 (half-life 15.7 million years), which dominate spent nuclear fuel radioactivity after a few thousand years. The most troublesome transuranic elements in spent fuel are Neptunium-237 (half-life two million years) and Plutonium-239 (half-life 24,000 years). Consequently, high-level radioactive waste requires sophisticated treatment and management to successfully isolate it from the biosphere. This usually necessitates treatment, followed by a long-term management strategy involving permanent storage, disposal or transformation of the waste into a non-toxic form.

Governments around the world are considering a range of waste management and disposal options, usually involving deep-geologic placement, although there has been limited progress toward implementing long-term waste management solutions. This is partly because the timeframes in question when dealing with radioactive waste range from 10,000 to millions of years, according to studies based on the effect of estimated radiation doses.

Since the fraction of a radioisotope's atoms decaying per unit of time is inversely proportional to its half-life, the relative radioactivity of a quantity of buried human radioactive waste would diminish over time compared to natural radioisotopes (such as the decay chain of 120 trillion tons of thorium and 40 trillion tons of uranium which are at relatively trace concentrations of parts per million each over the crust's 3 * 10¹⁹ ton mass). For instance, over a timeframe of thousands of years, after the most active short half-life radioisotopes decayed, burying U.S. nuclear waste would increase the radioactivity in the top 2000 feet of rock and soil in the United States (10 million km²) by ≈ 1 part in 10 million over the cumulative amount of natural radioisotopes in such a volume, although the vicinity of the site would have a far higher concentration of artificial radioisotopes underground than such an average.

Improvements to nuclear fission technologies

Newer reactor designs intended to provide increased safety have been developed over time. These designs include those that incorporate passive safety and Small Modular Reactors. While these reactor designs "are intended to inspire trust, they may have an unintended effect: creating distrust of older reactors that lack the touted safety features".

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).

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.

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

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”. 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”.

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”.

According to Areva's Southeast Asia and Oceania director, Selena Ng, Japan's Fukushima nuclear disaster is "a huge wake-up call for a nuclear industry that hasn't always been sufficiently transparent about safety issues". She said "There was a sort of complacency before Fukushima and I don't think we can afford to have that complacency now".

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.

According to Mycle Schneider, reactor safety depends above all on a 'culture of security', including the quality of maintenance and training, the competence of the operator and the workforce, and the rigour of regulatory oversight. So a better-designed, newer reactor is not always a safer one, and older reactors are not necessarily more dangerous than newer ones. The 1978 Three Mile Island accident in the United States occurred in a reactor that had started operation only three months earlier, and the Chernobyl disaster occurred after only two years of operation. A serious loss of coolant occurred at the French Civaux-1 reactor in 1998, less than five months after start-up.

However safe a plant is designed to be, it is operated by humans who are prone to errors. Laurent Stricker, a nuclear engineer and chairman of the World Association of Nuclear Operators says that operators must guard against complacency and avoid overconfidence. Experts say that the "largest single internal factor determining the safety of a plant is the culture of security among regulators, operators and the workforce — and creating such a culture is not easy".

Risks

The routine health risks and greenhouse gas emissions from nuclear fission power are small relative to those associated with coal, but there are several "catastrophic risks":

The extreme danger of the radioactive material in power plants and of nuclear technology in and of itself is so well-known that the US government was prompted (at the industry's urging) to enact provisions that protect the nuclear industry from bearing the full burden of such inherently risky nuclear operations. The Price-Anderson Act limits industry's liability in the case of accidents, and the 1982 Nuclear Waste Policy Act charges the federal government with responsibility for permanently storing nuclear waste.

Population density is one critical lens through which other risks have to be assessed, says Laurent Stricker, a nuclear engineer and chairman of the World Association of Nuclear Operators:

The KANUPP plant in Karachi, Pakistan, has the most people — 8.2 million — living within 30 kilometres of a nuclear plant, although it has just one relatively small reactor with an output of 125 megawatts. Next in the league, however, are much larger plants — Taiwan's 1,933-megawatt Kuosheng plant with 5.5 million people within a 30-kilometre radius and the 1,208-megawatt Chin Shan plant with 4.7 million; both zones include the capital city of Taipei.

• International Nuclear Events Scale
• Comparative Risk Assessment
• Statistical Risk Assessment
• Probabilistic risk assessment
  • Severe Accident Risks: An Assessment for Five U.S. Nuclear Power Plants NUREG-1150 1991
  • Calculation of Reactor Accident Consequences CRAC-II 1982
  • Rasmussen Report: Reactor Safety Study WASH-1400 1975
  • The Brookhaven Report: Theoretical Possibilities and Consequences of Major Accidents in Large Nuclear Power Plants WASH-740 1957

The AP1000 has a maximum core damage frequency of 5.09 x 10⁻⁷ per plant per year. The Evolutionary Power Reactor (EPR) has a maximum core damage frequency of 4 x 10⁻⁷ per plant per year. General Electric has recalculated maximum core damage frequencies per year per plant for its nuclear power plant designs:

BWR/4 -- 1 x 10^-5

BWR/6 -- 1 x 10^-6

ABWR -- 2 x 10^-7

ESBWR -- 3 x 10^-8

Black Swan events

Black Swan events are highly unlikely occurrences that have big repercussions. Despite planning, nuclear power will always be vulnerable to black swan events:

A rare event – especially one that has never occurred – is difficult to foresee, expensive to plan for and easy to discount with statistics. Just because something is only supposed to happen every 10,000 years does not mean that it will not happen tomorrow. Over the typical 40-year life of a plant, assumptions can also change, as they did on September 11, 2001, in August 2005 when Hurricane Katrina struck, and in March after Fukushima.

The list of potential black swan events is "damningly diverse":

Nuclear reactors and their spent-fuel pools are targets for terrorists piloting hijacked planes. Reactors may be situated downstream from dams that, should they ever burst, could unleash biblical floods. Some reactors are located close to earthquake faults or shorelines exposed to tsunamis or hurricane storm surges. Any one of these threats could produce the ultimate danger scenario like the ones that emerges at Three Mile Island and Fukushima – a catastrophic coolant failure, the overheating and melting of the radioactive fuel rods, and the deadly release of radioactive material.

Beyond design basis events

As Fukushima showed, external threats — such as earthquakes, tsunamis, fires, flooding, tornadoes and terrorist attacks — are some of the greatest risk factors for a serious nuclear accident. Yet, nuclear plant operators have normally considered these accident sequences (called 'beyond design basis' events) so unlikely that they have not built in complete safeguards.

Forecasting the location of the next earthquake or the size of the next tsunami is an imperfect art. Nuclear plants situated outside known geological danger zones "could pose greater accident threats in the event of an earthquake than those inside, as the former could have weaker protection built in". The Fukushima I plant, for example, was "located in an area designated, on Japan's seismic risk map, as having a relatively low chance of a large earthquake and tsunami; when the 2011 tsunami arrived, it was in excess of anything its engineers had planned for".

Transparency and ethics

According to Stephanie Cooke, it is difficult to know what really goes on inside nuclear power plants because the industry is shrouded in secrecy. Corporations and governments control what information is made available to the public. Cooke says "when information is made available, it is often couched in jargon and incomprehensible prose".

Kennette Benedict has said that nuclear technology and plant operations continue to lack transparency and to be relatively closed to public view:

Despite victories like the creation of the Atomic Energy Commission, and later the Nuclear Regular Commission, the secrecy that began with the Manhattan Project has tended to permeate the civilian nuclear program, as well as the military and defense programs.

In 1986, Soviet officials held off reporting the Chernobyl disaster for several days. The operators of the Fukushima plant, Tokyo Electric Power Co, were also criticised for not quickly disclosing information on radiation leaks from the plant. Russian President Dmitry Medvedev said there must be greater transparency in nuclear emergencies.

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, even 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.

Non-Nuclear Futures: The Case for an Ethical Energy Strategy is a 1975 book by Amory B. Lovins and John H. Price. The main theme of the book is that the most important parts of the nuclear power debate are not technical disputes but relate to personal values, and are the legitimate province of every citizen, whether technically trained or not.

Nuclear and radiation accidents

According to Zia Mian and Alexander Glaser, the "past six decades have shown that nuclear technology does not tolerate error". Nuclear power is perhaps the primary example of what are called ‘high-risk technologies’ with ‘catastrophic potential’, because “no matter how effective conventional safety devices are, there is a form of accident that is inevitable, and such accidents are a ‘normal’ consequence of the system.” In short, there is no escape from system failures.

Accident liability protection

See also: Price-Anderson Nuclear Industries Indemnity Act

Kristin Shrader-Frechette has said "if reactors were safe, nuclear industries would not demand government-guaranteed, accident-liability protection, as a condition for their generating electricity". No private insurance company or even consortium of insurance companies "would shoulder the fearsome liabilities arising from severe nuclear accidents".

2011 Fukushima I accidents

Three of the reactors at Fukushima I overheated, causing meltdowns that eventually led to hydrogen explosions, which released large amounts of radioactive gases into the air.

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

Despite all assurances, a major nuclear accident on the scale of the 1986 Chernobyl disaster happened again in 2011 in Japan, one of the world's most industrially advanced countries. Nuclear Safety Commission Chairman Haruki Madarame told a parliamentary inquiry in February 2012 that "Japan's atomic safety rules are inferior to global standards and left the country unprepared for the Fukushima nuclear disaster last March". There were flaws in, and lax enforcement of, the safety rules governing Japanese nuclear power companies, and this included insufficient protection against tsunamis.

A 2012 report in The Economist said: "The reactors at Fukushima were of an old design. The risks they faced had not been well analysed. The operating company was poorly regulated and did not know what was going on. The operators made mistakes. The representatives of the safety inspectorate fled. Some of the equipment failed. The establishment repeatedly played down the risks and suppressed information about the movement of the radioactive plume, so some people were evacuated from more lightly to more heavily contaminated places".

The designers of the Fukushima I Nuclear Power Plant reactors 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".

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. There was a rise in radiation levels on the outskirts of Tokyo, with a population of 30 million, 135 miles (210 kilometers) to the south.

Back-up diesel generators that might have averted the disaster were positioned in a basement, where they were quickly overwhelmed by waves. The cascade of events at Fukushima had been predicted in a report published in the U.S. several decades ago:

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.

The report was cited in a 2004 statement by Japan’s Nuclear and Industrial Safety Agency, but it seems adequate measures to address the risk were not taken by TEPCO. 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”.

According to the International Atomic Energy Agency, Japan "underestimated the danger of tsunamis and failed to prepare adequate backup systems at the Fukushima Daiichi nuclear plant". This repeated a widely held criticism in Japan that "collusive ties between regulators and industry led to weak oversight and a failure to ensure adequate safety levels at the plant". The IAEA also said that the Fukushima disaster exposed the lack of adequate backup systems at the plant. Once power was completely lost, critical functions like the cooling system shut down. Three of the reactors "quickly overheated, causing meltdowns that eventually led to explosions, which hurled large amounts of radioactive material into the air".

Louise Fréchette and Trevor Findlay have said that more effort is needed to ensure nuclear safety and improve responses to accidents:

The multiple reactor crises at Japan's Fukushima nuclear power plant reinforce the need for strengthening global instruments to ensure nuclear safety worldwide. The fact that a country that has been operating nuclear power reactors for decades should prove so alarmingly improvisational in its response and so unwilling to reveal the facts even to its own people, much less the International Atomic Energy Agency, is a reminder that nuclear safety is a constant work-in-progress.

David Lochbaum, chief nuclear safety officer with the Union of Concerned Scientists, has repeatedly questioned the safety of the Fukushima I Plant's General Electric Mark 1 reactor design, which is used in almost a quarter of the United States' nuclear fleet.

A report from the Japanese Government to the IAEA says the "nuclear fuel in three reactors probably melted through the inner containment vessels, not just the core". The report says the "inadequate" basic reactor design — the Mark-1 model developed by General Electric — included "the venting system for the containment vessels and the location of spent fuel cooling pools high in the buildings, which resulted in leaks of radioactive water that hampered repair work".

Following the Fukushima emergency, the European Union decided that reactors across all 27 member nations should undergo safety tests.

According to UBS AG, the Fukushima I nuclear accidents are likely to hurt the nuclear power industry’s credibility more than the Chernobyl disaster in 1986:

The accident in the former Soviet Union 25 years ago 'affected one reactor in a totalitarian state with no safety culture,' UBS analysts including Per Lekander and Stephen Oldfield wrote in a report today. 'At Fukushima, four reactors have been out of control for weeks -- casting doubt on whether even an advanced economy can master nuclear safety.'

The Fukushima accident exposed some troubling nuclear safety issues:

Despite the resources poured into analyzing crustal movements and having expert committees determine earthquake risk, for instance, researchers never considered the possibility of a magnitude-9 earthquake followed by a massive tsunami. The failure of multiple safety features on nuclear power plants has raised questions about the nation's engineering prowess. Government flip-flopping on acceptable levels of radiation exposure confused the public, and health professionals provided little guidance. Facing a dearth of reliable information on radiation levels, citizens armed themselves with dosimeters, pooled data, and together produced radiological contamination maps far more detailed than anything the government or official scientific sources ever provided.

As of January 2012, questions also linger as to the extent of damage to the Fukushima plant caused by the earthquake even before the tsunami hit. Any evidence of serious quake damage at the plant would "cast new doubt on the safety of other reactors in quake-prone Japan".

Two government advisers have said that "Japan's safety review of nuclear reactors after the Fukushima disaster is based on faulty criteria and many people involved have conflicts of interest". Hiromitsu Ino, Professor Emeritus at the University of Tokyo, says "The whole process being undertaken is exactly the same as that used previous to the Fukushima Dai-Ichi accident, even though the accident showed all these guidelines and categories to be insufficient".

In March 2012, Prime Minister Yoshihiko Noda acknowledged that the Japanese government shared the blame for the Fukushima disaster, saying that officials had been blinded by a false belief in the country's "technological infallibility", and were all too steeped in a "safety myth".

1986 Chernobyl disaster

Main articles: Chernobyl disaster and Chernobyl disaster effects

Map showing Caesium-137 contamination in Belarus, Russia, and Ukraine as of 1996.

The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine. An explosion and fire released large quantities of radioactive contamination into the atmosphere, which spread over much of Western USSR and Europe. It is considered the worst nuclear power plant accident in history, and is one of only two classified as a level 7 event on the International Nuclear Event Scale (the other being the Fukushima Daiichi nuclear disaster). The battle to contain the contamination and avert a greater catastrophe ultimately involved over 500,000 workers and cost an estimated 18 billion rubles, crippling the Soviet economy. The accident raised concerns about the safety of the nuclear power industry, slowing its expansion for a number of years.

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 predicted in 2005 that up to 4,000 additional cancer deaths related to the accident would appear "among the 600 000 persons receiving more significant exposures (liquidators working in 1986–87, evacuees, and residents of the most contaminated areas)". Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chernobyl disaster.

Other accidents

See also: List of civilian nuclear accidents, List of civilian radiation accidents, and List of military nuclear accidents

Serious nuclear and radiation accidents include the Chalk River accidents (1952, 1958 & 2008), Mayak disaster (1957), Windscale fire (1957), SL-1 accident (1961), Soviet submarine K-19 accident (1961), Three Mile Island accident (1979), Church Rock uranium mill spill (1979), Soviet submarine K-431 accident (1985), Goiânia accident (1987), Zaragoza radiotherapy accident (1990), Costa Rica radiotherapy accident (1996), Tokaimura nuclear accident (1999), Sellafield THORP leak (2005), and the Flerus IRE Cobalt-60 spill (2006).

Health impacts

Japan towns, villages, and cities around the Fukushima Daiichi nuclear plant. The 20km and 30km areas had evacuation and sheltering orders, and additional administrative districts that had an evacuation order are highlighted.

See also: Chernobyl disaster effects and Nuclear power debate

In spite of accidents like Chernobyl, studies have shown that nuclear deaths are mostly in uranium mining and that nuclear energy has generated far fewer deaths than the high pollution levels that result from the use of conventional fossil fuels.

Journalist Stephanie Cooke says that it is not useful to make comparisons just in terms of number of deaths, as the way people live afterwards is also relevant, as in the case of the 2011 Japanese nuclear accidents:

You have people in Japan right now that are facing either not returning to their homes forever, or if they do return to their homes, living in a contaminated area for basically ever... It affects millions of people, it affects our land, it affects our atmosphere ... it's affecting future generations ... I don't think any of these great big massive plants that spew pollution into the air are good. But I don't think it's really helpful to make these comparisons just in terms of number of deaths.

The Fukushima accident forced more than 80,000 residents to evacuate from neighborhoods around the plant.

A survey by the Iitate, Fukushima local government obtained responses from some 1,743 people who have evacuated from the village, which lies within the emergency evacuation zone around the crippled Fukushima Daiichi Plant. It shows that many residents are experiencing growing frustration and instability due to the nuclear crisis and an inability to return to the lives they were living before the disaster. Sixty percent of respondents stated that their health and the health of their families had deteriorated after evacuating, while 39.9 percent reported feeling more irritated compared to before the disaster.

Summarizing all responses to questions related to evacuees' current family status, one-third of all surveyed families live apart from their children, while 50.1 percent live away from other family members (including elderly parents) with whom they lived before the disaster. The survey also showed that 34.7 percent of the evacuees have suffered salary cuts of 50 percent or more since the outbreak of the nuclear disaster. A total of 36.8 percent reported a lack of sleep, while 17.9 percent reported smoking or drinking more than before they evacuated.

Developing countries

There are concerns about developing countries "rushing to join the so-called nuclear renaissance without the necessary infrastructure, personnel, regulatory frameworks and safety culture". Some countries with nuclear aspirations, like Nigeria, Kenya, Bangladesh and Venezuela, have no significant industrial experience and will require at least a decade of preparation even before breaking ground at a reactor site.

The speed of the nuclear construction program in China has raised safety concerns. The challenge for the government and nuclear companies is to "keep an eye on a growing army of contractors and subcontractors who may be tempted to cut corners". China is advised to maintain nuclear safeguards in a business culture where quality and safety are sometimes sacrificed in favor of cost-cutting, profits, and corruption. China has asked for international assistance in training more nuclear power plant inspectors.

Nuclear weapons plant security

There are ongoing concerns about terrorist groups acquiring nuclear bomb-making material. The notion of terrorist organizations using nuclear weapons (especially very small ones, such as suitcase nukes) has been a threat in American rhetoric and culture.

Various acts of civil disobedience since 1980 by the peace group Plowshares have shown how nuclear weapons facilities can be penetrated, and the groups actions represent extraordinary breaches of security at nuclear weapons plants in the United States. On July 28, 2012, three members of Plowshares cut through fences at the Y-12 National Security Complex in Oak Ridge, Tennessee, which manufactures US nuclear weapons and stockpiles highly enriched uranium. The group spray-painted protest messages, hung banners, and splashed blood.

The National Nuclear Security Administration has acknowledged the seriousness of the 2012 Plowshares action, which involved the protesters walking into a high-security zone of the plant, calling the security breach "unprecedented." Independent security contractor, WSI, has since had a weeklong "security stand-down," a halt to weapons production, and mandatory refresher training for all security staff.

Non-proliferation policy experts are concerned about the relative ease with which these unarmed, unsophisticated protesters could cut through a fence and walk into the center of the facility. This is further evidence that nuclear security -- the securing of highly enriched uranium and plutonium -- should be a top priority to prevent terrorist groups from acquiring nuclear bomb-making material. These experts have questioned “the use of private contractors to provide security at facilities that manufacture and store the government's most dangerous military material”.

Fusion power

Main articles: Fusion power and Fusion power § Safety and the environment

Fusion power is a developing technology still under research. It relies on fusing rather than fissioning (splitting) atomic nuclei, using very different processes compared to current nuclear power plants. Commercial plants and prototype generators are not anticipated before 2030 - 2050. Fusion has significant safety advantages over current fission methods.

Nuclear fusion uses only tiny amounts of fuel at any time, and requires precisely controlled conditions to generate any net energy. Fusion reaction processes are so delicate that this level of safety is inherent; no elaborate failsafe mechanism is required. The fuel itself is extremely safe at any temperature outside that of a working fusion reactor and only tiny amounts are used. If the reactor were damaged or control impaired, or the fuel supply stops, reactions and heat generation would cease almost immediately. For the same reason, there is also no risk of a thermal runaway or nuclear meltdown, since any significant change will render the reactions unable to produce excess heat. In comparison, a fission reactor is typically loaded with enough fuel for one or several years, enough fuel in a sufficiently small space will always produce thermal runaway or "meltdown", and no additional fuel is necessary to keep the reaction going. In the event of fire, calculations suggest that the total amount of radioactive gases from a typical fusion plant would be so small, about 1 kg, that they would have diluted to legally acceptable limits by the time they blew as far as the plant's perimeter fence.

In general terms, fusion reactors also create less radioactive material than a fission reactor, the material it would create is less damaging biologically, and the radioactivity "falls off" within a time period that is within existing engineering capabilities. The main byproduct is a small amount of helium, which is harmless to life. Of more concern is tritium, which, like other isotopes of hydrogen, is a very light gas, and difficult to retain completely. Although volatile and biologically active, the health risk is lower than most other radioactive contaminants, due to tritium's short half-life (12 years), very low decay energy (~14.95 keV), and the fact that it does not bioaccumulate (instead being cycled out of the body as water, with a biological half-life of 7 to 14 days). However the effect of widespread fusion power may require attention in this area.

Unlike fission reactors, whose used fuel rods and other waste remains highly radioactive for thousands of years, most of the radioactive material in a fusion reactor would be the reactor core itself, which would be dangerous for about 50 years, and low-level waste another 100. Fusion reactors can more easily be designed using "low activation" materials that do not easily become radioactive, such as vanadium or carbon fiber. Although the core of a decommissioned reactor will be considerably more radioactive during those 50 years than fission waste, the relatively short time period makes waste management fairly straightforward. By 300 years it would have the same radioactivity as coal ash.

In some designs, powerful magnets are used. Failure of their support structure could allow the magnets to fly outward. The severity of this event would be similar to any other magnet quench, and can be effectively stopped with a containment building.

The overlap with nuclear weapons technology is limited. Copious neutrons could be used to breed plutonium for an atomic bomb, but not without extensive redesign of the reactor, so that production would be difficult to conceal. The theoretical and computational tools needed for hydrogen bomb design are closely related to those needed for inertial confinement fusion, but have very little in common with the more scientifically developed magnetic confinement fusion. Tritium, if used, is a component of the trigger of hydrogen bombs, but not a major problem in production.

See also

• Lists of nuclear disasters and radioactive incidents
• Deep geological repository
• Design basis accident
• Environmental impact of nuclear power
• International Nuclear Events Scale
• Nuclear accidents in the United States
• Nuclear criticality safety
• Nuclear fuel response to reactor accidents
• Nuclear power debate
• Nuclear power plant emergency response team
• Nuclear power whistleblowers
• Nuclear weapon
• Passive nuclear safety
• Yucca Mountain nuclear waste repository
• Safety code (nuclear reactor)
• World Association of Nuclear Operators

External links

• International Atomic Energy Agency website
• Nuclear Safety Info Resources
• Nuclear Safety Discussion Forums
• The Nuclear Energy Option, online book by Bernard L. Cohen. Emphasis on risk estimates of nuclear.