Nuclear safety 4222539 226180719 2008-07-17T05:14:05Z Fanra 4083245 /* Failure modes of nuclear powerplants */ removed opinion. It is not fact. [[Image:Nuclear power defense in depth.png|280px|thumb| This diagram demonstrates the [[defense in depth]] strategy of design of modern [[nuclear power plants]]. Current plants may have some or all of these defenses, the defenses vary depending on the type of plant, the nation constructing them, the use (civilian, military, naval vessels) and the age.<br/> ''1st layer'' of defense is the inert, [[ceramic]] quality of the [[uranium oxide]] itself.<br/> ''2nd layer'' is the airtight [[zirconium]] alloy of the [[fuel rod]].<br/> ''3rd layer'' is the [[Nuclear reactor|reactor]] [[pressure vessel]] made of steel more than a dozen centimeters thick.<br/> ''4th layer'' is the pressure resistant, airtight [[containment building]].<br/> ''5th layer'' is the [[reactor building]] or in newer powerplants a second outer containment building.]] '''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, the use and storage of nuclear materials for medical, power, industry, and military uses. In addition, there are safety issues involved in products created with radioactive materials. Some of the products are legacy ones (such as [[Radioluminescence|watch faces]]), others, like [[Smoke_detector#Ionization_detector|smoke detectors]], are still being produced. [[Nuclear weapon]] safety, as well as the safety of military research involving nuclear materials, is generally handled by separate agencies than civilian safety, for various reasons, including secrecy. ==Agencies== Many nations utilizing [[nuclear power]] have special institutions overseeing and regulating nuclear safety. Internationally the [[International Atomic Energy Agency]] "works for the safe, secure and peaceful uses of nuclear science and technology." 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.<ref>[http://www.nrc.gov/about-nrc.html About NRC], [http://www.nrc.gov U.S. Nuclear Regulatory Commission], Retrieved 2007-6-1</ref><ref>[http://www.nrc.gov/about-nrc/governing-laws.html Our Governing Legislation], [http://www.nrc.gov U.S. Nuclear Regulatory Commission], Retrieved 2007-6-1</ref> In the UK nuclear safety is regulated by the [[Nuclear Installations Inspectorate]] (NII) and the Defence Nuclear Safety Regulator (DNSR). ==Key concepts== Nuclear safety imposes strict demands on the containment of toxic and/or radioactive materials. Contamination of surrounding communities and environment is regarded as a [[never events]] from the perspective of plant design. Due to the energetic nature of nuclear reactions, nuclear material in a chain reaction is not necessarily stable from an energy output perspective, often requiring [[Active safety | active control]] mechanisms to impose artificial stability. Systems are often designed with multiple [[Redundancy (engineering)|redundant]] backups to preclude system failure, with each independent system often designed with a conservative [[factor of safety]] in an attempt to preclude failure of the primary system in the first place. Elimination of [[Common mode failure]] mechanisms is integral to the design of nuclear facilities; preventing cascade failures. Many facilities are designed around the [[defence in depth]] approach, with multiple active and passive systems designed around preventing catastrophic failure. At the core of such a system one finds the [[Reactor Protective System]], with [[Ionising radiation protection]] incorporated to protect facility crews and emergency responders in the event of an accident. The final layer of protection is typically a large [[Containment building]] designed to prevent the release of nuclear material in the event that all active systems should be rendered inoperative. Finally, beyond just technological means, human factors must also be taken into account. Elimination of [[Conflict of interest]] is a key concern in regulatory strategy, and development of a [[Safety culture]] to ensure that operator error does not allow avoidable errors to occur. ==Failure modes of nuclear powerplants== There are concerns that a combination of human and mechanical error at a nuclear facility could result significant harm to people and the environment:<ref>[http://www.ucsusa.org/clean_energy/nuclear_safety/ Union of Concerned Scientists: Nuclear safety]</ref> <blockquote> Operating nuclear reactors contain large amounts of radioactive fission products which, if dispersed, could 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 deaths by cancer and other diseases.<ref>[http://www.globalsecurity.org/military/library/report/crs/rs21131.pdf Nuclear Power Plants: Vulnerability to Terrorist Attack] p. 3.</ref> </blockquote> 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|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]]. Because the heat generated can be tremendous, immense pressure can build up in the reactor vessel, resulting in a [[steam explosion]] such as happened at Chernobyl. Intentional cause of such failures may be the result of [[Nuclear terrorism]]. == Hazards of nuclear materiel == Nuclear material and materiel 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]] 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]]. Even when properly contained, fission by-products which are no longer useful generates [[Radioactive waste]], which must be properly disposed of. In addition, materiel exposed to nuclear material may become radioactive in its own right, or become contaminated with nuclear waste. Additionally, toxic or dangerous chemicals my be used as part of the plant's operation, which must be properly handled and disposed of. == Vulnerability of plants to attack == Nuclear power plants are generally (although not always) considered "hard" targets. In the US, 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.<ref>[http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/security-enhancements.html Nuclear Security – Five Years After 9/11] accessed [[23 July]] [[2007]]</ref> The NRC's "Design Basis Threat" criteria for plants is a secret, and so what size attacking force the plants are able to protect against is unknown. However, to [[scram]] a plant takes less than 5 seconds while unimpeded restart takes hours, severely hampering a terrorist force in a goal to release radioactivity. Attack from the air is a more problematic concern. The most important barrier against the release of radioactivity in the event of an aircraft strike is the containment building and its missile shield. The NRC's Chairman 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."<ref name="air attack">{{Cite web |url=http://www.nrc.gov/reading-rm/doc-collections/news/2007/07-013.html |title=STATEMENT FROM CHAIRMAN DALE KLEIN ON COMMISSION'S AFFIRMATION OF THE FINAL DBT RULE|accessdate=2007-04-07|publisher=Nuclear Regulatory Commission}}</ref> In addition, supporters point to large studies carried out by the US 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, 2001 attacks|September 11 terrorist attacks]] in the USA.<!-- Missing link. <ref name="wna-sonpr" />--> Spent fuel is usually housed inside the plant's "protected zone"<ref name="wna-tnfc">{{Cite web |url= http://www.world-nuclear.org/info/inf03.html |title=The Nuclear Fuel Cycle |accessdate=2006-11-10 |publisher=World Nuclear Association |year=2005 |work=Information and Issue Briefs}}</ref> or a [[spent 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.<ref name="tbotas-dbdj">{{Cite web |url= http://www.thebulletin.org/article.php?art_ofn=jf04koch |title=Dirty Bomber? Dirty Justice |accessdate=2006-11-10 |publisher=Bulletin of the Atomic Scientists |year=2004|author=Lewis Z Kock}}</ref> ==Risk assessment== * [[International Nuclear Events Scale]] * [[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<sup>-7</sup> per plant per year. The [[Evolutionary Power Reactor]] (EPR) has a maximum core damage frequency of 4 x 10<sup>-7</sup> per plant per year. <ref>[http://web.mit.edu/erc/docs/scourse/28.FridayPM.Buongiorno.pdf]</ref> General Electric has recalculated maximum core damage frequencies per year per plant for its nuclear power plant designs: <ref>[http://www.ans.org/pubs/magazines/nn/docs/2006-1-3.pdf Next-generation nuclear energy: The ESBWR]</ref> :BWR/4 -- 1 x 10<sup>-5</sup> :BWR/6 -- 1 x 10<sup>-6</sup> :[[ABWR]] -- 2 x 10<sup>-7</sup> :[[ESBWR]] -- 3 x 10<sup>-8</sup> ===Complexity=== Nuclear power plants are one of the most complex energy systems ever designed,<ref name=stor>[http://www.stormsmith.nl/ Nuclear power – the energy balance]</ref> and opponents of nuclear power have cricitized the sophistication and complexity of the technology. In their assessment, "nuclear power is a very dangerous, expensive way to boil water to generate energy..."<ref>[http://www.cleanenergy.org/programs/programs.cfm?ID=4 Southern Alliance for Clean Energy]</ref> Similarly, Dr [[Helen Caldicott]] has said: "... in essence, a nuclear reactor is just a very sophisicated and dangerous way to boil water -- analagous to cutting a pound of butter with a chain saw."<ref>Helen Caldicott (2006). ''Nuclear power is not the answer to global warming or anything else'', Melbourne University Press, ISBN 0 522 85251 3, p.xvii</ref> These critics of nuclear power advocate the use of [[energy conservation]] and appropriate [[renewable energy]] technologies to create our energy future.<ref>[http://www.cleanenergy.org/programs/programs.cfm?ID=4 Southern Alliance for Clean Energy]</ref> [[Amory Lovins]], from the [[Rocky Mountain Institute]], has argued that centralized electricity systems with giant power plants are becoming obsolete. In their place are emerging "distributed resources"—smaller, decentralized electricity supply sources (including efficiency) that are cheaper, cleaner, less risky, more flexible, and quicker to deploy.<ref>[http://www.rmi.org/sitepages/pid116.php]</ref>Such technologies are often called "[[soft energy technologies]]" and their impacts are seen to be more gentle, pleasant, and manageable than hard energy technologies such as nuclear power.<ref>Amory B. Lovins (1977). Soft Energy Paths: Toward a Durable Peace, Penguin Books.</ref> An issue related to complexity is that the nuclear energy systems have an exceedingly long stay time. The completion of the sequence of activities related to one commercial nuclear power station, from the start of construction through the safe disposal of its last radioactive waste, may take 100-150 years.<ref name=stor/> ==Enforcement organisations== * [[International Atomic Energy Agency]] ** [[International Nuclear Safety Advisory Group]] * [[United States Atomic Energy Commission]] ** [[Nuclear Regulatory Commission]] (U.S.A) * [[Canadian Nuclear Safety Commission]] * [[Autorité de sûreté nucléaire]], the French nuclear safety authority * [[Radiological Protection Institute of Ireland]] * [[Federal Atomic Energy Agency]] in [[Russia]] * [[STUK|Radiation and Nuclear Safety Authority]] of [[Finland]] * [[Nuclear Installations Inspectorate]] (UK) * [[Defence Nuclear Safety Regulator]] (UK) ==Nuclear accidents== * [[Chernobyl disaster]] * [[Three Mile Island accident]] * [[Windscale fire]] * [[List of civilian nuclear accidents]] * [[List of civilian radiation accidents]] * [[List of military nuclear accidents]] ==See also== *[[Threat]] *[[Hazard]] *[[Risk]] *[[Nuclear safety in the U.S.]] *[[Yucca Mountain]] Proposed repository of nuclear [[waste]]s *[[Deep geological repository]] *[[Demron]] *[[Nuclear weapon]] *[[Nuclear energy]] *[[Nuclear power]] *[[Passive nuclear safety]] *[[Nuclear criticality safety]] *[[Nuclear fuel response to reactor accidents]] ==References== {{Reflist}} {{Nuclear Technology}} [[Category:Nuclear safety]] [[Category:Environmental issues with nuclear technology]] [[de:Sicherheit von Kernkraftwerken]] [[pl:Bezpieczeństwo jądrowe]] [[fi:Ydinturvallisuus]]