Core damage frequency
Encyclopedia
Core damage frequency is a term used in probabilistic risk assessment
(PRA) that indicates the likelihood
of an accident
that would cause damage to a nuclear reactor core
. Core damage accidents are considered serious because damage to the core may prevent control of the nuclear reaction, which can lead to a nuclear meltdown
. Some sources on CDF consider core damage and core meltdown to be the same thing, and different methods of measurement are used between industries and nations, so the primary value of the CDF number is in managing the risk of core accidents within a system and not necessarily to provide large-scale statistics.
An assessment of permanent or temporary changes in a nuclear power plant is performed to evaluate if such changes are within risk criteria. For example, the probability of core damage may increase while replacing a component, but the probability would be even higher if that component were to fail because it wasn't replaced. Risk measures, such as core damage frequency and large early release frequency (LERF), determine the risk criteria for such changes.
This risk analysis allows decision making of any changes within a nuclear power plant in accordance with legislation, safety margins and performance strategies.
A 2003 study commissioned by the European Commission
remarked that "core damage frequencies of 5 × 10−5 [per reactor-year] are a common result" or in other words, one core damage incident in 20,000 reactor years. A 2008 study performed by the Electric Power Research Institute
, the estimated core damage frequency for the United States
nuclear industry is estimated at once in 50,000 reactor years, or 2 × 10−5.
Assuming there are 500 reactors in use in the world, the above numbers mean that, statistically, one core damage incident would be expected to occur somewhere in the world every 40 or 100 years, respectively.
Historically first nuclear power was achieved about 60 year ago. The 582 operational reactors that were built since account for about 14,400 reactor years. The numbers above would imply that this should have accounted for less than one accident. However, of these 582 reactors 11 reactors have suffered from serious core damage, resulting in a historical accident rate of 1 in every 1,309 reactor years, about 15 times more frequently than the EU estimate (1/20,000 reactor yrs) and about 35 more frequently compared to the US estimate (1/50,000 reactor yrs).
During the 2011 earthquake and resultant 15+ meter tsunami on the east coast of Japan
, the Fukushima I nuclear power plant
suffered core damages at three of its six reactors after the emergency core cooling systems failed due to the extreme beyond design basis conditions. The reactors were General Electric
BWR-3 and BWR-4 types inside Mark I containments. These had been estimated to have a core damage frequency between 10−4 and 10−7
Probabilistic risk assessment
Probabilistic risk assessment is a systematic and comprehensive methodology to evaluate risks associated with a complex engineered technological entity ....
(PRA) that indicates the likelihood
Likelihood
Likelihood is a measure of how likely an event is, and can be expressed in terms of, for example, probability or odds in favor.-Likelihood function:...
of an accident
Accident
An accident or mishap is an unforeseen and unplanned event or circumstance, often with lack of intention or necessity. It implies a generally negative outcome which may have been avoided or prevented had circumstances leading up to the accident been recognized, and acted upon, prior to its...
that would cause damage to a nuclear reactor core
Nuclear reactor core
A nuclear reactor core is the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place.- Description :...
. Core damage accidents are considered serious because damage to the core may prevent control of the nuclear reaction, which can lead to a nuclear meltdown
Nuclear meltdown
Nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. The term is not officially defined by the International Atomic Energy Agency or by the U.S. Nuclear Regulatory Commission...
. Some sources on CDF consider core damage and core meltdown to be the same thing, and different methods of measurement are used between industries and nations, so the primary value of the CDF number is in managing the risk of core accidents within a system and not necessarily to provide large-scale statistics.
An assessment of permanent or temporary changes in a nuclear power plant is performed to evaluate if such changes are within risk criteria. For example, the probability of core damage may increase while replacing a component, but the probability would be even higher if that component were to fail because it wasn't replaced. Risk measures, such as core damage frequency and large early release frequency (LERF), determine the risk criteria for such changes.
This risk analysis allows decision making of any changes within a nuclear power plant in accordance with legislation, safety margins and performance strategies.
A 2003 study commissioned by the European Commission
European Commission
The European Commission is the executive body of the European Union. The body is responsible for proposing legislation, implementing decisions, upholding the Union's treaties and the general day-to-day running of the Union....
remarked that "core damage frequencies of 5 × 10−5 [per reactor-year] are a common result" or in other words, one core damage incident in 20,000 reactor years. A 2008 study performed by the Electric Power Research Institute
Electric Power Research Institute
The Electric Power Research Institute conducts research on issues related to the electric power industry in USA. EPRI is a nonprofit organization funded by the electric utility industry. EPRI is primarily a US based organization, receives international participation...
, the estimated core damage frequency for the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
nuclear industry is estimated at once in 50,000 reactor years, or 2 × 10−5.
Assuming there are 500 reactors in use in the world, the above numbers mean that, statistically, one core damage incident would be expected to occur somewhere in the world every 40 or 100 years, respectively.
Historically first nuclear power was achieved about 60 year ago. The 582 operational reactors that were built since account for about 14,400 reactor years. The numbers above would imply that this should have accounted for less than one accident. However, of these 582 reactors 11 reactors have suffered from serious core damage, resulting in a historical accident rate of 1 in every 1,309 reactor years, about 15 times more frequently than the EU estimate (1/20,000 reactor yrs) and about 35 more frequently compared to the US estimate (1/50,000 reactor yrs).
During the 2011 earthquake and resultant 15+ meter tsunami on the east coast of Japan
2011 Tōhoku earthquake and tsunami
The 2011 earthquake off the Pacific coast of Tohoku, also known as the 2011 Tohoku earthquake, or the Great East Japan Earthquake, was a magnitude 9.0 undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST on Friday, 11 March 2011, with the epicenter approximately east...
, the Fukushima I nuclear power plant
Fukushima I Nuclear Power Plant
The , also known as Fukushima Dai-ichi , is a disabled nuclear power plant located on a site in the towns of Okuma and Futaba in the Futaba District of Fukushima Prefecture, Japan. First commissioned in 1971, the plant consists of six boiling water reactors...
suffered core damages at three of its six reactors after the emergency core cooling systems failed due to the extreme beyond design basis conditions. The reactors were General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
BWR-3 and BWR-4 types inside Mark I containments. These had been estimated to have a core damage frequency between 10−4 and 10−7