ACCIDENT RISK ASSESSMENT

The Massachusetts Institute of Technology (MIT) Interdisciplinary Study on the future of nuclear power notes that expert opinion using Probabilistic Risk Assessment (PRA) estimates the risk of an accident damaging the nuclear core of a power reactor to be about 1/10,000 per reactor per year in the US. (PRA estimates the frequency of possible failures that could lead to damage to the reactor core, such as pipe breaks or loss of coolant flow.) (Ansolabehere et al., 2003).

The MIT Study team envisaged a growth scenario leading to a near-tripling of nuclear output by 2055 to 1000 GWe, and concluded: “With regard to implementation of the global growth scenario during the period 2005-2055, both the historical and the PRA data show an unacceptable accident frequency. The expected number of core damage accidents during the scenario with current technology would be 4.”

Nuclear advocates claim significantly reduced risks for the ‘next generation’ of nuclear power reactors. The Switkowski Report (2006) states that improvements in design for future nuclear power plants are expected to lead to a risk of 1/100,000 per reactor per year for accidents damaging the nuclear reactor core. The IAEA safety target for future plants is 1/100,000.

Needless to say, risk assessments of reactor types that have yet to be built or operated are speculative. Moreover, even for existing reactors, PRA is based on a myriad of assumptions and estimates. Former ANSTO nuclear engineer Tony Wood (2001) notes that PRA failed to anticipate the events which led to the world’s worst reactor accident (Chernobyl) and the worst reactor accidents in the UK (Windscale) and the USA (Three Mile Island).

The US Nuclear Regulatory Commission (NRC) noted in a 2002 report: “Senior NRC officials confirmed that the agency is highly reliant on information from licensee risk assessments. Agency officials also noted that there are no PRA standards, no requirements for licensees’ PRAs to be updated or accurate, and that the quality of the assessments varies considerably among licensees.” (NRC, 2002b)