The probability of an accident is equally important. When consequences are very high, as they are from nuclear plant accidents, prudent risk management dictates that probabilities be kept very low. Nuclear plant risk assessments are really not risk assessments because potential accident consequences are not evaluated. Moreover, the accident probability calculations are seriously flawed. They rely on assumptions that contradict actual operating experience.
All probability analyses make assumptions.
For example, when you calculate that the probability of getting heads upon a single flip of a quarter is 50 percent, you are assuming that the coin will not land on its edge. By assuming that emergency equipment meets safety requirements when in fact it does not, the PRAs calculate better response capabilities than supported by reality. In other words, the core damage frequencies are really higher than reported by the PRAs. The NRC's Office for Analysis and Evaluation of Operational Data documented 3,540 design errors reported between 1985 and 1994. That means a design error was discovered at a nuclear power plant in the United States almost every single day for an entire decade.