Probabilistic Risk Analysis of Reactor Pressure Vessels

摘要

The radiation embrittlement is considered the major aging mechanism of reactor pressurevessels in nuclear power plants. To evaluate the degree of radiation embrittlement and ensure thesafety of vessels, the nuclear power plants in Taiwan adopt the standard set by the United StatesNuclear Regulatory Commission (USNRC) and carry out aging assessment programs periodically.Based on the deterministic assessment procedure as required by USNRC, the present study proposes aprobabilistic aging assessment model to estimate the probability of exceeding the required values setby USNRC in consideration of radiation embrittlement of reactor pressure vessels. Taking a particularnuclear reactor unit as an example, the present study shows that, under reasonable assumptions andbased on consideration of the adjusted reference temperature (ART), the reactor pressure vessel mightexceed the code-required value with a probability of 3.42 × 10-7 at the end of its design life. If thecalculation is based on consideration of the upper shelf energy (USE), the probability would become1.00 × 10-4 . Since the required values set by USNRC are based on the rather conservative deterministicconsideration, the real failure probability of the studied vessel owing to radiation embrittlement shouldbe lower than the above mentioned values.