Uncertainties remaining in severe accident phenomena and related research activities at JAERI

Abstract

Abstract In utilizing PSAs to safety-related issues such as provision of accident management, it is essentially important to understand the uncertainties in the results. However, large uncertainties still exist in level 2 PSA results even though worldwide research programs have been carried out to understand and analyze severe accidents. This paper summarizes the uncertainties due to lack of knowledge on severe accident phenomena and discusses their effects on the estimated severe accident progression and fission product source terms, mostly based on the researches conducted at the Japan Atomic Energy Research Institute (JAERI). Furthermore, the paper also discusses the uncertainties caused by incompleteness and simplification in modeling. Since most of the uncertainties in physical models will not be significantly reduced in the near future, the methodology is expected to effectively utilize the PSA results in decision making even with such large uncertainties, while continuous research efforts to reduce the uncertainties are required.