The development of LOCA analysis codes for nuclear power plant

This research aims at assessment of the best-estimate codes, so as to develop a reliable analysis method for their actual applications. There are two additional purposes in the study: The first is the development of methodology for sizing the safety systems for advanced reactor design using the best-estimate codes, and the other is the development of our own best-estimate methodology, referring to USNRC approval of the acceptance criteria for ECCS based on the best-estimate method. The use of the best-estimate codes as those assumed in FSAR by only input arrangement, has resulted in achievement of at least 250 K safety margin. The fact that the predicted PCT in LBLOCA analysis is well bounded within the acceptance criteria using the best-estimates codes, should be verified by the quantification of the code uncertainty in the future. In the case of computer code improvement, the reflood models have been improved and satisfactory results have been obtained. In the case of uncertainty evaluation, the calculational matrices based on the assessment of experiments with the improved RELAP5 code for the quantification of the code uncertainty have been formulated separately for blowdown and reflood phases. (Author)