Codes, methods and approaches for accident analyses of the core and fuel behaviour

摘要

Thermohydraulic and fuel behaviour computer codes developed for WWER reactors by the Nuclear Power Plants Research Institute, Trnava (SK), are described. The features of presently used codes PIN, DEFOS-1A, DEFOS-2A, SICHTA, FEMBUL, CALOPEA and DYN3D/M3, their utilization areas, interconnections and the safety analyses procedures are briefly described. General approach in safety simulation and evaluation is given. The interconnections between the proposed criteria - anticipated transients, postulated accidents and cladding failure - are shown. The acceptance criteria of IAEA are checked by the analyses of the transients using the corresponding codes. For most accident analyses, the transient simulation by means of the codes for system transient analysis (RECAP, DYNAMIKA etc.) is sufficient to provide evaluation of the criteria needed. For some transients more detailed analysis is necessary using DYN3D and SICHTA codes (e.g., reactivity initiated accidents). Parameters defining fuel behaviour are determined having in mind that for most of the typical WWER accidents no or very limited damage of fuel assemblies occurred. It allows, on one hand, the use of conservative criteria, and, on the other, to use approach of bounding accidents for proving some criteria like calculated doses below limits, local clad oxidation not exceeding 17% and hydrogen generation below limit. It limits in the current conditions the necessary use of PIN and DEFOS codes to not very large number of analyses. 1 tab., 8 refs. (Atomindex citation 27:045253)