DEVELOPMENT OF TOOLS FOR SAFETY ASSESSMENT OF VVER REACTOR UNITS IN THE FIELD OF THERMAL-HYDRAULIC ANALYSES IN SLOVAKIA

摘要

The paper presents overview of analytic tools (computer codes and methodology) that have been used for thermal-hydraulic analyses of nuclear power plant units with VVER reactors in the Slovak Republic. The analyses cover both best estimate approach (to enhance VVER 440 performance) and conservative approach (safety related issues, safety reports). Most applications are based on the codes of western origin, which were developed for specific PWRs, therefore the code adaptation to VVER design features is also presented (geometry of primary loops, horizontal steam generators etc.).rnBased on selected results, development in safety analyses is documented, showing this phenomena also from the point of view of new legislative requirements, as a response to an intensive effort in new Slovak legislative in nuclear safety area.rnExamples of safety improvements in the frame of the Bohunice V-1 nuclear power plant (NPP) safety upgrading and of additional safety measures, proposed and implemented for Bohunice V-2 and Mochovce NPPs are presented.rnExpected trends of further development in the thermal-hydraulic analysis approach and tools are described. Besides application in safety assessment of Mochovce NPP (the 1st unit is being prepared for start up this year), code and model validation is the main area of future activity. It creates a potential for international cooperation, in comparing methodologies for safety analyses as well as nuclear safety of VVERs and western PWRs.