RELAP5/MOD3.2 investigation of primary-to-secondary reactor coolant leakage in VVER440

This report discusses the results of the thermal-hydraulic analysis of an accident at the Rivne NPP. The accident was caused by primary-to-secondary reactor coolant leakage as a result of full and partial steam generator header covers lifting. The initiating event is full hot collector cover lifting in one of the sixth steam generators (SG#5) with equivalent diameter 107 mm. Hot collector cover lifting in other three SGs #1, #3 and #4 follows this event. Such accident provides a direct release path for contaminated primary coolant to the environment via the secondary side. RELAP5/MOD3.2 computer code (Fletcher, C.D., Schultz, R. R. 1995. RELAP5/MOD3 Code Manual. Userʹs guidelines. NUREG/CR-5535, INEL-95/0174, Vol.5, Rev.1) has been used to simulate the transient at the Rivne VVER440 Nuclear Power Plant (NPP). A model of the Rivne Unit 1 has been developed based on RELAP5/MOD3.2 thermal-hydraulic code at the National Taras Shevchenko University of Kiev (Borissenko, V., Fedorchenko, S., Krushynsky, A. 2002. Rivne NPP Standard Problem Analysis Report—Description of Rivne NPP Unit 1 RELAP Model. National Taras Shevchenko University of Kyiv, pp. 2–118) and has been given to the INRNE staff for performing of PRISE analyses. This investigation is a process that compares the analytical results obtained by the RELAP5 computer model of VVER440 mentioned above against the experimental transient data received from the Rivne VVER440 Nuclear Power Plant, Unit 1 (Elkin, I. D., et al. 1997. Guideline For Performing Code Validation Within The DOE International Nuclear Safety Center (INSC). US/Russian International Nuclear Safety Center, Argonne-Chicago and Moscow, pp. 1–6.). The results of this investigation provide an integrated evaluation of the complete RELAP5 VVER440/V213 model. As it is seen from the results RELAP5 predicts correctly the behavior of main plant parameters.