Thermal-hydraulic modeling for deterministic safety analysis of portable equipment application in the VVER-1000 nuclear reactor during loss of ultimate heat sink accident using RELAP5/MOD3.2 code

Thermal-hydraulic model is an important tool in deterministic safety analysis of the Nuclear Power Plant (NPP) which would confirm the adequacy and efficiency of provisions in the defense in depth concept to cope with challenges of the plant safety. In this paper, for the first time, a validated thermal-hydraulic model is presented for Deterministic Safety Analysis of the portable equipment to be applied in VVER-1000 nuclear reactor during severe accident. Therefore, the VVER-1000 as a case study reactor model is assessed and evaluated through RELAPS/MOD3.2 thermal hydraulic code during the loss of ultimate heat sink accident. Since LUHS accident is absent in the Final Safety Analysis Report of the nuclear power plant, this accident scenario is analyzed for the first time in this study. The simulation is done for two situations of with and without safety modification. This modification is related to portable equipment application which would maintain the primary or secondary circuit cooling in long term. The results of these simulations indicate that LUHS would lead to fuel failure and finally core meltdown. But, the modified LUHS simulation shows that this designed portable equipment can remove the decay heat of the core or transfer the heat into the ultimate heat sink in a continuous manner until the safety systems recovery become possible. Indeed, the most important achievements of this paper consist of: preparation of emergency instructions, accident management at the time of loss of ultimate heat sink and the training of NPP's personnel. (C) 2018 Elsevier Ltd. All rights reserved.