Analysis of the consequences of a LBLOCA with SBO severe accident in a generic VVER-1000 by means of ASTEC and JRODOS codes

Abstract

A reliable evaluation of the source term during severe accident scenarios in Nuclear Power Plant (NPP) is fundamental information to improve the effectiveness of the actions of the emergency and decision-making teams to manage such abnormal events. In this framework, a first-of-its-kind calculation platform of reference codes has been assessed to analyze and quantify the radiological impact of severe accident scenarios in NPPs.The Accident Source Term Evaluation Code (ASTEC) is used to simulate severe accident sequences of NPPs to calculate the Source Term (ST) for any severe accident sequence. The so-predicted source term is needed by tools like the Java based Real-Time On-Line Decision Support (JRODOS) to determine radiological dispersion and impact after a severe accident considering the local (European-wide and worldwide) weather conditions for a selected site of NPPs.This paper describes the analysis of a severe accident sequence, namely Large Break Loss of Coolant Accident (LBLOCA) with Station Blackout (SBO), of a VVER-1000 plant using the integral code ASTEC to predict the ST needed by the JRODOS-tool in order to assess the radiological impact at the Kozloduy site. For a realistic estimation of the ST with ASTEC, the nuclide inventory of a VVER-1000 core loading for end of cycle conditions is calculated with the in-house code KORIGEN and the obtained data is provided to ASTEC to simulate the release and transport of the fission products from the core to the primary circuit and containment. Based on the performed investigation, >1000 kg hydrogen is generated during transient until the basemat rupture and ST released to the environment reaches >2.42 PBq.It can be stated that the final contamination at the direction of the wind reaches 3.72 MBq/m2 by aerosols and 1.62 MBq/m2 by iodines resulting in a 54 mSv as effective dose and 281 mSv thyroid doses acutely. Adults living at that certain area might get an effective dose of 183 mSv dose and a thyroid dose of 540 mSV for lifetime as maximum.