A Qualitative Accident Scenario Analysis for a Very High Temperature Reactor

Abstract

This paper, therefore, presents an accident sequence analysis methodology for the possible initiating events. Initiating events which may occur in VHTRs were identified through MLD method in this study. For the possible initiating events, the accident sequences were developed with event tree modeling. The Very High Temperature gas-cooled Reactor (VHTR) is one of the six technologies classified by the Generation 4 International Forum as a high-energy heat source for nuclear hydrogen generation. The motivation on the VHTR concept stems from the high outlet temperatures. The high outlet temperature affords high efficiency electrical generation and the use of nuclear power for potential process heat applications. In order to prepare for the licensing of the VHTR demonstration reactor, it is necessary to develop a methodology for assessing the VHTR safety. The current licensing technology for nuclear facilities, however, is mainly for LWRs. Due to the inherent and passive features of the VHTR, the approach to modeling initiating events and event sequences should be modified in terms of size and complexity in comparison to that in a LWR model. These adjustments must not diminish the quality of the PRA, but facilitate the capability to model more accurately the VHTR features, events, and plant response. The results will be the baseline accident scenarios for the future probabilistic risk analysis. After analyzing the probability data of each heading in the event tree using reliability data analysis, it is possible to quantify the VHTR risk and identify the significance of the accident sequences.