Rapid accident source term estimation (RASTE) for nuclear emergency response in high temperature gas cooled reactor

Abstract

Rapid accident source term estimation (RASTE) is one of the key functions required by nuclear power plant (NPP) emergency. The results of RASTE are provided to the nuclear decision-making system in emergency, response to ranking accident by INES table and determining suitable protection. This paper proposes the RASTE system for high temperature gas-cooled reactor (HTR) to estimate accident source term based on the simplified methodology used in safety analysis report (SAR) and more realistic operation condition before and in an accident. RASTE simplifies the expression for normal radioactivity in the primary loop, re-suspended radioactivity, additional radioactivity release during the heating process, graphite dust generation, desorbed radioactivity from corrosion of graphite matrix and radioactivity released from failed coated fuel particle. Modifications are made to correct the different ingress water amounts and different fuel burnup. Some unclearly known parameters and processes are estimated from the operation experience as well as accident analysis by conservation rule. The integrated code of fundamental framework and user interface are also developed. This paper takes the High Temperature Gas Cooled Reactor Pebble-bed Module (HTR-PM), a demonstration project being constructed at Shidao Bay, Shandong Province, China, as the study case to discuss the applicability of RASTE. Considering three typical HTR-PM design basis accidents (DBAs), this paper selects P2, P4 as the representatives of LOCA accidents, selects SG6 and SG91 as the representatives of ingress accidents and selects T2 as the representative of transient accidents. Accuracy verification is made by comparing the environmental release estimated by RASTE to that in SAR. These compared targets include nuclide groups of inert gas, iodine, and aerosols, and key nuclides of Xe-133, I-131, Cs-134. Calculation results show that the methodology presented and RASTE is fit to estimate accident of HTR-PM. The development of RASTE system will contribute to form adequate capability of rapid emergency response for HTR nuclear power plant.