Preliminary Numerical Modeling of No-Core-Melt in the Generation Iv Canadian SCWR

Abstract

The Canadian supercritical water-cooled reactor consists of fuel channels, which are submerged in a subcooled heavy-water moderator pool inside a low-pressure calandria vessel. The moderator provides cooling to the fuel channels under postulated accident scenarios. This design feature enables the use of flash-driven passive moderator cooling - an inherent safety feature of the proposed design. A major safety goal is to achieve a passive ’no-core-melt’ configuration for the channels and fuel. This paper presents a numerical model of the Canadian fuel channel that consists of a pressure tube, a ceramic insulator enclosed inside a porous stainless steel sleeve, and a fuel string. The fuel channel is designed to maximize thermal flux from the fuel pellets to the heavy-water moderator in Loss of Coolant Accident (LOCA) conditions, while minimizing the rate of heat rejection in normal operation. The FEM software (VrSuite) has been utilized to model a thin segment of the reference de- sign fuel channel. Convection boundary conditions were used to simulate heat transfer from/to the supercritical water coolant and moderator in normal operation, whereas a radiation conductance was employed to model heat transfer from the fuel cladding in LOCA conditions. Temperature-dependent fluid and mechanical properties were used in conjunction with a coupled thermal-stress solver. The gaps between components change in LOCA conditions, resulting in increased thermal conductivity. The coupling of the thermal and stress solvers was necessary to track the relative motion of the various fuel channel components and the ensuing temperature distributions. The paper presents the heat rejection capability of the Canadian SCWR fuel channel in LOCA conditions and explores optimum gap values for the no-core-melt case.