Heat transfer performance of the solid microencapsulated fuel in light water reactors

Abstract

Solid Microencapsulated Fuel (SMF) is a kind of new accident-tolerant fuel (ATF) concept that disperses TRISO coated fuel particles directly into a type of matrix in the form of a solid rod. This paper aims to analyze the heat transfer performance of SMF based on a single pin, compared to the traditional fuel design in the 200 MW Nuclear Heating Reactor (NHR200-II). Two kinds of SMFs have been evaluated - fuel particles dispersed into a silicon carbide matrix and fuel particles dispersed into a zirconium matrix. The centerline temperature of the SMF rod at the beginning of life (BOL) was preliminarily calculated based on the effective thermal conductivity (ETC). The ETC was calculated by Maxwell, Chiew&Glandt, and d-EMT models, compared to the finite element models. The ETC of TRISO particle was also calculated before calculating that of the SMF rod because of its multilayer structure. To get a more realistic temperature distribution of SMF rod, a neutronic analysis was done by OpenMC by acquiring the power distribution of randomly distributed TRISO particles. Finally, a practical temperature distribution of SMF rod was achieved by the finite element model considering the random distribution of TRISO particles. This study showed that SMF has a better thermal transfer capacity than conventional fuel design and even fully ceramic microencapsulated (FCM) fuel because of its integral structure and higher matrix thermal conductivity. The helium gap in conventional fuel and FCM fuel would bring a temperature rise of nearly 150˚C in this case. The centerline temperature of SMF is much lower than the traditional fuel. A more refined temperature distribution of SMF rod based on the finite element model showed a lower maximum temperature than the ETC calculated. It also showed a less uniform temperature distribution because of the heat generation of fuel particles and the possible concentration of randomly distributed fuel particles.