TRISO Fuel Performance Modelling with BISON

Modeling of tristructural isotropic (TRISO)-coated particle fuel is being refined in the fuel performance code BISON. New developments include the implementation of an updated set of material properties, TRISO failure mechanisms, fission product diffusion parameters, and the design of a Monte Carlo scheme that allows BISON to calculate the probability of fuel failure within a population of TRISO particles and the subsequent fractional release of key fission products.

Numerical Simulation Research on the Irradiation-Thermal-Mechanical Performance Evolution of FCM Fuel

FCM fuel which microencapsulated TRISO particles in SiC matrix is a promising ATF (accident tolerant fuel) candidate fuel designed to replace the traditional pellet-cladding fuel rod. In order to predict the in-pile behavior of FCM fuel accurately and to optimize the design of FCM fuel, it is necessary to establish a numerical simulation method of irradiation-thermal -mechanical coupling behavior of FCM fuel. In this study, the related thermal effects and irradiation effects of FCM fuel and the effect of gap heat transfer are considered. User defined subroutines are compiled respectively, and the above-mentioned correlation effects are introduced into ABAQUS software to establish a numerical simulation method for the irradiation-thermal -mechanical coupling behavior of FCM fuel. Based on the established numerical simulation method, the performance evolution of FCM fuel in the reactor is simulated, and the possible failure modes of FCM fuel in the reactor are analyzed. The research results can provide guidance for the optimization design and performance prediction of FCM fuel.

NEUTRONICS ANALYSIS OF VVER-1000 CORE USING AT-FCM FUEL

Using the Fully Ceramic Microencapsulated (FCM) fuel in light water reactors has multiple advantages, as it is accident tolerant because of; no hydrogen generation due to the cladding interaction with steam at high temperature, better retention of fission fragments and proliferation resistant due to very small production of transuranic elements during the burnup as compared to the standard UO2 fuel. In this study neutronics analysis of AT-FCM fuel consisting of TRISO particles embedded in SiC matrix is performed for replacement in existing VVER-1000 reactors. Standard VVER-1000 fuel assembly is transformed to Accident Tolerant Fully Ceramic Microencapsulated (AT-FCM) fuel assembly based on hydraulic diameter of the VVER-1000 assembly, the number of fuel pins are decreased with increased diameter and enrichment to conserve the initial fissile loading in AT-FCM assembly. Fuel centerline temperature of the AT-FCM assembly is found to be lower than the reference UO2 fuel assembly at the same total power produced because of the much higher thermal conductivity. FCM-TRISO fuel assembly namely Array 15 with 169 pins is proposed and analyzed. Pin cell, assembly level and full core calculations have been performed with SERPENT code using implicit and explicit models. VVER-1000 full core is modelled using the transformed FCM assembly. The embedded TRISO particles in a SiC matrix and the use of FeCrAl cladding turns out to be the perfect case for accident tolerance. High burnup of AT-FCM core in terms of MWd/kgHM for the same number of EFPDs is observed as compared to reference UO2 core due to the small breeding of transuranic elements Pu-239, Pu-240 and Pu-241. Appreciable quantity of the power is produced due to the fission of transuranic elements in reference UO2 assembly so the burnup in MWd/kgHM remains smaller than the AT-FCM fuel. Comparatively more softening of spectrum is found in AT-FCM fuel cells and assemblies towards the middle of the cycle (MOC) and End of the Cycle (EOC), this softening of spectrum tends to increase the rate of U-235 depletion. Very small quantities of plutonium isotopes are produced in AT-FCM as compared to the reference UO2 assembly because of small loading of U-238 at the BOC. The neutronics performance of AT-FCM core with burnable poison consisting of Gd2O3 and Er2O3 turn out to be better than reference UO2 assembly as it exhibits smooth burnup. Fuel Temperature Coefficient (FTC) and Moderator Temperature Coefficient (MTC) of the AT-FCM assembly is negative for most part of the cycle however, towards the end of cycle it becomes less negative due to small quantities of resonance absorbers, softening of thermal flux and increased rate of fission absorption in UO2.

METHODS FOR CALCULATION OF SELF-SHIELDED CROSS SECTIONS OF FULLY CERAMIC MICRO-ENCAPSULATED FUEL DOUBLE HETEROGENEOUS SYSTEM

Fully ceramic micro-encapsulated (FCM) fuel is a kind of fuel that employs tri-structural isotropic (TRISO) particles to enhance safety. The FCM fuel assembly is a double heterogeneous system. The conventional self-shielding calculation methods cannot treat the DH effect. In this paper, three methods based on equivalent homogenization of the TRISO particle and the matrix are studied and compared: the hyper-fine energy group cross sections (XSs) homogenization based hyper-fine energy group method (HHM), the hyper-fine energy group XSs homogenization based subgroup method (HSM) and the subgroup XSs homogenization based subgroup method (SSM). These methods are implemented in a high-fidelity neutronics code NECP-X. Numerical results show that these methods are able to treat the double heterogeneity of the FCM fuel. The precision of the HHM and HSM is higher than that of the SSM.