Performance analysis of TRISO coated fuel particles with kernel migration

High temperature reactors (HTRs) are among the candidates of the possible next generation nuclear plant. HTRs are expected to offer attractive features such as inherent safety, low cost of electricity generation, and short construction period. The safety performance of high temperature gas cooled reactors mainly relies on the quality and integrity of the coated fuel particles. One of the possible failure mechanisms for TRISO coated fuel particles is kernel migration, in which the fuel kernel migrates through the buffer layer due to the overall high temperature gradient and the carbon monoxide formation. In this study, thermal and mechanical performances of a coated fuel particle with a migrated kernel are analyzed by the finite element technique. Calculations are performed for two different operating conditions represented by two different surface temperatures. Similar analyses are also carried out for a nominal particle without kernel migration for comparison. Temperatures and stress distributions are calculated and failure probabilities of the coated fuel particle are obtained based on the Weibull statistics. Further comparison is made in terms of the failure probability considering a coated fuel particle whose inner pyrolitic carbon layer is defective or already failed. Furthermore, stress distributions for the particle with kernel migration through the inner pyrolytic carbon layer has been obtained. Calculated temperature distributions, maximum stress values, and failure probabilities are reported to assess the influence of kernel migration on coated fuel particle behavior. Results show that high temperature operation, high burnup, and excessive temperature gradient on the fuel particle can lead to fuel failure. The pressure vessel failure is generally observed well before the failure by the kernel migration. In fact, these failure modes are interrelated and affect each other. (C) 2007 Elsevier B.V. All rights reserved.