3.24 - TRISO Fuel Performance Modeling and Simulation

Abstract

This chapter deals with the theoretical description of TRISO-coated particle performance and fission product release behavior. The first part of the chapter describes the modeling of the performance of a TRISO-coated particle both under normal operating and core heat up accident conditions of an high-temperature gas-cooled reactor (HTGR) considering various physical phenomena of particle behavior and possible mechanisms for a coated particle to fail. It includes a more detailed description of the approach used in the German PANAMA model and also outlines the characteristic features of other international fuel performance codes. This part is completed by a description of the efforts that have been made with regard to validation of the model approaches. In the second part, the fission product release behavior from a TRISO-coated particle is explained. Starting with the inventory buildup and initial distribution of the radiologically relevant fission product species, their transport and adsorption/desorption behavior is explained. Most transport models, with the FRESCO code given as a representative example, are based on the classical approach of diffusive transport through the various particle materials. This section also includes an outline of alternative methods of fission product release prediction, including some special cases such as release from the particle kernel or fission gas and iodine release. Finally, calculational results are given to demonstrate the models’ capabilities within the frame of code validation studies.