Fission Product Transport in TRISO Particles and Pebbles

Abstract

This document demonstrates completion of the goals described in the technical narrative of the FOA project titled: "Modeling and Simulation Development Pathways to Accelerating KP-FHR Licensing" regarding fission product transport in the Kairos-proposed fuel pebble by Idaho National Laboratory and Kairos Power. Showcased in this report are code developments and simulations in BISON that extend the state of the art in computation and understanding of fission product transport in a TRISO fuel particle and pebble.These enhancements lay the foundation for making predictions of fission product transport that can be used as input in the fuel licensing process. This was achieved by installing existing fuel material models originally used in PARFUME, developing a new failure probability method that is efficient and multidimensional, employing material homogenization, and expanding verification and validation simulations to demonstrate the efficacy of the work. All this work is leveraged to spotlight the main deliverable-a three-dimensional model and corresponding demonstration simulation of a pebble, which will serve as the starting point for models used to predict fission product release.

Progress on Near-Term Tasks for the Development of Advanced Reactor Mechanistic Source Term Modeling and Simulation Tools

“…Engineering-scale FP transport modeling in TRISO fuel was recently reviewed [18][19][20] and demonstrated with the BISON code [21], validating against AGR-2 data. This work builds on previous efforts in developing BISON's TRISO FP release functionality, which was initially validated against AGR-1 data [22,23], and also utilizes some models previously implemented in the PARFUME code [24].…”

“…Modeling FP transport in TRISO is achieved through the use of effective diffusion coefficients that are estimated from some combination of experimental data, mechanistic physics-based models such as atomistic techniques, and sensitivity studies to further optimize values. The use of effective diffusion coefficients is desirable due to the wide range of influential mechanisms that contribute to the phenomenon: [18] "Several mechanisms can be involved in the transport of mobile fission products through the kernel and coating layers of TRISO particles. Such mechanisms could include lattice diffusion, grain boundary diffusion, pore diffusion, nano-cracking, or vapor transport [25].…”

Matrix Graphite Material Models In Pebbles and Compacts For Bison

“…This model is considered valid over the temperature range [673 K, 1473 K], and for fast neutron fluences up to 8.0×10 25 n/m 2 .…”

“…A recent Bison capability is used to couple TRISO particles that are randomly generated from a Monte Carlo (MC) simulation to the host matrix so that the thermo-mechanical properties of the particles and the matrix are in simultaneous communication. For further details on the coupling approach, refer to [25]. The simulations are performed under the irradiation conditions listed in Table IV.…”

Efficient Failure Probability Calculations and Modeling Interface Debonding in TRISO Particles with BISON

“…. Over the last few years, the Bison fuel performance code [1] has undergone significant development to expand its tri-structural isotropic (TRISO) particle fuel performance modeling capabilities [2,3,4,5,6,7,8]. Such development included the implementation of material models from PARFUME [9] and the capability to perform statistical failure analysis on large sets of samples, utilizing a Monte Carlo (MC) scheme to execute fast-running, one-dimensional (1-D), spherically symmetric models.…”