Multiscale modeling of fission gas behavior in U3Si2 under LWR conditions

Abstract

In this work, we present a model of fission gas behavior in U 3 Si 2 under light water reactor (LWR) conditions for application in engineering fuel performance codes. The model includes components for intra-granular and inter-granular behavior of fission gases. The intra-granular component is based on cluster dynamics and computes the evolution of intra-granular fission gas bubbles and swelling coupled to gas diffusion to grain boundaries. The inter-granular component describes the evolution of grain-boundary fission gas bubbles coupled to fission gas release. Given the lack of experimental data for U 3 Si 2 under LWR conditions, the model is informed with parameters calculated via atomistic simulations. In particular, we derive fission gas diffusivities through density functional theory calculations, and the re-solution rate of fission gas atoms from intra-granular bubbles through binary collision approximation calculations. The developed model is applied to the simulation of an experiment for U 3 Si 2 irradiated under LWR conditions available from the literature. Results point out a credible representation of fission gas swelling and release in U 3 Si 2 . Finally, we perform a sensitivity analysis for the various model parameters. Based on the sensitivity analysis, indications are derived that can help in addressing future research on the characterization of the physical parameters relative to fission gas behavior in U 3 Si 2 . The developed model is intended to provide a suitable infrastructure for the engineering scale calculation of fission gas behavior in U 3 Si 2 that exploits a multiscale approach to fill the experimental data gap and can be progressively improved as new lower-length scale calculations and validation data become available.

BISON: A Flexible Code for Advanced Simulation of the Performance of Multiple Nuclear Fuel Forms

“…Through multiscale modeling approaches, it was determined that uncontrollable gaseous fission product swelling was not expected during operation at LWR temperatures. 82,83 Models have been incorporated into BISON for thermal conductivity and its degradation, 82,84 specific heat, 84 Young's modulus, 84 Poisson's ratio, 84 thermal creep, 85 solid swelling, 86 and FGR and gaseous swelling. 83 Further refinements to the FGR and thermal creep models through multiscale modeling approaches are underway.…”

BISON Development and Validation for Priority LWR-ATF concepts

“…The computational framework for computing the evolution of fission gases during irradiation in U 3 Si 2 was developed by [14] and summarized in [2]. The model utilized theoretical values for some parameters, as well as lower length calculations for others.…”

ATF material model development and validation for priority fuel concepts

“…The inter-granular component describes the evolution of grain-boundary fission gas bubbles coupled to fission gas release. The current Bison model is based on the development described in [69]. However, improvements have been made in the present version which are based on recent lower length-scale calculations.…”

“…′ = ( , − 1) , with , = ∕ being the average number of gas atoms per bubble, accounts for the fact that a bubble containing gas atoms will require on average − 1 homogeneous re-solution events before being destroyed. A detailed derivation is provided in [69].…”