Development of a Model for Irradiation-Assisted Grain Growth for Nanocrystalline UO2

TL;DR

This paper presents a calibrated model for irradiation-assisted grain growth in nanocrystalline UO2, highlighting the role of thermal spikes and their limited impact on larger grain sizes relevant to fuel performance.

Contribution

A new coupled phase field and heat conduction model for irradiation-assisted grain growth in UO2, calibrated with experimental data and emphasizing thermal spikes as the primary mechanism.

Findings

Thermal spikes are the main cause of irradiation-assisted grain growth.

Grain growth is significant only for grains smaller than 35 nm.

Model predictions align well with experimental data at different temperatures.

Abstract

In this work, we have developed a model for irradiation-assisted grain growth in nanocrystalline UO$_2$ using the MARMOT code. We include the impact of irradiation on UO$_2$ grain growth by coupling a phase field grain growth model with a heat conduction simulation that features a random heat source representing thermal spikes. Our model parameters have been calibrated against experimental measurements at 300 K. The calibrated model predicts grain growth in an irradiated UO$_2$ thin film that compares well with experimental data at 50 K. These results suggest that thermal spikes are the major cause of the irradiation-assisted grain growth observed in the UO$_2$ experiments. They also indicate that irradiation-assisted grain growth is only significant with average grain sizes less than 35 nm, and thus can be neglected when considering fuel performance of typical UO$_2$ fuel pellets.