High-fidelity multi-physics coupling for determination of hydride distribution in Zr-4 cladding

Hydride production in Zircaloy cladding continues to be one of the main limiting factors for extending the life of nuclear fuel rods in the core. The production of hydrides in the cladding comes as a direct result of corrosion with water during normal operation. Furthermore, the distribution of hydrogen in the cladding depends strongly on the temperature and temperature gradients inside the cladding. In order to accurately predict these temperature gradients, a high-fidelity multi-physics coupling is needed. The Department of Energy (DOE) recognized this need and sponsored a project at the Pennsylvania State University (PSU) in cooperation with North Carolina State University (NCSU) under the Nuclear Energy University Programs (NEUP). The overreaching goal of this project is to couple thermal-hydraulics, neutronics, and fuel performance codes together to predict the distribution of hydrogen and hydrides in the cladding as a function of time and space. This goal is attained through a two-step approach. The first step combines accurate high-fidelity thermal-hydraulic models for heat transfer, reactor physics models for neutron flux, and thermal-mechanics models for fuel performance calculations to acquire detailed temperature and stress distributions in the fuel rod. The second step develops a semi-analytical model and experimentally tests the temperature and/or stress dependent hydrogen pick-up, diffusion, and precipitation in the cladding. This paper aims to show the capabilities of the high-fidelity coupling, their effect on the power and temperature predictions, and subsequent effect on the distribution of hydrogen in the cladding, specifically in the inter-pellet gap region.