Multi-physics coupling behaviors on 3 × 3 helical cruciform fuel rods of U-50Zr alloy under normal and accident conditions

Abstract

Helical cruciform fuel (HCF) has strong potential for power uprate in nuclear reactors, due to enhanced turbulent mixing and heat transfer capacity. Accounting for the self-supporting effect between adjacent HCF rods, the thermal–mechanical coupled responses are unclear especially under high burnup condition. In this work, the thermomechanical coupled constitutive model and stress update algorithm of U-50Zr are proposed, and the multi-physics coupled simulations on 3 × 3 U-50Zr HCF rods are carried out under normal, RIA and LOCA conditions. Results show that the maximum temperature is less than 620 K and no sensitive to burnups and porosity. The low temperature indicates large thermal safety margins in case of accidents happening. As the burnup reaches to 6.43 % FIMA, the peak stress would increase to 262 MPa at the blade cladding region. Generally, the long cycle lifetime and robust fuel performance make U-50Zr HCF a good candidate for application under extreme scenarios.