Transient pellet-cladding interaction of LWR fuel rod — Computer code ISUNE-4

Abstract

The transient pellet-cladding interaction (PCI) of a typical fuel element in a light-water reactor (LWR) fuel rod (or subassembly) is analyzed, formulated and discussed by taking into consideration temperature distribution, fuel densification, fuel restructuring, pellet-cladding gap opening, closure and fuel-cladding “bambooing,” gap conductance, irradiation swelling, irradiation creep, thermal cycling, fuel cracking, and clad stress fatigue and stress corrosion cracking (SFC-SCC). Based on the postulated models or theories, analytical equations and experimental data, computer code ISUNE-4 (a series of ISUNE-1,-2 and -3) has been developed. The computer code analyzes typical transient PCI, verifies a large quantity of accepted experimental data, and predicts fuel performance and fuel rod safety (as well as reactor safety) of LWR power plants. To improve the fuel (sintered UO 2 pellets) performance and fuel rod safety at high burnup during transient PCI, it is very important 1. (a) to strive for increasing strength and ductility of cladding materials (Zircaloy), 2. (b) to provide relatively large gap thickness and plenum space for accommodating fission gas release, 3. (c) to keep power increase rate slow in order to avoid SFC-SCC at the inner cladding surface, and 4. (d) to reduce the intensity and frequency of transient PCI in the high temperature, irradiation swelling, irradiation creep, thermal cycling, and stress fatigue and stress corrosion cracking (SFC-SCC) environment.