With the continuous increase of discharge burnup, fission gas release (FGR) and rod internal pressure (RIP) have become key quantities in fuel safety review. At the nuclear safety level, they determine the end-of-life (EOL) cladding integrity margin and the effectiveness of the radioactive containment boundary, and serve as the initial conditions for fuel behavior and source-term evaluation under accident conditions. To support the domestic substitution of nuclear safety review software and the building of an independent verification capability, this paper adopts the domestically developed fuel performance review software FROBA, constructs a verification-and-validation matrix for the FGR and RIP models, performs confirmation using international benchmark problems, and carries out cross-comparison with internationally prevalent software. The results show that the code's predictions of fission gas release and internal pressure agree well with the benchmarked reference code, and it is thus applicable to safety margin analysis under high-burnup conditions. In addition, this paper analyzes the evolution of fission gas release and internal pressure with burnup and their influence on the end-of-life internal pressure. The results indicate that neither FGR nor RIP constitutes a limiting factor for fuel rod integrity; however, the available margin narrows as burnup is extended, which provides a basis for determining extended-burnup operating limits and for the conservative assumptions adopted in safety review. The study demonstrates that the domestically developed review software is capable of performing independent verification on the issues of fission gas release and internal pressure; the technical route established herein can serve as a methodological reference for high-burnup fuel safety review; and the obtained EOL gas inventory and internal pressure simultaneously provide the initial conditions for source-term and cladding-state evaluation in spent fuel storage, transportation and reprocessing, thereby supporting a safety assessment that covers the entire fuel lifecycle.
 

Fuel performance analysis; Fission gas release; Rod internal pressure; Cladding integrity; Safety margin; Verification and Validation (V&V)