| Popis: |
This paper describes a new approach to define an analytical fuel rod cladding failure criterion during fast power transients such as reactivity initiated accidents (RIAs). Though cladding failure is not a safety issue in itself in such situations, a criterion aiming at precluding this risk is a useful decoupling limit allowing to meet the safety issues. Based on experimental results, a failure limit, expressed in critical strain energy density (CSED) as a function of the waterside corrosion level or rod average burnup, has been determined. The CSED failure limit is then transposed for PWR conditions in terms of critical energy deposition (DHc) in the fuel. This is done by the means of CYRANO3 (steadystate) and SCANAIR (transient) calculations using relevant input data (rod design, power history, RIA transient shape, etc.). The DHc limit is a function of both rod average burnup and initial linear power. It is applicable to UO2 /Zy-4 rods submitted to rod ejection accidents (REAs), during which the cladding is subject to PCMI mechanical loading. It also precludes the risk of failure by oxidation and embrittlement at low burnup. The robustness of the DHc failure criterion is ensured by the penalties and uncertainties taken into account at the different steps of its elaboration |
