Assessment of fuel failure during LOCA

Full text: One of the major design basis accident is loss of coolant accident (LOCA). This accident is characterized by high sheath temperature and rapid depressurization of coolant. One of the ECCS acceptance criteria for this type of accident is for all LOCA events the release of radioactive material from the fuel in the reactor shall be limited such that the calculated radiological consequences at exclusion zone boundary are within acceptable limits for accidents as specified by AERB. The assessment of above criteria requires the estimation of fuel failure. Two phenomena which cause fuel failure during such condition are oxygen embrittlement and clad ballooning. Oxygen embrittlement is assessed by the amount of oxidation. Failure due to ballooning is analysed by calculating stress and strain on the clad and comparing with ultimate burst stress. Failure data generated by analysing these two phenomena are used in assessing damage on fuel. This paper discusses the criteria of fuel failure followed by various regulating agencies or countries along with Indian criteria. This paper also discusses the damage phenomena along with detailed method of assessment of fuel failure during LOCA