Fuel cladding failures following a large LOCA

Full text of publication follows: In 1999, an European Commission project was performed addressing the calculation of the extent of fuel clad failure following a large Loss-of-Coolant Accident (LOCA) at light water reactors. The analyses were performed for a variety of fuel designs and using different rupture criteria. IBERDROLA was one of the active participants of this exercise contributing with the particular analysis of large LOCA failures. The licensing approach used for evaluating the extent of fuel failure was the in-house IBERDROLA LOCA analysis methodology, that had been approved by the Spanish Nuclear Regulatory Authority. It uses the NUREG-0630 models to determine the extent of rod failure during the LOCA. The NUREG-0630 is a simple model that only considers the cladding hoop stress and the heating rate to determine the rupture temperature. This model, however, has been proved to give conservative results when compare to a wide range of experiments, including fast and slow ramp cases and PWR and BWR rod types. IBERDROLA has updated this study for Cofrentes NPP for actual operating conditions and new fuel rod designs. Additionally, new thermomechanical phenomena involved in LOCA scenarios as fuel relocation, has been considered in this new study in order to calculate a more realistic failure threshold for the rod burst model. A 3-D failure rod distribution is generated considering both realistic and conservative core census. IBERINCO, as engineering branch of IBERDROLA, has an active participation in the international programs about fuel reliability. The specific analyses has been used to verify the LOCA consequences severity. (author)