Management of fuel pin failures in Nuclear Electric's AGR reactors

Fuel failure in service is rare in commercial Advanced Gas Cooled (AGR) reactors, occurring much less frequently than in PWR where operation with failed fuel is commonplace. In contrast, AGR reactors operated by Nuclear Electric have generally been required to discharge failed fuel, whatever its severity, as soon as practicable after detection. In cases where failed fuel is not radiologically significant, this practice is clearly unnecessarily restrictive, and can lead to operational problems connected with disruption of the fuel cycle. In order to provide more flexibility in failed fuel management, specific cases have been made to permit continued operation of AGR's with recent fuel failures. These cases have considered the additional hazards posed by failed fuel in operational and fault conditions to impose limits on continued operation, the principal one being the 131I interspace inventory of the failures. Existing methods of estimating this quantity from measured AGR coolant activities were adapted to meet the needs of these cases. Following the discharge of these failures, Post irradiation examination (PIE) was carried out to ensure that no in-pile deterioration had taken place. This paper describes the events surrounding continued operation with one of these failures from Hinkley Point B. The safety aspects considered in deferring its discharge, the methods used to adhere to the resulting limits and the PIE carried out on the fuel are outlined. The lessons learned for more general operation with failed fuel are discussed. (author)