HEDL mixed oxide fuel pin breach experience in EBR-II

Mixed plutonium--uranium oxide fuel pins clad with stainless steel are being irradiated to cladding breach in the EBR-II for the Hanford Engineering Development Laboratory's (HEDL) Run-to-Cladding-Breach (RTCB) program. The objectives of these tests are to: (1) establish the burnup capability of mixed oxide fuel pins, (2) identify and characterize cladding breach mechanisms, (3) determine the effects of cladding breach on neighboring fuel pins and (4) provide data for developing fuel pin failure criteria. Breaches have occurred in 16 HEDL fuel pins in the RTCB program. Examination and characterization has been completed on 13, with the remaining three in some phase of detailed examination. Characterization, includes identification and classification of the probable cause of each breach. The breaches evaluated have been classified as being due to: local cladding overtemperature, subassembly coolant overtemperature, and cladding and wire wrap wear. The cause for one breach has not been conclusively established. The paper reviews characteristics and discusses the probable mechanisms and causes.