Field Assisted Sintering of Nuclear Fuel Simulants

The expected remaining lifetime of the UK's Advanced Gas-cooled Reactors (AGRs) will result in the generation of ~5,000t of AGR Spent Nuclear Fuel (SNF). The UK Nuclear Decommissioning Authority's (NDA's) preferred option for managing AGR SNF is interim storage - currently in ponds at the Sellafield site - prior to consignment to repository ca. 2075.

AGR fuel pins consist of UO2 pellets sealed inside steel cladding tubes. Whilst in-reactor, some of the cladding can be rendered susceptible to in-pond corrosion, potentially leading to through-wall cladding failure. This may result in pondwater contamination by the SNF and inter-granular corrosion of the pellets themselves with loss of pellet integrity.

Consequently, a transition to dry storage has been proposed - including the drying of wet stored SNF. This may carry further unknown risks which must be understood before implementation. Key knowledge gaps relating to this understanding include:

1. A mechanistic understanding of how pondwater-exposed wet-stored spent UO2 fuel pellets corrode in both the absence and, especially, the presence of a radiation field; and

2. A mechanistic understanding of the possible drying processes of fuel pellets, again both in the presence and absence of radiation fields - but especially in wet-to-dry transitioned fuel with failed cladding and that may have been subject to in-pond corrosion processes.