Hot Isostatic Pressing - Reducing the proliferation risk of stored plutonium

There is currently somewhere in the region of 550 tonnes of declared separated plutonium worldwide. This material carries a proliferation risk globally and will continue to do so until it is put beyond reach. As reprocessing contracts have reached completion in the UK, it currently holds a stockpile of 150 tonnes of civil separated PuO2, and the long-term management of the stockpile material is currently under significant review by the Nuclear Decommissioning Authority (NDA) and UK government. The NDA are considering multiple options for the long-term management of PuO2 including reuse options as reactor fuel(s) and immobilisation options for long-term storage and eventual disposal in a geological repository. One of the main technologies being developed as a process option for disposal is incorporation of the PuO2 into a ceramic zirconolite matrix and consolidating via hot isostatic pressing (HIP). This involves subjecting the material to high temperature and pressure inside a hermetically sealed canister, which leads to a dense, durable wasteform; naturally occurring mineral analogues have been shown to have compositional stability for over 2 billion years. The National Nuclear Laboratory (NNL) are currently developing the HIP100 active demonstrator facility to undertake the processing of the PuO2 stockpile at the 100 g scale. This will provide valuable data on wasteform properties and performance which will feed into the wider geological disposal facility (GDF) programme and the NDA’s roadmap for HIP technology which aims to be TRL 7 by 2031. The facility will produce samples from the suite of PuO2 produced over half a century of UK reprocessing operations, verifying that target wasteforms can be formed as well as feeding a process envelope over to full scale operations.