DEVELOPMENT OF A PROCESS FOR REMEDIATION OF ENRICHED URANIUM COOLANT TANKS AT AWE ALDERMASTON

摘要

Machining processes involving Enriched Uranium (EU) at the UK Atomic Weapons Establishment have historically required the use of a liquid coolant to ensure product quality and to provide protection against hazards associated with ignition of the EU swarf in the non-inert gloved air box atmosphere. This coolant is typically provided by closed circuit re-circulating systems utilising large volume tanks to contain the bulk coolant. Small losses of EU to the coolant tank are experienced during the machining process leading to accumulation over time. This is expected and appropriate measures are put in place to control such accumulations to ensure criticality safety during the operational phase. The original design intent made no specific provision for recovery of the EU as it was not expected to be required based on the anticipated losses and design lifetime of the tanks. However, in support of ongoing operations it has become necessary to develop a process to remediate out of service coolant tanks to recover the EU and to replace the coolant and some of the end-of-life tank components. Detailed optioneering has been undertaken to develop a process that addresses all the relevant hazards, including nuclear criticality safety. Non-destructive assay techniques have been developed to help determine the inventory of EU present and consequently the level of control required during the remediation process. This has led to the selection of favourable geometry collection vessels that not only afford significant defence-in-depth against criticality hazards during the remediation work but also satisfy interim storage requirements. These vessels may also be of interest to other operators. This paper presents an overview of the history of operation of the coolant tanks and proposed remediation process and provides an overview of the criticality safety case that has been developed to support it. It is anticipated that the remediation work will be undertaken before 2019 allowing the findings and lessons learnt (including validation of non-destructive assay results on expected hold up) to be reported at the next ICNC.