Design of a Storage Facility for Intermediate Level Waste at Hunterston “A” Decommissioning Site

Hunterston A Power Station Decommissioning Site (UK) is required to process and store on-site over 2500m³ of raw Intermediate Level Waste (ILW), conditioned into some 1500 packages until a National Repository becomes available. The waste has arisen mainly from irradiated fuel management throughout the operating life of the station and consists of graphite, metal, sludges and resins. Prior to storage the wastes will be recovered from various locations on the site, stabilised and packaged in a passive form suitable for ultimate disposal. The store will comprise a single concrete above ground vault structure serviced by a Package Handling Machine (PHM) and designed for an operating life in excess of 100 years with minimum through life maintenance. The store is intended to be a replicable solution suitable, with only minor modifications, for ILW storage on other decommissioning or operating sites. The paper describes the development of the concept design of the ILW Store up to and including the Preliminary Safety Report (PSR), supported by a Basis of Design. The paper also describes the commercial approach adopted to develop the store design and subsequently construct and commission the store. The factors affecting the design of the store incorporate the formal guidance provided by the Nuclear Installations Inspectorate (NII) [0], and take account of the requirements of the Scottish Environmental Protection Agency (SEPA), the Environment Agency (EA) together with the Local Planning Authorities. The safety assessment addressed factors such as the initial unmitigated consequences, Hazops, safestore safety criteria, passive safety principles and safety functional requirements. Key issues in the safety assessment were dominated by the passive nature of the packages and addressed the recovery requirements for the PHM in the event of failure, the definition of the seismic integrity requirements and the recovery and inspection principles for packages during storage. The generation and selection of options formed a significant part of the work and incorporated support from all disciplines needed for the Design, Construction and Operation of an ILW Store. Further significant areas affecting the design were the stability of stacked packages, provision of a suitable environment for package storage and the interface with the package delivery transporter and projects supplying the waste packages. BNFL has successfully developed a “fit for purpose” ILW Store design primarily for Hunterston A Decommissioning Site, with a high degree of confidence that this design could be adapted to any UK Site.