The birthplace of the UK nuclear industry, Harwell, is now being decommissioned and regenerated to form part of a major hi-tech business and science campus. The £900 million programme to clean up the Harwell site is well underway. To date, more than a million square feet of buildings and research facilities have been decommissioned and removed. The main programme will be complete by 2020 and the site totally restored by 2025.

UKAEA developed two alternative options for a new Waste Encapsulation Plant (WEP), through to scheme design; with teams led by Costain and RWE-Nukem. Halcrow initially provided scheme design to Costain. UKAEA selected a reduced scope proposal from RWE-Nukem and Halcrow was appointed by Norwest Holst (RWE Nukems’ civil and structural contractor) to provide a detailed design service.

The WEP is critical to UKAEA retrieving legacy intermediate level waste (ILW) on-site and preparing it for passively safe storage by 2015. It is currently estimated that the WEP will condition 1,300 (500 litre) drums of Intermediate Level Waste (ILW). The WEP is a compact facility with a shielded cell line constructed in reinforced concrete, complete with integral segregated grout cell. The purpose of the WEP is to retrieve and repackage remote-handled ILW from the B462 Vault Store. This involves inspection, immobilisation by cementation, checking and resealing the drums of ILW before returning them to storage. The facility also incorporates the provision for dealing with wastes classified as fines, those requiring additional special treatment and a facility for monitoring and inspecting the drums throughout the storage period. The design provides for easy connection of the WEP to a Waste Export Facility (WEF), which will allow drums retrieved from the store to be overpacked into road shielded transport containers for consignment to an interim storage facility on another site, in accordance with the Harwell’s Life Time Plan.

The plant will be automatically controlled, with the waste drums transferred through the facility on a series of roller conveyors. The waste drums in the Vault Store are free from external contamination and it is essential that the uncontaminated condition of the Store is maintained, by ensuring the grouted drums are returned in a clean state. The WEP includes a facility to inspect and, if necessary, clean drums before they are returned to the store. The WEP connects to the existing, active, Vault Store requiring the design of a seismic joint to link both structures. The design of the cell, particularly the design of the concrete reinforcement, required careful consideration for the incorporation of a number of en-cast liners and plates to facilitate the installation of cell features and in-cell equipment.

Halcrow worked closely with Norwest Holst and RWE NUKEM, value engineering the structural design, resulting in simplified construction and a reduced cost. The contract has been provided within the NEC professional services framework. During the scheme design stage, key personnel formed part of an integrated design team located on the Harwell site.

Halcrow’s service for the scheme design included:

	design of all civil and structural engineering works, for normal and abnormal (1 in 10,000 year) load conditions
	design of building services, including internal power, lighting, communications and alarm distribution systems
	design of the active ventilation system and discharge
	architectural input with regard to space planning and detailing of external and internal finishes
	specialist advice in respect of the cementation process and associated plant selection

Halcrow’s service for the constructed facility included:

	detailed design of all civil and structural engineering works, for normal and abnormal (1 in 10,000 year) load conditions
	detailed design of drainage and buried services, including foul drainage and rainwater systems
	engineering support during construction
	provision of lifetime quality records

The design stage of the WEP is complete; construction is ongoing and the facility is due for commissioning in 2008.