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Project background

The Active Waste Retrieval Programme involves supplying equipment and facilities for the retrieval, repackaging, cementation and storage of alpha, beta and gamma waste from below ground storage tubes. The programme is critical to the restoration of the Harwell site.

The Harwell tube stores hold a range of solid wastes – contained in around 10,000 waste cans of varying size (7-litre to 55-litre) and stored in approximately 1,800 storage tubes, originating from over 45 years of R&D work at the site. This represents probably the widest variety of solid alpha, beta and gamma radioactive material held in a single location in the world.

The condition of the mild steel waste containers in some of the tubes had deteriorated resulting in loose debris within the storage tubes. This meant that all stored wastes needed to be recovered and immobilised. The immobilised waste will be stored in a purpose-built store at Harwell, before being moved to the UK’s intermediate level waste repository.

Key challenges

Our job was to recover and immobilise all wastes from the tube stores by 2014. To do this, we would have to recover intermediate wastes in unknown conditions, provide new plant and equipment to sort and segregate waste forms, and provide a cementation plant to immobilise the wastes.

Our approach

We developed a mobile waste retrieval machine to remotely extract cans and debris from the storage tubes. The recovered waste is transferred by shielded flask to the processing line. Here waste is assayed, examined, sorted and finally packaged into Nirex-approved 500 litre drums. The drums are then transferred to a purpose-built, heavily-shielded vault above ground. A cementation plant will be built to enable cement to be added to the 500 litre drum.

The results

The concrete-shielded vault store, waste handling cells and the first mobile waste retrieval machine (RM1) are now in full operation – allowing us to recover and repackage waste.

The programme is on target, and over 1,000 cans of waste have already been recovered and processed. A second retrieval machine (RM2) was essential to enable the target date of 2014 to be achieved. RM2 has been constructed and is currently under active commissioning, ready to commence operation in the latter part of 2008.

A waste encapsulation plant (WEP) has been designed and is being built to enable the 500 litre drums stored in the vault with loose packed waste to be cemented up, providing a passively safe waste form. The cemented drums, when cured, will be returned to the vault pending transfer to a future off site store. Construction of the WEP started in 2006 and the plant is expected to be operational in 2009.