The Nuclear Decommissioning Authority

 

The Sellafield site in West Cumbria is widely acknowledged as having the most significant challenges for the UK nuclear clean-up mission.  In the first of a series of articles, we provide an overview of current activities, while future articles will look in detail at specific operations and projects to build a full picture of the most complex nuclear site in Europe.

Sellafield is the NDA's largest site, occupying 262 hectares, and incorporates the former separate sites of Windscale and Calder Hall. Packed within this area are a large number of diverse plants that share services and infrastructure. This presents logistical challenges for the operators, Sellafield Ltd, as they tackle the decommissioning agenda.

The main activities focus on high hazard reduction, the management of high and intermediate level waste and spent fuel, decommissioning and clean-up and land remediation. Reducing the risk from the highest hazards, many of which go back to the early days of the UK nuclear industry, is a priority.

These historic facilities were not built with decommissioning in mind, and can require novel uses of existing technology or the development of new technologies.

Decommissioning the Legacy Ponds and Silos is one such area, constructed in the 1950s-60s to store waste material from early reactor and reprocessing plant operations. These ageing facilities need to be appropriately maintained so that waste material can be safely retrieved. New facilities are being constructed to allow retrieval, treatment and packaging of this waste material which will then be placed in interim storage prior to final disposal.

In addition to the legacy ponds and silos, the Sellafield team is decommissioning the Windscale Pile reactors. Pile one was damaged by fire in 1957 and presents a unique challenge. Meanwhile decommissioning of the iconic Windscale Advanced Gas Cooled Reactor is well advanced.

Spent fuel management is an important part of the site's operations. A number of plants carry out reprocessing and fuel manufacturing, with interim waste stores supporting waste management activities. The Site's Thermal Oxide Reprocessing Plant (THORP), operational since 1994, separates spent nuclear fuel which has been used in reactors. The majority of spent fuel, 97%, can be recycled to produce new fuel which means waste is minimised. The MOX, or Sellafield Mixed Oxide Plant, and Magnox reprocessing operations are also part of the spent fuel management portfolio.

Dealing with the site's waste inventory is key to successful management of the nuclear legacy. The Sellafield Vitrification plant takes evaporated highly active liquor from reprocessing operations and converts it into a solid glass form which is then stored on site. An effluent and encapsulation plant treats and packages intermediate level solid and liquid wastes. This waste is then placed in interim storage on the site, awaiting long-term deep geological disposal. With the commitment of a skilled and multi-disciplined workforce, the challenging programme of work is progressing and the impact of the new Executive Team is beginning to show.

With a new Lifetime Plan being put together and a real focus on high hazard reduction and efficient operations, expectations are high on delivering significant progress over the next few years.