UKAEA ^{A World Leader in Decommissioning & Waste Management.}

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Project background

The fast reactors developed at Dounreay were unique in how they used liquid metals to transfer heat from the core to steam generators and produce electricity.

The Dounreay Prototype Fast Reactor was a 250Mwe (600 MWth) sodium-cooled pool type fast reactor, with an inventory of 1,500 tonnes of sodium. It was shut down for decommissioning in March 1994 after 20 years of operation.

Key challenges

We had to remove the hazardous inventory of radioactive, contaminated liquid sodium metal in a safe, environmentally responsible and cost-effective manner. To do this, we designed and built a facility for the disposal of radioactive contaminated liquid sodium.

We also developed innovative sodium draining techniques, a fluidic pump for removing liquid sodium from the reactor vessel, electrical heating devices to keep sodium liquid during draining and a transfer system for transferring liquid sodium from the reactor vessel to the disposal plant. It was important that we left the reactor vessel ready for the next phase of decommissioning.

Our approach

We built a new dedicated plant in the former reactor turbine hall. The plant reacts small quantities of sodium with large quantities of aqueous sodium hydroxide – once this has been neutralised with hydrochloric acid, it produces salt water.

The salt water is then passed through an ion exchange column to remove any radioactivity before it is discharged to sea, in accordance with the site’s waste disposal authorisation.

This process minimises the spread of contamination, as the majority of contamination is trapped in process liquids. Additionally it is safe, easy to control and shut down, and does not require specialist construction materials.

At the start of 2006, we removed as much sodium as possible from the reactor as part of phase 1 of the programme. Since then, we have been making preparations to remove the final 300 tonnes – this involves using specialist drilling techniques to release sodium held up in the reactor plenum.

We are scheduled to destroy all of the primary sodium from the reactor by the end of March 2007 – including the heel pool, which has 5-20 tonnes of sodium left in the base of the reactor. Through the use of innovative technology, we will remove as much sodium as possible and speed up the decommissioning process.

The results

The plant became operational in March 2004. Since then it has processed over 1,100 tonnes of sodium – breaking the world record for safe destruction of liquid metal, which was previously held by EBR2, a nuclear complex based in Idaho in USA. We have now safely destroyed over half of the hazardous metal left over from the fast reactor programme.