Nuvia (UK) announced on 29 August that it has secured a multi-million-pound contract for Dounreay Site Restoration Limited (DSRL) to design, procure, install and commission plant and equipment to remove the residual NaK (Sodium-Potassium) remaining in the Dounreay Fast Reactor’s (DFR) complex piping network. DFR was built during the 1950s at a time when there was a worldwide shortage of uranium for electricity generation and became the world’s first fast reactor to provide electricity to a national grid.

DFR’s reactor core was surrounded by a blanket of natural uranium elements and it was designed to ‘breed’ to create a new fuel, plutonium. The NaK was used as a liquid metal coolant for both the primary and secondary circuits. UK experimentation with fast breeders came to an end in the 1980s.

The NaK is to be removed by using an existing Water Vapour Nitrogen process (essentially steam) that will react with the residue, producing sodium hydroxide, potassium hydroxide and hydrogen. The resultant products will be collected and processed using existing gas filtration systems and the existing Ion Exchange Plant to make them safe for disposal. The works will be engineered in Nuvia’s design offices, from where the first stage procurement and manufacturing of pipework and equipment will also be managed. Installation and commissioning will be undertaken on the Dounreay site and will be managed utilising Nuvia’s local staff with support from the local Caithness and Sutherland supply chain. The contract, which began in July, is to be delivered over three years.

The DFR, with its iconic dome, closed in 1977 after which most of the core fuel was removed.  However, work stopped when some of the metallic casings in the zone surrounding the core were found to be swollen and jammed. According to the Nuclear Decommissioning Authority (NDA), which is responsible for the DFR, almost 1,000, or two-thirds of the total, were left in place. When the damaged elements were discovered, decommissioning effectively stopped for 20 years, until the decision was taken in 2000 to close down Dounreay and the creation of the NDA a few years later gave fresh momentum to the task. The elements were immersed in some 57 tonnes of highly reactive liquid metalwhich had to be removed and destroyed before remotely operated cameras could inspect the condition of the material. This difficult, hazardous programme took more than 10 years.

In September 2017, following extensive research and development trials inside the plant and at a test rig on the outskirts of Thurso, work began to remove the remaining breeder material. NDA sees decommissioning of the DFR as one of the most technically challenging projects in its estate, making removal of the breeder elements a top priority. Removal work is expected to take fewer than three years, NDA said, and then dismantling of the reactor can begin.