This was the last research fast reactor in the research programme. The next reactor would have been a commercial size demonstration fast reactor. Con­struction of PFR started in 1968 and it operated from 1974 to 1994 with an output of 250 MW. Although the reactor was not of commercial size, the PFR fuel assemblies were designed and manufactured at commercial size. It was cooled by sodium as enough experience and confidence had been gained from DFR operations to go forward without the need for a eutectic coolant.

After shutdown, the fuel was removed to the associated fuel pond where it remains until a decision on its final treatment and destination is made.

The experience gained from the early DFR NaK decommissioning enabled the world’ s largest sodium destruction plant to be designed and built during the late 1990s. The plant was built in the decommissioned and stripped out turbine hall. Around 1,500 tonnes of primary and secondary sodium were destroyed by the same process as that used for DFR. The dif­ference from DFR was that the sodium was only lightly contaminated as PFR fuel was in sealed elements whereas DFR fuel was in vented elements so reaction products contaminated the NaK.

As with DFR, there is a current programme for cleaning up the residual sodium and decommissioning the pipework, vessels and reactor compo­nents over the next decade. The additional challenge of decommissioning the PFR reactor itself is that it is 15 m below ground level and this requires the design and operation of special remote handling appliances.

Decisions in the UK and Scotland within the nuclear industry and with regulators on the concepts and practicability of in-situ disposal will have a bearing on the eventual end state of the decommissioned PFR reactor.