At its opening the Queen declared it to be “the result of a series of brilliant discoveries” and nuclear energy was touted as the energy source of the future, expected to generate electricity “too cheap to meter”. In fact Calder Hall was originally built as a producer of plutonium for the weapons programme. Its small size and high staffing levels have now rendered it uneconomic and in recent years its design has proved unreliable.

The final shutdown was marked with a celebration of the station’s achievements for current and past members of staff, local dignitaries and senior BNFL staff. BNFL is now preparing plans to decommission the reactor, a process that will take 100 years or more. Defuelling is expected to take 2-4 years. Uniquely, Calder Hall has no buffer storage facilities for spent fuel so the reactor cannot be defuelled until the fuel can be fed straight into the reprocessing line elsewhere on the Sellafield site.

The next ten years will be used for removal of low-active areas like the turbine hall. The defuelled core will finally be left for a further 80-100 years under “care and maintenance” before being dismantled. The nearby Chapel Cross site, whose four units are similar to Calder Hall, are also due to close, by March 2005.