The reprocessing of spent nuclear fuel at Sellafield has been the site’s ‘bread & butter’ work since the 1950’s when the UK’s politically driven nuclear weapons programme required plutonium to be extracted, via reprocessing, from Windscale Pile fuel. Since then the site has been transformed into a burgeoning nuclear complex with commercial, rather than military, reprocessing still at its heart. To support it, a range of other facilities are required such as storage ponds, material stores and plant to treat the nuclear waste produced during the process. Of those used in the early years, many are now closed and are being decommissioned (see Site History).
Two reprocessing plant are in operation today at Sellafield, the B205 Magnox plant and the Thermal Oxide Reprocessing Plant (THORP). Whilst the former reprocesses the spent fuel from the UK’s fleet of ‘first generation’ Magnox reactors such as Calder Hall, the latter reprocesses the fuel from the UK’s operating Advanced Gas Cooled Reactors (AGR) and Pressurised Water Reactors (PWR) used at Sizewell in Suffolk and in overseas nuclear power stations.
B205 was opened in 1964 and designed to reprocess at least 1500 tonnes of sent magnox fuel each year. A combination of ‘military ‘and ‘civil’ reprocessing in the early years saw this annual tonnage met routinely and sometimes exceeded. Latterly, as the plant has aged and become less reliable, its annual throughput of spent fuel has dropped to just 400-500 tonnes. The plant is currently schedule for closure in 2020 by when all magnox spent fuel should have been reprocessed.
Whilst the dry store of similar fuel has become practice recently in some countries, Sellafield has maintained that the corrosive effects on magnox fuel in storage ponds, demands that it be reprocessed. Though a decade of pressure to move to a dry storage system has led to a Plan B being belatedly announced – requiring the construction of drying facilities for the wetted fuel and buildings in which to store it, it is unlikely ever to be deployed as the development and construction times would take it significantly past the 2020 ending of reprocessing.
The UK’s politically driven weapons programme of the 1950’s, via the two plutonium-producing Windscale Pile reactors, saw the remote coastal site in West Cumbria in the north-west of England transformed from a small wartime munitions facility into a burgeoning nuclear complex. The construction of the Calder Hall military reactors in the mid to late 1950’s – primarily to keep pace with the demand for weapons plutonium – heralded the emergence of the UK’s civil nuclear power industry and the establishment of commercial reprocessing. To accomplish these operations – from plutonium production and recovery to the production of electricity – a number of major facilities were needed, many of which are still operating today.
Major facilities – a potted history.
The Windscale Piles (1&2), with their 110m tall ventilation stacks, were built in the late 1940’s as were the reprocessing plant in which the plutonium was recovered from the Pile fuel, and associated storage ponds. Pile 1 ‘went critical’ in 1950 and the first weapons grade plutonium was produced in 1952. Later the same year, the plutonium was used in Britain’s first atomic bomb test carried out in the Monte Bello Islands off the north-western coast of Australia.
Following the infamous Windscale Fire in 1957 when Pile 1 blazed for several days -its radioactive plume spreading south-eastwards over the UK and Europe – both Piles were shut down and put under a programme of decommissioning. Whilst the ventilation stack of Pile 2 was demolished in 2001, overall decommissioning work on the Piles will not be completed for decades.
Calder Hall. The four Calder Hall military reactors operated between 1956 and 2003. The first of the reactors was opened by the Queen in 1956 and, though dubbed as the UK’s first commercial reactors, their principal use was the production of weapons grade plutonium for nuclear weapons (officially ended in 1995). The 50MW Magnox-type reactors were fuelled with natural uranium encased in a magnesium alloy cladding and were gas-cooled with carbon dioxide. The production of electricity as a by-product of plutonium production was then officially described as being ‘too cheap to meter’. Though some electricity was fed into the National Grid, most was used to power the Sellafield site itself. The reactors’ cooling towers, for decades a major feature on the Sellafield skyline were demolished in 2007. De-fuelling the shut-down reactors started in 2011 and when completed will lead to their being placed under a ‘care & maintenane’ regime, with full decommissioning scheduled for completion in 2117.
Primary Separation Plant B204, This first reprocessing plant was built between 1947 and 1951 and, from 1952, used to recover plutonium from Windscale Pile fuel. From the late 1950’s to 1964, the plant reeprocessed Magnox fuel from the Cader Hall and other Magnox reactors. With the trasnfer of Manox fuel reprocessing to a new facilty (B205) in 1964, a section of the highly complex plant was modifed to undertake the initial stages of reprocessing fuel from the newer generation of Light Water Reactors (LWR) operating outside the UK. A ‘blow-back’ accidet in 1973 whilst reprocessing this overseas fuel resulted in 34 workers being radioactively contaminated and the plant being closed down permanently. The plant is now being decommissioned, with the first major hurdle being the removal of the 61m high stack.