-
Windscale B-204 (1951—52): The first British reprocessing plant used a new solvent called di-butoxy diethyl ether, and this method is known as the BUTEX process. One advantage of BUTEX was that no salting agents were required, reducing process stages and waste volumes. The primary driver for B-204 was to extract weapons-grade plutonium from the Calder Hall Magnox reactors. The first plutonium was ready by April 1952 and the UK detonated its first nuclear device just six months later. In total, B-204 produced 3.6 tonnes of weapons-grade plutonium.
-
Windscale B-205 (1964): A second plant was built. Initially both B-204 and B-205 only reprocessed metallic (Magnox) fuel. In 1969, B-204 was modified to act as a pre-handling facility so that B-205 could also reprocess oxide fuel from the new AGR reactors and some overseas BWR fuel. From 1969 to 1973, approximately 100 tonnes of oxide fuel were reprocessed. In 1973, an explosion during restart of B-204 released radioactive gas, contaminating the plant and exposing 34 workers to radioactive ruthenium-106. B-204 never reopened.
-
THORP at Sellafield (1994): The Thermal Oxide Reprocessing Plant (THORP) was built to reprocess oxide fuels using the PUREX process. The decision to build was taken in 1977 but construction took longer than expected and ran over budget, costing in excess of GBP 1,000 million. THORP had a design reprocessing capacity of 1,200 tonnes per year. In 2005, THORP suffered a serious leak of highly radioactive fluid inside a clarification cell. THORP permanently closed in 2018.
The THORP 2005 Leak
The 2005 THORP incident merits detailed discussion as a significant nuclear safety case study. In April 2005, operators discovered that approximately 83,000 litres of highly radioactive dissolved fuel solution (containing an estimated 22 tonnes of uranium and 160 kg of plutonium in nitric acid) had leaked from a fractured pipe in the feed clarification cell. The total activity of the spilled material was conservatively estimated at 100,000 TBq — comparable in magnitude to the total release from the Chernobyl accident, though crucially the material was entirely contained within the sealed, shielded cell and there was no release to the environment and no worker received a significant dose.
The leak was believed to have begun as early as August 2004 but was not detected until April 2005 because the cell was not routinely inspected (it was sealed and shielded). The incident was rated Level 3 on the International Nuclear Event Scale (INES) — a “serious incident” without off-site radiological consequences. THORP was shut down for over two years for investigation and remediation. The incident highlighted the importance of in-cell monitoring and leak detection systems, and led to significant improvements in process monitoring across the UK nuclear industry.