Power plant performance - the transformation of Dungeness B

Dungeness B, the first AGR nuclear power station to be ordered in the United Kingdom, was bedevilled with problems arising from deficiencies in design and concept throughout its construction and into its prolonged commissioning period in the 1980's. Two incidents are described which illustrate these problems. In 1986 during commissioning of Unit 2, a gag-valve, which is part of the unit controlling coolant flow through the fuel channel, failed. The outcome was a limitation imposed by the Nuclear Installations Inspectorate (NII) on the channel gas outlet temperature (CGOT), and hence on the power. Following the installation of a computer-based protection system, the NII have removed the CGOT limitation. The second incident, in 1989, involved the dropping of a fuel stringer which took nine months to remove. This incident and other difficulties led to a complete overhaul of the refuelling operation with a view to improving the station performance through increased refuelling rates. These changes, and others aimed in particular at reducing unnecessary reactor tripping, have produced excellent results. The plant is expected to reach an output target of 6.4 TWh for the year ending March 1994, well ahead of the previous year's record of 4.1 TWh. (UK)