The extra expenditure will affect the cost of operations at the company's new Thermal Oxide Reprocessing Plant (Thorp), which was completed more than a year ago and is awaiting government permission to start. However, BNFL's profit from Thorp will be unaffected, because its contracts allow BNFL to pass on much of the cost to its customers.
The existing Windscale Vitrification Plant converts highly radioactive liquid waste into glass blocks for long-term storage and disposal, but the plant has a history of safety problems and is working at less than half its capacity.
It has produced only half the 600 blocks a year which the company expected. BNFL may have to build a new vitrification line alongside the existing building if it is to process the backlog of radioactive waste and cope with the extra waste that will be generated by Thorp.
A spokeswoman for the company said that it was now aiming for throughput of 350 blocks a year as a result of several options for improving production currently being considered. The vitrification plant needed too much maintenance and too much equipment had to be replaced between runs, she said. She emphasised that building an additional plant adjacent to the existing one was only one of the options being studied.
About 1,400 cubic metres of waste, in the form of highly radioactive acid liquid, are held in double-walled steel tanks at Sellafield. The tanks of waste are a legacy of reprocessing operations which have been going on since the 1950s, extracting plutonium and reusable uranium from spent fuel originating in military reactors and Britain's first-generation Magnox power reactors. Thorp, which will reprocess fuel from the second- generation advanced gas-cooled reactors and from overseas pressurised water reactors, will add to the accumulation of waste.
Because of the radioactivity, all these operations have to be done remotely, inside process cells isolated from the environment by thick concrete walls. This makes it difficult to repair or replace equipment. The melters were designed to have an operational lifetime of about 100 days, but the company has to replace them after every run and each replacement is taking longer than expected.
BNFL built the vitrification plant to have two production lines, so that one could be used if the other was down for maintenance, but now the company is studying the possibility of building a third line. The plant has been troubled since it was opened in February 1991. Violations of safety regulations at the plant led to British Nuclear Fuels being prosecuted by the Nuclear Installations Inspectorate earlier this year. The company was fined pounds 6,000 on 26 February for breaking the terms of its nuclear site licence.