Doubts raised over safety at Sizewell

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The Independent Online
THE COMPUTER software responsible for the safety of the new pressurised water reactor at Sizewell in Suffolk is too long and complex to be completely reliable, according to the British Computer Society.

In an open letter sent to the Nuclear Installations Inspectorate, the society's task force for safety-critical software suggests that the secondary safety system - which uses switches directly wired without the use of computers - ought to be upgraded.

The letter follows a meeting between Nuclear Electric, which is building Sizewell B, and representatives of the society. It puts forward seven detailed recommendations to improve software safety.

The letter warns that it is 'unsatisfactory' to have to depend on every item in a computer program that is 100,000 lines long. It also states that there are gaps in demonstrating that the program conforms to its specification, 'which implies that some errors may remain in the software'.

Dr Brian Wichmann, the acting chairman of the safety critical software group, said that 'undoubtedly Nuclear Electric have done a good job, but you have to ask yourself if 100,000 lines of code can be relied upon. We have said it is unsatisfactory.'

Roy White, Nuclear Electric's control and instrumentation manager at Sizewell, said the letter was very positive: 'They have made a number of suggestions to which we will be responding in due course.' But he added that the overall safety case for the reactor did not depend on the perfect functioning of the software.

A spokesman for the Nuclear Installations Inspectorate said that the NII was considering the letter carefully.