HC Deb 01 December 1969 vol 792 cc188-9W
59. Mr. Wingfield Digby

asked the Minister of Technology what discussions he has had with the Central Electricity Generating Board and the Atomic Energy Authority about continued corrosion in six nuclear power stations on account of the carbon-dioxide coolant even whilst they are operating at lower temperatures; whether he is satisfied that remedial action will be effected in this type of reactor; and if he will make a statement.

Mr. Benn

I am in close touch with the Board and the Authority on this matter. I am circulating a statement on the present position with the OFFICIAL REPORT.

Following is the information: Since my announcement to the House on the 13th October, I have been advised by the C.E.G.B. that the operating temperatures of the six Magnox reactors affected by corrosion have been further reduced. They also advise me that this has been done solely as a precautionary measure against continuance of corrosion and to protect the long term capabilities of the reactors while technical investigations of the problem are developed. The C.E.G.B. reactor at Berkeley and the U.K.A.E.A. reactors at Calder Hall and Chapel-cross operate at lower temperatures; no significant corrosion has been observed at them, and it has not been necessary to reduce temperatures. The South of Scotland Electricity Board station at Hunterston A has, however, been affected, and is operating at reduced temperature. The extensive inspections made during the summer and the assessment of all relevant information have shown that all the affected stations can continue to be operated safely at the reduced temperatures. These additional restrictions at the C.E.G.B. stations mean a further reduction of 300MW in their rating, making a total of 700MW. This is about 1½ per cent. of the Board's gross capacity. The extra cost of making up this shortfall from other stations would be about £7 million in 1969–70. Some components of the Magnox station at Wylfa, which is due on loan in early 1970 have been modified but the reactor would still be subject to corrosion if operated at its design temperature. Restrictions similar to those imposed at other C.E.G.B. stations would mean a loss of about 300MW compared with design output. This with the 700MW loss already mentioned would cost about £10 million in a full year to make up from other stations. Notwithstanding the corrosion problem, the stations continue to achieve high availability, and high cumulative load factors. The longer term performance of individual stations compared with the load factor used for economic assessments of 75 per cent. over 20 years depends upon the prospects for retrieval of output. As to this, the C.E.G.B. are pressing on their investigations with all speed, with the assistance of the U.K.A.E.A. and the consortia. The investigations are, of course, complex and it is not feasible to accelerate the necessary experimental studies. It will not be possible to make any firm statement about the prospects of returning to a higher output until mid-1970. Equally, since this corrosion is a complex phenomenon, it is not possible to be categorical about the way in which the situation at the affected reactors will develop, but the Board are confident that the likelihood of an unscheduled shutdown from this cause is very low. Advanced Gas Cooled Reactors should not he affected by this corrosion, since their high design operating temperatures made it necessary to use special materials in the high-temperature zone. Designs of all stations under construction are, however, being checked to confirm that no components in other situations are at risk.

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