§ Mr. Hooleyasked the Secretary of State for Energy (1) if he will publish in the Official Reporta full description of the defects discovered in reactor 2 at Dungeness A nuclear power station;
(2) if he will publish in the Official Report a full description of the defects discovered in reactor 1 at Dungeness A nuclear power station.
§ Mr. Norman LamontI am advised by the CEGB that nuclear reactors are shut down for statutory inspection every two years as a requirement of the nuclear 827W site licences granted by the Health and Safety Executive. The programmes of work are agreed between the CEGB and the Nuclear Installations Inspectorate of the executive and in recent years reactors have been subjected to more comprehensive inspection than in earlier years, taking advantage of developments in inspection techniques.
Dungeness A reactor 2 was shut down for a statutory inspection in August 1978, and the planned outage was extended owing to the discovery of weld defects. This was reported in Hansard on 21 May 1979. These defects occurred in some of the structures of the coolant gas ducts which transfer hot gas from the reactor core to the boilers, where after being cooled the gas is pumped by circulators back to the core. The major defects were found in compensating bellows associated with the main gas circulators, and other defects were found in the gas duct attachments and restraint systems of the duct expansion bellows. Some of these defects were removed by a limited amount of grinding: where necessary others were repaired by approved weld procedures, while the remainder were small and accepted by the NH without repair. The defects were in the fillet welds where components are attached to the ducts, or in the fillet welds of the bellows restraints, but not in the main butt welds of the ductwork. The inspections were carried out using the magnetic particle technique supplemented by ultrasonic methods, use of the latter being more difficult because of access. Both methods are far more sophisticated and sensitive than the radiographic techniques used during construction many years ago, and which were the optimum techniques then available. The majority of the defects indicate parting or tearing of the weld material from the parent metal, or lack of fusion at the weld roots.
Reactor I was shut down for its statutory inspection in April 1979 and a programme of work taking account of the experience obtained from reactor 2 was started. In general similar defects have been found and remedial work is being carried out. Particular attention has been given to the internal restraint systems of the bellows, and improved ultrasonic equipment recently developed for the purpose has enabled more detailed information to be obtained. Recent inspections 828W and investigations of two of the bellows components revealed defects that reduced the margin of strength to an extent that required remedial action. It should be noted that the restraint structures can accept a considerable loss of strength in individual parts without the risk of overall failure occurring. The evidence indicates that the defects were present when the bellows were manufactured and did not develop during operation of the reactor.
During the reactor 2 shutdown in 1978 and 1979 similar parts were examined principally by magnetic particle inspection and at that time there were no indications of significant defects. However, this now needs to be checked by the more accurate ultrasonic method. Accordingly, the CEGB considered it prudent to shut down reactor 2 on 14 January 1980, instead of March, the next planned statutory shut down. This also has the advantage that any necessary repair work can be planned in conjunction with that for reactor 1.
There has been no health hazard either to the public or to the staff at the station, and the defects are in places where there is insignificant radiation, which permits remedial work without undue exposure of personnel. It is not possible to say at this stage when Dungeness A will resume electricity production, but I understand that the board is confident that the station will be back in service later this year. The inspection and repair work will be subject to the approval of the Nuclear Installations Inspectorate, and the station will not be returned to service until the inspectorate is satisfied.
§ Mr. Hooleyasked the Secretary of State for Energy if he will list in the Official Reportthe date on which the construction of Dungeness A nuclear power station first began, the date on which it first supplied power to the grid, and periods since that date during which it has been fully functioning or out of commission.
§ Mr. Norman LamontConstruction of Dungeness A nuclear power station started in July 1960 and reactor 1 began supplying electricity to the national grid in September 1965. Full power operation was achieved in November 1965 in reactor 1 and in December 1965 in reactor 2.
Each reactor has been shut down every two years for statutory inspection. I have 829W asked the chairman of the CEGB to write to the hon. Member with detailed information.
§ Mr. Hooleyasked the Secretary of State for Energy what are the total capital and running costs to date of Dungeness A nuclear power station; and what is the estimated revenue from electricity actually supplied to the grid during such time as the station has been in commission.
§ Mr. Norman LamontTotal capital costs of Dungeness A nuclear power station were £79 million and the total running costs to date are £99 million. These figures exclude interest and overheads which the CEGB does not charge separately to the costs of individual power stations. The output of Dungeness A in the period since its commissioning, valued at the average price at which the CEGB sold electricity in bulk to the area boards in those years, was £360 million