§ Dr. John Cunninghamasked the Secretary of State for Energy when he was informed about the incident that occurred at Windscale on 4 October; and if he will make a statement.
§ Mr. John Moore[pursuant to his reply, 19 October 1981, c. 80–81]: I have now received the Nuclear Installations Inspectorate's report on the results of its investigations into the circumstances of the release of radioactive iodine from the Sellafield site of British Nuclear Fuels Ltd. on 4 October 1981. A copy of the full text of the report has been placed in the Library of the House. I informed the House of this incident in the reply given to the hon. Member on 19 October.—[Vol. 10, c. 80–81.]
It has now been estimated that the total iodine 131 released to the atmosphere between 4 and 23 October, when the levels of iodine in milk had declined to normal, was about 8 curies. This, and calculations based on measurements of iodine 131 in milk, confirms the original estimates that the maximum radiation dose which could have been received by a member of the public was a small percentage of the annual limits recommended by the International Commission on Radiological Protection. The actual doses received are likely to have been very much less. I can therefore confirm that this incident caused no significant hazard to public health.
Investigations by both BNFL and the Central Electricity Generating Board have established that the cause of the release was the processing of six irradiated fuel rods only 27 days after they had been discharged from a reactor at the CEGB's Oldbury nuclear power station. Such fuel is not expected to arrive at the Sellafield fuel storage ponds if it has had less than a 90-day cooling period since being discharged from a nuclear reactor. This period allows radioactive iodine to decay to an acceptably low level. On 7 September seven fuel elements were taken in error from a fuel skip at Oldbury containing newly discharged fuel and sent in two skips to Sellafield with other fuel identified 69W as adequately cooled after removal from the reactor. The documentation of the two Oldbury skips showed no record of the seven "short-cooled" fuel rods.
At Sellafield, BNFL relies on the accuracy of the documentation and the fuel from one of the skips, containing six short-cooled rods, was sent for reprocessing in the normal way, but following the detection of abnormal levels of iodine the seventh short-cooled rod was identified in the second skip and retrieved. Before the first stage of processing at Sellafield, fuel rods pass through an installed monitoring device designed as an additional precaution to detect short-cooled fuel. Subsequent checks on this device, which is still in the development stage, showed that although it appeared to be in working order at the time of the incident it was not correctly positioned, and therefore allowed the short-cooled fuel to pass undetected.
The incident revealed shortcomings in the measures adopted by both the CEGB and BNFL to ensure that unacceptable releases of radioactivity do not occur in the course of reprocessing. The CEGB has formulated a number of proposals, which the NII endorses, for improving the control of operations at the power stations and which are to be applied, where necessary, at all commercial nuclear power stations. The main purpose of these proposals is to simplify where possible the procedures and instructions for all work in station cooling ponds and to strengthen the existing arrangements for ensuring its effective supervision. In addition, the CEGB has proposed the development of further independent technical safeguards to assist with the management of irradiated fuel in cooling ponds, including a monitoring device for recently discharged fuel for use at power stations.
Immediately following the incident BNFL placed an embargo on the processing of any fuel which could not be proved to be adequately cooled, either by having originated from a reactor which had not been in operation during the previous 100 days, or by having been in the Sellafield ponds for at least 60 days, or by independent gamma spectroscopy for each fuel rod. These checks are additional to the installed monitoring device at Sellafield, which as a result of the incident is now subjected to an increased frequency of testing and functional checks. Whilst these measures are essentially interim arrangements, the NII report emphasises that BNFL must continue to store for an additional 60 days any irradiated fuel delivered for processing, irrespective of the evidence of documentary records, until improved methods have been installed for measuring the cooling period of fuel after discharge from the reactor. BNFL will also be required to complete the development of monitoring equipment and to install the optimised system at Sellafield as soon as practicable.
The NII report draws attention to its view that BNFL should have informed the NII, the Radiochemical Inspectorate and the Ministry of Agriculture, Fisheries and Food of the incident before deciding to restart the plant. That is an important finding, and will be taken into account in the review of the procedures for reporting incidents to which I referred in my earlier reply. I fully recognise the concern and anxiety which incidents of this kind cause to the local community, however insignificant they may be in radiological terms. I intend to report further to the House on this matter in due course.