Windscale (Hansard, 19 October 1981)

§ Mr. John Moore:

At about 10.45 am on Sunday 4 October 1981 the radioactivity monitor on the exhaust stack from the magnox fuel separation plant at British Nuclear Fuels Limited (BNFL) site at Sellafield, Cumbria gave a warning of an abnormally high release of radioactivity. The monitor is set at low levels. The plant, in which irradiated magnox fuel is dissolved, was promptly shut down in accordance with the Company's safety procedures. Analysis of the stack samples confirmed that a release of the radioactive isotope iodine 131 had occurred. The plant was therefore kept shut down until Company personnel were satisfied that it was safe to restart operations. They concluded that some fuel which had been stored for too short a period in cooling ponds had been inadvertently fed to the dissolver. Pond storage is provided at nuclear power stations and reactor sites mainly to allow the iodine 131 in irradiated fuel to decay to an acceptably low level.

The BNFL management decided, after assessing the potential environmental effects, to restart the plant. The removeable iodine was flushed out of the dissolver and safely discharged to the sea. The plant was restarted at about 10 am on 5 October using fuel of proven long storage. Careful surveillance, including monitoring of further releases of iodine still within the plant, continued. The release from the stack of iodine 131, which had been measured at about 1.9 curies in the first 24 hours after the abnormal level was identified, had declined to about 0.4 curies per day by the morning of 8 October and has continued to decline. To date about 7 curies have been discharged. The Company are required by the authorising Departments, Department of the Environment and Ministry of Agriculture, Fisheries and Food to use the best practicable means to minimise discharges. Over the past four years the annual discharge has been less than one curie.

On Tuesday 6 October BNFL informed DOE and MAFF under arrangements for the reporting of abnormal releases to those Departments. At about 4 pm on that day, BNFL also informed the Nuclear Installations Inspectorate that further investigations had revealed a breach of a technical plant operating limit on 4 October in that irradiated fuel containing an excessive quantity of iodine 131 had been fed to the dissolver. On the late afternoon of 7 October BNFL advised the NIL DOE and MAFF that iodine 131 had been detected, by monitoring, in samples of milk gathered at two farms within a 2-mile radius of the Sellafield site. The highest value measured from the samples collected then and later was 5,000 picocuries (i.e. millionths of a curie) of iodine 131 per litre. On this basis it is estimated that radiation doses to the critical group most liable to be affected, i.e. young children drinking this milk would be no more than a small fraction of the International Commission on Radiological Protection's recommended annual limit to members of the public. On the basis of the daily information obtained, the MAFF, which is responsible for environmental monitoring of foodstuffs, considers that the measured levels of iodine in 83W milk confirm this. Milk sampling is continuing at 20 farms of which 12 are close to the site. MAFF has not considered it necessary at any stage to ban the sale of affected milk.

I am satisfied that this incident, although resulting in a release of iodine 131 has caused no hazard to public health. The amount released to the atmosphere was very small because safety precautions came into play. The NII is investigating the full circumstances of the incident. The inspectorate advise me that, in the light of its investigations, steps are being taken to ensure that no irradiated fuel will be moved from nuclear power stations to Windscale for reprocessing until it has been stored for at least 90 days, to allow the radio-iodine to decay.

My Department was informed on 7 October by the NII and BNFL of the incident. On 8 October the NII submitted a formal report to the Secretary of State on the basis of the information then supplied to it by BNFL. On 9 October, following the receipt of further detailed information from BNFL, the NII submitted a further report to the Secretary of State which amplified the initial report.

I have asked that the reporting procedures at all stages for such incidents be urgently examined by the Nuclear Installations Inspectorate. I intend to satisfy myself that such procedures are adequate, and that procedures for informing the local community in the event of such incidents are satisfactory.