Details of an incident involving a loss of vital cooling to the storage tanks that currently hold some 1000 cubic metres of highly radioactive liquid waste are now beginning to emerge. News of the incident was first divulged last week by Sellafield Limited’s new Managing Director Bill Poulson of Nuclear Management Partners Ltd (NMP), the company that operates the HLW plant under contract to the Nuclear Decommissioning Authority (NDA).
Whilst full details are still unavailable, responses from the Nuclear Installations Inspectorate (NII) and others to follow up questions from CORE reveal that the incident occurred on Thursday 2nd April and involved a loss of coolant water to all the storage tanks following the incorrect re-instatement of one of a number of control valves that had been isolated for maintenance.
Because some of the storage tanks have a higher heat loading (the liquid HLW is physically hot as well as being highly radioactive) than others, efforts to re-instate the cooling water supply were directed first at the three tanks with the highest heat loading. Cooling was restored to the first of these after 75 minutes, and to all three tanks after 3 hours. Reporting today on the incident, Sellafield’s in-house Newsletter states that cooling was restored to all tanks within 8 hours. This is perilously close to the timescale of 10.5 hours catered for in the Sellafield site’s emergency plan (see REPPIR below).
The incident is provisionally designated at Level 1 on the International Nuclear Event Scale (INES) and is under full investigation by the NII. Sellafield Ltd is carrying out its own in-house investigation with the possibility of a Board of Inquiry being set up.
CORE’s spokesman Martin Forwood commented: The catastrophic result of an extended loss of cooling to these dangerous and increasingly obsolete tanks is well documented and has major implications not only for Cumbria but also for the UK and its European neighbours. Last week’s worker-error incident, was dangerously and unacceptably close to resulting in a major off-site release of radioactivity with long term consequences for human life and the environment”.
Only last month the Norwegian Government’s Ministry of the Environment and the Director of its Department for Emergency Preparedness on Environmental Radioactivity issued a damning report on the calculated effects on Norway of an accident involving Sellafield’s HLW tanks. The report concluded that if just 1% of the tanks’ inventory was accidently released, the radioactive fallout in Norway would be five times greater in the areas worst affected by the Chernobyl accident. If 10% of the tanks’contents were released, the fallout would be fifty times the country’s maximum post-Chernobyl experience. CORE has informed Norway of the latest incident.
Since the closure of Sellafield’s Calder Hall reactors in 2003, an accident involving the loss of coolant to the HLW tanks is designated as the ‘Reference Accident’ (worst credible accident) for Sellafield’s Emergency Plans under the Radiation and Emergency Preparedness and Public Information Regulations (REPPIR). The Reference Accident is described as being ‘a failure of the entire cooling water distribution system to the High Level Radioactive Waste Store following a single flange failure or leak from a length of pipe. The accident scenario assumes a failure to reinstate the cooling system within a period of 10.5 hours and that it has not been possible to isolate the failed section of pipe’. Whether or not Cumbria County Council’s Emergency Planning Department was informed of last week’s incident remains part of the NII’s investigation.
The existing tanks, holding a significantly larger inventory of radioactive materials than were released during the Chernobyl accident, were commissioned between 1955 and 1990. They have long been subject of concern by the NII through the increasing failure of cooling components. Plans to construct and install new, smaller tanks are currently being assessed by Sellafield and the regulators.`