A statement on incidents at nuclear installations in Britain and during the transport of radioactive material(*), which meet Ministerial Reporting Criteria (MRC), is provided to the Secretary of State for the Department of Energy and Climate Change and the Secretary of State for Scotland, and is published each quarter by the Office for Nuclear Regulation.
(*This is the first statement to include a transport incident since ONR assumed responsibility for its regulation)
For the period, 1 January 2014 to 31 March 2014, there were two incidents, which met the MRC. The statement also includes an incident relating to the previous quarter (01 October 2013 to 31 December 2013) this has been included, as a result of further investigation, which produced updated information.
There was a partial loss of site power on the eastern side of the Sellafield site. Several nuclear facilities lost their electrical power supply and initiated local response actions.
The loss of power was caused by the failure of the insulation on the cable feeding a transformer located at the Waste Vitrification Plant (WVP) causing one of the three phases to discharge to earth. Had the electrical protection system operated as intended there would have been no interruption of power to any facility. However, the relay protecting against this fault failed to operate resulting in the loss of main substation feeding the east side of the site. The power fault affected ventilation systems within the WVP resulting in migration of radioactivity into the plant operating areas. The plant was evacuated, on loss of power, in accordance pre-planned arrangements and no operators were exposed to activity.
The findings from ONR's investigation are as follows:
Although the plant ventilation system shut down on loss of power in accordance with the design safety case the widespread release of radioactive material from the shielded cells into the working areas was not as expected and is not identified within the Safety case as a possible fault sequence.
ONR believes that Sellafield did not fully understand the design intent of the containment boundary. Therefore, it was not adequately maintained as a system and subsequently, did not perform as assumed in the safety case.
Enquiries revealed that some ventilation plant items, including the filters, which are designated as safety mechanisms, were not included in the plant maintenance schedule or subject to adequate examination, maintenance, inspection and testing regime.
Information provided, indicated that there was a lack of control of design changes that introduced new penetrations into the containment which together with the limited maintenance and testing compromised the ability of the containment to perform its overall function.
ONR believes that the consequence of the loss of power was not considered by Sellafield in the safety case for this plant.
ONR has completed its investigation of this event and enforcement action is being considered
Goods vehicle carrying 67 drums of naturally occurring low level radioactive material overturned on the A697 at North Thornton, Northumberland. The road was closed to traffic and a 45 metre cordon was set up by emergency services. Two drums were found to be damaged. The damaged drums were overpacked and all the drums were subsequently loaded onto another vehicle for onward transport. The cordon was removed early 22/1/2014 on Scotoil's Radiation Protection Supervisor's advice after consideration of the material being transported. Remedial work was undertaken by the consignor and no contamination remained in the vehicle, which had overturned; or the surrounding area.
ONR is still waiting for the final investigation report from the consignor. ONR has inspected the carrier and investigations are ongoing.
Further to reports that highlighted contamination around the Highly Active Storage Tank (HAST) 9 in the High Active Liquid Evaporation and Storage HALES facility and some contaminated clothing in a change room, it was believed that the unauthorised removal of the HAST 9 resistance thermometer (RT) had taken place. This RT has high radiation levels associated with it and was discovered in the HALES high radiation (shielded) waste storage area.
As a consequence of this event, an individual received an extremity radiation dose greater than 10% of the annual dose limit of 500mSv although this is not reportable. However, the level of contamination of both the equipment and the area, when tested, was found to exceed the acceptable levels (three times higher than permitted under the Ionising Radiation Regulation.
The RT device is stored in a secure location.
ONR investigated this event and as a result of our investigations, found no evidence that the particular activities were authorised in any way by Sellafield Ltd, or that Sellafield's systems of work for controlling such activities are deficient.
Enforcement action in the form of a formal caution has been taken, against the individuals who carried out unauthorised work contrary to their employer's safe system of work arrangements.