‘Complacency’ exacerbated Thorp leak
9 Jun 2005
The leakage of radioactive liquor into the fuel clarification cell at the Thorp nuclear fuel reprocessing facility at Sellafield was caused by metal fatigue to the piping from a suspended tank, according to an initial investigation from the British Nuclear Group.
The situation was made worse by ‘complacency’ in failure to react to plant information, the report adds.
The leakage of liquor, made up from spent nuclear fuel dissolved in nitric acid, was first identified on 19 April when a CCTV camera was introduced to the cell, after operators realised they could not account for all the spent fuel within the plant. Some 83m3 of liquid had escaped into the cell, containing around 20 tonnes of spent fuel.
The cell itself is made from concrete and lined with stainless steel, and acts as secondary containment for centrifuges and weighing tanks.It was the design of the weighing tanks which was at fault, the report states.
The tanks are suspended for weighing purposes, and according to the report, a ‘change in design intent’ led to changes to the mechanisms restraining the tanks, which in turn put more stress on the associated pipework.
Metal fatigue ensued, and may have begun as early as August 2004. The pipe itself failed in January. This is where complacency began to become an issue.
The report notes that between January and April, ‘opportunities, such as cell sampling and level measurements, were missed which would have shown that material was escaping to secondary containment.’
The failure itself would still have taken place, it notes, but the quantity of escaping liquid ‘could have been significantly reduced.’
Sellafield managing director Barry Snelson comments that he will ‘personally be ensuring that recommendations are implemented not just in Thorp but also across Sellafield.’
Snelson says that he is ‘disappointed’ that plant indicators were not acted upon, and will be ‘taking action to ensure that any complacency with respect to acting upon plant information is addressed.’
Thorp is still closed following the incident, and recovery of the escaped liquor is now underway. The cell is fitted with steam ejectors which are lifting the liquor from the floor and redirecting it to a process vessel.
