Details are only just emerging of an event at the Thermal Oxide Reprocessing Plant (THORP) on the 14th May this year when a holding tank was inexplicably filled with the wrong substance – formaldehyde instead of hydroxylamine. Both are used in the operation to reprocess spent reactor fuel but at wholly different stages of the process and for completely different outcomes.
According to Sellafield Ltd the mistake was discovered before the contents of the holding tank, located in advance of the plant’s radioactive process system, could be transferred into the spent fuel dissolution process itself in THORP’s Head-End – the initial stage of reprocessing. Despite the early discovery, the event was deemed sufficiently serious for The Office for Nuclear Regulation (ONR) to be informed and an internal investigation initiated by Sellafield Ltd.
But because the holding tank was ‘outside’ the reprocessing system itself and the formaldehyde had not yet become radioactively contaminated, the mistake was accordingly classified as a non-radiological event. As such it falls outside the requirement for the event to be reported publicly.
CORE spokesman Martin Forwood said today:
‘Had this major human error not been detected in time, as we are lead to believe, the consequences of introducing formaldehyde into the first stages of fuel dissolution could have been catastrophic for the THORP’s internal workings – and had the potential to initiate a site accident. The public have an absolute right to know about these worker-gaffes going on behind the perimeter fence – non-radiological or otherwise’.
It is understood that the hydroxylamine that should have been put in the holding tank is used to ‘separate’ plutonium from the dangerous liquid mixture of acid-dissolved spent fuel. For its part, formaldehyde is used to reduce acidity at the latter stages of reprocessing when the liquid high level wastes are evaporated. As one observer commented ‘the effects of the two are about as opposite as you can get – like putting Epsom salt in your tea instead of sugar’.
THORP is now in its 20th year of operation and, some 8 years behind schedule, is reduced to reprocessing just a quarter of the volume of spent fuel it was originally designed for. The plant has been scheduled to enter an 8-week ‘outage’ in June/July this year.