On April 18, a camera-based investigation of the clarification cell revealed that a pipe leading from one of the reprocessing facility’s so-called Accountability Tank had ruptured and caused a leak of some 20 tonnes of uranium and plutonium dissolved in nitric acid onto the for of the clarification cell. The clean up operation began May 19. There are as yet no cost estimates as to how much the clean up effort will cost

The BNG official sad that the incident—which ranked a “3”corresponding to a “serious incident” on the International Nuclear Event Scale (INES)—that conditions within the cell remain stable and safe. The “3” rating on the INES sale is one step short of a nuclear “accident without significant off-site risk.

Thorp’s fuel clarification cell comprises a stainless steel-lined space 60 metres long, 20 metres wide and 20 metres high and its concrete walls are 2 to 3 metres thick to absorb radiation. Another BNG official, Sellafield’s spokesman Nigel Monckton, said the cell was designed to withstand the possibility of a leak and, because stainless steel does not dissolve in nitric acid, the leak has been contained.

Thorp’s raw materials are the used fuel rods from nuclear power stations. After receipt at Thorp, they are stored for several months to allow the radioactivity of short-lived fission products to decay to safer levels. The 1-metre long, 1-centimetre diameter tubular rods are then cut up into small chunks and lowered in baskets into strong nitric acid.

The uranium, plutonium and fission products dissolve and the remnants of the steel rods are removed. But the fluid remaining from the process, called liquor, still contains small shards of steel, or tailings, from burrs created as the rods were chopped up. So the liquor must be centrifuged to get rid of the steel contaminants, a process called clarification. It is at this clarification stage that the leak occurred.