Nuclear plant closed after radioactive flood
New Scientist Breaking News - Nuclear plant closed after radioactive flood
18:32 09 May 2005
NewScientist.com news service
Paul Marks
Nuclear fuel reprocessing at the UK's Thermal Oxide Reprocessing Plant (THORP) at Sellafield in Cumbria has been halted indefinitely after a critical failure in the plant's pipe work. The leak led to 83 cubic metres of a highly radioactive liquor flooding the floor of a vast - but permanently unmanned - processing area.
THORP is designed to extract plutonium and uranium from spent nuclear fuel from around the world so a proportion of it can be reused in power stations. The leaked material comes from near the "front end" of the plant's process and is very highly radioactive. The leaked liquor contained 20 tonnes of plutonium and uranium dissolved in nitric acid.
Nigel Monckton, a spokesman for the British Nuclear Group, which runs Sellafield on behalf of the UK’s nascent Nuclear Decommissioning Authority (NDA), says the leak was discovered after a camera-based inspection. The processing area viewed, called a clarification cell, revealed where missing liquor from another part of the process was pooling.
The 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. Monckton says 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.
"There has been no radiation dose to Sellafield workers as a result of the leak and no release of radioactivity into the atmosphere," confirms a spokesman for the safety regulator, the Nuclear Installations Inspectorate.
Centrifugal forces
THORP’s raw materials are the used fuel rods from power stations. After receipt, they are stored for several months to allow the radioactivity of short-lived fission products to decay to safer levels. Then the 1-metre long, 1-centimetre diameter tubular rods are 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 liquor still contains small shards of steel, or tailings, from burrs created as the rod was chopped up. So the liquor must be centrifuged to get rid of the steel contaminants. It is at this "clarification" stage that the leak occurred.
However, the halting of work at THORP is a mixed blessing for anti-nuclear campaigners because the revenue the plant generates is crucial to the clean-up and decommissioning of the UK's old nuclear power stations.
About 25% of the NDA's £2.2 billion clean up budget for 2005 to 2006 was to have come from THORP. But with the plant out of action until a safe plan can be devised for repairing the broken pipe work and recovering the spilled liquor, revival of that revenue stream looks uncertain. “This year’s budget is likely to take a hit but it is too early to be absolutely clear by how much," says Sir Anthony Cleaver, NDA chairman.
THORP engineers are hopeful they can recover the leaked liquor without having to design any elaborate robotic systems to do so. "The clarification cell is not designed for man access but is a closed environment designed for the recovery of liquor back into tanks," says Monckton. He thinks liquor recovery, if not pipeline repair, can be done via clever use of the cell's pumps. "We do have extensive experience of conducting this sort of work," he says.
18:32 09 May 2005
NewScientist.com news service
Paul Marks
Nuclear fuel reprocessing at the UK's Thermal Oxide Reprocessing Plant (THORP) at Sellafield in Cumbria has been halted indefinitely after a critical failure in the plant's pipe work. The leak led to 83 cubic metres of a highly radioactive liquor flooding the floor of a vast - but permanently unmanned - processing area.
THORP is designed to extract plutonium and uranium from spent nuclear fuel from around the world so a proportion of it can be reused in power stations. The leaked material comes from near the "front end" of the plant's process and is very highly radioactive. The leaked liquor contained 20 tonnes of plutonium and uranium dissolved in nitric acid.
Nigel Monckton, a spokesman for the British Nuclear Group, which runs Sellafield on behalf of the UK’s nascent Nuclear Decommissioning Authority (NDA), says the leak was discovered after a camera-based inspection. The processing area viewed, called a clarification cell, revealed where missing liquor from another part of the process was pooling.
The 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. Monckton says 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.
"There has been no radiation dose to Sellafield workers as a result of the leak and no release of radioactivity into the atmosphere," confirms a spokesman for the safety regulator, the Nuclear Installations Inspectorate.
Centrifugal forces
THORP’s raw materials are the used fuel rods from power stations. After receipt, they are stored for several months to allow the radioactivity of short-lived fission products to decay to safer levels. Then the 1-metre long, 1-centimetre diameter tubular rods are 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 liquor still contains small shards of steel, or tailings, from burrs created as the rod was chopped up. So the liquor must be centrifuged to get rid of the steel contaminants. It is at this "clarification" stage that the leak occurred.
However, the halting of work at THORP is a mixed blessing for anti-nuclear campaigners because the revenue the plant generates is crucial to the clean-up and decommissioning of the UK's old nuclear power stations.
About 25% of the NDA's £2.2 billion clean up budget for 2005 to 2006 was to have come from THORP. But with the plant out of action until a safe plan can be devised for repairing the broken pipe work and recovering the spilled liquor, revival of that revenue stream looks uncertain. “This year’s budget is likely to take a hit but it is too early to be absolutely clear by how much," says Sir Anthony Cleaver, NDA chairman.
THORP engineers are hopeful they can recover the leaked liquor without having to design any elaborate robotic systems to do so. "The clarification cell is not designed for man access but is a closed environment designed for the recovery of liquor back into tanks," says Monckton. He thinks liquor recovery, if not pipeline repair, can be done via clever use of the cell's pumps. "We do have extensive experience of conducting this sort of work," he says.
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