The announcement came amid other bad news for the British nuclear industry, which is facing other inpediments at two British Energy-owned reactors at the nuclear stations of Hunterston B, in Ayrshire, and Hinkley Point B, Somerset. Both of these sites could need repairs to mend boiler cracks, the London Guardian reported Wednesday.

The Thorp plant was closed in April of 2005 when it was discovered that a pipe rupture in its fuel clarification cell had, over a period of nine months, leaked 20 tonnes – or 83,000 litres – of plutonium and uranium liquor mixed with nitric acid, constituting Britain’s worst nuclear mishap in 14 years.

“We deeply regret the incident, which clearly should not have happened and are determined to do everything necessary to ensure that nothing similar can ever happen again,” said a BNG spokeswoman in a statement to Bellona Web Thursday.

“The safety of our employees, local communities and the environment remains our number one priority. At no time did this incident pose any actual or potential threat from a health, safety or environment perspective.”

A Bellona Foundation visit to the Cumbria-based plant in July 2005 confirmed that assertion. Immediately following the accident, nuclear officials held public meetings in local communities to explain the ramifications of the incident, which at no time posed a radiation contamination threat.

BNG officials, however, did tell Bellona Web at the time that they could have been faster to notify the nation as a whole and international governments, which found out about the incident from scare headlines run in the Guardian in May 2005 – a month after the incident occurred.

Shifting deadlines
BNG, which was slapped with a £2m ($3.8m) fee deduction from the Nuclear Decommissioning Authority (NDA) for failing to meet high quality safety and environmental requirements – and still faces an unlimited crown court fine for the incident – had hoped to bring Thorp back on line over the summer.

After failing to meet that deadline, it was announced the plant was looking at an autumn target date.

When it became apparent that obtaining the necessary permissions to restart the plant from the Nuclear Installations Inspectorate (NII) and the NDA would take more time for its safety evaluations, BNG announced the plant would not be back in operation until next year. Workers – who have meantime been monitoring the plant and attending retraining seminars – were told the news on Friday.

“Whilst all necessary improvements to the plant will be completed by the end of September, it is now clear that the process of closing out the NII recommendations and related work will take some time,” said the BNG spokeswoman.

“British Nuclear Group and the NII are seeking to complete this work as quickly as possible but it is likely that this will run until the end of December, leading to a restart in early 2007.”

The delay has further sullied the image of the £1.8 billion flagship reprocessing plant, which had even before the accident, been falling behind on customer orders and earning bad-word-of-mouth advertisements among international nuclear industry clients. BNG Sellafield, though, does not expect to suffer any financial loss as a result of the new delay.

But the NDA reported on its website that the NDA itself may lose money from the Thorp shutdown, saying that spent fuel reprocessing is substantially below target, resulting in a delay of £87m.

The Thorp event, classified by the seven-level International Nuclear Event Scale (INES), was rated at a “3.” This established the Thorp leak, in the INES scale’s terms, as one step short of a full blown nuclear accident, and fixed it as a “serous incident.”

Since the leak from a fractured pipe within the feed clarification cell, BNG has been giving Thorp staff training in “behaviour and technical matters,” the News and Star reported. Additionally a new closed circuit TV camera has been installed to more closely monitor the workings of the cell to allow workers to more quickly respond to any incidents.

The repairs to THORP
The April 2005 incident was not discovered until plant workers began to notice a drop in the level of plutonium and uranium held in one of Thorp’s two so-called accountancy tanks, which hold the toxic mixture of uranium, plutonium and nitric acid, and where other elements such as metallic uranium, or tailings, are separated out.

More camera equipment could have alerted workers to the incident earlier. Sellafield officials acknowledged to Bellona Web that the leak could have been going on since August 2004 due in part to the lack of video surveillance of the cell.

“The preferred option for returning the plant to service involves isolating the affected accountancy tank and pipework associated with the failure of primary containment and using the other unaffected tank, subject to a revised operating regime,” said the BNG spokeswoman.

“We have now completed all the necessary physical modifications to the Feed Clarification Cell and associated equipment.”

The spokeswoman added that the safety measures described were approved by the NII in July. A BNG official said that BNG had “made all the necessary changes and met the requirements of authorities, and they are satisfied with what we have done.” He added that BNG considers that Thorp is essentially ready to restart, depending on the nod from the NDA.

What is the clarification cell?
Thorp’s fuel clarification cell is comprised of 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. BNG 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 had been contained.

Thorp’s raw materials are used fuel rods from nuclear power stations. After receipt at Thorp, the assemblies 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 are 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.

NDA response to the Thorp delay
In the time immediately following the incident, the NDA considered shutting down Thorp altogether. The federal decommissioning body – which owns 18 of Britain’s more troubled nuclear sites – quickly back-tracked when the dimensions of the Thorp incident were fully understood, and opted for repairs.

The most recent delay again tabled the idea of shutting down the plant, but the NDA has said it still considers Thorp viable for a restart.

In remarks reported in the News and Star, an unidentified NDA spokesman said: “any final decision to restart Thorp will be made by the NDA. The plant’s date to restart has always been tentative given that this was a major incident.”

“We always place safety as the absolute priority. We understand that the NII must have the time it needs to complete its assessments and determine whether the plant is safe to re-start,” he said.