The company is likely to resist the move, which will make it more difficult to meet the Health and Safety Executive's requirements for a steady reduction in stocks of highly radioactive liquid wastes.
In 1996, ENDS revealed that levels of technetium-99 had increased dramatically in the Irish Sea, causing significant contamination in lobsters and some other shellfish (ENDS Report 262, pp 15-16 ). The isotope has now been detected as far away as the Arctic coast of Norway.
The UK has come under strong international pressure to end the discharges. In 1998, an Ospar agreement on radioactive discharges included a promise that UK Ministers would address the matter in a review of Sellafield's discharge consents. Ministers also agreed "progressive and substantial reductions" of radioactive discharges, with the aim that concentrations in the environment above historic levels are close to zero by 2020 (ENDS Report 282, pp 50-51 ).
The technetium-99 discharge is found in medium active concentrate (MAC) wastes from reprocessing of Magnox reactor fuel. Discharge of untreated MAC ceased in 1980, and the waste was stored at Sellafield pending completion of the EARP treatment plant. EARP, which was commissioned in 1994, does not remove technetium. As BNFL worked through the MAC stockpile, marine concentrations of the isotope shot up dramatically.
In January 2000, the Agency cut the annual limit on Sellafield's technetium-99 discharges from 200TBq to 90TBq (ENDS Report 298, pp 14-15 ). It also began a full review of the site's authorisations, with a separate fast-track review of options for further reducing technetium discharges. In September, the Agency sent its proposed decision on technetium-99 to the Environment and Health Secretaries for approval.
By March 2003, BNFL will have to divert new arisings of MAC to its vitrification plants for incorporation into glass blocks. However, the current discharge limit of 90TBq will be retained until 2006 - allowing the company to send all of its MAC stockpile for treatment and discharge to sea. Thereafter, a discharge limit of 10TBq would apply.
The Agency ruled out several more ambitious options. Sending all MAC for vitrification would be impracticable without building a new process line, the costs of which would be "grossly disproportionate to the benefits."
Another option would be to stop all MAC discharges while an end-of-pipe treatment plant is built to remove technetium. This would cost about £100 million and could not be operational until 2006-10. Moreover, storage of large quantities of MAC would run counter to the HSE's drive to reduce the hazards from liquid wastes on the site. MAC is currently held in a 50-year old, open-topped tank complex - and prolonging its storage would require a larger and costly new facility.
The final option would be to capture technetium in the EARP treatment plant by complexing it with an organic precipitant. However, waste disposal company Nirex has told BNFL that the resulting solid waste would be too unstable and mobile to accept in a future repository. Even so, the Agency has required BNFL to continue with research into this option and to implement it if the problems can be overcome.
BNFL had argued that the continued discharge of technetium-99 to sea is the best practicable environmental option as well as being £14-90 million cheaper than vitrification. The discharges would continue until 2017, five years after the closure of the Magnox fuel reprocessing facilities.
The Agency's proposals would reduce the total technetium discharge by only 40%. The regulator claims that its approach is in line with "the spirit and the letter" of the Ospar agreement.
Diverting MAC to the vitrification line could affect BNFL's efforts to reduce its stockpile of highly active liquor (HAL) arising from reprocessing. The company's two existing vitrification lines have been plagued by technical difficulties since their commissioning ten years ago. A third £320 million line is due for commissioning this autumn.
In January, the HSE set statutory limits requiring BNFL progressively to reduce the amount of HAL in storage. Current stocks of 1,500m3 must fall to a buffer level of 200m3 by 2015. The HSE has made clear that it will stop BNFL's reprocessing activities if it fails to keep within the limits.
The Agency accepts that diverting MAC to the vitrification process "could adversely affect the achievement of [the HSE's] targets, with the potential to have a knock-on effect on reprocessing." It considers that "BNFL should have the resources and expertise to manage the situation."
However, the HSE has not yet formally approved the plan to divert MAC - and will only do so once it has considered BNFL's safety case. The company has already expressed disappointment with the Agency's decision, and can be expected to make the safety case as unconvincing as possible.
The terrorist attacks on America could, however, greatly increase pressure on BNFL to speed up its vitrification programme. The HAL, and indeed MAC, stockpiles at Sellafield present a significant hazard. The Office for Civil Nuclear Safety and the HSE are now reviewing precautions, particularly the site's vulnerability to aircraft crashes.