Sellafield decommissioning showing important signs of progress

Publish date: June 17, 2013

Written by: Charles Digges

Over the course of four years, the enormous Sellafield site on the English coast of the Irish Sea has managed to reduce by 40 percent the amount of liquid highly radioactive stored in tanks at the facility since 2009, a major sign of progress toward the site’s eventual decommissioning.

The results were revealed at the annual conference, dubbed the InfoArena, among Sellafield Ltd, Britain’s Nuclear Decommissioning  Authority (NDA)Bellona, and Guardians of our Common Seas last Thursday, June 13. InfoArena 2013 was also attended by Norwegian Environmental Minister Bård Solhjell, representatives of the Nordic Council, members of Norwegian Parliament, and Norwegian and UK nuclear regulators.

The conference was held in Oslo as part of ongoing dialogue over the Sellafield site between the UK and Norway, which would bear the brunt of excessive radioactive discharges in the event of an accident.

For Norwegian authorities and environmental NGOs, maintaining transparent relations with Sellafield is critical: a major catastrophe at Sellafield, according to the Norwegian Radiation Protection Authority (NRPA) could have consequences to the Norwegian environment seven times worse than the Chernobyl accident.

Perhaps the most important indicator of improving conditions at Sellafield, said Bellona’s General Director and nuclear physicist Nils Bøhmer, who moderated much of the Thursday conference, is the reduction of high level radioactive waste stored in tanks at Sellefield, and the number of tanks it is stored in.

The number of these tanks in use, called HAL tanks, which store highly active liquid waste from the reprocessing of spent nuclear fuel, has been reduced by about half from 21, and the stocks of the tanks has fallen by 40 percent since 2009, both Bøhmer and Sellafield’s Steven Walker told the conference.

[picture1 {Norwegian Environmental Minister Bård Vegar Solhjell delivers opening remarks at InfoArena 2013.}]

This marks an important achievement, said Bøhmer.

“The less highly radioactive material stored in the tanks and the fewer the tanks means that less heat is generated within them,” said Bøhmer. “The less high level radioactive waste remaining in the tanks, the safer it is for Norway.”

Overall highlights and shortcomings since last year

As reported by Peter Wylie, head of site strategy, the crowing achievements over the last year have been the HAL stock reductions, the beginnings of retrievals of long standing waste in legacy ponds, construction of major plants to retrieve and treat this waste, and the deployment of a best practice program.

But Wylie was disappointing with this year’s progress toward reprocessing spent nuclear fuel at Sellafeild’s Magnox reactors, which burn uranium metal as opposed to more traditional ceramic uranium oxide; a slowing at efforts in vitrification a process in which high level liquid wastes are mixed with glass and melted in a furnace, which when cooled forms a solid block of glass – and other schedule slippages in some major site decommissioning projects.

But the main hurdles to decommissioning the rest of the Sellafield site are bring reprocessing to an end and ridding the site of its HAL tank stocks, said Bøhmer, and efforts to shut down reprocessing both at the Thorp and Magnox facilities seem to be on target for 2018.

[picture2 {From left to right: Nils Bøhmer, Environmental Minister Bård Vegar Solhjell, and Per-Kaare Holdal of Guardians of our Common Seas}]

Long-term spent fuel storage

The hunt for long term geological repositories for the waste produced not only at Sellafield, but the UK nuclear industry as a whole, also remains in progress, but with a few hiccups.

Britain seemed to be approaching the final siting and building of a repository, but the country council of Cumbria, which hosts the Sellafield site, voted down the plan, despite the Cumbrian Borough of Copeland’s desire to host the site.

Rene McTaggert, head of International Policy on Nuclear Safety and Radioactive Waste for the UK Department of Energy and Climate Change told the conference that learning the lessons of where the Cumbrian repository fell short was critical. The UK’s policy on building such a repository is based entirely on communities volunteering to host such sites, and now the government is waiting for another to step forward.

This question becomes more critical by the minute as the UK, unlike many nations in the wake of Fukushima, intends to continue building new nuclear plants – but with fuel storage stipulations attached.

McTaggert said that new nuclear power plants would not have the option of reprocessing their spent nuclear fuel. With average life expectancies of 40 years, the plants would be required to safely store spent nuclear fuel onsite for 50 years, plus another 50 beyond that, in hopes that a permanent geological repository will have been completed by then.

If such plans fall flat, said Bellona’s Bøhmer, “the UK will be stuck with a lot of spent nuclear fuel.”

McTaggart acknowledged that this scenario was possible.

Gains for the HAL tanks

Sellafeild’s Walker explained the specific gains in safety in conjunction with the HAL tanks. He said the heat loads in the tank had been reduced partly as a result of the Feed Clarification Cell event at the Thorp reprocessing facility, during which a nine-month long leak of 20 tons of plutonium and uranium liquor mixed with nitric acid into the facilities clarification cell was discovered.

The incident led to a three-year outage of the Thorp plant and hence affected its reprocessing throughput and output of highly radioactive liquor. Though the plant still has a number of foreign reprocessing orders to fill, it is expected to shut down by 2018. Thorps reprocessing tasks are at 78 percent complete.

The overall reduction to HAL stocks in the 2012 to 2013 fiscal years was some 800 tones of uranium, said Walker. Further good news relative to the reduction of the HAL stocks is that there is now no requirement that Magnox and Thorp liquors meet the vitrified residue return program, meaning that heat can be more evenly distributed throughout the tanks.

This presents the additional safety benefit that the tanks’ contents do not have a sufficient heat load to reach boiling.

Though Sellafield’s scheduled for vitirfication fell behind schedule, Walker noted that Sellafield’s waste vitrification lines 2 and 3 performed in line with program waste reductions during the last half of the fiscal year.

The snag in vitrification schedules led to Sellafield missing the NDA set target of vitrifying 1873 tons of uranium last fiscal year, achieving instead 1414 tons of uranium, Walker reported.

He also said that the stretch target to reach the HAL stocks buffer level by March 2014 will have to be pushed back until later in the year. But he concluded that overall, HAL stock reductions set by the UK’s Office of Nuclear Regulation will still be met ahead of schedule, which is set for July 2015

Magnox reprocessing shutdown

Shutting down of reprocessing Magnox fuel, however, still remains problematic. Even though Magnox reprocessing is 93 percent complete, shuttering this particular reprocessing endeavor has gone past several deadlines. In 2008, it was expected Magnox reprocessing would be completed in 2012, which was then revised to 2016.

The current target for shutting down reprocessing of Magnox fuel are set optimistically at 2018. Meeting this target will be possible in the event that Magnox reprocessing throughput can be maintained at 664 tons per year until 2018. Should throughput drop to 450 tons per year, then the closure of reprocessing would be further delayed to 2020.

“A level of 350 tons would put us even further back,” Bostock told the conference. “Problems may come up that throw us off schedule, other problems may be fixable.”  

Various bottlenecks, such as working evaporators, necessary to the process of reprocessing Magnox fuel remain poised to cause future delays. Evaporator B is scheduled to come back online in September this year where Evaporator D is out of commission until 2016.

Contingencies for Magnox failures

Continued wet storage of Magnox fuel poses special dangers due to the high potential of corrosion of metallic uranium. The decay of metallic uranium while stored in water produces uranium oxide and uranium hydride, both of which are flammable. Discharges of radioactive Technetium-99 (Tc-99) from Magnox reprocessing, were finally abated by some 95 to 98 percent after a decade long battle with the British government waged by Bellona to add Tetraphenylphosphonium bromide (TPP) to liquid waste emissions from Sellafield’s Magnox fuel reprocessing plant.

Dr. Adrian Simper of the NDA said several contingencies were being weighed if Magnox reprocessing did not hit its target. Storing the fuel in reactors was one approach that he said was less than ideal. The other was drying out the fuel.

Leaving fuel in reactors would not, however, leave the reactors themselves “in an end state,” said Simper, while drying the fuel would require investments in additional technologies.

“Should reprocessing break down we have investments in alternatives to bring forward,” said Simper. “If Magnox reprocessing fails we will explore fuel drying technologies – we are at the edge of performance levels we can have before bringing in contingency plans.”

Bostok added that Magnox reprocessing does not lead to enormous amounts of radioactive liquor, but some two thirds to a quarter less.  

Britain’s Office of Nuclear Regulation concluded, however, that the ideal situation was that all fuel from the Magnox reactors would be reprocessed. 

Conference joint statement

The gathered parties concluded the conference by issuing a joint statement (downloadable at right) stressing the importance of maintaining “precise information as basis for Norway’s emergency preparedness” and said, “abroad contact base including, of course, NGOs, is essential.

“We are making significant progress in improving safety Sellafield and we are committed to safe, secure stewardship of our site,” wrote Kilss McNeel, director of Environment, Health and Safety at Sellafield in the joint statement. “We are doing this against a backdrop of reducing risks in our operations, especially in the area of highly active waste. Reducing HAL stocks is always an important focus of this conference.”

She stressed that Sellafield was ahead of regulators’ schedules in this regard.

The gathered parties stressed the transparency that the annual conferences allow for and underscored that the would continue in an open spirit “until the goals that are set are reached.” 

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