First radioactive waste removed from Magnox storage pond
24 March 2015
The very first radioactive sludge has been removed from the First Generation Magnox Storage Pond (FGMSP) at Sellafield in north-west England. The FGMSP is one of the site's four Legacy Pond and Silo facilities.
.jpg "First sludge retrieval - 460 (Sellafield)") |
| The sludge retrieval machine (Image: Sellafield Ltd) |
Constructed in the 1950s to store, cool and prepare used Magnox nuclear fuel for recycling into new fuel, the FGMSP "urgently" needs to be emptied of 1500 cubic metres of radioactive sludge lying at the bottom of the pond which is equivalent to more than half an Olympic sized swimming pool, Sellafield Limited said. The FGMSP is "one of the most hazardous nuclear plants in Europe", it added.
During the FGMSP's 26 year operating lifetime it processed approximately 27,000 tonnes of fuel - almost 2.5 million fuel rods. Used nuclear fuel from the UK's nine Magnox stations, along with Magnox fuel from both Italy and Japan was held in the FGMSP. The pond holds some 14,000 cubic metres of contaminated water, in which is stored Magnox used nuclear fuel, radioactive sludge, miscellaneous nuclear wastes and skips. The plan is to progressively retrieve and treat the radiological inventory residing in the facility, reducing the on-going risk posed by its storage and then reducing the inherent hazard posed by the materials.
"We're making history at Sellafield by transferring the first sludge using a tried and tested pump to a new £240 million ($359 million) state-of-the-art sludge storage plant containing three enormous stainless steel buffer storage vessels, each of which is the same volume as seven double decker buses," Martin Leafe, head of the FGMSP, said.
The vessels were brought to the Sellafield site in separate sections and then welded together before being slid into the reinforced concrete building. The welding of each vessel involved over 2000 metres of weld run, "which was done 99% right first time", the company said. All welds were then radiographed to ensure the required integrity and that there will be no leaks.
"Working with both Westinghouse and Energy Solutions, the technology already in use at European reactor stations has been adapted for our needs at Sellafield and rigorously tested in a full scale test facility at Forth Engineering here in West Cumbria," Leafe added.
The sludge is a similar consistency to sand and has to be carefully removed, whilst leaving the water in place to provide a radioactive shield for the stored nuclear fuel. Its retrieval from the pond will enable the remaining radioactive inventory to be progressively removed to reduce the inherent hazard posed by the facility. The pond holds some 14,000 cubic metres of contaminated water, in which is stored Magnox used nuclear fuel, miscellaneous nuclear wastes and skips all of which is draped in blanket of radioactive sludge.
The pond has thick reinforced concrete walls however it was built with no roof and is "open to the elements", Sellafield Limited said, so sludge has been accumulating at the bottom of the pond "just like in any other garden pond". The difference is that this sludge is radioactive made up of nuclear fuel corrosion products, algae and windblown material, so it requires careful handling, it added.
"The pond is six metres deep and we've spent years devising an engineering solution to literally suck up the radioactive sludge from the bottom of the pond, which in places is over one metre deep. What makes the job more difficult is that the pond is very congested and full of large metal boxes containing nuclear fuel, so we need to work around these and ensure these remain fully submerged at all times. Just to make matters more difficult we have to drive the platform remotely from a control cabin to minimize the radiation dose to the workforce," Leafe said.
"We transfer the sludge in batches to the new plant where it settles in one of the enormous buffer storage tanks and then the top layer of water is sent back to the pond. It will take several months of work to transfer enough sludge to fully test and commission the sludge plant and in parallel we'll install the bulk sludge removal equipment."
Pete Lutwyche, the Nuclear Decommissioning Authority's Sellafield Program director, said the clean-up of Sellafield's legacy facilities is the NDA's number one priority task. "Our relentless focus on tackling Sellafield's legacy facilities – and our prioritisation of funding for the task – is starting to bear fruit. We are now seeing the removal of decades-old material from Sellafield's legacy ponds on a daily basis, significantly reducing the risk at these historic facilities," he said.
Andy Lindley, the Office for Nuclear Regulation's lead of the Sellafield Program, added that the first transfer of sludge is a further significant milestone in the regulator's long-term aim to drive forward reduction of hazard and risk at Sellafield. "This is a complex operation and a first of its kind at Sellafield. There will be challenges in removing this material and we acknowledge that there may be some setbacks. This is highly hazardous waste and its removal will take some years to complete. But the longer term benefit is huge in terms of overall hazard and risk reduction," he said.
Nuclear Management Partners is the parent body leading the site. NMP chairman Dave Swindle said the company was proud of the way in which the Sellafield Limited workforce has responded to the priorities of high hazard retrieval. "We can all take pride in this significant decommissioning step," he said.
Researched and written
by World Nuclear News