N E W S R E L E A S E from FURMANITE INTERNATIONAL
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FIL/122:W
23 May 2005
New process for maximum safety and efficiency in disposal of spent fuel flask liners
BNFL and Furmanite combine skills for innovative approach
An innovative method of decommissioning spent fuel transport flask liners for maximum safety and efficiency in disposal has been developed by BNFL using technical skills and engineering expertise from Furmanite International, the speciality services company geared to maximising asset uptime.
The novel approach involved the first ever dismantling of the massive and exceptionally robust and resilient transport flasks' lead liners, by cutting them into segments for disposal or recycling. This deploys Furmanite's high level on-site machining skills and ability to engineer bespoke solutions, including designing and building the equipment needed to meet the specialist machining requirements.
The flasks were used in the transportation of radioactive spent fuel and their design follows exceptionally stringent guidelines. They are made up of steel flask body into which the lead liner sits providing the necessary radiation shielding. The container used to carry the spent fuel locates within the liner.
Constructed of stainless steel and lead (15 lead rings encased in 12mm thick stainless steel), measuring 4.8 metres long and 1.4 metres outside diameter, the liners contribute 40 tonnes of the flasks' total weight of up to 110 tonnes for a payload of 5 tonnes of spent fuel. The flasks are built to ensure no radiation risk, and are subjected to rigorous tests to demonstrate their safety.
"The robust design of the flask liners, coupled with the fact that this was the first time one had been dismantled, made this no easy task," Furmanite technical officer Peter Rawley commented. "Given the possibility of contamination when the outer skin was cut, the liners were first pressure tested, then lead sampling was undertaken to prove that no contamination was present and it was safe to proceed.
"We used various CNC milling machines and cutters, all purpose-designed for the job, as well as designing and building specialist equipment such as a segment lifting tool, plus the various stands, baseplates, and other assemblies required to mount the equipment or carry out the work."
The process of decommissioning the liners involved a number of stages, the first of which was to remove the external details. To achieve this Furmanite designed a kicking stool to take the liner into the horizontal position, and designed and built support stools to hold the liner horizontally, while the necessary machining was undertaken.
A special CNC milling machine, bespoke-designed and built by Furmanite, was then fitted to a base plate and set up so that Phase One - the milling - could be undertaken to remove the keyway angle plates and channels.
Phase Two then required the liner to be returned to the vertical position, for cutting into segments. A stand with bottom lifting brackets fitted was designed and built for this purpose, onto which the liner was seated, and a bespoke flask severing machine (external and internal cutting machines, along with inner and outer swarf trays in each case), was then mounted and the lead liner and inner and outer casings cut and separated into segments, each measuring some 30cm high and weighing 2.7 tonnes.
As the segments were cut they were lifted away from the liner one at a time, for which specially-developed segment-lifting equipment was fitted. This comprised four T-blocks which were located in the 5mm wide cut line so as to lift the liner segment clear of the liner. A trunion support assembly allowed the last two cuts to be completed, by turning the liner to enable removal of the 50mm thick bottom plate, and then cutting to separate the last segments.
With each liner segment lifted and fitted safely onto a purpose-built worktable, the next challenge was to remove the cooling tubes, which had been used to circulate cooling water within the flask. To achieve this, a further piece of bespoke equipment - a cooling tube extractor - was designed and built by Furmanite. With the weld from the outer and inner stainless steel liners machined away and three 8mm holes tapped in the cooling tube, this could then be attached to the extractor and hydraulically removed.
This done, a standard milling machine fitted to the segment with a mounting bracket then machined the inner and outer stainless steel casing and liner, leaving the uncontaminated solid lead section for recycling.
In the event that any contamination had been discovered in the lead, contaminated liner lifting equipment was developed, so that the liner could be boxed off with capping-off plates welded to the liner and removed from the pit using the lifting equipment.
"Dismantling the liners in this way has enabled us to have strict control by methodically dealing with each segment in turn," commented BNFL project manager Steve Smith. "Ensuring that the lead rings and stainless steel cladding was clean and clear for release as scrap has greatly reduced the amount of material going to the Low Level Waste facility at Drigg. The reduction has been from a potential 40 tonnes to a maximum 0.5 tonnes, consisting of only the cooling tubes and swarf produced during the cutting process which could not be adequately monitored. It enables us to keep the contaminated material requiring disposal to a minimum, and the rest to be used for recycling - so it's a safe and more environmentally-friendly solution all round."
Rawley adds: "This is a perfect example of the service Furmanite offers - the ability to understand a problem or objective, and apply our breadth of experience and expertise and wide range of technologies to engineer a solution that represents optimum value to the customer. Being able to help BNFL in this way has been an exciting and rewarding challenge."
The first flask liner to be decommissioned in this manner was completed last year. Having established and proven this innovative method of decommissioning the flask liners, it enables the programme of decommissioning redundant flasks to be implemented.
For further press information contact:
Sarah Manwaring-White, Keep in Touch Ltd,
Tel: +44 (0)1451 844 488 Email: sarah_mw@keepintouch.co.uk
Issued on behalf of Furmanite International Ltd