The decommissioning of Dounreay nuclear power plant is being speeded up, which means extra buildings need to be built to handle radioactive waste. Joanna Booth went to see how Balfour Beatty is building one of the new plants
IF YOU thought the Christmas post was slow, try waiting for a delivery of nuclear waste. It involves a bit more than a 'fragile' label and a prayer.To transfer drums of waste in and out of a storage compound, UKAEA decided it would need to build a bespoke import export facility with concrete walls 1,200 mm thick and remote handling capabilities.
Within miles of John O'Groats, Dounreay nuclear power facility dominates the bleak highland landscape of Caithness. Imposing metal bars enclose the compound and the famous golf ball reactor even dwarfs the ranks of steel-clad hangars that contain equipment designed to handle the deadly nuclear waste.The silence, broken only by the continual ticking of counters monitoring radiation levels, belies the constant activity, with 2,000 workers beavering away steadily to return Dounreay to a brownfield state by the deadline of 2036.
The latest project to get going is an import-export facility for drums of cemented waste. It will enable flasks of residual reprocessing waste from commercial contracts with foreign reactor operators to be returned to their countries of origin and will also speed the decommissioning of the Dounreay plant itself by giving greater flexibility to the way waste can be moved around the site.
Nuclear waste is placed in cement to render it inactive and a cementation plant was built at Dounreay in 1985.Though it was accepted that the waste would need to be taken out of its current storage in the future there was scant information available on the type of flasks that would be used to transport it, so UKAEA postponed building an import export facility until Nirex's transport specifications were clear. But after a safety audit at Dounreay in 1998 the Scottish Environment Protection Agency decided that a transport facility should be built at the earliest possible opportunity.
The facility will enable Dounreay to return reprocessed fuel elements from Australian, Spanish, German and Belgian test reactors once customers have completed their waste storage arrangements - scheduled for 2007. It will also transfer Dounreay's conditioned Materials Test Reactor waste to a drum store, where it will remain in 500 litres drums until 2036 when a national repository will be on-line and the waste will be moved to its final resting place.
A store for 200 litres drums of intermediate level waste will become full in 2006, and the import export facility is particularly crucial in providing a route for these on their way to being rehoused in new locations.Without this capability decommissioning would have to cease.This waste is 10 times more reactive than the solutions from the Materials Test Reactor and will eventually be handled and repackaged at a new treatment plant, scheduled to be completed by 2011. Currently the store cannot transfer 200 and 500 litres drums at the same time and the changeover period is significant.The new facility will solve this problem.
Land for the import export facility was available to the east of the existing drum store. Extensive preparation was necessary to keep the site infrastructure running and took two years under a separate contract managed by UKAEA.Above ground services had to be diverted and those below ground protected, an access road with lighting and drainage built, buildings demolished and over 4,000 tonnes of spoil segregated and removed.
In a departure from normal procedure UKAEA let the design and construction of the facility separately. In January 2002 Taylor Woodrow began the concept and detailed design.
'The critical path for this project went through the site de-risking, ' explains John Swanson, UKAEA import-export facility project manager at Dounreay.'It took a long time to complete, and there was a time advantage to getting the design done in that period.'
The site is ready for Balfour Beatty, as part of a consortium with Amec (which is undertaking mechanical and electrical works) to begin construction of the facility. It will be a steel framed and clad building forming a weatherproof envelope for the cranes and hoists that handle the waste drums.Within this is a reinforced concrete shielded area where operations on the drums inside the lead-sealed flasks are performed.The facility is connected to the cementation plant complex by a similarly shielded corridor.
Preparatory works have exposed the bedrock, so the first operation will be a mass concrete pour, spreading 150 cu m over the site to bring it to a uniform level.Within this, various shutterings for the steelwork foundation pads will be inserted.
Then formwork for the 1,200 mm thick concrete shield will be craned into position.One of the major challenges of the job is getting the penetrations for slave manipulation equipment, in-cast steel plates to support shield doors and lead glass windows as thick as the walls themselves perfectly positioned within the concrete.'Before every pour all measurements will be double checked, not only by an engineer but again by a sub agent and also the construction manager, ' explains project manager Willie Currie.'There's no margin for error - tolerances are stringent compared to other civils works - some in-cast plates have to be within 1mm.'
Much of the steelwork and cladding will be completed before the mechanical equipment is delivered. Specialist pieces are predominantly being installed by the manufacturers but Amec will install equipment for handling and cleaning the drums as well a 75 tonne hoist and a 26 tonne crane.
'The east gable wall is being left partially open, and with some temporary external steelwork, ' says Mr Currie.'The crane will be put on to temporary rails outside the building and skidded into place before final cladding is complete.'
Security on site is predictably tight.There is a constant police presence and all visitors must give at least 24 hours notification. Site workers undergo a full background investigation, which can take more than 10 weeks.The 11 staff are all long-term Balfour Beatty and Amec employees who have made the trip up to the northernmost tip of the British Isles but general operatives are recruited locally.Delivery drivers need to apply for clearance in advance - a local firm whose drivers already hold the correct paperwork to allow them within the compound will supply the concrete.
Balfour Beatty is principal contractor on the project - the first 'outside' contractor to be put in charge of works within the cordoned off fuel cycle area.
'UKAEA has always taken on supervision of works directly before, ' says Mr Swanson.'There has previously been a reluctance to delegate safety to a contractor.We have to demonstrate to the regulator that we're complying with our 36 site licence conditions and that's difficult without direct involvement. But we did a test contract outside the site, on an office accommodation block, and it worked.We're adopting the same safety model here.'
Mr Currie explains that extra precautions are being taken.'Every operative is fully briefed, with method statements and risk assessments clearly explained, and a different tool box talk every day.We have our own onsite safety manager.'
The next 31 years of Dounreay's future may be planned meticulously but one thing is not certain.This April the Nuclear Decommissioning Authority will be launched. From then on UKAEA will be under contract to manage decommissioning at all its sites and may have to compete to retain the work.The race for every nuclear player to prove itself is on.