Giant machines to roam at Dounreay

Dounreay, UK - Engineers at Dounreay Site Restoration Ltd (DSRL) have designed a giant robot with two large pincer arms and roving photographic eyes, nicknamed ‘Reactorsaurus’ to help dismantle the redundant Dounreay reactor. The company is also installing a huge ventilation system to protect workers decommissioning some of the hazardous facilities at Dounreay.

The 75-tonne Reactorsaurus device features a large traversing carriage incorporating two remotely operated manipulators and robotic arms that can reach 16 metres down into the radioactive reactor vessel.

Activated from a central control room, the arms will operate an array of cutting and handling tools, such as diamond wire and disks, hydraulic shears, oxy/propane and plasma cutting. An integral camera system built in to the device, with six radiation tolerant cameras, will relay images and sound back to the control room.

The project team will initially trial a life-sized simulated model of the remotely controlled manipulator in an off-site test facility, replicating the circular reactor roof and three sectors of the reactor core. This will also allow them to develop techniques and processes for the size reduction and removal of the reactor components.

A contract for the construction of the mock up will be awarded later this year, with construction expected to take a further two years to complete, according to DSRL. The real thing, it said, is scheduled to be ready in 2013 when commissioning will begin within the actual reactor.

“The reactor dismantling project is critical to the Nuclear Decommissioning Authority’s site restoration plan for Dounreay,” commented Simon Coles, PFR projects delivery manager. “Inventions like Reactorsaurus is one of the reasons Dounreay ‘s leading the way with worldwide nuclear decommissioning.”

The robot will dismantle the liquid sodium-filled prototype fast reactor that ceased operation in 1994. Once the sodium has been removed, it will cut up all equipment, including the pipework and the shield rods and remove them from the reactor.

A containment cell will be built over the top of the reactor and the RDM will be deployed on a set of rails and dropped down into the port. Its manipulator arms will reach 16m to access the outer regions of the reactor. The first task will be to lift out the shield rods in the centre, using a large shear to cut the 30cm-thick solid-carbon rods into smaller sections.

Once the robot has lifted the rods out, it will have access to the pipework, using one of its manipulators to grab the pipes and the other to wield a cutting tool.

Special cutting tools are to be developed and tested at an off-site facility to select the one most suitable for the job. Potential tools include propane mixed with iron powder, and plasma cutting for steel parts. The engineers are also considering using diamond-wire encrusted disks and standard hydraulic shears and developing a diamond-wire cassette system. Water jetting could also potentially be used, but only when the operators are certain all the sodium has been removed, because of its intense reaction with water.

Operators will control all the motion on the system from the carriage to the hydraulically operated booms that extend in and out from a central control room. The RDM has dual redundancy built in, so if one system fails it has a back-up that can be retrieved in the event of an emergency.

Specialist materials will be used to withstand the high levels of radiation, including specially selected types of rubber, steel and hydraulic fluids. All the electronics will be radiation resistant, including the cameras used to guide the RDM, which cost in the region of £40,000 per unit.

The robot will cost around £3 million to build and will be commissioned in 2013. It will take around three years to complete its work, after which it will be decontaminated and disposed of as low-level waste and be decommissioned along with the reactor itself.

In a separate project, DSRL is installing a massive ventilation system to protect workers decommissioning the hazardous facilities at Dounreay. The network of fans, electrical infrastructure, supports, ducts, chambers and stacks will vent the airflow during the next stages of cleaning out and dismantling the key plants that made up the Fuel Cycle Area.

The Fuel Cycle Area was the part of the site where nuclear fuels were assembled, dissolved, examined and re-assembled. Its decommissioning is expected to cost £550 million and involves dismantling sealed facilities that are contaminated with some of the most hazardous radioactive debris.

Some of these plants have already been cleaned out and one, the former fuel fabrication plant, has been demolished the first plant of its type ever successfully decommissioned in Scotland.

The installation of a modern ventilation system will allow teams of decommissioning staff to complete the clean-out and demolish the rest of the facilities by 2025. The steelwork, weighing some 300 tonnes in total, was delivered to the site in pre-fabricated sections in 150 lorry-loads and installation is now almost 90% complete.

The main contractor is JGC Engineering and Technical Services, with a team of about 40 people now working on the £9 million project.

"We're on schedule to inactively commission the system by the end of October," said project manager Iain Lyall of DSRL. "This will be followed by a period of testing, with a target of the end of March 2010 to complete active commissioning.

Each of the dozen buildings that make up the heart of the Fuel Cycle Area has its own extract ventilation system with high integrity fans and ductwork, extracting contaminated air through high efficiency filters and exhausting into common ducts which terminate in the existing 55m high, 4.5m diameter vent stack.

By next March, the existing stack will have been replaced by a new system comprising two 30m high vent stacks, each 2m in diameter, fed by duty/standby inverter-driven 90kW & 132kW fans connected to the existing common ducts. The variable duty provided by inverter control will meet the decreasing ventilation needs as the facilities are demolished sequentially over the coming years.

Halifax Fans, West Yorkshire, supplied the four fans which, at 69 ins and 78 ins impeller diameters and weighing 8.5 tonnes each, were the largest nuclear specification gas-tight fans ever built by the company.

The fan impeller design was based upon Halifaxs Beaufort fans, with self-cleaning backward curved impellers which can be withdrawn from the drive side so that should it prove necessary, this can be achieved without the need to disconnect any ductwork.

The exterior steelwork was shot blasted and painted with a high integrity offshore/chemical works 3-coat paint system with a minimum dry film thickness of 220µm. The fans were fitted with rotation sensors and vibration monitoring equipment along with gas-tight EPDM rubber flexible connections on the fan inlets and outlets and each unit was supported on anti-vibration mounts.

Following fabrication, all four fans were pneumatically pressure tested in-house and witness run-tested prior to despatch to site.