Perched on the northernmost tip of Scotland, Dounreay is home to one of the oldest nuclear installations in the U.K. It required mega engineering feats to construct the former center for fast reactor R&D. Now, nearly 60 years later, decommissioning is posing just as many challenges, as Dounreay Site Restoration Limited (DSRL) and its 1,000 engineers and ancillary staff who are charged with the task can attest.
One of the biggest challenges comes from the 254-MW reactor, which is too hazardous for humans to approach. DSRL’s engineers have proposed using a remotely operated, 75-ton robotic system. Lovingly dubbed the Reactorsaurus, it’s a two-armed machine with 10 eyes and four ears.
Operators will be able to listen in on the action using two microphones on each of the arms.
The robot will only be used after 2013. Before then, decommissioning engineers will practice techniques in a full-size simulated model of the reactor built off-site. A tender to construct the model should be issued this year; it will take two years to build.
Robots also are playing a critical part in other locations around the site, according to the June issue of the in-house newsletter Dounreay News (www.dounreay.com/UserFiles/File/Dounreay%20News/June_2009.pdf). Last year, for example, a Brokk 180 robotic demolition machine helped reduce Dounreay’s plutonium criticality laboratories to rubble. Its latest role was in a storage area where it had to raze 32 two-foot wide, reinforced concrete plinths, originally designed as shielding between four-inch thick slab tanks that once held radioactive liquor.
The project team called in a remote-operated-vehicle expert from contractor Baker Dougan Nuclear, Portsmouth, England, to operate the Brokk at finger-tip precision.
Some of the plinths had been in a tight area, notes Bob McKiddie, DSRL project engineer. “The contractor had amazing control of the machine to drag out the concrete without damaging the containment,” he says. The demolition generated around 130 metric tons of concrete rubble, which has since been dealt with as low-level waste.
The Brokk is undergoing decontamination before getting a final clean up. “We coated parts of the Brokk with ALARA strippable coating, so that we could just peel off the contamination once we had finished with the machine,” explains Kevin Mackay, project supervisor. Once the machine is cleaned up, it will trundle off to another area of the site where it can be put to another use.
Another bit of complex engineering at Dounreay concerns a new ventilation system designed to protect workers involved in the ongoing decommissioning work. The 1,500 parts involved will eventually create a network of fans, electrical infrastructure, supports, ducts, chambers and stacks to vent airflow during the next stages of cleaning out and dismantling the key plants that made up the fuel cycle area.
Decommissioning this area alone is expected to cost £550 million (around US$800 million); it 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 — according to Dounreay News, 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 clean-out and demolish the rest of the facilities by 2025.
Steelwork, weighing 300 tons, was delivered to the site in pre-fabricated sections in 150 truckloads and installation is almost 90% complete. The main contractor involved has a team of 40 working on the £9 million ($14 million) project.
“We’re on schedule to inactively commission the system by the end of October,” says Iain Lyall, DSRL project manager. “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;these that will be replaced by the new system.
Seán Ottewell is Chemical Processing's Editor at Large. You can e-mail him at email@example.com.