Robotics in planned Dounreay decommissioning

Citation

(2002), "Robotics in planned Dounreay decommissioning", Industrial Robot, Vol. 29 No. 4. https://doi.org/10.1108/ir.2002.04929dab.003

Robotics in planned Dounreay decommissioning

Robotics in planned Dounreay decommissioning

Keywords: Nuclear, Robotics

Whatever the future may hold for nuclear powered electricity generation and whether new plants are designed or not, there will be massive amounts of work, including the application of automation and advanced robotics, simply to deal with the existing plants. Clean-up, decommissioning and eventual dismantling are likely to tax the skills of engineering designers for many decades to come. And, while the car industry may talk of long terms projects spanning three to five years, the nuclear decommissioning industry is looking at time spans of ten, 20 or even 50 years.

These potentially long time scales are exemplified in the recent announcements of contracts by the UK Atomic Energy Authority (UKAEA) for the decommissioning of the Dounreay Fast Reactor (DFR), which was built as an experimental reactor to test fast breeder technology, operating from 1959 until its closure in 1977. The reactor is housed in a concrete vault 30m in diameter, which is housed in the lower half of a spherical steel containment vessel measuring over 40m in diameter. The reactor and sphere weigh 10,000 tonnes and sit on reinforced concrete foundations 3m deep and 18m in diameter.

UKAEA estimates it will take until 2013-2022 to complete the whole process. This includes the removal and destruction of the sodium-potassium (NaK) coolant used in the reactor, decommissioning the DFR fuel pond, removing the breeder fuel, and removing and cleaning the NaK-wetted primary circuits, at a cost in the region of £173 million. The total estimated cost of decommissioning DFR by 2026-2042 is in the region of £250 million.

The contract for the highly complex decommissioning project has been awarded to an alliance of six companies. Robots will be used inside the concrete vault of the experimental fast reactor, to cut up and remove more than 9km of pipework that is contaminated by the liquid metal used to cool the reactor (Figure 1). Decontamination of the reactor vessel and its associated pipework is due to begin once most of the coolant has been drained and after work has started to remove the remaining breeder fuel. It will take until 2013 at least to complete and cost up to £30 million.

There are 57 tonnes of the liquid NaK coolant in the primary circuit to be removed, 73 tonnes having been extracted from the secondary circuit shortly after the reactor's closure in 1977. It will not be until 2004-2005 that the bulk of this remaining coolant is removed and destroyed.

Figure 1 Examples of the piping in the primary cooling circuits at Dounreay

UKAEA site director Peter Welsh said, "When this alliance finishes its task, we will have successfully completed the first and most crucial stage of decommissioning a reactor, which represents one of the major engineering and environmental challenges on this site".

The six companies in the DFR Primary Circuit Decontamination Alliance with UKAEA are Halcrow (design), Interserve (mechanical and electrical), Edmund Nuttall (building and civil works) Mitsui Babcock (plant operations), NNC (safety and environment) and Framatome (robotics).

Approximately £10 million of the contract value is expected to go to locally-based companies, with an initial 50 jobs created or retained locally. A key feature of the alliance will be the transfer of specialist skills, such as robotics, from major contractors to local firms. This will improve their ability to compete for future decommissioning work at Dounreay and elsewhere in the world.

The cutting and removal of the labyrinth of pipes that carried the radioactive NaK coolant within the heavily shielded concrete vault must be carried out remotely because of the levels of radiation present. Remotely operated vehicles, working in a temperature of –18C to eliminate the risk of ignition in the NaK-wetted circuits, will lay their own working platforms before cutting sections of pipework into pieces that will be removed for cleaning and disposal.

The company responsible for this work, Framatome ANP (Advanced Nuclear Power) was founded in January 2001 with headquarters in Paris. It combines the former nuclear activities of Framatome and Siemens to form the world's premier nuclear supplier with a worldwide workforce of approximately 13,000 and annual revenues averaging e2.5 billion. Framatome undertakes the engineering, instrumentation and control and nuclear services for many reactor designs, including pressurised and boiling water reactors (PWR and BWRs), as well as the development and construction of nuclear power plants and research reactors, and is the OEM for more than 90 nuclear plants in 11 countries – almost 30 percent of the world's nuclear generating capacity. It supplies fuel to 85 PWRs and 14 BWRs around the world.

Framatome will bring to the Dounreay project experience it has gained in inspection, repair, and maintenance services on all types of PWR and BWR reactors, including reactor vessel disassembly and re-assembly (Plate 3). The concepts to be applied in Scotland are still being developed but the company can call on a number of robotic system designs to implement the programme. Many of these are based on segmented-articulated-manipulators (SAMs), which utilise a series of discs strung together on cables with the actuators located on the arm's base, operated in a master-slave mode.

Plate 3 The latest versions of the Framatome (remotely operated generator examination and repair) ROGER™ manipulator enable inspection and repair of all steam generator tubes without having to be repositioned

One example is revolving turret reeled cable incremental link extending vacuuming robot (ReTRIEVR), designed to vacuum or pump waste from confined-space tanks and silos. This long-reach robot combines a segmented-link platform that extends to approximately 20m with an industrial master-slave robot on the platform end. Each link measures approximately 450mm in diameter 3m in length and a hinge along the axis of the link permits clamshell closure around the working cables. Links are joined by one hinge pin and one hydraulic cylinder to permit active articulation. In addition, a jib crane can assist in manually adding or removing links to extend or retract ReTRIEVR from its contamination-barrier enclosure. The six degree-of-freedom dexterous robotic arm on the end-of-link platform can hold a vacuuming tube and/or a series of mining tools.