Maintenance

If a fusion reactor does not use aneutronic fuel, the neutrons produced in the fusion reactions will be absorbed in the surrounding materials causing them to become radioactive. Most of the radioactivity decays quickly, causing heating in the reactor structures during and soon after operation. However, a proportion of the activated materials have long decay times (half-lives), so for years after operations have ceased most materials in the device or removed from it generate a dose rate (primarily from gamma rays) that would be lethal to a human in close proximity to it in a few seconds. Therefore, various forms of remote handling (RH) equipment are required for removal, disassembly, repair and disposal of components following operation.

Especially in early generations of fusion reactors, it can be expected that minor failures of in-vessel components (e.g. damaged plasma-facing armour tiles or leaks from coolant pipes) will occur relatively often. Therefore, unless sufficient redundancy has been provided in the component design that allows operation to continue, such failures must be recoverable quickly to minimise their impact on machine availability. This will require RH devices that can be deployed and used in the machine quickly and have an appropriate range of end-effectors to deal with a range of tasks.

The scheduled maintenance interventions will require large, heavy and highly radioactive assemblies to be removed, requiring substantial openings into the machine to permit access by a range of bespoke and high load capacity remote handling equipment. Ensuring this can be done safely, i.e. without radioactively contaminating the reactor hall or exposing the work-force to unacceptable radiation doses, will be an essential aspect of the machine design process.

After removal, these assemblies will need to be safely transported to one or more hot cells for storage before refurbishment or disassembly and disposal as low or intermediate level radioactive waste. In the hot cells, components that have been removed will generate gamma radiation at levels not much less than when they were inside the reactor, again necessitating RH equipment for work upon them. Therefore, RH equipment will be needed to undertake a range of functions, including detritiation, radiation assay, disassembly, refurbishment of components, size reduction and waste packaging to the standards required by the disposal site.

Commercial off-the-shelf (COTS) components and assemblies are to be preferred wherever possible when designing RH equipment but the high cost of lost electricity sales during interventions may justify using bespoke design solutions to minimise the duration of time-critical operations.

Comprehensive training/proving facilities will be required to ensure efficient use of the RH equipment and its supporting ancillaries such as lights and cameras/scanners.  Training will also be needed for the decontamination and repair, maintenance and storage of the RH equipment itself.