FUSION | BUILDING A REGULATORY FRAMEWORK
Above left: An arial view of the Tokamak Fusion Test Reactor at Princeton Above right: Much of the tritium guidance does not reflect the practical experience gained from existing fusion facilities like JET in the UK
● Hazards typical of large industrial energy-producing facilities such as: high magnetic fields; thermal shock from plasma disruption; loss of coolant and cooling; hydrogen or dust explosions; chemical hazards, cryogenic releases; the use of high-power lasers.
Fusion energy systems may use low-activation materials (eg ferritic/martensitic steels, vanadium alloys, and silicon carbide/silicon carbide composites) and they do not produce long-lived, highly radioactive waste that requires cooling before being moved to a repository. As a result most of the waste from fusion energy systems will be low-level radioactive waste. However, some proposed designs may produce greater-than-Class-C11 waste and tritiated waste that will need to be assessed as developers of commercial- scale fusion energy systems prepare for licensing. Disposal pathways for waste volumes will be part of the
licensed system, with a decommissioning funding plan. NRC understood that the volumes of waste coming from fusion systems might be greater than those from a fission reactor, depending on the design, the materials used and how the systems are operated. There is uncertainty also over whether radionuclides that would be in question were previously in waste classification tables used in current definitions, such as ‘Class’ C waste. That means the licence application would have to set
out expected waste volumes, plans for disposal and cost, so waste from fusion systems can be disposed of with low- level radioactive waste under the existing framework. Near-term fusion energy systems are expected to differ
from historically considered facilities. The latter were based on deuterium-tritium tokamaks operating at above 3 GWt. However, a survey by the FIA revealed that anticipated near- term fusion power plants are expected to vary greatly in size, starting from as little as a few kilowatts. For the purposes of assessing regulatory frameworks
for fusion energy systems, the NRC staff focused on the potential near-term concepts under development for deployment in the USA. The expectation for devices under
development is that: ● No fissile material is present, and criticality is not possible. Currently contemplated fusion energy systems would need active engineered features (eg plasma
28 | November 2024 |
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confinement mechanisms, vacuum maintaining systems, fuel injection, external heating) to achieve a self- sustaining fusion reaction.
● Energy and radioactive material production from fusion reactions cease without an intervention in off-normal events or accident scenarios.
● Active post shutdown cooling of the fusion containing radioactive material is not necessary to prevent a loss of radiological material.
● Radionuclides present in the fusion device, in processing or storage, or in activated materials, in any significant mobilisable amount are expected to result in low doses to workers and member of the public during credible accident
Based on these characteristics, the NRC staff expects that for purposes of minimising doses to workers and members of the public, the safety focus of fusion energy systems will be on the control, confinement, and shielding of radioactive material present at the site rather than on the performance and control of the device. In an online meeting the NRC staff said it believed
current 10 CFR Part 20 requirements were adequate for the tritium used in fusion. Activation products might fall under a different rule (Part 37) and that would become clearer as developing fusion energy systems resulted in a better understanding of the isotopes that could be produced. Storage and aggregation would be considered. An NRC representative said “we can state with
certainty that fusion facilities will be required to have emergency response capability with offsite response being commensurate to the radiological hazard.” Emergency preparedness and response terminology might be aligned with other bodies such as the Federal Emergency Management Agency (FEMA), the DOE and state and local offsite response organisations.
Areas of discussion Responding to a draft of the rulemaking in May 2024, the Fusion Industries Association had several areas of reflection for the NRC staff. First among them were two definitions crucial to the new rulemaking: particle accelerator and fusion system. FIA and
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