Sehila M. Gonzalez de Vicente
IAEA Nuclear Fusion Physicist
Scientific Secretary of the DEMO workshop
Photo of the 6th IAEA DEMO Programme Workshop participants. Courtesy of Rosatom Technical Academy
A DEMOnstration Power Plant, or DEMO, is a proposed nuclear fusion power station, which could act as an intermediate step between the experimental fusion reactor ITER and a pilot fusion power plant. Unlike in the case of ITER, there is no single common definition or design for a DEMO Power Plant Although key fusion players suggest different concepts for DEMO, there are few basic common principles in all of them: a DEMO machine should be more advanced than ITER and key technologies like tritium self-sufficiency should be demonstrated.
Countries that are currently developing experimental reactors under the DEMO umbrella are deciding on different approaches for composition and configuration of the breeding blanket, the coolant and the first wall, although they agree on DEMO being a D-T tokamak reactor, such as ITER. However, there is an international agreement on the main technological and scientific issues that must be resolved if the proposed reactor is to achieve its objectives, as it has to not only use the knowledge and experience gained at ITER, but expand upon them. DEMO is meant to precede a commercial power plant and, as such it must also prove that it can generate electricity safely, consistently, reliably and remotely, due to the high levels of in-site radiation.
The construction and success of a DEMO machine requires a platform supporting international coordination and collaboration. The IAEA has established a series of biannual DEMO Programme Workshops, which promote international cooperation and pave the way to a single roadmap to fusion. The workshops discuss main scientific and technical challenges of DEMO. Although each country may have different priorities, the objective of the workshops is to coordinate mutually beneficial efforts and facilitate international collaboration, leading to the best possible structured roadmap to the future of fusion.
Last week, the 6th IAEA DEMO Programme Workshop, which took place in Moscow, Russian Federation, discussed the following topics:
• plasma transients, disruptions & ELMs, including effects in stellarators;
• irradiation damage and lifetimes of materials, components, impact of operational conditions;
• materials engineering of PFCs & PFMs.
Around 60 senior experts representing 14 Member States, Fusion for Energy and the ITER Organisation met for the DEMO workshop at the Moscow Branch of Rosatom Tech. The workshop included a technical visit to the Kurchatov institute, where the first T-1 tokamak was built in1958. Currently T-10 (no longer in operation) and T-15U (under construction) are there.
T-10: “History of the T-10 Tokamak: Creation and Development”- V. S. Strelkov, Institute of Nuclear Fusion (INF), Russian Research Centre Kurchatov Institute (https://link.springer.com/article/10.1134/1.1409715)
Main conclusions of the workshop were:
- Due to extreme loading conditions (> ITER) and impact on DEMO mission (reliable power production), disruptions have to be extremely rare events once DEMO goes into 'production mode'. Analysis of impact of ELM heat loads in a DEMO suggests they have to be mitigated by large factors (> 40) or avoided altogether. This will require a different approach than in present day tokamaks. Operational point has to be 'passively safe' and have sufficient margin against component failure. Disruption avoidance starts from the monitoring of the operational point. More emphasis is needed on the investigation of component failure modes in order to achieve the required RAMI avoiding transients. In many areas, ITER will be crucial to guide the DEMO design.
For a long-term structural reliability and lifetime, synergistic loads, time-dependent phenomena, gradient, distribution, and anisotropy of loads and material properties, material properties database and handbook, prediction and validation, and criteria and rules are the key factors. The preliminary application of RAMI methodology in blanket (using fission data bases) shows the impact of the extremely large number of welds in producing large component failure rate. RAMI assessment based on a fusion failure rate data bank (with irradiation data) is required to calculate the probabilistic failure rate of components, in a situation where the occurrence of a single failure (for example leakage in a welding) can cause the total failure of the component.
- Knowledge on edge plasma parameters is crucial for the design of plasma facing component and materials and for DEMO conditions. Further improvements are required for both material and joining technologies, against "heat loading" and "neutron irradiation", for DEMO application. Manufacturing technologies and facilities along with various testing, inspection and other equipment developed at ITER construction can be certainly used at DEMO construction, but further developments are needed.
Modeling can identify critical processes and mechanisms that contribute to radiation-induced property changes. However, modeling alone is unlikely to be sufficient to replace data from experiments in representative irradiation environments, particularly in regulatory space. A combination of modeling and fission/ion irradiations can help guide use of fusion neutron source, screen and select candidate materials. A 14 MeV fusion dedicated neutron source is mandatory for the development and qualification of DEMO materials/component.