Core working group:
Ed Cheng, Tom Shannon, John Perkins, Bick Hooper,
Mark Tillack, Siegfried Malang, Rich Mattas, Lance Snead
Main subtopics:
Prospectus
The key challenge in fusion technology is to develop and test advanced materials and configuration concepts that would lead to an attractive fusion power plant. This challenge necessarily involves both non-irradiation and irradiation test programs. Given the current budget constraints, it is prudent to develop a consensus within the fusion technology/materials science community on the priority of development of different large-scale facilities. Issues associated with the balance between structural materials and non-structural materials research will be discussed in Key Question #7.
The role of a non-irradiation test facility is in the area where the neutron field effect does not play the dominating factor in determining feasibility. It is particularly attractive for the liquid wall concept where the feasibility of establishing a stable hydrodynamics configuration in a large, complex geometry can be investigated. Major facilities to investigate tritium extraction issues, material compatibility, etc. are also pertinent. The non-irradiation tests provide data useful for making decisions regarding whether the concept should continue to be pursued or which future proof-of-performance experiments should be performed. These tests comprise basic property data tests, single-effect experiments and some of the multiple-effect/multiple interaction tests. Specifically, the single effect tests address issues where the controlling phenomena can be quantified using a non-irradiation, fusion relevant operating condition, such as magnetic field, surface heat flux, particle flux and mechanical force. Experiments in non-irradiation test facilities are typically relatively fast in schedule and are important and useful in reducing the large costs and risks associated with tests in the overall fusion environment.
One of the major materials issues is the effect of the intense neutron fluxes associated with DT fusion concepts. The first-wall neutron spectrum which contains a large 14 MeV component not only results in very high displacement rates (~20 dpa/yr at 2 MW/m2) but also typically causes much higher transmutation rates in materials compared to fission reactors. The elements He and H are of particular concern, but other impurities can also be important. The influence of these transmutation products on property changes has been well established, e.g., the role of He in swelling behavior and high temperature embrittlement. Although fission reactors will continue to be the main irradiation facilities for the foreseeable future, the uncertainties associated with fission/fusion neutron spectrum effects and the generally poor capability of fission reactors for integrated in-situ testing of fusion blanket components does not allow experimental proof of performance testing of the critical fusion technologies.
Previous fusion program reviews have generally concluded that two different materials test facilities would be utilized: 1) a high-flux materials irradiation facility which would primarily be used for testing structural materials, ceramic breeders, and special purpose materials (sometimes referred to as a point neutron source), and 2) a fusion technology integrated-component test facility (sometimes referred to as a volume neutron source). Both accelerator and plasma-based sources have been considered for the materials irradiation facility, whereas plasma-based sources are leading candidate for the technology test facility. In some proposals, a single plasma-based source would be used as a dual-purpose facility to test materials and components. The main advantage of an accelerator source is that the required accelerator technology is essentially in hand, and the estimated construction cost is significantly less than for a plasma-based source. The main disadvantage of an accelerator source is the limited irradiation volume, which precludes testing of integrated components in the high-flux (>2 MW/m2 equivalent neutron flux) region of the facility. It is also difficult to perform meaningful tests on high heat flux (plasma facing) components in an accelerator facility.
Key issues:
What are the key technology issues that require construction of major facilities, based on the fusion technology roadmap? Possible non-neutron facilities include thermal gradient coolant loops for corrosion tests, high heat flux facilities to investigate erosion, cracking and thermal fatigue, etc. What is the optimal strategy for resolving these key issues?
Can a combination of existing neutron sources and advanced computational modeling eliminate the need for fusion neutron test facilities? What is the role of fission reactors for the next 10 years?
Is the urgency for developing fusion neutron test facilities reduced if thick-liquid wall reactor or alternative fuel cycle concepts prove to be viable?
Is an accelerator-based (e.g., d-Li) neutron source an essential facility for the development of fusion-relevant materials, and a necessary precursor to any high-fluence fusion plasma based device? (how can a high-fluence plasma-based source be built without knowledge about the appropriate damage-resistant structural materials? Why spend 0.5B$ for an accelerator source if a plasma-based source can be used as a test facility for both structural materials and integrated components).
What is an appropriate schedule for the deployment of fusion neutron test facilities? What are the criteria for launching a major neutron or non-neutron test facility?
Other key issues include cost (capital and operating), reliability/availability, nature of operation (e.g., pulsed and steady-state operating capabilities), capability for spectral tailoring to match neutron environment in various regions of the fusion power plant, and capability for testing integrated components (e.g., miniaturized blanket modules).
Preliminary Report outline: