RESULTS OF AN INTERNATIONAL STUDY ON A HIGH-VOLUME PLASMA-BASED NEUTRON SOURCE FOR FUSION BLANKET DEVELOPMENT

An international study conducted by technical experts from Europe, Jap an, Russia, and the United States has evaluated the technical issues a nd the required testing facilities for the development effusion blanke t/first-wall systems and has found that some of the key requirements f or the engineering feasibility of blanket concepts cannot be establish ed prior to extensive testing in the fusion environment. However, beca use of availability and low cost, testing in nonfusion facilities (e.g ., fission reactors and laboratory experiments)serves a critical role in blanket research and development (R&D) and reduces the risks and co sts of the more complex and expensive fusion experiments. A comprehens ive analysis shows that the fusion testing requirements for meeting th e goal of demonstrating a blanket system availability in DEMO >50% are as follows: a 1 to 2 MW/m(2) neutron wall load, a steady-state plasma operation, a >10-m(2) test area, and a fluence of >6 MW . yr/m(2). Th is testing fluence includes 1 to 3 MW . yr/m(2) for concept performanc e verification and >4 to 6 MW . yr/m(2) for component engineering deve lopment and reliability growth/demonstration. Reliability and availabi lity analyses reveal critical concerns that need to be addressed in fu sion power development. For a DEMO reactor availability goal of 50%, t he blanket availability needs to be similar to 80%. For a mean time to recover from a failure of similar to 3 months, the mean time between failure (MTBF) for the entire blanket must be >1 yr. For a blanket tha t has 80 modules, the corresponding MTBF per module is 80 yr. These ar e very ambitious goals that require an aggressive fusion technology de velopment program. A number of scenarios for fusion facilities were ev aluated using a cost/benefit/risk analysis approach. Blanket rests in the International Thermonuclear Experimental Reactor (ITER) alone with a fluence of 1 MW . yr/m(2) can address most of the needs for concept verification, bur it cannot adequately address the blanket component reliability growth/demonstration testing requirements. An effective pa th to fusion DEMO is suggested. It involves two parallel facilities: ( a) ITER to provide data on plasma performance, plasma support technolo gy, and system integration and (b) a high-volume plasma-based neutron source (HVPNS) dedicated to testing, developing, and qualifying fusion nuclear components and material combinations for DEMO. For HVPNS to b e attractive and cost effective, its capital cost must be significantl y lower than ITER, and it should have low fusion power (similar to 150 MW). Exploratory studies indicate the presence of a design window wit h a highly driven plasma. A testing and development strategy that incl udes HVPNS would decisively reduce the high risk of initial DEMO opera tion with a poor blanket system availability and would make it possibl e - if operated parallel to the ITER basic performance phase - to meet the goal of DEMO operation by the year 2025. Such a scenario with HVP NS parallel to ITER provides substantial savings in the overall R&D co st to ward DEMO compared with an ITER-alone strategy. The near-term co st burden is negligible in the context of an international fusion prog ram with HVPNS and ITER sited in two different countries.