A volumetric neutron source for fusion nuclear technology testing and development

Abstract

Abstract Research and development (R&D) needs to construct and operate fusion nuclear technology (FNT) components for DEMO have been investigated. Non-fusion facilities, i.e. non-neutron test stands, fission reactors and accelerator-based neutron sources, can and should play a role in FNT R&D because of their availability and low cost. However, none of the FNT critical issues will be resolved by testing in non-fusion facilities because of their serious limitations on simulating multiple integrated effects of the fusion environment and their lack of adequate test volume. Testing of FNT components, particularly blankets, in fusion facilities is necessary. The FNT requirements on fusion testing are a 1–2 MW m−2 neutron wall load, steady state plasma operation, a fluence of greater than 6 MW years m−2 and a test area greater than 10 m2. Requirements on reliability growth and component engineering development are the most demanding. Calculations of both expected and tolerable failure rates and reliability growth testing requirements for the blanket lead to a number of important conclusions: (1) achieving a fluence of about 6 MW years m−2 at the test modules with about six to 12 test modules per blanket concept is crucial to achieving a DEMO reactor availability in the 40–50% range with 90% confidence, (2) achieving a DEMO reactor availability of 60% may not be possible with 90% confidence for any practical blanket test program with present design concepts. The required mean time between failure for the blanket is much longer than that achieved in other existing and perhaps less complex technologies, (3) the mean down-time to replace (MTTR) or to recover from a random failure in the blanket must be kept on the order of 1 week or less in order to achieve the required blanket and reactor system availabilities and (4) the length of MTTR must be by itself one of the crucial objectives for testing in fusion facilities. Scenarios for fusion facilities to provide the data base for DEMO have been evaluated. A strategy based on the International Thermonuclear Experimental Reactor (ITER) alone results in unacceptably high risk and long delays in DEMO operation. A plasma-based volumetric neutron source (VNS) facility is proposed for construction and operation parallel to ITER. VNS will serve as a dedicated facility to test and develop FNT components for DEMO. An attractive design envelope for a small-sized tokamak VNS exists with driven (Q ≈ 1–3) steady state plasma and normal conducting copper toroidal field coils. Operation of VNS in parallel to ITER reduces the risk to DEMO and results in net savings in the overall R&D cost to DEMO.