Fusion materials and component testing at PALLAS, a new MTR

Full text of publication follows: Fusion power plant operation will strongly depend on the economy and reliability of crucial components, such as first wall modules, tritium breeding blankets and divertors. Their operating temperature shall be high to accomplish high plant efficiency. The materials properties and component fabrication routes shall also assure long reliable operation to minimize plant outage. The components must be fabricated in large quantities based on demonstrations with a limited amount of test beds. Mock-ups and test loops will, through iteration processes, demonstrate the reliable operation under reference thermal-hydraulic conditions. Although 14 MeV neutrons dominate the nuclear conditions near the first wall, neutron transport analyses have shown that large portions of the components near the plasma have to cope with a neutron spectrum resembling a fission core. Present MTR's offer fluxes relevant for large parts of the fusion major components. The mixed and fast fission spectra though is not representative for all fusion conditions. The strong point of MTR's is their ability to generate sufficient displacement damage in the materials in a relatively short time. They provide sufficient space for irradiation of representative cut-outs of components to allow integrated functional and materials tests in a high flux neutron field. In recent years the pebble bed assembly, PBA, irradiated in the HFR, Petten, has shown the feasibility of the helium-cooled concept with lithium ceramics and beryllium multiplier pebble beds. Similarly, activities are ongoing to perform in-pile testing of primary wall components, allowing to address fatigue type loading conditions. In the next decade 14 MeV sources such as ITER, IFMIF and maybe a volumetric source will support the crucial demonstration of components under near fusion plasma nuclear conditions. These sources have limitations in accumulated total damage (ITER) irradiation volume (IFMIF) and control. MTR's will thus continue to supply essential facts on component behaviour and materials in parallel to 14 MeV sources. The present generation of MTR's will be closed in this and next decade because they reach their end of life. The new generation will be utilised for 4 major areas of nuclear interest: energy, science, health and environmental issues. Fusion and the next generation fission (Generation 4) power plant development will share the areas energy and science in the next decades. The design and concept of the new MTR's will centre on faster development cycles, thus higher fluxes up to 5*1018 n.m-2. The conceptual design of the replacement for the HFR, Petten, named PALLAS envisages a fruitful co-operation of the experimenters for advanced fission power reactor and fusion plant components. Materials science will also be able to use modern MTR facilities for the modelling of radiation damage in both fission and fusion environments. The development of primary fusion components such as blankets and first wall modules will be well served also with the new MTR generation. (authors)