IFMIF Li target back-plate design integration and thermo-mechanical analysis

The International Fusion Materials Irradiation Facility (IFMIF) is an accelerator-driven intense neutron source where fusion reactor candidate materials will be tested. The neutron flux is produced by means of a deuteron beam (current 250 mA, energy 40 MeV) that strikes a liquid lithium target circulating in a lithium loop. The support on which the liquid lithium flows, i.e. the back-plate, is the most heavily exposed component to neutron flux. A '' bayonet '' concept solution for the back-plate was proposed by ENEA with the objectives of improving the back-plate reliability and simplifying the remote handling procedures. On the base of this concept, a back-plate mock-up was fabricated and validated. Starting from the findings of the mock up design, a back-plate design integration exercise was carried out in order to check if the back-plate geometrical features are compatible with the target assembly and the Vertical Test Assemblies (VTA). The work carried out has demonstrated that even with the changes operated for the design integration (increase of in-plane dimensions and reduction of thickness) the bayonet concept is able to guarantee a tight connection to the target assembly. A thermo-mechanical analysis of the back-plate has been carried out by means of ABAQUS code. The thermal load used as input for the calculations, i.e. the neutron heat generation, has been estimated by means of Monte Carlo Mc-Delicious code. The two boundary constraint cases (full and minimum contact with target assembly) considered for each back-plate geometry option represent the extreme cases of the real operating condition of the plate. The influence of the contact heat exchange coefficient and the back-plate thickness has been also evaluated. For all these reasons, the results of the analysis can be considered as the domain of variability of the real working conditions. The results show that AISI 316L steel is not suitable as black-plate material: the stress induced in the plate, in every configuration of constraints and back-plate geometry, exceed those admissible according to ASME standard. Conversely, both the F82H and the T91 steels satisfy ASME requirements. A thin plate solution appears preferable both for the stresses and the maximum displacements. The profile deformation of the liquid lithium is small (<0.5 mm) and qualitatively similar in the different boundary cases; their effect on the lithium flow stability is expected to be modest. (author)