Development and application of an alternative modelling approach for the thermo-mechanical analysis of a DEMO water-cooled lithium lead breeding blanket segment

In the frame of the EUROfusion research activities devoted to the design of the DEMO breeding blanket (BB), the Water-Cooled Lithium-Lead BB (WCLL) concept is one of the candidates currently assessed in EU. To this end, an intense research campaign is ongoing to develop a robust geometric configuration for the WCLL BB Central Outboard Segment (COB). Since the current reference design of the WCLL COB segment is not mature enough to allow a full thermal-hydraulic assessment, an alternative procedure aimed at obtaining a thermal field for the whole segment without performing its complete thermal-hydraulic analysis is presented and applied in this work. The scope of the work is to obtain a thermal field for the whole WCLL COB segment detailed enough to ensure a reliable prediction of the secondary stress spatial distribution, which is pivotal for the segment structural analysis. The procedure is articulated in three steps. Firstly, a thermal analysis of the equatorial region of the WCLL COB is performed, in order to calculate the thermal field in the most loaded region of the segment. Then, a multi-region interpolation is carried out in order to obtain a set of polynomial functions of the radial and toroidal variable, accurately representing the thermal field of the assessed equatorial BB slice. Finally, the calculated functions are applied to the whole COB to impose a realistic thermal field to the segment for the prediction of the stress, strain and displacement fields. Since the mesh for the analysis of the whole segment is expected to be coarser than that used for the assessment of its equatorial region, in this paper a mesh independence assessment of the interpolating functions is reported. In particular, their predictive power both in terms of temperature and secondary stress (i. e. thermal-induced stress) is assessed taking into account a decreasing level of detail of the adopted spatial discretization grid. The obtained results, widely reported and discussed hereafter together with the models and the adopted assumptions, show a great predictive power of the adopted polynomial functions, with a good mesh independence of the calculated temperature and stress values.