Experimental tests and thermo-mechanical analyses on the HEXCALIBER mock-up

HEXCALIBER was designed and manufactured to reproduce a portion of the former HCPB-TBM with two Lithium Orthosilicate and two Beryllium pebble bed cells both heated by couples of flat electrical heaters. The mock-up will be tested in HE-FUS 3 facility, under adequate adjustment of bed temperatures, temperature gradients, coolant temperatures, flow distributions and mechanical constraints, to assess the thermo-mechanical performance of the pebble beds under steady state and cyclic heat power conditions. The first test campaign is planned to be performed in the first part of 2007 using Lithium Orthosilicate (0.24-0.40 mm in diameter) pebbles as breeder material and Beryllium (1 mm in diameter) pebbles recently qualified as neutron multiplier. Among other experimental results, the temperatures, both in lithiated ceramics and Beryllium beds, and the overall displacements of the box will provide useful data to be compared with the theoretical ones computed by FEM codes with adequate models for pebble beds. The paper presents the main features of the HEXCALIBER mock-up, the detailed description of its experimental set-up and the first results of the experimental campaign. Moreover, the numerical simulation carried out by DIN on a 3D FEM model of HEXCALIBER, in the frame of the benchmark exercise, is also presented with details on the mock-up and cooling system nodalization and adopted loads and boundary conditions. Finally, the most significant numerical results, concerning temperatures and displacements at the instrumented points of the mock-up, are critically compared with the relevant measured values. (orig.)