Measurement of Flux Spectra and Tritium Production Rates in an ITER TBM Mock-Up Irradiated with 14-MeV Neutrons

A mock-up of the European Helium-Cooled Pebble Bed TBM was irradiated with DT neutrons in pulsed and continuous mode at the Fusion Neutronics Laboratory of the University of Technology Dresden. The aim was to measure fast neutron and gamma-ray flux spectra as well as time-of-arrival spectra of the slow neutron flux. The results of the experiments were analysed by the Monte Carlo code MCNP and nuclear data from the European Fusion File (EFF-3),and the Fusion Evaluated Nuclear Data Library (FENDL-2.0/2.1). It was found that the calculation of the fast neutron flux above 3 MeV tends to overestimate while the gamma-ray flux and slow neutron flux in two measurement positions in the mock-up was underestimated. The mock-up was also irradiated at FNG/ENEA Frascati to measure tritium breeding rates by means of small Li₂CO₃ pellet detectors inserted into the breeding layers. The breeding experiment was analysed at FZ Karlsruhe with emphasis on determining sensitivities of the TPR to relevant cross section uncertainties of all materials in the mock-up. It was found that the TPR calculation shows a tendency to underestimate. From the sensitivity analysis it was found that the total TPR is most sensitive to the elastic scattering in Be and the ⁷Li(n,T) reaction.