Measurement and analysis of dose rates and gamma-ray fluxes in an ITER shut-down dose rate experiment

Abstract

A materials mock-up of the International Thermonuclear Experimental Reactor (ITER) vacuum vessel was irradiated at the Frascati Neutron Generator with DT-neutrons, and, after shut-down, the gamma-ray dose rate inside the mock-up was measured as a function of decay time over a period of 3 weeks with a tissue-equivalent scintillator. The gamma-ray flux spectra were determined at several decay times with an organic scintillation spectrometer. Also the neutron flux spectrum during the irradiation was measured. The experimental results were analysed with ITER computational tools. The Monte Carlo code MCNP was used for the calculation of the neutron transport in the mock-up during the irradiation and for the gamma-ray transport, after shut-down, from the activated material to the position of measurement. Production and decay of the radionuclides were calculated with the inventory code FISPACT. The Fusion Evaluated Nuclear Data Library (FENDL/MC-2.0 and FENDL/A-2.0) was used as data base. The comparison of experimental and calculated results shows validation of these tools within about ±15% for both shut-down dose rate and spectral gamma-ray flux calculations.