TRIGA-SSR Thermal Column Neutron Characterization by Foil Activation Method

Knowledge of neutron flux densities is needed both for the reactor control and for the use of neutron fields or neutron beams. This paper is dedicated to the neutron field characterization of an irradiation site created into the graphite thermal column of the TRIGA steady state reactor operated by RATEN ICN Pitesti. Neutron flux and spectrum have been measured by using multiple foil activation method followed by spectrum unfolding. The measured flux densities are reported to the Self-Powered Neutron Detector (SPND) Silver monitor placed into the Beryllium reflector, near to the thermal column. Foil activation detectors, bare and Cadmium covered, dedicated for thermal neutron spectra, were used. Experimental corrections for neutron self-shielding as well as for gamma activity measurements have been applied. The irradiation site is placed relatively near to the reactor core. This is why the fast neutron contribution evaluation has been also an important issue. The unfolding results, reported to 10 MW reactor operation power, showed a thermal neutron flux density of 2 1011 n/cm2s with a fast neutron contribution less than 1%. The Cadmium ratio for the Gold reaction, as an indicator of the neutron spectrum thermalization, was measured at the value of 52. (author).