Preliminary Calculations in Support of the Experimental Campaign to Evaluate the Neutron Energy Spectrum Inside the JS']JSI TRIGA Mark II Research Reactor

Preliminary calculations performed in support of an experimental campaign to evaluate the neutron spectrum inside the JSI TRIGA reactor are presented. Focus is in the on-line determination of the epi-thermal and fast parts of the neutron spectrum. Measurements will be performed using fission chambers with different fissile deposit materials with higher fission cross section for fast neutron energies (Np-237 and Pu-242) covered with thermal neutron transmission filters (Cd, Gd). Preliminary calculations have been performed to establish optimal experimental conditions. The radial and axial dependence of the fission rates in the core was evaluated and compared for different measurement positions. A preliminary design of the transmission filters was established in order to evaluate the effect of the filter geometry (length, opening). It was found out that presence of top and bottom openings in the filter can significantly increase the detector signal, especially in case of the U-235 fission chamber, however the effect can be reduced by increasing the filter length.