On the Optimisation of Large Sample In-Core Irradiation Channel in the JSI TRIGA Reactor

In aim to choose optimal design for a new triangular channel in TRIGA Mark II in Ljubljana, a detailed computational designs for different possible geometrical configurations using Monte Carlo neutron transport code MCNP were made and their impact on physical quantities was studied. It was found out that the impact on multiplication factor is from -730 pcm to -1020 pcm, depending on configuration studied. The hot rod power peaking factors was calculated to be from 1.393 to 1.403. The relative deviation in total neutron flux in central channel, compared to the bare configuration, was evaluated to be from -1.45 % to -1.72 %. The deviation in total neutron flux in triangular channel between different triangular channel configurations was established to be up to 6 %. The total power density peaking factor, axial power peaking factor and radial power density peaking factor were calculated to be approximately 2.70, 1.27 and 2.09 respectively, and did not deviate significantly between different configurations. When studying 640 group energy spectrum in different triangular channel configurations it was found out that the highest thermal peak has configuration 4 (lifted channel), followed by configuration 2 (graphite insert), which is expected due to the presence of reflector. The study of rotary groove showed high impacts of triangular channel on neutron flux in 3 energy groups, however the deviations between different channel designs were not significant. Silicon dose equivalent and 1 MeV flux equivalent, important for radiation hardness testing of electronics, deviated between different configurations up to 3.5 %. To sum up, calculations confirmed no significant deviation between different channel designs and final design can be chosen based on technical limitations.