Monte Carlo calculations of neutron spectrum parameters at the JRTR NAA channels

Abstract

The neutron spectra at the irradiation channels of the Jordan Research and Training Reactor have been calculated using the MCNP and McCARD codes. This work aims to validate the calculation models and tools by comparing the calculated spectrum parameters to results obtained from a recently published study which employed Cadmium Ratio measurements at three of the irradiation channels. An analysis methodology to evaluate spectrum parameters based on the calculated spectra is presented, highlighting the importance of distinguishing between alternative definitions of the thermal and epithermal fluxes when comparing data from reactor physics calculations to data from neutron activation analysis.The deviations between calculated and measured thermal-to-epithermal ratios ranged from about 3% to 12% which were considered acceptable given the identified sources of error and uncertainty in the simulation and measurement results. The simulations were also employed to study the sensitivity of the neutron spectrum parameters to changes in the reactor core and irradiation conditions, concluding that the thermal-to-epithermal ratio is significantly sensitive to the axial location of the sample within the irradiation rabbit and to the configuration of the reactor core, and less sensitive to the temperature and burnup conditions.