Monte Carlo Characterisation of the Radiation Field in the Thermal Column of the Portuguese Research Reactor

The Monte Carlo program MCNP-4B was used to simulate the vertical access of the thermal column of the Portuguese Research Reactor. The reactor core was included in the simulations and two models for the neutron source were studied. Measurements were done with activation detectors. The order of magnitude of the thermal flux and gamma dose at the vertical access were predicted by using a neutron source obtained with a criticality calculation. A better agreement between experimental and measured values depends on a better description of the fuel burn-up and the geometry of the vertical access, where some arbitrary assumptions were made.