Neutron flux characterization in the SM1 sub-critical multiplying complex of the Pavia University

SM1 is a thermal Sub-critical Multiplication complex located at the University of Pavia (Italy) and used mainly for research in radiochemistry since its installation in 1962. This work is mainly focused on the characterization, by means of the Monte Carlo code MCNP and direct measurements, of the neutron flux distribution inside the complex and the calculation of the effective multiplicative coefficient (keff) in the actual SM1 thermal configuration. For two specific irradiation channels, experimental measurements of the neutron fluxes were performed by foils activation technique and neutron spectrum de-convolution based on the SAND II code. Measurements were compared with simulation results showing a good agreement. Furthermore, a comparison between the preliminary results of the simulations of the SM1 plant in fast configuration, characterized by a solid lead diffuser, and the actual thermal configuration is also presented. The fast configuration of SM1, if implemented, will give the opportunity to carry out preliminary studies for the analysis of sub-critical fast-neutron installations and their applications.