High enriched to low enriched fuel conversion in YALINA Booster facility

The YALINA Booster zero power facility is a subcritical assembly located in Minsk (Belarus). This assembly has the special feature of operating on fast and thermal neutron spectra in different zones. The fast zone of the assembly uses a lead matrix and uranium fuels with different enrichments: 90% and 36%, 36%, or 21%. The thermal zone of the assembly contains 10% enriched uranium fuel in polyethylene matrix. This study discusses the high enriched to low enriched fuel conversion. In order to increase the neutron multiplication of the assembly loaded with low (21%) enriched fuel in the fast zone, the number of fuel rods in the thermal zone cannot be augmented. Consequently, the effective multiplication factor of the configuration with 21% enriched uranium fuel in the fast zone has been enhanced by changing the position of the boron carbide and the natural uranium absorber rods, located in-between the fast and the thermal zones, to form a circular rather than a square arrangement. The MCNP computer simulation results obtained with the circular arrangement of the absorber rods are in good agreement with the experimental data.