Calculation and comparison of xenon and samarium reactivities of the HEU, LEU core in the low power research reactor

• The MCNP4C and GETERA codes are used for the conversion of the fuel from HEU to LEU in the MNSR.
• The precise calculations of 135Xe and 149Sm concentrations and reactivities were carried out and compared.
• The 135Xe and 149Sm reactivities did not reach their equilibrium reactivities during the daily operating time.
• The 149Sm reactivities could be neglected compared to 135Xe reactivities during operating.
• The best candidate was the UO2 fuel since it gave the lowest 135Xe reactivity.

Comparative studies for the conversion of the fuel from HEU to LEU in the Miniature Neutron Source Reactor (MNSR) have been performed using the MCNP4C and GETERA codes. The precise calculations of 135Xe and 149Sm concentrations and reactivities were carried out and compared during the MNSR operation time and after shutdown for the existing HEU fuel (UAl4–Al, 90% enriched) and the potential LEU fuels (U3Si2–Al, U3Si–Al, U9Mo–Al, 19.75% enriched and UO2, 12.6% enriched) in this paper using the MCNP4C and GETERA codes. It was found that the 135Xe and 149Sm reactivities did not reach their equilibrium reactivities during the daily operating time of the reactor. The 149Sm reactivities could be neglected compared to 135Xe reactivities during the reactor operating time and after shutdown. The calculations for the UAl4–Al produced the highest 135Xe reactivity in all the studied fuel group during the reactor operation (0.39 mk) and after the reactor shutdown (0.735 mk), It followed by U3Si–Al (0.34 mk, 0.653 mk), U3Si2–Al (0.33 mk, 0.634 mk), U9Mo–Al (0.3 mk, 0.568 mk) and UO2 (0.24 mk, 0.448 mk) fuels, respectively. Finally, the results showed that the UO2 was the best candidate for fuel conversion to LEU in the MNSR since it gave the lowest 135Xe reactivity during the reactor operation and after shutdown.