The impact of HEU to LEU conversion of commercial MNSR: Determination of neutron spectrum parameters in irradiation channels of NIRR-1 using MCNP code

• Published in: Annals of nuclear energy Vol. 39; no. 1; pp. 15 - 17
• Main Authors: Jonah, S.A., Ibrahim, Y.V., Ajuji, A.S., Onimisi, M.Y.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 2012
• Subjects: Channels; Energy distribution; Energy use; Irradiation; LEU conversion; Mathematical analysis; MCNP; MNSR; Neutron spectrum parameters; NIRR-1; Nuclear power generation; Nuclear reactor components; Nuclear reactors; Neutron spectrum parameters; NIRR-1; MNSR; MCNP; LEU conversion
• ISSN: 0306-4549; 1873-2100
• DOI: 10.1016/j.anucene.2011.08.026

► A computational method was used to assess the impact of conversion of MNS reactors on utilization. ► Neutron spectrum parameters in irradiation channels of NIRR-1 HEU and LEU cores were calculated. ► Data obtained for HEU core agree well with measured data, which underscores the computational method. ► Results indicate that the impact of HEU to LEU conversion of commercial MNSR on utilization is minimal. Miniature Neutron Source Reactor (MNSR) facilities are equipped with 10 irradiation channels mainly for NAA and limited radioisotope production. A neutronics feasibility study has shown that it would be feasible to convert commercial MNSR from HEU (90.2%) to LEU (∼12.5%) fuel. In this work, the impact of the proposed LEU fuel on neutron spectrum parameters in the irradiation channels has been studied. The MCNP code was used to calculate the neutron flux distribution in 640 neutron energy group structure and the cross section data of monitor reactions also in 640 neutron energy group structure were extracted from ENDF libraries. On the basis of the data, the Cd ratios for Au, Co, Th, and U were computed and used to estimate the thermal-to-epithermal neutron ratio, f, as well as the non-ideality of epithermal neutron spectrum, α. In order to verify the calculations, measured experimental data for the current HEU core are compared with calculations. Results obtained indicate slightly “hardened” neutron spectra distributions in the inner and outer irradiation channels of the proposed LEU core with no significant impact on utilization.