Neutronic evolution and isotopic assessment of NIRR-1 under alternative fuel enrichment configurations: a WIMS-ANL/REBUS-ANL study

Dennis Solomon Balami; John Simon; Asuku Abdulsamad; Yakubu Ibrahim Viva; Rabiu Nasiru; Emmanuel Likta Wana

Issue

Vol. 4 No. 4 (2025): November 2025 Issue

Issue Published : November 15, 2025

Neutronic evolution and isotopic assessment of NIRR-1 under alternative fuel enrichment configurations: a WIMS-ANL/REBUS-ANL study

Dennis Solomon Balami

Department of Physics, University of Maiduguri, Nigeria

John Simon

National Open University Nigeria, Abuja, Nigeria

Asuku Abdulsamad

Centre for Energy Research and Training (CERT), Ahmadu Bello University Zaria, Kaduna State, Nigeria

Yakubu Ibrahim Viva

Centre for Energy Research and Training (CERT), Ahmadu Bello University Zaria, Kaduna State, Nigeria

Rabiu Nasiru

Department of Physics, Ahmadu Bello University Zaria, Kaduna State, Nigeria

Emmanuel Likta Wana

Department of Physics, University of Maiduguri, Nigeria

Corresponding Author(s) : Dennis Solomon Balami

dennisolomon59@gmail.com

Future Energy, Vol. 4 No. 4 (2025): November 2025 Issue
Article Published : October 26, 2025

Abstract

The Nigerian Research Reactor-1 (NIRR-1), a Miniature Neutron Source Reactor (MNSR), transitioned from highly enriched uranium (HEU) to low-enriched uranium (LEU) fuel to align with global non-proliferation objectives, necessitating a detailed evaluation of its neutronic behavior and isotopic evolution. This study employs the WIMS-ANL and REBUS-ANL computational framework to compare the burnup dynamics, reactivity profiles, and radionuclide inventories of NIRR-1’s HEU () and LEU core configurations under a representative operational schedule of 20 effective full-power days per year. Results reveal a steeper reactivity decline in the LEU core (17.02 pcm/EFPD) compared to the HEU core (13.97 pcm/EFPD), driven by enhanced resonance absorption, yet the LEU core’s higher initial mass extends its operational lifetime to 56.4 years versus 50.3 years for HEU. The LEU configuration produces 2.24 times more (0.767 g vs. 0.342 g at 252/282 EFPD), raising long-term waste management considerations. Both cores maintain robust safety through strongly negative temperature coefficients and low peak temperatures, supported by natural convection cooling. Comprehensive isotopic inventories and decay heat analyses (1620 W LEU vs. 1450 W HEU at shutdown) inform safety assessments and decommissioning strategies. Sensitivity studies highlight operational power and enrichment as critical lifetime influencers, with uncertainties validated against experimental data. These findings enhance NIRR-1’s operational strategy, support global MNSR conversion efforts, and provide critical data for safety and waste management planning, emphasizing proactive reactivity control and advanced fuel design exploration.

Keywords

NIRR-1 HEU-to-LEU conversion Reactor physics Burnup analysis Radionuclide inventory MNSR Nuclear security

Balami, Dennis Solomon, John Simon, Asuku Abdulsamad, Yakubu Ibrahim Viva, Rabiu Nasiru, and Emmanuel Likta Wana. 2025. “Neutronic Evolution and Isotopic Assessment of NIRR-1 under Alternative Fuel Enrichment Configurations: A WIMS-ANL/REBUS-ANL Study”. Future Energy 4 (4):40-54. https://fupubco.com/fuen/article/view/583.

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References

Khamis, I., & Jamal, M. H., “Prediction of the in-core power and the average core temperature using dose-rate measurements in the Syrian Miniature Neutron Source Reactor,” Journal of Radioanalytical and Nuclear Chemistry, pp. 269, 81–85. https://doi.org/10.1007/s10967-006-0233-3, 2006.
Osei, B., Baidoo, I. K., Odoi, H. C., Gasu, P. D., & Nyarko, B. J. B., “The low enriched uranium miniature neutron source reactor (LEU-MNSR) neutron spectrum characterization for k₀-INAA.,” Nuclear Instruments and Methods in Physics Research Section A, 1005, Article 165397, p. https://doi.org/10.1016/j.nima.2021.165397, 2021.
International Atomic Energy Agency, “Analyses supporting conversion of research reactors from high enriched uranium fuel to low enriched uranium fuel: The case of the Miniature Neutron Source Reactors (IAEA-TECDOC-1844),” Vienna: IAEA. , pp. https://www-pub.iaea.org/MTCD/Publications/PDF/TE1844-Web.pdf, 2018.
International Atomic Energy Agency, “Practical aspects of operating a neutron activation analysis laboratory (IAEA-TECDOC-564),” Vienna: IAEA, pp. https://www-pub.iaea.org/MTCD/Publications/PDF/te_564_web.pdf, 1990.
Ibrahim, Y. V., Ofori, T. Y., & Jonah, S. A, “Neutron spectrum parameters in irradiation channels of the Nigeria Research Reactor-1 (NIRR-1),” Applied Radiation and Isotopes, pp. 95, 57–61. https://doi.org/10.1016/j.apradiso.2014.10.002, 2015.
Balogun, G. I., Jonah, S. A., & Umar, I. M., “Thermal neutron flux characterization in the irradiation channels of the Nigerian Research Reactor-1 (NIRR-1),” Annals of Nuclear Energy, vol. https://doi.org/10.1016/j.anucene.2009.06.008, pp. 36(9), 1377–1381. , 2009.
SAR, “Safety Analysis Reports of Nigerian Research Reactor-1,” Technical Report-CERT/NIRR-1/FSAR, 2012.
Mweetwa, B. M., Ampomah-Amoako, E., & Akaho, E. H. K., “Transient studies of Ghana Research Reactor-1 after nineteen (19) years of operation using PARET/ANL code,” World Journal of Nuclear Science and Technology, pp. 7(4), 223–231. https://doi.org/10.4236/wjnst.2017.74018, 2017.
Olander, D., “Nuclear fuels – Present and future.,” Journal of Nuclear Materials, p. https://doi.org/10.1016/j.jnucmat.2009.01.297, 2009.
Dawahra, S., Khattab, K., & Saba, G., “Reactivity temperature coefficients for the HEU and LEU fuel of the MNSR reactor,” Progress in Nuclear Energy, vol. https://doi.org/10.1016/j.pnucene.2015.11.012, pp. 88, 28–32, 2016.
Simon, J., Ibrahim, Y. V., Adeyemo, D. J., Garba, N. N., & Asuku, A., “Comparative analysis of core life-time for the NIRR-1 HEU and LEU cores,” Progress in Nuclear Energy, pp. 141, 103970, 2021.
Jonah, S. A., Umar, I. M., Oladipo, M. O. A., Balogun, G. I., & Adeyemo, D. J., “Standardization of NIRR-1 irradiation and counting facilities for instrumental neutron activation analysis,” Applied Radiation and Isotopes, 64(7), 818–822, p. https://doi.org/10.1016/j.apradiso.2006.01.012, 2006.
Jonah, S. A., Liaw, J. R., & Matos, J. E., “Monte Carlo simulation of core physics parameters of the Nigeria Research Reactor-1 (NIRR-1),” Annals of Nuclear Energy, 34(12), 953–957, p. https://doi.org/10.1016/j.anucene.2007.05.010, 2007.
International Atomic Energy Agency, “Countries move towards low enriched uranium to fuel their research reactors,” pp. IAEA News. https://www.iaea.org/newscenter/news/countries-move-towards-low-enriched-uranium-to-fuel-their-research-reactors, 2020, February 21.
Travelli, A., “Status report of the RERTR program (NEA/CRP report),” (Historical/primary overview of the RERTR program inception and early progress)., 1984.
Asuku, A., Ibrahim, Y. V., Jonah, S. A., Umar, S., & Simon, J., “Application of SCALE code for reactor physics analysis of the as-built Nigeria miniature neutron source reactor operating with low enriched uranium fuel,” Nuclear Engineering and Design, pp. 411, 112416, 2023.
Yasin, Z., “Comparative study of fuel burn-up and radioactive inventory for proliferation and proliferation resistant fuel lattices,” Annals of Nuclear Energy, 36(9), 1635–1638, p. https://doi.org/10.1016/j.anucene.2009.08.004, 2009.
Lamarsh, J. R., & Baratta, A. J., “Introduction to nuclear engineering (3rd ed.),” Prentice Hall., 2001.
Jonah, S. A., Ibrahim, Y. V., Ajuji, A. S., & Onimisi, M. Y., “The impact of HEU to LEU conversion of commercial MNSR: Determination of neutron spectrum parameters in irradiation channels of NIRR-1 using MCNP code,” Annals of Nuclear Energy, pp. 39(1), 15-17, 2012.
Askew, J. R., Fayers, F. J., & Kemshell, P. B., “A general description of the lattice code WIMS,” Journal of the British Nuclear Energy Society, pp. 5, 564–585, 1966.
Marcinkowska, Z. E., & Kulikowska, T. A., “Reliability of neutronics characteristics prediction for reactor MARIA core conversion to LEU fuel,” Annals of Nuclear Energy, 59, 92–99., p. https://doi.org/10.1016/j.anucene.2013.03.042, 2013.
Yahaya, B., Ahmed, Y. A., Balogun, G. I., & Agbo, S. A., “Estimating NIRR-1 burn-up and core life time expectancy using the codes WIMS and CITATION,” Results in physics, pp. 7, 596-603, 2017.
Dennis Solomon Balami, Y.V. Ibrahim, R. Nasiru, “Comparative Analysis of core life time for the NIRR-1 HEU and LEU Cores,” FUW Trends in Science & Technology Journal, pp. e-ISSN: 24085162; p-ISSN: 20485170, 2022.
Ibikunle, K., Sadiq, U., Ibrahim, Y. V., & Jonah, S. A., “MCNP Simulation of Physics Parameters of Dispersion Fuels for Conversion of NIRR-1 to LEU,” World Journal of Nuclear Science and Technology, pp. https://doi.org/10.4236/wjnst.2018.82003, 8(02), 23, 2018.
Khattab, K., & Khamis, I., “Calculation of the top beryllium shim plate worths for the Syrian miniature neutron source reactor,” Progress in Nuclear Energy, , pp. 44(1), 33-42., 2004.
Ahmed, Y. A., Balogun, G. I., Jonah, S. A., & Funtua, I. I., “The behavior of reactor power and flux resulting from changes in core-coolant temperature for a miniature neutron source reactor,” Annals of Nuclear Energy, pp. 35(12), 2417–2419. https://doi.org/10.1016/j.anucene.2008.08.005, 2008.
Odoi, H. C., “Efforts made for the conversion of Ghana’s MNSR to LEU (RERTR-35 conference paper),” Presented at the 35th International Meeting on Reduced Enrichment for Research and Test Reactors (RERTR), p. https://www.rertr.anl.gov/RERTR35/pdfs/S1P3_Paper_Odoi.pdf, 2014.

References

Khamis, I., & Jamal, M. H., “Prediction of the in-core power and the average core temperature using dose-rate measurements in the Syrian Miniature Neutron Source Reactor,” Journal of Radioanalytical and Nuclear Chemistry, pp. 269, 81–85. https://doi.org/10.1007/s10967-006-0233-3, 2006.

Osei, B., Baidoo, I. K., Odoi, H. C., Gasu, P. D., & Nyarko, B. J. B., “The low enriched uranium miniature neutron source reactor (LEU-MNSR) neutron spectrum characterization for k₀-INAA.,” Nuclear Instruments and Methods in Physics Research Section A, 1005, Article 165397, p. https://doi.org/10.1016/j.nima.2021.165397, 2021.

International Atomic Energy Agency, “Analyses supporting conversion of research reactors from high enriched uranium fuel to low enriched uranium fuel: The case of the Miniature Neutron Source Reactors (IAEA-TECDOC-1844),” Vienna: IAEA. , pp. https://www-pub.iaea.org/MTCD/Publications/PDF/TE1844-Web.pdf, 2018.

International Atomic Energy Agency, “Practical aspects of operating a neutron activation analysis laboratory (IAEA-TECDOC-564),” Vienna: IAEA, pp. https://www-pub.iaea.org/MTCD/Publications/PDF/te_564_web.pdf, 1990.

Ibrahim, Y. V., Ofori, T. Y., & Jonah, S. A, “Neutron spectrum parameters in irradiation channels of the Nigeria Research Reactor-1 (NIRR-1),” Applied Radiation and Isotopes, pp. 95, 57–61. https://doi.org/10.1016/j.apradiso.2014.10.002, 2015.

Balogun, G. I., Jonah, S. A., & Umar, I. M., “Thermal neutron flux characterization in the irradiation channels of the Nigerian Research Reactor-1 (NIRR-1),” Annals of Nuclear Energy, vol. https://doi.org/10.1016/j.anucene.2009.06.008, pp. 36(9), 1377–1381. , 2009.

SAR, “Safety Analysis Reports of Nigerian Research Reactor-1,” Technical Report-CERT/NIRR-1/FSAR, 2012.

Mweetwa, B. M., Ampomah-Amoako, E., & Akaho, E. H. K., “Transient studies of Ghana Research Reactor-1 after nineteen (19) years of operation using PARET/ANL code,” World Journal of Nuclear Science and Technology, pp. 7(4), 223–231. https://doi.org/10.4236/wjnst.2017.74018, 2017.

Olander, D., “Nuclear fuels – Present and future.,” Journal of Nuclear Materials, p. https://doi.org/10.1016/j.jnucmat.2009.01.297, 2009.

Dawahra, S., Khattab, K., & Saba, G., “Reactivity temperature coefficients for the HEU and LEU fuel of the MNSR reactor,” Progress in Nuclear Energy, vol. https://doi.org/10.1016/j.pnucene.2015.11.012, pp. 88, 28–32, 2016.

Simon, J., Ibrahim, Y. V., Adeyemo, D. J., Garba, N. N., & Asuku, A., “Comparative analysis of core life-time for the NIRR-1 HEU and LEU cores,” Progress in Nuclear Energy, pp. 141, 103970, 2021.

Jonah, S. A., Umar, I. M., Oladipo, M. O. A., Balogun, G. I., & Adeyemo, D. J., “Standardization of NIRR-1 irradiation and counting facilities for instrumental neutron activation analysis,” Applied Radiation and Isotopes, 64(7), 818–822, p. https://doi.org/10.1016/j.apradiso.2006.01.012, 2006.

Jonah, S. A., Liaw, J. R., & Matos, J. E., “Monte Carlo simulation of core physics parameters of the Nigeria Research Reactor-1 (NIRR-1),” Annals of Nuclear Energy, 34(12), 953–957, p. https://doi.org/10.1016/j.anucene.2007.05.010, 2007.

International Atomic Energy Agency, “Countries move towards low enriched uranium to fuel their research reactors,” pp. IAEA News. https://www.iaea.org/newscenter/news/countries-move-towards-low-enriched-uranium-to-fuel-their-research-reactors, 2020, February 21.

Travelli, A., “Status report of the RERTR program (NEA/CRP report),” (Historical/primary overview of the RERTR program inception and early progress)., 1984.

Asuku, A., Ibrahim, Y. V., Jonah, S. A., Umar, S., & Simon, J., “Application of SCALE code for reactor physics analysis of the as-built Nigeria miniature neutron source reactor operating with low enriched uranium fuel,” Nuclear Engineering and Design, pp. 411, 112416, 2023.

Yasin, Z., “Comparative study of fuel burn-up and radioactive inventory for proliferation and proliferation resistant fuel lattices,” Annals of Nuclear Energy, 36(9), 1635–1638, p. https://doi.org/10.1016/j.anucene.2009.08.004, 2009.

Lamarsh, J. R., & Baratta, A. J., “Introduction to nuclear engineering (3rd ed.),” Prentice Hall., 2001.

Jonah, S. A., Ibrahim, Y. V., Ajuji, A. S., & Onimisi, M. Y., “The impact of HEU to LEU conversion of commercial MNSR: Determination of neutron spectrum parameters in irradiation channels of NIRR-1 using MCNP code,” Annals of Nuclear Energy, pp. 39(1), 15-17, 2012.

Askew, J. R., Fayers, F. J., & Kemshell, P. B., “A general description of the lattice code WIMS,” Journal of the British Nuclear Energy Society, pp. 5, 564–585, 1966.

Marcinkowska, Z. E., & Kulikowska, T. A., “Reliability of neutronics characteristics prediction for reactor MARIA core conversion to LEU fuel,” Annals of Nuclear Energy, 59, 92–99., p. https://doi.org/10.1016/j.anucene.2013.03.042, 2013.

Yahaya, B., Ahmed, Y. A., Balogun, G. I., & Agbo, S. A., “Estimating NIRR-1 burn-up and core life time expectancy using the codes WIMS and CITATION,” Results in physics, pp. 7, 596-603, 2017.

Dennis Solomon Balami, Y.V. Ibrahim, R. Nasiru, “Comparative Analysis of core life time for the NIRR-1 HEU and LEU Cores,” FUW Trends in Science & Technology Journal, pp. e-ISSN: 24085162; p-ISSN: 20485170, 2022.

Ibikunle, K., Sadiq, U., Ibrahim, Y. V., & Jonah, S. A., “MCNP Simulation of Physics Parameters of Dispersion Fuels for Conversion of NIRR-1 to LEU,” World Journal of Nuclear Science and Technology, pp. https://doi.org/10.4236/wjnst.2018.82003, 8(02), 23, 2018.

Khattab, K., & Khamis, I., “Calculation of the top beryllium shim plate worths for the Syrian miniature neutron source reactor,” Progress in Nuclear Energy, , pp. 44(1), 33-42., 2004.

Ahmed, Y. A., Balogun, G. I., Jonah, S. A., & Funtua, I. I., “The behavior of reactor power and flux resulting from changes in core-coolant temperature for a miniature neutron source reactor,” Annals of Nuclear Energy, pp. 35(12), 2417–2419. https://doi.org/10.1016/j.anucene.2008.08.005, 2008.

Odoi, H. C., “Efforts made for the conversion of Ghana’s MNSR to LEU (RERTR-35 conference paper),” Presented at the 35th International Meeting on Reduced Enrichment for Research and Test Reactors (RERTR), p. https://www.rertr.anl.gov/RERTR35/pdfs/S1P3_Paper_Odoi.pdf, 2014.

Issue

Vol. 4 No. 4 (2025): November 2025 Issue

Neutronic evolution and isotopic assessment of NIRR-1 under alternative fuel enrichment configurations: a WIMS-ANL/REBUS-ANL study

Corresponding Author(s) : Dennis Solomon Balami

Abstract

Keywords

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