DEPLETION ANALYSES OF LOW ENRICHED URANIUM FUELS FOR THE NIGERIA RESEARCH REACTOR-1
DEPLETION ANALYSES OF LOW ENRICHED URANIUM FUELS FOR THE NIGERIA RESEARCH REACTOR-1
No Thumbnail Available
Date
2023-05
Authors
ASUKU, ABDULSAMAD
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The use of advanced, accident-tolerant, Low Enriched Uranium (LEU) fuel types is one approach to improving the safety, security and fuel cycle performance of nuclear reactors. In spite of the acceptability of UO2 fuel, uranium-silicide and uranium-molybdenum fuels are being proposed in order to increases the accident tolerance of nuclear reactor cores. Although the as-built fuel of the Nigeria Research Reactor-1 (IRR-1) LEU core is 13% enriched UO2 clad in Zircalloy, previous research have demonstrated that specific uranium-silicide and uranium-molybdenum such as 19.75% enriched U3Si2, U3Si, and U9Mo dispersion LEU fuels clad in aluminum also present comparable neutronic characteristics within recommended safety limit for the NIRR-1 Miniature Neutron Source Reactor (MNSR). However, analysis of the depletion characteristics of the as-built UO2 core as well as the investigated fuel alternates are yet to be conducted as these data are important for optimization of safety, security, fuel management and decommissioning plan a well as conversion of other MNSRs from High Enriched Uranium (HEU) to LEU. Consequently, the SCALE 6.2.3 code system was used to develop new models of the NIRR-1 and perform criticality calculations and depletion analysis for the as-built UO2, U3Si2-Al, U3Si-Al, and U9Mo-Al LEU cores in the present study, using the HEU core as a benchmark. The results showed that the three Dimensional (3D) KENO-VI estimates of the Clean Cold Core Excess Reactivity (CCCER of the core are in good in good agreement with measured data with a bias of less than 4 %. Consequently, the 3D KENO-VI module of the SCALE 6.2.3 code can be used for criticality safety calculations of MNSRs and similar reactors. The neutron flux distribution data indicated a reduction in the magnitude of the average thermal neutron flux in the alternative LEU cores in the range of 7 – 10 % when compared to that of the HEU core. This implies that the thermal power of the U3Si2-Al, U3Si-Al, and U9Mo-Al LEU cores would have to be raised by their corresponding magnitude of percentage flux reduction to match the flux of the HEU core. However, the thermal neutron flux in the as-built LEU-UO2 core is essentially the same with that of the HEU core. Hence, the as-built LEU core will not compromise NIRR-1 utilization for thermal Neutron Activation Analysis. Although the results show that both the HEU and the LEU cores have a burnup of less than 1 % at the End of Cycle of 216 Effective Full Power Days (EFPD), the Uranium-Silicide fuels have a higher burnup when compared to the UO2 fuel. The depletion rates were estimated to be – 0.00120 mk/h, - 0.00124 mk/h, - 0.00123 mk/h and – 0.00105 mk/h for the as-built UO2, U3Si2, U3Si and U-9Mo LEU cores respectively. In all cases, the LEU cores depleted at a slower rate than the HEU core implying an improvement in the fuel economy of the cores compared to the HEU core. The core lifetimes after addition of top Beryllium Shim plates when the reactor is operated continuously for 216 EFPD were estimated to be 38.62, 37.34, 37.53, and 43.78 years for the as-built UO2, U3Si2, U3S i and U-9Mo LEU cores respectively. These estimated core lifetimes are 26% higher than that of the HEU. Consequently, the LEU cores show better fuel cycle performance and demonstrated an advantage of extended core lifetime for utilization in Neutron Activation Analysis. These results are useful in the development of a decommissioning plan for the NIRR-1 and fuel management of accident-tolerant alternative fuels to optimize their performance as promising alternatives to the UO2 fuel.
Description
A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILMENT FOR THE AWARD OF DOCTOR OF PHILOSOPHY IN NUCLEAR PHYSICS
DEPARTMENT OF PHYSICS, FACULTY OF PHYSICAL SCIENCE, AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA