The buildup of fission products in the 19.75% UO₂ core for the Nigeria Research Reactor-1

Abstract

In this work, the VENTURE PC coding system was used to perform the burnup/depletion analysis of the Nigeria Research Reactor-1 (NIRR-1) for the
proposed Low Enriched Uranium (LEU) core in order to determine the buildup of fission product in the core of the reactor. The LEU fuel selected for the core conversion studies in this work is fuel enriched to 19.75% U-235. The fuel geometry in the LEU core is exactly the same with that of the present HEU (90.2% U-235) system. A number of short MATLAB codes for pre and Post processing of the results from the main codes was also used. The two important saturating fission products say Xe-135 and Sm-149 rose to the equilibrium level within the first few days of NIRR-1 operation, while the other never buildup to the equilibrium concentration in the core of the system. The lumped fission products continue to buildup linearly with time from the beginning of life till the end of fuel cycle. The result obtained shows that the concentration of Sm-149 as a fission product built up in the core of the NIRR-1 can never get to equilibrium level in the core of this reactor since the half-life of the NIRR-1 is about 10 years. Similarly, it was also found that the lumped fission products continue to grow exponentially with time throughout the life cycle of the NIRR-1 system.