Changes in Isotopic Composition of the Fuel Material in the Core of the Nigeria Research Reactor-1 (NIRR-1)

During reactor operation, isotopes in the fuel material are consumed for fission reaction while others are converted to new isotopes in addition to fission products produced in the fission process. The Nigeria Research Reactor-1 (NIRR-1) has been in operation since 2004 till date and the expected changes in isotopic composition of the fuel material during this period of operation have been calculated. The result from the depletion/burnup calculations shows that the present Nigeria Research Reactor (NIRR-1) has a burnup of less than 1% in approximately 10 years of its operation. The conversion ratio of the system is also less than one as the average number of fissile atoms produced in the system is very much less than the fissile atoms consumed in the fuel. One of the two important saturating fission products 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 effective multiplication factor of the system decrease very rapidly within the first few days of its operation and continue to decrease gradually with time.