International Conference on Management of Spent Fuel from Nuclear Power Reactors: An Integrated Approach to the Back End of the Fuel Cycle

Criticality Safety and Burnup credit Analysis for MOX Fuel

Not scheduled

Board Room A (VIC)

POSTER

Speaker

Mr Moustafa aziz Ibrahim (head of nucleae safety department)

Description

Burnup credit is defined as the consideration of the reduction in reactivity associated with the use of the fuel in power reactors. Changes in the isotopic composition during fuel burnup which result in a reduced reactivity can be conveniently characterized by the reduction of the net fissile content, the build-up of actinides, the increase of the concentration of fission products, and the reduction of burnable absorber concentration where applicable. In practice, the conservative use of burnup credit requires consideration of all fissile isotopes, and allows consideration of any neutron absorbing isotopes for which properties and quantities are known with sufficient certainty[1]. The present research analyse the burn up and neutronic parameters of an assembly of MOX fuels. The discharge burnup is extended up to 70 GWd/T. In the assembly benchmark problems , important parameters for in core fuel management such as local power peaking factors and reactivity coefficients were included in the analysis. A PWR MOX fuel assembly is the same geometrical configuration as 17x17 type PWR fuel design. The assembly pitch 21.505 cm , fuel rod pitch 1.265 cm , pellet outer diameter 0.824 cm , cladding outer diameter 0.952 cm The average Pu fissile content is 11 % wt assuming 21 full effective power months operations using three batch loading strategy . The assembly is composed of low , middle and high Pu content fuel rods[2]. A typical compositions of low , medium and high Pu and the structure content can be found at reference [1]. The power density is 36.6 MW/TH. The density of water coolant at hot and cold conditions are given at reference [2]. MCNPX computer code package ( which is based on Monte Carlo method reference [3] ) is used to model the assembly and a three dimensional computer model has been designed to simulate the burn up of the assembly in a typical operation conditions of PWR reactor The results indicate burnup dependency of multiplication factor and local peaking factor, burnup dependency of fission rate distributions , Figure 2 illustrates the assembly multiplication factor versus fuel burn up (MWd/T)

Country/ int. organization

Egypt/Nuclear and Radiological Regulatory Authority