Radial and Axial Neutron Flux Profiling of Small Heterogeneous Reactor Cores by Redistribution of Fuel.

摘要

The lifetime of small heterogeneous reactor cores can be increased significantly by flattening the neutron flux radially and axially across the core region. After a reactor core is defined in terms of desired size, weight, and fuel loading, it is programmed into KENO, a three-dimensional multigroup Monte Carlo criticality computer program, which then calculates k(eff) (a measure of reactor criticality) and fission densities throughout the core. The results are graphically represented and attempts are then made to flatten the shapes both axially and radially by changing the position of fuel within the core. Two ways of profiling the radial fission density shape are considered: (1) holding the radii of rings of elements constant and varying the number of elements in each ring and (2) holding the number of elements in each ring constant and varying the radii of the rings. Axial flattening is accomplished by moving fuel pellets within a fuel rod. A more precise technique is obtained by varying the fuel concentration axially along the core length. For simplicity all fuel element rods are considered identical, and the fuel pellets within each rod are symmetrical along its length about the central cross section. The progressive alternations toward final neutron flux profiling are illustrated. This method is an tool for the design of small heterogeneous reactor systems where fuel inventory and system life are critical.