FUNDAMENTAL BURN-UP MODES OF RADIAL FUEL SHUFFLING

This paper is a theoretical study of the mechanism of a radial standing wave, which can be applied in the so-called traveling wave reactor (TWR). One dimensional cylindrical core geometry is considered and the fuel is assumed to drift radially, which corresponds to a radial fuel shuffling scheme in practice. The key purpose of this study is to look for a standing wave solution under both conditions of inward and outward fuel drifting motions. A one-group diffusion equation coupled with burn-up equations is set up, as done in author's previous papers for axial drifting waves, where the burn-up solution were obtained as functions of neutron fluence, since the natural radioactive processes are neglected there. The uranium-plutonium (U-Pu) conversion cycle with pure 238 U as fresh fuel is considered under conditions of a typical sodium cooled fast reactor with UOX fuel loaded. The 1-D cylindrical coordinate problem is not analytically solvable like in the 1D plane coordinate one. But standing wave solutions can be obtained here numerically for certain eigenvalues keff. Two representative examples are shown for the inward and outward fuel drifting motions, respectively. Besides several other discussions, it can be concluded that the inward fuel drifting utilizes the burning/breeding process better than the outward one, where the former keff is higher than the latter one.