Study of power end peaking for NRU loop fuel calculations

End-flux peaking effects in fuel bundles irradiated in the NRU (National Research Universal reactor) loop test sections are investigated using MCNP (the Monte Carlo N-Particle transport code). The current method for calculating powers in the loop bundles only allows for an integrated end-power-peaking correction. In this paper, an element axial power ratio (APR), determined as the 3D MCNP-calculated fission power at an element axial location relative to the 2D WIMS (Winfrith Improved Multigroup Scheme lattice transport code) power, is introduced. This may be used, as supplementary information to BURFEL (the Burnup of Fuel Elements code and database system), to obtain the accurate axial distributions of element powers, thereby, enabling the quantification of those element-end power increases that are important for design of bundles and safety analysis. (author)