Power peakings in mixed TRIGA cores

Power distribution in the reactor core is normally calculated by the diffusion codes (e.g. TRIGLAV package) in 2-D approximation. Diffusion codes normally treat the fuel rods and surrounding water as homogeneous regions called unit cells. Modern Monte-Carlo codes (e.g. MCNP) allow calculation of the power density distribution in 3-D geometry assuming detailed geometry without unit-cell homogenization. The power density distribution (and its maximum value - the peaking) can be calculated point-wise with the resolution of approximately 1 mm. Results of the detailed power density distribution calculated by MCNP are presented for 250 kW TRIGA Mark II reactor, assuming various realistic and hypothetical core loading patterns with focus on the mixed cores. Combinations of 8.5 w/o, 12 w/o and 20 w/o low enriched (20%) TRIGA fuel elements are systematically treated in the mixed cores. (author)