Power peakings in mixed TRIGA cores

Modern Monte–Carlo codes (e.g. MCNP) allow calculation of the power density distribution in 3D 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, 20 w/o and 30 w/o low-enriched (20%) fresh TRIGA fuel rods are systematically treated in the mixed cores. The power peaking factor value and position strongly depends on the core configuration. Power peakings are usually found in fuel rods with higher uranium content especially if they are inserted near the core centre. The results are conservative and can be applied in planning realistic mixed core-loading patterns.