TRIGA Mark II criticality benchmark experiment with burned fuel

The experimental results of criticality benchmark experiments performed at the Jozef Stefan Institute TRIGA Mark II reactor are presented. The experim ents were performed with partly burned fuel in two compact and uniform core configurations in the same arrangements as were used in the fresh fuel cri ticality benchmark experiment performed in 1991. In the experiments, both c ore configurations contained only 12 wt% U-ZrH fuel with 20% enriched urani um. The first experimental core contained 43 fuel elements with average bur nup of 1.22 MWd or 2.8% U-235 burned. The last experimental core configurat ion was composed of 48 fuel elements with average burnup of 1.15 MWd or 2.6 % 235U burned. The experimental determination of k(eff) for both core confi gurations, one subcritical and one critical, are presented. Burnup for all fuel elements was calculated in two-dimensional four-group diffusion approx imation using the TRIGLAV code. The burnup of several fuel elements was mea sured also by the reactivity method.