Sensitivity studies of the TRIGA benchmark critical experiment

On the basis of critical benchmark experiments performed on the TRIGA Mark II reactor in Ljubljana, a benchmark model was proposed. To estimate effects of various uncertainties in the effective multiplication factor, extensive sensitivity studies were performed. Sensitivity studies included geometry sensitivity studies, where the effects of geometry simplifications and geometrical inaccuracies were investigated and material sensitivity studies, where effects of fuel composition of fresh and burned fuel as well as other materials were investigated. The MCNP Monte Carlo code and WIMSD2 and ORIGEN4 codes were used in these studies. Results showed that one of largest uncertainties of the effective multiplication factor arises from inaccurately known fresh fuel composition. For burned fuel, WIMS and ORIGEN2 gave similar results, which indicates that the calculated burned fuel composition may be used reliably. Another important uncertainty in the effective multiplication factor arises from fabrication tolerances and material composition of stainless steel cladding, of fuel elements.(author)