Scaling capabilities of thermalhydraulic system codes

Natural circulation experiments available from differently scaled integral test facilities simulating PWR plants, are the basis of the present work. Relap5/Mod2 code calculations are performed to reproduce the measured scenarios and to predict the evolution of the same phenomena in a real plant. Code results are compared with relevant experimental data. An attempt is made to evaluate the variation of the prediction accuracy when the dimensions of the involved facilities are varied; an estimation of the uncertainty in the prediction of the plant behaviour is reported. (author)