The effect of code user and Boundary conditions on Relap calculations of MTR research reactor transient scenario

The safety eval u a tion of nu clear power and re search re ac tors is a very im por tant step be - fore their con struc tion and dur ing their op er a tion. This eval u a tion based on the best es - timate calculations requires qualified codes, qualified users, and qualified nodalizations. The ef fect of code us ers on the RELAP5 re sults dur ing the anal y sis of loss of flow tran - sient in MTR re search re ac tors is pre sented in this pa per. To clar ify this ef fect, two nodalizations for re search re ac tor dif fer ent in the sim u la tion of the open wa ter sur face bound ary con di tions of the re ac tor pool have been used. Very dif fer ent re sults are ob - tained with few choices for code us ers. The core nat u ral cir cu la tion flow with the be gin - ning of core boil ing does n’t stop but in creases. The in creas ing in the nat u ral cir cu la tion flow shifts out the boil ing from the core and the clad tem per a ture de creases be low the local saturation temperature.