INFLUENCE OF FUEL BUNDLE LOADING ERRORS ON THE SUBCRITICALITY DURING REFUELING CAMPAIGNS FOR THE PRESENT BWR CORES OF KRB-II

On the basis of real fuel assembly inventories as they are presently a vailable in KRB-II, the influence of fuel bundle loading errors on the subcriticality during refueling campaigns was investigated with the c alculational methods of the incore fuel management. To this, control r od cells which show the least shut-down reactivity were considered and less reactive fuel assemblies were successively exchanged with fuel a ssemblies of highest possible reactivity from distant core regions. Th e results show that the total shut-down reactivity is only reduced by a comparatively small amount. The stuck rod shut-down reactivity, on t he other hand, is strongly diminished with increasing number of locall y concentrated mislocated fuel assemblies of highest possible reactivi ty. Thus, unintentional criticality cannot be reached during refueling campaigns with all control rods inserted. In conjunction with the del iberate withdrawal of one control rod, two or three mislocated fuel as semblies can cause criticality, depending on the absolute value of the realized stuck rod shut-down reactivity. (C) 1997 Elsevier Science S. A.