SARA Project. Reflooding calculations for Oskarshamn 3 BWR with SCDAP/RELAP5

Calculations have been carried out for postulated severe accident scenarios including late reflooding of an overheated core for the Swedish Oskarshamn 3 BWR by means of the severe accident computer code SCDAP/RELAP5. The transients were initiated by assumption of total loss of power so that all coolant systems became unavailable. The reactor core is then gradually uncovered and overheated, which leads to degradation of the core beginning with melting of control rods. Before fuel damage and relocation takes place, it was assumed that the power supply is restored. Thus the various emergency cooling systems are again available and facilitates reflooding of an overheated and partly control rod free core. The aim of the calculations is to determine the core state and initial conditions prior to reflooding, as well as the consequences of the recooling with respect to further core damage. No reactivity effects are considered here. The results from SCDAP/RELAP5 will then be input to following recriticality calculations with the SIMULATE-3K code, which is the ultimate goal of Task 1 in the SARA project. The Oskarshamn 3 plant was chosen since existing data adapted to the SIMULATE-3 code were available which facilitated simulation of realistic operating conditions for a full size BWR plant. Present work constitutes a part of Task 1 of the SARA project, which is funded by the Swedish Nuclear Power Inspectorate, and the European Commission within the EC fourth Framework Programme on Nuclear Fission Safety