Development of TACOS code for loss of flow accident analysis of SCWR with mixed spectrum core

TACOS(Transient Analysis Code Of SCWR) code has been developed to analyze the safety characteristics of SCWR-M for present work. In the code TACOS, the single channel model, point kinetic model, heat transfer model and control system model were used. Four different heat transfer correlations were applied to the steady state calculation of SCWR with mixed spectrum core (SCWR-M). After the comparison of four correlations, Bishop Correlation was selected for transient analysis.Using TACOS code, preliminary analysis of loss of flow accident (LOFA) for SCWR-M has been performed. Partial loss of flow and total loss of flow accident were discussed respectively. For the total loss of flow, the results indicate that the maximum cladding surface temperature (MCST) in the thermal zone was much higher than that in the fast zone. A “special flow mode” similar to natural circulation between coolant channels and moderator channels in the thermal zone has been found. The co-current flow mode design in the thermal zone would cause disadvantage to safety performance because it has a negative effect on the flow rate of coolant channels after the startup of Auxiliary Feedwater System (AFS). The sensitivity analyses of pump coastdown time and AFS flow rate for total loss of flow accident were also carried out.

► A safety analysis code for SCWR-M has been developed.
► MCST in thermal zone is much higher than that in fast zone.
► A “special flow mode” similar to natural circulation has been found.
► The co-current flow mode design in the thermal zone causes disadvantage.
► The larger flow rate of the AFS eliminates danger of cladding.