Study of thermal hydraulic behaviors during steam generator multiple tube rupture events in PWR

Since the occurrence probability of multiple steam generator tube rupture (MSGTR) in PWR is low, analytical or experimental investigation for termination of such accidents is not performed explicitly. Therefore, thermal-hydraulic analysis of the plant behavior under the MSGTR (10 and 50 tubes) in all loops or in a single loop with station black out (SBO) were made in this study with use of the code RETRAN3D, and investigations for accident management (AM) of such accidents were made in order to contribute to continuous risk reduction efforts in the future. This study indicated that the water supply function to the SG is quite important for coping with accidents involving MSGTR accompanied by SBO to prevent core damage. Further, if the auxiliary feed water system loses its function, the time to reach the core exposure is predicted to be reduced by 1 hour or more in a MSGTR case as compared to a single-tube SGTR case. Therefore, in order to prevent the core damage during MSGTR, it is desirable to have alternative water injection equipment operable to quickly replace auxiliary feed water system if it fails and to increase the reliability of the auxiliary feed water system. (author)