Evaluation of Wash-down Debris Transport during LOCA for Recirculation Sump Performance of OPR-1000 Plant

Currently, for the resolution of GSI (General Safety Issue)-191, ECCS (Emergency Core Cooling System) strainer clogging, many countries are making much effort. Among them, the report, NEI 04-07 of Nuclear Energy Institute is one of noticeable methodologies. According to the baseline methodology of NEI 04-07, it proposed methodologies on break selection, debris generation, latent debris, debris transport, and head loss. As to the debris transport evaluation, it used a debris transport chart which is composed of blow-down transport, wash-down transport, and pool fill-up transport. According to this methodology, 100% transport is assumed for the wash-down transport. In the appendix of safety evaluation report (SER) to NEI 04-07 of the USNRC (United State Nuclear Regulatory Committee), USNRC has quantitatively evaluated the wash-down transport and concluded the recommended that wash-down transport fraction in NEI 04-07 was sufficiently conservative. However, the methodology of USNRC on the wash-down transport seems very complicated and includes so many uncertainties depending on the containment shape and engineering judgment in the evaluation steps. Due to the dependency on plant type, there is a limitation to generalize the conclusion on wash-down transport of USNRC, when the considered plant is different from the volunteer plant or the same type plant in SER. This study introduced a new wash-down transport analysis with the proposed free over-fall flow based on the containment spray flow, condensate water flow, and floor flow characteristics including floor configuration. In addition, a wash-down transport analysis has also conducted for Ulchin 3 and 4 and is also presented