Abstract: The block of containment sump strainer is one of the primary safety concerns. A regulatory guide of RG1.82 WATER SOURCES FOR LONG-TERM RECIRCULATION COOLING FOLLOWING A LOSS-OF-COOLANT ACCIDENT was published by US NRC. The chemical element in generated debris will be dissolved in the containment spray and sump fluid after LOCA, and those chemical elements will precipitate following the decreasing of temperature of the sump fluid. The precipitates will deposite on the debris bed on the sump strainer surface to worsen the performance of sump strainer’s pressure loss. These phenomena called chemical effect. An analysis methodology related to chemical effect called WCAP is introduced in this paper.