Examination and analysis of the water tightness of watertight doors in nuclear facilities (Water tightness of the watertight doors beyond design conditions)

A test on the water tightness performance of watertight doors was conducted to obtain knowledge on the fragility beyond design conditions. The performance test was conducted on three types of standard single-swinging watertight doors used for nuclear facilities. Assuming tsunami conditions during an earthquake, the water pressure and the shear strain caused by horizontal force were applied on the watertight door during the test. A shear strain of up to 4000 μ and a water pressure of up to 0.3 MPa were loaded step by step. The water that leaked from the door was measured at each step. The test results showed that the water pressure was related to the leakage quantities, but no clear relationship was observed between the shear strain and leakage quantities. Subsequently, a confirmation test was conducted focusing on the sealed portion of the watertight doors. The condition of the packing and the leakage of the seal during water pressure loading was observed. Consequently, we found that a large quantity of leakage under water pressure was caused by protrusion of the packing, and we inferred that leakage would occur by the same mechanism in actual watertight doors. Using the test results, we considered a method for evaluating the water tightness limit of the door. An analysis on the performance test was conducted using the evaluation method. The result showed that the water pressure that formed a leakage path in the analysis was consistent with the water pressure that caused a large quantity of leakage in the test.