After the earthquake and tsunami that severely damaged the nuclear reactor at Fukushima, Japan, the importance of the resistance of materials, particularly during loss-of-coolant accidents (LOCA), is receiving increasing attention. Seal leakage has always been a safety concern, and seal maintenance and replacement are costly and time consuming for current-generation plants. However, even with the most advanced designs, it is impossible to completely eliminate seals from the detail design and equipment. Postulated design basis accidents (DBA) consider seals consisting of organic materials to be components that could be seriously damaged. In particular, rubber gaskets are considered to be the weakest. Consequently, it is extremely important to understand how rubber deteriorates under DBA conditions.

When selecting a rubber compound, it is very important to consider both the characteristics required for each specification and the deterioration factors under normal plant operation and DBA conditions. However, the selection of deterioration characteristics has not been possible owing to a lack of precise and sufficient data.

In our previous study [3,4], we described compression set tests, swelling tests, and FTIR analysis, which indicated that the chemical structure of both ethylene propylene diene monomer (EPDM) and silicone rubber might be destroyed by radiation and that the crosslinking of elastomers by radiation might progress simultaneously. In fact, EPDM compounds exhibited good compression set test results after radiation exposure, whereas silicone rubber compounds did not.

In the current study, we evaluate the changes to the characteristics of rubber under more severe conditions, specifically when gamma ray exposure is over 3 MGy and exposure time is over 400 h. From the result of the experiments, we expect to determine the types of rubber that are most suitable under operational and DBA conditions.

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