Influence of Oxygen on Insulation Performance of Safety-related Low-voltage Cables for Nuclear Power Plants under Severe Accident Conditions

Abstract

Some safety-related low-voltage cables used in nuclear power plants are required to maintain the insulation performance even during severe accidents. It is not clear whether oxygen affects the insulation performance of the cable in the steam exposure during a severe accident. In this study, we investigated the influence of oxygen on the insulation performance in an assumed severe accident condition for flame-retardant ethylene propylene diene rubber insulation (FR-EPDM) cables used as safety-related cables. Cables pre-aged by accelerated aging and non-treated ones were used as samples. The following points were found. When oxygen is present in water vapor, the oxygen concentration decreases during the exposure since oxygen is consumed by the oxidation of insulators and other materials. Whether or not the cable was subjected to aging does not alter the insulation resistance of the cable significantly under the assumed severe accident condition. The oxygen contained in water vapor affects the insulation resistance of the cable scarcely under the condition.