Effect of pre-aging on flame retardancy of safety-related low voltage cables in nuclear power plants

Cables used in nuclear power plants are required to be flame retardant as a measure of fire protection. Cables with polymer insulation, such as silicone rubber (SiR) insulated cables, flame-retardant ethylene propylene diene rubber (FR-EPDM) insulated cables and flame-retardant cross-linked polyethylene (FR-XLPE) insulated cables, are commonly used as safety-related low voltage cables in nuclear power plants. This paper describes results of flame-propagation tests conducted in accordance with IEEE Std 383-1974 and IEEE Std 1202-2006, and oxygen index measurement tests conducted in accordance with JIS K 7201-2:2007, which were carried out to investigate the effect of pre-aging on flame retardancy of the cables. The samples employed in the tests were un-aged cables and pre-aged cables by accelerated simultaneous thermal and radiation aging to simulate aging in their service life under normal operating environment in nuclear power plants. In addition, decomposition temperatures were measured by thermogravimetry for pre-aged insulation samples of SiR, FR-EPDM and FR-XLPE to evaluate the results of flame-propagation tests and oxygen index measurement tests. As a result of flame-propagation tests and oxygen index measurement tests, flame retardancy of the cables was not degraded by the pre-aging process of this study. From the thermogravimetry, the significant decrease in decomposition temperature due to pre-aging was not observed. © 2017 The Institute of Electrical Engineers of Japan.