Qualifications of class 1E cables for nuclear power generating stations

The cables of class 1E used for nuclear power stations have been strictly required to be flame retardant. IEEE Standard 383 has been instituted for such cables, which mainly requires the radiation resistance test and the pressure and temperature resistance test for the simulation of loss of coolant accident, and firing test with the cables hanged to vertical trays. Though these tests are slightly different for PWR, BWR and HTGR, the requirements are explained in detail. The firing test on vertical trays aims at, in short, the judgement on the degree of propagating fire and of self extinction when the fire source is removed. The judgement does not include the damage in outer sheaths and insulators. The recent trend indicates the transition of cross-linked polyethylene and ethylene propylene rubber to flame-retardant polyethylene and ethylene propylene rubber in insulator materials, and the change of polyvinyl chloride to low-hydrochloric acid vinyl and glass fibre or asbestos braid to chloroprene braid in sheath materials. Intention to employ the flame retardant materials for supports and holding tapes is also presented. Meanwhile, the trend is noticeable that the content of corrosive gases in combustion gas is checked or smoke generation in firing is tested. (Wakatsuki, Y.)