Investigation into the toxicity of combustion products for CR/EPR cables based on aging period

The toxicity of combustion product gas of CR/EPR cables, which are widely used in nuclear power plants, has been investigated according to the aging period. The cable specimens were prepared by thermal acceleration aging method, from non-aged to 40-year-old cables at spans of 10 years. The cable sheath and insulation materials were tested separately. The test was conducted in accordance with the Naval Engineering Standard 713 standard code, which measures the amount of 13 exhaust toxic gases when 1 gram of the test specimen is burnt. The toxicity index and the amount of emission gases were varied irregularly with respect to the aging period, and the reason for this result could not be clearly explained due to the lack of information on cable material. However, the reason could be qualitatively estimated to have two conflicting effects: (1) Reduced flame retardant performance as the devolatilization process proceeded over time, and (2) the enhanced stabilization of double bonds between carbon compounds and flame retardant elements, such as chlorine or bromine, as the cable is aged. The toxicity of the accelerated aging period of 20 years was much higher than that of non-aged cables, which signifies increased probability of fire risks of aged cables from the viewpoint of toxicity. Furthermore, when comparing the adjusted toxicity index calculated without CO, CO₂, and NO_x emission, it can be clearly determined that the average toxicity index of aged cables is higher than that of non-aged cables. Thus, in conclusion, human hazardousness of a cable fire increases from the viewpoint of toxicity of emission gases as it deteriorates, so safety regulations or maintenance guides for old nuclear power plants should be reinforced considering this toxicity variation. The results obtained from this study can be used to improve the reliability of operator manual actions for safety-shutdown and fire-suppression activities and to provide basic information for studies on fire suppression.