Effect of relative humidity and temperature on PVC degradation under gamma irradiation: Evolution of HCl production Yields

The separate and combined effects of the relative humidity and temperature were investigated on the HCl production yields arising from two types of PVC subjected to gamma irradiation (pure PVC and PVC formulated with plasticizing additives). The test procedure developed included experiments performed at different dose rates (400 Gy h−1 and 4 kGy h−1), temperatures (room temperature and 70 °C) and relative humidity values (<10%, 70−75%, and 100%), for irradiation doses ranging from 0.1 to 4 MGy. These operating conditions are representative of applications in a nuclear environment. For the plasticized PVC at low dose rates, raising the temperature increases the HCl production by a factor of about 1.3, with either low or high relative humidity. For pure PVC, depending on the humidity and dose rate, G(HCl) varies differently with the temperature: at low humidity and low dose rates, G(HCl) increases by a factor of 1.7 for a 45 °C temperature increase; at high humidity, the same temperature increase does not result in a significant increase of G(HCl). The influence of the relative humidity on HCl production has not been clearly identified and interpreted. The relative humidity appears to be a factor limiting the effects of temperature on the formation of HCl from pure PVC at high dose rates. The G values remain constant and even diminish under some experimental conditions. For plasticized PVC, the relative humidity has no influence on the HCl production yields.