Radiolytic degradation of high density polyethylene used for storage of water treatment waste from Fukushima Daiichi NPS

Barr, L.; Idesaki, Akira*; Taguchi, Mitsumasa*; Yamaguchi, Tetsuji 

Water treatment waste from the ALPS system at Fukushima Daiichi Nuclear Power Station is stored in high density polyethylene containers. During the storage period radiation leads to degradation of the polymer properties. This study investigated the extent and rate of polymer degradation induced by radiation. The irradiation conditions were altered to represent the storage environment and the composition of the waste produced by the ALPS system. Increasing the irradiation temperature changes the rate of diffusion of reactive species and leads to greater oxidative degradation of the polymer. More aromatic antioxidants provide greater protection against radiation compared with aliphatic additives. Irradiation in water rather than air limits the availability of oxygen and reduces the degree of oxidative degradation. Increasing the pH of the aqueous phase results in an increase in tensile strength of the polymer than irradiation in deionised water, which is attributed to the increased formation of double bonds and crosslinks following hydrogen extraction by the reactive water radiolysis products. The results of the study show the importance of the specific environment and conditions of irradiation and highlight the different degradation pathways that containers will be subjected to throughout their operational lifetime.