Temperature and LET effects on radiation-induced modifications in non-perfect polyethylenes

Abstract

Regarding the nuclear safety, the potential accumulation of explosive gases during storage, transport and final disposal of Intermediate Level Long Lived Wastes (IL-LLW) has to be well understood and precisely evaluated. In this paper, we have investigated the Linear Energy Transfer (LET) effect that takes into account the different emitters present in the packages, but also the temperature impact in transport safety cases. We have focused our study on polyethylene, as this polymer presents one of the highest hydrogen radiation chemical yield (G0(H2)), and because of the explosive and inflammable nature of this gas. Chemical defects included in the polymer in the form of carbonyl (C=O) and vinyl (C=C) groups were explored. Depending on the atmosphere of irradiation, they are the main defects formed in polyethylene under irradiation and they are known to be effective energy and radical scavengers. Characterization of the chemical structure of pristine materials has been done. Hydrogen radiation chemical yields were quantified after polymers irradiation. Additionally, the carbon monoxide release was measured for polyethylenes with C=O moieties. Whatever the type of double bonds present in the polymer and whatever the irradiation conditions, hydrogen emission decreases compared to neat materials. Double bonds are effective scavenging groups to which energy is transferred regardless the irradiation nature. Underlying phenomena are explained in this work.