The nuclear industry generates radioactive waste posing long-term risks to both human health and the environment. The accepted disposal depth of different waste fractions, depends on their activity and the half lives of their radionuclides. The disposal of spent nuclear fuel (SNF), containing long lived actinides as well as high activity fission products entails geological disposal, at hundreds to thousands of meters below surface. The IAEC is evaluating the feasibility of SNF disposal in the Yamin plain within the Ghareb formation.

This study focused on impact of gamma irradiation on Type-IIS kerogen bearing rocks from the Ghareb formation. The rocks total organic content is up to 15wt%, along with total sulfur content (i.e. pyrite, gypsum and organic sulfur) of up to 4wt%. Both outcrop and borehole rocks were irradiated.

Gamma irradiation of kerogen bearing rocks causes gas formation, along with alterations in residual rock composition and bitumen content. The increase in total gamma doses from 107 to 108 rad, increases the gas amount, while keeping similar gas ratios. The two main gases generated were hydrogen and carbon dioxide, while other gases like carbon monoxide and short chain hydrocarbons were order of magnitude lower in concentrations.

The gas composition formed via kerogen radiolysis is significantly different from pyrolysis gas composition across thermal maturation stages. Notably, unlike pyrolysis, radiolysis does not lead to significant H2S generation. Additionally, the observed gas compositions diverge from thermodynamic predictions based on bond-strength considerations, breaking primarily C-H bonds while retaining C-S bonds. The composition of the gas and the total amount measured (up to 546 mlGas/kgRock) in the experiments can be used to evaluate the potential risk of radioactive waste disposal in the Ghareb formation.