Superplasticizers degradation in a deep geological disposal for nuclear waste cementitious matrix an analytical investigation

Abstract : The conditioning by solidification in A cementitious matrix of radioactive waste coming from French nuclear industries is a widely used solution. For safety reasons it is important to evaluate and control the production of hazard flammable gas such as dihydrogen. Yet water in cementitious matrices ex-posed to ionizing radiation emitted by waste (radiolysis phenomenon) can contribute significantly to dihydrogen formation. The main objective of the Matrice project (Materials resistant to irradiation based on cement) with Leon Grosse, Vicat and CEA, Andra (The French National Radioactive Waste Management Agency) as partners is to optimize the formulations of cementitious materials in order to limit dihydrogen emissions to an acceptable level while optimizing the conditioning of highly radioac-tive waste. Most of investigated approaches require the addition of superplasticizers (SPs), which are water-reducing agents. Thus, it is important to study degradation of these compounds in the nuclear waste context. Radi-olysis and/or alkaline conditions can potentially induce formation of small organic molecules that can form stable complexes with radionuclides or affect radionuclide mobility. The objective of this study is to characterize the degradation molecules of two types of SPs a polyaromatic sulphonate (radioresistant but with poor plasticizing properties) and a polyether based superplasticizer (less radi-oresistant but with excellent plasticizing properties).