Spectroscopic Investigation of the Formation of Radiolysis by-Products by 13/9 Mev Linear Accelerator of Electrons (LAE) in Salt Solutions.

In the near-field chemistry of a salt repository, the radiolytically-induced redox reactions in concentrated saline solution are of particular importance because the radiolysis of saline solutions results in oxidizing chlorine-containing species, which may oxidize actinide species to higher oxidation states. If the brines are irradiated, the solutions containing radiolytic species such as hypochlorite, hypochlorous acid or hydrogen peroxide, their pH and Eh may be altered. The oxidation and complexation states of actinides, which might be present in the salt brine, will change thus influencing their speciation and consequently their mobility. Furthermore, radiolytically formed oxidizing species such as ClO- or H2O2 may enhance the corrosion of the canister material. Therefore, radiation effects on salt brines must be integrated into the database, which described the chemical processes near a disposal site. Investigations in that context usually focus on the radiation chemistry of solid NaCl however our focus is on the radiolytic products, which are formed when salt brines are irradiated by a 10 MeV linear accelerator of electrons (LAE). We attempt to quantify the irradiation-induced formation of typical radiolysis by-products such as the hypochlorite ion (OCl-) by using a 13/9 MeV LAE with doses between 120 KGy to 216 KGy while monitoring the pH of the brine solution

Simulation of radiolysis in the near field of a nuclear repository and the spectrophotometric investigation of the formation of radiolysis by-products by applying high energy beam-like experiments

In the event of inundation of a nuclear waste repository located in a geological salt formation, chloride brines in contact with nuclear waste will be exposed to different kind of radiation depending on waste-form conditions. Ionizing radiations, however, have the ability to significantly affect the groundwater chemistry of the brines through the formation of free radicals, ionic- and molecular species; among them the typical byproducts of a-radiolysis: hypochlorite (OC1-) and hypochlorous acid (HOCl). In the absence of effects which arc supposed to dominate the redox conditions in the repository (corrosion of metals, microbial activity) the presence of OC1- is known to increase the redox potential of the brines and further to influence the stability of actinide waste-forms by accelerating their dissolution arid - most importantly - to oxidize actinides to their higlier oxidation states, whicli are gcncrally the most soluble ones. We are presenting a new approach to determine the radiation-induced formation rates of hypochlorite and hypochlorous acid as a first step to assess long-term steady-state repository conditions. To ovt:rcome the serious constraints of conventional radiocheinical work with GBq activity levels, we are simulating a-irradiation of chloride brines by the adaptation of ion-beam-line experiments. Therefore, we irradiate liquid chloride brine targets with 5 MeV protons, and 5 MeV helium ions. The irradiation-induced formation rates of OCX- and HOC1 were determined by UV-Vis spectrophotometry. To give an example, the measured G values for the HOCl formation in 3.7 M MgC12.6H20, pW 4.42, irradiated by 5 MeV protons was determined to be 0.0374 {+-} 0.0022, and 0.0536 {+-} 49 by irradiating with 5 MeV helium. The distinguished ltnowledge about the radiation-induced production of oxo-chloride species is the first step towards the assumption of their steady-state concentrations in the irradiation field of the repository