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 solutions

Spectroscopic investigation of the formation of hypochlorite, radiolysis by-product in 5 M NaCI featuring high-energy proton beam line experiments.

Because geological salt formations are considered possible sites for radioactive waste disposal, plausible inundation scenario of salt repository will allow chloride brines to be formed, which consequently will be exposed to radiation from the waste. Key radioelements in Intermediate Level Waste (ILW),H igh Level Waste (HLW) or TRU waste have been found to be plutonium, americium, neptunium, uranium, and technetium. Therefore, the effect of radiolysis on high-saline brine under simulated repository conditions are of particular importance because it results in oxidizing chlorine-containing species, such as hypochlorite (OC1-), and hypochlorous acid (HOCI), which may oxidize actinide species to higher oxidation states. Meaningful predictions of long-term redox conditions in a nuclear repository strongly rely on estimations of G-values of the irradiation-induced formation of the oxidizers OC1- and HOCI. G-values not only depend on the total absorbed doses over the relevant timeframe, but also on the kind of irradiation involved. In fact, the G-values of hypochlorite produced by {alpha}-, {beta}-, {gamma}-, or neutron irradiation differ by an order of magnitude, depending on different LET cross-sections. To overcome the serious constrains and obstacles of conventional radiochemical work within GBq/L activity levels, we are going to simulate {alpha}-irradiation of chloride brines by the adaptation of beam-line experiments. Our long-term goal is to demonstrate how the main oxidizing chloride species such as hypochlorite caused by radiolysis may affect the overall behavior of actinides under salt repository conditions. This paper describes our first steps towards the production, the identification and the determination of these oxidizing species by beam line experiments

SOLVENT EXTRACTION OF {sup 99}Tc FROM RADIOACTIVE INTERMEDIATE LIQUID WASTE BY DIBENZO-18-CROWN-6

Technetium is one of the most prominent problems since its most stable specie in the environment, the pertechnetate ion, is highly mobile and considered as a long-term hazard in nuclear waste disposal. Because of the small activities of 99Tc relative to other fission products 137Cs or 90Sr, and its long half-life time (t1/2 = 2.1 x 105 yrs), 99Tc is one of the key isotopes that should always be analyzed in the radioactive liquid waste streams from the reprocessing industry where the largest concentrations are to be expected. Furthermore, as a pure beta-emitter, 99Tc has to be isolated from the intermediate level waste (ILW) stream prior to any measurement in such complex media. We have developed a method for 99Tc extraction providing recommendations that will be useful for extracting it from acid and basic ILW. The extraction of 99Tc from ILW by dibenzo-18-crown-6 (DB18C6) has been investigated and a simplex optimization of key parameters involved in the procedure has allowed us to set u p their best values. Experiments have been carried out on synthetic and real effluents from La Hague reprocessing plant, France, and results show that DB18C6 is highly selective towards 99Tc. The application of this procedure has been successfully demonstrated through the analysis of actual waste streams coming from two reprocessing plants at La Hague and Marcoule, France

Spectrophotometric investigation of U(VI) chloride complexation in the NaCl/NaClO{sub 4} system

The option of a nuclear waste disposal in deep salt formations such as Gorleben in Germany, and the WIPP (Waste Isolation Pilot Plant) in southeastern New Mexico, US has generated, over the last ten years, interests in thermodynamic data of radioactive trace elements in concentrated electrolyte solutions. Furthermore, post closure radioactive release scenarios from geologic salt formation, such as the WIPP include hydrologic transport of radionuclides through a chloride saturated aquifer. Consequently, the understanding of actinide solution chemistry in brines is essential for modeling requiring accurate knowledge of the interaction between AnO{sub 2}{sup 2+} and chloride ions. The goal is to develop models capable of predicting their behavior in natural multicomponent brines of high concentration. Complexation constants of two U(VI) chloride species, UO{sub 2}Cl{sup +} and UO{sub 2}Cl{sub 2}{sup 0}, have been intensively studied for about 40 years using different methods. However, large uncertainties reflect the general difficulty in determining accurate stability constants of weak complexes. In order to model the behavior of U(VI) in brines, the authors studied the formation of its chloride complexes by UV-Vis spectroscopy as a function of the NaCl concentration at 25 C

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

Charge Distribution and Local Structure and Speciation in the UO2+x and PuO2+x Binary Oxides for x <0.25.

The local structure and chemical speciation of the mixed valence, fluorite based oxides UO2+x (0.00pxp0.20) and PuO2+x PuO2+xy(OH)2y zH2O have been determined by U Pu LIII XAFS spectroscopy. The U spectra indicate (1) that the O atoms are incorporated as oxo groups at short (1.75A) U O distances consistent with U(VI) concomitant with a large range of U displacements that reduce the apparent number of U neighbors and (2) that the UO2 fraction remains intact implying that these O defects interact to form clusters and give the heterogeneous structure consistent with the diffraction patterns. The PuO2+x system, which does not show a separate phase at its x 1:4 0:25 endpoint, also displays (1) oxo groups at longer 1.9A distances consistent with Pu(V+d), (2) a multisite Pu O distribution even when x is close to zero indicative of the formation of stable species with H2O and its hydrolysis products with O2, and (3) a highly disordered, spectroscopically invisible Pu Pu component. The structure and bonding in AnO2+x are therefore more complicated than have previously been assumed and show both similarities but also distinct differences among the different elements.JRC.E.6-Actinides researc