Gamma radiation can have an influence on the integrity of the copper canisters used in deep geological repositories for isolating radioactive waste. Understanding the interactions between aqueous radiolysis products and container materials, particularly at the copper-water interface, is essential for assessing the canister integrity. This study investigates the gamma-radiation-induced products on copper specimens and water through experimental methods. Cu specimens were exposed to gamma radiation, and corrosion products were analysed using cathodic reduction, XPS, ICP-MS, and FT-IR. Results show that Cu2O is the dominant corrosion product formed during irradiation. Pre-oxidized Cu specimens, especially those formed at evaluated temperatures (140 °C), exhibited less corrosion depths and much more homogeneous coloration on the surfaces compared to literature data of irradiated bare Cu specimens and pre-oxidized 90 °C Cu specimens, suggesting the possibility that high temperature pre-oxidation enhances corrosion resistance under irradiation conditions. Additionally, the enhanced formation of alkane species, such as CH4, was observed in irradiated water, likely originated from the reduction of CO2 and HCO3− by radiation-induced reducing agents (H, H2, and eaq−). This observation raises new questions about the chemical transformations occurring under irradiation. The findings highlight the importance of understanding initial Cu oxide layer properties and suggest that optimizing temperature and environmental conditions in DGRs can improve the long-term performance of Cu canisters. Future studies are encouraged to explore localized corrosion mechanisms in Cl−-rich environments and to further investigate the implications of alkane production on the chemical stability of DGR systems.

One of the key-features in the safety assessment of geological repositories for spent nuclear fuel is the rate of radionuclide release from fuel in contact with groundwater. This process is driven by the radioactivity of the fuel itself through the radiolysis of the groundwater producing oxidative species capable of converting the fuel matrix (UO<inf>2</inf>) to more soluble U(VI). Models describing this process are often based on the spatial dose rate distribution which is derived from the radionuclide inventory (often considered to be homogeneously distributed in the fuel). However, in reality the inventory is radially distributed with higher concentrations of fission- and neutron activation products closer to the fuel pellet surface. In this work, we have explored the impact of the spatial radionuclide distribution on the dose rate profile and rate of fuel matrix dissolution using SCALE and MCNP calculations in combination with a previously developed steady-state approach for radiation-induced dissolution of UO<inf>2</inf>. When accounting for the spatial radionuclide distribution, the calculated maximum rate of dissolution is 2–3 times higher than when assuming homogeneous radionuclide distribution.

This study presents the fabrication of double-layer electrospun nanofibrous membranes (DL-ENMs) using polyvinylidene fluoride (PVDF) and polyether sulfone (PES) based polymers with different degrees of hydrophilicity (PES, sulfonated PES, and PES with hydroxyl terminals). A comparative analysis was carried out with single-layer electrospun nanofiber membranes (SL-ENM) with a total thickness of about 375 μm. Using feed solutions, including sodium chloride, sodium nitrate, and simulated nuclear wastewater (SNWW), the performance of DL-ENMs was evaluated for desalination and radionuclide decontamination by direct contact membrane distillation (DCMD) and air gap membrane distillation (AGMD) techniques. The results showed that DL-ENMs, especially those incorporating a sulfonated PES-based hydrophilic layer, exhibited superior permeate fluxes, reaching values of 72.72 kg/m2.h and 73.27 kg/m2.h in the DCMD using aqueous feed solutions of NaCl and NaNO3, respectively, and 70.80 kg/m2.h and 41.96 kg/m2.h using aqueous feed solutions of SNWW in DCMD and AGMD, respectively. Both SL-ENMs and DL-ENMs exhibited high rejection efficiencies and decontamination factors for the feed solutions (>99.9%). In addition, the prepared ENMs were exposed to gamma radiation to evaluate their applicability in real-life applications. The result of irradiation revealed the negative impact of gamma radiation on the fluorine content of PVDF which could be a critical point in using PVDF as a hydrophobic material for decontaminating nuclear wastewater by membrane distillation.

H2O2 produced from water radiolysis is expected to play a significant role in radiation induced oxidative dissolution of spent nuclear fuel under the anoxic conditions of a deep geological repository if the safety-barriers fail and ground water reaches the fuel. It was recently found that the coordination chemistry between U(vi), HCO32− and H2O2 can significantly suppress H2O2 induced dissolution of UO2 in 10 mM bicarbonate. This was attributed to the much lower reactivity of the U(vi)O22+-coordinated O22− as compared to free H2O2. We have extended the study to lower bicarbonate concentrations and explored the impact of ionic strength to elucidate the rationale for the low reactivity of complexed H2O2. The experimental results clearly show that dissolution of U(vi) becomes suppressed at [HCO3−] < 10 mM. Furthermore, we found that the reactivity of the peroxide in solutions containing U(vi) becomes increasingly more suppressed at lower carbonate concentration. The suppression is not influenced by the ionic strength, which implies that the low reactivity of O22− in ternary uranyl-peroxo-carbonato complexes is not caused by electrostatic repulsion between the negatively charged complex and the negatively charged UO2-surface as we previously hypothesized. Instead, the suppressed reactivity is suggested to be attributed to inherently higher stability of the peroxide functionality as a ligand to UO22+ compared to as free H2O2.

Boric acid and its counter-base, borate, are a commonly used buffer pair in many systems where hydroxyl radicals are generated. Boric acid is also used in light water-cooled nuclear reactors to control the excess reactivity of the nuclear fuel. Hydroxyl radicals are generated within the cooling water of the reactor because of intense radiation. The reactivity of the hydroxyl radical toward boric acid has previously been studied, but to the best of our knowledge, only upper limits of the rate constants are available in the literature. In this study, the rate constants for the reaction between the hydroxyl radical and boric acid and its counter-base including several polyborates that form at high boron concentration are determined. The rate constants were determined from competition kinetics using steady-state gamma radiolysis and coumarin-3-carboxylic acid as the competing reactant. By varying the pH and accounting for boron speciation, it was possible to determine the rate constant for the different boron species using multilinear regression. The rate constants for boric acid and the counter-base were determined to be 3.6 x 10(4) and 1.1 x 10(6) M-1 center dot s(-1), respectively, which is very close to the previously determined upper limits of the rate constants. For the polyborate species diborate and tetraborate, the rate constant was determined to be 6.4 x 10(6) and 6.8 x 10(6) M-1 center dot s(-1), respectively.

Xyloglucan (XG) is a cellulosic backbone polysaccharide commercially used for food applications, but also widely investigated in biomedical applications, for its gelling properties and specific biological activity. In this study, the possibility of using gamma radiation to cleave XG and generate lower molecular weight variants was explored. The impact of absorbed dose and irradiation conditions on the XG molecular weight distribution was investigated. Two other cellulosic polysaccharides, hydroxypropyl cellulose (HPC) and an oxidized variant of XG (CXG), were also studied for comparison. Before irradiation, the polymers were characterized with thermal gravimetric analysis and, after irradiation, with gel permeation chromatography. The results showed that for XG irradiated in dilute aqueous solution, a dose of 10 Gy is sufficient to significantly reduce the polymer molecular weight, while HPC is less affected by irradiation under identical conditions. When the polymers were irradiated in the solid form, either dry or humid, the reduction in average molecular weight is much less pronounced. Interestingly, for HPC the cleavage of the chains is more pronounced for the dry than for the humid powder. A similar behavior, but less pronounced, was observed for XG and CXG. Arguably, when water was present in the system as bound water it had a protective effect. This is probably due to energy transfer from the polymer to the bound water preventing chain scission. Indeed, humid HPC has more bound water than XG and CXG. Conversely, when water was present as solvent, water radiolysis products were able to efficiently induce depolymerization. Graphical abstract: [Figure not available: see fulltext.].

In this work, we have experimentally studied UO2 dissolution in pure water and in 1 M aqueous solutions of either Cl- or Br- exposed to γ-radiation. It has previously been found that high ionic strength can facilitate adsorption of dissolved UO22+ on UO2 surfaces. The adsorption is also affected by the solution pH relative to the point of zero charge of UO2. In our experiments, Br3- was observed in 1 M Br- solution exposed to γ-radiation. Experiments confirmed that Br3- can quantitively oxidize UO2. XPS and UPS were used to characterize potential surface modifications after exposure. The XPS results show that the UO2 surfaces after exposure to γ-radiation in pure water and in 1 M aqueous solutions of either Cl- or Br- were significantly oxidized with U(V) as the dominating state. U 4f7/2 and O 1 s spectra of the UO2 surface after exposure to γ-radiation in pure water demonstrates the formation of uranyl peroxide secondary phases. UPS results indicate that there is a large percentage of U(VI) on the ultra-thin outer layer of UO2 after exposure to γ-radiation in 1 M aqueous solutions of Br- and Cl-, and 100 % of U(VI) in the pure water case.

Using a recently developed approach for numerical simulation of radiation-induced oxidative dissolution of spent nuclear fuel, we have explored the impact of three possible contributions to the inhibiting effect of molecular hydrogen. The three contributions are (1) effect on oxidant production in irradiated water, (2) reduction of oxidized uranium catalyzed by noble metal inclusions (fission products) and (3) reaction with surface-bound hydroxyl radicals preventing the oxidation of uranium. The simulations show that the first contribution is of fairly small importance while the second contribution can result in complete inhibition of the oxidative dissolution. This is well in line with previous work. Interestingly, the simulations imply that the third contribution, the reaction between H2 and the surface-bound hydroxyl radical formed upon reaction between the radiolysis product H2O2 and UO2, can account for the inhibition observed in systems where noble metal inclusions are not present. This is discussed in view of previously published experimental data.

Understanding the possible change in UO2 surface reactivity after exposure to oxidants is of key importance when assessing the impact of spent nuclear fuel dissolution on the safety of a repository for spent nuclear fuel. In this work, we have experimentally studied the change in UO2 reactivity after consecutive exposures to O2 or γ-radiation in aqueous solutions containing 10 mM HCO3-. The experiments show that the reactivity of UO2 toward O2 decreases significantly with time in a single exposure. In consecutive exposures, the reactivity also decreases from exposure to exposure. In γ-radiation exposures, the system reaches a steady state and the rate of uranium dissolution becomes governed by the radiolytic production of oxidants. Changes in surface reactivity can therefore not be observed in the irradiated system. The potential surface modification responsible for the change in UO2 reactivity was studied by XPS and UPS after consecutive exposures to either O2, H2O2, or γ-radiation in 10 mM HCO3- solution. The results show that the surfaces were significantly oxidized to a stoichiometric ratio of O/U of UO2.3 under all the three exposure conditions. XPS results also show that the surfaces were dominated by U(V) with no observed U(VI). The experiments also show that U(V) is slowly removed from the surface when exposed to anoxic aqueous solutions containing 10 mM HCO3-. The UPS results show that the outer ultrathin layer of the surfaces most probably contains a significant amount of U(VI). U(VI) may form upon exposure to air during the rinsing process with water prior to XPS and UPS measurements.