Effect of hydrogen gas and leaching solution on the fast release of fission products from two PWR fuels

To study the dissolution of UOX spent nuclear fuel in a deep geological environment and the fast release of a selection of relevant radionuclides for long-term safety of this high level waste, leaching experiments were performed with spent nuclear fuel samples originating from the pressurized water reactors (PWRs) Tihange 1 and Gösgen with a similar burnup (50 – 55 MWd.kgHM−1) but different irradiation histories. Six experiments were conducted to investigate the effect of two critical parameters: (1) the highly alkaline environment caused by the presence of cementitious materials in the “Supercontainer design”, which is currently the reference design for the long-term management of the high-level nuclear waste forms in Belgium, and (2) the reducing conditions imposed by the presence of hydrogen from the corrosion of iron-based materials present in the engineered barriers. The experiments were performed using autoclaves under pressure from 1 to 40 bar with a pure Ar atmosphere or a mixture of H2/Ar. Divided into two consecutive phases, the total experimental duration was about 1400 days. The Phase I provided mainly information about the fast release of the fission products while the perspective of the Phase II was to study the long-term evolution of the spent fuel matrix. During the leaching experiment, concentrations of a selection of radionuclides (238U, 129I, 137Cs, 90Sr and 99Tc) were monitored in solution and the amounts of Kr and Xe were measured in the gas phase. Based on results of the experiments conducted for up to 40 months (i.e. during Phase I of the experimental program), we observe that there is a continuous release of 137Cs, 90Sr and of the fission gases and a clear impact of the irradiation history on the release of certain fission products

Effect of alpha radiolysis on doped UO2_2 dissolution under reducing conditions

The aim of the present work is to quantify the influence of alpha radioactivity of 225Ac doped UO2 on the dissolution rate under reducing conditions at pH 6. The doped or undoped material was prepared by precipitation and the size of particles was about 3 nm. The total alpha activity of the doped material was about 2000 MBq g-1 UO2, about 4 times higher than that of 15 years old spent fuel. The solution was kept under reducing conditions during the experiment by permanent electrochemical reduction under inert atmosphere. The results showed that the dissolution rate of doped material was a function of alpha activity and thus a function of the dose

Oxidation and dissolution rates of UO2UO_2(s) in carbonate-rich solutions under external alpha irradiation and initially reducing conditions

This paper describes the effects of aqueous carbonate concentrations on the UO2 oxidation and dissolution rates under an alpha beam irradiation in a cyclotron. As solid samples, UO2 colloids were synthesized by nano-particle precipitation. The specific surface area obtained is 85.3 m2/g. All aqueous solutions were buffered in the pH range

Electrochemical aspects of radiolytically enhanced UO2_2 dissolution

Experiments were performed, irradiating UO2 colloids of 3 nm diameter by a 5 MeV alpha beam of a cyclotron. Both the dissolution rate of these colloids and the production rate of hydrogen peroxide have been measured. The experimentally measured corrosion rate of these colloids is very similar to the corrosion rates measured for bulk UO2 samples, indicating on the one hand that similar reaction mechanism prevail and on the other hand that the UO2 colloids are well representative for bulk UO2. The results were compared with two current models for radiolytical dissolution of spent fuel. Additionally a new coupling between water radiolysis reactions and spent fuel dissolution has been established. The coupling is not anymore based on rate constants for direct reaction of oxidants with UO2, but on the electrochemical coupling of anodic dissolution reactions with cathodic reduction of molecular and radical radiolysis products. The model not only describes well the experimental data, it also allows to predict both the establishment of corrosion potentials and of fractional reaction orders with respect to oxidant concentrations. Model results can also be compared with experimental data (corrosion potential ...) using UO2 as an electrode

Anatomical Considerations of Infrageniculate Popliteal Artery Puncture: Alternative Pathway for Retrograde Access After Failed Re-entry

International audienceBACKGROUND: A distal approach in endovascular procedures for revascularization of lowers limbs can be considered in case of no re-entry in subintimal recanalization. The aim of this study is to evaluate the feasibility of a medial approach to the infrageniculate popliteal artery (IPA) using existing computed tomography (CT) scan simulation and punctures performed on cadavers. METHODS AND RESULTS: CT angiographies of lower extremities were used to simulate IPA puncture and puncture trajectory. Tissues damaged during the trajectory between the puncture site and the access-related injuries were analyzed. Anatomical punctures on cadaverous model were also performed. Corpses were placed in supine position, the hip in slight flexion (40°) and abduction (external rotation of 60°). A 16 G needle was used for the IPA puncture. Twelve CT angiography simulations were made. Of these 12 simulations, 9 revealed an isolated lesion of the popliteal vein and 2 isolated lesions of the tibial nerve. A lesion of the tibial nerve and the popliteal vein on the same simulation was once observed. Damage to the medial gastrocnemius muscle could not be avoided in each case. Ten punctures were performed on cadavers with technical success. There were 6 popliteal vein lesions, 3 tibial nerve lesions, and 1 case without lesion. In all cases, damage to the medial gastrocnemius muscle was seen. CONCLUSIONS: This medial approach was feasible and is accompanied by trauma of elements of the popliteal pedicle. Preoperative CT angiography could anticipate best site of puncture and potential access-related injury

Origin of the hydrogen involved in iron corrosion under irradiation

In the perspective of long term geological storage, high level nuclear wastes will be overpacked in low carbon steel containers. In that context, we have studied the influence of oxygen dissolved in water on iron corrosion. Therefore, leaching experiments were performed in desaerated D$\_2$O and in aerated H$\_2$O and a kinetic study of iron corrosion under proton irradiation was lead in aqueous media with two different dissolved oxygen concentrations. The leaching experiments underline the major role of dissolved oxygen in oxydoreduction reactions which take place as far as iron is in contact with water. But the kinetic study of iron corrosion under irradiation put in evidence the balance between the oxydoreduction reactions and the corrosion rate induced by radicals species generated by water radiolysis. In addition, to check if, in the atomic % concentration range, hydrogen diffuse from the air/Fe interface through the foil an irradiation experiment was performed in argon. It proved that no hydrogen permeation occurs at a concentration level of the atomic percent