Depleted Uranium Oxide Research Articles

Experiences from the cutting of metallic blocks from simulant Fukushima Daiichi fuel debris

ABSTRACT CEA has manufactured a series of Fukushima Daiichi fuel debris simulants, either with depleted uranium oxide or with hafnium oxide as a surrogate of UO2. In ex-vessel compositions resulting from an interaction between corium and concrete, the oxidic phase density becomes lighter than that of the metallic phase, which segregates at the bottom. Three of these metallic phases have been mechanically cut at CEA Cadarache with handsaw and with core boring tool in FUJISAN facility. It appeared that two of these metallic blocks were extremely hard to cut (one from a fabrication with uranium oxide, the other from a simulant block) while the last one was more easily cut. The similarities and differences in metallographic analyses (SEM-EDS and XRD) of these three metal blocks will be presented and discussed. This experience provides useful learnings in view of the cutting and retrieval of fuel debris from Fukushima Daiichi.

Depleted uranium oxide supported nickel catalyst for autothermal CO2 methanation in non-adiabatic reactor under induction heating

Undoped nickel-based catalysts supported on depleted uranium oxide allow one to carry out CO2 methanation process under extremely low reaction temperature under atmospheric pressure and powered by a contactless induction heating. By adjusting the reaction conditions, the catalyst is able to perform CO2 methanation reaction under autothermal process operated inside a non-adiabatic reactor, without any external energy supply. Such autothermal process is possible thanks to the high apparent density of the UOx which allows one to confine the reaction heat in a small catalyst volume in order to confine the exothermicity of the reaction inside the catalyst and to operate the reaction at equilibrium heat in-heat out. Such autothermal operation mode allows one to significantly reduce the complexity of the process compared to that operated using adiabatic reactor, where complete insulation is required to prevent heat disequilibrium, in order to reduce as much as possible, the heat exchange with the external medium. The catalyst displays an extremely high stability as a function of time on stream as no apparent deactivation. It is expected that such new catalyst with unprecedented catalytic performance could open new era in the field of heterogeneous catalysis where traditional supports show their limitations to operate catalytic processes under severe reaction conditions.

Not Just Another Methanation Catalyst: Depleted Uranium Meets Nickel for a High‐Performing Process Under Autothermal Regime

Invited for this month's cover are collaborating teams from academia-the French ICPEES and IS2M of Centre national de la recherche scientifique (CNRS) and the Italian ICCOM of Consiglio Nazionale delle Ricerche (CNR)-and industry with the participation of the ORANO group. The cover picture shows a CO2 -to-CH4 process promoted by nickel nanoparticles supported on depleted uranium oxide under exceptionally low temperature values or autothermal conditions. The Research Article itself is available at 10.1002/cssc.202201859.

Front Cover: Not Just Another Methanation Catalyst: Depleted Uranium Meets Nickel for a High‐Performing Process Under Autothermal Regime (ChemSusChem 5/2023)

The Front Cover shows nickel nanoparticles supported on depleted uranium oxide (DU) beads as effective and durable “microreactors” for promoting CO2 methanation. DU allows a controlled management of the extra heat generated by the process’ exothermicity, harvesting it, and turning it back as additional energy for running the process itself. As a result, methanation can be operated efficiently already under exceptionally low reactor temperatures or even under an autothermal regime (i.e., external heater switched off). More information can be found in the Research Article by L. Truong-Phuoc et al.

A novel protocol to recycle zirconium from zirconium alloy cladding from used nuclear fuel rods

A potential new zirconium recycling protocol has been demonstrated using unirradiated Zircaloy-based claddings and depleted uranium oxide for the chemical removal of zirconium alloy cladding in used nuclear fuel (UNF) rods from light water reactors. This protocol is based on the application of three new scientific findings. First, a new lower temperature chlorination reaction of zirconium with sulfur monochloride is described. Second, the high solubility of zirconium chloride in thionyl chloride is used to separate it from uranium oxide fuel and fission and activation contaminants. Finally, in the third step, the zirconium chloride is purified by simple recrystallization from thionyl chloride. Utilizing sulfur chloride solvents for a lower temperature liquid-based chemical digestion and purification of zirconium alloy claddings reduces technical complications experienced by current high temperature gas phase chlorination strategies, such as contamination of product streams. This novel protocol has been demonstrated on a 3–50 g scale of unirradiated zirconium alloy, with no significant change in the time required for complete chlorination (3–4 h). This zirconium chlorination protocol has also been performed in the presence of depleted uranium oxide pellets. The depleted fuel pellets do not affect zirconium chlorination, and the chlorination protocol does not chemically or physically alter the fuel pellets. A preliminary description of an industrial protocol to recycle nuclear grade zirconium from UNF rods is presented.

Not Just Another Methanation Catalyst: Depleted Uranium Meets Nickel for a High-Performing Process Under Autothermal Regime.

Ni-based catalysts prepared through impregnation of depleted uranium oxides (DU) have successfully been employed as highly efficient, selective, and durable systems for CO2 hydrogenation to substituted natural gas (SNG; CH4 ) under an autothermal regime. The thermo-physical properties of DU and the unique electronic structure of f-block metal-oxides combined with a nickel active phase, generated an ideal catalytic assembly for turning waste energy back into useful energy for catalysis. In particular, Ni/UOx stood out for the capacity of DU matrix to control the extra heat (hot-spots) generated at its surface by the highly exothermic methanation process. At odds with the benchmark Ni/γ-Al2 O3 catalyst, the double action played by DU as a "thermal mass" and "dopant" for the nickel active phase unveiled the unique performance of Ni/UOx composites as CO2 methanation catalysts. The ability of the weakly radioactive ceramic (UOx ) to harvest waste heat for more useful purposes was demonstrated in practice within a rare example of a highly effective and long-term methanation operated under autothermal regime (i. e., without any external heating source). This finding is an unprecedented example that allows a real step-forward in the intensification of "low-temperature" methanation with an effective reduction of energy wastes. At the same time, the proposed catalytic technology can be regarded as an original approach to recycle and bring to a second life a less-severe nuclear by-product (DU), providing a valuable alternative to its more costly long-term storage or controlled disposal.

TOPOGRAPHIC RELATIONSHIPS OF MORPHOLOGICALLY HETEROGENEOUS ORGANS IN REACTIONS TO DEPLETED URANIUM

Annotation: Researches of the effect of radionuclides on the human body remain relevant up to date. Their effect of penetrating the body is characterized by involvement of numerous systems of human body. The causal significance of the effects of depleted uranium exposure has not been specifically defined, however, people who live in zones of armed conflict, as well as armed forces personnel, had health problems of "unknown origin", and with remote symptomatic etiology. The risk of possible exposure is also may appear when manufacture of nose spikes for armor piercers and atomic energetics products. In view of these perspectives, depleted uranium, which used in various types of weapons, has been considered as the cause of complaints. Acute uranium intoxication is appeared in polytropic effect that is apparently depended on the resistance of the body. Getting into the internal milieu, depleted uranium exhibits radiation effect of exposure followed by alpha particles radiation. Long-term consequences after oral incorporation of depleted uranium with drinking water are matters of particular interest. The study purpose is defined by assessing of morphofunctional state of the trachea and thyroid gland, united by topographic proximity and different by morphological heterogeneity, upon one month after a single oral incorporation of an aqueous solution of depleted uranium oxides. General histological and histochemical staining methods on thin paraffin slices have been performed for studying on morphological and functional state of the trachea and thyroid gland The results of the morphological and statistical analysis of the trachea wall upon staining with hematoxylin and eosin revealed changes in the structural components that determined deformation of its functionality a month after oral incorporation of an aqueous solution of depleted uranium oxides. Morphological diagnosis was characterized by a change thickness of the epithelial layer, its multi-rowed structure, the cellular composition of the epithelium, and the loss of special organelles. Modifying effect of depleted uranium is also extended to the glandular epithelium with exposure of secretory segments hypertrophy and excretory ducts. There was revealed the diffuse lymphocyte infiltration of the tracheal membranes and formation of lymph nodules. Histochemical analysis of hormone formation in the thyroid gland has demonstrated a change in the ratio of follicles according to the degree of iodization of colloid amino acids with accurate predomination of non-iodized amino acids of irregular shape with accurate smaller diameter against target parameters, with flat or low cubic epithelium, indicating a decrease of gland functionality. The bioeffect of depleted uranium, independently from organ implementation and tissue organization, was prolonged indicating a functional inability.

Cellular reactions of the mucous membrane of the intestinal system after uranium incorporation

A pilot study, which was performed on white laboratory male rats and included a morphological study of the mucous membrane of the jejunum and colon, revealed the long-term effect of a single oral exposure to an aqueous solution of depleted uranium oxides; this supported dynamic changes in the studied criteria determining metabolic, regenerative, and local regulatory processes in one, three and six months. A lymphoid component appeared to be the criterion of high radio sensitivity and a marker of nonspecific protection indicating deterioration of homeostasis. In the time dynamics of long-term periods, a change in all the parameters was detected when using immunohistochemical, histochemical, and specific methods at the level of the epithelium lining the relief formations of the mucous membranes of the intestinal system organs. The oxidative stress resulting in three months after exposure to depleted uranium, which was evidenced by a significant decrease in the content of anti-apoptotic Bcl-2 protein in the epithelial cells of the jejunely mucosa. Signs of its delayed effect after six months in the colon induced the pronounced nature of the reactions of stromal cell components that determined patterns of protective mechanisms of the intestinal-associated immune system with a greater expressiveness in the jejunum. The factual material cited in the work suggests the existence of a homeostatic immune response in the mucous membrane of the small and large intestines that controls cell proliferation, as a special form of immune surveillance of the state of cytodifferentiation.

Direct determination of uranium in sintered deeply depleted uranium oxide pellets by wavelength dispersive X-ray fluorescence spectrometry

This paper presents studies on direct non-destructive determination of uranium in sintered deeply depleted (DD) uranium oxide (UO2) pellets by wavelength dispersive X-ray fluorescence (WDXRF) spectrometry. A special collet was designed and fabricated for holding the sintered DDUO2 pellets for direct analysis, thus avoiding the sample preparation steps. The samples were analyzed using a calibration plot obtained from WDXRF spectra of matrix matched calibration standards. The WDXRF determined uranium values were found to be in very close agreement with titrimetric values and has reproducibility better than 0.05% (RSD, 1 s, n = 10) for the sintered DDUO2 pellets having U: 86.81–88.04 wt%.

Electronically Coupled Uranium and Iron Oxide Heterojunctions as Efficient Water Oxidation Catalysts

AbstractThe most critical challenge faced in realizing a high efficiency photoelectrochemical water splitting process is the lack of suitable photoanodes enabling the transfer of four electrons involved in the complex oxygen evolution reaction (OER). Uranium oxides are efficient catalysts due to their wide range optical absorption (Eg ≈ 1.8–3.2 eV), high photoconductivity, and multiple valence switching among uranium centers that improves the charge propagation kinetics. Herein, thin films of depleted uranium oxide (U3O8) are demonstrated grown via chemical vapor deposition effectively accelerate the OER in conjunction with hematite (α‐Fe2O3) overlayers through a built‐in potential at the interface. Density functional theory simulations demonstrate that the multivalence of U and Fe ions induce the adjustment of the band alignment subject to the concentration of interfacial Fe ions. In general, the equilibrium state depicts a type II band edge as the favored alignment, which improves charge‐transfer processes as observed in transient and X‐ray absorption (TAS and XAS) spectroscopy. The enhanced water splitting photocurrent density of the heterostructures (J = 2.42 mA cm−2) demonstrates the unexplored potential of uranium oxide in artificial photosynthesis.

ANALYSIS OF FUNCTIONAL CHANGES IN THE RODENTS CENTRAL NERVOUS SYSTEM AT A SINGLE UPTAKE OF DEPLETED URANIUM OXIDE MIXED WITH WATER

Behavioral responses in experimental animals were studied in an experiment after a single uptake of aqueous solution of mixed depleted uranium oxide using standard techniques. The experimental research showed pronounced integrative functions disorders in the rodents brain which are associated with impacts of uranium compounds on structures providing coordination of motor acts, on conditioned reflex activity as well as anxiety-phobic and emotional state of animals. Temporary neurotoxic effects of depleted uranium may be a result of both direct oxidant activity impact of uranium compounds on neurons and consequence of their effect on the neurotransmitter metabolism .

Depleted and enriched uranium exposure quantified in former factory workers and local residents of NL Industries, Colonie, NY USA

BackgroundBetween 1958 and 1982, NL Industries manufactured components of enriched (EU) and depleted uranium (DU) at a factory in Colonie NY, USA. More than 5 metric tons of DU was deposited as microscopic DU oxide particles on the plant site and surrounding residential community. A prior study involving a small number of individuals (n=23) indicated some residents were exposed to DU and former workers to both DU and EU, most probably through inhalation of aerosol particles. ObjectivesOur aim was to measure total uranium [U] and the uranium isotope ratios: 234U/238U; 235U/238U; and 236U/238U, in the urine of a cohort of former workers and nearby residents of the NLI factory, to characterize individual exposure to natural uranium (NU), DU, and EU more than 3 decades after production ceased. MethodsWe conducted a biomonitoring study in a larger cohort of 32 former workers and 99 residents, who may have been exposed during its period of operation, by measuring Total U, NU, DU, and EU in urine using Sector Field Inductively Coupled Plasma - Mass Spectrometry (SF-ICP-MS). ResultsAmong workers, 84% were exposed to DU, 9% to EU and DU, and 6% to natural uranium (NU) only. For those exposed to DU, urinary isotopic and [U] compositions result from binary mixing of NU and the DU plant feedstock. Among residents, 8% show evidence of DU exposure, whereas none shows evidence of EU exposure. For residents, the [U] geometric mean is significantly below the value reported for NHANES. There is no significant difference in [U] between exposed and unexposed residents, suggesting that [U] alone is not a reliable indicator of exposure to DU in this group. ConclusionsNinety four percent of workers tested showed evidence of exposure to DU, EU or both, and were still excreting DU and EU decades after leaving the workforce. The study demonstrates the advantage of measuring multiple isotopic ratios (e.g., 236U/238U and 235U/238U) over a single ratio (235U/238U) in determining sources of uranium exposure.

Environmental assessment of depleted uranium used in military armor‐piercing rounds in terrestrial systems

Depleted uranium (DU) from the military testing and use of armor-piercing kinetic energy penetrators has been shown to accumulate in soils; however, little is known about the toxicity of DU geochemical species created through corrosion or weathering. The purpose of the present study was to assess the toxic effects and bioaccumulation potential of field-collected DU oxides to the model terrestrial invertebrates Eisenia fetida (earthworm) and Porcellio scaber (isopod). Earthworm studies were acute (72 h) dermal exposures or 28-d spiked soil exposures that used noncontaminated field-collected soils from the US Army's Yuma and Aberdeen Proving Grounds. Endpoints assessed in earthworm testing included bioaccumulation, growth, reproduction, behavior (soil avoidance), and cellular stress (neutral red uptake in coelomocytes). Isopod testing used spiked food, and endpoints assessed included bioaccumulation, survival, and feeding behavior. Concentration-dependent bioaccumulation of DU in earthworms was observed with a maximum bioaccumulation factor of 0.35; however, no significant reductions in survival or impacts to cellular stress were observed. Reproduction lowest-observed-effect concentrations (LOEC) of 158 mg/kg and 96 mg/kg were observed in Yuma Proving Ground and a Mississippi reference soil (Karnac Ferry), respectively. Earthworm avoidance of contaminated soils was not observed in 48-h soil avoidance studies; however, isopods were shown to avoid food spiked with 12.7% by weight DU oxides through digital tracking studies.

Nuclear material identification using resonant ultrasound spectroscopy

Resonant ultrasound spectroscopy (RUS) is a well-established method for determination of the full tensor of elastic moduli of a solid sample in a single frequency sweep. The elastic moduli, together with density, can provide information related to materials fabrication processes, providing a unique signature, or fingerprint, of a material. The goal of this study was to provide forensics for nuclear materials in solid ceramic or metallic form, including composition. The premise of this study was that it is really difficult to find two materials whose density and shear and /or bulk modulus match. We used RUS to determine the bulk and shear modulus for a total of 27 samples. The samples consisted of depleted uranium oxide (MOX) with different doping of Ce, Pu, and Nd oxides, and different methods of fabrication. They were in form of cylinders with flat and parallel faces. Two-dimensional and three-dimensional spaces were investigated, using shear modulus, bulk modulus, and density as variables. The densities varied between 9.0 and 10.6 g/cc, while the shear modulus was 55–80 GPa, with a bulk modulus of 150–240 GPa. The results obtained suggest that there is a good correlation between the elastic moduli and density for samples of different compositions/origins.

A model study on the absorbed dose of radiation following respiratory intake of 238U3O8 aerosols

Aerosols of depleted uranium oxides, formed upon high-energy impact of shells on hard targets during military operations, are able to disperse, reach the alveolar region of the lungs and be absorbed and distributed throughout various parts of the body. The absorbed particles are subjected to clearance in the upper respiratory tract, distribution to other body districts, dissolution and excretion. While the soluble forms of uranium are known to deliver a small dose of radiation to the body due to their homogeneous distribution and the low specific activity of (238)U, ceramic particles exhibit a low dissolution rate and irradiate a limited volume of tissue for a long time with alpha particles with an energy of 4.267 MeV. The extent of the irradiated tissues depends on the radius of the particles and the total intake of uranium oxides. For the measured intake of U3O8 of a war veteran (15.51 μg) the number of particles ranges from 5.56×10(4) to 6.95×10(6) for sizes of 0.4-2.0 μm. Modelling the distribution of the particles between two compartments of the body, the averaged dose absorbed in 20 y by tissues surrounding the particles and within the range of the alpha particles varies from 6.8 mGy to 0.85 Gy for lungs and 8.1 mGy to 1.0 Gy for the lymph nodes, respectively. Correspondingly, due to the clearance and redistribution, the mass irradiated by 2.0-μm particles falls in 20 y from 6.06 mg to 0.94 μg in the lungs and grows from 0 to 1.0 mg in the lymph nodes. The estimated rate of formation of hydroxyl radicals upon radiolysis of water in the lungs and lymph nodes is 5.17×10(4) d(-1) per cell after 1 y.

Fusion of Radiation and Electromagnetic Induction Data for Buried Radioactive Target Detection and Characterization

In general, buried penetrators made of Depleted Uranium (DU) become hazardous waste. In addition to the detection of DU waste, it is also of interest to know their state of oxidation. However, radioactive target detection techniques usually do not differentiate between metal and oxide. In this study, data fusion techniques are applied to combine results from both the radiation detection and the electromagnetic induction (EMI) detection, so that further differentiation among DU metal, DU oxide, and non-DU metal debris may be achieved. A two-step approach is developed to accomplish decision level fusion. The approach is based on techniques such as majority voting (MV) and weighted majority voting (WMV), in combination with a set of decision rules. The fusion approach has been tested successfully with survey data collected on simulation targets.

The Gulf War Depleted Uranium Cohort at 20 years

During the 1991 GulfWar, U.S. service members were exposed to depleted uranium (DU) through friendly-fire incidents involving DU munitions and vehicles protected by DU armor. Routes of exposure to DU involved inhalation of soluble and insoluble DU oxide particles, wound contamination, and retained embedded DU metal fragments that continue to oxidize in situ and release DU to the systemic circulation. A biennial health surveillance program established for this group of Veterans by the U.S. Department of Veterans Affairs has shown continuously elevated urine DU concentrations in the subset of veterans with embedded fragments for over 20 years. While the 2011 assessment was comprehensive, few clinically significant U-related health effects were observed. This report is focused on health outcomes associated with two primary target organs of concern for long term effects of this combat-related exposure to DU. Renal biomarkers showed minimal DU-related effects on proximal tubule function and cytotoxicity, but significant biomarker results were observed when urine concentrations of multiple metals also found in fragments were examined together. Pulmonary tests and questionnaire results indicate that pulmonary function after 20 y remains within the clinical normal range. Imaging of DU embedded fragment-associated tissue for signs of inflammatory or proliferative reactions possibly associated with foreign body transformation or with local alpha emissions from DU was also conducted using PET-CT and ultrasound. These imaging tools may be helpful in guiding decisions regarding removal of fragments.

Determination of high burn-up nuclear fuel elastic properties with acoustic microscopy

We report the measurement of elastic constants of non-irradiated UO 2, SIMFUEL (simulated spent fuel: UO 2 with several additives which aim to simulate the effect of burnup) and irradiated fuel by focused acoustic microscopy. To qualify the technique a parametric study was conducted by performing measurements on depleted uranium oxide (with various volume fraction of porosity, Oxygen-to-metal ratios, grain sizes) and SIMFUEL and by comparing them with previous works presented in the literature. Our approach was in line with existing literature for each parameter studied. It was shown that the main parameters influencing the elastic moduli are the amount of fission products in solution (related to burnup) and the pore density and shape, the influence of which has been evaluated. The other parameters (irradiation defects, oxygen-to-metal ratio and grain sizes) mainly increase the attenuation of the ultrasonic wave but do not change the wave velocity, which is used in the proposed method to evaluate Young’s modulus. Measurements on irradiated fuel (HBRP and N118) were then performed. A global decrease of 25% of the elastic modulus between 0 and 100 GWd/tM was observed. This observation is compared to results obtained with measurements conducted at ITU by Knoop indentation techniques.

Enhanced CO2 Storage and Sequestration in Deep Saline Aquifers by Nanoparticles: Commingled Disposal of Depleted Uranium and CO2

Geological storage of anthropogenic CO2 emissions in deep saline aquifers has recently received tremendous attention in the scientific literature. Injected buoyant CO2 accumulates at the top part of the aquifer under a sealing cap rock. Potential buoyant movement of CO2 has caused some concern that the high-pressure CO2 could breach the seal rock. However, CO2 will diffuse into the brine underneath and generate a slightly denser fluid that may induce instability and convective mixing. Onset times of instability and convective mixing performance depend on the physical properties of the rock and fluids, such as permeability and density contrast. We present the novel idea of adding nanoparticles (NPs) to injected CO2 to increase density contrast between the CO2-rich brine and the underlying resident brine and, consequently, decrease onset time of instability and increase convective mixing. The analyses show that 0.001 volume fraction of NPs added to the CO2 stream shortens onset time of mixing by approximately 80% and increases convective mixing by 50%. If it thus originally takes 5 years for the overlying CO2 to start convective mixing, by adding NPs, onset time of mixing reduces to 1 year, and after initiation of convective mixing, mixing improves by 50%. A reduction of the CO2 leakage risk ensues. In addition to other metallic NPs, use of processed depleted uranium oxide (DU) as the NPs is also proposed. DU-NPs are potentially stable and might be safely commingled with CO2 to store in saline aquifers.

Sorption of Np by UO2 under repository conditions

This work is a part of the joint Russian – American Program on Beneficial Use of Depleted Uranium. The production of nuclear fuels results in the accumulation of large quantities of depleted uranium (DU) in the form of uranium hexafluoride (UF6), which is converted to uranium oxides. Depleted uranium dioxide (DUO2) can be used as a component of radiation shielding and as an absorbent for migrating radionuclides that may emerge from casks containing spent nuclear fuel (SNF) that are stored for hundreds of thousands of years in high-level wastes (HLW) and SNF repositories (e.g. Yucca Mountain Project). In this case DU oxides serve as an additional engineered chemical barrier. It is known that the primary radioisotope contributor to the calculated long-term radiation dose to the public at the Yucca Mountain SNF repository site boundary is neptunium-237 (237Np). This paper describes the sorption of 237Np in various media (deionized water and J-13 solution) by DUO2. Samples of DUO2 used in this work originated from the treatment of UF6 in a reducing media to form UO2(DUO2-1 at 600°C, DUO2-2 at 700°C, and DUO2-3 at 800°C). All species of DUO2 sorb Np(V) and Np(IV) from aqueous media. Equilibrium was achieved in 24 hours for Np(V) and in 2 hours for Np(IV). Np(V) sorption is accompanied with partial reduction of Np(V) to Np(IV) and vice versa. The sorption of Np(V) onto DUO2 surfaces is irreversible. The investigations on DUO2 transformations were performed under dynamic and static conditions. Under static conditions the solubility of the DUO2 samples in J-13 solution is considerably higher than in DW. When the pre-treatment temperature is decreased, the solubility of DUO2 samples raises regardless of the media. The experiments on interaction between DUO2 and aqueous media (DW and J-13 solution) under dynamic conditions demonstrated that during 30-40 days the penetration/filtration rate of DW and J-13 solution through a thin DUO2 layer decreased dramatically, and then slowed and stabilized. The filtration rate of J-13 solution through DUO2layer is several times lower than that of DW. If Np were sorbed by UO2 in SNF rather than being transported to the site boundary, the site boundary dose would be more than an order of magnitude lower than that calculated. If this is so, the remaining primary contributors to site boundary dose would be 129I and the decay products of 238U. One could provide an additional barrier, a chemical barrier, to radionuclide release by surrounding the SNF with UO2. The experiments also indicate that a relatively thin layer of UO2 essentially stops water penetration. Such a barrier would deny water access to the SNF. Such a repository SNF configuration would provide reduced radionuclide transport from the drift as well as sorbing released nuclides from failed SNF pins.