UO2 surface oxidation by mixtures of water vapor and hydrogen as a function of temperature

In the present work, X-Ray Photoelectron Spectroscopy (XPS) was used to study the effect of water vapor on the UO2 surface as a function of temperature. The experiments were performed in situ inside a high pressure chamber attached to the XPS instrument. UO2 samples were put in contact with either hydrogen or argon streams, saturated with water at room temperature, and the sample surface evolution was analyzed by XPS. In the case of the water vapor/argon experiments, one experiment at 350°C was performed and, in the case of the water vapor/hydrogen experiments, the temperatures used inside the reactor were 60, 120, 200 and 350°C. On one hand, in presence of argon, the results obtained showed that the water vapor in the argon stream oxidized 93% of the U(IV) in the sample surface. On the other hand, the degree of UO2 surface oxidation showed a different dependence on the temperature in the experiments performed in the presence of hydrogen: the maximum surface oxidation occurred at 120°C, where 65.4% of U(IV) in the sample surface was oxidized, while at higher temperatures, the surface oxidation decreased. This observation is attributed to the increase of hydrogen reducing effect when temperature increases which prevents part of the oxidation of the UO2 surface by the water vapor.Peer ReviewedPostprint (author's final draft

Retention of cesium and strontium by uranophane, Ca(UO2)2(SiO3OH)2·5H2O

This work determines the capacity of uranophane, one of the long-term uranyl secondary solid phases formed on the spent nuclear fuel (SNF), to retain radionuclides (cesium and strontium) released during the dissolution of the SNF. Sorption was fast in both cases, and uranophane had a high sorption capacity for both radionuclides (maximum sorption capacities of 1.53·10-5¿mol¿m-2 for cesium and 3.45·10-3¿mol¿m-2 for strontium). The high sorption capacity of uranophane highlights the importance of the formation of uranyl silicates as secondary phases during the SNF dissolution, especially in retaining the release of radionuclides not retarded by other mechanisms such as precipitation.Peer ReviewedPostprint (published version

Oxidative dissolution mechanism of both undoped and Gd2O3-doped UO2(s) at alkaline to hyperalkaline pH†

The dissolution rates of unirradiated UO2 and unirradiated UO2 doped with Gd2O3 were determined as a function of pH using flow-through experiments in the presence of O2(g) and bicarbonate. The dissolution rate of non-doped UO2 was very low under hyperalkaline conditions (pH 12–13) whereas it increased drastically as the pH decreased to 9. The dissolution of non-doped UO2 in the pH range of 9–13 was consistent with the oxidative dissolution mechanism already described for UO2 dissolution in the presence of bicarbonate and oxygen. XPS analysis performed on the solid after dissolution experiments at pH 10 and 13 supported the bicarbonate effect to complex UO22+ and accelerate dissolution. Moreover, UO2 doped with Gd2O3 (5 wt% and 10 wt%) showed dissolution rates as low as non-doped UO2 under hyperalkaline conditions, which were maintained throughout the pH range studied (9–13). No substantial differences in the dissolution rates between these two doping levels were found. XPS analysis evidenced a similar surface composition both at pH 10 and 13, with U(V) being the dominant oxidation state. The low dissolution rates were assumed to be a consequence of the gadolinium capacity to retard the oxidation of U(V) to U(VI). The slight increase in dissolution rates observed in the hyperalkaline region was attributed to a shift in the oxidative dissolution mechanism, in which the presence of OH- promotes the formation of soluble uranyl hydroxo complexes.Peer ReviewedPostprint (published version

Oxidation by H2O(g) in the presence of H2(g) of UO2 doped with Pd nanoparticles

This is a post-peer-review, pre-copyedit version of an article published in Journal of Radioanalytical and Nuclear Chemistry. The final authenticated version is available online at: http://dx.doi.org/10.1007/s10967-018-6217-2.This work studies the influence of epsilon particles and metallic precipitates, simulated through the deposition of Pd nanoparticles on non-irradiated UO2, on the oxidation of the spent nuclear fuel (SNF). The presence of Pd nanoparticles favored the reduction by hydrogen of oxidized uranium phases located on the UO2 surface, decreased the oxidation of the UO2 by H2O in the absence of hydrogen, and, in the presence of hydrogen and water vapor, no oxidation of the UO2 by water was detected, contrasting experiments without Pd nanoparticles.Peer ReviewedPostprint (author's final draft

Contribution of phases segregated from the UO2 matrix to the release of radionuclides from spent nuclear fuel and duration of the Instant Release Fraction (IRF)

During the dissolution of the spent nuclear fuel (SNF) some radionuclides are released to the solution simultaneously from different sources in the fuel. This is of particular importance to some radionuclides that contribute to the Instant Release Fraction (IRF), which govern the initial radiation dose during the dissolution of the SNF. In this work a model that is able to discriminate between the different contributions responsible for the total concentration of a radionuclide in solution was developed. The model permits to establish that uranium and radionuclides that dissolved congruently with the UO2 matrix came from two sources as a function of time: oxidized phases on the surface of the SNF including fines and the matrix itself. Other radionuclides such as Ru and Rh were released from metallic precipitates with dissolution rates lower than the matrix dissolution rate. In the case of radionuclides that were expected to contribute to the IRF, this work showed that Cs, Rb and Sr had initial release rates higher than uranium because a fraction of such radionuclides were segregated from the matrix during the irradiation. Actually it was calculated that the fraction of those radionuclides in the grain boundaries in a BWR SNF powder sample from the center part of a pellet (burnup 42 MWd/kgU) was 2.1%, 0.9%, and 0.6% for Cs, Rb, and Sr, respectively. In addition, the model permitted to calculate the duration of their contribution to the IRF, matrix dissolution governed the release of such radionuclides after 137 days, 75 days, and 164 days for Cs, Rb, and Sr, respectively (at these times, the contribution of the release from grain boundaries was lower than the 0.1%).Peer ReviewedPostprint (author's final draft

Diamine oxidase (DAO) supplement reduces headache in episodic migraine patients with DAO deficiency: A randomized double-blind trial

Background & Aims: Histamine intolerance is a disorder in the homeostasis of histamine due to a reduced intestinal degradation of this amine, mainly caused by a deficiency in the enzyme diamine oxidase (DAO). Among histamine related symptoms, headache is one of the most recorded. Current clinical strategies for the treatment of the symptomatology related to this disorder are based on the exclusion of foods with histamine or other bioactive amines and/or exogenous DAO supplementation. The aim of this study was to assess the efficacy of a food supplement consisting of DAO enzyme as a preventive treatment of migraine in patients with DAO deficiency through a randomized double-blind trial. Methods: 100 patients with confirmed episodic migraine according to current International Headache Society (IHS) criteria and DAO deficiency (levels below 80 HDU/ml) were randomized in two groups. One group received DAO enzyme supplementation and the other received placebo for one month. Clinical outcomes assessed were duration and number of attacks, perception of pain intensity and adverse effects during treatment. The use of triptans was also recorded. Results: Great variability was found in the duration of migraine attacks reported by placebo and DAO groups. A significant reduction (p=0.0217) in hours of pain was achieved in patients treated with DAO supplement, with mean durations of 6.14 (±3.06) and 4.76 (±2.68) hours before and after treatment, respectively. A smaller reduction without statistical signification was also observed for this outcome in the placebo group, from 7.53 (±4.24) to 6.68 (±4.42) hours. Only in DAO group, a decrease in the percentage of patients taking triptans was observed. The number of attacks and the scores of pain intensity showed a similar reduction in both groups. No adverse effects were registered in patients treated with DAO enzyme. Conclusions: Migranous patients supplemented with DAO enzyme during one month significantly reduced the duration of their migraine attacks by 1.4 hours. No statistically significant reduction was found in placebo group before and after treatment. The reduction of pain hours observed in placebo group (0.9 hours) could explain the lack of significant differences between both study groups. One month of DAO supplementation has demonstrated a positive trend in the improvement of migraine but more studies with a longer treatment period are needed to better assess the efficacy of DAO supplementation. Clinical trial registration number ISRCTN10091019; www.isrctn.org

Low serum diamine oxidase (DAO) activity levels in patients with migraine.

Histamine intolerance is a disorder in the homeostasis of histamine due to a reduced intestinal degradation of this amine, mainly caused by a deficiency in the enzyme diamine oxidase (DAO). Among the several multifaced symptoms associated with histamine intolerance, headache is one of the most recognised and disabling consequences. The aim of this study was to determine the prevalence of DAO deficiency in patients with a confirmed migraine diagnosis according to the current International Headache Society (IHS) and in non-migraine subjects. DAO activity was assessed in a total of 198 volunteers recruited at the Headache Unit of the Hospital General de Catalunya, 137 in the migraine group and 61 as a control group. DAO enzyme activity in blood samples was determined by ELISA test. Values below 80 HDU/ml (Histamine Degrading Unit/ml) were considered as DAO deficient. Mean value of DAO activity from migraine population (64.5 ±33.5 HDU/ml) was significantly lower (p<0.0001) than that obtained from healthy volunteers (91.9 ± 44.3 HDU/ml). DAO deficiency was more prevalent in migraine patients than in the control group. A high incidence rate of DAO deficiency (87%) was observed in the group of patients with migraine. On the other hand, 44% of non-migranous subjects had levels of DAO activity lower than 80 HDU/ml. Despite the multifactorial etiology of migraine, these results seem to indicate that this enzymatic deficit could be related to the onset of migraine

Discovery and validation of an NMR-based metabolomic profile in urine as TB biomarker

Despite efforts to improve tuberculosis (TB) detection, limitations in access, quality and timeliness of diagnostic services in low- and middle-income countries are challenging for current TB diagnostics. This study aimed to identify and characterise a metabolic profile of TB in urine by high-field nuclear magnetic resonance (NMR) spectrometry and assess whether the TB metabolic profile is also detected by a low-field benchtop NMR spectrometer. We included 189 patients with tuberculosis, 42 patients with pneumococcal pneumonia, 61 individuals infected with latent tuberculosis and 40 uninfected individuals. We acquired the urine spectra from high and low-field NMR. We characterised a TB metabolic fingerprint from the Principal Component Analysis. We developed a classification model from the Partial Least Squares-Discriminant Analysis and evaluated its performance. We identified a metabolic fingerprint of 31 chemical shift regions assigned to eight metabolites (aminoadipic acid, citrate, creatine, creatinine, glucose, mannitol, phenylalanine, and hippurate). The model developed using low-field NMR urine spectra correctly classified 87.32%, 85.21% and 100% of the TB patients compared to pneumococcal pneumonia patients, LTBI and uninfected individuals, respectively. The model validation correctly classified 84.10% of the TB patients. We have identified and characterised a metabolic profile of TB in urine from a high-field NMR spectrometer and have also detected it using a low-field benchtop NMR spectrometer. The models developed from the metabolic profile of TB identified by both NMR technologies were able to discriminate TB patients from the rest of the study groups and the results were not influenced by anti-TB treatment or TB location. This provides a new approach in the search for possible biomarkers for the diagnosis of TB

Actividad de la diamino-oxidasa en pacientes con migraña y efecto de la suplementación enzimática como tratamiento preventivo de la migraña episódica.

La migraña es una de las causas más habituales de cefalea. Se relacionan diversos neurotransmisores en su origen, entre ellos la histamina. La histamina es una amina biógena muy abundante en la dieta. Su degradación es producida en gran medida por la diamino-oxidas (DAO). Una alteración es esta vía metabólica podría provocar un aumento de la concentración de histamina plasmática con un consecuente riesgo de crisis de migraña. Material y Métodos El estudio consta de una primera parte en que se realiza un estudio poblacional en que se miden los niveles de actividad DAO en HDU/ml en 137 pacientes con migraña y se compara con un grupo de 61 pacientes sin antecedentes de cefalea. En la segunda parte se realiza una suplementación con enzima DAO a 50 pacientes con migraña, comparándose con un grupo control de 50 a los que se administró placebo. Se valora en número de crisis, horas de dolor, intensidad del dolor y consumo de triptanes durante un mes basal y se repiten las valoraciones durante un mes de tratamiento. Resultados El estudio observacional muestra un claro predominio del déficit en la actividad DAO de los pacientes con migraña (p< 0,005). En el ensayo clínico se muestra una reducción en el número de crisis y la duración de las mismas en el grupo tratado con DAO (p<0,005). La intensidad de dolor se reduce en ambos grupos sin diferencias significativas. Existe una disminución significativa del consumo de triptanes en los pacientes tratados con DAO que presentaban entre 5 y 10 crisis al mes. Dentro de las variables relacionadas con el acúmulo de histamina, se aprecia una reducción significativa del prurito en los pacientes tratados con DAO. Conclusiones El déficit de DAO es significativamente más prevalente en pacientes con migraña. La suplementación con DAO ha conseguido reducir el número y duración de crisis con una menor demanda de triptanes. El tratamiento se ha mostrado seguro al no presentarse reacciones adversas al mismo

Secondary phase formation on UO2 in phosphate media

he dissolution of UO2 (a chemical analog of uraninite and of spent nuclear fuel) has been studied by using a flow-through reactor. The UO2 dissolution rates at total View the MathML source concentrations of 10−4, 10−5, and 10−6 mol dm−3 have been determined to be: 1.3 × 10−10 mol m−2 s−1, 6.7 × 10−11 mol m−2 s−1, and 2.0 × 10−11 mol m−2 s−1, respectively. The dissolution rates determined are found to be higher than the ones determined for similar carbonate concentrations. Moreover, the surface of the UO2 has been studied in static tests by means of the scanning force microscopy technique (SFM) in order to follow the formation of any secondary solid phase on its surface. The formation of chernikovite (H2(UO2)2(PO4)2 · 8H2O) has been observed at a 10−4 M total View the MathML source concentration, while no uranyl-phosphate secondary phases have been found at lower View the MathML source concentrations. In experiments performed in the presence of both carbonate and phosphate, no precipitation of secondary phases has been observed. It is postulated that this is due to the formation of the highly stable uranyl-carbonate complexes in solution.Peer ReviewedPostprint (published version