Dissolution, Reactor, and Environmental Behavior of ZrO2-MgO Inert Fuel Matrix: Quarterly Report, January 2006 to March 2006

This project will examine inert matrix fuels containing ZrO2 and MgO as the inert matrix, with the relative amount of MgO varied from 30% to 70% in ZrO2. Reactor physics calculations will be used to examine suitable quantities of burnable poisons from the candidate elements Gd, Er, or Hf with reactor grade Pu providing the fissile component, with up to 10% of 239Pu. Ceramics will be synthesized and characterized based on the reactor physics results. The solubility of the fuel ceramics, in reactor conditions, reprocessing conditions, and repository conditions, will be investigated in a manner to provide thermodynamic data necessary for modeling. The fuel matrix will be designed based on neutronic properties, repository behavior, and reprocessing characteristics. The matrix should be as neutron transparent as possible. Burnable poisons will be used to maintain constant reactivity. The matrix should also act as a suitable host form for fission products and actinides in a repository environment. Finally, the matrix should be compatible with reprocessing schemes under development in the advanced fuel cycle. Work accomplished last quarter: The synthesis of the entire range of Zr to Mg, with Ce and Er concentrations being held at 5% and 2.5% respectively, has been completed with enough material for characterization and solubility studies. X-ray fluorescence has been performed on all ten batches to verify concentrations. X-ray diffraction has shown the range of Mg required for a single phase solid solution of cubic zirconia to be 10% to 28% Mg at current concentrations of Ce and Er. Pressure vessel experiments have begun. Acid dissolution studies suggest that it could be possible to leach uranium out of the ceramic without dissolving it. Therefore, these studies will be performed with uranium samples once they are prepared. The soxhlet studies have yielded quantitative data on water absorption, magnesium hydration, and corrosion of the ceramic. Calculations were performed on 3 dimensional full core neutronic modeling of MgO-ZrO2 fertile free fuel with previously selected most promising burnable poison designs. Work performed this quarter: Optical Microscopy and SEM (scanning electron microscopy) where used to image the ceramic material. Elemental scanning by microprobe showed CeO2 to be the least soluble in the 2 ZrO2. Microprobe analysis showed the periclase phase to be pure MgO and gave stoichiometric data on the ZrO2 phase. The entire range of ZrO2 to MgO was synthesized replacing CeO2 with UO2 as the plutonium analog. XAFS (X-ray absorption fine structure) and XANES (X-ray absorption near edge spectroscopy) were performed at Argonne National Lab. Pressure vessel dissolution studies showed that although the pellet could be physically destroyed, nothing was dissolved in the water. Sulfuric acid was successful in dissolving sintered material and may therefore be a possible head-in to a reprocessing scheme. The Soxhlet apparatus shows increasing corrosion rates with increasing MgO concentration

Zirconia-magnesia inert matrix fuel and waste form: Synthesis, characterization and chemical performance in an advanced fuel cycle

There is a significant buildup in plutonium stockpiles throughout the world, because of spent nuclear fuel and the dismantling of weapons. The radiotoxicity of this material and proliferation risk has led to a desire for destroying excess plutonium. To do this effectively, it must be fissioned in a reactor as part of a uranium free fuel to eliminate the generation of more plutonium. This requires an inert matrix to volumetrically dilute the fissile plutonium. Zirconia-magnesia dual phase ceramic has been demonstrated to be a favorable material for this task. It is neutron transparent, zirconia is chemically robust, magnesia has good thermal conductivity and the ceramic has been calculated to conform to current economic and safety standards. This dissertation contributes to the knowledge of zirconia-magnesia as an inert matrix fuel to establish behavior of the material containing a fissile component. First, the zirconia-magnesia inert matrix is synthesized in a dual phase ceramic containing a fissile component and a burnable poison. The chemical constitution of the ceramic is then determined. Next, the material performance is assessed under conditions relevant to an advanced fuel cycle. Reactor conditions were assessed with high temperature, high pressure water. Various acid solutions were used in an effort to dissolve the material for reprocessing. The ceramic was also tested as a waste form under environmental conditions, should it go directly to a repository as a spent fuel. The applicability of zirconia-magnesia as an inert matrix fuel and waste form was tested and found to be a promising material for such applications

Red-Emitting Manganese-doped Aluminum Nitride Phosphor

We report high efficiency luminescence with a manganese-doped aluminum nitride red-emitting phosphor under 254 nm excitation, as well as its excellent lumen maintenance in fluorescent lamp conditions, making it a candidate replacement for the widely deployed europium-doped yttria red phosphor. Solid-state reaction of aluminum nitride powders with manganese metal at 1900 °C, 10 atm N2 in a reducing environment results in nitrogen deficiency, as revealed diffuse reflectance spectra. When these powders are subsequently annealed in flowing nitrogen at 1650 °C, higher nitrogen content is recovered, resulting in white powders. Silicon was added to samples as an oxygen getter to improve emission efficiency. NEXAFS spectra and DFT calculations indicate that the Mn dopant is divalent. From DFT calculations, the UV absorption band is proposed to be due to an aluminum vacancy coupled with oxygen impurity dopants, and Mn2+ is assumed to be closely associated with this site. In contrast with some previous reports, we find that the highest quantum efficiency with 254 nm excitation (Q.E. = 0.86 ± 0.14) is obtained in aluminum nitride with a low manganese doping level of 0.06 mol.%. The principal Mn2+ decay of 1.25 ms is assigned to non-interacting Mn sites, while additional components in the microsecond range appear with higher Mn doping, consistent with Mn clustering and resultant exchange coupling. Slower components are present in samples with low Mn doping, as well as strong afterglow, assigned to trapping on shallow traps followed by detrapping and subsequent trapping on Mn

Comparing results of X-ray diffraction, \ub5-Raman spectroscopy and neutron diffraction when identifying chemical phases in seized nuclear material, during a comparative nuclear forensics exercise

This work presents the results for identification of chemical phases obtained by several laboratories as a part of an international nuclear forensic round-robin exercise. In this work powder X-ray diffraction (p-XRD) is regarded as the reference technique. Neutron diffraction produced a superior high-angle diffraction pattern relative to p-XRD. Requiring only small amounts of sample, \ub5-Raman spectroscopy was used for the first time in this context as a potentially complementary technique to p-XRD. The chemical phases were identified as pure UO 2 in two materials, and as a mixture of UO 2 , U 3 O 8 and an intermediate species U 3 O 7 in the third material

Genetic Determinants of Serum Testosterone Concentrations in Men

Testosterone concentrations in men are associated with cardiovascular morbidity, osteoporosis, and mortality and are affected by age, smoking, and obesity. Because of serum testosterone's high heritability, we performed a meta-analysis of genome-wide association data in 8,938 men from seven cohorts and followed up the genome-wide significant findings in one in silico (n = 871) and two de novo replication cohorts (n = 4,620) to identify genetic loci significantly associated with serum testosterone concentration in men. All these loci were also associated with low serum testosterone concentration defined as <300 ng/dl. Two single-nucleotide polymorphisms at the sex hormone-binding globulin (SHBG) locus (17p13-p12) were identified as independently associated with serum testosterone concentration (rs12150660, p = 1.2×10−41 and rs6258, p = 2.3×10−22). Subjects with ≥3 risk alleles of these variants had 6.5-fold higher risk of having low serum testosterone than subjects with no risk allele. The rs5934505 polymorphism near FAM9B on the X chromosome was also associated with testosterone concentrations (p = 5.6×10−16). The rs6258 polymorphism in exon 4 of SHBG affected SHBG's affinity for binding testosterone and the measured free testosterone fraction (p<0.01). Genetic variants in the SHBG locus and on the X chromosome are associated with a substantial variation in testosterone concentrations and increased risk of low testosterone. rs6258 is the first reported SHBG polymorphism, which affects testosterone binding to SHBG and the free testosterone fraction and could therefore influence the calculation of free testosterone using law-of-mass-action equation

Genetic determinants of heel bone properties: genome-wide association meta-analysis and replication in the GEFOS/GENOMOS consortium

Quantitative ultrasound of the heel captures heel bone properties that independently predict fracture risk and, with bone mineral density (BMD) assessed by X-ray (DXA), may be convenient alternatives for evaluating osteoporosis and fracture risk. We performed a meta-analysis of genome-wide association (GWA) studies to assess the genetic determinants of heel broadband ultrasound attenuation (BUA; n = 14 260), velocity of sound (VOS; n = 15 514) and BMD (n = 4566) in 13 discovery cohorts. Independent replication involved seven cohorts with GWA data (in silico n = 11 452) and new genotyping in 15 cohorts (de novo n = 24 902). In combined random effects, meta-analysis of the discovery and replication cohorts, nine single nucleotide polymorphisms (SNPs) had genome-wide significant (P < 5 × 10(-8)) associations with heel bone properties. Alongside SNPs within or near previously identified osteoporosis susceptibility genes including ESR1 (6q25.1: rs4869739, rs3020331, rs2982552), SPTBN1 (2p16.2: rs11898505), RSPO3 (6q22.33: rs7741021), WNT16 (7q31.31: rs2908007), DKK1 (10q21.1: rs7902708) and GPATCH1 (19q13.11: rs10416265), we identified a new locus on chromosome 11q14.2 (rs597319 close to TMEM135, a gene recently linked to osteoblastogenesis and longevity) significantly associated with both BUA and VOS (P < 8.23 × 10(-14)). In meta-analyses involving 25 cohorts with up to 14 985 fracture cases, six of 10 SNPs associated with heel bone properties at P < 5 × 10(-6) also had the expected direction of association with any fracture (P < 0.05), including three SNPs with P < 0.005: 6q22.33 (rs7741021), 7q31.31 (rs2908007) and 10q21.1 (rs7902708). In conclusion, this GWA study reveals the effect of several genes common to central DXA-derived BMD and heel ultrasound/DXA measures and points to a new genetic locus with potential implications for better understanding of osteoporosis pathophysiology

New genetic loci link adipose and insulin biology to body fat distribution.

Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms

Synthesis and characterization of actinide zironia pyrochlores

Zirconate based pyrochlores are very promising host phases for the minor actinides (MA = Np, Am, Cm) and plutonium as they are highly durable against aqueous alteration and radiation damages [1,2]. Pyrochlores are chemically very flexible structures with the general formula A2B2X6Y, which are known to form solid solutions. Here, we have focused on ZrO2 based pyrochlores with A = La, Nd, Eu, Pu, Cm; B = Zr; X = O; Y = O. Based on a wet chemical synthesis route, which was developed using non-radioactive surrogates, the solid solution formation of zirconia based pyrochlores with Pu and Cm was studied. A simultaneous co-precipitation of the Nd-, Zr- and Pu-hydroxides was applied to yield highly homogeneous pyrochlores. The crystallisation of the (Nd,Pu)2Zr2O7 pyrochlore solid solution was carried out during a sintering step under reducing conditions. Several samples with a Pu concentration of 5 mol% or 10 mol% were synthesised. Powder X-ray diffraction (XRD) measurements showed a systematic shift of the reflexes of the pyrochlore with the different Pu contents, indicating the structural uptake of Pu. However, the presence of additional PuO2 could not be excluded by XRD measurements. Furthermore, scanning electron microscopy (SEM) was carried out on a Nd1.9Pu0.1Zr2O7 pellet. The SEM images and energy-dispersive X-ray spectroscopy (EDX) confirmed a homogeneous distribution of Pu within the whole pellet. An insight into the structural environment of MA within the pyrochlore was obtained using time resolved laser fluorescence spectroscopy (TRLFS) [3]. Fluorescence spectra were obtained by UV and direct excitation of Cm and Eu doped La2Zr2O7. The observed splitting of the major species after direct excitation indicates the presence of Cm or Eu at the A position of the pyrochlore crystal structure. The maximum splitting of the 5D0 - 7F1,2 transition for the minor species in the pyrochlore structure is caused by disordered vacancies in the nearby environment of the A position, which are typical for the defect fluorite structure. Zirconia based pyrochlores are known to transform to the defect fluorite structure due to radiation damage. In future studies, the distinction of the defect fluorite and pyrochlore environment may allow the quantification of radiation damages in zirconia based pyrochlores via TRLFS

A new incorporation mechanism for trivalent actinides into bioapatite : a TRLFS and EXAFS study

One of the most toxic byproducts of nuclear power and weapons production is the transuranics, which have a high radiotoxicity and long biological half-life due to their tendency to accumulate in the skeletal system. This accumulation is inhomogeneous and has been associated with the chemical properties and structure of the bone material rather than its location or function. This suggests a chemical driving force to incorporation and requires an atomic scale mechanistic understanding of the incorporation process. Here we propose a new incorporation mechanism for trivalent actinides and lanthanides into synthetic and biologically produced hydroxyapatite. Time-resolved laser fluorescence spectroscopy and extended X-ray absorption fine structure have been used to demonstrate that trivalent actinides and lanthanides incorporate into the amorphous grain boundaries of apatite. This incorporation site can be used to explain patterns in uptake and distribution of radionuclides in the mammalian skeletal system

Crystallographic Study of Product Phases of Carbothermic Reduction and Nitridation of Hafnium Dioxide

Details of the carbothermic reduction/nitridation to synthesize hafnium nitride (HfN) and hafnium carbide (HfC) are scarce in the literature. Therefore, this current study was carried out to evaluate two pathways for synthesizing these two refractory materials: direct nitridation and carbothermic reduction/nitridation. Two mixtures of hafnium dioxide and carbon with C/HfO2 molar ratios of 2.15 and 3.1 were nitridized directly using flowing nitrogen gas at elevated temperatures (1300–1700 °C). The 3.1 C/HfO2 molar ratio mixture was also carbothermically reduced under flowing argon gas to synthesize HfC, which was converted into HfN by introducing a nitridation step under both N2(g) and N2(g)-10% H2(g). X-ray diffraction results showed the formation of HfN at 1300 and 1400 °C and HfC1–yNy at ≥1400 °C under direct nitridation of samples using a C/HfO2 molar ratio of 2.15. These phase analysis data together with lower lattice strain and greater crystallite sizes of HfC1–yNy that formed at higher temperatures suggested that the HfC1–yNy phase is preferred over HfN at those temperatures. Carbothermic reduction of 3.1 C/HfO2 molar ratio samples under an inert atmosphere produced single-phased HfC with no significant levels of dissolved oxygen. Carbothermic reduction nitridation made two phases of different carbon levels (HfC1–yNy and HfC1–y′Ny′, where y′ y), while direct nitridation produced a single HfC1–yNy phase under both N2 and N2-10% H2 cover gas environments