The Chemistry os Spent Nuclear Fuel From X-Ray Absorption Spectroscopy

Present and future nuclear fuel cycles will require an understanding of the complex chemistry of trace fission products and transuranium actinides in spent nuclear fuel (SNF). Because of the unique analytical challenges presented by SNF to the materials scientist, many of its fundamental physical and chemical properties remain poorly understood, especially on the microscopic scale. Such an understanding of the chemical states of radionuclides in SNF would benefit development of technologies for fuel monitoring, fuel performance improvement and modeling, fuel reprocessing, and spent fuel storage and disposal. We have recently demonstrated the use of synchrotron x-ray absorption spectroscopy (XAS) to examine crystal chemical properties of actinides and fission products in extracted specimens of SNF. Information obtained includes oxidation state, chemical bond coordination, and quantitative elemental concentration and distribution. We have also used XAS in a scanning mode to obtain x-ray spectral micrographs with resolution approaching 1 micron. A brief overview of the technique will be presented, along with findings on uranium, plutonium, neptunium, technetium, and molybdenum in commercial PWR SNF specimens

Microscopic Examination of a Corrosion Front in Spent Nuclear Fuel

Spent uranium oxide nuclear fuel hosts a variety of trace chemical constituents, many of which must be sequestered from the biosphere during fuel storage and disposal. In this paper we present synchrotron x-ray absorption spectroscopy and microscopy findings that illuminate the resultant local chemistry of neptunium and plutonium within spent uranium oxide nuclear fuel before and after corrosive alteration in an air-saturated aqueous environment. We find the plutonium and neptunium in unaltered spent fuel to have a +4 oxidation state and an environment consistent with solid-solution in the UO{sub 2} matrix. During corrosion in an air-saturated aqueous environment, the uranium matrix is converted to uranyl U(VI)O{sub 2}{sup 2+} mineral assemblage that is depleted in plutonium and neptunium relative to the parent fuel. At the corrosion front interface between intact fuel and the uranyl-mineral corrosion layer, we find evidence of a thin ({approx}20 micrometer) layer that is enriched in plutonium and neptunium within a predominantly U{sup 4+} environment. Available data for the standard reduction potentials for NpO{sup 2+}/Np{sup 4+} and UO{sub 2}{sup 2+}/U{sup 4+} couples indicate that Np(IV) may not be effectively oxidized to Np(V) at the corrosion potentials of uranium dioxide spent nuclear fuel in air-saturated aqueous solutions. Neptunium is an important radionuclide in dose contribution according to performance assessment models of the proposed U. S. repository at Yucca Mountain, Nevada. A scientific understanding of how the UO{sub 2} matrix of spent nuclear fuel impacts the oxidative dissolution and reductive precipitation of neptunium is needed to predict its behavior at the fuel surface during aqueous corrosion. Neptunium would most likely be transported as aqueous Np(V) species, but for this to occur it must first be oxidized from the Np(IV) state found within the parent spent nuclear fuel [1]. In the immediate vicinity of the spent fuel's surface the redox and nucleation behavior is likely to promote/enhance nucleation of NpO{sub 2} and Np{sub 2}O{sub 5}. Alternatively, Np may be incorporated into uranyl (UO{sub 2}{sup 2+}) alteration phases [2]. In some cases, less-soluble elements such as plutonium will be enriched near the surface of the corroding fuel [3]. We have used focused synchrotron x-rays from the MRCAT beam line at the Advanced Photon Source (APS) at Argonne National Lab to examine a specimen of spent nuclear fuel that had been subject to 10 years of corrosion testing in an environment of humid air and dripping groundwater at 90 C [4]. We find evidence of a region, approximately 20 microns in thickness, enriched in plutonium and neptunium at the corrosion front that exists between the uranyl silicate alteration mineral rind and the unaltered uranium oxide fuel (Figures 1 and 2). The uranyl silicate is itself found to be depleted in these transuranic elements relative to their abundance relative to uranium in the parent fuel. This suggests a low mobility of these components owing to a resistance to oxidize further in the presence of a UO{sub 2}{sup 2+}/U{sup 4+} couple [5]

In vivo molecular imaging of chemokine receptor CXCR4 expression in patients with advanced multiple myeloma

CXCR4 is a G-protein-coupled receptor that mediates recruitment of blood cells toward its ligand SDF-1. In cancer, high CXCR4 expression is frequently associated with tumor dissemination and poor prognosis. We evaluated the novel CXCR4 probe [(68)Ga]Pentixafor for in vivo mapping of CXCR4 expression density in mice xenografted with human CXCR4-positive MM cell lines and patients with advanced MM by means of positron emission tomography (PET). [(68)Ga]Pentixafor PET provided images with excellent specificity and contrast. In 10 of 14 patients with advanced MM [(68)Ga]Pentixafor PET/CT scans revealed MM manifestations, whereas only nine of 14 standard [(18)F]fluorodeoxyglucose PET/CT scans were rated visually positive. Assessment of blood counts and standard CD34(+) flow cytometry did not reveal significant blood count changes associated with tracer application. Based on these highly encouraging data on clinical PET imaging of CXCR4 expression in a cohort of MM patients, we conclude that [(68)Ga]Pentixafor PET opens a broad field for clinical investigations on CXCR4 expression and for CXCR4-directed therapeutic approaches in MM and other diseases

Multitechnique Characterization of a Polyaniline Iron Carbon Oxygen Reduction Catalyst

This paper summarizes a XANES, XPS, XRD, and Mo amp; 776;ssbauer study of an oxygen reduction reaction ORR catalyst obtained via a heat treatment of polyaniline, iron, and carbon black. The catalyst was characterized at several critical synthesis stages and following heat treatment at various temperatures. The effect of sulfur during the synthesis was also investigated. XANES linear combination fitting XANES LCF was used to determine the speciation of iron using 16 iron standards. The highest ORR activity was measured with a catalyst heat treated at 900 C, with the largest Fe amp; 8722;Nx content, as determined by the XANES LCF, also characterized by the highest microporosity. An absence or a reduction in the amount of a sulfur based oxidant in the aniline polymerization was found to lead to an increase in the amount of iron carbide formed during the heat treatment and a decrease in the number of Fe amp; 8722;N4 centers, thus attesting to an indirect beneficial role of sulfur in the catalyst synthesis. Using principal component analysis PCA , a good correlation was found between the ORR activity and the presence of Fe amp; 8722;Nx structure

The effects of porcine somatotropin (pST) and dietary lysine level on growth performance and carcass characteristics of finishing swine

Seventy-two finishing pigs averaging 130 lb were utilized to determine the effects of PST and dietary lysine on growth performance and carcass characteristics. Pigs were injected daily with 4 mg PST in the extensor muscle of the neck and fed either a pelleted corn-sesame meal diet (.6% lysine, 17.7% crude protein) or diets containing .8, 1.0, 1.2, or 1.4% lysine provided by L-lysine HCl. All diets were formulated to contain at least 200% of NRC (1979) recommendations for other amino acids. Control pigs received a placebo injection and the .6% lysine diet. Increasing levels of dietary lysine resulted in increased average daily gain (ADG) and improved feed conversion (F/G; linear and quadratic, P<.01) for PST-treated pigs. Adjusted backfat thickness (ABF) was not affected by dietary lysine; however, PST-treated pigs had less backfat (P<.05) than control pigs. Longissimus muscle area (LMA), trimmed ham, and loin weights increased as dietary lysine was increased among PST-treated pigs (linear and quadratic, P<.01). Percentage of moisture and crude protein of the longissimus muscle increased, (linear P<.05, linear and quadratic P<.05, respectively), whereas dry matter and fat content decreased (linear P<.05). Similar trends in composition were observed for other ham muscles (semimembranous, semitendinosus, and biceps femoris). Heart, liver, kidney, spleen, and lung weights were not affected by PST or lysine treatment. Urea concentrations in plasma on day 28 decreased linearly (P<.O I) as lysine level increased, whereas plasma lysine and insulin increased (linear and quadratic, P<.OI). Plasma glucose and free fatty acid concentrations on day 28 tended to increase (quadratic P<. I0) with increasing dietary lysine level. Plasma somatotropin level was elevated 2 to 3 times in PST-treated pigs compared to control pigs, but was not affected by dietary lysine level. Our results indicate a relatively high requirement for lysine in PST-treated pigs. Growth performance and carcass traits were optimized at dietary lysine levels of 1.2 to 1.4%, which corresponds to lysine intakes of 30 to 36 g/day. These results demonstrate that PST-administration nearly doubles the lysine requirement of finishing swine