S. G. Johnson

A Description of the Ceramic Waste Form Production Process from the Demonstration Phase of the Electrometallurgical Treatment of EBR-II Spent Fuel

Abstract The electrometallurgical treatment (EMT) process has been designed and developed for stabilizing sodium-bonded, metallic fuel into two high-level waste forms. This process has recently been successfully demonstrated with irradiated EBR-II fuel at Argonne National Laboratory-West. Part of the EMT process is to immobilize fission-product-bearing waste salt, which results from electrorefining, in a ceramic waste form—a glass-bonded sodalite. The sodalite is formed by hot isostatically pressing salt-loaded zeolite at temperatures up to 850°C and pressures up to 100 MPa. The specific unit operations that comprise ceramic waste production include steps for salt grinding, zeolite drying, blending salt and zeolite and glass frit in a v-blender, and consolidating the powders in a hot isostatic press. The results of testing these unit operations with irradiated salt from the EMT demonstration are summarized and include some preliminary characterization of the final irradiated ceramic waste form created by this process.

Characterization of a glass-bonded ceramic waste form loaded with U and Pu

This paper presents microscopic characterization of four samples of a ceramic waste form (CWF) developed for disposal of actinide-containing electrorefiner salts. The four samples were prepared to investigate the influence of water content and the Pu:U ratio on CWF microstructure and performance. While the overall phase content is not strongly influenced by either variable, the presence of water in the initial zeolite has a detectable effect on CWF microstructure. It is found to influence the distribution of the major actinide host phase, a (U,Pu)O{sub 2} mixed oxide.

Characterization of a ceramic waste form encapsulating radioactive electrorefiner salt

Argonne National Laboratory has developed a ceramic waste form to immobilize radioactive waste salt produced during the electrometallurgical treatment of spent fuel. This study presents the first results from electron microscopy and durability testing of a ceramic waste form produced from that radioactive electrorefiner salt. The waste form consists of two primary phases: sodalite and glass. The sodalite phase appears to incorporate most of the alkali and alkaline earth fission products. Other fission products (rare earths and yttrium) tend to form a separate phase and are frequently associated with the actinides, which form mixed oxides. Seven-day leach test results are also presented.

Laser ablation inductively coupled plasma atomic emission spectrometry of a uranium-zirconium alloy: ablation properties and analytical behavior

Abstract The ablation properties and analytical behavior of a uranium-zirconium alloy have been examined using tandem laser ablation/pneumatic nebulization sample introduction in conjunction with inductively coupled atomic emission spectrometry (LA-ICP-AES). An apparent change in composition of the laser ablation aerosol (1–15 GW cm −2 Zr deficient, 40–250 GW cm −2 Zr rich) is observed. This phenomenon is independent of laser wavelength. After collection and bulk chemical analysis of the ablation product, this phenomenon is attributed to an atomization interference in the ICP. Two distinct modes of laser ablation have been observed which depend upon the wavelength of the ablating laser (visible or near infrared). These two modes result in characteristic ablation crater types and analyte emission behavior. Ablation yields at 1064 nm are dependent upon laser power density only, whilst yields at 532 nm are dependent upon both laser power density and illumination area. The latter is considered to be symptomatic of direct interaction of the laser light with the surface, and the former, of indirect coupling of laser energy, via a micro-plasma, into the surface.

Isotopic uranium determination by inductively coupled plasma atomic emission spectrometry using conventional and laser ablation sample introduction

The use of inductively coupled plasma atomic emission spectrometry (ICP-AES) for the determination of 235U: 238U isotope ratios in U–Zr metal alloys (90% m/m U, 10% m/m Zr) is described. Conventional pneumatic nebulization and laser ablation sample introduction techniques were utilized. The results of the determination agreed, within experimental uncertainty, with isotope ratios determined by thermal ionization mass spectrometry (TIMS), e.g., 235U: 238U for conventional nebulization = 2.091 ± 0.006, for laser ablation = 2.092 ± 0.015 and for TIMS = 2.0940 ± 0.0004. The precision, i.e., the relative standard deviation (RSD), of the sequential determination of the intensities of the 235U and 238U components of the U emission line and the resultant isotope ratios was improved significantly by the use of an intrinsic internal standard (Zr), i.e., RSD = 1.6% to RSD = 0.17%.

High-Resolution Inductively Coupled Plasma Atomic Emission Spectrometry for the Determination of Burnup in Spent Nuclear Fuel:

The development of a method for the estimation of burnup of nuclear fuels by the determination of 236U by high-resolution inductively coupled plasma spectrometry has been demonstrated. Linear calibration curves are obtained and a limit of quantification of ∼ 3 atom % burnup established. The precision, in terms of the relative standard deviation (RSD) of the determination, was 3.7% RSD for 1.58 atom % of 236U. These results were obtained by using a spectrometer with a resolving power of 2.3 × 105 and with the application of a spectral deconvolution using a nonlinear curve-fitting algorithm. A complementary method, the determination of 139La, was also investigated and proved to be accurate (recovery = 101.5%) and precise (RSD = 2.2%) with a limit of quantification of ∼ 0.5 atom % burnup. These methods were developed with the use of model solutions which approximate digests of irradiated fuels but which contained no active fission product species.

Glass-Ceramic Waste Forms for Immobilizing Plutonium

Results are reported on several new glass and glass-ceramic waste formulations for plutonium disposition. The approach proposed involves employing existing calcined high level waste (HLW) present at the Idaho Chemical Processing Plant (ICPP) and an additive to: (1) aid in the formation of a durable waste form and (2) decrease the attractiveness level of the plutonium from a proliferation viewpoint. The plutonium, PuO{sub 2}, loadings employed were 15 wt% (glass) and 17 wt% (glass-ceramic). Results in the form of x-ray diffraction patterns, microstructure and durability tests are presented on cerium surrogate and plutonium loaded waste forms using simulated calcined HLW and demonstrate that durable phases, zirconia and zirconolite, contain essentially all the plutonium.

Determination of burnup in spent nuclear fuel by application of fiber optic high-resolution inductively coupled plasma atomic emission spectroscopy (FO-HR-ICP-AES)

Abstract The determination of burnup, an indicator of fuel cycle efficiency, has been accomplished by the determination of 139La by high-resolution inductively coupled plasma atomic emission spectroscopy (HR-ICP-AES). Solutions of digested samples of reactor fuel rods were introduced into a shielded glovebox housing an inductively-coupled plasma (ICP) and the resulting atomic emission transmitted to a high-resolution spectrometer by a 31 m fiber optic bundle. Total and isotopic U determination by thermal ionization mass spectrometry (TIMS) is presented to allow for the calculation of burnup for the samples. This method of burnup determination reduces the time, material, sample handling and waste generation associated with typical burnup determinations which require separation of lanthanum from the other fission products with high specific activities.

Laser ablation–inductively coupled plasma atomic emission spectrometry for the determination of lanthanides and uranium in fuel reconditioning materials: problems, solutions and implications

The successful determination of uranium, lanthanum, cerium, neodymium and yttrium by LA–ICP-AES is reported. LA was performed using a Q-switched Nd:YAG laser operating at 1064, 532 or 355 nm. Ablation at 355 nm was shown to offer optimum performance. The sample matrix consisted of a mixture of lithium and potassium chlorides which, when molten, form the electrolyte for an electro-refining process for the treatment of spent nuclear fuels. Analytical recoveries in the range 96–103% were obtained with a relative standard deviation of 1–3%, i.e., U = 100%, La = 100%, Ce = 96%, Nd = 97% and Y = 103%. The detection limit for uranium was 25 µg g–1 using the optimum LA conditions. The use of solid standards closely matching the sample material was found to be essential if accurate analyses were to be obtained. Calibration using uranium compounds other than the specific compound found in the sample was unsuccessful. For results of the highest quality, single phase materials were produced to allow for accurate internal standardization. Spectral interferences were minimized by the use of high resolution spectrometry. The reliability of the analyses was improved by the introduction of additional aerosol processing in the form of a Scott-type spray chamber between the ablation cell and the ICP torch.

Microstructure and Leaching Characteristics of a Technetium Containing Metal Waste Form

Argonne National Laboratory is developing an electrometallurgical treatment for spent fuel from the experimental breeder reactor II. A product of this treatment process is a metal waste form that incorporates the stainless steel cladding hulls, zirconium from the fuel and the fission products that are noble to the process, i.e., Tc, Ru, Pd, Rh, Ag. The nominal composition of this waste form is stainless steel/15 wt% zirconium 1-4 wt% noble metal fission products. The behavior of technetium is of particular importance from a disposal point of view for this waste form due to its long half life, 2. 14E5 years, and its mobility in groundwater. To address these concerns a limited number of spiked metal waste forms were produced containing Tc. These surrogate waste forms were then studied using scanning electron microscopy and selected leaching tests.