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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on U7Mo by Materials Project

U7Mo crystallizes in the orthorhombic Pmmm space group. The structure is three-dimensional. there are five inequivalent U sites. In the first U site, U is bonded in a 10-coordinate geometry to six U and two equivalent Mo atoms. There are four shorter (2.98 Å) and two longer (2.99 Å) U–U bond lengths. Both U–Mo bond lengths are 2.96 Å. In the second U site, U is bonded in a 4-coordinate geometry to four equivalent U and four equivalent Mo atoms. All U–U bond lengths are 2.86 Å. All U–Mo bond lengths are 2.98 Å. In the third U site, U is bonded in a distorted q6 geometry to ten U atoms. There are a spread of U–U bond distances ranging from 2.98–3.08 Å. In the fourth U site, U is bonded to ten U and two equivalent Mo atoms to form a mixture of distorted edge, face, and corner-sharing UU10Mo2 cuboctahedra. Both U–U bond lengths are 3.00 Å. Both U–Mo bond lengths are 3.55 Å. In the fifth U site, U is bonded in a distorted q6 geometry to ten U atoms. Both U–U bond lengths are 3.00 Å. Mo is bonded in a distorted body-centered cubic geometry to twelve U atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The Effect of Homogenization Heat Treatment on the Texture Evolution in U-10Mo Alloy

Uranium alloyed with 10 wt% Mo (U-10Mo) undergoes discontinuous precipitation (DP) when subjected to sub-eutectoid heat-treatment. It is hypothesized that the crystallographic texture of the U-10Mo can be modified to minimize the degree of DP, however the evolution of texture throughout the manufacturing process is not well understood. Crystallographic textures of two U-10Mo samples homogenized at 900°C and 1000°C were studied after uniaxial rolling and annealing. A total of 6 samples were analyzed upon rolling using a combination of hot and cold rolling conditions to strains of 83%, 90% and 97% and subsequently annealed at 700°C for one hour. Microstructures and textures were analyzed via electron backscatter diffraction (EBSD) for each homogenization, strain and post-annealed states. Results show that the U-10Mo exhibits typical rolling textures seen in body-centered cubic materials with increasing intensities of both a- and ?-fibers with increasing strain. After recrystallization, the texture appeared to be effectively randomized in all samples. Homogenization temperature showed no effect on the rolling and recrystallization behavior. Potential factors leading to the randomization of texture are discussed along with the implications of textures on the minimization of DP.

nuclear fuel, texture, rolling↗
DOE OSTI2022

Delayed onset of discontinuous precipitation-based phase transformation in U10Mo alloys doped with Silicon

A uranium-10 wt% molybdenum (U-10Mo) alloy is one of the primary candidates for metallic fuels that would use low-enriched uranium in place of highly enriched uranium, to support nuclear nonproliferation efforts. Optimal performance of a U-based metallic nuclear fuel can be achieved by retaining the high-temperature, body-centered cubic (bcc) allotrope (γ-U) at room temperature, which can be accomplished in the U-10Mo alloy. However, presence of minor alloying elements can influence the final constitution of room-temperature phases in the U10Mo alloy, specifically, formation of α-U phase which results in anisotropic behavior of the fuel in reactor. Further, through a detailed transmission electron microscopy analysis, the present study reports the constituent phases that are present in a U10Mo alloy containing ~0.1 wt% Si after it is subjected to homogenization heat treatment and thermomechanical processing. For comparison, results from an undoped U10Mo alloy are also included. The experimental results reveal that γ-UMo solid solution is the major phase in a hot-rolled, Si-doped U10Mo alloy metallic fuel foil, along with U 2 MoSi 2 C, UC, and U 2 Mo, after isothermal annealing at 460 °C for 10h. In contrast, after the same heat treatment, the undoped U10Mo alloy metallic fuel had formed a noticeable amount of α-U along prior γ-UMo grain boundaries through discontinuous precipitation (DP, area fraction: ~27.9%) with characteristic lamellar morphology, together with γ-UMo, UC, and U 2 Mo. This result indicates that doping with Si could mitigate the DP reaction in U10Mo alloy and prevent formation of undesirable α-U. This work sheds light on optimizing Si-doping–dominated microstructure in U10Mo fuels and facilitates designing and tuning of microstructures of U10Mo alloys for tailoring the final designed performance of the fuel under irradiation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1997

Geochemistry of approximately 1.9 Ga sedimentary rocks from northeastern Labrador, Canada

Fifty-eight rock chips from fifteen samples of sedimentary rocks from the Ramah Group (approximately 1.9 Ga) in northeastern Labrador, Canada, were analyzed for major and minor elements, including C and S, to elucidate weathering processes on the Earth's surface about 1.9 Ga ago. The samples come from the Rowsell Harbour, Reddick Bight, and Nullataktok Formations. Two rock series, graywackes-gray shales of the Rowsell Harbour, Reddick Bight and Nullataktok Formations, and black shales of the Nullataktok Formation, are distinguishable on the basis of lithology, mineralogy, and major and trace element chemistry. The black shales show lower concentrations than the graywackes-gray shales in TiO2 (0.3-0.7 wt% vs. 0.7-1.8 wt%), Al2O3 (9.5-20.1 wt% vs. 13.0-25.0 wt%), and sigma Fe (<1 wt% vs. 3.8-13.9 wt% as FeO). Contents of Zr, Th, U, Nb, Ce, Y, Rb, Y, Co, and Ni are also lower in the black shales. The source rocks for the Ramah Group sediments were probably Archean gneisses with compositions similar to those in Labrador and western Greenland. The major element chemistry of source rocks for the Ramah Group sedimentary rocks was estimated from the Al2O3/TiO2 ratios of the sedimentary rocks and the relationship between the major element contents (e.g., SiO2 wt%) and Al2O3/TiO2 ratios of the Archean gneisses. This approach is justified, because the Al/Ti ratios of shales generally retain their source rock values; however, the Zr/Al, Zr/Ti, and Cr/Ni ratios fractionate during the transport of sediments. The measured SiO2 contents of shales in the Ramah Group are generally higher than the estimated SiO2 contents of source rocks by approximately 5 wt%. This correction may also have to be applied when estimating average crustal compositions from shales. Two provenances were recognized for the Ramah Group sediments. Provenance I was comprised mostly of rocks of bimodal compositions, one with SiO2 contents approximately 45 wt% and the other approximately 65 wt%, and was the source for most sedimentary rocks of the Ramah Group, except for black shales of the Nullataktok Formation. The black shales were apparently derived from Provenance II that was comprised mostly of felsic rocks with SiO2 contents approximately 65 wt%. Comparing the compositions of the Ramah Group sedimentary rocks and their source rocks, we have recognized that several major elements, especially Ca and Mg, were lost almost entirely from the source rocks during weathering and sedimentation. Sodium and potassium were also leached almost entirely during the weathering of the source rocks. However, significant amounts of Na were added to the black shales and K to all the rock types during diagenesis and/or regional metamorphism. The intensity of weathering of source rocks for the Ramah Group sediments was much higher than that of typical Phanerozoic sediments, possibly because of a higher PCO2 in the Proterozoic atmosphere. Compared to the source rock values, the Fe3+/Ti ratios of many of the graywackes and gray shales of the Ramah Group are higher, the Fe2+/Ti ratios are lower, and the sigma Fe/Ti ratios are the same. Such characteristics of the Fe geochemistry indicate that these sedimentary rocks are comprised of soils formed by weathering of source rocks under an oxygen-rich atmosphere. The atmosphere about 1.9 Ga was, therefore, oxygen rich. Typical black shales of Phanerozoic age exhibit positive correlations between the organic C contents and the concentrations of S, U, and Mo, because these elements are enriched in oxygenated seawater and are removed from seawater by organic matter in sediments. However, such correlations are not found in the Ramah Group sediments. Black shales of the Ramah Group contain 1.7-2.8 wt% organic C, but are extremely depleted in sigma Fe (<1 wt% as FeO), S (<0.3 wt%), U (approximately l ppm), Mo (<5 ppm), Ni (<2 ppm), and Co (approximately 0 ppm). This lack of correlation, however, does not imply that the approximately 1.9 Ga atmosphere-ocean system was anoxic. Depletion of these elements from the Ramah Group sediments may have occurred during diagenesis.

Non-NASA Center↗
DOE OSTI2025

Identifying Challenges in Safeguards for Metallic Fuel Fabrication Facilities

As new advanced reactors gain popularity, there is an increasing interest in metallic fuel fabrication for fast reactors. While metallic fuels themselves are not a new idea, as many of the first reactors employed metallic fuels, new designs, compositions, and fabrication methods are appearing throughout the nuclear community. As the interest grows and facilities are constructed, both domestic and international safeguards will need to be heavily involved to support safeguards-by-design (SBD) measures from the start. This work compiles a review of historical and modern fuel types and fabrication methods, fabrication processes, safeguards gaps, and potential safeguards solutions. Metallic nuclear fuel types have been around for many decades and were included in some of the first reactors including the Experimental Breeder Reactor (EBR)-I and -II, the Fermi 1 reactor, the Integral Fast Reactor (IFR), and the Dounreay Fast Reactor (DFR). These reactors used various compositions including pure uranium (U) metal, U-zirconium (Zr) alloys, plutonium (Pu)-aluminum (Al) alloys, U-fissium (Fs) alloys, U-Pu-Zr alloys, and U-molybdenum (Mo) alloys [1, 2, 3, 4, 5]. These small alloying additions are included to improve the material properties of the pure U metal. The alpha-phase U (stable below 661C) suffers elongation in one direction causing grain boundary cracking and increasing creep rate due to irradiation growth, thermal cycling, and preferential crystal orientation. It is ideal to utilize the gamma-phase U (typically stable above 769C) by adding small amounts of alloying elements such as Zr or Mo to stabilize this phase down to room temperature [3]. Additionally, some research has been focused on U with transuranic (TRU) elements present, typically coming from the used fuel recycling process. Including these elements in fast reactor fuel can aid in the reduction of nuclear waste by burning minor long-lived actinides. However, the additions of TRU elements can cause concerns to arise when trying to fabrication or safeguard metallic fuels. A typical metallic fuel element is shown in Figure 1. Sodium is added into the cladding to create a thermal bond between the fuel slug and cladding wall. The fuel slug is then inserted and the end plug is welded on to the top of the fuel element. A gas plenum is left to create a headspace for gaseous fission products to escape rather than continue to build in the fuel itself [1, 5]. Other fuel element geometries exist as well, such as the Lightbridge twisted cruciform geometry shown in Figure 2 [6]. This design allows for better cooling performance and provides room for fuel rod swelling without impacting the fuel rod diameter. There are many different fabrication methods for metallic fuels, which is one of the many benefits of these fuel types. Many of these fabrication methods are relatively easy and cost-efficient. The most popular fabrication method is injection casting, sometimes called vacuum induction melting (VIM), shown in Figure 3 [4, 8, 9, 7, 10]. This method was largely used for EBR-II fuel fabrication. The injection casting system is contained inside of a vessel consisting of a Y2O3-coated graphite crucible surrounded by an induction coil with ZrO2-coated quartz molds suspended above the crucible. The fuel feedstock is placed inside of the graphite crucible and melted using the induction furnace. The induction furnace utilizes a dual frequency with the high frequency melting the feedstock and the low frequency causing stirring of the melted feedstock to form a homogeneous mixture. The mixture is heated to approximately 1600C in an argon environment. The vessel is evacuated and then the quartz molds are lowered into the graphite crucible containing the molten metal and the vessel is repressurized to inject the metal fuel upwards into the molds. The molds are removed and then shattered to release the fuel slugs. This fabrication method was used to fabricate 39,000 metallic fuel pins for EBR-II. While injection casting has been the most common metallic fuel fabrication method throughout the decades, many other methods have been explored including low-pressure gravity casting, microwave casting, continuous casting, centrifugal casting, coextrusion, and many others [11, 12, 8, 13, 14, 15]. Some of these methods aim to mitigate challenges that arise with americium (Am) volatilization during the casting process for TRU-containing fuel feedstocks, an issue with injection casting. Coextrusion is one of the methods explored at the Idaho National Laboratory (INL) and has been utilized for the initial fabrication tests of Lightbridge's unique fuels, as well as other metallic fuels with cladding coextruded. In this process, large billets are formed and machined and then inserted into a molten salt bath for approximately 30 minutes. The billets are then loaded into the extrusion press and extruded. This process can be seen in Figure 4 [15].

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Materials Data on UMo13P9 by Materials Project

UMo13P9 crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. U is bonded to six equivalent Mo and six equivalent P atoms to form distorted face-sharing UMo6P6 cuboctahedra. All U–Mo bond lengths are 3.12 Å. All U–P bond lengths are 2.91 Å. There are four inequivalent Mo sites. In the first Mo site, Mo is bonded in a 5-coordinate geometry to five P atoms. There are four shorter (2.46 Å) and one longer (2.72 Å) Mo–P bond lengths. In the second Mo site, Mo is bonded in a 6-coordinate geometry to two equivalent U and four P atoms. There are two shorter (2.41 Å) and two longer (2.53 Å) Mo–P bond lengths. In the third Mo site, Mo is bonded in a 5-coordinate geometry to five P atoms. There are a spread of Mo–P bond distances ranging from 2.42–2.71 Å. In the fourth Mo site, Mo is bonded in a 6-coordinate geometry to six equivalent P atoms. All Mo–P bond lengths are 2.47 Å. There are three inequivalent P sites. In the first P site, P is bonded in a 8-coordinate geometry to two equivalent U and six Mo atoms. In the second P site, P is bonded in a 8-coordinate geometry to eight Mo atoms. In the third P site, P is bonded in a 7-coordinate geometry to seven Mo atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U2B6Mo by Materials Project

U2MoB6 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are two inequivalent U3+ sites. In the first U3+ site, U3+ is bonded in a 2-coordinate geometry to fourteen B2- atoms. There are a spread of U–B bond distances ranging from 2.64–2.80 Å. In the second U3+ site, U3+ is bonded in a 12-coordinate geometry to one U3+ and twelve B2- atoms. The U–U bond length is 2.53 Å. There are a spread of U–B bond distances ranging from 2.63–2.74 Å. Mo6+ is bonded in a 10-coordinate geometry to ten B2- atoms. There are a spread of Mo–B bond distances ranging from 2.38–2.42 Å. There are six inequivalent B2- sites. In the first B2- site, B2- is bonded in a 3-coordinate geometry to four equivalent U3+, two equivalent Mo6+, and three B2- atoms. There are a spread of B–B bond distances ranging from 1.77–1.82 Å. In the second B2- site, B2- is bonded in a 3-coordinate geometry to four U3+, two equivalent Mo6+, and three B2- atoms. There is one shorter (1.69 Å) and one longer (1.81 Å) B–B bond length. In the third B2- site, B2- is bonded in a 3-coordinate geometry to four U3+, two equivalent Mo6+, and three B2- atoms. There is one shorter (1.76 Å) and one longer (1.79 Å) B–B bond length. In the fourth B2- site, B2- is bonded in a 3-coordinate geometry to four U3+, two equivalent Mo6+, and three B2- atoms. There is one shorter (1.68 Å) and one longer (1.82 Å) B–B bond length. In the fifth B2- site, B2- is bonded in a 3-coordinate geometry to four U3+, two equivalent Mo6+, and three B2- atoms. In the sixth B2- site, B2- is bonded in a 8-coordinate geometry to six U3+ and two B2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on UB4Mo by Materials Project

UMoB4 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. U4+ is bonded in a 2-coordinate geometry to fourteen B+1.50- atoms. There are a spread of U–B bond distances ranging from 2.67–2.81 Å. Mo2+ is bonded in a 10-coordinate geometry to ten B+1.50- atoms. There are a spread of Mo–B bond distances ranging from 2.33–2.45 Å. There are four inequivalent B+1.50- sites. In the first B+1.50- site, B+1.50- is bonded in a 9-coordinate geometry to four equivalent U4+, two equivalent Mo2+, and three B+1.50- atoms. There are a spread of B–B bond distances ranging from 1.75–1.88 Å. In the second B+1.50- site, B+1.50- is bonded in a 3-coordinate geometry to four equivalent U4+, two equivalent Mo2+, and three B+1.50- atoms. There is one shorter (1.74 Å) and one longer (1.75 Å) B–B bond length. In the third B+1.50- site, B+1.50- is bonded in a 9-coordinate geometry to two equivalent U4+, four equivalent Mo2+, and three B+1.50- atoms. There is one shorter (1.75 Å) and one longer (1.77 Å) B–B bond length. In the fourth B+1.50- site, B+1.50- is bonded in a 3-coordinate geometry to four equivalent U4+, two equivalent Mo2+, and three B+1.50- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U2Mo2C3 by Materials Project

U2Mo2C3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. U4+ is bonded in a pentagonal planar geometry to five C4- atoms. There are three shorter (2.43 Å) and two longer (2.46 Å) U–C bond lengths. Mo2+ is bonded to four C4- atoms to form a mixture of edge and corner-sharing MoC4 trigonal pyramids. There are a spread of Mo–C bond distances ranging from 2.11–2.18 Å. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to four equivalent U4+ and two equivalent Mo2+ atoms to form CU4Mo2 octahedra that share corners with twelve equivalent CU3Mo3 octahedra, edges with two equivalent CU4Mo2 octahedra, and faces with two equivalent CU3Mo3 octahedra. The corner-sharing octahedra tilt angles range from 40–59°. In the second C4- site, C4- is bonded to three equivalent U4+ and three equivalent Mo2+ atoms to form CU3Mo3 octahedra that share corners with six equivalent CU4Mo2 octahedra, edges with six equivalent CU3Mo3 octahedra, and a faceface with one CU4Mo2 octahedra. The corner-sharing octahedra tilt angles range from 40–59°.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Separation and purification of Mo-99 produced from natural U 3 0 8 targets via photo-fission

The most-used medical isotope is 99m Tc (t½ = 6.0 h), which comprises over 80% of isotopes used in nuclear medicine today. It is normally derived from its transient equilibrium parent 99 Mo (t½ = 66 h). A recent surge of interest in using the more proliferation-resistant low-enriched uranium (LEU) under the American Medical Isotope Production Act (AMIPA) has presented this technical challenge: can a domestic supplier meet the estimated weekly U.S. demand of 1500 6–day Ci of 99 Mo?

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Materials Data on UMoC2 by Materials Project

UMoC2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. U6+ is bonded to seven C4- atoms to form distorted UC7 pentagonal bipyramids that share corners with four equivalent UC7 pentagonal bipyramids, corners with three equivalent MoC5 trigonal bipyramids, edges with four equivalent UC7 pentagonal bipyramids, edges with seven equivalent MoC5 trigonal bipyramids, and faces with two equivalent UC7 pentagonal bipyramids. There are a spread of U–C bond distances ranging from 2.38–2.51 Å. Mo2+ is bonded to five C4- atoms to form MoC5 trigonal bipyramids that share corners with three equivalent UC7 pentagonal bipyramids, corners with four equivalent MoC5 trigonal bipyramids, edges with seven equivalent UC7 pentagonal bipyramids, and edges with two equivalent MoC5 trigonal bipyramids. There are a spread of Mo–C bond distances ranging from 2.15–2.21 Å. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to three equivalent U6+ and three equivalent Mo2+ atoms to form CU3Mo3 octahedra that share corners with nine equivalent CU4Mo2 octahedra, edges with nine CU3Mo3 octahedra, and a faceface with one CU4Mo2 octahedra. The corner-sharing octahedra tilt angles range from 14–58°. In the second C4- site, C4- is bonded to four equivalent U6+ and two equivalent Mo2+ atoms to form a mixture of edge, face, and corner-sharing CU4Mo2 octahedra. The corner-sharing octahedra tilt angles range from 14–58°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U2Mo2C3 by Materials Project

U2Mo2C3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. U4+ is bonded to five C4- atoms to form UC5 square pyramids that share corners with two equivalent UC5 square pyramids, corners with seven equivalent MoC4 trigonal pyramids, edges with five equivalent UC5 square pyramids, and edges with three equivalent MoC4 trigonal pyramids. There are a spread of U–C bond distances ranging from 2.40–2.47 Å. Mo2+ is bonded to four C4- atoms to form MoC4 trigonal pyramids that share corners with seven equivalent UC5 square pyramids, corners with three equivalent MoC4 trigonal pyramids, edges with three equivalent UC5 square pyramids, and edges with two equivalent MoC4 trigonal pyramids. There are a spread of Mo–C bond distances ranging from 2.08–2.20 Å. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to three equivalent U4+ and three equivalent Mo2+ atoms to form CU3Mo3 octahedra that share corners with three equivalent CU4Mo2 octahedra and edges with nine CU3Mo3 octahedra. The corner-sharing octahedra tilt angles range from 18–26°. In the second C4- site, C4- is bonded to four equivalent U4+ and two equivalent Mo2+ atoms to form a mixture of edge and corner-sharing CU4Mo2 octahedra. The corner-sharing octahedra tilt angles range from 18–26°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U2Ge4Mo3 by Materials Project

U2Mo3Ge4 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. U is bonded in a 7-coordinate geometry to two equivalent Mo and seven Ge atoms. There are one shorter (3.14 Å) and one longer (3.27 Å) U–Mo bond lengths. There are a spread of U–Ge bond distances ranging from 2.86–3.01 Å. There are two inequivalent Mo sites. In the first Mo site, Mo is bonded to six Ge atoms to form distorted corner-sharing MoGe6 octahedra. The corner-sharing octahedral tilt angles are 47°. All Mo–Ge bond lengths are 2.69 Å. In the second Mo site, Mo is bonded in a 6-coordinate geometry to two equivalent U and six Ge atoms. There are a spread of Mo–Ge bond distances ranging from 2.55–2.69 Å. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a 9-coordinate geometry to four equivalent U, four Mo, and one Ge atom. The Ge–Ge bond length is 2.76 Å. In the second Ge site, Ge is bonded in a 9-coordinate geometry to three equivalent U, five Mo, and one Ge atom. The Ge–Ge bond length is 2.78 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Hot Hydrogen Testing of W-Coated UN Kernels in a Mo30W Matrix

Ceramic uranium mononitride (UN) is being considered as a reactor fuel for nuclear thermal propulsion. To avoid or reduce the dissociation of UN at the high temperatures needed, embedding it in a metallic matrix (cermet) has been proposed. To assess the viability of this concept, hot hydrogen testing of tungsten-coated UN kernels embedded in a Mo-30 wt% W (Mo30W) alloy matrix has been performed at temperatures from 1800°C to 2300°C. Both the isolated kernels and kernels consolidated by spark plasma sintering in the Mo30W matrix were tested. In addition to direct observations and mass loss measurements, the samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS) after each run. The decomposition of UN started at 1800°C despite the coating and matrix, and increased at 2000°C. Uranium seeped through the tungsten grain boundaries of the coating at all temperatures. The consolidated sample expanded irregularly at 2000°C through the formation of voids, and SEM/EDS analysis showed uranium-containing veins in the matrix consisting of U 2 Mo according to the XRD data. The observed pore generation at 2000°C was explained by the formation of water vapor from residual oxides and diffused hydrogen. At 2200°C and above, both the kernels and the consolidated samples melted through the formation of uranium or low–melting point uranium-molybdenum alloys.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

An investigation of the phase behaviors for quaternary U-Nb/Mo-Ti-Zr metallic fuel alloys

We report quaternary fuel alloys containing U, Nb/Mo, Ti, and Zr are proposed as fuel candidates for sodium-cooled fast reactors (SFRs). In this work, two Nb-bearing alloys, i.e., U-NT5Z (U-2.5Nb-2.5Ti-5.0Zr in wt%) and U-NT7Z (U-1.5Nb-1.5Ti-7.0Zr in wt%), and two Mo-bearing alloys, i.e., U-MT5Z (U-2.5Mo-2.5Ti-5.0Zr in wt%) and U-MT7Z (U-1.5Mo-1.5Ti-7.0Zr in wt%) were characterized and compared. The characterization techniques were differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). DSC was performed to obtain the transition behaviors, and XRD and SEM/EDS were applied for phase identification. The results were combined to obtain the solid-state phase transitions between 500 °C and 850 °C for the alloys. It is found that the Nb-bearing alloys comprise similar phase transition behaviors as the Mo-bearing alloys. The phase transitions in U-NT5Z are a →γ at 608 °C and U 2 Ti → γ at 627 °C, which are ~40 °C higher than that of U-MT5Z. The phase transition in U-NT7Z is a → γ at 645 °C, and is 23 °C higher than that of U-MT7Z.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Distribution of U, Pu and Np in a Mo-99 Recovery Process using Sachtopore NP (titania based) Absorbent Material

A laboratory scale mockup of a prototypical Mo-99 recovery process has been operated in a radioactive materials hood at Savannah River National Laboratory. This equipment has been operated with realistic concentrations of uranium (U-238), plutonium (94% Pu-239), neptunium (Np-237), and non-radioisotopes of common fission products (including Mo). The goal of this work was to determine the amounts of U, Pu, and Np in the liquid waste streams created by the wash streams for the production process. The key question was how the initial acid wash volume will be handled, as this solution contains residual raffinate which amounted to ~ 3% ofthe mass ofthe feed solution in this experiment. If the initial 1.9 bed volumes (BV) of acid wash were recycled as in this experiment then the combined wash solutions can be expected to contain 0.4 g U/L, 2.7 pg Pu/L and < 14 pg Np/L. If, on the other extreme, the entire acid wash solution was discarded as waste, then the combined wash solutions can be expected to contain 11 g U/L, 3.8 pg Pu/L and ~ 80 pg Np/L. The Sachtopore NP absorbent (for Mo-99 recovery) retains a minuscule fraction ofthe U (2.3 mg U per g titania or 0.03% ofthe U in the feed). The uncertainties are too large to determine how close the absorbent is to saturation with U. Less mass but a higher fraction ofthe total Np was retained by the absorbent (0.7 pg Np per g titania or ~2% of the Np in the feed). As has been reported elsewhere, a large fraction ofthe Pu fed to the titania bed was retained by the absorbent (92% of Pu in the feed or 20 pg per g titania).

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗