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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Technical Guidance for Creation of 237 NP Irradiation Target Fabrication Packages

This document describes the process used to document the fabrication of irradiation targets that may be inserted into either the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL), or the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL). The targets are being irradiated to produce 238 Pu (5.48Mev alpha decay, T1/2 = 87.7 y) used in the fabrication of radioisotope thermoelectric generators (RTGs). RTGs powered by 238 Pu are an established power source technology for National Aeronautics and Space Administration space missions where solar power is not viable. The documentation included in fabrication files demonstrates full traceability of all materials, components, and assemblies used to build 237 Np targets. To accomplish this, all documentation (e.g., certified material test reports, weld reports, leak test reports) will be maintained and reviewed throughout materials procurement, component fabrication, and target assembly.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2022

Flow Measurements in Pressurized Helium Gas Cooling Channels

Production of metastable Technetium-99 (Tc-99m) is vital to the medical imaging community. It is a radioactive tracer that emits gamma rays as it decays and it is these gamma rays that are then detected through imaging. Tc-99m is extracted from the decay of Molybdenum-99 (Mo-99) which has a half-life of about 2-3 days. One method of generating Mo-99 is using accelerator based technology, through the irradiation of Mo-100 using an electron beam. This is part of the NNSA’s mission to produce Mo-99 commercially, within the US, without the use of highly enriched uranium (HEU) in support of nonproliferation and global security. Los Alamos National Laboratory (LANL) is working with NorthStar medical Radioisotopes (NMR) on their efforts to produce Mo-99 from the irradiation of Mo-100 targets. The NMR target consists of an Inconel window that allows the electron beam to penetrate and irradiate a stack of Mo-100 discs. The irradiation process generates large amounts of heat and requires extensive cooling of the Mo-100 targets and target housing using pressurized helium gas. Before beam on target, the design of the target stack and target housing is tested at LANL using laser based diagnostics experiments. We quantify the velocity field of the helium gas around the target housing to estimate whether the cooling provided is sufficient for the design and to validate computational fluid dynamics (CFD) models. Fiber optic imaging is also developed for use during cold testing (without beam on target) as well as during irradiation, to obtain real time information on disc performance.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2022

Pulsed Beam Heating Analysis of Curved Inconel Window with Pressurized Helium Gas Cooling

Los Alamos National Laboratory (LANL) is working with NorthStar medical Radioisotopes (NMR) on their efforts to produce Mo-99 through the irradiation of Mo-100 using Rodotron electron accelerators. Two Rhodotron accelerators are used to irradiate a double sided target. LANL collaborates with NMR to experimentally investigate beam effects on the target which consists of two Inconel 718 windows on either side of a stack of Mo-100 discs. LANL simulates the beam heating using an induction heater.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2022

Status of Additive Manufacturing Capabilities for Processing Refractory Alloys Under the Mo-99 Program

The enriched 100 Mo target, denoted as aMo, that Northstar Medical Radioisotopes is developing to produce 99 Mo from an accelerator-based method is a disk-type geometry with a 0.5–0.715 mm thickness and a 29 mm outer diameter. A press and sinter method was adopted to fabricate these samples from aMo powder feedstock. Inherent porosity from the press and sinter method makes the disks more easily dissolvable during 99 Mo postprocessing. However, the disk-type geometry will be subject to thermal stresses due to temperature variations once the geometry is in line with the accelerated electron beam, causing warping and possible failure. Additive manufacturing (AM) processes such as laser powder bed fusion (LPBF) enable the manufacturing of custom, complex geometries that may otherwise be difficult to produce with more conventional methods (e.g., press and sinter approach). Therefore, the National Nuclear Security Administration’s Molybdenum-99 Program invested in developing an AM facility dedicated to processing and printing refractory powders. This report details the LPBF process, how irregular refractory powder can be prepared for LPBF, and the equipment that is available to support the program.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Small Punch Testing of Molybdenum-99 Targets

Northstar Medical Radioisotopes is developing an accelerator-based method to produce 99 Mo, which is a parent isotope of the commonly used 99m Tc medical isotope. The Mo targets being designed for the accelerator will be produced from enriched 100 Mo, also known as aMo . Pressed and sintered powder feedstock is used to fabricate aMo targets, producing 29 mm disk-shaped targets. The targets are subjected to 1–6 days in line of an electron beam with subsequent dissolution of the disk to retain the 99 Mo, which decays to 99m Tc at radio-pharmacies. The press and sinter method is advantageous because the inherent porosity produced by this method enables increased surface area and therefore increased flow of dissolution media, decreasing the dissolution time and reducing the need for a highly acidic media. Although porosity aids in dissolution, it reduces the mechanical strength and ductility. Targets require good mechanical integrity when subjected to the conditions in the accelerator. Therefore, Northstar is seeking methods to rapidly test disk samples after fabrication to assure mechanical performance metrics are achieved. This report details the design and testing of a small punch test (SPT) that accommodates the 29 mm disk. Initial data were used to relate the SPT data to tensile properties, such as the yield strength (YS), ultimate tensile strength (UTS), and total elongation to failure. Although the SPT has been established as a somewhat reliable method for testing metallic materials, few studies have applied the SPT to refractory materials such as Mo. Based on tensile testing performed at Oak Ridge National Laboratory on different Mo samples, correlation between the Mo tensile and SPT properties could be performed, establishing a standard calibration that could be applied to other Mo samples. To test the efficacy of the SPT with Mo, multiple different disk batches were fabricated under different conditions (e.g., pressure, lubricant) with commercially available pure Mo powder. Generally, only a UTS could be well defined because the press and sinter disks failed under brittle fracture, making it difficult to determine the YS and elongation. Compared with disks fabricated with aMo powder, the aMo samples underperformed their pure nat Mo counterparts. This report summarizes the current status of the SPT, but further evaluation is needed before it can be applied as a reliable quality assurance tool.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Development of Laser-Induced Breakdown Spectroscopy for the Californium-252 Supply Program

Calibration-free–laser-induced breakdown spectroscopy (CF-LIBS) is suggested as an alternative to traditional LIBS because it does not rely on calibration curves and instead relies on previously reported parameters called transition probabilities. Transition probabilities are fundamental parameters that describe the probability a specific transition from an upper energy to a lower energy will occur. These values act as internal calibrations and allow concentrations to be calculated based on the plasma temperature and electron density, which can be determined from Saha-Boltzmann methods. CF-LIBS provides the ability to perform elemental concentration estimations on samples without the need for chemical dilutions and only nanograms of material are ablated into the plasma. These benefits can be applied remotely inside hot cells, glove boxes, and radiation hoods through optical fibers. This report summarizes recent efforts to develop CF-LIBS methods for future applications within Oak Ridge National Laboratory’s radioisotope production portfolio, such as the Cf-252 Supply Program. Summaries are provided for the developed Python scripts for data analysis and two studies employing these programs to determine unreported transition probabilities of relevant lanthanides. Additionally, a review of fiber-delivered LIBS and a discussion of a LIBS fiber probe design are provided.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2023

Formation of Zeolites Responsible for Waste Glass Rate Acceleration: An Experimental and Computational Study for Understanding Thermodynamic and Kinetic Processes

Before nuclear waste glasses can be disposed at geological disposal facilities, a performance assessment (PA) must be conducted to provide confidence to the regulators and public that the release rates of radioisotopes and hazardous materials into the environment are below the regulatory limits. Because the release rate of radionuclides is directly related to the dissolution rate of the radionuclide-containing glass, the corrosion behavior of the glass must be well understood for the disposal site lifetime. For simplicity, glass dissolution in static conditions has been categorized into three different stages, referred to as initial rate (Stage I), residual rate (Stage II) and, depending upon the secondary phases formed, a possible delayed resumption in the alteration rate (Stage III). The last of these stages is the least understood and has the possibility to drive radionuclide release rates above regulatory thresholds.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Numerical Analysis and Flow Induced Vibration Studies in Pressurized Helium Gas Cooling Channels

Los Alamos National Laboratory (LANL) is working with NorthStar Medical Radioisotopes (NMR) on their efforts to produce Mo-99 from the irradiation of Mo-100 targets. The NMR target consists of an Inconel window that allows the electron beam to penetrate and irradiate a stack of Mo-100 discs. The irradiation process generates large amounts of heat and is cooled using pressurized helium gas flowing at 400 g/s. LANL provides both numerical analysis support and experimental support. Computational fluid dynamics (CFD) simulations for both 300 g/s and 400 g/s are performed on the NMR target to analyze the helium flow through the NMR system. The pressure drop, the mass flow rate through each of the disc and window channels and the force applied on the first disc are some of the quantities estimated using CFD. These results will be combined with Monte Carlo N-Particle (MCNP) estimates of heat flux into the system from the electron beam to perform conjugate heat transfer analysis (CHT). The experiments presented in this report focus on the effect of the flow induced vibrations from helium flowing through the coolant gaps between the discs. There is concern that the flow induced vibrations may lead to excessive mass loss of the enriched Mo-100 discs, and the goal would be to mitigate the mass loss. This work presents benchtop tests of flow through a subset of the target stack which involves high speed imaging and displacement measurements used to estimate disc vibration, as well as mass loss.

42 ENGINEERING↗
DOE OSTI2022

Models to Incorporate Reaction Mechanisms into DG-OSPREY: Fixed-Bed Simulations for Organic Iodides Capture Using Ag 0 Z

As one of the most potent radioisotopes released during spent nuclear fuel reprocessing, 129 I is strictly regulated and must be removed before discharge. Organic iodides (primarily alkyl iodides with different chain lengths, i.e., CH 3 I, C 4 H 9 I, and C 12 H 25 I) comprise ~2% of the total iodine in the reprocessing off-gases and are primarily present in vessel off-gas (VOG). Reduced silver mordenite (Ag 0 Z) is predominantly considered for the removal of radioiodine; however, its capture performance and underlying interaction processes with long-chain organic iodides are not fully understood. Two major tasks were accomplished in this study. First, to improve upon the previous experimental studies where Ag 0 Z was used to capture CH 3 I, C 4 H 9 I, and C 12 H 25 I at different concentrations, we comprehensively investigated the corresponding capture mechanisms by characterizing fully loaded Ag 0 Z samples. Second, computational codes were implemented to perform fixed-bed simulations that account for transport and reaction mechanisms. Scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), powder X-ray diffraction (PXRD), UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and thermogravimetric analysis (TGA) were conducted on Ag 0 Z samples that are saturated with I 2 , CH 3 I, C 4 H 9 I, and C 12 H 25 I), respectively. Results indicate that AgI is the predominant adsorption product regardless of the adsorbed iodine species, yet alkyl iodides with different carbon chain lengths may have different compositions of α- and γ-AgI. Synchrotron pair distribution function (PDF) measurements and TGA coupled with a Fourier transformed infrared detector (TGA FTIR) have been performed, and experimental data are currently analyzed. Results are expected to provide further insights into the adsorption mechanisms. The fixed-bed capture performance for CH 3 I was successfully simulated by solving mathematical equations that describe the underlying transport processes and adsorption reactions. The computational framework, Catalytic After Treatment System (CATS), that was originated in our research group, was used to solve the governing equations. Kinetic parameters, including the pore diffusivity and reaction rate constant were obtained by optimization techniques using data from thin-bed experiments performed at Oak Ridge National Laboratory. The performance of a deep bed predicted using the optimized parameters showed promising agreement with the experimental data.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Preliminary Thermal-Hydraulic Analysis of the UTA–2 Subcritical Linear Accelerator–Driven System

The National Nuclear Security Administration’s mission includes establishing a reliable supply of 99 Mo without highly enriched uranium. Oak Ridge National Laboratory (ORNL) supports this objective through collaborative research and development with industrial partners. Niowave Inc., a current partner, is currently designing a subcritical linear accelerator-driven system (ADS) and preparing for the US Nuclear Regulatory Commission’s licensing process. Niowave’s system has the potential to efficiently supply medical radioisotopes. The technology includes a superconducting electron accelerator and a pile of both natural and low-enriched uranium (LEU) targets. The process fissions uranium and many valuable isotopes can then be extracted from the targets. Niowave is currently iterating through conceptual and detailed design processes for several system sizes. This report discusses UTA–2, which is at the demonstration stage. UTA–2 will validate numerical modeling results with experimental measurements before progressing to the detailed design of UTA–3, the commercial-sized ADS. The thermal-hydraulic behavior of the UTA–2 core design was numerically investigated using STAR-CCM+, as described in this report. STAR-CCM+, a state-of-the-art computational fluid dynamics (CFD) software that was commercially developed by Siemens, has an extensive user base and a set of validation studies. It is also compliant with the American Society of Mechanical Engineers’ Nuclear Quality Assurance 1 standard. Three cases are investigated in this report. Case 1 quantified the temperature field within the UTA–2 assembly and water tank using only conduction as the method of thermal energy transport. This simplified approach was overly conservative and yielded wetted cladding temperatures above the coolant saturation temperature. In this case, the maximum temperature of the wetted cladding surface of the highest power rod exceeded the saturation temperature of water by 63.8°C. Because of the overly conservative approach taken in Case 1 and its negative subcooled margin, buoyancy-driven natural circulation flow physics were implemented in Case 2. Adding coolant motion significantly distributed the thermal energy of the system through convective heat transfer. This relatively small amount of convective heat transfer significantly reduced system temperatures and increased the subcooled margin from –63.8 to 61.3°C. This margin confirmed that no boiling was expected during normal operation of UTA–2 at 230 W. Case 3 had no additional physics models but considered an overpower event during which the power of each LEU and natural uranium rod was at its respective peak values. This resulted in a study with the total assembly power equal to 176% of the nominal power of 230 W considered in Cases 1 and 2. The resulting natural circulation flows were slightly enhanced. The subcooled margin decreased slightly to 46.3°C, which is still a significant margin to local boiling of the water within the tank. This margin confirmed that no boiling was expected during an abnormal operation of UTA–2 at 406 W.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2023

Radionuclide Waste Disposal: Development of Multi-scale Experimental and Modeling Capabilities (Final Report)

The DOE EPSCoR Implementation project “Radioactive waste management: Development of multi-scale experimental and modeling capabilities” helped to develop a team of scientists and engineers from Clemson University, South Carolina State University, and the University of South Carolina to address the disposition of nuclear wastes and study the transport of radioisotopes from a waste repository in the near and far field. The project involved 20 faculty from the three institutions as well as 13 postdoctoral fellows, 32 graduate students, and 32 undergraduate students and was active from 2014-2019. Additionally, we forged new collaborations with nine researchers from DOE laboratories SRNL, LLNL, and ANL as well as the University of Manchester and the China Academy of Engineering Physics. The overarching goal of the project was to understand the conditions under which important classes of co-reactants, ranging from counter ions in crystal lattices to dissolved oxygen in pores, control the chemistry and transport characteristics of radionuclides in engineered waste forms and natural soils. Our approach was to characterize the time and length scales over which non-equilibrium states are maintained by rate-limiting, or rate-enhancing, reactions between radionuclides and co-reactants due to interactions between physical mass-transfer processes (i.e., advection, diffusion) and (biogeo) chemical reactions. We have focused our project on three specific classes of reactions relevant to radionuclide transport at DOE legacy sites: ion exchange/substitution, ligand complexation, and redox-mediated reactions. Understanding radionuclide migration requires detailed knowledge of how changes to a system – whether engineered or natural – drive the behavior of co-reactants, which in turn provide the geochemical context controlling radionuclide transport. Student engagement and training were a primary focus of the project in order to create a pipeline of researchers who could work in the area of nuclear waste disposition to support the state and the nation. Over the duration of the project we worked with 32 undergraduate, graduated 18 M.S. students and 14 Ph.D. students, and advised 13 postdoctoral fellows. The Ph.D students and postdocs have primarily taken positions at DOE laboratories, academia, and industry. Through our collaborative team, numerous follow on projects have been started with over $5M in sponsored research. Additionally, thus far the team has published 53 peer reviewed papers and given over 75 technical presentations.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Specifications of EBR-II Neutron Radiography Method Description and Digitization Approach

All neutron radiography (NRAD) images of fuel pins in Argonne’s collection were originally generated using the NRAD imaging facility established in the Hot Fuel Examination Facility (HFEF) at Idaho National Laboratory (INL). The NRAD reactor facility was built in 1977 and has been operating since. The reactor is a TRIGA-type reactor operating at a power level of 250 kWth to provide a neutron source for radiography imaging. The reactor is equipped with two beam tubes (i.e., east beam tube and north beam tube) to guide the neutron beams to two radiography stations. The east radiography station is directly under the HFEF main cell and is dedicated for specimens already in the HFEF hot cell. The north radiography station is outside of the main HFEF hot cell and allows NRAD imaging of non-irradiated items. The NRAD images of EBR-II irradiated metallic fuel pins were taken in the east radiography station. Thermal neutrons have the capability to transmit through most materials and are ideal for NRAD imaging. However, because of their high thermal neutron absorption cross-section, fissile materials (e.g., highly-enriched nuclear fuels) may not be as transmissible to thermal neutrons. This is also the case for oversize specimens with extraneous thickness. Epithermal neutron imaging is therefore used as a complement to thermal neutron NRAD imaging. At HFEF’s NRAD facility, both thermal and epithermal neutrons can be used for NRAD imaging. Irradiated nuclear fuels emit high levels of γ radiation that can easily darken X-ray films, so direct exposure NRAD cannot be used to image them. Instead, an indirect NRAD imaging method was developed at HFEF’s NRAD facility. In this method, foils made of materials that can be activated by neutrons (i.e., with large neutron absorption cross section) are used to collect transmitted neutron signals. Then the activated foils are then placed against X-ray films and enclosed in a vacuum cassette so that the γ decay from the activated foils can produce images on the X-ray films. Then, general X-ray film processing procedures are used to digitize and store the images. By using different foil materials, different energy neutrons can be used for NRAD imaging. At the HFEF NRAD station, two types of films are commonly used: dysprosium (Dy) foils with thickness of 130 microns are used to capture thermal neutron signal, while indium (In) foils with thickness of 130 microns are used to capture epithermal neutron signal. A cadmium or gadolinium foil is put before the indium foil to work as a thermal neutron filter. The thermal and epithermal NRAD images can be taken simultaneously by using a Dy/Cd/In sandwiched foil combination. The typical NRAD exposure time is approximately 20 minutes. Then the exposed foils are transferred to film vacuum cassettes. The vacuum ensures that there is no gap between the foil and the film. The foil-to-film exposure time is at least three half-lives of the corresponding radioisotopes, which are 3 hours for In and 7.5 hours for Dy, respectively. Exposed films are processed using an automatic film processor to produce completed NRAD images.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Characterization of Aluminum Metal Powders for Plutonium-238 Program

As part of radioisotope thermoelectric generator (RTG) production for power sources in deep space exploration, Oak Ridge National Laboratory (ORNL) produces plutonium-238 ( 238 Pu). To produce 238 Pu, neptunium-237 ( 237 Np) targets are fabricated at ORNL and subsequently irradiated at the High Flux Isotope Reactor (HFIR) at ORNL and the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL). Specifically, current flowsheets utilize neptunium dioxide ( 237 NpO 2 ) targets. Aluminum (Al) powder is blended with 237 NpO 2 target material to improve thermal conductivity during irradiation. The current composition of 237 NpO 2 /Al pellets (i.e., cermets, or ceramic–metallics) is 20% 237 NpO 2 , 70% Al, and 10% void space. Al powders utilized by the 238 Pu program are high-fired under vacuum before blending into targets. The primary objective of this work is to measure the physical, chemical, and thermal properties of Al before and after the high-firing process. Properties of interest include the morphology, surface texture, particle size, crystal phase(s), and thermal conductivity of the material. These properties are measured with existing materials characterization equipment at ORNL, including powder x-ray diffraction (pXRD), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), laser flash analysis (LFA), and thermogravimetric analysis (TGA). A secondary objective of this work is to compare the Al powders before and after the high-firing procedure to determine the effects of high-firing on chemical, physical, and thermal properties and to determine the efficacy of the high-firing process.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Volume 6: Experiment Facility Spectrum Tailoring (HFIR Futures – Enhanced Capabilities Series)

In-core irradiation experiment research, such as materials and fuels irradiation research and radioisotope production, is one of the primary missions of Oak Ridge National Laboratory’s (ORNL) versatile High Flux Isotope Reactor (HFIR). In support of the HFIR-Sustaining and Enhancing Neutron Science (SENSe) Initiative, a technically diverse group of ORNL irradiation research subject matter experts formed the Spectrum Tailoring Working Group, with the goal of developing a compendium of experiment facility concepts to enhance irradiation experiment conditions via neutron spectrum tailoring capabilities. The purpose of this report is to document the concepts developed in FY22 and the associated scientific justifications, identify potential facility sponsors, and estimate costs and schedules for each concept. This report documents the efforts performed in FY22, which may continue in FY23 or later pending the direction of the HFIR-SENSe Initiative and the interested sponsors.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2020

Measurement of Argon-37 Background Concentrations in the Atmosphere

Radioisotopes of noble gases, primarily xenon and argon, are important indicators of underground nuclear explosions. The Comprehensive Nuclear-Test-Ban Treaty (CTBT) includes monitoring capabilities to identify potential nuclear explosions conducted in violation of the CTBT. This monitoring currently focuses on measurement of the xenon isotopes 133 Xe, 135 Xe, 131 mXe and 133 mXe. However, it is predicted that within 100 days of an underground nuclear explosion (UNE) 37 Ar would be released to the atmosphere at higher concentrations than xenon isotopes (Haas et al. 2010). Therefore, inclusion of 37 Ar measurement capabilities at atmospheric International Monitoring System (IMS) stations could improve the capability to detect a nuclear explosion. At an IMS station, it could be difficult to determine what constitutes an elevated concentration as a result of an UNE without first understanding the expected range of background concentrations. This work describes our analysis of atmospheric samples for 37 Ar to evaluate the range of background concentrations. The range of 37 Ar concentrations measured in atmospheric air samples was relatively narrow ranging between less than 1 mBq/m 3 to greater than 2 mBq/m 3 . The average atmospheric concentration of all samples was 0.98 mBq/m 3 , with a standard deviation of 0.5 mBq/m 3 . This is consistent with previous published results. The results presented here demonstrate the capability to detect background concentrations of 37 Ar in atmospheric air.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2023

2020 Postclosure Groundwater Monitoring and Inspection Report, Central Nevada Test Area, Subsurface Corrective Action Unit 443

This report presents the groundwater monitoring data collected by the U.S. Department of Energy (DOE) Office of Legacy Management (LM) from the Central Nevada Test Area (CNTA), Nevada, Site, Subsurface Corrective Action Unit (CAU) 443 in Nye County, Nevada (Figure 1). The CNTA is the site of an underground nuclear test in 1968 that resulted in residual contamination near the detonation depth of 3200 feet (ft); the contamination requires long-term monitoring. Responsibility for the environmental restoration and long-term monitoring was transferred from DOE’s National Nuclear Security Administration, Nevada Field Office, to LM on October 1, 2006. The environmental restoration and site closure process were completed in 2015 in accordance with the amended 1996 Nevada Federal Facility Agreement and Consent Order (FFACO) (State of Nevada et al. 1996, as amended) and all applicable Nevada Division of Environmental Protection (NDEP) policies and regulations. The Closure Report, Central Nevada Test Area, Subsurface Corrective Action, Unit 443 (DOE 2018), also called the Closure Report, originally was completed in January 2016 and revised in October 2018; it describes LM’s plan for long-term postclosure monitoring. This includes monitoring of the radioisotopes of interest and water elevations, inspecting the site and maintaining the institutional controls (ICs), evaluating and reporting data, and documenting the site’s records and data management processes (DOE 2018).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Alternative Power and Propulsion for Space Systems

What are the main sources of power and propulsion for space systems and what are their advantages, disadvantages, how do they work, and what are the politics behind them? The following topics will be analyzed solar panels, batteries, radioisotope thermoelectric generator (RTG), advanced Stirling radioscopic generator (ASRG), reactors, nuclear thermal rockets (NTP), thermionic experiment with conversion (TOPAZ), electrothermal plasma thruster (VASIMR), ion propulsion, and finally nuclear pulse propulsion. The production of Pu-238 is extremely controversial but a vital source of fuel for many of these space systems. Soral and Batteries are the most common and the least controversial forms of power used in space systems today. However, is ineffective for deep space exploration as they only function for up to four years without needing to be recharged. This is where nuclear systems come into play. Nuclear systems such as an RTG will “live” up to 88 years. For example, Voyager 1 is powered by an RTG It has been traveling since 1977 and has left out solar system in 2012 and has yet to run out of power. However, this type of technology (nuclear) has many hurtles it needs to jump through before advancements in can go much further.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2023

Conjugate Heat Transfer Analysis in Pressurized Helium Gas Cooling Channels

Los Alamos National Laboratory (LANL) is working with NorthStar Medical Radioisotopes (NMR) on their efforts to produce Mo-99 from the irradiation of Mo-100 targets. The NMR target consists of an Inconel window that allows the electron beam to penetrate and irradiate a stack of Mo-100 disks. The irradiation process generates large amounts of heat and is cooled using pressurized helium gas flowing at 400 g/s. LANL provides both numerical analysis support and experimental support. Computational fluid dynamics (CFD) and conjugate heat transfer (CHT) analysis are performed on the NMR target to analyze the helium flow and volumetric heating through the NMR system. In this iteration of numerical analysis, we update the Mo-100 disk thickness to 0.74 mm and the gap between the Inconel window and the first disk to 0.69 mm. Estimates of the heat flux from the electron beams from Monte Carlo N-Particle code (MCNP) analysis were combined with CFD to perform the CHT analysis. The pressure drop through the targets, force applied on the first disk, beam window and target disk temperatures are some of the quantities estimated using the simulations. The pressure drop through the target was estimated as 0.198 MPa, while the force due to venturi effects across the first disk was estimated to be 100 N. The results show maximum window temperatures over 600 °C and peak disk temperatures over 1600 °C. Past work has shown that beyond 650-700 °C, the Inconel window becomes susceptible to yield and rupture. The increased temperature in these results reduces the margin of error possible on beam spot size. The disk temperatures showed a sinusoidal distribution with the 6 th – 8 th disk from each window exhibiting highest disk temperatures. The peak temperature of the stainless steel housing was close to 316 °C and that of the laminations and spacers was approximately 582 °C.

43 PARTICLE ACCELERATORS↗