Radioisotope Thermoelectric Generators Research Articles

Quantitative Particle Analysis of Neptunium-237 Oxides: Optimization of MAMA Analysis for Modified Direct Denitration Products.

The production of plutonium-238 through irradiation of neptunium-237 (237Np) target materials for the use in radioisotope thermoelectric generators is paramount for continued deep space exploration. This work employs scanning electron microscopy to analyze 237Np materials coupled with a well-developed image analysis framework (Morphological Analysis for Material Attribution, or MAMA) to determine the degree of micron-scale homogeneity in the materials. This work demonstrated how the quantification of particle characteristics can validate production materials and affirm the qualitative similarities observed in micrographs. The 237Np oxide particle analysis determined that the materials from five production runs were quantitatively homogenous (significant at α = 0.05) in particle area, circularity, equivalent circular diameter, and ellipse aspect ratio, with two of the sampling dates having statistically significant different means for one of the four characteristics. These metrics not only confirm general homogeneity of the material but also expand the application of MAMA workflows to 237Np materials, demonstrating the utility of MAMA analysis for a wider breadth of nuclear materials than previously reported. In the open literature, this study is the first time that these microanalytical techniques were applied to 237Np materials to this degree.

Self-powered wireless sensor networks based on the radioisotope thermoelectric generator for aquatic temperature monitoring

This study focuses on the development of ultra-long-life wireless sensor network (WSN) node based on the thermoelectric effect for use in areas such as aquatic temperature monitoring. A long-lasting radioisotope thermoelectric generator (RTG) was used as the energy source for the WSN node to address issues such as short runtime and pollution associated with traditional chemical batteries and solar cells. A compact RTG was fabricated by developing thermoelectric modules with high adaptability to cylindrical heat sources. The electrical output performance at the ocean surface and in the underwater environment was analyzed, with the maximum output power reaching 2326.6 μW. An integrated circuit module comprising direct current to direct current (DC-DC) boost converters, control switch circuits, and supercapacitors was employed to power the WSN node from the RTG directly. Powered by the RTG, a WSN node for monitoring ocean temperature was also constructed. Its performance was evaluated under different environmental conditions by investigating the effects of RTG’s output, sensor data variations, distance, and other factors on WSN node stability. Results demonstrate that the designed self-powered WSN node can operate stably and continuously at the ocean surface and in underwater environments, thereby showing its promising prospects.

The Graph Becomes the Dataset: Compiling Historical and Current RTG Data into One Place

Radioisotope thermoelectric generator (RTG) technology has a very long and incredibly successful history of providing heat and power to some of humankind’s most successful space exploration missions. Members of the community that support and maintain this technology often like to show the entire history of RTG performance on “The Graph.” Meant to impress, The Graph does its job in that regard. Unless you were connected to the right people, however, it was very difficult to get a copy of The Graph or its underlying data. This made it difficult for many to dive into the technical details or evaluate individual RTG performance from historical missions. To make matters worse, the performance for several missions in The Graph were incomplete. In 2020, with a little extra time on their hands thanks to COVID, the authors reached throughout the RTG community to locate and collate the missing RTG data. This information was then published as an open-source tabular Dataset. Users can now build their own version of The Graph or use the data for a more detailed analysis of RTG performance. Updates to the currently operating missions in The Dataset are expected to occur on a roughly annual basis. This Dataset represents the most comprehensive, authoritative, up-to-date repository of all RTG performance available today.

Tri-objective and multi-parameter geometric optimization of two-stage radioisotope thermoelectric generator based on NSGA-II

Radioisotope thermoelectric generator (RTG) is one of ideal power sources for deep space exploration due to the long service life and high stability. To further extend service life and improve electrical output, this study is first to simultaneously optimize electrical output and mechanical stability induced by thermal stress of the two-stage RTG using non-dominated sorting genetic algorithm-II. Skutterudite and bismuth telluride are used as the thermoelectric materials in hot-stage and cold-stage thermoelectric generators, respectively. The maximum von Mises stress of the skutterudite-stage (VonSKD) and bismuth telluride-stage (VonBT) thermoelectric generator and the conversion efficiency of the two-stage RTG (ηtwo) are set to the three objectives, and twelve geometrical parameters of two-stage RTG are used as variables. Electrical output and mechanical stability are simulated with COMSOL 6.0 Multiphysics software based on the finite element method. Results show that the ranges of ηtwo, VonSKD, and VonBT in the Pareto front are 4.81–7.57 %, 112.2–228.46 and 19.24–87.33 MPa, respectively, when the temperature difference is 300 K. TOPSIS decision-making method is used to select the specific optimal solution on the Pareto front according to the weight of the different objectives. Comparisons between tri- and bi-objective as well as single-stage optimization are also carried. Results show that there are strong influences among these three objectives. The performance of one objective would improve at the expense of the performance of the remaining objectives decrease if a larger weight was given. The VonSKD has the greatest importance among the three objectives, followed by ηtwo, and the smallest is VonBT. Skutterudite-stage thermoelectric generator should be particularly considered in the design of two-stage RTGs. The two-stage RTGs with different weight factors exhibit different electrical performances due to different geometrical parameters. This research can provide references for two-stage thermoelectric generators in more scenarios to improve electrical performances and extend service life.

Sintering trials and microstructural changes mechanism of analogues of americium oxides for radioisotope power systems

Radioisotope thermoelectric generators (RTGs) are deal energy supply devices for deep space and deep-sea exploration, and it is also the energy core of the operation of the working equipment. Except for 238Pu (Plutonium), 241Am (Americium) was also used as a nuclide in the radioactive energy system for future space exploration missions. In this work, neodymium oxide (Nd2O3) was used as analogues for Am2O3. Cold-press-and-sinter methods was used. Different particle parameters (morphology, size, and crystal structure) and synthesized parameters of Nd2O3 were investigated. The synthesized powders contained lath-shaped particles, and batches with different particle sizes and microscopic topography were made and sintered. The results show that the optimal precipitation temperature of Nd2O3 is 25 °C. The optimal thermal decomposition temperature range is 900 °C to 1100 °C, and the optimal thermal decomposition heating rate is 10 °C min−1. The samples of Nd2O3 pellets without cracking is obtained with relative density of 85%–90 %. The Vickers hardness of Nd2O3 pellets was also studied. This paper provides an important scientific guiding significance for the cold-press-and-sinter of radioisotope 241Am batteries in the future.

Feasibility of a Small, Low-Power RTG Concept Utilizing a GPHS Heat Source

Over the past 25 years, the average cadence of National Aeronautics and Space Administration (NASA) missions that employ radioisotope thermoelectric generators (RTGs) or other radioisotope power systems (RPSs) is approximately one per decade. Currently, the only flight-qualified RPS in the NASA inventory for space power applications is the multi-mission RTG, which has a beginning-of-life (BOL) power output of approximately 120 W(electric). In addition, NASA and the U.S. Department of Energy also manage the Next Generation Radioisotope Thermoelectric Generator Development Project, with a projected BOL power of around 245 W(electric). However, if a lower-power RPS unit was available, would there be sufficient mission pull to increase the cadence of RPS-powered missions? We believe the answer to this question is yes, which drove the evolution of a concept study that examines the feasibility of a low-power RPS based on a single general purpose heat source (GPHS) that could be developed rapidly with low risk and cost. This paper discusses the results of a concept study of an RPS system that utilizes novel ruggedized silicon germanium thermoelectric modules with a projected BOL power of 15 W(electric). This new RTG design could help enable a new class of low-powered space exploration missions for NASA, the European Space Agency, or commercial applications. In addition, this paper addresses the next steps required to evolve the concept beyond its current status to conceptual design.

High-purity La3-xTe4 Material with Superior Thermoelectric Performance Synthesized via Te-vapor Transport and Solid-State Diffusion.

La3-xTe4 is a very promising high-temperature candidate applied in next-generation Radioisotope Thermoelectric Generators (RTGs). Conventional synthesis of such materials is based on the mechanochemical method, which makes the sample difficult to purify due to the high-energy ball milling. In this report, a novel synthetic method is developed, which utilizes Te-vapor transport and solid-phase diffusion to efficiently produce the RE3-xTe4 phases (RE = La, Ce, Pr, Nd). Notably, this method obviates the requirement for high-energy ball-milling instruments, conventionally indispensable in the mechanochemical syntheses. For as-synthesized La2.74Te4 material, a high figure of merit of 1.5 is achieved at 1073K, owning to the reduced electronic thermal conductivity with metal impurities well eliminated.

First-principles studies of the structural, mechanical, electronic, magnetic and transport properties of inner transition based RaMO3 perovskites (M = Cm, Bk)

In the quest for new materials, we introduce self-consistent ab initio simulations to investigate the structural and mechanical stability, electronic profile, and transport properties of f-electron-based RaMO3 (M = Cm, Bk) perovskites by employing density functional theory. The energy optimization indicates that these alloys exhibit stability in the ferromagnetic phase. The examination of mechanical parameters demonstrates the ductile nature of these materials. To elucidate the electronic structure of these alloys, we employed a combination of two approximations: Generalized Gradient Approximation (GGA) and GGA + mBJ. Both approximations confirm the alloys’ half-metallic character. The magnetic moments calculated using both approximations were approximately 6 µB for RaCmO3 and approximately 7 µB for RaBkO3. The thermoelectric performance of these materials is evaluated by investigating different transport parameters such as the Seebeck coefficient, electrical and thermal conductivity and power factor. The comprehensive investigation of these two alloys has the potential to expand their applications in spintronics, thermoelectric devices, and radioisotope thermoelectric generators (RTGs).

Distributable, metabolic PET reporting of tuberculosis

Tuberculosis remains a large global disease burden for which treatment regimens are protracted and monitoring of disease activity difficult. Existing detection methods rely almost exclusively on bacterial culture from sputum which limits sampling to organisms on the pulmonary surface. Advances in monitoring tuberculous lesions have utilized the common glucoside [18F]FDG, yet lack specificity to the causative pathogen Mycobacterium tuberculosis (Mtb) and so do not directly correlate with pathogen viability. Here we show that a close mimic that is also positron-emitting of the non-mammalian Mtb disaccharide trehalose – 2-[18F]fluoro-2-deoxytrehalose ([18F]FDT) – is a mechanism-based reporter of Mycobacteria-selective enzyme activity in vivo. Use of [18F]FDT in the imaging of Mtb in diverse models of disease, including non-human primates, successfully co-opts Mtb-mediated processing of trehalose to allow the specific imaging of TB-associated lesions and to monitor the effects of treatment. A pyrogen-free, direct enzyme-catalyzed process for its radiochemical synthesis allows the ready production of [18F]FDT from the most globally-abundant organic 18F-containing molecule, [18F]FDG. The full, pre-clinical validation of both production method and [18F]FDT now creates a new, bacterium-selective candidate for clinical evaluation. We anticipate that this distributable technology to generate clinical-grade [18F]FDT directly from the widely-available clinical reagent [18F]FDG, without need for either custom-made radioisotope generation or specialist chemical methods and/or facilities, could now usher in global, democratized access to a TB-specific PET tracer.

Flash Diffusivity Measurement of Semiporous Insulation Material Intended for Radioisotope Thermoelectric Generators

This research involves the analysis of flash-heating data pursuant to find the thermal diffusivity of a semiporous insulation material (Min-K) that is being considered for use in a radioisotope thermoelectric generator (RTG). An RTG uses radioactive nuclear fuel to produce electricity through a temperature difference imposed on a bimetallic thermocouple. Insulation is required to protect sensitive equipment from high temperatures and to conserve heat in the fuel. Using flash diffusivity temperature data, various simulations were fitted in order to find the most appropriate heat transfer model for the experiments. Four models were allowed to compete, and the standard deviation of the residuals was compared for each model in evaluating model performance. The residuals are simply the difference in temperatures between the measurements and the mathematical models at each measurement point.

Irradiation Effect in Thermoelectric Polymer Polyaniline Induced by High-Energy Electron Beam

A comprehensive investigation was conducted on the relationships between molecular structure, morphology and thermoelectric properties of HCl-doped polyaniline (PANi) nanorods subjected to 10[Formula: see text]MeV electron beam irradiation. Morphological and structural characterization revealed that the crystallinity of irradiated PANi nanorods remained almost unchanged, and minimal oxygen content was detected. This resulted in minimal alterations to the thermo-stability. In addition, the thermoelectric properties of PANi were enhanced. A maximum conductivity of 22.85[Formula: see text]S/cm was obtained at 50[Formula: see text]kGy, which was 1.46 times that of pristine PANi. Interestingly, the Seebeck coefficient reached a maximum of −3.56[Formula: see text][Formula: see text]V/K at 100[Formula: see text]kGy, indicating [Formula: see text]-type organic semiconductor properties. However, a peak power factor of 0.024[Formula: see text][Formula: see text]W[Formula: see text]m[Formula: see text] K[Formula: see text] was achieved with 60[Formula: see text]kGy irradiation, which was slightly enhanced compared to 0.018[Formula: see text][Formula: see text]W[Formula: see text]m[Formula: see text][Formula: see text]K[Formula: see text] for pristine PANi. These results demonstrate that PANi exhibits good irradiation resistance after irradiated with a dose of 100[Formula: see text]kGy. Thus, PANi could be used in high-[Formula: see text] ray (electron) environments, such as radioisotope thermoelectric generators (RTGs).

Surface morphology and oxidation products of DOP-26 iridium alloy upon high-temperature exposure to air

The DOP-26 Ir alloy is employed for fuel sealing in isotope batteries and exhibits superior oxidation resistance at high temperatures under low oxygen conditions. This study investigated the oxidation behavior of the DOP-26 Ir alloy in air, focusing on the correlation between the oxidation temperature and time. X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy were conducted to examine the phase, morphology, and valence of the alloy upon oxidation. The findings provide a comprehensive understanding of the high-temperature oxidation kinetics of DOP-26 Ir alloy in the air, and these results could potentially be applied to the design and application of radioisotope thermoelectric generators.

Comprehensive modeling and characterization of the General-Purpose Heat Source Radioisotope Thermoelectric Generator for solar system missions

The radioisotope thermoelectric generator relies solely on radioactive decay for its energy and generates power through the thermoelectric effect. The General-Purpose Heat Source Radioisotope Thermoelectric Generator (GPHS-RTG) represents the RTG with the largest power and highest conversion efficiency ever built, and its energy supply supported four daring interplanetary missions (Galileo, Ulysses, Cassini, New Horizons). To explore the use potential of the GPHS-RTG in the solar system, its conservative application range and performance should be determined. In this work, a comprehensive model of the GPHS-RTG was developed, and its calculated results agreed well with Lockheed Martin’s test report (temperature relative error < 1 %). The study demonstrates that within the Earth orbit, the distance of the mission area from the sun and the angle of incidence sunlight significantly affect the thermoelectric performance and hot-junctions’ temperature. Moreover, conservative application ranges and their extending methods (changing coating material, thermal loading, and operational voltage) for GPHS-RTG at different attitudes in the solar system were determined for the first time by comparing the proportion of the hot-junction over-temperature area. The temperature distribution and its cause of formation in the axial and circumferential directions of the GPHS-RTG during solar system missions were revealed in the end. This work is valuable for future RTG design and mission planning.

The Design of CubeSats for Outer Solar System Scientific Missions

In the past decade, CubeSats have emerged as a cost-effective solution for scientific missions beyond Earth’s orbit, though they have not yet gone further than orbiting Mars, as with NASA’s MarCO CubeSats. This paper discusses the technical challenges and solutions for designing CubeSats for Outer Solar System missions, specifically in the context of the proposed Astraeus Mission to Titan. These CubeSats, called the Mites, aim to measure heavy anions in Titan’s upper atmosphere and have undergone analysis to determine their optimal size and drag coefficient. A significant challenge addressed is the CubeSats’ power system, with solar panels being less effective at greater distances from the Sun. The paper proposes investigating Radioisotope Power Systems (RPS) as an alternative. However, there is the additional challenge of packaging the RPS in a sufficiently small form factor so that the upper atmospheric experiment can be completed. This must cover the greatest range of longitudes, latitudes, and ranges hence the orbital decay rate must be controlled to achieve this. The paper also explores the Mites’ long-duration exposure to space during transit and strategies to minimise cosmic radiation exposure. Whilst this is completed in the context of the Astraeus Mission, the data obtained can guide similar missions and aid others in overcoming the limitations of CubeSats so that they can be used more frequently for Outer Solar System science missions. Keywords: Titan, CubeSat, Radioisotope Thermoelectric Generator, Orbital Decay, Outer Solar System

Exploring the structural, mechanical, magneto-electronic and thermophysical properties of f electron based XNpO3 perovskites (X = Na, Cs, Ca, Ra).

Here, we present systematic investigation of the structural and mechanical stability, electronic profile and thermophysical properties of f-electron based XNPO3 (X = Na, Cs, Ca, Ra) perovskites by first principles calculations. The structural optimization, tolerance factor criteria depicts the cubic structural stability of these alloys. Further, the stability of these materials is also determined by the cohesive and formation energy calculations along with mechanical stability criteria. The electronic structure is explored by calculating band structure and density of states which reveal the well-known half-metallic nature of the materials. Further, we have calculated different thermodynamic parameters including specific heat capacity, thermal expansion, Gruneisen parameter and their variation with temperature and pressure. The thermoelectric effectiveness of these materials is predicted in terms of Seebeck coefficient, electrical conductivity and power factor. All-inclusive we can say that calculated properties of these half-metallic materials extend their route in spintronics, thermoelectric and radioisotope generators device applications.

Radiopharmaceuticals: Production, Physics, and Clinical Applications in Nuclear Medicine: A Short Review

Introduction: The use of radioactive atoms in medicine is growing, particularly in nuclear medicine, where radiation is emitted from the body. Radiopharmaceuticals or radiotracers are artificial short-living radioisotopes labeled with special pharmaceuticals. There are around 1800 radioisotopes, but only around 200 are suitable for general applications. There are four methods for generating radioisotopes: reactor-producing, neutron activation, charged acceleration, and radioisotope generators. Cyclotrons are used to produce many other radioisotopes for medical applications. Physical and biomedical characteristics are crucial for radiopharmaceuticals for clinical use. Physical aspects include the type and energy of radiation, mother and daughter radioactive elements, purity, and half-life of radioactives. Biomedical considerations include easy adhesion to biomolecules, a dynamic time course in the body, toxicity, and high tissue targeting. Radiopharmaceuticals used in diagnosis differ from those used in therapy, with positron emission tomography (PET) using radioisotopes, and gamma-emitting radioisotope-labeled radiopharmaceuticals suitable for SPECT imaging. Over 90% of radiopharmaceuticals are used for diagnostic purposes. Conclusion: Nuclear medicine, as an inevitable part of modern medicine, follows different methods to create more effective diagnostic and therapeutic radiopharmaceuticals with respect to several physical and biological considerations.

Thermal and Electrical Performance Analyses of a 100-W Radioisotope Thermoelectric Generator for Space Exploration

A 100-W radioisotope thermoelectric generator (RTG) is by far the most suitable power supply for long-term deep space exploration where solar power would not be feasible. Understanding the thermal performance and electrical performance of the RTG under operational conditions is paramount for its nominal and safety performance during the space mission. In this paper, modeling and experimental studies on the thermal behavior and electrical performance of the 100-W RTG have been conducted. The RTG uses high conversion efficiency skutterudite-based thermoelectric convertor (TEC) arrays thermally coupled with a radioisotope heat unit (RHU) to generate electricity. A comprehensive finite element model and an electrical heating prototype of the 100-W RTG have been built to assess the performance of the RTG designs. Critical temperature, generated power, and energy conversion efficiency were evaluated. The simulation results show that the maximum output power of the RTG can reach about 120 W(electric); the temperature of the hot end of the TECs is about 853 K, and the temperature of the cold end is about 473 K, making a temperature difference of about 380 K. The RTG prototype with Bi2Te3 TECs generated about 60 W(electric) of electrical power in the first experimental research stage. These research results have significant reference for extension of the RTG prototype to the actual power source of the RHU and allow for future research and development improvements of the 100-W RTG.

A Novel Optimization Method for TEG System Performance Based on Temperature and Heat Flux

The thermoelectric generator (TEG) can convert heat to electricity and is widely used. To overcome the limitation for low efficiency of thermoelectric materials, optimizing the performance of TEG in given system is necessary. This study proposes a method to match individual TEG components to the system environment based on two boundary conditions—temperature and heat flux. With this method, TEG geometrical parameters can be determined to optimize the system performance by varying temperature as an independent variable. Using this method, the TEG in an undersea Radioisotope thermoelectric generator (u‐RTG) is optimized. The TEG system exhibits an output power of 14.10 W when powered by a 200 W heat source. The simulate result in the comprehensive system model of u‐RTG is 14.04 W, which has 0.45% deviation from the TEG optimization result. It is proved that the TEG optimized by this method matches the system, the optimization results are accurate.

Radioisotope thermoelectric generators (RTGs): a review of current challenges and future applications.

Nuclear power sources can be effectively employed to generate renewable energy as a counter to global reliance on fossil fuels and increasing energy demands. Nuclear radiation can be utilized in numerous ways to produce energy. Along with their use as fuel for nuclear power plants, the decay process of radioisotopes can also be used to create electrical energy. A radioisotope thermoelectric generator (RTG) is one such example, as it is tasked to convert the decay energy of radioisotopes into heat energy, which is later converted into electrical power using the Seebeck effect. Radioisotopes have high energy densities and certain isotopes can generate considerable heat energy for prolonged timescales. As such, RTGs have found applications in powering interplanetary exploration and interstellar space missions due to their long half-life. They are also commonly used in remote regions of the earth where frequent replacement, charging and maintenance of power sources is difficult. In this review, we will discuss the working principle and architecture of RTGs, challenges faced in further development and potential applications of this technology.

Thermoelectric materials for space explorations

This review explores the development of thermoelectric materials for space applications, specifically in radioisotope thermoelectric generators. It details the selection criteria for these materials and methods to enhance their performance.