Radioisotope Thermoelectric Generators Research Articles

Activation imaging of drugs with hybrid Compton camera: A proof-of-concept study

The visualization of drugs is essential for cancer treatment. Although several methods for visualizing drugs have been proposed, a versatile method that can be easily applied to various drugs has not yet been established. Therefore, we propose “activation imaging,” in which a drug is irradiated with thermal neutrons and becomes radioactive, enabling visualization using emitted x rays and/or gamma rays. Activation imaging does not require the conjugation of specific tracers with drugs. Therefore, it can be easily applied to a variety of drugs, drug carriers (e.g., metal nanoparticles), and contrast agents. In this study, neutron activation, gamma-ray spectroscopy, and imaging of drug carriers, anticancer drug, and contrast agents were performed. Gold nanoparticles (AuNPs) and platinum nanoparticles were used as drug carriers, cisplatin was used as an anticancer drug, and gadoteridol and iohexol were used as contrast agents. As a neutron source, the RIKEN accelerator-driven compact neutron source II (RANS-II) was utilized. The imaging was performed using a hybrid Compton camera (HCC). The HCC can visualize x rays and gamma rays ranging from a few keV to nearly 1 MeV, which enables the imaging of various x rays and gamma rays emitted from the activated drugs. As a result, the gamma-ray spectra indicated the generation of radioisotopes through neutron irradiation, and AuNPs and iohexol were visualized.

Radiation protection evaluation and spontaneous discharge performance of betavoltaic tritium batteries using well-aligned titanium dioxide nanotube arrays

Nuclear power plants produce the largest amount of tritium. Tritium is a by-product of nuclear reactors. Currently, it can only be placed in sealed storage tanks. Radioactive waste can be used as a source of energy for radioisotope battery. Since isotope energy is continuously converted into electrical energy for a long period of time, it is considered an ideal choice for remote applications. The mechanism of current generation of nuclear batteries is similar to that of solar cells. The only difference is that the electron holes are generated from radiation, not from light. The novel technologies of betavoltaic batteries would make use of the synthetic strategy for TiO2 semiconductors and the radioactive wastes radiation sources (H-3) stored in INER (Institute of Nuclear Energy Research, Taiwan). The radioactive waste can become a source of energy for radioisotope generators. At first, this study evaluates the radiation shielding safety distance required for radioactivity used in a betavoltaic tritium battery. The technological innovation includes the experimental synthesis of TiO2 nanotube in a complete array and the use of TiO2 nanotube arrays (TNTAs) as the semiconductor inside radioisotope batteries. In this work, combining the technology of TiO2 synthesizing TiO2 nanotube arrays with liquid waste radiation sources (tritium, H-3), the betavoltaic tritium battery (Ni/H-3/TNTAs/Ti) have successfully created and analyzing the characteristics of betavoltaic battery. Durability was assessed using analytical parameters of betavoltaic batteries compared to lithium-ion batteries. Such betavoltaic batteries have practical advantages in tritium handling applications and long-term battery performance.

Planetary Protection Assessment of Radioisotope Thermoelectric Generator (RTG)-Powered Landed Missions to Ocean Worlds: Application to Enceladus.

Landed missions to icy worlds with a subsurface liquid water ocean must meet planetary protection requirements and ensure a sufficiently small likelihood of any microorganism-bearing part of the landed element reaching the ocean. A higher bound on this likelihood is set by the potential for radioisotope thermoelectric generator (RTG) power sources, the hottest possible landed element, to melt through the ice shell and reach the ocean. In this study, we quantify this potential as a function of three key parameters: surface temperature, ice shell thickness (i.e., heat flux through the shell), and thickness of a porous (insulating) snow or regolith cover. Although the model we describe can be applied to any ocean world, we present results in the context of a landed mission concept to the south polar terrain of Saturn's moon Enceladus. In this particular context, we discuss planetary protection considerations for landing site selection. The likelihood of forward microbial contamination of Enceladus' ocean by an RTG-powered landed mission can be made sufficiently low to not undermine compliance with the planetary protection policy.

Novel geometric design of thermoelectric leg based on 3D printing for radioisotope thermoelectric generator

• A design concept of geometry of 3D printing thermoelectric (TE) legs is proposed. • Two TE legs with geometrical shapes of helix and spoke are designed. • The improvement effect of geometric design on output performance of TE legs is analyzed. • 3D printed TE modules with special shapes exhibit outputs of more than 30% increments. To meet the power supply development needs of electronic devices in spacecraft, the optimized design and fabrication of geometric configuration of thermoelectric (TE) legs to increase the power output of radioisotope thermoelectric generators are proposed. The principle of performance enhancement is the increase of heat dissipation on the increased side area, which is analyzed according to Fourier’s law. Helix-shaped and spoke-shaped TE legs with special geometrical shapes are proposed and fabricated by 3D printing technology. The geometric design makes the TE legs produce a larger temperature difference and inevitably brings about an increase in resistance. Variation of TE legs’ output performance with the geometrical parameters is analyzed based on the finite element method. Results show that the helix-shaped TE legs with the appropriate geometrical parameters can produce maximum output power of 2.78 mW, which are 2.55 times of the traditional cylinder-shaped TE legs with the same mass. And the spoke-shaped TE legs can produce maximum output power of 2.28 mW, which are 2.09 times of the traditional cylinder-shaped TE legs. Nine TE legs with special shapes and sixteen with traditional shapes are integrated into the same space (16.5 mm × 16.5 mm). The results show that the combination of TE legs with special shapes produce a higher power density, more than 66%–98% compared with traditional shapes due to lighter mass. TE modules with different shapes are fabricated by direct-writing 3D printing technology, and their output performances are tested. TE modules with special shapes exhibit greater open-circuit voltage and output power than the traditional shapes, which are consistent with the simulation results. The simulation and experimental results indicate that the geometric design of TE legs with larger side areas can improve the output performance of TE devices. This design concept of optimizing the geometry to increase the temperature difference can be applied to thermoelectric generators under the condition of natural heat dissipation to improve power output and heat dissipation, and reduce weight.

How does radioisotope thermoelectric generator (RTG) work

Demand for energy has increasing rapidly in the last decade. In 2021 an increase in 5% was observed. Half of this demand was covered by fossil fuels, increasing CO2 emissions to record levels. With the need for new reliable steady supply sources to be used in places where maintenance is difficult, Radioisotope Thermoelectric Generators (RTG) have been given renewed attention in the past 10 years. RTGs uses radioactive decay to generate electricity. This work presents in a simple manner, the basics of RTG operation, the requirements for construction, and is followed by an example developed at KAERI. Basic Radiation Physics Concepts, RTG configuration requirements, Thermoelectric effect and materials, and calculations for electric power were presented.

Detection of Radio Thermal Emission from the Kuiper Belt Object (486958) Arrokoth during the New Horizons Encounter

The New Horizons spacecraft encountered the Kuiper Belt object (KBO) Arrokoth (486958), originally designated as 2014 MU69 and formerly called “Ultima Thule,” on 2019 January 01. At 43.3 au from the Sun and 44.4 au from Earth, this was the most distant spacecraft reconnaissance of a solar system body to date. The Radio Science Experiment (REX) on New Horizons performed radiometry measurements of the KBO's thermal emission at λ = 4.2 cm in two observation slots, one before (dayside) and one after (nightside) the point of closest approach. Owing to the small size of the target, the intensity of the thermal emission was expected to be only marginally detectable. The KBO was not detected on approach because of unexpectedly large variations in the REX system temperature. A brightness temperature T b = 29 ± 5 K was derived for the nightside observation, considerably less than the predicted equilibrium temperature of ∼50 K derived for Arrokoth on the dayside. A model explaining this day−night contrast is used to constrain the global values of emissivity, thermal inertia, and electrical skin depth of the KBO. In particular, models with small values of thermal inertia and small values of electrical skin depth are excluded. Relatively high values of the effective radio emissivity (E eff > 0.8) provide better agreement with the REX observation.

Silicon–Germanium: The Legacy Lives On

Alloy systems comprised of silicon with germanium, lead with tellurium, and bismuth with antimony have constituted a majority of thermoelectric applications during the last half-century. These legacy materials are primarily covalently bonded with a maximum ZT near one. Silicon–germanium alloys have provided the thermal to electrical conversion for many of NASA’s radioisotope thermoelectric generator (RTG) configurations and for nearly all of its deep space and outer planetary flights, such as Pioneer I and II, Voyager I and 11, Ulysses, Galileo, and Cassini. The remarkable success of these materials and their respective devices is evidenced by the fact that there has never been a failure of the RTG systems even after over 1 billion cumulative mission-hours. The history of this alloy system as a thermoelectric conversion material spans over six decades and research to further improve its performance continues to this day. Si-Ge alloys have long been a mainstay of thermoelectric research because of a fortuitous combination of a sufficiently high melting temperature, reasonable energy band gap, high solubility for both n- and p-type dopants, and the fact that this alloy system exhibits complete miscibility in the solid state, which enable tuning of both electrical and thermal properties. This article reviews the history of silicon–germanium as a thermoelectric material and its use in NASA’s RTG programs. Since the device technology is also a critical operational consideration, a brief review of some of the unique challenges imposed by the use in an RTG is also discussed.

A new production route of Gadolinium-148 for use in Radioisotope Thermoelectric Generators

The production of Gd-148 had challenges for available methods in the literature, such as its high cost and low production amount. Therefore, we recommend a new production route of Gd-148 on natural Sm and Eu targets via particle accelerators. For this aim, we calculated and simulated cross-section, activity, the yield of product, and integral yield curves for 21 different nuclear reaction processes under certain conditions. Based on the obtained results, we proposed the radioisotope Gd-148 to use Radioisotope Thermoelectric Generators for deep space and planetary explorations in spacecraft and space-probes as a suitable energy source, instead of Pu-238.

Multi-Mission Thermoelectric Generator Fueling Testing and Integration Operations for Mars 2020

The Space Nuclear Power and Isotope Technologies (SNPIT) Division at Idaho National Laboratory fuels, performs acceptance testing, and provides spacecraft integration support of radioisotope power systems in support of National Aeronautics and Space Administration missions. Recently, the SNPIT team completed fueling, testing, and launch support of the Multi-Mission Radioisotope Thermoelectric Generator for the Mars 2020 Perseverance Rover mission.

Performance of 113Sn/113mIn Generator Prototype based on Zirconium Oxide for Radiotracer Applications in Industry

This paper describes the results of the research of 113Sn/113m radioisotope generator at the Centre for Applied Nuclear Science and Technology - National Nuclear Energy Agency with the aim of making radioisotope generator for radiotracer applications in industry. This research discussed the need of short half-life radiotracer for several material phases such as oil, water, gas and solid. Based on desired physical properties of half life, radiation type and energy, 113mIn radioisotope was selected. Thus, the performance of 113Sn/113mIn generator prototype based on zirconium oxide was determined for this purpose. The final product specification in the form of 113mInCl3 is clear solution, pH 2 with obtained yield of 95 %, radionuclide purity of 95 % and radiochemical purity of 95 %.

Space solar power satellite for the Moon and Mars mission

This paper presents an overview of space solar power satellites for the Moon and Mars mission and simultaneously demonstrates the compression of traditional power generation methods for the orbiter, lander, and habitat on Mars and the Moon. Interplanetary missions are where the space engineers work on the satellites, conceptual design of space habitat, and exploration system. The state of the art in those missions relies on radioisotope thermoelectric generators or solar panels attached with batteries to store power, both of which are plagued by limitations. For instance, when a spacecraft moves away from the Sun, the energy collection efficiency on the solar panel is reduced, and at temperatures below -100°Celsius, individual solar cells degrade unpredictably, deteriorating the performance of solar arrays. Furthermore, these power generation unit satellites carry a pack of batteries to store energy whose total system accounts for more than 10-25 % of the mass of the satellites. In an interplanetary mission, power generation and management are essential for research and investigation on the surface. For Mars, sandstorms affect the collection of energy at the attached solar panel to the rover. Moreover, the rovers must investigate at the far side of the Moon, where sunlight is unavailable for few consecutive days. This challenge can be suitably overcome by employing space solar power satellites, which can be used for wireless power transmission, independent of its location. Such techniques have possible applications towards power transmission for unmanned aerial vehicles for faster mapping purposes. As such, the dependence of those aerial vehicles towards fixed energy storage becomes alleviated. In hindsight, space solar power satellite serves as a potential for an improved energy transmission source than the traditional method for interplanetary rovers and habitat.

Mechanisms Responsible for Adsorption of Molybdate ions on Alumina for the Production of Medical Radioisotopes

Abstract In this work, the mechanisms responsible for the adsorption of molybdate ions on alumina are investigated using in-depth surface analyses of alumina specimens immersed in solutions containing different molybdate ions at different pH values. The obtained results reveal that when alumina is immersed in an acidic solution containing molybdate ions, the hydroxyl groups present on the surface are removed to generate positively charged sites, and molybdate ions (MoO42− or AlMo6O24H63−) are adsorbed via an electrostatic interaction. Alumina dissolves slightly in an acidic solution to form AlMo6O24H63−, which is more easily desorbed than MoO42−. Furthermore, the enhancement in the Mo adsorption or desorption property may be achieved by enriching the surface of the alumina adsorbent with many –OH groups and optimizing Mo solution to adsorb molybdate ions on alumina as MoO42− ions. These findings will assist researchers in engineering more efficient and stable alumina-based adsorbents for molybdenum adsorption used in medical radioisotope (99Mo/99mTc) generators.

Impact tests and modelling for the ESA radioisotope power systems

Since 2009, ESA has been conducting R&D activities leading towards the development of a European capability in radioisotope power systems for space. The programme is focused on the use of americium-241 as an innovative alternative to the plutonium-238 currently used by the USA and Russia. Two different technologies are being developed by the University of Leicester in the UK: radioisotope thermoelectric generators and radioisotope heater units.The development of the fuel containment architectures, known as heat sources, has recently evolved from the design stage to more representative prototypic systems. Multiple containment layers ensure that the heat sources can survive accident conditions from launch failures to Earth re-entry, minimising the risk of inadvertently releasing radioactive material into the environment. Validated accident models are necessary for the design iteration process of these systems, and for the creation of a safety case for their launch.The research project here presented was a collaboration, supported by ESA, between the University of Leicester in the UK and ArianeGroup in France. The goals of this activity were to perform the first-ever impact tests for the European Am-based heat sources, and to start developing computer models to simulate the behaviour of the containment systems under different impact conditions in accident scenarios. Tested samples were then characterized both at ESA/ESTEC and at the University of Leicester, in order to understand the behaviour of the fuel containment materials under the most relevant accident conditions.

Modeling of Am-241 as an alternative fuel source in a radioisotope thermoelectric generator

Radioisotope thermoelectric generators (RTGs) have been utilized in the USA to power satellites and space exploration equipment for over half a century. In our preceding paper, Dustin and Borrelli (2021), we assessed the performance of 241Am as an alternative to 238Pu by modeling the specific decay-heat and gamma spectra of several potential radioisotopes in SCALE-ORIGEN, and comparing these with 238Pu An analysis of heat output, heat stability, safety, availability and required mass showed that of the isotopes reviewed, 241Am had the greatest potential for replacing 238Pu, with additional design considerations. In our current work, we have assessed radiation transport for two configurations of an 241Am powered Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), due to the potential health effects for operators, fabricators, and others with the potential to be exposed to neutrons and lower energy gamma rays. We have modeled the use of americium as a fuel source replacement for plutonium in current MMRTG designs. The assessment has been performed using MCNP6, in terms of neutron and gamma emissions that might interfere with sensitive equipment and power system production. The radiation transport behavior in terms of dose rate of the 241Am fueled models is compared with that of a 238Pu fueled model. Additional work was performed to validate modeling simplifications with regards to thermocouple material configurations.

Thermal Properties and Behaviour of Am-Bearing Fuel in European Space Radioisotope Power Systems

The European Space Agency is funding the research and development of 241Am-bearing oxide-fuelled radioisotope power systems (RPSs) including radioisotope thermoelectric generators (RTGs) and European Large Heat Sources (ELHSs). The RPSs’ requirements include that the fuel’s maximum temperature, Tmax, must remain below its melting temperature. The current prospected fuel is (Am0.80U0.12Np0.06Pu0.02)O1.8. The fuel’s experimental heat capacity, Cp, is determined between 20 K and 1786 K based on direct low temperature heat capacity measurements and high temperature drop calorimetry measurements. The recommended high temperature equation is Cp(T/K) = 55.1189 + 3.46216 × 102 T − 4.58312 × 105 T−2 (valid up to 1786 K). The RTG/ELHS Tmax is estimated as a function of the fuel thermal conductivity, k, and the clad’s inner surface temperature, Ti cl, using a new analytical thermal model. Estimated bounds, based on conduction-only and radiation-only conditions between the fuel and clad, are established. Estimates for k (80–100% T.D.) are made using Cp, and estimates of thermal diffusivity and thermal expansion estimates of americium/uranium oxides. The lowest melting temperature of americium/uranium oxides is assumed. The lowest k estimates are assumed (80% T.D.). The highest estimated Tmax for a ‘standard operating’ RTG is 1120 K. A hypothetical scenario is investigated: an ELHS Ti cl = 1973K-the RPSs’ requirements’ maximum permitted temperature. Fuel melting will not occur.

Thermoelectric properties and service stability of Ag-containing Cu2Se

In 1970s, great efforts had been spent to develop Ag-containing Cu2Se-based radioisotope thermoelectric generators (RTG), but unfortunately the activity was completely stopped in 1981 because the Ag-containing Cu2Se-based thermoelectric module demonstrated poor service stability. Since then, a prevailing mindset in thermoelectric society is that Cu2Se, and related Cu-based thermoelectric materials, can not be fabricated into stable modules. In this study, a series of Ag-containing Cu2Se samples are synthesized. Their thermoelectric properties and service stability under current and/or temperature gradient are systematically investigated. It is found that introducing Ag in Cu2Se has significant influence on the thermoelectric properties but little influence on the stability. The critical voltages for Ag-containing Cu2Se samples, which represent the threshold for thermodynamic stability under electric field and/or temperature gradient, are determined by the total content of Cu and Ag rather than just the Cu content. Likewise, electrical conductivity is proposed to be a simple indicator to rapidly predict the stability and thermoelectric performance of Cu2Se-based materials. Based on the measured critical voltages, the rational ranges of leg geometry are recommended to fabricate the stable and efficient Cu1.97Ag0.03Se-based thermoelectric modules.

Uncovering the Structure and Stability of Thermoelectric La3–xTe4–Ni Composites Using High-Resolution and In Situ TEM

Lanthanum telluride (La3–xTe4) is a high-performance, next-generation thermoelectric material with a thermoelectric dimensionless figure of merit (zT) of 1.1 at 1273 K (x = 0.23) and has potential applications in radioisotope thermoelectric generators (RTGs) to power the space missions conducted by National Aeronautics and Space Administration (NASA). It has been shown that the zT can be increased by 30% when nickel (Ni) nanoparticle inclusions are introduced to the La3–xTe4 matrix. The coherent interfaces between La3–xTe4 and Ni are likely a key factor determining the stability and performance of the La3–xTe4–Ni composites, but their role and nature are not well understood. It is important to determine the stability of the La3–xTe4/Ni interface in deep-space conditions, in addition to the effect of heat and oxygen on the mechanisms and kinetics of interface degradation. Here, we show the high-resolution structural characterization and the epitaxial crystallographic relationship of La3–xTe4–Ni thermoelectric composites and their interfaces at high-vacuum and ambient-temperature conditions using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). We further demonstrate the La3–xTe4/Ni interface degradation and Ni diffusion over its operating temperature range (25–1000 °C), in the presence and absence of oxygen, in real time, using in situ TEM.

Radioisotope research and development at the Linear Accelerator of the Institute for Nuclear Research of RAS

Radioisotope research at the linear accelerator of INR RAS has been developing since 1989. In 1992, a facility for the irradiation of isotope targets and radioisotope production was built, operating on a diverted proton beam with an energy of 160 MeV and a current of more than 120 μA, which was the most productive facility in the world at that time. The facility is used for both fundamental and applied research. The main focus is the study of the processes of the generation and recovery of medical radioisotopes, as well as the development of technology for their production. The main radionuclides produced now are strontium-82 and actinium-225. A Russian 82 Sr/82 Rb generator for PET-diagnostics has been developed by INR RAS and is being introduced for medicine. New types of 225Ac/213Bi generators are also being developed for the treatment of oncological diseases. In addition, the study of the process for the production and chemical recovery of medical radionuclides 117mSn, 68 Ge, 72Se, 64, 67Cu, 223Ra, 230 Pa, and 230U is being carried out, as is the study of some generators with some of these isotopes. The technology developed at INR is used in Russia and abroad. Physical processes of proton interaction with different nuclei are also investigated in the laboratory of the radioisotope complex of INR RAS. The produced 22Na, 83Rb, 109Cd, and radioactive sources with these radionuclides are used in physical research and technology.

Plutonium-238: The Fuel Crisis

Plutonium-238 is currently still the best fuel to power satellites to be sent to deep space in regions where the solar panels can no longer efficiently receive the sunlight. For 50 years, the National Aeronautics and Space Administration (NASA) has used this radioisotope as a fuel in radioisotope thermoelectric generators (RTGs) installed on satellites such as Pioneer 10 and 11, Voyager 1 and 2, Cassini-Huygens and New Horizons, as well as the various rovers sent to the Moon and to Mars, among others. Plutonium-238 is not a naturally occurring isotope on the planet, it was produced in greater quantity during the Cold War period as a by-product of the production of Plutonium-239 used for nuclear bombs. However, after the shutting down of the Savannah River reactors in 1988 and the ending of the Soviet Union in 1991, the United States stock of Plutonium-238 has been increasingly reduced, which threatens NASA's future space projects. This paper presents a brief bibliographic review about the subject, as well as commentaries on the options available to the United States, from restarting the production of this fuel, to possible alternatives for a new type of fuel or equipment that may supply the spacecrafts.

Mission analysis of a Neptune detector with a 10 kWe nuclear reactor power generator

<p indent=0mm>Based on a comparative analysis of the advantages and disadvantages of radioisotope and nuclear reactor power generators in space applications, this paper determines that the space reactor power generator is the energy scheme of the Neptune exploration mission, proposes four kinds of major scientific problems involved in Neptune exploration, and introduces preliminary scheme ideas, such as the function module, fight orbit, and design constraints of the mission. Then, focusing on the reactor, the thermal-electric conversion device, the technical route, nuclear safety and radiation protection, the study elaborates the technical scheme of a 10 kWe space reactor power generator. The Neptune detector bus scheme, including TT&C communication, electric propulsion, independent operation and management, high-reliability and long-life design, payload, and microsatellite probe, can provide reference for the demonstration and implementation of Neptune exploration.