Radioisotope Thermoelectric Generators Research Articles

An Overview and Prospect of Nuclear Battery

The nuclear battery has many advantages, including high energy density, stable performance, no manual intervention etc., which can be widely utilized in cases requiring long-term reliable power supply. Among them, the Radioisotope Thermoelectric Generators (RTG) is the earliest used and the most technically matured one, while betavoltaic battery is now commercialized. However, there are still some problems including self-absorption effect, low energy conversion efficiency and severe radiation damage which restrict the application of betavoltaic batteries. Additionally, for an actual nuclear battery, it should be noticed that the component and density of the source will be changed because the radiation source decays continually, which leads to the electrical performance decline. In this review, the major events in nuclear battery development are listed on a timeline, and the principles and applications of different types of nuclear batteries are also introduced. For betavoltaic battery, the existence of self-absorption effect is pointed out as an important scientific problem, and for batteries with 63Ni and TiT2 source, the time-related electrical properties are also obtained. This paper also pointed out that, fine and precise calculations are very crucial in the optimized designing processes for a particular structure of the practical nuclear battery. Finally, researching assumptions including combining the source and the energy converting material and the use of energy converting structures with heavier isotopes are presented, which are benefit to solve the self-absorption problem, rise the output power of the nuclear battery and reduce the influence of radiation damage.

An Update on Extemporaneous Preparation of Radiopharmaceuticals Using Freeze-Dried Cold Kits.

The field of nuclear medicine is rapidly evolving due to the high demand of radiopharmaceuticals for diagnostic and therapeutic applications. The availability of a vast array of radioisotopes, improvement in radiolabeling strategies, and advancements in detection systems have also contributed to the progress in this field. Radiopharmaceuticals are mainly classified based on their application as diagnostic or therapeutic radiopharmaceuticals. These are available either as ready to use preparations or prepared at hospital radiopharmacy either using automated synthesis modules or by using freezedried cold kit formulations. Availability of freeze-dried cold kits for preparation of varied radiopharmaceuticals for targeting various organs and tumors played an essential role in the extensive use of 99mTc radiopharmaceuticals for diagnostic imaging by single-photon emission computed tomography (SPECT) imaging. Cold kits are especially suitable for the preparation of radiopharmaceuticals labeled with isotopes like 177Lu with relatively long half-life or radionuclides produced by radioisotope generators. A simplified procedure for the preparation of positron emission tomography (PET) radiopharmaceuticals is also desired to achieve images with higher resolution and sensitivity offered by PET. Robust kit formulations will simplify the preparation of PET radiopharmaceuticals and will contribute to extensive applications of positron emitters such as 68Ga. Several therapeutic radiopharmaceuticals are also being made using cold kits of the ligands. This review provides an update on diagnostic and therapeutic radiopharmaceuticals prepared using cold kits.

Technological breakthrough and scientific achievement of Chang'e-4 project

Chang'e-4 is the first man-made probe that accomplished landing and roving on the far side of the moon, setting a new mile-stone in lunar exploration. This paper gives a brief introduction to the state of international lunar exploration and reviews the implementation process of the Chang'e-4 project. After sorting the important technological breakthroughs in the aspects such as Earth-Moon relay communications, high-precision landing on the far side of the moon and radioisotope thermoelectric generators (RTG), this paper summarizes a number of original scientific research achievements in the topography of the far side of the moon, mineral composition and environmental detection. It could provide references for further lunar exploration, planetary exploration and scientific research.

Using N,N-dialkylamides for neptunium purification from other actinides for space applications

ABSTRACT Tributylphosphate (TBP) has been reliably used in the solvent extraction of actinides for decades. One current application of TBP is the purification of plutonium-238 (238Pu), a heat source for radioisotope thermoelectric generators. Part of the 238Pu production process includes irradiating neptunium-237 (237Np) previously purified using di-(2-ethylhexyl)phosphoric acid (HDEHP). However, radiolytic decomposition of TBP and HDEHP forms several problematic phosphate-based degradation products. These non-incinerable byproducts contaminate the final 238Pu product and complicate the recycle of 237Np. In contrast, alternative extractants, such as the N,N-diakylamides, have incinerable byproducts. Nonbranched N,N-dialkylamides (N,N-dihexylhexanamide (DHHA) and N,N-dihexyloctanamide (DHOA)) and branched N,N-dialkylamides (N,N-di(2-ethylhexyl)butanamide (DEHBA) and N,N-di(2-ethylhexyl)isobutanamide (DEHiBA)) were considered for Np/Pu and Np/Th separations to replace TBP or HDEHP in 238Pu production. To understand the extraction potential of N,N-dialkylamides, all four N,N-dialkylamides were used to extract actinides (Th, U, Np, Pu, Am) across a range of solution-accessible oxidation states. Those results were then compared based on the actinides’ oxidation state (III - VI) to illustrate some of the similarities and differences in extraction behavior.

Development of Micro-radioisotope Thermoelectric Power Supply for Deep Space Exploration Distributed Wireless Sensor Network

A radioisotope thermoelectric generator (RTG) is a device that directly converts the decay heat of a radioisotope into electrical energy using the Seebeck effect of a thermoelectric material. The constant decay of the radioisotope heat source produces heat as a system energy source. The thermoelectric module uses materials to obtain electric energy by Seebeck effect. The structure and size of the thermoelectric converter need to be optimized for different radioisotope heat sources. The power has stable output performance, sustainable operation, and strong environmental adaptability. Space micro-scientific instruments require power supplies that are sustainable, stable, and long-life. The micro radioisotope thermoelectric generator can be invoked as a sustainable long-life power supply in low-power device applications. The miniaturized RTG can be applied in long-term service meteorological/seismic monitoring stations that are widely distributed on the surface of the planet, small landing vehicles at extreme latitudes or areas with low solar flux, atmospheric-surface-flow monitoring systems, underground detectors, deep space micro spacecraft, wireless sensor networks, self-powered radiation sensors, deep-space robot probes, and radio observatories on the lunar surface. This study innovatively proposes micro stacked-integrated annular-radial radioisotope thermoelectric generator and prepares an integrated prototype to drive an RF2500-based radiofrequency wireless sensor network, and monitors the temperature of each node for a long time as a demonstration. A high-performance micro radioisotope thermoelectric generators module based on the flexible printed circuit and bismuth telluride thick film was designed and prepared by screen printing. They are tested by a loading electrically heated equivalent radioisotope heat source. The output performance of the micro-RTG at different ambient temperatures is further evaluated. When loaded with 238PuO2 radioisotope heat sources, an integrated prototype would generate an open-circuit voltage of 0.815 V, a short-circuit current of 0.551 mA, and an output power of 114.38 µW at 0.408 V. When loaded with a 90SrTiO3 or 241AmO2 radioisotope heat source, the prototype produced 66.38% and 6.15% of the output power (compared to 238PuO2), respectively. In the impact evaluation on ambient temperature, the electrical output performance of the prototype increases with increasing temperature (− 30 to 120 °C). In the evaluation of the effects of long-term radioisotope irradiation, the output performance decreased slightly as the irradiation dose was increased during the service period. The stack-integrated micro radioisotope thermoelectric generator developed in this study is expected to provide reliable power support for space micro-scientific instruments, especially distributed wireless sensor networks.

Melt-Spun SiGe Nano-Alloys: Microstructural Engineering Towards High Thermoelectric Efficiency

Silicon-germanium (SiGe) alloys are prominent high-temperature thermoelectric (TE) materials used as a powering source for deep space applications. In this work, we employed rapid cooling rates for solidification by melt-spinning and rapid heating rates for bulk consolidation employing spark plasma sintering to synthesize high-performance p-type SiGe nano-alloys. The current methodology exhibited a TE figure-of-merit (ZT) ≈ 0.94 at 1123 K for a higher cooling rate of ∼3.0 × 107 K/s. This corresponds to ≈ 88% enhancement in ZT when compared with currently used radioisotope thermoelectric generators (RTGs) in space flight missions, ≈ 45% higher than pressure-sintered p-type alloys, which results in a higher output power density, and TE conversion efficiency (η) ≈ 8% of synthesized SiGe nano-alloys estimated using a cumulative temperature dependence (CTD) model. The ZT enhancement is driven by selective scattering of phonons rather than of charge carriers by the high density of grain boundaries with random orientations and induced lattice-scale defects, resulting in a substantial reduction of lattice thermal conductivity and high power factor. The TE characteristics of synthesized alloys presented using the constant property model (CPM) and CTD model display their high TE performance in high-temperature regimes along with wide suitability of segmentation with different mid-temperature TE materials.

Assessment of a possibility to use 232U in radioisotope thermoelectric generators

The paper analyzes advantages and drawbacks of the radioisotope thermoelectric generators (RTG) based on application of 238Pu and 232U. Currently, the RTG on 238Pu are widely used for long-term autonomous power supply of spaceships due to the following positive properties of 238Pu: high specific heat generation rate, long half-life, weak emission of neutrons and γ-rays. Isotope 238Pu may be produced by neutron irradiation of 237Np (main component of transuranium radioactive wastes) in nuclear reactors. The paper considers application of 232U for the same purpose because of the following positive properties of 232U: power elevation during initial 10 years of the RTG operation (effect of α and β-emitters in 232U decay chain), long half-life (comparable with 238Pu half-life). Unfortunately, 232U decay chain includes also intense emitters of high-energy γ-rays. As a compromise, a possibility is considered to create the RTG based on mixture of 238Pu with small (below 5%) additive of 232U. Such RTG will be able to keep long-term stable operation at high power level. The following two-step technology is proposed to produce 232U: generation of 231Pa in thorium blanket of hybrid thermonuclear reactors and subsequent neutron irradiation of 231Pa in nuclear reactors till accumulation of significant 232U quantities.

Experimental optimization of small–scale structure–adjustable radioisotope thermoelectric generators

Small–scale radioisotope thermoelectric generators (RTGs) offer a flexible and scalable power supply for space missions. However, high-performance small-sized RTGs remain challenging. The performance of thermoelectric materials was optimized by Taguchi orthogonal method in this work. Three preparation parameters, including the slurry ratio, cold pressing pressure, and the sintering temperature, along with 4 levels were taken into account. The orthogonal array quickly determined the sensitivity of the performance to the variations of 3 factors. The influences of 3 factors on the ZT value were ranked as: cold pressing pressure > slurry ratio > sintering temperature. The optimum operation was 10% paint proportion, 35 MPa pressure, and 598.15 K sintering temperature. Based on this, the optimal ZT values of the P/N–type thermoelectric materials reached 0.92 and 1.03 at room temperature, respectively. The principle prototype of the fan–shaped and annular RTGs were well prepared by the cold sintering and molding methods. Those RTGs obtained open–circuit voltages of 1.17 and 1.56 V, and maximum output powers of 1.9 and 3.39 mW at 398.15 K. These stable and adequate energy is able to directly power for meteorological monitoring equipment, seismometer, and microsatellites.

Geometry design and performance optimization of a terrestrial radioisotope thermoelectric generator based on finite element analysis

Radioisotope thermoelectric generator (RTG) has been widely regarded as a promising battery for space missions. To broaden RTG’s application on earth, a terrestrial radioisotope thermoelectric generator (tRTG) was demonstrated in this paper. By employing the finite element analysis, an octagonal cylinder-shaped substituted electric heater and a fin-shaped radiator were manufactured, the heater was designed to have a higher surface temperature and better temperature uniformity meanwhile the fin-shaped radiator could dissipate heat at its optimal heat-sinking capacity. Then, the effects of temperature, electric connection on the output performance of the tRTG were studied experimentally. Lastly, the finite element analysis was carried out to optimize the geometry of thermoelectric converters within a certain area, as a result, the tRTG possessed an enhanced output power of 10.5 W which increased by 26.5%. Throughout this paper, the geometry design and performance optimization of tRTG were presented and discussed.

Investigation of oxygen sources and subsequent thorium oxidation in the iridium DOP‐26 cladding material and PuO2 fuel system

AbstractEarlier experimental work on materials used in radioisotope thermoelectric generators (RTG) has shown that the Ir DOP‐26 cladding material experiences intensified grain growth due to the unpinning of grain boundaries and diffusion of thorium to the surface of the material. This phenomenon has shown considerable dependence on high temperature environments, long duration, and partial pressures of oxygen in the system. When an oxygen source is present in the system, it exacerbates this grain growth by the formation of ThO2. Continued experimentation to analyze this grain growth dependence can be costly and at times infeasible. In this article, a simple approach was used that involves first‐principles atomistic calculations and computational thermodynamics to simulate, understand and plan for potential mitigation of the grain growth in the cladding material without changing the configuration or composition of the structure and/or materials in order to avoid costly recertification processes and experimentation. An emphasis was made on identifying the potential sources of oxygen and determining the oxidation stability of thorium in the Ir‐Th system (used to mimic alloy DOP‐26 in the first approximation). The overall results improve qualitative understanding of the potential oxygen sources and the stability of oxidation. Supplemented by the kinetic studies in the future, this research effort would represent a steppingstone to design and build better RTGs for the future deep space missions.

An Experimental Study on the Ablation Properties of Carbon/Carbon Composites Using Thermal Plasma

The ablation properties of two carbon/carbon (C/C) composites currently considered as thermal protection materials for radioisotope thermoelectric generators (RTGs) were investigated using a plasma wind tunnel with a heat flux between the range of 2–4 MW/m2. The ablation properties were identified through an analysis of erosion rates and microstructures after testing. During ablation, erosion reactions of the matrix were faster than those of fibers and pores, and the defects and cracks between the fibers and matrix grew. The fibers eroded from their outer surface and ablation led to the formation of sharp tapered tips. Lower density C/C composites appeared to lose more matrix than higher density C/C composites. The erosion rate increased with heat flux. The ablation properties were compared with the test results using a vacuum plasma spray (VPS) facility and an E-beam facility. It was shown that both thermochemical and thermomechanical erosion occurred via oxygen in the plasma flow, and a rapid high-pressure heat stream occurred in tests using the plasma wind tunnel while only thermal ablation occurred in tests using the VPS and E-beam facilities.

Enhancing the performance of fully-scaled structure-adjustable 3D thermoelectric devices based on cold–press sintering and molding

Abstract The growing concern over the global energy crisis strengthened the research on thermoelectricity. It would be logical to prepare practical thermoelectric device to effectively utilize various low-quality heat. In this study, the high-performance structure-adjustable 3D thermoelectric devices were fabricated by cold-press sintering and molding technologies. The thermoelectric figures of merit (ZT) of pressurized P and N–type materials reached the maximum of 1.09 and 0.5 at room temperature, respectively. The holes introduced by the binder and pressurization process reduced thermal conductivity and enhanced electrical properties. The in–depth influence on the thermoelectric devices was shown via simulation calculation. Fully-scaled thermoelectric devices suitable for various occasions were fabricated by one–time forming. The tandem of small and large arrayed thermoelectric devices respectively generated open–circuit voltages (Voc) of 584 mV and 573.8 mV and maximum output powers (Pmax) of 627.7 μW and 1.2 mW at 398.15 K. The Voc values of arched and annular thermoelectric devices were 265 mV and 332.1 mV at 398.15 K, respectively, and the Pmax values were 948.5 μW and 1.2 mW, respectively. On account of its good structure adjustability and high performance, thermoelectric devices fabricated will be broadly applied in solar–thermal conversion systems, automotive heat reclaimer and radioisotope thermoelectric generator.

Response of p-type and n-type Half-Heusler thermoelectric materials to fast neutron irradiation

The thermoelectric materials working in radioisotope thermoelectric generators or space reactor power system will be exposed to neutron irradiation in space missions. Herein, the influences of neutron irradiation with doses of 1013n/cm2 and 1015n/cm2 on the transport properties of p- and n-type Half-Heusler thermoelectric alloys were investigated. It was found that, neutron irradiation showed negative effects on thermoelectric properties of p-type Hf0.5Zr0.5CoSb0.85Sn0.15 and p-type Hf0.5Ti0.5CoSb0.85Sn0.15. But neutron irradiation had no effects on thermoelectric properties of n-type Hf0.5Zr0.5NiSn0.985Sb0.015 and n-type ZrNiSn0.985Sb0.015. After 1015n/cm2 neutron irradiation, the electrical conductivity, power factor and ZT of p-type Half-Heusler alloys decreased by 7–22%, which was caused by the decreased carrier concentration. However, the radiation-induced changes in the thermoelectric properties proved to be essentially healed by annealing at 773 K ~ 873 K. The anti-annealing effects were also studied.

Geradores Betavoltaicos para Sistemas Eletrônicos Portáteis

Betavoltaic Generators for Portable Electronic Systems Conventional energy sources, based on electrochemical processes, have become an everyday element, being used in countless electronic equipment, such as smartphones and notebooks. However, even with advances in technology in the last decade, they show a lower evolution than expected, causing a limitation of electronic devices, creating a need for more powerful energy sources. The development of a radioisotope generator, based on betavoltaic systems, which uses non-thermal processes generating electrical energy based on the emission of beta radiation, a technology that would allow an electronic device to function for long periods, without the need for recharging or replacement. However, despite the advantages that this technology presents us, we have the challenge regarding health risks caused by undue exposure to radiation, where the Comissão Nacional de Energia Nuclear (CNEN), which establishes dosage limits, which must be followed to design of a betavoltaic generator using materials and techniques, allowing such devices to be developed for safe handling and use, based on the level of beta radiation emitted and the behavior of the radioisotope employed, allowing the dimensioning of an efficient shield and safe.

The Plutonium-238 Radioisotope Thermoelectric Generator in the Deep Space Exploration

The Plutonium-238 radioisotope thermoelectric generator (Plutonium-238 RTG) can work continuously without maintenance for a long time in harsh environment. It can supply power and thermal energy at the same time, which is an ideal energy source for deep space exploration missions. Firstly, the electricity power generation theory, basic structure, application history and development tendency of Plutonium-238 RTG are described in this paper. Then the key technologies for the development of Plutonium-238 RTG are presented, combined with the technology development of Plutonium-238 RTG in foreign countries and the requirements for deep space exploration. The above-mentioned key technologies are analyzed and discussed, providing a reference to the technology development and engineering application of Plutonium-238 RTG in China.

Enhancing NASA's Multi-Mission Radioisotope Thermoelectric Generator Using Highly Efficient Thermoelectric Materials

This project proposal aims to enhance NASA’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) by identifying and analyzing new material technologies that have been researched for their excellent thermoelectric properties at higher temperatures. By choosing the most efficient thermoelectric material available, the MMRTG’s energy conversion efficiency will be greatly improved as thermoelectric generator efficiencies are largely determined by the properties of the materials within the thermocouple devices used to convert the heat into energy. A project that focuses on enhancing the MMRTG is imperative for the future of space exploration as there is global shortage of plutonium fuel production, limiting future missions to available supplies. A more efficient generator will minimize the use of this fuel while maximizing power output, allowing for increased mission capabilities and better conservation of the scarce plutonium fuel. In this report, lanthanum telluride, Yb14MnSb14, and a multiple-filled skutterudite (SKD) compound are analyzed for their excellent thermoelectric performance. The multiple filled SKD compound is chosen as the ideal material to enhance the MMRTG based on the low cost and low risks associated with the material while producing a nearly identical efficiency relative to the other candidates. Keywords: eMMRTG, MMRTG, thermoelectric materials, thermoelectric generator, efficiency

Production of Polonium-208, 209 and 210 for use in nuclear battery via particle accelerator

Nuclear reaction processes are used for the production of energetic 208,209,210Po nuclei from Pb and Bi targets with particle accelerators, instead of the production with a nuclear reactor, for use in the nuclear battery and radioisotope thermoelectric generator technologies. The cross-section curves, simulated activity and yields of product of each reaction process were calculated under particular conditions, including 24 h of irradiation with a particle beam current of 1 mA for the energy range Eparticle = 200 → 1 MeV. Based on the calculated and simulated results, to produce 208,209,210Po nuclei, the appropriate target nuclei, nuclear reaction processes, and energy region of reactions were discussed by comparing the obtained results with the experimental data of literature and TENDL database in detail.

The Search for MeV Electrons 2–45 au from the Sun with the Alice Instrument Microchannel Plate Detector Aboard New Horizons

Abstract The Alice UV spectrograph aboard NASA’s New Horizons mission is sensitive to MeV electrons that penetrate the instrument’s thin aluminum housing and interact with its microchannel plate detector. We have searched for penetrating electrons at heliocentric distance of 2–45 au, finding no evidence of discrete events outside of the Jovian magnetosphere. However, we do find a gradual long-term increase in the Alice instrument’s global dark count rate at a rate of ∼1.5% per year, which may be caused by a heightened gamma-ray background from aging of the spacecraft’s radioisotope thermoelectric generator fuel. If this hypothesis is correct, then the Alice instrument’s global dark count rate should flatten and then decrease over the next 5–10 years.

Pluto Orbiter–Kuiper Belt Explorer: Mission Design for the Gold Standard

A mission design study was conducted demonstrating for the first time the feasibility of a combined Pluto orbiter–Kuiper Belt explorer mission using present-day electric propulsion (EP) performance and launch vehicles, assuming that radioisotope thermoelectric generator (RTG)–sourced electricity would power the EP system, a not-yet-demonstrated but low-risk capability. This mission breaks the scientific conundrum between desires to study the Pluto system in more detail using an orbiter and desires to reconnoiter other bodies in the Kuiper Belt. This study also includes the first demonstration that a wide suite of Pluto orbiter scientific objectives can be accomplished with an orbital trajectory primarily using Charon gravity-assist maneuvers to maneuver in the system. The study further demonstrates that Pluto system escape back into the Kuiper Belt can be accomplished using Charon gravity assists, thereby further reducing onboard propulsion requirements. The primary technical challenges for this mission are the long (75 years) mission duration imposed by current-day RTG nuclear systems required to power the spacecraft and its EP system, and the need for high-bit-rate communications () to make the Pluto orbiter continuously effective. As discussed in this study, the communications challenges can be overcome without new systems developments or unreasonable mass challenges. More reasonable mission durations (e.g., ) will require the development of multi-kilowatt nuclear fission reactor power generation systems; still shorter mission durations require both more power and higher EP thrust, as in multiple electric engines operating simultaneously.

Assessment of water content in martian subsurface along the traverse of the Curiosity rover based on passive measurements of the DAN instrument

This paper presents the method of estimating water-equivalent hydrogen (WEH) content from neutron sensing data that were measured by the Dynamic Albedo of Neutron (DAN) instrument onboard the Curiosity rover. Analyzed data are derived from the DAN passive operations, when the instrument measures the flux of neutron albedo from the surface, which is produced by bombardment by Galactic Cosmic Rays (GCR) and irradiation from Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) installed onboard the rover. The suggested Method of Referencing by Active Data (MRAD) for the analysis of DAN passive data is compared with the previously suggested Method of Numerical Simulation (MNS, see Tate et al. 2015, 2018 and 2019) for the analysis of DAN passive data: the qualitative agreement between them is shown with some systematic increase of WEH for the second one. The possible reason for that is explained in Section 6. Results for the DAN passive data analysis by MRAD are presented obtained for almost 20 km of the rover's traverse (until November 2, 2018 or sol 2218). The range of WEH average concentration of (2.6 ± 0.7) wt% is found for this part of the traverse, which is consistent with a method of active neutron sensing (Mitrofanov et al., 2014, 2016; Lisov et al., 2018).