Radioisotope Thermoelectric Generators Research Articles

Synergetic enhancement of thermoelectric and mechanical properties of n-type SiGe-P alloy through solid state synthesis and spark plasma sintering

Silicon-germanium (SiGe) alloy is a potential and an attractive high temperature (>1000 °C) thermoelectric material used in space applications as radioisotope thermoelectric generators (RTGs). However, the lower figure of merit (ZT) is the main setback in the SiGe alloy, and a lot of research strategies are demonstrated to improve the performance. The current investigation details the fabrication of high dense (>99%) SiGe alloy doped with phosphorus (P) (0.5–2.0 at.%) by mechanical alloying (10 h) followed by spark plasma sintering (SPS). The synthesised SiGe-P2.0 at.% alloy demonstrates the enhanced ZT 1.03 at 750 °C. Concurrently, the superior hardness of 9.8 ± 0.17 GPa and fracture toughness (KIC) of 2.3 ± 0.15 MPa√m are achieved in SiGe-P1.5 at.% and SiGe-P2.0 at. % alloys, respectively.

Impedance spectroscopy characterization of neutron irradiated thermoelectric modules for space nuclear power

The European Space Agency is currently supporting the research and development of advanced radioisotope power systems utilising thermoelectric modules. The performance of thermoelectric modules following exposure to neutron radiation is of significant interest due to the likely application of radioisotope thermoelectric generators in deep space exploration or planetary landers requiring prolonged periods of operation. This study utilises impedance spectroscopy to characterise the effects of neutron irradiation on the performance of complete thermoelectric modules, as opposed to standalone material. For a 50 We americium-241 radioisotope thermoelectric generator design, it is estimated that the TE modules could be exposed to a total integrated flux of approximately 5 × 1013 neutrons cm-2 (>1 MeV). In this study, an equivalent neutron dose was simulated experimentally via an acute 2-hour exposure in a research pool reactor. Bi2Te3-based thermoelectric modules with different leg aspect ratios and microstructures were investigated. Gamma-ray spectroscopy was initially used to identify activated radionuclides and hence quantify irradiation induced transmutation doping. To evaluate the thermoelectric properties pre- and post-irradiation, impedance spectroscopy characterization was employed. Isochronal thermal annealing of defects imparted by the irradiation process, revealed that polycrystalline based modules required significantly higher temperature than those with a monolithic microstructure. Whilst this may indicate a greater susceptibility to neutron irradiation, all tested modules demonstrated sufficient radiation hardness for use within an americium-241 radioisotope thermoelectric generator. Furthermore, the work reported demonstrates that impedance spectroscopy is a highly capably diagnostic tool for characterising the in-service degradation of complete thermoelectric devices.

Hybrid Stand-alone Power Supply Systems for the Arctic Polar Stations

Hybrid power supply systems based on the renewable energy sources, electrochemical rechargeable batteries, and fuel cells are considered. Such systems provide stable power supply and offer some advantages both over the traditional hydrocarbon-fueled diesel generators and over the radioisotope thermoelectric generators. The innovative technology of group connection to the Russian Satellite Communications Company resources is considered as a tool for the remote control of operation modes of various power generation sources under changing environmental parameters and payload. It is proposed to use such hybrid power systems to provide power supply for autonomous observation stations in the Russian Arctic.

Radioactive contamination mitigation in the Arctic region

This article discusses the most significant sources of large-scale radioactive contamination to which the Arctic has been exposed since the middle of the last century, which are identified as 1) radioactive fallout and deposition from nuclear weapon testing; 2) plum waste from the Sellafield radiochemical plant (United Kingdom) and Cap de la Ag (France) nuclear fleet operation; 3) radioisotope thermoelectric generators; and 4) submerged and sunken radioactive objects. The article assesses the comparative contribution and associated radioecological risks of these sources, and special attention is focused on the “nuclear legacy” of the USSR/Russian nuclear fleet and the search for solutions. The article describes the content and implementation results of the “Development of a Strategic Master Plan for Disposition of Decommissioned Russian Nuclear-Powered Fleet and Rehabilitation of Hazardously Radioactive Sites and Facilities of Its Support Infrastructure” which was developed with broad international cooperation. Attention is drawn to remaining environmental problems associated with submerged and sunken objects that contain spent nuclear fuel and radioactive waste in the Arctic, and the article presents generalized data on such objects and associated risks of water contamination as identified by analyses of model studies of possible accident consequences.

Fan‐Shaped Flexible Radioisotope Thermoelectric Generators Based on BixTeyand BixSb2‐xTeyFabricated Through Electrochemical Deposition

This article employs electrochemical deposition to prepare thermoelectric film materials to achieve a miniaturized radioisotope thermoelectric generator (RTG). First, the optimal composition and material properties are obtained by optimizing the deposition potential and the concentration of the electrolyte. The n‐type material can reach the highest thermoelectric power factor of 812.34 μW m−1 K−2at a deposition potential of 0 V vs Ag/AgCl, and its composition is Bi1.92Te3.08. The highest power factor of 137.18 μW m−1 K−2of the p‐type material is obtained when the ratio of the concentration of SbO+to Bi3+ions in the electrolyte solution is set to 6 with the deposition potential of −0.12 V vs Ag/AgCl. The composition is Bi0.68Sb1.24Te3.08. Then, a principle fan‐shaped RTG (FRTG) with an overall size of 11 mm (height) × 33.8 mm (diameter) is manufactured and tested. The FRTG generates an open‐circuit voltage of 170.21 mV, a maximum output power of 247.55 nW, and a temperature difference of 57.8 K at 1.5 W heat source. Compared with the RTG prepared by mechanical cutting in previous research, the FRTG exhibits a volume that is reduced by 12.45 times and a voltage that is increased by 60.71%.

Exergy analysis of a lunar based solar thermal power system with finite-time thermodynamics

Abstract The exploration of the moon and the construction of the manned lunar outpost are the important parts of the deep space exploration. The continuous supply of thermal energy and power for deep space explorers and scientific equipment is a crucial issue to accomplish manned lunar missions. For most locations on the lunar surface, darkness lasts for periods of about 350 hours, so it is a great challenge for the solar photovoltaic cells and radioisotope thermoelectric generators to launch too much material from Earth. In the mission of manned deep space exploration, it is very necessary to utilize in situ resource effectively and sufficiently to reduce the hardware must be brought from Earth and to meet the requirement of energy and life support system. This paper describes an exergy analysis of a lunar based solar thermal power system using the method of finite-time thermodynamics. The calculations indicate that the system can provide the desired energy for the equipment. The aim of this article is to provide the basis for the design of a solar-powered Stirling engine using thermal energy from the processed lunar regolith.

Small Autonomous kW-Level Power Generation Based on Radioisotope and Renewable Energy Sources for the Arctic Zone and the Far East

In the near future, the demand for autonomous kW-level electric power generating plants in the Arctic zone and in the Far East will number in the tens and hundreds. In the present article, the operational characteristics of radioisotope thermoelectric generators with direct conversion of heat into electricity, which are being decommissioned, are analyzed. Schemes for autonomous electric power plants based on renewable sources of energy and electrochemical cells are proposed as alternatives. The problems arising in the development of such plants are analyzed. The results achieved in meeting concrete orders from operating organizations are discussed. It is concluded that autonomous electric power plants with renewable sources of energy and fuel cells hold promise.

Improving the performance of a screen-printed micro-radioisotope thermoelectric generator through stacking integration

Space microscientific instruments require power supplies that are sustainable, stable, and long life. A micro-radioisotope thermoelectric generator can be used as a sustainable long-life power supply for low-power-device applications. This study innovatively proposes micro stacked-integrated annular-radial radioisotope thermoelectric generator and prepares a multilayer prototype to drive various LEDs as a demo. A high-performance micro-radioisotope thermoelectric generator module based on a flexible printed circuit is designed and prepared by screen printing. At a temperature difference of 48 K, the voltage density is 2.21 V cm−3, and the power density is 514.25 μW cm−3. When loaded with 1.564 W heat sources, a 10-layer prototype generates an open-circuit voltage of 0.815 V, a short-circuit current of 0.551 mA, and an output power of 114.38 μW. The maximum series voltages are 0.929 and 2.2 V for the 10- and 30-layer prototypes. The short-circuit current of the 5-layer parallel prototype is 1.18 mA, and the voltage is hardly reduced. In the impact evaluation on ambient temperature, the electrical output of the prototype increases with increased temperature (−30 °C–120 °C). In the different configurations of the prototype, the 10-layer, 30-layer series, and 5-layer parallel prototypes are proposed, thereby providing considerable output. The developed generator is expected to provide reliable power support for space microscientific instruments.

The Question of Clean-Up of Radioactive Contamination in the Arctic Region

This article considers the most significant sources of large-scale radioactive contamination in the Arctic from the middle of the last century: radioactive fallout from nuclear weapon tests, discharges of waste from the Sellafield (the United Kingdom) and Cap de la Hague (France) radiochemical plants, radioactivity carry-over by the northern rivers of Russia, nuclear Navy operation, radioisotope thermoelectric generators, and submerged and sunken radioactive objects. Their comparative contribution and associated radioecological risks are assessed. Special attention is focused on the analysis of the “nuclear legacy” of the Soviet/Russian nuclear Navy and the search for its solution. The content and results of the implementation of the Strategic Master Plan for the disposal of decommissioned nuclear Navy and radioecological rehabilitation of the service infrastructure, developed as part of broad international cooperation, is described. Attention is drawn to the remaining unsolved environmental problems in the Arctic associated with submerged and sunken objects containing spent nuclear fuel and radioactive waste. Summary data on such objects and the risks of radioecological pollution of aquatic areas, estimated on the basis of simulation of the consequences of possible accidents, are presented.

American Space Nuclear Electric Systems

S: Since the 1960’s the United States of America has launched several space missions using nuclear technology as a mean for propulsion and power supply. The majority of the American nuclear powered spacecrafts were based in radioisotope generators, with the exception of the SNAP-10A (1965), which was the only American reactor ever launched. However, some of the most notorious nuclear reactor based projects developed in the USA in the last four decades were the SPAR/SP-100(an evolution of the Space Power Advanced Reactor program), the Space Prototype (SP-100), the Prometheus, and the Fission Surface Power (FSP). The latter is still in progress and the others were closed before its completion. This paper describes the main details about each one of these projects with the purpose of serving as a review of the technical history for the major realization steps that were conducted in the USA. This manuscript also approaches the contemporary state-of-the-art, with emphasis to the Demonstration Using Flattop Fission (DUFF) experiment and it’s follow-on project, the Kilopower prototype reactor.

Preparation and optimization of miniaturized radioisotope thermoelectric generator based on concentric filament architecture

Given independent and flexible power supply requirements of space apparatus, miniaturized radioisotope thermoelectric generators are currently playing an increasing role in space power systems. This study creatively proposes a miniaturized integrated-design radioisotope thermoelectric generator based on concentric filament architecture and is the first to formulate a practical battery entity. When heat source temperature is 398.15 K, the maximum open-circuit voltage of 418.82 mV and the maximum output power of 150.95 μW are obtained. The COMSOL is used to simulate precisely the thermoelectric conversion process and optimize the structural size of the radioisotope thermoelectric generator. The optimal results are obtained when the ratio of N- to P-type circle radius and the thermoelectric filament's length are 0.1 and 20 mm, respectively. In this case, the battery obtains the maximum output power of 423.50 μW and open-circuit voltage of 605.84 mV when heat source temperature is 398.15 K. When the thermoelectric filament's curvature is 170°, the electrical density value increases more remarkably than that of 0°. Its effective open-circuit voltage density and output power density are 73.79 mV cm−3 and 53.76 μW cm−3, respectively. The optimized miniaturized radioisotope thermoelectric generator is able to provide power support for space microelectronic devices.

Industrial radiotracer application in flow rate measurement and flowmeter calibration using 99mTc and 198Au nanoparticles radioisotope

The flow rate or fluid velocity measurement is important to maintain fluid flow quality performance in the systems. This study focuses on determination of volumetric flow rate measurement and to calibrate the conventional flowmeter using industrial radiotracer approach in quadrilateral gas-liquid bubble column reactor. In this work, two different radioisotopes which emit γ-ray have been chosen as radioactive tracer which is 99mTc produced from 99Mo/99mTc radioisotope generator and 198Au nanoparticle form neutron activation at research nuclear reactor TRIGA Mark II. Both radioisotopes representing liquid and solid tracer purposely designed for tracing liquid flow. The peak to peak radiotracer method known as pulse velocity method was applied to determine the volumetric flow rate. The radiation signals were monitored using 4 unit NaI scintillation detectors located at 4 different points nearby the inlet and outlet of the quadrilateral bubble column reactor process stream. The water volume inside the bubble column reactor was fixed at 0.04 m3 and liquid flow rates in this reactor were specified on installed flowmeter at different reference value which is 4 lpm, 8 lpm, and 12 lpm, respectively. The experimental result shows very good linearity and repeatability by following the theoretical equations with less uncertainty in volumetric flow rate measurement. The obtained results also validated the effectiveness of the proposed method for the installed flowmeter calibration efficiency.

Simultaneous enhancement in thermoelectric performance and mechanical stability of p-type SiGe alloy doped with Boron prepared by mechanical alloying and spark plasma sintering

Silicon-Germanium (SiGe) based alloys are the promising and an attractive thermoelectric candidate for radioisotope thermoelectric generators (RTGs) at high temperature (>1000 °C) application. Intensive efforts are being made to enhance the thermoelectric properties and mechanical stability of p-type SiGe alloy. The current work reports on synthesis of SiGe alloy doped with Boron (B) with varying concentration (0.5–2.0 at.%) through mechanical alloying (MA) followed by spark plasma sintering (SPS). The synthesised SiGe alloy doped with B1.5 at.% showcase the superior figure of merit (ZT) ̴ 0.525 at 800 °C which results in the significant enhancement of ∼9.38% than the p-type RTG SiGe alloy. The synthesised SiGe alloys exhibit an improvised thermoelectric compatibility factor of 0.968 V-1 (∼16% higher than RTG SiGe alloy). The SiGeB1.5 alloy demonstrated an ever-achieved physical robustness with the bench marked micro hardness of 9.93 ± 0.12 GPa and fracture toughness (KIC) of 2.36 ± 0.173 MPa√m (48% higher than SiGe alloy).

Thermoelectric generator electrical performance based on temperature of thermoelectric materials

In space applications, the radioisotope thermoelectric generators are being used for the power generation. The energy storage devices like fuel cells, solar cells cannot function in remote areas, in such cases the power generating systems can work successfully for generating electrical power in space missions. The efficiency of thermo electric generators is around 5% to 8% . Bismuth telluride has high electrical conductivity (1.1 x 105S.m /m2) and very low thermal conductivity (1.20 W/ m.K). A Thermoelectric generator has been built up consisting of a Bi2Te3 based on thermoelectric module. The main aim of this is when four thermoelectric modules are connected in series, the power and efficiency was calculated. The thermoelectric module used is TEP1-1264-1.5. This thermoelectric module is having a size of 40mmx40mm. The hot side maximum temperature was 1600C where the cold side temperature is at 400C. At load resistance, 15Ω the maximum efficiency calculated was 6.80%, at temperature of 1600C. The maximum power at this temperature was 15.01W, the output voltage is 16.5V, and the output current is 0.91A. The related and the corresponding graphs between efficiency, power, output voltage, output current was drawn at different temperatures. The efficiency of bismuth telluride, thermoelectric module is greater than other thermoelectric materials.

99Mo/99mTc generators based on aluminum molybdate gel matrix prepared by nano method

A procedure for preparation of 99Mo/99mTc radioisotope generator based on low specific activity neutron activated 99Mo was developed. Aluminum molybdate(VI)-99Mo of high Mo(VI) content (~ 364 mg/g Al99Mo) was prepared by mixing low specific activity molybdate(VI)-99Mo and aluminum mixture solution with isoamyl alcohol. Al99Mo gel matrix was precipitated when the pH of the mixture solution was raised to ~ 5 by addition of NaOH to the mixture. Radiometric measurements indicate the strong fixation of Molybdate(VI)-99Mo species in the form of the sparingly insoluble Al99Mo gel matrix. The prepared AlMo gel matrix was physiochemically characterized. Al99Mo gel matrix was used as a base material for preparation of 99Mo/99mTc generator. The 99mTc eluted from 99Mo/99mTc radioisotope generator was found to have relatively high elution yield (84 ± 2.3%), radionuclidic (≥ 99.99%), radiochemical (98.1 ± 0.9%) and chemical purity.

99Mo/99mTc radioisotope generator based on adsorption of 99Mo (VI) on cerium (IV) molybdate column matrix

Abstract Based on neutron activated 99Mo, a procedure for preparation of 99Mo/99mTc radioisotope generator was developed. Batch equilibration method was used to investigate the sorption behavior of Mo (VI) (10−4 M) in chloride and nitrate solutions on cerium (IV) molybdate gel matrix using 99Mo radiotracer. The breakthrough sorption capacity of cerium molybdate gel matrix for 99Mo (VI) (3×10−2 M) were found to be 0.54 mmol/g of the sorbent [1 g column (0.6 cm i.d.)]. Elution performance of the generated 99mTc from cerium molybdate-99Mo chromatographic column was investigated as a function of inside diameter of the column, amount of the bed matrix and flow rate of the eluent. Based on the obtained results, 99Mo/99mTc radioisotope generator was prepared based on adsorption of neutron activated 99Mo (VI) of low specific activity onto chromatographic columns packed with 5 g cerium molybdate gel matrix. The radioactivity of 99mTc is periodically eluted with 10 mL 0.9% NaCl solution at a flow rate of 1 mL/min. Elution yield of 78±5% was obtained with high chemical, radionuclidic (99Mo breakthrough 1×10−3±0.3×10−3%) and radiochemical purity (97±2%).

Estimation of lung absorption parameters for oxides of 238Pu

Following inhalation of an aerosol of relatively insoluble particles, it is usually found that the fractional dissolution rate of material retained in the lungs decreases with time, and the amount remaining undissolved can be represented simply by a decreasing exponential function with two or more components. A few exceptions are known, in which the dissolution rate increases with time. The most important in the context of radiological protection is probably that of 238Pu dioxide. Several published comprehensive data sets, from animal studies and accidental human exposures, have been analysed using the Human Respiratory Tract Model (HRTM) of the International Commission on Radiological Protection. The HRTM contains a simplified representation of particle dissolution in the respiratory tract, suitable for routine radiological protection purposes. Still, it was found to have sufficient flexibility to represent the measurement data in most of these cases. Although the 238Pu dioxide showed a wide range of behaviour in the different studies, there was good agreement between the absorption behaviour modelled for two studies involving ‘ceramic’ 238Pu dioxide as used in spacecraft radioisotope thermoelectric generators: a long-term experimental study in dogs and an accidental exposure involving a group of workers.

An Optimal Algorithm for the Formation of Unbiased Estimates of the Effective Noise Temperature of a Stochastic Radio Thermal Signal

The main optimal signal processing operation is shown to be the division of the energy estimates for the random processes observed in the adjacent time intervals. It is justified that this processing may be deemed the primary one and it is necessary to introduce the secondary processing - averaging the unbiased primary estimates of the effective noise temperature. The potential fluctuation sensitivity of the radiometer and the limiting errors of the joint estimates of the noise temperature and the gain instability parameter have been determined.

Screen-printed radial structure micro radioisotope thermoelectric generator

The micro radioisotope thermoelectric generator can be invoked as a long-life power supply in low-power device applications. Improving the current, voltage and power of power sensors by enhancing the properties of thermoelectric material composites matters in low-power device applications. The micro radioisotope thermoelectric generator driven by the temperature difference between radial thermoelectric legs printed on polyimide substrate and the loaded central heat source is reported in this study. The electrical conductivity of n-type Bi2Te2.7Se0.3, p-type Bi0.5Sb1.5Te3, and p-type Sb2Te3 radial thermoelectric legs are 24.57–165.8 S·cm−1, with Seebeck coefficients of −176.6, 223.3 and 139.7 µV·K−1 respectively. Thermoelectric legs are prepared by screen printing with a paste consisting of epoxy resin and BiTe-based powders. The generator has five couples of radial thermoelectric legs, and their material properties are optimized through selecting the preliminary curing temperature. The electrical conductivity of n-type Bi2Te2.7Se0.3, p-type Bi0.5Sb1.5Te3, and p-type Sb2Te3 thermoelectric legs are 24.57–165.8 S·cm−1, with Seebeck coefficients of −176.6, 223.3 and 139.7 µV·K−1 respectively. When loaded with 1.5 W isotope heat sources, the prototype generator would generate an open-circuit voltage of 68.41 mV, a short-circuit current of 329.0 µA, and an output power of 5.81 µW at 39.20 mV. Stacking and series-parallel can harvest considerable energy.

High-performance and integrated design of thermoelectric generator based on concentric filament architecture

A concentric thermoelectric filament structure used for radioisotope thermoelectric generator (RTG) is designed to satisfy low-power and high-voltage demands for aerospace microelectronic devices. The thermoelectric filament is proven to have a better output voltage than the traditional thermoelectric structure by using COMSOL. The unbreakable thermoelectric filament and corresponding devices are prepared by employing a simple and easy brush coating process. A single thermoelectric filament obtains an open-circuit voltage (Voc) of 6.0 mV and a maximum power output (Pmax) of 2.0 μW at 398.15 K hot surface temperature. An array of thermoelectric filaments is fabricated for the radioisotope heat source of planar heat surface, which obtains Voc of 83.5 mV and Pmax of 32.1 μW at the hot surface temperature of 398.15 K, thereby verifying the practicability of the concentric filament structure in devices. Another radial thermoelectric filament device is designed for the cylindrical heat source. This device exports 84.5 mV Voc and 42.5 μW Pmax at the hot surface temperature of 398.15 K. These thermoelectric devices could gain larger electrical performance in small space through further series connection and fabrication, which will be a commendable design scheme for the radioisotope thermoelectric generator.