Radioisotope Heat Source Research Articles

Feasibility study on radioisotope-powered thermophotovoltaic/thermoelectric hybrid power generation system used in deep-sea: From design to experiment

This study aims to comprehensively examine the feasibility of a hybrid power generation system that integrates solar and thermoelectric technologies, with a focus on utilizing a radioisotope heat source (RHU) for deep-sea applications. The investigation encompasses the whole design process as well as rigorous testing procedures. The self-designed coupling device establishes a connection between the silicon photovoltaic (PV) cell and the bismuth telluride (Bi2Te3) thermoelectric modules (TEMs), therefore creating a photovoltaic-thermoelectric (PV-TE) hybrid system. The measuring platform incorporates the system to investigate the influence of varying light intensity (ranging from 400 to 1600 W/m2) on the electrical properties of the system, specifically focusing on three subgroups of PV cell temperature (20 °C, 25 °C, and 30 °C). The findings suggest that the enhanced performance of the photovoltaic (PV) cell and thermoelectric modules (TEMs) under identical PV cell temperatures may lead to an improvement in the electrical performance of the system due to variations in light intensity. Nevertheless, when the temperature of the photovoltaic (PV) cell increases, there is a gradual decline in the growth rate of the output power. The subsequent research provide evidence that there exist discrete mechanisms responsible for the reduction in intensity between thermoelectric modules (TEMs) and photovoltaic (PV) cells. The processes arise due to the impact of thermal effect on the photovoltaic materials and the increased temperature difference between hot and cold junctions of the thermoelectric modules (TEMs), respectively. Furthermore, a control group is incorporated by calculating the performance of the hybrid system under the same operating conditions as the single thermoelectric (S-TE) system. According to a comparative analysis comparing the Radioisotope Thermal-Photovoltaic-Thermoelectric (RTPV-TE) hybrid power production systems and the S-TE system, it has been shown that the former exhibits a potential increase in output power of up to 271% while operating under identical conditions. This work offers insights and methodologies for the design and measurement of RTPV-TE hybrid power generating systems in engineering application situations.

Modified Stirling cycle thermodynamic model IPD-MSM and its application

A Stirling cycle is a thermoelectric conversion method with high efficiency and reliability. The Stirling cycle applies to small- and medium-sized power space nuclear reactors or radioisotope heat sources. A high-precision and well-predicted Stirling cycle thermodynamic model is the key to optimizing and improving the Stirling engine for space. The present study modified the classical Simple model by incorporating the local pressure loss into the pressure loss. An improved second-order adiabatic model based on the Simple model, namely the Incorporated Pressure Drop-modified Simple Model (IPD-MSM), was proposed. The prediction of the IPD-MSM shows well with the changing tendency of the GPU-3 Stirling engine experimental data. Moreover, this model has better prediction accuracy at high-pressure and high-frequency conditions than other adiabatic models, such as CAFS and ISAM. The thermodynamic properties of He, H2, and Helium-Xenon mixtures in the Stirling cycle were also analyzed. Results show that the He-Xe mixture reaches the highest output power and thermal efficiency when the mole percentage of Xe is approximately 2%. The mechanism is as follows: the addition of Xe leading to the reduction in non-ideal heat transfer loss exceeds the increase in pressure loss. The addition of Xe leads the pressure loss to increase abruptly as the mole percentage of Xe exceeds 2%. The characteristics and application analysis of H2, He, and He-Xe mixture were discussed. The present study provided theoretical support for the Stirling cycle analysis for space missions and the selection of working fluids.

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.

High-temperature and radiation-resistant spinel-type ferrite coating for thermo-optical conversion in radioisotope thermophotovoltaic generators

High-temperature radioisotope heat source surface coated with excellent performance of thermo-optical conversion coating can greatly improve thermophotovoltaic energy utilization. However, long-term high-temperature and radiation resistance of the thermo-optical conversion pose a great challenge. In this work, spinel-type ferrite thermo-optical conversion coating was proposed to improve the heat and irradiation stability and output power of a radioisotope thermophotovoltaic (RTPV) prototype. Under the continuous irradiation of 32.64 kGy for 24 h at 1400 K, the emissivity of the spinel-type ferrite thermo-optical conversion coating could maintain more than 90%. In addition, the surface morphology of the coating was changed under high temperature, which enhanced its surface emissivity. Spinel-type ferrite thermo-optical conversion coating was applied to the RTPV prototype, which achieved a maximum output power of 144.23 mW. Compared with the RTPV prototype without coating, the overall output increased to 181.51%. Spinel-type ferrite thermo-optical conversion coating showed great application potential in the fields of thermo-optical conversion and high-efficiency utilization of thermal energy.

Space Nuclear Power and Propulsion at USNC-Tech

USNC-Technologies (USNC-Tech) is an advanced nuclear company focused on developing space nuclear power and propulsion systems to enable high-impact science missions and the growth of a self-sustaining in-space economy. As a subsidiary of Ultra Safe Nuclear Corporation (USNC), USNC-Tech has leveraged the technologies and experience gains from the design, licensing, and deployment of terrestrial gas-cooled reactors for these space systems. The result is a family of reactor concepts and designs with shared technology bases able to meet near-term and long-term customer needs in the space arena. Key examples include the Pylon surface fission power reactor, the Ready 2 Demonstrate Technology On Orbit (R2DTOO) nuclear thermal propulsion reactor, and the chargeable atomic battery radioisotope heat source.

A Concept Study on Advanced Radioisotope Solid Solutions and Mixed-Oxide Fuel Forms for Future Space Nuclear Power Systems

Radioisotope power systems (RPSs) have transformed our ability to explore the solar system. RPSs have been in existence for almost seven decades. Most missions have utilized 238Pu as the radioisotope of choice to generate electrical power and to produce heat for the operation and thermal management of spacecraft systems. In Europe, for the past decade 241Am has been selected for RPS research programs. This paper hypothesizes that the inclusion of small quantities of relatively short-lived radioisotopes such as 232U and 244Cm, particularly when dealing with long-lived radioisotope 241Am, could have beneficial implications for future RPS designs. This paper focuses on the thermal output implications and impact on system-level design. The authors recognize that the selection of any new or modified radioisotope heat source material will require extensive research on fuel form stability, the radiological impact, cost of production, containment, and launch safety considerations.

Radioisotope Heat Sources and Power Systems Enabling Ocean Worlds Subsurface and Ocean Access Missions

Radioisotope Heat Sources and Power Systems Enabling Ocean Worlds Subsurface and Ocean Access Missions

Microsphere Plutonium-238 Oxide Fuel to Revolutionize New Radioisotope Power Systems and Heat Sources for Planetary Exploration

Microsphere Plutonium-238 Oxide Fuel to Revolutionize New Radioisotope Power Systems and Heat Sources for Planetary Exploration

Development of a Novel Miniature Power Converter for Low-Power Radioisotope Heat Sources: Numerical and Experimental Results

Creare is developing a miniature, low-power, free-piston energy conversion system. Our converter is designed to transform thermal energy from radioisotope heater units into on-demand electricity essential to space exploration probes, unmanned surface rovers, small landers, small satellites, and similar small-scale systems operating in darkness. We have achieved a simple system design with a single moving part that requires no recuperator and no regenerators or valves. Our converter technology promises a high-efficiency system in an extremely compact enclosure. This work describes preliminary design, analysis, and testing efforts for our miniaturized converter. We fabricated a laboratory-scale prototype and acquired experimental data at prototypical temperatures to validate our performance models. Our numerical model was able to accurately predict converter losses. In doing so, we also demonstrated the feasibility of our novel thermodynamic cycle through the generation of net positive pressure-volume work of the system at its design temperature (~873 K). These results have been used to guide subsequent converter design modifications. Future work includes the fabrication, testing, and detailed performance assessment of a complete prototype converter.

High-Temperature and Radiation-Resistant Spinel-Type Ferrite Coating for Thermo-Optical Conversion in Radioisotope Thermophotovoltaic Generators

High-temperature radioisotope heat source surface coated with excellent performance of thermo-optical conversion coating can greatly improve thermophotovoltaic energy utilization. However, long-term high-temperature and radiation resistance of the thermo-optical conversion pose a great challenge. In this work, spinel-type ferrite thermo-optical conversion coating was proposed to improve the heat and irradiation stability and output power of a radioisotope thermophotovoltaic (RTPV) prototype. Under the continuous irradiation of 32.64 kGy for 24 h at 1400 K, the emissivity of the spinel-type ferrite thermo-optical conversion coating could maintain more than 90%. In addition, the surface morphology of the coating was changed under high temperature, which enhanced its surface emissivity. Spinel-type ferrite thermo-optical conversion coating was applied to the RTPV prototype, which achieved a maximum output power of 144.23 mW. Compared with the RTPV prototype without coating, the overall output increased to 181.51%. Spinel-type ferrite thermo-optical conversion coating showed great application potential in the fields of thermo-optical conversion and high-efficiency utilization of thermal energy.

Features of Lunar Rover Design Considering Radiation Effects from Outer Space and Onboard Radioisotope Heat Sources

The dose effect on the onboard equipment of the lunar rover from ionizing radiation from outer space and from radioisotope sources intended for providing the thermal regime of the spacecraft in a lunar night are considered. Calculations are made to determine the requirements for radiation hardness of devices and their components, as well as the possibility of using the instrumentation reserve developed for the current Moon research projects in a prospective mission with a lunar rover.

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.

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.

An approach to design a 90Sr radioisotope thermoelectric generator using analytical and Monte Carlo methods with ANSYS, COMSOL, and MCNP

In this study, a 90Sr radioisotope thermoelectric generator (RTG) with power of milliWatt was designed to operate in the determined temperature (300–312K). For this purpose, the combination of analytical and Monte Carlo methods with ANSYS and COMSOL software as well as the MCNP code was used. This designed RTG contains 90Sr as a radioisotope heat source (RHS) and 127 coupled thermoelectric modules (TEMs) based on bismuth telluride. Kapton (2.45mm in thickness) and Cryotherm sheets (0.78mm in thickness) were selected as the thermal insulators of the RHS, as well as a stainless steel container was used as a generator chamber. The initial design of the RHS geometry was performed according to the amount of radioactive material (strontium titanate) as well as the heat transfer calculations and mechanical strength considerations. According to the Monte Carlo simulation performed by the MCNP code, approximately 0.35 kCi of 90Sr is sufficient to generate heat power in the RHS. To determine the optimal design of the RTG, the distribution of temperature as well as the dissipated heat and input power to the module were calculated in different parts of the generator using the ANSYS software. Output voltage according to temperature distribution on TEM was calculated using COMSOL. Optimization of the dimension of the RHS and heat insulator was performed to adapt the average temperature of the hot plate of TEM to the determined hot temperature value. This designed RTG generates 8mW in power with an efficiency of 1%. This proposed approach of combination method can be used for the precise design of various types of RTGs.

Simulation of a thermoelectric generator with radioisotope heat source as a long-lived energy source

Simulation of a thermoelectric generator with radioisotope heat source as a long-lived energy source

Self-induced electrostatic-boosted radioisotope heat sources

In this paper the possibility of stimulated self-induced electrostatic fields in radioisotope heat sources for power enhancement is discussed. Because electrons have higher mobility than the positively charged fragments from radioactive decay, a build-up of positive charges can be promoted, leading to an internal induced electrostatic field. This, in turn, results in a repulsive force acting on positive charges, endowing them with additional kinetic energy, and heat release after these charged particles are stopped by inelastic collisions with the boundary wall. Utilizing a simplified geometrical model, an analytical expression for the attainable power enhancement is derived. It is shown that the proposed concept could result in power enhancements of 5–10% for beta sources but enhancements are negligible for alpha sources.

Development of Kabila rocket: A radioisotope heated thermionic plasma rocket engine

A new type of plasma rocket engine, the Kabila rocket, using a radioisotope heated thermionic heating chamber instead of a conventional combustion chamber or catalyst bed is introduced and it achieves specific impulses similar to the ones of conventional solid and bipropellant rockets. Curium-244 is chosen as a radioisotope heat source and a thermal reductive layer is also used to obtain precise thermionic emissions. The self-sufficiency principle is applied by simultaneously heating up the emitting material with the radioisotope decay heat and by powering the different valves of the plasma rocket engine with the same radioisotope decay heat using a radioisotope thermoelectric generator. This rocket engine is then benchmarked against a 1N hydrazine thruster configuration operated on one of the Pleiades-HR-1 constellation spacecraft. A maximal specific impulse and power saving of respectively 529s and 32% are achieved with helium as propellant. Its advantages are its power saving capability, high specific impulses and simultaneous ease of storage and restart. It can however be extremely voluminous and potentially hazardous. The Kabila rocket is found to bring great benefits to the existing spacecraft and further research should optimize its geometric characteristics and investigate the physical principals of its operation.

Development of a Radioisotope Heated Hollow Cathode

A new type of hollow cathode using a radioisotope heat source instead of a conventional sheathed heater was introduced and it achieved thermionic emission performances similar to the ones of conventional hollow cathodes. Strontium-90, Plutonium-238 and Curium-244 were chosen as radioisotope heat sources and a thermal reductive layer was also used to obtain precise thermionic emissions. A new system design methodology called the Self-Sufficiency Principle was introduced and was applied by powering the keeper electrode with the radioisotope decay heat using a radioisotope thermoelectric generator (RTG). The heater supply of the hollow cathode power configuration was replaced with a RTG supply and the mode of operation of the device was modified because radioisotope heat sources cannot be switched off. This hollow cathode was then benchmarked against two ion thruster configurations and a maximal overall power saving of 3% was achieved. Its advantages are its power saving capability and scalability but it can however be voluminous, heavy and potentially hazardous. Further research in this field ought to explore the range of applications of this new power-free electron emission technology.

Titanium tritide radioisotope heat source development: Palladium-coated titanium hydriding kinetics and tritium loading tests

For applications requiring 5–20mW electrical power for 10–20years, tritium-based radioisotope thermoelectric generators may be an alternative to Pu-238 based devices. Tritium can be stored compactly on a titanium bed. However, one of the main challenges then becomes loading the heat source at temperatures compatible with existing bismuth telluride thermoelectric module technology (<300°C). We find that a 180nm palladium coating enables titanium to be loaded with hydrogen isotopes without the typical 400–500°C vacuum activation step. Further, we observe that the hydriding kinetics of Pd coated and vacuum activated Ti are similar; both of which can be described by the Mintz–Bloch adherent film model, where the rate of hydrogen absorption is controlled by diffusion through an adherent metal-hydride layer. Finally, we design a prototype heat source vessel and demonstrate that it can be loaded completely, at temperatures below 300°C, in less than 10h.

A Mars hopping vehicle propelled by a radioisotope thermal rocket: thermofluid design and materials selection

Rocket-propelled vehicles capable of travelling a kilometre or more in a ballistic ‘hop’ with propellants acquired from the Martian atmosphere offer the potential for increased mobility and planetary science return compared with conventional rovers. In concept, a radioisotope heat source heats a core or ‘thermal capacitor’, which in turn heats propellant exhausted through a rocket nozzle to provide thrust. A systematic study of the thermodynamics, heat transfer and selection of core materials for a Mars hopper was undertaken. The aim was to advance the motor design and assess technical risks and feasibility. Analytical and numerical motor models were developed; the former to generate thermodynamic performance limits, an ideal hop distance and plot a materials selection chart using simple explicit relations. The numerical model assessed the effect of core configuration and geometry. A hop coefficientChopis shown to characterize the effect of core geometry independently of core material and temperature. The target hop distance of 1 km is shown to be robust. A moderate advantage to pebble-bed cores over a core consisting of straight channels was suggested. High-performance engineering ceramics such as boron carbide offer the longest hop providing the core temperature can be increased significantly above 1200 K.