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Direct charging nuclear batteries (DCNB) have the potential of being widely used to meet the special requirements in the area of aerospace and ocean. The current application of direct charging nuclear batteries is restricted by the low energy conversion efficiency, commonly less than 10%. This low efficiency is limited mainly by issues of low source efficiency and shunt factor among others, such as collection and geometry factors. Based on a numerical simulation and empirical calculations we here propose a design of DCNB by utilization of a sub-micrometer thickness radiation source to increase the source efficiency, both-side emission, and collection of decay particles to improve the collection and geometry factors, as well as impedance matching of batteries and load to improve the shunt factor, among other various optimizations. The energy conversion efficiency of DCNB with this design reaches over 20%. The successful deployment of the current design should vastly improve the energy conversion efficiency of DCNBs, and also establish a theoretical foundation for extending the scope of applications of DCNBs in the future. • A new design for DCNB with sub-micrometer thickness radiation source, both-side emission and collection. • The energy conversion efficiency of DCNB with this design may reaches over 20% in theory. • This work will establish a theoretical foundation for application of DCNBs in the future. [ABSTRACT FROM AUTHOR]

This paper discusses the use of one of the safest isotopes known isotopes, Kr-85, as a candidate fuel source for deep space missions. This isotope comes from 0.286% of fission events. There is a vast quantity of Kr-85 stored in spent fuel and it is continually being produced by nuclear reactors. In using Kr-85 with a novel Dual Cycle Conversion System (DCCS) it is feasible to boost the system efficiency from 26% to 45% over a single cycle device while only increasing the system mass by less than 1%. The Kr-85 isotope is the ideal fuel for a Photon Intermediate Direct Energy Conversion (PIDEC) system. PIDEC is an excellent choice for the top cycle in a DCCS. In the top cycle, ionization and excitation of the Kr-85:Cl gas mixture (99% Kr and 1% Cl) from beta particles creates KrCl* excimer photons which are efficiently absorbed by diamond photovoltaic cells on the walls of the pressure vessels. The benefit of using the DCCS is that Kr-85 is capable of operating at high temperatures in the primary cycle and the residual heat can then be converted into electrical power in the bottom cycle which uses a Stirling Engine. The design of the DCCS begins with a spherical pressure vessel of radius 13.7 cm with 3.7 cm thick walls and is filled with a Kr-85:Cl gas mixture. The inner wall has diamond photovoltaic cells attached to it and there is a sapphire window between the diamond photovoltaic cells and the Kr-85:Cl gas mixture which shields the photovoltaic cells from beta particles. The DCCS without a gamma ray shield has specific power of 6.49 W/kg. A removable 6 cm thick tungsten shield is used to safely limit the radiation exposure levels of personnel. A shadow shield remains in the payload to protect the radiation sensitive components in the flight package. The estimated specific power of the unoptimized system design in this paper is about 2.33 W/kg. The specific power of an optimized system should be higher. The Kr-85 isotope is relatively safe because it will disperse quickly in case of an accident and if it enters the lungs there is no significant biological half-life. [ABSTRACT FROM AUTHOR]

Radiation damage is a significant concern with both alphavoltaic and betavoltaic cells because their performance degrades, especially with high-energy - (>200 keV) beta and alpha particles. Indirect excitation methods, such as the Photon Intermediate Direct Energy Conversion (PIDEC) framework, can protect the transducer from radiation. A nuclear battery using a 90 Sr beta source was constructed by the author's research group, which demonstrated the radiation resistance of a PIDEC cell driven by beta particles (PIDECβ cell). Use of alpha sources to drive nuclear batteries would appear to be much more attractive than beta sources due to higher potential power density. However, they are also subject to higher rates of radiation damage. This paper describes the successful incorporation of alpha particles into the PIDEC framework using the alpha emitter 210 Po to form a PIDECα cell. The PIDECα cell transducer was exposed to alpha particles for over one year without experiencing adverse effects from radiation damage. [ABSTRACT FROM AUTHOR]

Nuclear batteries based on silicon carbide betavoltaic cells have been studied extensively in the literature. This paper describes an analysis of design parameters, which can be applied to a variety of materials, but is specific to silicon carbide. In order to optimize the interface between a beta source and silicon carbide p-n junction, it is important to account for the specific isotope, angular distribution of the beta particles from the source, the energy distribution of the source as well as the geometrical aspects of the interface between the source and the transducer. In this work, both the angular distribution and energy distribution of the beta particles are modeled using a thin planar beta source (e.g., H-3, Ni-63, S-35, Pm-147, Sr-90, and Y-90) with GEANT4. Previous studies of betavoltaics with various source isotopes have shown that Monte Carlo based codes such as MCNPX, GEANT4 and Penelope generate similar results. GEANT4 is chosen because it has important strengths for the treatment of electron energies below one keV and it is widely available. The model demonstrates the effects of angular distribution, the maximum energy of the beta particle and energy distribution of the beta source on the betavoltaic and it is useful in determining the spatial profile of the power deposition in the cell. [ABSTRACT FROM AUTHOR]

• We propose the safety assessment of a transportable, plug-and-play, heat-pipe-cooled microreactor. • We make use of an advanced safety framework that embeds STPA, modeling and simulation, and GTST-MLD. • The work provides qualitative, quantitate, and dynamic risk insights. • The safety framework makes use of the RELAP code. • We identify previously unknown threats and hazards relevant to the novel microreactor design. A safety analysis of a transportable, plug-and-play, heat-pipe-cooled microreactor – or Nuclear Battery (NB)– designed at MIT is presented. The considered design is a semi-autonomous 5 MW (thermal) high-temperature heat-pipe-cooled, yttrium-hydride moderated NB envisioned to be a transportable, flexible, affordable, and distributed low-carbon energy source. The analysis makes use of a recently proposed methodology that integrates i) System-Theoretic Accident Model and Processes (STAMP) to guide a qualitative exploration of the NB threats and hazards, ii) Modeling and Simulation (M&S) to investigate the NB dynamic behavior during accident scenarios, and iii) Goal-Tree Success-Tree Master Logic Diagram (GTST-MLD) to assess risk quantitatively. The methodology has been shown to provide systematic risk insights without the need to rely on prior operating experience, and enables a dynamic evaluation of the risk profile. Moreover, it identifies unknown threats and hazards relevant to the novel microreactor design and explores the related accident scenarios. The key findings of the safety analysis performed on the nuclear microreactor considered are the identification of vulnerabilities related to the use of yttrium hydride as the moderator, the assessment of threats and accident scenarios associated with the loss of sodium from the heat pipes, and, for such scenarios, the quantification of the grace time, i.e., the period during which human operators can intervene to avoid unacceptable consequences. [ABSTRACT FROM AUTHOR]

• We propose a novel methodology for dynamic risk assessment. • The methodology integrates STAMP, modeling and simulation, and GTST-MLD. • The methodology provides qualitative, quantitate, and dynamic risk insights. • The methodology makes use of RELAP code. • The methodology is validated considering the safety assessment of a micro-reactor. Accidents may occur as a result of complex dynamic processes in interconnected socio-technical systems. Such accidents cannot be explained solely in terms of static chains of failures. Therefore, the traditional Probabilistic Risk Assessment (PRA) framework, which stands on the consideration that accidents are caused by direct failures or chains of events, is not apt to describe the dynamic behavior of the relevant Systems, Structures and Components (SSCs) and assess the risk. This work proposes a novel framework that embeds (i) System-Theoretic Accident Model and Processes (STAMP) principles to guide a qualitative exploration of the SSC threats and hazards, (ii) Modeling and Simulation (M&S) to investigate the SSC dynamic behavior during accidental scenarios, and (iii) the Goal-Tree Success-Tree Master Logic Diagram (GTST-MLD) framework to assess risk quantitatively. The integration of STAMP, M&S and GTST-MLD allows a systematic analysis to provide risk insights, with due account to the SSC dependencies and interactions, and enables a dynamic assessment of the risk profile. The effectiveness of the proposed framework is shown by means of its application to the safety assessment of Nuclear Batteries (NBs), a unique class of nuclear micro-reactors which is gaining attention as a transportable, flexible, affordable, and distributed low-carbon power source. [ABSTRACT FROM AUTHOR]

A radioluminescent nuclear battery was fabricated and the performance was measured and calculated at temperature of 223.15–323.15 K. Experimental and theoretical results indicate that J sc minimally decreases with the increase in temperature, whereas V oc linearly decreases. P max rapidly decreases with temperature. The mechanism of temperature effect is discussed using the temperature dependency of semiconductor parameters. This study significantly guides the selection of batteries' power source under various temperature. The nuclear battery may also be used as a long-life temperature transducer. [ABSTRACT FROM AUTHOR]

Based on the theory of ADS (Accelerator Driven Subcritical reactor), a new type of nuclear battery was investigated, which was composed of a subcritical fission module and an isotope neutron source, called NBDEx (Nuclear Battery Driven by External neutron source). According to the structure of GPHS-RTG (General Purpose Heat Source Radioisotope Thermoelectric Generator), the fuel cell model and fuel assembly model of NBDEx were set up, and then their performances were analyzed with MCNP code. From these results, it was found that the power and power density of NBDEx were almost six times higher than the RTG's. For fully demonstrating the advantage of NBDEx, the analysis of its impact factors was performed with MCNP code, and its lifetime was also calculated using the Origen code. These results verified that NBDEx was more suitable for the space missions than RTG. [ABSTRACT FROM AUTHOR]

Abstract: Gallium Nitride (GaN) Schottky betavoltaic nuclear batteries (GNBB) are demonstrated in our work for the first time. GaN films are grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD), and then GaN Schottky diodes are fabricated by normal micro-fabrication process. Nickel with mass number of 63 (63Ni), which emits β particles, is loaded on the GaN Schottky diodes to achieve GNBB. X-ray diffraction (XRD) and photoluminescence (PL) are carried out to investigate the crystal quality for the GaN films as grown. Current–voltage (I–V) characteristics shows that the GaN Schottky diodes are not jet broken down at −200V due to consummate fabrication processes, and the open circuit voltage of the GNBB is 0.1V and the short circuit current density is 1.2nAcm−2. The limited performance of the GNBB is due to thin effective energy deposition layer, which is only 206nm to absorb very small partial energy of the β particles because of the relatively high dislocation density and carrier concentration. However, the conversion efficiency of 0.32% and charge collection efficiency (CCE) of 29% for the GNBB have been obtained. Therefore, the output power of the GNBB are expected to greatly increase with growing high quality thick GaN films. [ABSTRACT FROM AUTHOR]

Abstract: A micro-battery powered by tritium is being developed to utilize tritium produced from the Wolsong Tritium Removal Facility. The 3D p–n junction device has been designed and fabricated for energy conversion. Titanium tritide is adopted to increase tritium density and safety. Sub micron films or nano-powders of titanium tritide is applied on silicon semiconductor device to reduce the self absorption of beta rays. Until now protium has been used instead of tritium for safety. Hydrogen was absorbed up to atomic ratio of ∼1.3 and ∼1.7 in titanium powders and films, respectively. [Copyright &y& Elsevier]

Abstract: Beta particle surface fluxes for tritium, Ni-63, Pm-147, and Sr-90 sources were calculated in this work. High current density was experimentally achieved from Pm-147 oxide in silica–titana glass. A 96GBq (2.6Ci) Pm-147 4π-source with flux efficiency greater than 50% was used for constructing a direct charge capacitor with a polyimide coated collector and vacuum as electrical insulation. The capacitor connected to high resistance (TΩ) loads produced up to 35kV. Overall conversion efficiency was over 10% (on optimal load). [Copyright &y& Elsevier]

Abstract: A number of approaches were explored for improving characteristics of the encapsulated nuclear heat source (ENHS) reactor and its fuel cycle, including: increasing the ENHS module power, power density and the specific power, making the core design insensitive to the actinides composition variation with number of fuel recycling and reducing the positive void coefficient of reactivity. Design innovations examined for power increase include intermediate heat exchanger (IHX) design optimization, riser diameter optimization, introducing a flow partition inside the riser, increasing the cooling time of the LWR discharged TRU, increasing the minor actinides'' concentration in the loaded fuel and split-enrichment for power flattening. Another design innovation described utilizes a unique synergism between the use of MA and the design of reduced power ENHS cores. Also described is a radically different ENHS reactor concept that has a solid core from which heat pipes transport the fission power to a coolant circulating around the reflector. Promising features of this design concept include enhanced decay heat removal capability; no positive void reactivity coefficient; no direct contact between the fuel clad and the coolant; a core that is more robust for transportation; higher coolant temperature potentially offering higher energy conversion efficiency and hydrogen production capability. [Copyright &y& Elsevier]

A nuclear battery based on the direct energy conversion of the fission products is presented. Such energy conversion is possible by using a nuclear reactor with ultra-thin fuel elements of 0.2 μm of 242mAm. The amount of nuclear fuel is 376 g and the dimensions of the battery are 2.4×2.4×2.4 m3 (including the vacuum spacing), with a BeO moderator and Be electrodes. The total power of the reactor is 10.6 MW and the electrical power is 0.652 MW. [Copyright &y& Elsevier]

This work provides further step in considering artificial diamond crystals doped with beta-emitter 14C as chemically durable and environmentally friendly material to be applied as a core of nuclear electric photo-voltaic batteries. In order to investigate features of diamond radioluminescence the metallic radioactive technetium 99Tc and electron beam treatment have been used as external sources of beta-radiation simulating diamond self-glowing from admixture of 14C. Three types of commercially produced artificial diamonds have been applied: Ib, IIa and IIb. Intensive radioluminescence and cathodoluminescence have been observed for two diamond types: IIa and IIb, which can be suggested for further doping by 14C. It had been demonstrated that simulation of diamond self-glowing from 14C using 99Tc and electron beam were insufficiently different due to technical aspects of the experiment, not the difference in the excitation energy. Cathodoluminescence technique can be used in the future for the study of diamonds when optimizing it spectral properties. [Display omitted] • Artificial diamonds of different types were synthesized using HPHT technique. • Optical and luminescent properties of diamonds were studied. • Cathodoluminescence and radioluminescence spectra of diamonds were compared. • Artificial diamonds are considered to be used in electric photo-voltaic batteries. [ABSTRACT FROM AUTHOR]

• The effect of various factors on the battery efficiency is investigated by MCNPX code. • The beta spectrum of 35S is calculated. • The Total diameter of the optimized betavoltaic battery is approximately 594 µm. • The energy conversion efficiency of this battery is about 2.513%. • It's useful for biomedical devices, sensors and wireless communication systems. In the present work, the radioactive solution of 0.10 Molar 35S-aqua regia with half-life of 86.35 ± 0.17 days and specific activity of 519 Ci/cm3 was considered as a source. First, the beta spectrum of 35S was calculated. Then, by MCNPX code the effects of factors such as radius variation, height variation, type of substrate and type of side surface coating on the source efficiency were investigated. Also, by discussing the effect of minority carrier diffusion length, junction depth, geometric shape of P-N junction and doping concentration on the property of betavoltaic batteries, the present work concluded that the best parameters for betavoltaic batteries are the use of silicon and the radioactive solution of 0.10 Molar 35S-aqua regia, thickness of the titanium coating around the radioactive solution of 0.1 µm and junction depth of 0.2 µm, spherical P-N junction, N d (doping concentration of N-type region) = 1.000 × 1017 cm−3 and N a (doping concentration of P-type region) = 4.500 × 1016 cm−3. Under these parameters the short circuit current, open circuit voltage and energy conversion efficiency are 0.926nA, 0.233 V and 2.513%, respectively. Also, the amounts of the short circuit current, open circuit voltage, and energy conversion efficiency were calculated for the titanium coating with thicknesses 0.5, 1, 2, and 10 µm. It is not easy to build the titanium coating with a thickness of 0.1 µm. So, in the manufacturing process, the titanium coating with a thickness 10 µm can be used. Since the relationship between battery parameters and activity is linear. To offset the amounts of the short circuit current, open circuit voltage and energy conversion efficiency, the activity needs to be increased about 6.521 times. [ABSTRACT FROM AUTHOR]