HEAT-ELECTRICITY CONVERTION SYSTEMS FOR A BRAZILIAN …

2013 International Nuclear Atlantic Conference - INAC 2013 Recife, PE, Brazil, November 24-29, 2013 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-05-2

HEAT-ELECTRICITY CONVERTION SYSTEMS FOR A BRAZILIAN SPACE MICRO NUCLEAR REACTOR

Lamartine N.F.Guimarães1*,2, Natália B. Marcelino1*, Guilherme M. Placco1*, Jamil A.

Nascimento1, Eduardo M. Borges1 and Ary Garcia Barrios Jr.2

1 Instituto de Estudos Avançados - IEAv

Trevo Coronel Aviador José Alberto Albano do Amarante, no 1 12228-001 Putim, São José dos Campos, SP Fone: (12) 3947-5474 - Fax (12) 3944-1177

[email protected] [email protected]



1* Instituto de Estudos Avançados - IEAv

PG-CTE Trevo Coronel Aviador José Alberto Albano do Amarante, no 1

12228-001 Putim, São José dos Campos, SP [email protected]

[email protected]

2Faculdade de Tecnologia São Francisco - FATESF Av. Siqueira Campos, 1174

12307-000 Jacareí, SP [email protected]

ABSTRACT This contribution will discuss the evolution work in the development of thermal cycles to allow the development of heat-electricity conversion for the Brazilian space micro nuclear Reactor. Namely, innovative core and nuclear fuel elements, Brayton cycle, Stirling engine, heat pipes, passive multi-fluid turbine, etc... This work is basically to set up the experimental labs that will allow the specification and design of the space equipment. Also, some discussion of the cost so far, and possible other applications will be presented.

1. INTRODUCTION This paper presents an overview of the TERRA project [1, 2] being developed at the Institute for Advanced Studies – IEAv (“Instituto de Estudos Avançados”). The TERRA name is an acronym for advanced fast reactor technology in Portuguese. The central idea for the TERRA project [3, 4] is to investigate the most relevant technologies to allow the development of the concept and further building, of an electric generating nuclear power plant for space applications, suited for the Brazilian future deep space ambitions. As can be seen from this description there is no specific mission as yet. So, the nowadays interests were divided in a

INAC 2013, Recife, PE, Brazil.

three way investigation: an advanced nuclear reactor concept, a sound heat-electric conversion system(s) and, surely, a heat rejection system. For the nuclear reactor concept all the work is being realized as a very sophisticated computer design [5, 6] exploring combinations of new materials, geometric layouts and novel ideas as will be described in more detail in section 2. The computer design approach was chosen to allow for the understanding of what it is truly needed. It is also hoped for a lot of good criticism from pears. And to define of a clear development path, which will increase safety when dealing with nuclear material experimentally. As for the heat-electric conversion system a more experimental approach was chosen. It was verified [7] a great interest in closed Brayton cycles for this purpose, when power is in the range of a few tenths of kW up to tenths of MW. The work that has been produced [3, 4] in this area will be discussed in section 3. Fact is that below tenths of kW [8, 9, 10] in power, another cycle appears to be of interest and even in the lower part of the previous range. This cycle is the Stirling cycle, the work performed on the Stirlings will be presented in section 4. A new piece of technology called passive multi fluid turbine [11, 12] was found interesting to increase power in space power cycles with little pressure drop add. This will be talked in section 5. Finally, in section 6 a brief account of the heat pipe development will be presented. All the handling of these technologies is starting to point to a solid way for the future developments of the TERRA project. The work done so far is providing a view for continuing development.

2. SPACE NUCLEAR REACTOR CONCEPT This section will provide a brief description of the fuel elements and core arrangement. One has to keep in mind that this subject is still a matter of discussion and constructive criticisms do apply. To start the definition of the core concept a design philosophy [6] was imposed at the beginning. This philosophy requires of the reactor: 1- portability, to be used in different environments, 2- flexibility to be used in electricity and heat generation, 3- transportability, the micro-reactor platform must be able to be transported to the target environment, 4- safety, fail-safe, passive shutdown and robustness, 5- longevity, long-life without maintenance, and 6- extrapolation, adherence to the GEN-IV requirements for terrestrial applications (modular core, simple replacement). With that philosophy a set of minimal technical requirements [5] were also defined, such as: 1- power around 1,000 kWth, 2- target output core temperature of about 1,000 oC, 3- long life, about 5-10 years, and 4- advance fuel and structural materials (UN, Mo-Re, Ta-Re, Pb, Li). The design presented in Fig. 1 is an example of the fuel packing. It is important to emphasize that the fuel spheres are made of uranium nitrate and for the actual calculation enrichment an excess of 90% was assumed. This sphere packing is composed of at least three different diameters. This packing is set inside hexagonal canister shown in Fig. 2. It is important to understand that the pin representation actually shown in Fig. 2, are not pin fuel elements. In reality, they are heat pipes, which are the thermal conductor for extracting heat from inside the canisters. Those heat pipes will interface with the heat-electric convertor, in this case assumed a closed Brayton cycle. The canisters are made of molybdenum-rhenium alloy. Also, lead is used inside the canisters, among the fuel spheres as a sort gluing element. Actually, in a broader sense the reactor fuel element may be considered the Hexagonal Fuel Canister – HFC. Some of the dimensions HFC are 12.5 cm (flat-to-flat) and an active height of 35 cm. In principle, only one canister could be used as


critical unity. That fact satisfies flexibility. The arrangement shown in Fig. 2 is supposed to generate the 1,000 kWth. It is also important to mention that the reactivity control and safety is performed by 12 rotating drums coated with B4C and neutron reflector materials, such as BeO. This form of control is inspired in several other designs presented in the literature. Also, given that the reactor core computer design is done independently from the studies of the closed Brayton cycle, the thermal powers will not match, at this moment. That is natural and expected in a project such as that. The matching will be performed in a latter phase, and the differences in thermal power are manageable. Finally, all these calculations that allow the production of these preliminary results were performed in the “Laboratório Computacional de Tecnologia Nuclear”, which has the proper software and hardware tools for this work.

Figure 1: Spheres of UN of at least three different diameters in a random packing arrangement.

Figure 2: Fuel canister containing the spherical fuel elements.

3. CLOSED BRAYTON CYCLE AS A HEAT-ELECTRIC CONVERSION SYSTEM The closed Brayton cycle was the first conceptual idea to really gain a very detailed design. Unfortunately, it is proving to be the hardest to be built. In Fig. 3 one can see the heat source of 300 kWth furnace. That furnace was supposed to be a gas heated furnace. Its design was actually simple. A heavy structure that would support the weight (150 kg) of the heat


exchanger, through which would circulate the closed Brayton Cycle working fluid. Several problems appear to prevent the building of that furnace. Most of these problems were of non-technical nature. But they were sizable, to a point where the furnace was changed to be electric. Fig. 4 shows a photo of the heat exchanger and gives an idea of its size. This heat exchanger will be fit inside the electric furnace, which will be like a giant oyster and the furnace a big metallic pearl. The basic parameters for the heat source did not change, the 300 kWth requirement continues. Also, the maximum operating temperature is of about 700 oC. This year it was decided to acquire all the sensors for the closed Brayton cycle. The sensors will be: one flow meter (Venturi type), actually shown in Fig. 3; 7 thermocouples and 6 pressure transducers. These sensors will be distributed along the cycle. Parallel to the flow meter section there will be an empty metal pipe. Through this section the colder working fluid that has produced work in the turbine is conducted to the heat exchanger that works as a heat sink for the cycle. This section, actually, will be substituted for another pipe that will serve as the test bed to heat pipes. The heat pipes will be plugged into this pipe. This section is supposed to have flexibility to allow any desired equipment to be tested.

Figure 3: Detailed scheme of the closed Brayton cycle loop being designed.

Figure 4: Photo of the heat exchanger for the heat source of the closed Brayton cycle.


4. STIRLING ENGINE AS SMALL POWER CONVERSION SYTEM

The Stirling engine was proposed as a conversion unity for radioisotope space power system [13], and for a small fission [9] space power source. This fact makes its development of interest to the TERRA project. Fig. 5 shows the original Stirling engine donated by EMBRAPA to IEAv. Note that the quality of the materials used, is very poor. That is an excellent characteristics of a Stirling engine, it works in the most unfavorable conditions. Fig. 5 also shows the drawing of the Stirling engine parts performed as a study case, in order to allow building a new engine and the development of a mathematical simulating model. Fig. 6 and 7 shows the new engine. In Fig. 6, the new engine is presented disassembled at the side of the old engine also disassembled. A few differences between both engines, besides materials, are: the new engine has the heat sink in the form of disks, and they are welded on the external cylinder, whereas in the old machine they were longitudinal and attached by a tight wire. The new design improves heat dissipation. Fig. 7 shows the new engine assembled. The mathematical model is still in development and it is not ready for presentation. It will be published sometime in the near future. Also, a magnetic heat element is being developed to simulate the radioactive heating element. As can be seen the Stirling engine has a linear piston. An independent experimental study was realized with Samarium-Cobalt permanent magnets in order to produce electricity. The device was built using a compressed air linear piston and for a crude first experiment, voltage was generated in the range 0.22-1.9 V. As said before, this is a very preliminary result and it is not integrated in the Stirling engine. These reports serve to show that all aspects of the complete Stirling engine generator is being looked at.

Figure 5: Left photo is the EMBRAPA Stirling engine donated to IEAv. Right scheme is

the disassembled parts of the same Stirling engine.


Figure 6: Photo showing to the left the new Stirling engine parts built at IEAv, and to the right the old Stirling engine parts.

Figure 7: Photo of the new Stirling engine assembled.

5. PASSIVE MULTI FLUID TURBINE

The passive multi fluid turbine is an evolution of the Tesla Turbine. A Tesla turbine uses disks instead of blades. And it was developed to work with water as working fluid. The passive multi fluid turbine is supposed to work with gases. The working principle of the passive multi fluid turbine is as follows: gas is blown through an inlet hole, tangential to a set of disks that are hard connected with shaft. The gas acts over the disks by means of a shear stress and generates the force that will provide the rotating movement of the turbine shaft. Fig. 8, to the left, shows the velocity field [11] generated by air as it enters the turbine and


pushes the rotating disk. This representation is generated, actually, with a computer-simulated model [11] generated with the ANSYS FLUENT. Fig. 8, to the right, shows a photo of the first passive multi fluid turbine [11] running and generating electricity to power a 55 W electric bulb. This turbine runs with air, at room temperature, provided by a compressor. Air enters the turbine by the aluminum pipe on its left side. Note that its body is made of acrylic plates that allows seeing the disks rotating. These disks are originate from damaged computer HDs. Fig. 9 shows the components of the second passive multi fluid turbine [12]. Note that its body is made of stain less steel. This allows the use of heated gas, which is the case for the tests performed with it. In this case, steam was used, besides compressed air. The second turbine reached very high RPM, around 65,000 RPM. Fig. 9, to the right, shows a detail of the geometric quality of the gas inlet role. Fig. 10 shows a Schlieren photograph of the wave profile generated as the air enters the turbine. A comparison of this front wave registered with the Schlieren photograph and simulated with the ANSYS FLUENT is presented at a contribution of this conference [14]. Fig. 11 shows a control system arrangement built for the third passive multi fluid turbine. For that arrangement, a PCL was used coupled with a PC and a set of sensors. Compressed air is the working fluid for this run. Air enters the turbine and rotates its axis. The rotating axis connects with an electric generator that produces electricity to the LED lamps shown in the Fig. 11. The amount of voltage generated is fixed at 4 V in order to light the LED lamps. Therefore, the rotation must be adjusted and that requires adjusting the airflow. A valve regulates the airflow controlled by the PCL. Fig. 11 shows the PCL and the regulating valve. Fig 11 shows the turbine in-between the computer flat monitor and the voltmeter, over the table. That was a preliminary test to check turbine´s behavior, control capability. This test was performed with air at room temperature. In spite that, this third turbine was built to run with steam. For that, a compatible Rankine circuit is being built and will be running by the time of the Conference. It is hoped that more data that are relevant will be available for presentation then.

Figure 8: To the left shows a drawing of the air velocity field inside a Passive Multi Fluid Turbine CFD model. To the right a photo of the first Passive Multi Fluid Turbine

powering a 55 W electric bulb.


Figure 9: To the left photo shows the Second Passive Multi Fluid Turbine components.

To the right photo of the inlet orifice of the Second Passive Multi Fluid Turbine.

Figure 10: Schlieren photography of the airflow coming out of the Second Passive Multi

Fluid Turbine inlet orifice.

Figure 11: Photo of the control system for the third Passive Multi Fluid Turbine.


6. HEAT PIPES AND ITS SYSTEM Historically, when the heat pipes' concept was defined, [15] its space application had already been expected for two main reasons. First, heat pipe is a passive heat transfer device without moving mechanical parts. This fact helps to improve safety. Also, it only needs heat to work. Second, it was believed that it could work without gravity, just with capillary pumping and this turn out to be true. Two different heat pipe systems will be needed for the project TERRA. The first one will be used to cool the nuclear reactor and power the closed Brayton cycle. And the other one will form the heat rejection system for the closed Brayton cycle. Considering the HFC with 1,000 kWth there will be using 259 heat pipes total, inside the nuclear reactor. Each heat pipe has an external diameter of 1.5 cm and a power transfer capability of ~ 4.3 kWth. Fig. 12 shows the three different meshes for the heat pipe testing, to be used for the HFC. The metal pipe and meshes are made of a Mo-Re alloy. The working fluid will be chosen, conveniently. Usually, liquid sodium is considered for this hole [16]. Our research is still in progress to identify the best options. Some Mo-Re piping and screen are to be acquired to produce the heat pipe.

Figure 12: Heat pipes meshes, from left to right: groove, composite screen wick and screen covered groove.

6. CONCLUSIONS This paper have presented all the major areas of the research conducted inside the TERRA project. As may be seen the major areas of a space nuclear power plant is addressed, as for instance: an innovative nuclear reactor core concept, a testing bench for a heat electric power conversion system, in the form of a closed Brayton cycle and a Stirling machine. A study of heat pipes and its possible applications either as heat rejection system or as nuclear heat extraction system are being looked at. In addition, innovative concepts are also being considered such as the passive multi fluid turbine, which may help to increase cycle efficiency. Initially, this turbine was thought to be used in space closed Brayton cycles. Recently, this concept was also suggested as an extension for the ECCS of an ordinary nuclear power plant. Add to that a patent process is ongoing for some of the internal characteristics of the last passive multi fluid turbine built. Apparently, the efforts and the long-term space missions’ interests of IEAv, through the TERRA project, have been noticed for potential interested partners. IEAv was considered to participate in two major international events that include nuclear energy space applications. They are The Workshop on Human Space Technology, to be held in Beijing, China, between 16th to 20th September 2013; and the MEGAHIT workshop, which is to be held in Brussels, between 2nd to 4th December 2013. For the Chinese event, the participants are unknown.


However, the event is co-sponsored by the United Nations, Office for Outer Space affairs. The MEGAHIT workshop is a European effort and involves nominally: The European Science Foundation, the German DLR, the French CNES, the Italian Thales Alenia Space, the British National Nuclear Laboratory and the Russian KeRC. Just being considered for these events is an international recognition of the Brazilian interest in deep space exploration.

ACKNOWLEDGMENTS The authors are grateful for the assistance ships conceded for some of them, provided by the TERRA project. In addition, they are thankful for the CNPq under the grants: Universal no. 472863/2011-8, DT no. 310233/2011-9 and “MCT/CNPq/AEB nº 33/2010 - Formação, Qualificação e Capacitação de RH em Áreas Estratégicas do Setor Espacial” no. 559928/2010-6. Finally, they are thankful to FAPESP under the grant no. 2009/10209-9.

REFERENCES 1. L. N. F. Guimarães, G. M. Placco, N. B. Marcelino, A. G. Barrios Jr., E. M. Borges and J.

A. Nascimento, “Advances in Power Conversion on the Brayton Cycle Loop of the TERRA Project,” Proceedings of Nuclear and Emerging Technologies for Space 2013, Albuquerque, NM, February 25-28, 2013, 8pp., Paper 6747.

2. L. N. F. Guimarães, G. P. Camillo, G. M. Placco, A. G. Barrios Jr., J. A. Nascimento, E. M. Borges and P. D. C. Lobo, “Basic Research and Development Effort to Design a Micro Nuclear Power Plant for Brazilian Space Application,” JBIS – Journal of the British Interplanetary Society, vol. 64, pp. 1-6, 2012.

3. L. N. F. Guimarães, “Nuclear Applied Research for Space Exploration: a Brazilian Effort,” presented at Nuclear and Emerging Technologies for Space, Albuquerque, NM, USA, February 25-28th, 2013.

4. Projeto TERRA, http://www.ieav.cta.br/enu/projetos_enu.php (2013). 5. J A. Nascimento, L. N. F. Guimarães and S. Ono, “Fuel, Structural Material and Coolant

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7. R. Taylor, Prometheus Project Final Report, National Aeronautics and Space Administration, Jet Propulsion Laboratory, California Institute of Technology, Passadena, CA, USA, 982-R120461, October, 2005.

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9. L. S. Mason, M. Gibson and D. Poston, “Kilowatt-class Fission Power Systems for Science and Human Precursor Missions,” Proceedings of Nuclear and Emerging Technologies for Space 2013, Albuquerque, NM, February 25-28, 2013, 7pp., Paper 6814.


10. D. Woerner, V. Moreno, L. Jones, R. Zimmerman and Eric Wood, “The Mars Science Laboratory (MSL) MMRTG In-Flight: A Power Update”, Proceedings of Nuclear and Emerging Technologies for Space 2013, Albuquerque, NM, February 25-28, 2013, 8pp., Paper 6748.

11. G. M. Placco, L.N.F. Guimarães and G. P. Camillo, 2010 “Parâmetros de Funcionamento de uma Turbina de Tesla Funcionando a Ar Comprimido”, Congresso Nacional de Engenharia Mecânica, CONEM, Campina Grande, PB, Brasil, 2010.

12. G. M. Placco, "Construção e Análise de uma Turbina de Tesla a Vapor", Trabalho de Conclusão de Curso, Faculdade de Tecnologia São Francisco, FATESF, Jacareí, SP, Brasil, 2012.

13. N. A. Schifer, and S. Oriti, “Summary of Stirling Convertor Testing at NASA Glenn Research Center in Support of Stirling Radioisotope Power System Development,” Proceedings of Nuclear and Emerging Technologies for Space 2013, Albuquerque, NM, February 25-28, 2013, 15pp., Paper 6816.

14. G. M. Placco, L.N.F. Guimarães and R. S. dos Santos, “Passive Residual Energy Utilization System In Thermal Cycles On Water-Cooled Power Reactors,” 2013 International Nuclear Atlantic Conference - INAC 2013, Recife, PE, Brazil, November 24-29, 2013.

15. G. M. Grover, T. P. Cotter and G. F. Erickson, “Structures of Very High Thermal Conductance”, Journal of Applied Physics, 35, pp.1990-1991 (1964), DOI: 10.1063/1.1713792.

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HEAT-ELECTRICITY CONVERTION SYSTEMS FOR A BRAZILIAN …