Jean-Michel Tournier

SCoRe - Concepts of Liquid Metal Cooled Space Reactors for Avoidance of Single-Point Failure

Space nuclear Reactor Power Systems (SRPSs) are being developed to meet electrical power requirements for NASA’s planetary exploration missions early next decade. In addition to enjoying some degree of autonomy, these systems need to operate reliably through the end of the mission, which could not be realized solely through a redundancy in the reactor’s coolant loop. Besides increasing the total system mass, such hardware redundancy does not eliminate a single‐point failure in the reactor and subsequent loss of coolant. This paper presents three concepts of the liquid metal cooled. Sectored, Compact Reactor (SCoRe) for the avoidance of single‐point failure. The SCoRe‐S, ScoRe‐M, and SCoRe‐L concepts are for small, medium, and large reactor cores, covering a wide range of electrical power requirements, from 10’s of kWe to a few MWe. As a common feature in all SCoRe concepts, the reactor core is divided into six sectors that are neutronically coupled but thermal‐hydraulically decoupled. The dividers of the ...

Liquid Metal Loop and Heat Pipe Radiator for Space Reactor Power Systems

This paper presents four radiator configurations that could be stowed in the launch bay of the DELTA-IV Heavy vehicle and have effective areas of 69.1 to 350 m 2 . The radiator for a space reactor power system with a lithium-cooled sectored compact reactor and thermoelectric converters has an effective area of 203 m 2 and lowest specific mass. The sectored compact reactor and thermoelectric converters system generates ∼114 kWe for 7-10 years. The radiator consists of six panels, each having a forward, fixed segment and two rear, deployable segments, and rejects heat into space using rubidium heat pipes with carbon-carbon armor and fins. The D-shaped heat pipes operate below 50 % of the prevailing sonic or capillary limit. The radiator operates at a constant pressure drop of 12 kPa and inlet and exit temperatures of 780 and 755 K. Investigated are the effects on the radiators specific mass and lithium inventory of 1) tapering and changing width of coolant channels, 2) thermal-hydraulically coupling the panel segments in parallel, and 3) using perforated dividers between inlet- and exit-channels. The radiator with perforated dividers has a wet specific mass of 6.82 kg/m 2 , a liquid-lithium inventory of 179.3 liters, and a stowed height of 8 m.

AMTEC/TE static converters for high energy utilization, small nuclear power plants

Abstract A conceptual design of static converters for small, co-generation modular nuclear power plants is developed and analyzed. Each converter is comprised of an alkali metal thermal-to-electric conversion (AMTEC) top cycle and thermoelectric (TE) bottom cycle cooled by natural convection of air. In addition to electricity production at a net efficiency in the low thirties, the small nuclear power plants with AMTEC/TE converters could provide co-generation heat for space heating, seawater desalination and/or high temperature process heat or steam. For the potassium AMTEC/TE converter, the conversion efficiency is about 1% point higher, the hot side temperature >100 K lower and the co-generation heat is slightly lower than for the sodium AMTEC/TE converter when operated at the same anode vapor pressure. On the other hand, when operated at the same hot side temperature, the efficiency of electricity production of power plants with K-AMTEC/TE converters could be ∼25% higher, while the co-generation thermal energy for space heating is ∼25% lower than with Na-AMTEC/TE converters. The present analysis showed that K- and Na-AMTEC/TE converters could be sized to produce up to 64 and 81 kWe each at hot side temperatures of 1030 and 1150 K, respectively, while achieving >90% total utilization of the nuclear reactor’s fission energy for the plant.

An analytical model for liquid-anode and vapor-anode AMTEC converters

This paper describes a lumped analytical model of liquid-anode single-tube and vapor-anode multi-tube AMTEC cells. The model results agreed well with experimental data for Mo, NbN and TiN electrodes. Results showed that Mo and NbN electrodes exhibit high B values between 400 and 600 A.K1/2/Pa.m2, and have the potential for peak power densities slightly above 1 W/cm2, with efficiencies as high as 28%. In contrast, TiN electrodes have lower temperature-independent exchange currents, between 120 and 135 A.K1/2/Pa.m2, lower peak power densities between 0.5 and 0.75 W/cm2, and efficiencies below 24% at a BASE temperature of 1200 K. These values of B compare well with that reported by other investigators.

Performance comparison of potassium and sodium vapor anode, multi-tube AMTEC converters

Abstract An analysis is conducted to compare the performance of Mo–41%Re, eight-tube, potassium and sodium alkali metal thermal-to-electric converters of identical design. The results showed that the operation envelope of the potassium converter is severely limited by incipient dryout in the evaporator wick due to the lower surface tension and higher molecular weight of potassium compared to sodium. As a result of this operational limit, at the same load voltage, the potassium converter delivers lower electrical power and has a lower conversion efficiency than the sodium converter. Moving the evaporator wick surface further away from the hot plate (and shortening its total length) expands the operation envelope of the potassium converter by raising the incipient dryout limit. At the same load voltage, the potassium converter with the remote evaporator wick can deliver the same electrical power as the reference sodium converter, while operating at a 50 K lower hot side temperature and a 90 K lower optimum condenser temperature. When operating at a hot side temperature of 1174 K and 2.7 V, the potassium converter with the remote evaporator wick delivers a peak electrical power of 8.5 We at an efficiency of 17.4%, compared, respectively, to 6.2 We and 16.4% for the reference potassium converter, and 7.3 We and 15.5% for the reference sodium converter.

Noble-Gas Binary Mixtures for Closed-Brayton-Cycle Space Reactor Power Systems

The advantages and limitations of pure helium and noble-gas binary mixtures as working fluids for space nuclear reactor power systems with closed Brayton cycles are examined. Helium has the best transport properties, but its small molecular weight increases the aerodynamic loading of the impeller blades. The binary mixture of He-Xe with a molecular weight of 40 g/mol is the recommended working fluid because it has the same heat transfer coefficient as helium, but results in a significant reduction in the aerodynamic loading (10% of that with helium) and hence, in the size and mass of the turbomachines and the power system. The performance parameters of a power system with no single-point failure in reactor cooling, three independent closed-Brayton-cycle loops, and He-Xe binary-mixture working fluid (40 g/mol) are presented and compared with those reported for similar systems.

High Temperature Water Heat Pipes Radiator for a Brayton Space Reactor Power System

A high temperature water heat pipes radiator design is developed for a space power system with a sectored gas‐cooled reactor and three Closed Brayton Cycle (CBC) engines, for avoidance of single point failures in reactor cooling and energy conversion and rejection. The CBC engines operate at turbine inlet and exit temperatures of 1144 K and 952 K. They have a net efficiency of 19.4% and each provides 30.5 kWe of net electrical power to the load. A He‐Xe gas mixture serves as the turbine working fluid and cools the reactor core, entering at 904 K and exiting at 1149 K. Each CBC loop is coupled to a reactor sector, which is neutronically and thermally coupled, but hydraulically decoupled to the other two sectors, and to a NaK‐78 secondary loop with two water heat pipes radiator panels. The segmented panels each consist of a forward fixed segment and two rear deployable segments, operating hydraulically in parallel. The deployed radiator has an effective surface area of 203 m2, and when the rear segments are...

Radiation/conduction model for multitube AMTEC cells

A radiation/conduction model was developed for calculating parasitic heat losses and temperatures in vapor-anode, multitube AMTEC cells. The model accounted for the presence of an internal circumferential radiation shield, and a conduction stud between the hot end of the cell and the BASE tubes support plate. The radiation view factors were calculated using either closed-form algebraic solutions or approximate relations, and all reciprocity and enclosure relations were satisfied. In the integrated cell model, the present thermal model was coupled to a vapor pressure loss model, and an electrochemical and electrical circuit model, using an efficient iterative solution procedure. The integrated cell model predictions were compared with experimental results of PX-4C, PX-5A and PX-3A cells, that were tested in vacuum at the Air Force Research Laboratory. Results illustrated the effects of using a CREARE condenser and a conduction stud, reducing the number of BASE tubes, and changing the size of the cell diame...

Selection of Noble Gas Binary Mixtures for Brayton Space Nuclear Power Systems

Binary noble gas mixtures are more suitable working fluids than pure gases for use in nuclear reactor space power systems, with Closed Brayton Cycle (CBC) engines. Helium has the best thermal properties but the smallest molecular weight, which increases the aerodynamic loading and hence, the size and mass of the turbomachinery. Mixing He with heavier gases of Krypton (Kr) and Xenon (Xe) to molecular weights of

Conceptual Design of HP‐STMCs Space Reactor Power System for 110 kWe

A conceptual design of a Heat Pipe‐Segmented Thermoelectric Module Converters (HP‐STMCs) space reactor power system (SRPS) for a net power of 110 kWe is developed. The parametric analysis changed the number of radiator’s potassium heat pipes from 224 to 336 and calculated the effects on the operation parameters and total mass of the system. The reactor has a hexagonal core comprised of 126 heat pipe modules, each consists of three UN, 1.5 cm OD fuel pins brazed to a central lithium heat pipe of identical diameter. The Re cladding of the fuel pins is brazed along the active core length to the lithium heat pipe using 6 Re tri‐cusps. The reactor control is accomplished using 12 B4C/BeO control drums, a large diameter one on each side of the hexagonal core and a small diameter one at each corner. The control drums are placed within the radial BeO reflector (7.1–9.1 cm thick). The fuel pin peak‐to‐average power ratio in the reactor core is 1.12–1.19. Despite its very high density and fabrication challenge, usi...