Passive Thermal Energy Transport and Energy Conversion Methods for SLIMM Small Modular Reactor

Description

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 63/561,099, filed on Mar. 4, 2024, which is incorporated herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH & DEVELOPMENT

Not applicable.

INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

The present invention concerns design optimization and multi-physics modeling capabilities of liquid metal heat pipe-thermoelectric (LMHP-TE) modules in a Scalable Liquid Metal cooled small Modular (SLIMM) reactor for generating auxiliary DC electrical power. This auxiliary power generation is active during reactor operation and after shutdown and during a Fukushima type accident with a full loss of on-site and off-site power conditions.

BRIEF SUMMARY OF THE INVENTION

The embodiments of the present invention enhance safety, reduce technological uncertainties, demonstrate potential performance and scalability, and help identify critical issues of future fabricability and testing of the LMHT-TE modules and their integration into the SLIMM reactor design. The embodiments detailed herein help move the SLIMM conceptual design to market and obtain a cost estimate of electricity production, including the secure, reliable, and fully passive auxiliary power generation using LMHP-TE modules, particularly in case of a full loss of off-site and on-site power.

In another embodiment of the present invention, the reactor is cooled using heat pipes. The heat pipes may be arranged on the outside of the reactor vessel to capture some the heat dissipated and transport it to one or more thermoelectric element modules. The modules are cooled by natural circulation of ambient air. This passive generation of electric power continues during reactor operation and after shutdown and is of a vital importance in case of Fukushima type accident with a complete loss of both off-site and on-site power sources.

In another embodiment, the present invention includes a porous wick on the inside walls of the liquid metal heat pipes.

In another embodiment of the present invention, heat supplied by the heating source evaporates a working fluid residing within the porous wick on the inside walls of the liquid metal heat pipes.

In another embodiment of the present invention, a capillary action of the porous wick circulates the condensate back through underlying the heat pipes to the evaporator section.

In another embodiment of the present invention, the liquid metal heat pipes are partially filled with inert gas.

In another embodiment of the present invention, the inert gas is argon.

In another embodiment of the present invention, extended heat pipe fins enhance cooling by natural circulation of ambient air.

In another embodiment of the present invention, the cold side of the thermoelectric elements are attached to the condenser section of the heat pipes.

In another embodiment of the present invention, the liquid metal heat pipes operate independent of each other.

In another embodiment of the present invention, the liquid metal heat pipes are fully enclosed.

In another embodiment of the present invention, the liquid metal heat pipes are fully enclosed and operate independent of each other and are typically designed at 50-75% of their prevailing operating limit.

In other embodiments, the present invention provides a system and method of design optimization and multi-physics modeling capability of liquid metal heat pipe-thermoelectric (LMHP-TE) modules in conjunction with a SLIMM reactor for generating auxiliary DC electrical power, independent of off-site and on-site power sources.

In other embodiments, the present invention provides a system and method wherein the capability will help with materials selection for and the performance optimization of the TE elements and the LMHPs.

In other embodiments, the present invention provides a system and method wherein the capability will quantify the potential of the fully passive LMHP-TE modules with no single point failures for providing tens of kilowatts of auxiliary power 24/7 during reactor nominal operation and after shutdown.

In other embodiments, the present invention provides a system and method of using multi-physics modeling and simulation capabilities to evaluate the performance of LMHP-TE modules of a SLIMM reactor for generating auxiliary electrical power.

In other embodiments, the present invention provides a system and method of further including the use of multi-physics models of the TE elements of different n- and p-leg materials and of the liquid metal heat pipes with different working fluids, depending on the operation temperature.

In other embodiments, the present invention provides systems and methods of wherein models evaluated include (a) extended water heat pipe fins to enhance cooling by natural circulation of ambient air to be used for space heating and, (b) forced convection of water and transport to air-cooled radiators for space heating or low-grade heat for industrial applications.

In other embodiments, the present invention provides a system and method that provides a physics-based liquid metal heat pipe model that explores potential design options and their effects on the performance of the heat pipes. These options include the selections of wall and wick materials and working fluid and using longitudinal arteries to return the working fluid condensate to the evaporator section of the heat pipes.

In other embodiments, the present invention provides a system and method that provides a 3-D CFD thermal-hydraulics analyses that investigates mixing of liquid sodium in the upper plenum of the SLIMM reactor vessel to estimate the heat transfer coefficient on the inside of the reactor vessel wall, as function of the circulation rate and the core exit temperature of the in-vessel liquid sodium for reactor thermal powers from 10-100 MW.

In other embodiments, the present invention provides system and method wherein the reactor vessel in the upper plenum is conductively coupled to the evaporator sections of the liquid metal heat pipes laid on the outside of the vessel wall.

In other embodiments, the present invention provides a system and method wherein modeling and simulation capability of integrated LMHP-TE modules are used to estimate the auxiliary electric power generation by the LMHT-TE modules for the SLIMM reactor and quantify of the options of removing the residual heat rejected by the TE elements.

In other embodiments, the present invention provides system and method wherein the modeling and simulation includes investigating (a) structural and thermal coupling issues for laying the LMHP-TE modules along the wall of the SLIMM reactor primary vessel, (b) optimizing the geometry, dimension and design of the heat pipes; and (c) the effects of the heat pipes working fluid on the power throughput, operation limits, internal vapor pressure, and the thickness of the heat pipe wall.

In other embodiments, the present invention provides a system and method wherein the selection of the HP working fluid and wall materials are based on considerations of chemical compatibility, availability, cost, minimum or little corrosion, a fast startup from a frozen state, potentially long operation life, and safe handling.

In other embodiments, the present invention provides systems and methods used to: (a) investigate the scalability and modularity of the LMHP-TE modules, commensurate with the SLIMM reactor nominal thermal power, and (b) explore the manufacturing and testing needs for the developed design of the LMHP-TE modules.

In other embodiments, the present invention provides a plurality of heat pipes that are conductively coupled to the reactor vessel wall to partially remove some of the heat generated in the reactor and circulated by in-vessel sodium through the reactor vessel. The heat pipes are used to power a multitude of energy conversion modules of thermoelectric elements.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The drawings, which are not necessarily drawn to scale, like numerals, may describe similar components throughout the several views. For example, numerals with different letter suffixes may represent different instances of similar components. The drawings illustrate, by way of example, but not by limitation, a detailed description of specific embodiments discussed in the present document.

FIG. 1A is a line diagram of a LMHP-TE module for use in conjunction with SLIMM reactor for auxiliary electrical power generation.

FIG. 1B shows thermoelectric energy conversion elements (TE) for auxiliary power generation modules would comprise of TAGS-85 p-legs and PbTe (2N) n-legs.

FIG. 1C shows thermoelectric elements having segmented legs for higher conversion efficiency.

FIG. 2 provides a Figure-of-Merit of thermoelectric materials as a function of temperature.

FIG. 3 is a comparison of HPTAM (heat pipes transient analysis model) predictions of axial distributions of wall and vapor temperatures with measurements for the startup of a sodium heat pipe from a frozen state.

DETAILED DESCRIPTION OF THE INVENTION

Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed method, structure or system. Further, the terms and phrases used herein are not intended to be limiting, but rather to provide an understandable description of the invention.

The present invention provides design optimization and multi-physics modeling capabilities of liquid metal heat pipe-thermoelectric (LMHP-TE) modules in conjunction with a SLIMM reactor for generating auxiliary DC electrical power, independent of off-site and on-site power sources. The capabilities will help in material selection for and the performance optimization of the TE elements and the LMHPs (FIG. 1a,c). In addition, the modeling and simulation capabilities of the present invention will quantify the potential of the fully passive LMHP-TE modules with no single point failures for providing tens of kilowatts of auxiliary power 24/7 during reactor nominal operation and after shutdown.

FIGS. 1a-1c show a layout of a LMHP-TE module for the SLIMM reactor for an embodiment of the present invention. As shown, an embodiment of the present invention provides a SLIMM reactor 100 comprising a vessel 102 comprising core 104 containing a material 106 to be heated (discussed in more detail below) by heat source 108. Vessel 102 includes an evaporation section 110, adiabatic section 112 and condenser section 114. Also included is liquid return section 116 comprised of a plurality of heat pipes 118A and 118B as well as porous section, which may be a porous wick 120.

FIGS. 1a and 1c show the capabilities of two options of removing the residual thermal power from the TE elements, for different potential applications of the SLIMM reactor for electrical power generation. In the first option, the residual thermal power would be removed from the TE elements or TE converter assembly 120, which may include a plurality of assemblies in a string, by circulating water and transported to space radiators 122 for district heating (FIG. 1a) or used as low-grade heat in applications such as water desalination. The electric power for circulating the cooling water using heat exchanger 130, pump 132 and pumped circulating loop 134 would be a fraction of that generated by the TE elements (FIG. 1a).

In the second option, suitable for cold regions, the residual thermal power would be removed from the TE elements by natural circulation of ambient air using fins 140 and used directly for space heating (FIG. 1a). Both options may result in total utilization of the thermal power generated in the SLIMM reactor.

A unique feature of the SLIMM reactor design is using variable conductance, liquid-metal heat pipes (LMHP) which are thermally coupled to TE elements, for passive and reliable generation of auxiliary electric power both during nominal reactor operation and after shutdown, and independent of on-site and off-site conventional sources. The heat pipes 118A and 118B, as shown in FIG. 1a, are laid along the outer surface of the reactor primary vessel (RV) 102 and partially embedded in the vessel wall 200. The evaporator sections of these fully passive and redundant thermal power transport devices are thermally coupled to the in-vessel liquid sodium coolant of the SLIMM reactor, which is circulating by natural convection on the inside of the RV wall in the upper plenum 210. The condenser sections 114 at the opposite end of the heat pipes are thermally coupled to a multitude of static, TE elements for energy conversion. These elements will be electrically connected in series in a number of parallel strings for redundancy and the avoidance of single point failures. The number of the series TE (120) in the string depends on the required load voltage, e.g., ˜400 VDC, while the number of the parallel strings will be dictated by the desired load current.

The thermal power removed by conduction through the reactor vessel wall from the circulating liquid Na on the inside of the reactor vessel wall is conducted to the evaporator sections of the variable conductance LM heat pipes. The supplied heat evaporates the working fluid residing within a thin, porous wick 220 on the inside walls of heat pipes 118A and 11B (FIG. 1a). The generated vapor traverses to the opposite end of the heat pipes where it condenses into liquid. The capillary action of the wick circulates the condensate back through the porous wick and the underlying longitudinal arteries to the evaporator sections 110. Potential liquid metal (LM) working fluids for the current application in cold regions are frozen at room temperature. Thus, to speed up the start up from a frozen state, the LM heat pipes 118A and 118B are partially filled with inert gas, such as argon. As the heat pipe thermal power throughput increases, the generated vapor sweeps the inert fill gas and reduces its extent at the end of condenser section 114, and thus regulates the effective length of the condenser section of the heat pipes for the heat rejection commensurate with thermal power removed from the reactor vessel wall and the temperature of the in-vessel liquid sodium 250. This self-regulating operation is behind the term variable conductance heat pipes.

The TE elements for auxiliary power generation modules 300 may be comprised of TAGS-85 p-legs 302 and PbTe (2N) n-legs 304 (FIG. 1b). Alternatively, for higher thermal efficiency, the TE electric elements 400 will have segmented legs p-legs 402A and 402 B and segmented legs n-legs 404A and 404 B (FIG. 1c). The p-leg comprises a hot segment of TAGS-85 and a bottom segment of BiTe, and the n-leg comprises a hot PbTe segment and a BiTe cold segment. These design options of the TE elements take advantage of the higher figure-of-merits of the selected materials for achieving high thermal efficiency of 8% or higher (FIG. 2). This figure compares the Figure-of-Merits (FOMs) of different thermoelectric materials as functions of operating temperatures. Note that the selected TE materials for the SLIMM reactor auxiliary power generation modules have the highest FOMs in the range of temperatures of interest (700-350K). The contact resistances of the n- and p-legs in the TE elements will affect their performance (terminal voltage, electric current and thermal efficiency) as well as the electrical power and the load-following characteristic. These effects will be investigated as a part of this technical task.

It is projected that the LMHP-TE modules could remove 0.5-1.0 MW of thermal power from the outer surface of the reactor vessel wall in the upper section, provided by the in-vessel liquid sodium coolant of the reactor which is circulating in the upper plenum of the SLIMM reactor vessel during nominal operation. The amount of thermal power removed will depend on the reactor nominal thermal power and temperature of the circulating liquid sodium and hence the heights of the in-vessel chimney and the upper plenum in the reactor vessel. The chimney height affects the flow rate and hence flow mixing in the upper plenum. For reactor nominal thermal power of 100 and 10 MW, the chimney is 8 and 2 m tall, respectively. However, the diameter of the reactor vessel is the same for all nominal thermal power levels of the SLIMM reactor, and so is the number of the LMHP-TE modules. While the amount of thermal power removed by these modules from the circulating liquid sodium in the upper plenum of the SLIMM reactor vessel depends on the lengths of the evaporator and condenser sections 114 of heat pipes 118A and 118B, the cross-section dimensions and the number of heat pipes would be the same for all reactor nominal thermal powers. This modular design approach ensures scalability of the LMHP-TE modules commensurate with for the SLIMM reactor thermal power and operating temperature, during nominal operation and after shutdown.

Following an unlikely malfunction of the in-vessel sodium-sodium helically coiled tubes heat exchanger 130, the SLIMM reactor shuts down and LMHP-TE modules will contribute to effectively remove the decay heat generated in the reactor core. During the first 48 hours after shutdown, these modules together with the large thermal mass of the in-vessel liquid sodium in the SLIMM reactor vessel (˜40.4 MT with 8-m tall chimney) maintain a large safety margin of several hundred degrees from the boiling point of the in-vessel liquid sodium. Furthermore, the natural circulation of ambient air along the outer surface of the SLIMM reactor guard vessel wall with longitude metal fins 140 could remove more than 1.0 MW of the thermal power generated in the reactor core by the radioactive decay of fission products after shutdown.

The plurality of heat pipes 118A and 118B are fully enclosed and operate independent of each other and are typically designed at 50-75% of the prevailing operating limit. Therefore, a failure of up to 25-50% of the heat pipes would not compromise the remaining LMHP-TE modules for generating auxiliary electrical power and increase the conversion efficiency of the TE elements.

For the operating hot temperature of interest for the SLIMM reactor's LMHP-TE modules of >700 K, the choices of the working liquid metal working fluid are Cesium (Cs), Rubidium (Rb), and Potassium (K), in the order of decreasing vapor pressure. While Potassium is suitable for operating at temperatures >700 K, because of its lower vapor pressure and high boiling temperature (1,032 K), both Rubidium and Cesium are suitable for operating at somewhat (˜100 K) lower temperatures because of their relatively higher vapor pressure. The SLIMM reactor's LMHPs would be designed to operate sonic limited below 500 K to avoid excessive cooling and keep the in-vessel sodium liquid from freezing for an extended period of weeks after reactor shutdown.

FIG. 3 compares the results of HPTAM for the startup of a sodium heat-pipe from a frozen state with reported experimental measurements. This figure shows excellent agreement of HPTAM predictions with the reported measurements of the wall temperature along the heat pipes at different times during the startup transient. The predicted vapor temperature and the prevailing flow regime in the test heat pipe are also presented. Backfilling of the LMHPs for the SLIMM reactor TE modules partially with a noble gas, such xenon or argon, would reduce the time during startup from a frozen state to reach the vapor continuum flow regime and realize the highest power throughput to the TE elements.

For other embodiments, two options for removing the residual heat from the TE elements 120 may be used. In one option, extended water heat pipe fins 140 are used to enhance cooling by natural circulation of ambient air to be used for space heating. In another option, forced convection of water and transport to air-cooled radiators 122 for space heating or low-grade heat for industrial applications. The hot and cold side temperatures of the TE elements will help the potential choice of the materials for the n- and p-legs and the performance of the TE elements.

The modeling and simulation capability of the integrated LMHP-TE modules of the present invention may be used to estimate the auxiliary electric power generation by the LMHT-TE modules for the SLIMM reactor and investigate the effects of the options of removing the residual heat rejected by the TE elements 120 (FIG. 1a).

The thermal power removed by the LMHP-TE modules depends on the lengths of the evaporator and condenser sections of the heat pipes. These will vary commensurate with the reactor thermal power. However, the cross-section dimensions and the number of the heat pipes used would be the same, regardless the SLIMM reactor nominal thermal power. This modular design approach ensures the scalability of the LMHP-TE modules for the SLIMM reactor.

In use, the plurality of heat pipes are conductively coupled to the reactor vessel wall. This allows the heat pipes to partially remove some of the heat generated in the reactor and circulated by in-vessel sodium through the reactor vessel. The heat pipes may then be used to power energy conversion modules of thermoelectric elements. In a preferred embodiment, the heat pipes may be arranged on the outside of the reactor vessel allowing for the capture of some, but not all, of the heat generated by the reactor. This allows for some the heat generated by the reactor to be dissipated and transported to thermoelectric element modules, which may be cooled by natural circulation of ambient air.

The ability of the embodiments of the present invention to continue to dissipate heat after reactor shutdown is of a vital importance in case of Fukushima type accident with a complete loss of both off-site and on-site power sources. Thus, the embodiments of the present invention are not only able to passively generate electric power during the normal operation of the reactor but can continue to passively generate electric power even after reactor shutdown.

While the foregoing written description enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The disclosure should therefore not be limited by the above-described embodiments, methods, and examples, but by all embodiments and methods within the scope and spirit of the disclosure.