WO2018169588A2

WO2018169588A2 - Salt compositions for molten salt nuclear power reactors

Info

Publication number: WO2018169588A2
Application number: PCT/US2017/066803
Authority: WO
Inventors: Michael E. HANSON; Paul SCHUCK; Gary POVIRK; Jonathan Witter; Youssef BALLOUT; Sebastian CORBISIERO; Kieran DOLAN; Gabriel Schneck
Original assignee: Elysium Industries Ltd.
Priority date: 2016-12-15
Filing date: 2017-12-15
Publication date: 2018-09-20
Also published as: WO2018169588A3

Abstract

A salt composition is provided. The salt composition can include a mixture of salts containing chlorides of uranium, potassium, sodium, and calcium. Optionally, a magnesium chloride can be substituted for calcium chloride or added in addition to calcium chloride. The salt composition possess a relatively low melting point, good neutron physics properties, and good thermophysical properties for use as fuel in a molten salt nuclear reactor.

Description

SALT COMPOSITIONS FOR MOLTEN SALT NUCLEAR POWER REACTORS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 62/434,960, filed December 15, 2016, entitled "Salt Compositions For Molten Salt Nuclear Power Reactors," the entirety of which is incorporated by reference.

BACKGROUND

Field

[0002] Systems, methods, and devices are provided for molten salt reactors and, in particular, salt compositions for use as fuel for molten salt nuclear reactors.

[0003] The global demand for energy has largely been fed by fossil fuels. This typically involves taking reduced carbon out of the Earth and burning it. However, those hydrocarbons are in limited supply and burning the hydrocarbons can produce carbon dioxide. According to the U. S. Environmental Protection Agency, more than 9 trillion metric tons of carbon are released into the atmosphere each year. Nuclear power is an appealing alternative to fossil fuels due to relative abundance of nuclear fuel and carbon-neutral energy production.

[0004] Light water reactors (LWRs) are the predominant commercial nuclear reactor for electricity production. In LWRs, light water (ordinary water) is used as a moderator as well as a cooling agent and the mechanism by which heat is removed to produce steam for use in generating electricity (e.g., turning turbines of electric generators).

[0005] LWRs have significant drawbacks, however. In one example LWRs can use solid fuels that have long radioactive half-lives. As a result, LWRs can produce dangerous and long-lived waste products. In another example, light water reactors operate at high pressure, requiring expensive engineering and materials. Additionally, LWRs can require expensive safety systems to avoid complicated and expensive accidents.

[0006] Molten salt reactors (MSRs) have been researched since the 1950s to improve on LWR technologies. MSRs are a class of nuclear fission reactors in which the primary coolant, or even the fuel itself, can be a molten salt mixture. In general, MSRs can provide energy more safely and cheaply than LWRs. As an example, MSRs can operate at relatively lo pressures and they can be potentially less expensive and passively safer than LWRs. Furthermore, compared to LWRs, MSRs can also provide advantages such as lower levelized cost on a per-kilowatt hour (kWh) basis, fuel and waste inventories of relatively benign composition, and more efficient fuel utilization. Accordingly, as LWR maintenance and upgrade costs continue to rise, there is renewed interest in MSRs, given their advantages over LWRs. SUMMARY

[0007] In one exemplary embodiment, a composition is provided and it can include about 25 mol % to about 40 mol % UCU, about 20 mol % to about 70 mol % NaCl, about 10 mol % to about 70 mol % KC1, and about 1 mol % to about 10 mol % CaCb.

[0008] In another embodiment, the composition can include about 5 mol % CaCh

[0009] In another embodiment, the composition can include about 30 mol % to about 40 mol % UC1₃.

[0010] In another embodiment, the composition can include MgCh. [001 1] In another embodiment, the composition can include UCU. [0012] In another embodiment, the composition can include PuCU. [0013] In another embodiment, the composition does not include Pu.

[0014] In another embodiment, the composition can include at least one of AICU and AIC . [0015] In another embodiment, the composition can include ZrCU.

[0016] In another embodiment, the melting temperature of the composition can be within the range from about 418°C to about 500°C.

[0017] In one exemplary embodiment, a composition is provided and it can include about 25 to about 40% UCh, about 20 to about 70% NaCl, about 10 to about 70% KC1, and about 1 to about 10% MgCl₂.

[0018] In another embodiment, the composition can include about 5 mol % MgCh.

[0019] In another embodiment, the composition can include about 30 mol % to about 40 mol % UCh.

[0020] In another embodiment, the composition can include CaCh.

[0021 ] In another embodiment, the composition can include UCU.

[0022] In another embodiment, the composition can include PuCh.

[0023] In another embodiment, the composition does not include Pu.

[0024] In another embodiment, the composition can include at least one of AlCh and AICU.

[0025] In another embodiment, the composition can include ZrCU.

[0026] In another embodiment, the melting temperature of the composition can be within the range from about 418°C to about 500°C. BRTEF DESCRIPTION OF THE DRAWINGS

[0001] These and other features will be more readily understood from the following detailed description taken in conj unction with the accompanying drawings, in which:

[0027] FIG. 1 is a schematic diagram illustrating one exemplary embodiment of a nuclear thermal generating plant (NTGP) including a molten salt reactor (MS ) system;

[0028] FIG. 2 is a calculated phase diagram for a KCI / NaCl / UCb ternary salt;

[0029] FTG. 3 is a calculated pseudo phase diagram for the KCI / NaCl / UCb / CaCb quaternary system (5% CaCb off-axis);

[0030] FIG. 4A is a plot of neutron capture and fission cross-sections for selected isotopes as a function of incident neutron energy; and

[0031] FIG. 4B is an expanded view of a portion of FIG. 4A.

[0032] For a thorough understanding of the present disclosure, reference should be made to the following detailed description, including the appended claims, in connection with the above- described drawings. Although the present disclosure can be described in connection with exemplary embodiments, the disclosure can be not intended to be limited to the specific forms set forth herein. It can be understood that various omissions and substitutions of equivalents can be contemplated as circumstances can suggest or render expedient.

DETAILED DESCRIPTION

[0033] Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the systems, devices, and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the systems, devices, and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention. Further, in the present disclosure, like-named components of the embodiments generally have similar features, and thus within a particular embodiment each feature of each like-named component is not necessarily fully elaborated upon.

[0034] Embodiments of the disclosure provide salt compositions for use in molten form as nuclear fuel in nuclear systems including, but not limited to, molten salt reactors (MSRs). In general, MSRs can provide a variety of cost and safety advantages over conventional light water reactors (LWRs), which employ solid nuclear fuels. Examples of such advantages can include: • MSRs can operate at lower pressures and can possess higher heat capacity, allowing the use of containment vessels that are smaller and thinner, reducing the cost of containment.

• Fission products generated during operation of MSRs can be removed in-service, rather accumulating between during shutdown periods. As a result, environmental risks arising from a worst case accident scenario (e.g., release of radioactive materials into the environment) can be reduced.

• Molten fuel salts are generally non-reactive with the environment, reducing the likelihood of explosion in the event of a containment breach.

• Fission products in molten fuel salts are chemically bound and physically frozen. Thus, the fission products are prevented from release if the molten salt leaks from the reactor.

• In LWRs, solid fuels can melt and breach their containment in the event of a cooling failure. In contrast, molten fuel salts are in no danger of melting, since they are already in a molten form.

• MSRs can employ passive safety features (e.g., walk-away safe emergency shutdown systems) that do not require operator action or electronic feedback to safely shut down operation in the event of an emergency.

[0035] FIG. 1 schematically illustrates an embodiment of an MSR 100 in the form of a molten configured to use a molten fuel salt or a fuel salt constituent (collectively referred to herein as fuel salt) to generate electrical energy from nuclear fission. As shown, the MSR 100 includes a reactor system 102 and a secondary system 104. The reactor system 102 includes a primary heat exchanger 106 connected to a reactor vessel 1 10 having a reactor core 1 12 containing a fuel salt composition 114. The reactor system 102 also includes a fuel conditioning system 120 in fluid communication with the reactor vessel 110.

[0036] In general, fluids of three types can be contained in and/or circulated through the MSR 100, namely fuel, coolant, and moderator (e.g., any substance that slows neutrons). Various fluids can perform one or more of the fuel, coolant, and moderator functions simultaneously. One or more fluids, including more than one fluid of each functional type, can be contained within or circulated through the reactor core 112. Examples of fluids contained within or circulated through the reactor core 112 can include, but are not limited to, liquid metals, molten salts, supercritical FhO, supercritical CO2, and supercritical N2O.

[0037] Upon absorbing neutrons, nuclear fission can be initiated and sustained in the fuel salt composition 1 14 by chain-reaction within the MSR 100, generating heat that elevates the temperature of the fuel salt composition 114 to a temperature T ot (e.g., about 650°C or about 1,200°F). The heated fuel salt composition 114 can be transported from the reactor core 112 to the primary heat exchanger 106 via a primary fluid loop 122 via a pump, discussed in greater detail below. The primary heat exchanger 106 can be configured to transfer heat generated by nuclear fission occurring in the fuel salt composition 114. [0002] Transfer of heat from the fuel salt composition 1 14 can be realized in various ways. For example, the primary heat exchanger 106 can include a pipe 124 and a secondary fluid 126. The fuel salt composition 114 can travel through the pipe 124, while the secondary fluid 126 (e.g., a coolant) can surround the pipe 124 and absorb heat from the fuel salt composition 114. After heat transfer occurs within the primary heat exchanger 106, the temperature of the fuel salt composition 114 can be reduced from Thot to T_coid (ΔΤ) and the fuel salt composition 114 can be subsequently transported from the primary heat exchanger 106 back to the reactor core 1 12.

[0003] The secondary system 104 can also include a secondary heat exchanger 130 configured to transfer heat from the secondary fluid 126 to a tertiary fluid 132 (e.g., water). As shown in FIG. I , the secondary fluid 126 is received from primary heat exchanger 106 via fluid loop 134 and circulated through secondary heat exchanger 130 via a pipe 136.

[0004] Additionally or alternatively, in another embodiment (not shown), heat exchange can occur within the reactor core 1 12 prior to heat exchange within the secondary heat exchanger 130. As an example, heat from the fuel salt composition can pass to a solid moderator, then to a liquid coolant circulating through the reactor. Subsequently, the liquid coolant circulating through the reactor can be transported to the secondary heat exchanger. As required by basic thermodynamics, after one or more stages of exchange, heat can be finally delivered to an ultimate heat sink, e.g., the overall environment (not shown).

[0005] Heat received from the fuel salt composition 114 can be used to generate power (e.g., electric power) using any suitable technology. For example, when the tertiary fluid 132 in the secondary heat exchanger 130 is water, it can be heated to a steam and transported to a turbine 140 by a fluid loop 142. The turbine 140 can be turned by the steam and drive an electrical generator 144 to produce electricity. Steam from the turbine 140 can be conditioned by an ancillary gear 148 (e.g., a compressor, a heat sink, a pre-cooler, and a recuperator) and it can be transported back to the secondary heat exchanger 130 through the fluid loop 142.

[0006] Additionally, or alternatively, the heat received from the fuel salt composition 1 14 can be used in other applications such as nuclear propulsion (e.g., marine propulsion), desalination, domestic or industrial heating, hydrogen production, or combinations thereof.

[0038] The discussion below presents embodiments of fuel salt compositions 1 14 that exhibit improved (e.g., lower) melting temperatures. Beneficially, the fuel salt compositions 114 can increase the temperature differential ΔΤ, without raising Thot. The melting temperature of the salt composition can be within the range from about 418°C to about 500°C. This low melting temperature can enable the cold-leg temperature (T_coi_d) of the MSR 100 to be as low as about 458°C which assumes an approximately 40°C temperature margin between T_coi_d and the salt melting point. Calcium dichloride (CaCh), and/or magnesium dichloride (MgCh) may also be added to the salt to either further lower the melting temperature or to improve other thermophysical properties of the salt. [0039] In an embodiment, the following the salt composition can include the following components (in mol % of the total composition): about 25 % to about 40% UCh, about 20 % to about 70% NaCl, about 10 % to about 70% KCl, and about 1 % to about 10 % CaCl₂, as discussed below.

[0040] FTG. 2 shows a calculated KCl / NaCl / UCI3 phase diagram. The composition with the lowest melting point is about 15% KCl, about 48% NaCl, and about 37% UCI3. A shaded area indicates an embodiment of a targeted UCh concentration, as discussed in detail below.

[0041] CaCh can also be added to the salt composition to modify the phase behavior of the ternary salt (to produce a quaternary salt) to make the salt perform better in the MSR 100. Beneficially, the addition of CaCh can lower the melting point further, to broaden the composition range at which the salt remains at an adequately low melting point, and/or to provide a more favorable density. Embodiments of CaCh concentrations can be selected from the about 1 mol % to about 10 mol %.

[0042] In alternative embodiments, MgCh can be added in lieu of or in addition to CaCh to further lower the melting temperature or to improve other thermophysical properties of the salt.

[0043] In further embodiments, at least one of AICI3, AlCh, and ZrCU can be added in addition to CaCh, MgCh, or combinations of CaCh and MgCh to improve other thermophysical properties of the fuel salt composition 114.

[0044] No published data is known to exist for the KCl / NaCl / UCh / CaCh quaternary system. However, FIG. 3 shows a calculated pseudo-quaternary phase diagram for a salt composition including KCl, NaCl, and UCh along with about 5% CaCh off-axis. Three non-limiting embodiments of fuel salt composition 114 are called out for use in the MSR. Note that the phase diagram of FIG. 3 presents an expanded area of the total phase diagram, therefore the mole fractions on the axes do not range from 0 to 1.

[0045] The target region of FIG. 3 is a UCh target concentration region of about 30 mol % to about 40 mol % that can favor core physics. The hexagons represent approximately ± 2.5% compositional variations to allow for inconsequential compositional shifts during reactor start-up and operation and are listed below in Table 1.

TABLE 1 - UCb / NaCl / KCl / CaCh Quaternary Salt Compositions

Composition 1 Composition 2 Composition 3

Melting

470 485 495

Point (°C)

Specific

Heat 645 630 610

(J/kg K)

Ratio/ Quaternary Ratio/ Quaternary Ratio/ Quaternary no Ca Composition no Ca Composition no Ca Composition (mol %) (mol %) (mol %) (mol %) (mol %) (mol %)

UCb 29 27 6 31 29.5 33 31.4

NaCl 53 50 47 44.8 42 40

KC1 18 17 22 21.0 25 23.8

CaCh 5.0 5.0 5.0

[0046] Embodiments of the fuel salt composition 1 14 described herein can possess a relatively low melting point at the uranium loadings suitable for use in a molten chloride fast reactor. Modifying the salt melting point without increasing the vapor pressure and/or corrosivity (as in the case of UCU or ZrC additions), or by adding plutonium to the salt (because of the political difficulties in obtaining this material) can be desirable, but is not required. Ca and K can exhibit approximately the same neutron capture cross sections in the spectral energy range of interest to a MCFR, as illustrated in FIGS. 4A-4B.

[0047] Embodiments of the fuel salt composition 114 can provide a fuel salt with thermo- physical properties that can allow a smaller, more affordable, more efficient nuclear reactor power plant to be designed and built. The attributes of lower melting temperature and higher heat capacity can be beneficial in providing a more optimal heat transport flow loop for circulating pumps, heat exchangers, and flow areas (piping diameters). The larger ΔΤ can allow lower flow rates, which can increase the in-core residence time for better neutronic performance. The larger ΔΤ can also allow ex-core salt volumes to be reduced, which can create higher effective power density in the full salt volume, which can be better for the breeding/burning fuel cycle.

[0048] In order to reduce melting point of the fuel salt composition 114 further, at least one of UCU and PuCb can optionally be added to the salt composition. A quaternary salt (e.g., KC1 / NaCl / CaCh / UCU) can produce a salt with favorable melting point properties, compositional range, and density properties for the MSR 100.

[0049] All references cited throughout this application, for example patent documents including issued or granted patents or equivalents, patent application publications, and non-patent literature documents or other source material, are hereby incorporated by reference herein in their entireties, as though individually incorporated by reference, to the extent each reference is at least partially not inconsistent with the disclosure in this application. For example, a reference that is partially inconsistent is incorporated by reference except for the partially inconsistent portion of the reference.

[0050] One of ordinary skill in the art will appreciate that starting materials, biological materials, reagents, synthetic methods, purification methods, analytical methods, assay methods, and biological methods other than those specifically exemplified can be employed in the practice of embodiments of the disclosure without resort to undue experimentation. All art-known functional equivalents, of any such materials and methods are intended to be included in the disclosed embodiments

[0051] When a group of substituents is disclosed herein, it is understood that all individual members of that group and all subgroups, including any isomers, enantiomers, and diastereomers of the group members, are disclosed separately.

[0052] When a Markush group, or other grouping is used herein, all individual members of the group and all combinations and sub-combinations possible of the group are intended to be individually included in the disclosure.

[0053] When a compound is described herein such that a particular isomer, enantiomer, or diastereomer of the compound is not specified, for example, in a formula or in a chemical name, that description is intended to include each isomers and enantiomer of the compound described individual or in any combination. Additionally, unless otherwise specified, all isotopic variants of compounds disclosed herein are intended to be encompassed by the disclosure. For example, it will be understood that any one or more hydrogens in a molecule disclosed can be replaced with deuterium or tritium. Isotopic variants of a molecule are generally useful as standards in assays for the molecule and in chemical and biological research related to the molecule or its use. Methods for making such isotopic variants are known in the art. Specific names of compounds are intended to be exemplary, as it is known that one of ordinary skill in the art can name the same compounds differently.

[0054] As used herein, and in the appended claims, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to "a cell" includes a plurality of such cells and equivalents thereof known to those skilled in the art, and so forth. Additionally, the terms "a" (or "an"), "one or more" and "at least one" can be used interchangeably herein.

[0055] As used herein, the term "comprising" is synonymous with "including," "having," "containing," and "characterized by" and each can be used interchangeably. Each of these terms is further inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0056] As used herein, the term "consisting of excludes any element, step, or ingredient not specified in the claim element.

[0057] As used herein, the term "consisting essentially of does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. In each instance herein any of the terms "comprising", "consisting essentially of," and "consisting of may be replaced with either of the other two terms.

[0058] The embodiments illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein. [0059] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which the disclosed embodiments belong.

[0060] Whenever a range is given in the specification, for example, a temperature range, a time range, a composition range, or a concentration range, all intermediate ranges and sub-ranges, as well, as all individual values included in the ranges given, are intended to be included in the disclosure. As used herein, ranges specifically include the values provided as endpoint values of the range. For example, a range of 1 to 100 specifically includes the end point values of 1 and 100. It will be understood that any subranges or individual values in a range or sub-range that are included in the description herein can be excluded from the claims herein.

[0061] In the descriptions above and in the claims, phrases such as "at least one of or "one or more of may occur followed by a conjunctive list of elements or features. The term "and/or" may also occur in a list of two or more elements or features. Unless otherwise implicitly or explicitly contradicted by the context in which it is used, such a phrase is intended to mean any of the listed elements or features individually or any of the recited elements or features in combination with any of the other recited elements or features. For example, the phrases "at least one of A and Β;" "one or more of A and Β;" and "A and/or B" are each intended to mean "A alone, B alone, or A and B together." A similar interpretation is also intended for lists including three or more items. For example, the phrases "at least one of A, B, and C;" "one or more of A, B, and C;" and "A, B, and/or C" are each intended to mean "A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together." In addition, use of the term "based on," above and in the claims is intended to mean, "based at least in part on," such that an unrecited feature or element is also permissible.

[0062] The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claimed embodiments. Thus, it should be understood that although the present application may include discussion of preferred embodiments, exemplary embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art. Such modifications and variations are considered to be within the scope of the disclosed embodiments, as defined by the appended claims. The specific embodiments provided herein are examples of useful embodiments of the present disclosure and it will be apparent to one skilled in the art that they may be carried out using a large number of variations of the devices, device components, and methods steps set forth in the present description. As will be obvious to one of skill in the art, methods and devices useful for the present methods can include a large number of optional compositions and processing elements and steps. The following documents are incorporated by reference, in their entirety:

• Desyatnik, V.N., Dubinin, B Y, Raspopin, S.P., Phase Diagram of the Sodium Chloride-Potassium Chloride-Uranium Trichloride System, Izv. Vyssh. Ucheb. Zaved., Tsvet. Met., 17, 61 (1974).

• Thoma, Roy E , Fast Reactor Fuel, U.S. Patent No 3,287,278

• Cisneros JR., et al., Molten Nuclear Fuel Salts and Related Systems and Methods, U.S. Patent Publication No. 2016/0189813.

• Cheatham ITT, Molten Chloride Fast Reactor and Fuel, U.S. Provisional Patent Application No. 62/234,889.

Claims

CLAIMS What is claimed is:

1. A composition comprising:

about 25 mol % to about 40 mol % UCb;

about 20 mol % to about 70 mol % NaCl;

about 10 mol % to about 70 mol % KC1; and

about 1 mol % to about 10 mol % CaCb.

2. The composition of claim 1, comprising about 5 mol % CaCb

3. The composition of claim 1, comprising about 30 mol % to about 40 mol % UCb.

4. The composition of claim 1 , further comprising MgCb.

5. The composition of claim 1, further comprising UC .

6. The composition of claim 1 , further comprising PuCh.

7. The composition of claim 1, wherein the composition does not include Pu.

8. The composition of claim 1, further comprising at least one of AlCb and AIC .

9. The composition of claim 1, further comprising ZrCU.

10. The composition of claim 1, wherein the melting temperature is within the range from about 418°C to about 500°C.

11. A composition comprising:

about 25 to about 40% UCb;

about 20 to about 70% NaCl;

about 10 to about 70% KC1; and

about 1 to about 10% MgCb.

12. The composition of claim 1 1, comprising about 5 mol % MgCb.

13. The composition of claim 11, comprising about 30 mol % to about 40 mol % UCb.

14. The composition of claim 1, further comprising CaCb.

15. The composition of claim 1 1 , further comprising UCU.

16. The composition of claim 11, further comprising PuCb.

17. The composition of claim 1 1 , wherein the composition does not include Pu.

18. The composition of claim 10, further comprising at least one of AlCb and AICU.

19. The composition of claim 1 1, further comprising ZrCU.

20. The composition of claim 11, wherein the melting temperature is within the range from about 418°C to about 500°C.