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WO2025083189A1 - Sels de chlorure de thorium dans des réacteurs nucléaires à sels fondus - Google Patents

Sels de chlorure de thorium dans des réacteurs nucléaires à sels fondus Download PDF

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WO2025083189A1
WO2025083189A1 PCT/EP2024/079453 EP2024079453W WO2025083189A1 WO 2025083189 A1 WO2025083189 A1 WO 2025083189A1 EP 2024079453 W EP2024079453 W EP 2024079453W WO 2025083189 A1 WO2025083189 A1 WO 2025083189A1
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mixture
salt
mole fraction
mgch
rbci
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Jaén OCÁDIZ FLORES
Sander DE GROOT
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Thorizon Holding BV
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Thorizon Holding BV
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
    • G21C3/42—Selection of substances for use as reactor fuel
    • G21C3/44—Fluid or fluent reactor fuel
    • G21C3/54—Fused salt, oxide or hydroxide compositions
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C1/00—Reactor types
    • G21C1/02—Fast fission reactors, i.e. reactors not using a moderator ; Metal cooled reactors; Fast breeders
    • G21C1/03—Fast fission reactors, i.e. reactors not using a moderator ; Metal cooled reactors; Fast breeders cooled by a coolant not essentially pressurised, e.g. pool-type reactors
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C1/00—Reactor types
    • G21C1/04—Thermal reactors ; Epithermal reactors
    • G21C1/06—Heterogeneous reactors, i.e. in which fuel and moderator are separated
    • G21C1/22—Heterogeneous reactors, i.e. in which fuel and moderator are separated using liquid or gaseous fuel
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C3/00—Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
    • G21C3/02—Fuel elements
    • G21C3/22—Fuel elements with fissile or breeder material in contact with coolant
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E30/00—Energy generation of nuclear origin
    • Y02E30/30—Nuclear fission reactors

Definitions

  • the invention relates to salt mixtures comprising Thorium chloride and their use in a molten salt nuclear reactor systems.
  • the invention further pertains to the use of thorium chloride- containing salt mixtures in reducing the corrosivity of the molten salt towards (transition) metals and/or reducing ceramic degradation in molten salt nuclear reactors.
  • plutonium a long living isotope of which large supplies have been accumulated over the years and that has a large risk of proliferation as it can be used also for non-peaceful activities. Attempts have been made to decrease the volume of plutonium.
  • plutonium is added to present day mixed oxide (MOX) fuels, yet a large fraction of the initial loading remains.
  • the substantial remaining plutonium which can be recovered from spent MOX fuel is enriched in non-fissile isotopes, and reprocessing is uneconomical.
  • only a small percentage ( ⁇ 5%) of minor actinides may be added to MOX fuels.
  • the complexity and costs of MOX fuel production mainly lies in the tight quality assurance and control required for solid fuels, the (re-)qualification of composition variations, for example (potential) heterogeneity or isotopic content variations, the limits of introducing minor actinide ( ⁇ 5%), in combination with the radiological hazards of handling and managing radiotoxic powders and dust.
  • One of the newer generation nuclear plants are so-called molten salt reactors.
  • a molten salt reactor is a type of nuclear reactor where the primary coolant, or even the fuel or target material itself is a molten salt mixture.
  • the early concepts and many current ones rely on nuclear fuel dissolved in molten fluoride salt. The fluid would reach criticality by flowing into a core where a moderator such as graphite can be present.
  • Many known concepts rely on fuel flowing through channels in a graphite matrix with the molten salt providing low pressure, high temperature cooling.
  • the coolant fuel composition can be adjusted relatively conveniently.
  • fluoride salts have been the most used and considered so far, largely due to the fact that fluorine is mono-isotopic and does not require enrichment
  • molten chloride salts have been proposed since very early on in Molten Salt Reactor (MSR) development. For instance, Bulmer, J. J. Fused salt fast breeder: reactor design and feasibility study. Vol. 56. No. 8-204. United States Atomic Energy Commission, Technical Information Service Extension, 1957 and Dumaire et al.
  • WO2017/106509 described salt compositions for molten salt reactors based on UCh, which may be in the combination of UCIS-PuCh-and discloses the use of ThCL as a fuel salt.
  • WO2017/106509 teaches that melting point reduction can be achieved by UCI4. As the presence of UCI4 can lead to increased corrosivity of the structural alloys in view of the electrochemical potential, it is suggested to replace UCI4 with ThCL as it can provide a comparable reduction of the melting point but without the corrosive effects of UCI4.
  • US 2016/0189813 also describes molten salt reactors, focuses on the use of uranium as a fissile material and fuel embodiments including end-members such as UCI3, ThCL, UCI4, and PuCh, alkali chlorides, and alkaline earth chlorides.
  • Molten salt fuels unlike solid ones like MOX, do not need to maintain thermomechanical properties or mechanical integrity, complex solid fuel requalification for each new composition and a complex, expensive and hazardous powder step in the manufacturing process.
  • thermodynamic and transport properties of the fuel must be known as a function of temperature and composition.
  • any nuclear fuel with the advantage that the properties of liquid fuels are state functions. That is, they do not depend on manufacturing history or are influenced by radiation damage, as is the case for solid fuels. Summary of the invention
  • the present inventors have now, in essence, found a set of chloride salt compositions suitable for use in molten salt reactors.
  • the compositions are useful in a burning mode, i.e. burn synthetic transuranics, these being the major actinide plutonium and the minor actinides neptunium, americium, and curium.
  • the compositions are also useful in a breeding mode, i.e. generate fissile isotopes (e.g. 233 U and 239 Pu), for the subsequent generation of energy.
  • the compositions of the invention combine low melting temperatures, relatively high boiling points, reduced redox potential, and reduced solubility for transition metal chlorides, notably those of chromium, nickel, and iron which aids in reducing corrosivity.
  • the invention pertains to a salt mixture for a molten salt reactor comprising thorium tetrachloride (ThCU) and one or more of NaCI, KCI, RbCI, MgCh, CaCh, wherein the ThCU mole fraction in the mixture is from 0.05 to 0.70.
  • ThCU thorium tetrachloride
  • a second aspect relates to a molten salt nuclear reactor comprising the salt mixture of the invention.
  • Fig. 1 shows a quasi-ternary composition diagram displaying a domain , having vertices with composition coordinates 1a: 0.95MCI x -0.05ThCl4, 1 b: 0.3MCIx-0.7ThCl4, 1c: 0.57MCL- 0.03ThCl4-0.4AnCl y and 1d: 0.18MCI x -0.42ThCl4-0.4AnCl y .
  • Another preferred domain with coordinates 2a: 0.90MCIx-0.10ThCI 4 , 2b:0.35MCIx-0.65ThCI 4 , 2c: 0.585MCI x -0.065ThCI 4 - 0.350AnCl y and 2d: 0.228MCI x -0.422ThCl4-0.350AnCl y .
  • Further preferred isa domain with coordinates3a: 0.85MCI x -0.15ThCI 4 , 3b: 0.5MCI x -0.5ThCI 4 , 3c: 0.567MCI x -0.100ThCI 4 - 0.333AnCl y , 3d: 1/3MCI x -1/3ThCl4-1/3AnCl y .
  • MCI X denotes either an alkali chloride, alkaline earth chloride, or mixture thereof, while AnCl y denotes an actinide chloride other than ThCk
  • Fig. 3 is a solubility curve of CrCh in different low-melting chloride mixtures.
  • the invention pertains to a salt mixture for a molten salt reactor comprising thorium tetrachloride (ThCU) and one or more of NaCI, KCI, RbCI, MgCh, CaCh, wherein the ThCU mole fraction in the mixture is from 0.05 to 0.70, preferably from 0.10-0.65, more preferably from 0.15-0.50.
  • the salt mixture of the present invention contains thorium chloride in combination with one or more alkali (Na, K, Rb) or alkaline earth metal (Mg, Ca) chlorides or a combination of alkali (Na, K, Rb) and alkaline earth metal (Mg, Ca) chlorides.
  • ThCU in binary, ternary or quaternary mixtures, i.e. ThCU in combination with one, two or three further salts selected form NaCI, KCI, RbCI, MgCh, and/or CaCh.
  • the ThCU mole fraction in the mixture is from 0.05 to 0.70, preferably from 0.10-0.65, more preferably from 0.15-0.50.
  • compositions which are useful in the design of molten salt reactors and aims to close the current nuclear fuel cycle (i.e. make maximum use of nuclear materials resources, while minimizing the amount of long-lived radiotoxic elements generated, or even reduce the amount of long-lived radiotoxic elements).
  • the thorium fuel cycle (conversion of Th to II) may also be begun in parallel.
  • the salt compositions of the invention are rather specific and are selected to meet performance requirements in several thermophysical characteristics such as melting point and boiling point. Chloride salts can be more easily produced from reprocessing facilities, can accommodate higher actinide concentrations which are favourable for fast spectrum applications, provide lower melting temperatures leading to more manageable system operating temperatures and lower heat load, while the enrichment technology has been developed to levels where enriched chlorine is both available and affordable.
  • Molten salt systems containing natural actinides have certain advantages. Thorium is one such actinide. Its key advantages, used in molten salt reactor systems or in other nuclear reactor systems, include: i) the relative abundance of thorium on the Earth’s crust, especially when compared to that of uranium; ii) its widespread availability as a by-product of rare earth mining, iii) it does not need enrichment; iv) the hard gamma emitters in its fuel cycle, desirable from a safeguards perspective; v) U-233 fuel bred from Th-232 has favorable fission characteristics; vi) a reduced tendency to produce transuranics. The latter characteristic makes it especially preferred as a component in nuclear fuels designed to produce a net decrease in the inventory of transuranics.
  • the salt mixture is a mixture of ThCU with NaCI, KCI, or RbCI, wherein the ThCU mole fraction in the salt mixture is from 0.05 to 0.70, , preferably 0.10-0.65, more preferably from 0.15-0.50.
  • the second salt is NaCI
  • the salt mixture comprises NaCI-ThCU and preferably the mole fraction of ThCU in the salt mixture is 0.20 - 0.55, preferably 0.22-0.50, more preferably 0.25-0.46.
  • a third salt may be present, a mixture of ThCU with NaCI and RbCI .
  • the third salt is RbCI, more preferably the salt mixture comprises NaCI-RbCI-ThCU and preferably the mole fraction of RbCI in the NaCI-RbCI mixture is 0.40-0.70, more preferably 0.45-0.65, even more preferably 0.50 - 0.60.
  • the second salt next to ThCU is KCI, and preferably the mole fraction of ThCU in the salt mixture is 0.40-0.60, preferably 0.43-0.55, more preferably 0.45- 0.52, even more preferably 0.46-0.50.
  • the second salt is RbCI
  • the mole fraction of ThCU in the total salt mixture is 0.40-0.60, preferably 0.43-0.55, more preferably 0.45-0.52, even more preferably 0.46-0.50.
  • the second salt is CaCh
  • the mole fraction of ThCU in the total salt mixture is 0.40-0.60, preferably 0.43-0.55, more preferably 0.45-0.52, even more preferably 0.46-0.50.
  • the mole fraction of ThCU in the salt mixture is 0.40-0.60, preferably 0.43-0.55, more preferably 0.45-0.52, even more preferably 0.46-0.50.
  • the salt mixture is a mixture of ThCU with, in addition to ThCU, two or more salts selected from the group consisting of NaCI, KCI, RbCI, MgCh, or CaCh.
  • a preferred mixture is thorium chloride in combination with a salt combination selected from the group consisting of NaCI-KCI, NaCI-RbCI, KCI-RbCI, NaCI- CaCh, NaCI-MgCh, KCI-MgCh, or RbCI-MgCh.
  • the salt mixture is a mixture of ThCU and a NaCI-KCI mixture wherein the mole fraction of KCI in the NaCI-KCI mixture is 0.35-0.65, preferably 0.40-0.60, more preferably 0.45 - 0.55.
  • the salt mixture is a mixture of ThCU and a KCI-RbCI mixture wherein the mole fraction of RbCI in the KCI-RbCI mixture is 0.50-0.70, preferably 0.52-0.65, more preferably 0.54 - 0.62.
  • the salt mixture is a mixture of ThCU and an NaCI-CaCh mixture wherein the mole fraction of CaCh in the NaCI-CaCh mixture is 0.40- 0.60, preferably 0.45-0.58, more preferably 0.48-0.56, even more preferably 0.50 - 0.54.
  • the salt mixture is a mixture of ThCU and an NaCI-MgCh mixture wherein the mole fraction of MgCh in the NaCI-MgCh mixture is 0.30- 0.55, preferably 0.35-0.50, more preferably 0.38-0.48, even more preferably 0.40 - 0.46.
  • the salt mixture is a mixture of ThCU and a KCI-MgCh mixture wherein the mole fraction of MgCh in the KCI-MgCh mixture is 0.20-0.40, preferably 0.25-0.35, more preferably 0.28 - 0.33.
  • the salt mixture is a mixture of ThCU and an RbCI-MgCh mixture wherein the mole fraction of MgCh in the RbCI-MgCh mixture is 0.20- 0.35, preferably 0.22-0.33, more preferably 0.24 - 0.28.
  • the salt mixture is a mixture of ThCk- NaCI-KCl-MgCh
  • the mole fraction of NaCI is 0.15-0.25, preferably 0.17-0.23, more preferably 0.19 - 0.21
  • the mole fraction of KCI is 0.45-0.60, preferably 0.47-0.55, more preferably 0.52 - 0.53
  • the mole fraction of MgCh is 0.20-0.32, preferably 0.25-0.30, more preferably 0.27 - 0.28;
  • the salt mixture is a mixture of ThCk with three salts selected from the group consisting of NaCI, KCI, RbCI, CaCh.
  • a preferred salt mixture is, in addition to ThCI 4 , KCI-RbCI-MgCh.
  • the salt mixture is a mixture of ThCk- KCI-RbCI-MgCh
  • the mole fraction of KCI is 0.40-0.50, preferably 0.41-0.47, more preferably 0.42 - 0.43
  • the mole fraction of RbCI is 0.22-0.25, preferably 0.23-0.26, more preferably 0.25 - 0.27
  • iii. the mole fraction of MgCh is 0.25-0.40, preferably 0.27-0.37, more preferably 0.30 - 0.35;
  • the salt mixture is a mixture of ThCk- KCI-RbCI-MgCh
  • the mole fraction of KCI is 0.40 - 0.55, preferably 0.45-0.50, more preferably 0.47 - 0.49
  • the mole fraction of RbCI is 0.14-0.20, preferably 0.15-0.19, more preferably 0.16 - 0.18
  • iii. the mole fraction of MgCh is 0.25-0.45, preferably 0.28-0.42, more preferably 0.32 - 0.40.
  • Table 1 lists examples of useful embodiments within the composition spaces discussed above, satisfying melting point, boiling point, and viscosity requirements.
  • the inventors have found melting points lower than 670 K ( -400 degrees Celsius). This is lower than what has been reported to date in the art for similar actinide-bearing chloride salts. Additionally, the inventors have found broad areas in the vicinity of the eutectics in which the liquidus surface rises slowly with respect to changes in composition.
  • the preferred salt mixtures of the invention share that the salt mixture has a melting point below 600 degrees Celsius, preferably below 500 degrees Celsius, more preferably below 400 degrees Celsius.
  • Boiling point A core meltdown scenario is not possible in molten salt reactors, since the fuel is already in the liquid state.
  • the main criterion for composition selection in WO 2017/105609 A1, for example, is the melting point.
  • the boiling point is just as crucial, as a plant shutdown scenario in which the decay heat from fission products is not removed at an adequate rate, due to loss of secondary coolant for instance, may lead to temperature increases which could bring the fuel salt to boil.
  • the composition domain is chosen because the boiling point is more than about 1300 K (-1027 degrees Celsius) everywhere. Combined with the aforementioned low melting points generally found within the domain, fuel compositions with a large solidification- to-boiling margin are found.
  • the preferred salt mixtures of the invention share in preferred embodiments that the salt mixture has a boiling point higher than 1000 degrees Celsius, preferably higher than 1100 degrees Celsius or even 1200 degrees Celsius, even more preferably higher than 1300 degrees Celsius (see Table 1).
  • the salt mixtures of the invention are hence advantageously suitable as salt mixture for molten salt nuclear reactors.
  • the principal domain in the phase diagram in Fig. 1 and hence the salt mixture of the invention is also advantageous because of a favorable viscosity.
  • the viscosity found for the salt mixtures of the invention is found to have an upper bound of about 30 mPa.s near the lowest eutectic temperatures within the domain (e.g. T ⁇ 400 degrees Celsius), and of about 5 mPas (see Table 1) at widely foreseen operating temperatures for molten salt reactors, e.g. above 500 degrees Celsius.
  • the viscosity of the fuel is expected to remain within these bounds with fuel burnup, as a great portion of the fission products will be lanthanide trichlorides with similar viscosities as those of the actinide trichlorides.
  • Alkali chlorides and alkaline earth metal chlorides which will also be soluble in the fuel matrix, in general have a lower viscosity at a given temperature than both lanthanide and actinide trichlorides, and so are also not expected to raise the upper bounds in viscosity.
  • insoluble fission products such as noble gases and metals will have a negligible effect on the liquid fuel viscosity, as they will plate and bubble out of solution, respectively.
  • the salt mixture of the present invention can be used in a breeding mode.
  • breeding in a nuclear reactor, the salt mixture comprising thorium is subjected to a neutron flux allowing thorium to be converted into fissionable product such as uranium.
  • the salt mixture containing uranium can be used as a fuel.
  • the decay daughters of U-232 present in the uranium vector bred from Th-232, emit hard gamma radiation which might give the fuels and blankets disclosed herein strong nonproliferation characteristics. Indeed, such an intense gamma radiation makes unauthorized handling of these salt mixtures very difficult to conceal from relevant safeguards authorities such as Euratom or the International Atomic Energy Agency.
  • UCh or IICI4 natural or depleted uranium as UCh or IICI4, such that the U-233 content in the uranium vector becomes diluted.
  • Such an addition may be in the order of 1-20 mol% of the ThCU mole fraction.
  • salts preferably in the form of salts can be added, preferably in the form of natural or depleted uranium, i.e. rich in the U-238 isotope.
  • the salt mixtures of the invention are combined with an actinide chloride (other than thorium chloride).
  • an actinide chloride other than thorium chloride.
  • the salt mixture is made up of three and up to four chloride salt families: thorium tetrachloride, an alkali chloride and/or alkaline earth metal chloride, or a mixture of alkali chloride and alkaline earth chloride, and a further actinide chloride.
  • This kind of embodiment affords more flexibility and allows the use of thermal, epithermal, and fast reactor designs and to burn the major actinide plutonium, and the minor actinides neptunium, americium, and curium.
  • the use of the salt composition in a nuclear reactor is aimed at the burning of plutonium and/or other minor actinides.
  • the salt mixture in addition to the thorium and the alkali and alkaline earth chlorides, further contains other actinide chlorides than thorium.
  • actinide chlorides can be one or more chosen from the group consisting of UCh, UCI4, NpCh, PuCh, AmCh, and CmCh.
  • PuCh, NpCh, AmCh, and CmCh are preferred as the main actinide components.
  • Such a salt mixture can also be used as an actinide burning blanket.
  • 1-20% of the ThCU mole fraction can be replaced by a natural or depleted uranium salt, preferably UCh and/or IICI4.
  • a natural or depleted uranium salt preferably UCh and/or IICI4.
  • a natural or depleted uranium salt preferably UCh and/or IICI4.
  • an initial salt with the following composition in mole fractions: 0.60NaCI-0.20ThCI4-0.20PuCI3 20% of the ThCI4 fraction is replaced with LICI3 (20% of 0.2 is 0.04)
  • the overall composition ends up being 0.60NaCI-0.16ThCI4-0.04UCI3-0.20PuCI3.
  • One reason for the addition of a uranium salt is to dilute the U-233 vector bred from ThCU with other uranium isotopes, as described above.
  • the amount of UCU is at most 5% of the uranium mole fraction calculated on the total amount of IICI3 and UCU, so as to limit the redox potential of the fuel, as well as its volatility.
  • Fig 1 presents a quasi-ternary composition diagram.
  • One end-member is an alkali chloride, alkaline earth chloride, or a mixture of both, denoted by MClx.
  • Another end member is thorium tetrachloride (ThCU).
  • Yet another member is an actinide chloride (not ThCU), either pure or mixed with other actinide trichlorides.
  • KCI-ThCU- NpCh is thus a system which belongs to this notation, for example, but so is (Na a , Mgb)Cl a +2b- ThCI 4 -(Pu, Am)CI 3 .
  • the salt mixture of the invention can also be characterised as a composition that, preferably in a ternary phase diagram, lies between the following mole fractions: 0.95MCI x -0.05ThCl4, 0.7MCIx-0.3ThCI 4 , 0.57MCIx-0.03ThCI 4 -0.4AnCl y and 0.18MCIx-0.42ThCI 4 -0.4AnCl y .
  • the salt mixture of the invention can be characterised as a composition that, preferably in a ternary phase diagram, lies between the following mole fractions: 0.90MCIx-0.10ThCI 4 , 0.65MCIx-0.35ThCI 4 , 0.585MCIx-0.065ThCI 4 -0.350AnCl y and 0.228MCIx-0.422ThCI 4 -0.350AnCl y .
  • the salt mixture of the invention can be characterised as a composition that, preferably in a ternary phase diagram, lies between the following mole fractions: 0.85MCIx-0.15ThCI 4 , 0.5MCIx-0.5ThCI 4 , 0.567MCIx-0.100ThCI 4 -0.333AnCl y , 1/3MCI x -1/3ThCl4-1/3AnCl y .
  • M is an alkali or alkaline earth selected from the group consisting of Na, K, Rb, Mg, Ca and An is a non-Thorium actinide.
  • FIG. 1 displays a shaded domain, having vertices with composition coordinates 0.85MCI x - 0.15ThCI 4 , 0.5MCIx-0.5ThCI 4 , 0.567MCIx-0.100ThCI 4 -0.333AnCl y , 0.333MCIx-0.333ThCI 4 - 0.333AnCl y , where AnCl y denotes an actinide chloride other than thorium tetrachloride. That is, in preferred embodiments, the global ThCU mole fraction desired is 0.15 ⁇ X(ThCl4) 0.5, while the remaining actinide chloride mole fraction is preferably between 0 ⁇ X(AnCly) ⁇ 0.333.
  • some of the preferred embodiments may be chosen from the KCI-ThCU- PuCI 3 system, within the domain of the invention (FIG. 1), such as compositions in the vicinity of 0.49KCI-0.37ThCI 4 -0.14PuCI 3 and 0.56KCI-0.18ThCI 4 -0.26PuCI 3 .
  • AmCI 3 might be chosen to be 5 mol% of the overall (non-Th) actinide trichloride mole fraction, leaving PuCI 3 as the remaining 95 mol%, such that the global mole fractions become 0.49KCI-0.37ThCI 4 -0.133PuCI 3 -0.007AmCI 3 and 0.56KCI-0.18ThCI 4 -0.247PuCI 3 -0.013AmCI 3 , respectively.
  • Another preferred embodiment might be chosen from the quasi-binary system formed by the phase Na2ThCle and a 1 :1 :1 mixture of NpCI 3 -PuCI 3 -AmCI 3 .
  • Other preferred embodiments in this quasi-ternary system would include 0.579NaCI- 0.315ThCI 4 -0.107AnCI 3 , 0.638NaCI-0.257ThCI 4 -0.104AnCI 3 , and 0.515NaCI-0.399ThCI 4 - 0.086AnCI 3 .
  • the salts of the invention can be used in a molten salt reactor, in the ‘breeding’ configuration and/or in the ‘burning’ configuration, as explained herein elsewhere.
  • a suitable configuration can be a conventional molten salt reactor. It can also be (preferably) a modular core reactor as described in WO2020/225156.
  • the configuration is made up of a constellation of independent salt-loaded cartridges.
  • the salt cartridges individually are subcritical, but together form a critical constellation to sustain an fission reaction.
  • the central cartridge, where the neutron flux is highest could be loaded with such an actinide blanket to perform the transmutation. Alternatively, such a blanket could be used on the outermost cartridges of the core, using a longer residence time to achieve the same level of transmutation.
  • molten salt mixtures of the invention lies in the fuel cycle flexibility they can afford, namely in fissioning and thus extracting value from synthetic actinides which otherwise constitute a radiotoxic burden to be managed at great expense for generations.
  • synthetic transuranic actinides include the major actinide plutonium and the minor actinides neptunium, americium, and curium. They comprise the bulk of what is termed long- lived nuclear ‘waste’.
  • fission products In a molten salt reactor, the chemical speciation of fission products may be classified as saltsoluble, metallic, and noble gases. Within the salt soluble products, there are also those with a high volatility or tendency to evaporate, and their tendency to remain in the fuel salt may not be taken for granted, as in WO 2017/105609 A1 , where it is declared that ‘fission products in molten fuel salts are chemically bound and physically frozen’. Csl is expected to be one a fission product with a tendency to vaporize from the salt.
  • the salt mixtures of the invention express a higher retention of Csl than other viable MSR fuels, such as those based on the LiF-ThF4 system.
  • Iron, nickel, and chromium make up a large fraction of typical steels and alloys used and foreseen in the nuclear industry.
  • One of the issues with nuclear reactors lies in corrosion. It is well established from thermodynamic considerations and static and dynamic experiments that the most susceptible metal to corrosion in chloride media is chromium.
  • the invention thus also involves the use of the salt mixture of the present invention comprising ThCI 4 in the reduction of corrosivity and in the reduction of the solubility of transition metal chlorides, especially CrCh, in molten salt reactors. Since the mass transport of metal from the hot section of a molten salt circuit to its cold leg is proportional to the solubility gradient between the sections, the reduced solubility of the transition metal chlorides in the salt mixtures of the invention is an important feature and advantage of the present invention, especially because large thermal gradients are desired to maximize the power extracted from a reactor. In the tables below, corrosion rates are given in micrometers per year.
  • ThCI 4 has a beneficial effect on the corrosion rate.
  • salt mixtures of the invention preserving or maintaining the integrity of ceramic structural materials
  • actinide trichlorides with ThCI 4 and optional minor additions of UCI 4 minimize said attack and the production of volatile silicon tetrachloride.
  • the fission of the actinide trichlorides mostly results in a combination of noble metals or gases and lanthanide trichlorides which are able to hold chlorine largely to the same extent as the original salt: the net valence state changes little.
  • burnup calculations by the inventors have shown that thorium breeds more uranium slowly. Whatever uranium-233 is bred has favorable fissile characteristics, keeping the overall inventory low.
  • uranium tetrachloride is able to form at a given level of redox potential has its chemical activity diminished, in effect being dissolved by ThCI 4 .
  • Other ceramic materials such as carbon fiber composite, graphite, AI2O3, BeO, MgO, silicon nitride, silicon oxide, Y2O3- stabilized zirconia, ZrO2, may also be corrosion-resistant towards mixtures in the chosen region (Fig. 1).
  • the salt mixture of the invention can also be used to reduce deterioration of ceramic materials in molten salt reactors.

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  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)

Abstract

L'invention concerne un ensemble de compositions de sel contenant du tétrachlorure de thorium, destiné à être utilisé dans des réacteurs nucléaires à sels fondus. Un premier sous-ensemble de modes de réalisation implique des mélanges de ThCl4 avec des chlorures alcalins NaCl, KCl et RbCl, des chlorures alcalino-terreux MgCl2, CaCl2 ou des mélanges de ceux-ci, dans différentes proportions. Les plages de composition les plus utiles sont spécifiées. Un second sous-ensemble de modes de réalisation comprend en outre des chlorures d'actinides autres que le thorium, tels que UCl3, UCl4, PuCl3, et les trichlorures d'actinides mineurs. Les domaines de composition idéals sont également fournis pour ce sous-ensemble de modes de réalisation, et ont été choisis pour s'inscrire dans une enveloppe de conception limitée par les exigences de point de fusion, de point d'ébullition, de viscosité et de rétention de produits de fission. En outre, l'espace de composition comprend des modes de réalisation utiles dans des réacteurs destinés à produire de nouveaux combustibles ou à brûler des éléments transuraniens synthétiques. Dans tous les cas, la présence de ThCl4 confère une corrosivité réduite vis-à-vis des alliages d'ingénierie et une tendance réduite à dégrader les céramiques dans les environnements de réacteurs nucléaires, par rapport aux sels ayant une enveloppe de conception similaire mais sans ThCl4.
PCT/EP2024/079453 2023-10-19 2024-10-18 Sels de chlorure de thorium dans des réacteurs nucléaires à sels fondus Pending WO2025083189A1 (fr)

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