WO2018132366A1 - Contrôle de réacteur nucléaire - Google Patents

Contrôle de réacteur nucléaire Download PDF

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Publication number
WO2018132366A1
WO2018132366A1 PCT/US2018/012929 US2018012929W WO2018132366A1 WO 2018132366 A1 WO2018132366 A1 WO 2018132366A1 US 2018012929 W US2018012929 W US 2018012929W WO 2018132366 A1 WO2018132366 A1 WO 2018132366A1
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WIPO (PCT)
Prior art keywords
volume
absorbent material
nuclear reactor
neutrons
control rod
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PCT/US2018/012929
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English (en)
Inventor
Matthew Shawn ELLIS
Samuel Christopher SHANER
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Yellowstone Energy, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Application filed by Yellowstone Energy, Inc. filed Critical Yellowstone Energy, Inc.
Publication of WO2018132366A1 publication Critical patent/WO2018132366A1/fr

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Classifications

    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C15/00—Cooling arrangements within the pressure vessel containing the core; Selection of specific coolants
    • G21C15/28—Selection of specific coolants ; Additions to the reactor coolants, e.g. against moderator corrosion
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21C—NUCLEAR REACTORS
    • G21C7/00—Control of nuclear reaction
    • G21C7/06—Control of nuclear reaction by application of neutron-absorbing material, i.e. material with absorption cross-section very much in excess of reflection cross-section
    • G21C7/08—Control of nuclear reaction by application of neutron-absorbing material, i.e. material with absorption cross-section very much in excess of reflection cross-section by displacement of solid control elements, e.g. control rods
    • 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

  • Nuclear reactors produce energy based on fission of fuel through interaction between neutrons and the fuel.
  • the fission of fuel produces more neutrons, which leads to further fission of fuel in a neutron chain reaction.
  • the rate of the neutron chain reaction can increase as the temperature of the fuel, coolant, or other reactor components increases.
  • a coolant is used to conduct heat away from the fuel.
  • the density of the coolant decreases. With such a decrease in density, neutron flux in the positive reactivity reactor increases, producing a corresponding increase in the rate of the neutron chain reaction.
  • the use of a coolant to conduct heat away from the fuel can present challenges for controlling certain nuclear reactors to avoid or reduce the likelihood of a runaway neutron chain reaction, particularly during power excursions.
  • Devices, systems, and methods of the present disclosure are generally directed to controlling temperature of a nuclear reactor (e.g., a fast neutron reactor) that is at least partially cooled by a molten salt.
  • the molten salt can cooperate with an absorbent material in at least one control rod in a core of the reactor to control reactivity in the nuclear reactor.
  • Such control can be useful for reducing the likelihood of a runaway nuclear chain reaction during power excursions of the nuclear reactor.
  • a method of controlling a nuclear reactor includes producing a neutron chain reaction, passing heat and neutrons from the neutron chain reaction through a molten salt, a moderator material and into a volume defined by at least one control rod, and absorbing at least a portion of the neutrons in a vapor phase of an absorbent material in the volume of the at least one control rod.
  • the moderator material decreases energy of the neutrons passing though the moderator material, and the heat passing into the volume defined by the at least one control rod increases pressure of the vapor phase of the absorbent material in the volume.
  • the molten salt can have a macroscopic elemental absorption cross-section of greater than about 0.003 [1/cm] at about 0.025 eV.
  • the molten salt can include one or more of a nitrate salt, a fluoride salt, and a chloride salt.
  • the molten salt can include a nitrogen-enriched nitrate salt.
  • a combined temperature coefficient of the molten salt and the at least one control rod can be negative.
  • a rate of the neutron chain reaction can decrease as a rate of absorption of the neutrons in the volume defined by the at least one control rod increases, and the rate of absorption of the neutrons in the volume can increase with an increase in the pressure of the vapor phase of the absorbent material in the volume.
  • the at least one control rod can be thermally conductively insulated from the neutron chain reaction.
  • the at least one control rod can be thermally conductively insulated from the neutron chain reaction by one or more of a vacuum sleeve, a gas sleeve, and a low thermal conductivity solid sleeve.
  • passing heat and neutrons from the chain reaction through the molten salt and the moderator material and into the volume defined by the at least one control rod can include radiative transfer of heat into the volume through absorption of photons (e.g., gamma rays) in the absorbent material in the volume.
  • a rate of radiative heat transfer into the volume can be greater than a rate of conductive heat transfer into the volume.
  • the moderator material can include a metal hydride (e.g., zirconium hydride). Additionally, or alternatively, the moderator material includes one or more of hydrogen, beryllium, lithium, and carbon.
  • a metal hydride e.g., zirconium hydride
  • the moderator material includes one or more of hydrogen, beryllium, lithium, and carbon.
  • the neutron chain reaction can include fission of a fuel (e.g., uranium).
  • a fuel e.g., uranium
  • absorbing at least a portion of the neutrons in the vapor phase of the absorbent material transmutes nuclei of the absorbent material.
  • transmuting nuclei of the absorbent material forms a stable isotope of the absorbent material.
  • the absorbent material can include mercury, and absorbing at least a portion of the neutrons in the vapor phase of the absorbent material forms a mercury isotope. Additionally, or alternatively, the absorbent material can include boron halide (e.g., boron iodide), and absorbing at least a portion of the neutrons in the absorbent material forms lithium.
  • boron halide e.g., boron iodide
  • pressure of the vapor phase of the absorbent material in the volume can increase non-linearly with an increase in temperature of the volume resulting from the heat passed into the volume of the at least one control rod.
  • pressure of the vapor phase of the absorbent material in the volume can double with about a 50 °C increase in temperature of the volume.
  • the absorbent material in the volume upon passing the heat and the neutrons into the volume, can be above a boiling temperature of the absorbent material at atmospheric pressure.
  • the absorbent material in the volume can have a boiling temperature of greater than about 0 °C and less than about 600 °C at atmospheric pressure.
  • the volume can contain a second material (e.g., one or more of rubidium, sodium, and potassium) having an elemental cross-section less than an elemental cross-section of the absorbent material such that the second material is relatively inert, as compared to the absorbent material, as the neutrons are received in the volume.
  • the absorbent material and the second material can have respective vapor pressures.
  • the vapor pressure of the absorbent material can vary with temperature according to a first rate
  • the vapor pressure of the second material can vary with temperature according to a second rate, the first rate differing from the second rate over at least a portion of a temperature range from about 0 °C to about 1000 °C.
  • a first portion of the absorbent material can be in a liquid phase and a second portion of the absorbent material can be in a vapor phase.
  • the absorbent material in the liquid phase can occupy greater than about 5 percent and less than about 15 percent of the volume.
  • the at least one control rod includes a substantially cylindrical housing, the substantially cylindrical housing defining the volume.
  • the volume can be a constant volume up to at least about 100 atmospheres.
  • producing the neutron chain reaction includes producing more than about 50 percent of power of the nuclear reactor by neutrons with an energy of about 1 keV or greater.
  • producing the neutron chain reaction includes producing less than about 50 percent of power of the nuclear reactor by neutrons with an energy of about 1 keV or less.
  • a nuclear reactor can include a core, a plurality of fuel rods disposed in the core, a molten salt movable through the core to conduct thermal energy away from the plurality of fuel rods, a moderator material, the molten salt movable in the core between the moderator material and the plurality of fuel rods,, energy of neutrons from a neutron chain reaction of the plurality of fuel rods reduceable by the moderator material, at least one control rod defining a volume, heat and the neutrons from the neutron chain reaction passable into the volume via at least the molten salt, and an absorbent material in the volume, pressure of a vapor phase of the absorbent material increasable as heat passes into the volume, and at least a portion of the neutrons in the volume absorbable by the absorbent material in the vapor phase.
  • the moderator material can be disposed about at least a portion of the at least one control rod, and heat and neutrons from the neutron chain reaction are passable into the volume via the molten salt and the moderator material.
  • the moderator material can be spaced apart from the at least one control rod, and the molten salt is movable in the core between the moderator material and the at least one control rod.
  • the molten salt can have a macroscopic elemental absorption cross-section of greater than about 0.003 [1/cm] at about 0.025 eV.
  • the molten salt includes a nitrate salt.
  • the nitrate salt can be enriched with N-15 nitrogen.
  • the nuclear reactor can further include an insulator disposed about the at least one control rod, the insulator thermally conductively insulating the at least one control rod from the molten salt.
  • the insulator can include a sleeve disposed about the at least one control rod.
  • the insulator can include a vacuum sleeve, a gas sleeve, a solid sleeve, or a combination thereof.
  • radiative heat can be passable into the volume at a rate greater than conductive heat is passable into the volume.
  • the moderator material includes a metal hydride (e.g., zirconium hydride). Additionally, or alternatively, the moderator material can include one or more of hydrogen, beryllium, lithium, and carbon.
  • a metal hydride e.g., zirconium hydride
  • the moderator material can include one or more of hydrogen, beryllium, lithium, and carbon.
  • the plurality of fuel rods includes uranium.
  • nuclei of the absorbent material are transmutable by absorption of the neutrons to form a stable isotope of the absorbent material.
  • the absorbent material can include mercury.
  • the absorbent material can include boron halide (e.g., boron iodide).
  • pressure of the vapor phase of the absorbent material in the volume is non-linearly increasable with an increase in temperature of the volume as heat passes into the volume.
  • pressure of the vapor phase of the absorbent material in the volume can double with about a 50 °C increase in temperature of the volume.
  • the absorbent material in the volume can have a boiling temperature of greater than about 0 °C and less than about 600 °C at atmospheric pressure.
  • the system can further include a second material (e.g., one or more of rubidium, sodium, and potassium) in the volume.
  • the second material can have, for example, an elemental cross-section less than an elemental cross-section of the absorbent material such that the second material is relatively inert, as compared to the absorbent material, with respect to neutrons passing into the volume.
  • the absorbent material and the second material can have respective vapor pressures, the vapor pressure of the absorbent material varying with temperature according to a first rate, the vapor pressure of the second material varying with temperature according to a second rate, the first rate differing from the second rate over at least a portion of a temperature range from about 0 °C to about 1000 °C.
  • the volume can be substantially cylindrical. [0034] In certain implementations, the volume can be a constant volume up to at least about 100 atmospheres.
  • Implementations can include one or more of the following advantages.
  • the nuclear reactor includes a molten salt.
  • the molten salt can be a useful alternative to lead-based or sodium-based coolants used in certain types of nuclear reactors.
  • the molten salt can offer advantages with respect to one or more of cost, corrosion, chemical reactivity, melting point, and operational challenges in certain types of nuclear reactor designs.
  • the molten salt can be used as a coolant in a fast neutron reactor design, in which propagation of a neutron chain reaction is dependent upon fast neutrons.
  • the nuclear reactor includes an absorbent material in a volume defined by at least one control rod.
  • the absorbent material can have a vapor phase having a pressure that increases with an increase of absorbed heat. Because the vapor phase of the absorbent material absorbs at least a portion of neutrons passing through the vapor phase and the pressure of the vapor phase increases with absorbed heat, the absorbent material can have a negative temperature coefficient. In certain instances, the negative temperature coefficient of the absorbent material can be useful for facilitating the use of a molten salt as a coolant in a nuclear reactor design in which a positive temperature coefficient of the molten salt is otherwise prohibitive.
  • the absorbent material can be placed in a position and in an amount suitable for achieving a reactivity temperature coefficient that is negative, neutral, or otherwise achieves a target value in a nuclear reactor cooled by a molten salt.
  • the absorbent material can facilitate the use of a molten salt as a coolant in a wider range of reactor designs to realize one or more of the advantages associated with the use of the molten salt as an alternative to other types of coolants such as, for example, lead-based or sodium-based coolants.
  • the nuclear reactor includes an absorbent material in a volume defined by at least one control rod, with a temperature coefficient of the absorbent material in the volume being substantially self-regulating.
  • the absorbent material in the volume defined by the at least one control rod can facilitate, for example, rapid and robust control of a nuclear reactor over power excursions.
  • FIG. 1 is a schematic representation of a nuclear reactor.
  • FIG. 2 is a cross-section of the core of the nuclear reactor of FIG. 1, the cross- section taken along line A-A in FIG. 1.
  • FIG. 3 is a two-dimensional schematic representation of a fuel assembly of the core of FIG. 2.
  • FIG. 4 is a cross-section of a control rod of the fuel assembly of FIG. 3.
  • FIG. 5 is a graph of simulated normalized fission rates as a function of axial height of the nuclear reactor of FIG. 1 with and without the at least one control rod of FIG. 4.
  • FIG. 6 is a flow chart of a method of controlling a nuclear reactor.
  • FIG. 7 is a cross-section of a control rod of a fuel assembly with an insulator disposed about the control rod.
  • FIG. 8 is a graph of a simulation of macroscopic absorption cross-section as a function of energy for a nitrate salt and for a nitrate salt enriched with N-15 nitrogen.
  • FIG. 9 is a schematic representation of a vapor phase of an absorbent material and a second material mixed with one another in a volume defined by the at least one control rod of FIG. 4.
  • FIG. 10 is a graph of a simulated combined temperature coefficient of a molten salt and different compositions of a material contained in the control rod of FIG. 4, the simulated combined temperature coefficient shown as a function of temperature.
  • FIG. 11 is a two-dimensional schematic representation of a fuel assembly of a core.
  • temperature coefficient should be understood in the context of temperature feedback in a control loop including a neutron chain reaction.
  • a negative temperature coefficient of an element or elements of a reactor should be understood to refer to a decrease in power of the reactor as the local temperature of the element or elements increases.
  • a positive temperature coefficient of an element or elements of a reactor should be understood to refer to an increase in power of the reactor as the local temperature of the element or elements increases.
  • such a positive temperature coefficient in an element or elements of a reactor can increase the likelihood of a runaway condition of the neutron chain reaction (e.g., with an increase in temperature of the element increasing the rate of the neutron chain reaction which, in turn, increases the temperature of the element, etc.).
  • reactivity temperature coefficient is an overall temperature coefficient of the reactor.
  • the temperature coefficient of each element can contribute to the reactivity temperature coefficient.
  • an element with a positive temperature coefficient can be controlled through an arrangement of one or more elements with a negative temperature coefficient such that the reactivity temperature coefficient of the reactor is negative, neutral, or otherwise tuned to a desired reactivity temperature coefficient.
  • a nuclear reactor 10 can include a core 12 and a cooling system 14 in fluid communication with the core 12.
  • the core 12 can include a pressure vessel 16 in which one or more fuel assemblies 18 is disposed.
  • Each fuel assembly 18 can include, for example, a plurality of fuel rods 20, at least one control rod 22, and a moderator material 24 disposed about at least a portion of the at least one control rod 22.
  • the nuclear reactor 10 can be, for example, a fast neutron reactor in which a neutron chain reaction is propagated by fast neutrons moving through each fuel assembly 18.
  • a fast neutron reactor should be understood to include a nuclear reactor in which a majority (e.g., greater than about 50 percent) of power is produced by neutrons with an energy of about 1 keV or greater.
  • the at least one control rod 22 can have a negative temperature coefficient that is self-regulating through power excursions of the nuclear reactor 10.
  • the negative temperature coefficient of the at least one control rod 22 can be used in combination with a molten salt 26 (which can have a macroscopic elemental absorption cross-section of greater than about 0.003 [1/cm] at 0.025 eV and a positive temperature coefficient) to achieve an overall negative, neutral, or otherwise tune reactivity temperature coefficient of the nuclear reactor 10.
  • a molten salt 26 which can have a macroscopic elemental absorption cross-section of greater than about 0.003 [1/cm] at 0.025 eV and a positive temperature coefficient
  • the devices, systems, and methods of the present disclosure should be understood to facilitate the use of the molten salt 26 in fast neutron reactors, in which the positive temperature coefficient of the molten salt 26 would otherwise be considered unsuitable.
  • the devices, systems, and methods of the present disclosure can facilitate using the molten salt 26 as an alternative to other types of coolants used in fast neutron reactors, such as lead-based and sodium-based coolants, which can offer significant advantages with respect to, for example, one or more of cost, corrosion, chemical reactivity, melting point, and operational challenges.
  • the core 12 can include, for example, an extrusion defining a plurality of substantially parallel orifices in which one or more of the plurality of fuel rods 20, the at least one control rod 22, and the moderator material 24 can be positioned.
  • the core 12 can include an active fuel section of about 2 meters and a radial dimension of about 2 meters and, more generally, can be of a size sufficient to facilitate retrofitting existing reactor designs to replace light water reactors (-33 percent efficient) with more efficient fast neutron reactors (e.g., greater than about 40 percent efficient) cooled by a proven coolant such as the molten salt 26.
  • an outer portion of the core 12 can include a material that reflects neutrons such that the neutrons produced in the neutron chain reaction of the material of the plurality of fuel rods 20 remains substantially within the core 12.
  • the plurality of fuel rods 20 can include an actinide (e.g., uranium, plutonium, or a combination thereof).
  • the plurality of fuel rods 20 can include fuel in a pellet oxide form. Additionally, or alternatively, the plurality of fuel rods 20 can extend through at least a portion of each fuel assembly 18 such that the molten salt 26 flows through the core 12 in a direction substantially parallel to an axial direction of the plurality of fuel rods 20 (e.g., in a direction from the bottom of the core 12 to the top of the core 12).
  • the molten salt 26 can be solid at standard temperature and pressure and a thermally stable liquid at an operating temperature of the nuclear reactor 10.
  • the molten salt 26 can be in a thermally stable liquid phase at a temperature of greater than about 150 °C and less than about 525 °C.
  • the molten salt 26 can include one or more of a nitrate salt, a fluoride salt, and a chloride salt.
  • the cooling system 14 can move the thermally stable liquid phase of the molten salt 26 into the core 12.
  • the cooling system 14 can pump the molten salt 26 through the core 12 at a rate based on one or more of an operating temperature of the core 12 and power output of the nuclear reactor 10.
  • the cooling system 14 can be a closed system such that the molten salt 26 is recirculated through the cooling system 14 during operation of the nuclear reactor 10.
  • the cooling system 14 can move the molten salt 26 through a heat exchanger external to the core 12. More generally, unless otherwise specified or made clear from the context, it should be understood that the cooling system 14 can be any one or more of various different cooling systems known in the art for moving a coolant through a core of a nuclear reactor.
  • the molten salt 26 can be in thermal communication with the plurality of fuel rods 20.
  • the molten salt 26 can be in thermally conductive communication with the plurality of fuel rods 20 through one or more thermally conductive layers between the molten salt 26 and the plurality of fuel rods 20.
  • each of the fuel rods 20 can be disposed in a sleeve (e.g., a steel sleeve) and the molten salt 26 can be in contact with the respective sleeve of each fuel rod of the plurality of fuel rods 20 to conduct heat away from the plurality of fuel rods 20. It should be appreciated that such a sleeve can be useful for protecting the material of the plurality of fuel rods 20 from direct contact with the molten salt 26.
  • the molten salt 26 can flow in each fuel assembly 18 to conduct thermal energy away from the plurality of fuel rods 20 in the respective fuel assembly 18. As the molten salt 26 conducts thermal energy away from the plurality of fuel rods 20, at least a portion of the neutrons generated by the nuclear chain reaction of the material of the plurality of fuel rods 20 can pass through the molten salt 26. Thus, more generally, at least a portion of the thermal energy and neutrons generated by the nuclear chain reaction of the material of the plurality of fuel rods 20 can move through the molten salt 26 and into the at least one control rod 22 via the moderator material 24.
  • the density of the molten salt 26 can decrease as the temperature of the molten salt 26 increases. As the density of the molten salt 26 decreases, more neutrons can pass through the molten salt 26 which, in turn, can increase the rate of propagation of the nuclear chain reaction of the plurality of fuel rods and, thus, further increase temperature of the molten salt 26. Thus, in such implementations, the molten salt 26 should be understood to have a positive temperature coefficient. As described in greater detail below, the increase in neutrons passing through the molten salt 26 as temperature increases can be counteracted by a combination of the moderator material 24 and the at least one control rod 22, as described in greater detail below.
  • the moderator material 24 can act as a flux trap for at least a portion of the neutrons generated in a neutron chain reaction of the plurality of fuel rods 20. That is, the moderator material 24 can absorb at least a portion of the energy of some of the neutrons to slow down the neutrons (e.g., through collisions with atoms of the moderator material 24). As described in greater detail below, in the context of a fast neutron reactor, slowing down at least a portion of the neutrons through the moderator material 24 can be useful for controlling an operating temperature of the nuclear reactor 10 through the use of the at least one control rod 22.
  • the moderator material 24 can be substantially stationary with respect to the plurality of fuel rods 20 and the at least one control rod 22.
  • the molten salt 26 can flow between the moderator material 24 and the plurality of fuel rods 20 as the material of the plurality of fuel rods 20 undergoes a neutron chain reaction.
  • the moderator material 24 can be disposed in a sleeve such that the molten salt 26 does not come into direct contact with the moderator material 24. Such isolation of the moderator material 24 from the molten salt 26 can be useful, for example, for prolonging the life of the moderator material 24 by reducing the likelihood of unintended reactions between the moderator material 24 and the molten salt 26.
  • the sleeve can be formed of one or more materials having a high thermal conductivity (e.g., steel) such that heat in the molten salt 26 is readily conducted into the moderator material 24 through the sleeve.
  • a high thermal conductivity e.g., steel
  • the moderator material 24 can be, for example, disposed among the plurality of fuel rods 20 in each fuel assembly 18. As a more specific example, the moderator material 24 can be positioned as pins spaced at regular intervals with respect to the plurality of fuel rods 20. More generally, the amount and position of the moderator material 24 in each fuel assembly 18 can be based on a variety of factors related, for example, to absorbing neutrons in the at least one control rod 22 to achieve a target reactivity temperature coefficient of the nuclear reactor 10.
  • the moderator material 24 can be any one or more of a solid, a liquid, or a gas confined to a respective pin of the moderator material 24 within the core 12.
  • the moderator material 24 can include any one or more of zirconium hydride, hydrogen, beryllium, lithium, and carbon. Additionally, or alternatively, the moderator material 24 can include a metal hydride. More generally, the moderator material 24 can be any one or more material suitable for absorbing energy from neutrons through collisions between atoms of the moderator material 24 and the neutrons. In certain implementations, the moderator material 24 can be formed of layers of different types of material.
  • the moderator material 24 can define an orifice to accommodate positioning the at least one control rod 22.
  • the at least one control rod 22 can be slid into the moderator material 24 as the core 12 is assembled.
  • the at least one control rod 22 can be in less than all of the pins of the moderator material 24.
  • the at least one control rod 22 can define a volume 28.
  • an axial dimension of the volume 28 can be larger than a radial dimension of the volume 28.
  • the volume 28 can be substantially cylindrical, which can, among other advantages, facilitate withstanding high pressures of gasses in the volume 28.
  • the volume 28 can be a constant volume up to at least about 100 atmospheres.
  • the axial dimension of the volume 28 can be substantially parallel to an axial dimension of the plurality of fuel rods 20 and an axial dimension of the moderator material 24.
  • Such parallel positioning of the axial dimension of the volume 28 relative to the respective axial dimensions of the plurality of fuel rods 20 and the moderator material 24 can be useful for presenting a maximum area of the volume 28 as a target for neutrons moving from the plurality of fuel rods 20 through the moderator material 24.
  • the at least one control rod 22 can be penetrable by conductive heat, radiative heat (e.g., photons in the form of gamma rays), and neutrons passing through the moderator material 24 such that the heat and neutrons can pass from the moderator material 24 into the volume 28.
  • the at least one control rod 22 can be formed of steel.
  • the at least one control rod 22 can be formed of a material having a thickness greater than about 200 microns and less than about 1500 microns. Such a range of material thickness can, for example, provide sufficient structural strength of the at least one control rod 22 (e.g., to resist deformation under pressure of contents of the volume 28) while facilitating suitable passage of heat and neutrons into the volume 28 to achieve temperature control, as described in greater detail below.
  • An absorbent material 30 can be contained by the volume 28 defined by the at least one control rod 22. Pressure of a vapor phase 30v of the absorbent material 30 can increase as heat passes into the volume 28, and at least a portion of the neutrons in the volume 28 are absorbable by the absorbent material 30 in the vapor phase 30v. Thus, an increase in
  • the absorbent material 30 should be understood to be a passive control mechanism with a negative temperature coefficient. As compared to actively controlled mechanisms (e.g., actuators, valves, etc.), the passive control achievable through changes in the vapor phase 30v of the absorbent material 30 in the volume 28 can, for example, provide advantages with respect to safe operation of the nuclear reactor 10 through excursions in power.
  • the response of the vapor phase 30v of the absorbent material 30 to heat and neutrons in the volume 28 can be useful for overcoming certain constraints associated with the positive temperature coefficient of the molten salt 26.
  • the combined temperature coefficient of the molten salt 26 and the absorbent material 30 can be negative.
  • achieving the combined negative temperature coefficient of the molten salt 26 and the absorbent material 30 is based on balancing design tradeoffs associated with the nuclear reactor 10.
  • the absorbent material 30 has a negative temperature coefficient
  • the vapor phase 30v of the absorbent material 30 absorbs neutrons that would otherwise be used to produce power and, thus, the absorbent material 30 can be associated with a slight power offset as compared to a reactor without the absorbent material 30.
  • the negative temperature coefficient of the molten salt 26 and the absorbent material 30 can be achieved through the use of a large volume of the absorbent material 30 relative to the molten salt 26, it is generally desirable to use as little of the absorbent material 30 as required to achieve the desired combined negative temperature coefficient of the molten salt 26 and the absorbent material 30.
  • FIG. 5 is a graph of simulated normalized fission rates 51 and 52 as a function of axial height of the nuclear reactor 10 (FIG. 1).
  • the simulated normalized fission rate 51 corresponds to a condition in which the at least one control rod 22 is inserted in the core 12
  • the simulated normalized fission rate 52 corresponds to a condition without the at least one control rod 22 inserted in the core 12.
  • the simulated normalized fission rates 51 and 52 were calculated with a three-dimensional fuel assembly model in a Monte Carlo nuclear reactor analysis code.
  • the simulated normalized fission rates 51 and 52 correspond to fission rates of fuel rods of the plurality of fuel rods 20 next to the position of the at least one control rod 22 at a steady state operating condition of the nuclear reactor 10. As shown by a comparison of the simulated normalized fission rate 51 to the simulated normalized fission rate 52 in FIG. 5, the absorbent material 30 can be selectively positioned in the nuclear reactor 10 in a quantity that has little to no impact on the normalized fission rates of the plurality of fuel rods 20 under steady state operation of the nuclear reactor 10.
  • the absorbent material 30 can have a boiling point in a range suitable for achieving an increase in vapor pressure of the vapor phase 30v of the absorbent material 30 at typical operating temperature of the nuclear reactor 10.
  • the absorbent material 30 can have a boiling temperature of greater than about 0 °C and less than about 600 °C at atmospheric pressure.
  • the portion of the absorbent material 30 that is not in the vapor phase 30v can be, for example, in a liquid phase, a solid phase, or a combination thereof.
  • the pressure of the vapor phase 30v of the absorbent material 30 can increase through sublimation of a solid to a vapor.
  • the pressure of the vapor phase 30v of the absorbent material 30 can increase through evaporation of a liquid to a vapor.
  • the vapor phase 30v of the absorbent material 30 is within a pressure range of about 1 atmosphere to about 100 atmospheres in the volume 28.
  • the vapor phase 30v of the absorbent material 30 can occupy less than about 95 percent and greater than about 85 percent of the volume 28 over a pressure range of about one atmosphere to about 100 atmospheres.
  • the presence of at least a portion of the absorbent material 30 in a non-vapor phase in the volume 28 can be useful, for example, for temperature control that can accommodate brief variations in conditions beyond intended design points.
  • nuclei of the absorbent material 30 can be transmutable by absorption of the neutrons to form a stable isotope of the absorbent material.
  • the absorbent material 30 can include mercury. In such instances, neutrons penetrating the at least one control rod 22 and entering the volume 28 can be absorbable by the absorbent material 30 to form a mercury isotope. Additionally, or alternatively, the absorbent material 30 can include a boron halide (e.g., boron iodide). In such instances, neutrons penetrating the at least one control rod 22 and entering the volume 28 can be absorbable by the absorbent material 30 to form lithium.
  • boron halide e.g., boron iodide
  • the at least one control rod 22 may need to be replaced periodically over the life of the nuclear reactor 10 to ensure that a sufficient amount of the absorbent material 30 is present in the volume 28 to achieve suitable temperature control of the nuclear reactor 10.
  • pressure of the vapor phase 30v of the absorbent material 30 in the volume 28 can be non-linearly increasable with an increase in temperature of the volume 28 as heat (through conductive heat transfer, radiative heat transfer, or both) passes into the volume 28.
  • a non-linear increase in pressure of the vapor phase 30v as a function of temperature can be useful for providing rapid control in a given temperature range.
  • the pressure of the vapor phase 30v of the absorbent material 30 in the volume 28 can double with about a 50 °C increase in temperature of the volume 28.
  • FIG. 6 is a flow chart of an exemplary method 60 of controlling a nuclear reactor. Unless otherwise specified or made clear from the context, the exemplary method 60 can be carried out using any one or more of the corresponding devices and systems described herein. Thus, for example, any one or more of the various different implementations of the absorbent material 30 (FIG.4) can be used to carry out the exemplary method 60 unless otherwise indicated or made clear from the context.
  • the exemplary method 60 can include producing 62 a neutron chain reaction, passing 64 heat and neutrons from the neutron chain reaction through a molten salt, a moderator material, and into a volume defined by at least one control rod, and absorbing 66 at least a portion of the neutrons in a vapor phase of the absorbent material in the volume of the at least one control rod.
  • the moderator material can be, for example, any of the various different moderator materials described herein and, in general, can decrease energy of the neutrons passing 64 through the moderator material to facilitate absorbing 66 at least a portion of the neutrons in the vapor phase of the absorbent material.
  • heat passing into the volume can increase pressure of the vapor phase of the absorbent material in the volume to increase the number of neutrons absorbed 66 in the vapor phase of the absorbent material. Because the absorption of the neutrons can reduce the rate of the production 62 in the neutron chain reaction, it should be appreciated that the increased absorption 66 of neutrons resulting from increased heat passed into the volume of the at least one control rod results in a negative temperature coefficient useful for controlling temperature of a nuclear reactor during, for example, power excursions.
  • producing 62 the neutron chain reaction can include reacting fuel formed as a plurality of fuel rods.
  • a nuclide of the fuel can undergo a nuclear chain reaction in which a neutron interacts with the nuclide to form a compound nucleus (e.g., U-236), which can fission into two fission products to emit neutrons, photons (e.g., high energy photons such as gamma rays), and heat.
  • the interaction of the neutrons with additional nuclides of the fuel can propagate a nuclear chain reaction, with the rate of propagation being a function of temperature.
  • Passing 64 heat and neutrons from the neutron chain reaction through a molten salt, a moderator material, and into the volume can be based on relative positioning of the molten salt and the moderator material relative to the plurality of fuel rods such that the passing 64 heat and neutrons from the neutron chain reaction occurs passively during operation of the nuclear reactor.
  • the amount of heat and neutrons passed 64 into the volume is a function of the temperature of the nuclear reactor. Because the temperature is a function of the rate of propagation of the nuclear chain reaction, the amount of heat and neutrons passed 64 into the volume should be understood to be a function also of the rate of propagation of the nuclear chain reaction. Thus, as the temperature of the nuclear reactor and, thus, the rate of propagation of the nuclear chain reaction increases for a given set of conditions, the amount of heat and neutrons passing into the volume increases.
  • the absorbent material in the volume should be understood to have a negative temperature coefficient useful for controlling the temperature of the nuclear reactor, particularly given that the molten salt has a positive temperature coefficient.
  • the negative temperature coefficient of the absorbent material is based on properties of the absorbent material itself, the negative temperature coefficient of the absorbent material should be understood to be rapid and self- regulating.
  • controlling temperature of the nuclear reactor through the use of the absorbent material can offer significant advantages with respect to safe operation of the nuclear reactor.
  • an insulator 70 can be disposed about the at least one control rod 22.
  • the insulator 70 can be, for example, a sleeve disposed between the at least one control rod 22 and the moderator material 24.
  • the insulator 70 can insulate the at least one control rod from conductive heat transfer from the molten salt (e.g., conductive heat transfer from the molten salt 26 in FIGS. 1 and 3).
  • high energy photons e.g., gamma rays
  • the insulator 70 can facilitate heating the absorbent material 30 in the volume primarily through radiative heat transfer. Because conductive heat transfer from the fuel rods into the volume 28 can be significantly slower than radiative heat transfer from the fuel rods into the volume 28, conductive heat transfer into the volume 28 can, in some implementations, interfere with the control of temperature using the absorbent material 30 in the volume. Accordingly, the insulator 70 can facilitate rapid control of temperature of the nuclear reactor 10 (FIG. 1) as the nuclear reactor 10 undergoes rapid changes in operating conditions.
  • the insulator 70 can have a thermal conductivity less than a thermal conductivity of one or both of the at least one control rod 22 and the moderator material 24.
  • the insulator 70 can include a vacuum sleeve.
  • the insulator 70 can include a gas sleeve.
  • the insulator can include a solid sleeve.
  • the insulator has been described as being a discrete material, separate from the at least one control rod and the moderator material, it should be appreciated that other configurations are additionally or alternatively possible.
  • one or both of the at least one control rod and the moderator material can be formed of a low thermal conductivity material to insulate the volume 28 from thermally conductive heat transfer.
  • molten salt has been described as including, in certain implementations, one or more of a nitrate salt, a fluoride salt, and a chloride salt
  • other components can be additionally or alternatively added to the molten salt to achieve target performance parameters in a given reactor design.
  • FIG. 8 is a graph of
  • the macroscopic absorption cross-sections as a function of energy is shown for a nitrate salt 81 and for a nitrate salt enriched with N-15 nitrogen 82.
  • the macroscopic absorption cross-section values were calculated from the E DF/B-VII.1 ACE data, the Brookhaven National Laboratory National Nuclear Data Center, available at http://www.nndc.bnl.gOv/endf/b7. l/acefiles.html.
  • Nitrogen is naturally about 99.6% N-14 and about 0.4% N-15.
  • the absorption cross-section of N-14 is much larger than the absorption cross-section of N-15.
  • enriching the nitrate salt with N-15 can substantially reduce the absorption cross-section of nitrate salt. This can be useful, for example, for reducing the number of control rods required to achieve suitable temperature control in a given reactor design. That is, the nitrogen-enriched nitrate salt can have a lower temperature coefficient than the unenriched nitrate salt and, thus, for a given reactor design, fewer control rods can be used to achieve a target reactivity temperature coefficient.
  • the vapor phase 30v of the absorbent material 30 can be mixed with a second material 90 in a volume (e.g., the volume 28 of the at least one control rod 22 in FIG. 4).
  • the second material can facilitate, for example, achieving a target reactivity
  • the second material 90 can have an elemental cross-section that is less than an elemental cross-section of the vapor phase 30v absorbent material 30 such that the second material 90 is relatively inert with respect to neutrons passing into the volume 28 (FIG. 4).
  • the absorbent material 30 and the second material 90 can have respective vapor pressures.
  • the vapor pressure of the absorbent material 30 can vary with temperature according to a first rate
  • the vapor pressure of the second material 90 can vary with temperature according to a second rate differing from the first rate over a temperature range from about 0 °C to about 1000 °C.
  • the second material 90 can include one or more of rubidium, sodium, and potassium.
  • FIG. 10 is a graph of the simulated temperature coefficient expressed as a function of temperature of various compositions of material contained in a control rod (e.g., the at least one control rod 22 in FIGS. 3 and 4).
  • the control rod was placed in a reactor cooled by a molten salt (e.g., the molten salt 26 in FIGS. 1 and 3) and the simulated combined temperature coefficient was computed.
  • the results shown in FIG. 10 are based on a simulation of the nuclear reactor 10 using a Monte Carlo reactor analysis tool. Multiple Monte Carlo reactor simulations were performed at varying power levels (i.e.
  • FIG. 10 shows the influence of changing the nuclide composition of the absorbing material in the control rod. More specifically, FIG. 10 shows temperature coefficient as a function of temperature for a nitrate salt along curve 102, for a combination of Hg and nitrate salt along curve 104, for Hg along curve 106, and for 199 Hg along curve 108.
  • the use of 199 Hg in the at least one control rod can facilitate achieving a strongly negative combined temperature coefficient that decreases as the temperature increases.
  • the combined temperature coefficient and thus the reactivity temperature coefficient, can be tuned by adjusting the composition of the contents in the material in the at least one control rod.
  • the combined temperature coefficient of the molten salt and the contents of the at least one control rod can be increased slightly through the addition of sodium.
  • the nuclear reactor 10 can be a thermal reactor or an epi- thermal reactor (e.g., a reactor in which a greater than about 50 percent of the powder is produced by neutrons with an energy of less than about 1 keV).
  • one or more of the size, type, and position of the moderator material 24, and the at least one control rod 22, or a combination thereof can be varied to achieve neutron energy levels suitable for configuring the nuclear reactor 10 as a given type of reactor. That is, a thermal reactor configuration of the nuclear reactor 10 can generally include more of the moderator material 24 than a fast neutron reactor configuration of the nuclear reactor 10.
  • the molten salt 26 can be used as a coolant instead of water (which is commonly used as a moderator material in thermal reactors). Because water reduces neutron energy and, thus, acts as a moderator in a thermal reactor, it should be appreciated that replacing water with the molten salt 26 can require the use of a separate moderator material.
  • the degree of neutron moderation required to configured the nuclear reactor 10 as a thermal reactor can be achieved by using a larger amount of the moderator material 24, the at least one control rod 22, or a combination thereof, as compared to analogous amounts used in a fast reactor configuration.
  • the molten salt 26 has a higher boiling point. Accordingly, as compared to the use of water as a coolant in a thermal reactor, the use of the molten salt 26 in the nuclear reactor 10 configured as a thermal reactor can facilitate the use of a higher outlet temperature (resulting in higher efficiency) at lower pressures. By facilitating achievement of higher efficiency at lower pressures as compared to water, the use of the molten salt 26 in a configuration in which the nuclear reactor 10 is configured as a thermal reactor can have significant advantages with respect to safety, as compared to water. Given such advantages, it should be appreciated that it can be desirable to form the nuclear reactor 10, configured as a thermal reactor, through retrofitting a water-cooled thermal reactor.
  • a fuel assembly 18' can include the plurality of fuel rods 20, at least one control rod 22', and a moderator material 24'.
  • the at least one control rod 22' can be separate from the moderator material 24' such that, for example, the molten salt 26 can move between the at least one control rod 22' and the moderator material 24' .
  • the at least one control rod 22' should be understood to be the same as the at least one control rod 22 described above with respect to FIG. 3, except that the at least one control rod 22' is spaced apart from the at moderator material 24' .
  • fuel assembly 18' can be used
  • the above systems, devices, methods, processes, and the like may be realized in hardware, software, or any combination of these suitable for the control, data acquisition, and data processing described herein.
  • a realization of the processes or devices described above may include computer-executable code created using a structured programming language such as C, an object oriented programming language such as C++, or any other high-level or low-level programming language (including assembly languages, hardware description languages, and database programming languages and technologies) that may be stored, compiled or interpreted to run on one of the above devices, as well as
  • a structured programming language such as C
  • an object oriented programming language such as C++
  • any other high-level or low-level programming language including assembly languages, hardware description languages, and database programming languages and technologies
  • processors may be distributed across devices such as the various systems described above, or all of the functionality may be integrated into a dedicated, standalone device. All such permutations and combinations are intended to fall within the scope of the present disclosure.
  • Embodiments disclosed herein may include computer program products comprising computer-executable code or computer-usable code that, when executing on one or more computing devices, performs any and/or all of the steps of the control systems described above.
  • the code may be stored in a non-transitory fashion in a computer memory, which may be a memory from which the program executes (such as random access memory associated with a processor), or a storage device such as a disk drive, flash memory or any other optical, electromagnetic, magnetic, infrared or other device or combination of devices.
  • any of the control systems described above may be embodied in any suitable transmission or propagation medium carrying computer-executable code and/or any inputs or outputs from same.
  • performing the step of X includes any suitable method for causing another party such as a remote user, a remote processing resource (e.g., a server or cloud computer) or a machine to perform the step of X.
  • performing steps X, Y and Z may include any method of directing or controlling any combination of such other individuals or resources to perform steps X, Y and Z to obtain the benefit of such steps.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Structure Of Emergency Protection For Nuclear Reactors (AREA)

Abstract

Les dispositifs, systèmes et procédés de la présente invention concernent généralement la régulation de température d'un réacteur nucléaire (par exemple, un réacteur à neutrons rapides) qui est au moins partiellement refroidi par un sel fondu. Le sel fondu peut coopérer avec un matériau absorbant dans au moins une tige de commande dans un cœur du réacteur pour contrôler la réactivité dans le réacteur nucléaire. Un tel contrôle peut être utile pour réduire la probabilité d'une réaction de chaîne nucléaire d'emballement pendant des excursions de puissance du réacteur nucléaire.
PCT/US2018/012929 2017-01-12 2018-01-09 Contrôle de réacteur nucléaire WO2018132366A1 (fr)

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WO2024086974A1 (fr) * 2022-10-24 2024-05-02 中广核研究院有限公司 Matrice, tige de commande, ensemble de commande de réacteur, et système

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Publication number Priority date Publication date Assignee Title
US20130083878A1 (en) * 2011-10-03 2013-04-04 Mark Massie Nuclear reactors and related methods and apparatus
US20150117589A1 (en) * 2012-05-30 2015-04-30 Takashi Kamei Molten Salt Reactor
US20160005497A1 (en) * 2013-02-25 2016-01-07 Ian Richard Scott A practical molten salt fission reactor

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20130083878A1 (en) * 2011-10-03 2013-04-04 Mark Massie Nuclear reactors and related methods and apparatus
US20150117589A1 (en) * 2012-05-30 2015-04-30 Takashi Kamei Molten Salt Reactor
US20160005497A1 (en) * 2013-02-25 2016-01-07 Ian Richard Scott A practical molten salt fission reactor

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2024086974A1 (fr) * 2022-10-24 2024-05-02 中广核研究院有限公司 Matrice, tige de commande, ensemble de commande de réacteur, et système

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