JP2016156729A - Nuclear reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nuclear reactor which does not require a control rod, a control rod drive device, an emergency core cooling pump, and an emergency power source for stopping nuclear fission reaction, and which is excellent in safety.SOLUTION: A nuclear reactor (10) including a reactor core (1) uses such characteristics that the leakage of neutrons from the reactor core (1) increases due to rise of temperature of the reactor core(1) so that a chain of nuclear fission in the reactor core (1) is naturally extinguished.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nuclear reactor installed in a nuclear power plant or the like.

  Nuclear power plants and large military ships are equipped with nuclear reactors. A nuclear reactor is a device for continuing nuclear fission reactions. The nuclear reactor was designed to be rugged to accommodate the core containing the nuclear fuel material, the control rod installed in a removable manner with respect to the core, the control rod drive for driving the control rod, and the core And a nuclear reactor vessel. The power control of the nuclear reactor is performed by controlling the nuclear fission reaction by inserting and removing the control rod from the core (see, for example, Patent Document 1).

  The nuclear reactor is also provided with an emergency core cooling pump and an emergency power supply for supplying power for operating the emergency core cooling pump. These operate in the event that a nuclear reactor fails and control of the nuclear fission reaction becomes impossible, thereby preventing a rise in the temperature of the core.

JP 2012-163438 A

  However, in the nuclear reactor having the above-described configuration, the control rod and the control rod driving device are complicated in structure, so that installation and maintenance are not easy, which causes a decrease in the safety of the nuclear reactor. In addition, when a reactor in operation fails and the emergency core cooling pump fails or the emergency power supply is lost, the temperature rise of the core cannot be suppressed and a criticality accident of the reactor occurs. There is a safety problem that there is a risk of doing.

  Therefore, in view of the circumstances described above, the present invention aims to provide a nuclear reactor that ensures the safety of the core and eliminates the need for a control rod, a control rod drive device, an emergency core cooling pump, and an emergency power source. And

  In order to achieve the above object, a first invention is a nuclear reactor including a core, and the property that the neutron leakage from the core increases due to the temperature rise of the core and the nuclear fission chain naturally disappears. Is a nuclear reactor characterized by the use of

  A second invention is the nuclear reactor according to the first invention, wherein the nuclear power is connected to a power generation facility that converts electric energy generated by heat generated by the core into electric energy and supplies electric power, and It is a nuclear reactor that utilizes the property that the fission reaction follows as the temperature of the core changes according to the increase or decrease.

  A third invention is the nuclear reactor according to the first or second invention described above, wherein the fuel of the core is formed from a metal fuel.

  In a fourth invention, the metal fuel of the nuclear reactor of the third invention described above has uranium and plutonium, and uranium immerses the used metal fuel in a molten salt, and uses the used metal fuel as an anode. It has uranium recovered from spent metal fuel by a process including a step of applying a voltage by setting an iron bar installed in the molten salt as a cathode, and plutonium contains a crucible containing liquid cadmium in the molten salt. The plutonium recovered by the process including the step of charging, applying the voltage by setting the spent fuel as the anode and liquid cadmium as the cathode, and heating the alloy formed inside the crucible Is a nuclear reactor characterized by

  A fifth invention is the nuclear reactor according to any one of the first to fourth inventions described above, comprising a nuclear reactor vessel that accommodates the core, and the nuclear reactor vessel has a single-wall structure. It is a nuclear reactor characterized by this.

  According to the first invention, even when the temperature of the core rises in an emergency, the nuclear fission chain naturally disappears, so that the reactor can be safely and reliably stopped. In this way, the safety of the core is ensured, so there is no need to provide a facility for stopping the fission reaction in the nuclear reactor, such as a control rod, a control rod drive device, an emergency core cooling pump, or an emergency power supply. . In addition, a reactor vessel that accommodates an extremely safe core as described above can have a simpler and less expensive structure. Therefore, it is possible to provide a nuclear reactor that is extremely safe and can be installed at low cost.

  In the nuclear reactor of the second invention, when the power demand in the power generation facility increases, the amount of energy transferred from the reactor to the power generation facility increases, so that the temperature of the core decreases and the density of the core increases. Then, it becomes difficult for neutrons to leak out of the core, the nuclear fission reaction increases, and the power of the reactor automatically increases. Conversely, when the power demand in the power generation facility decreases, the amount of energy transferred from the reactor to the power generation facility decreases, so that the temperature of the core rises and the density of the core decreases. Then, neutrons easily leak out of the core, the nuclear fission reaction decreases, and the power of the reactor automatically decreases. Thus, the output of the nuclear reactor of the second invention automatically follows in accordance with the increase or decrease in power demand in the power generation facility. Therefore, in the reactor of the second invention, since it is not necessary to control the output of the reactor from the outside during operation, it is not necessary to provide a facility for controlling the output of the reactor such as a control rod and a control rod driving device, Naturally, the operator of these facilities is also unnecessary. Therefore, according to the second invention, it is possible to provide a nuclear reactor that can be installed and operated at a lower cost.

  In the nuclear reactor according to the third aspect of the invention, a metal fuel is employed as a fuel constituting the core. However, a metal fuel has a higher thermal conductivity and a smaller heat capacity than an oxide fuel (ceramic fuel), and therefore, thermal expansion. The ratio is high, and the fuel density lowers as the temperature of the core rises, so that the fission reaction can be more effectively reduced when the temperature of the core rises. Further, when the metal fuel rises to a certain temperature, the metal fuel itself becomes a foam, and the fission reaction cannot be continued. Therefore, according to the third aspect of the invention, even when the temperature of the core rises in an emergency, the reactor can be stopped more safely and reliably.

  According to the fourth invention, the metal recovered from the used metal fuel is used for a part or all of the metal fuel, so that the metal resources constituting the metal fuel can be effectively used.

  According to the fifth invention, since the reactor vessel is formed with a single-wall structure, the reactor is manufactured and maintained easily and at a lower cost than in the case of a multi-wall structure. be able to.

It is a schematic sectional drawing which shows an example of the nuclear reactor which concerns on 1st Embodiment. It is a schematic block diagram which shows an example of the electric power generation system which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below. In the drawings, in order to describe the embodiment, the scale is appropriately changed and expressed, for example, a part of the drawing is enlarged or emphasized.

<First Embodiment>
First, the configuration of the nuclear reactor according to the first embodiment of the present invention will be described. The nuclear reactor of the first embodiment is installed in a nuclear power plant, for example. FIG. 1 is a schematic configuration diagram illustrating an example of a nuclear reactor according to the first embodiment. As shown in FIG. 1, the nuclear reactor 10 includes a core 1, an annular reflector 2, and a nuclear reactor vessel 3.

  The core 1 has a metal fuel. As the metal fuel, for example, an alloy composed of 60 to 80% uranium (U), 10 to 30% plutonium (Pu) and 7 to 15% zirconium (Zr), or 85 to 20% enriched uranium. An alloy having a composition of 93% and zirconium of 7 to 15% is used. However, since 20% enriched uranium is expensive, an alloy of the former configuration using inexpensive plutonium is desirable as the metal fuel. The metal fuel formed from the alloy having the above-described structure has flexibility because it contains zirconium, and fuel breakage occurs even if the reactor 10 is repeatedly used for a long period of 30 years or more after repeated increases and decreases. Hateful. Therefore, it is unnecessary or can reduce the frequency of the fuel exchange during the operation period of the nuclear reactor. As the metal fuel, an alloy in which a burnable poison (combustible poison) is mixed with the above-described alloy may be employed. In this case, the neutron absorption ability is reduced by the combustion (fission) of the metal fuel. Therefore, it becomes possible to use metal fuel for a longer period. Specifically, the metal fuel of the first embodiment is an alloy composed of 70% uranium 238, 20% plutonium 239, and 10% zirconium. However, the metal fuel is not limited to the above configuration.

  One reactor core 1 is installed in the reactor vessel 3. The core 1 is formed in a substantially cylindrical shape, and is arranged so that the length direction is the vertical direction. The dimensions of the core 1 are not particularly limited. For example, the height (length) H is 2 meters or less, and the cross-sectional area diameter (width) D in the direction orthogonal to the axial direction (length direction) is 1 meter. Set to: The core 1 having this configuration can output about 20,000 kilowatts. The core 1 of the first embodiment is specifically an ultra-compact core in which the height H is set to 2 meters and the diameter D is set to 0.9 meters, and the output of the reactor 10 is set to 10,000 kilowatts. The

  The core 1 is formed by bundling a number of fuel pins (not shown). The fuel pin is filled with metal fuel. The fuel pin is formed into a shape such as a prism or a cylinder having a cross-sectional width (outer diameter) of 1 centimeter and a length of 2 meters, for example.

  The annular reflector 2 is formed, for example, in a cylindrical shape, and the thickness is set, for example, to 0.5 meters. The annular reflector 2 is provided in the nuclear reactor vessel 3 and is installed so as to be slidable from below the core 1 while surrounding the core 1.

  The nuclear reactor vessel 3 is formed so as to accommodate the core 1 and the annular reflector 2. The nuclear reactor vessel 3 has a cylindrical shape, and its inner diameter is set to 1.5 meters, for example. The reactor vessel 3 is filled with a first coolant 4 and an inert gas 5. The reactor vessel 3 has a single-wall structure. Therefore, the manufacturing, installation, and maintenance costs of the reactor vessel 3 are reduced as compared with a reactor vessel having a multi-wall structure.

The first coolant 4 is for transmitting heat energy generated by nuclear fission in the core 1 to a heat exchanger 30 described later, and circulates between the reactor vessel 3 and the heat exchanger 30. As the first coolant 4, liquid sodium (Na) is used, but pressurized water (H ₂ O) or the like may be used instead. The inert gas 5 is accommodated above the liquid level of the first coolant 4 in the reactor vessel 3. As the inert gas 5, for example, argon gas (Ar) is used.

Next, the operation of the nuclear reactor 10 will be described.
First, when neutrons collide with plutonium 239 in the metal fuel of the core 1, nuclear fission (combustion) occurs and the core 1 generates heat. At that time, neutrons leak outside from the core 1, but in the lower part of the core 1 surrounded by the annular reflector 2, the leaked neutrons are reflected by the annular reflector 2 and return to the core 1. Nuclear fission is maintained. The heat generated by such fission is directly transferred to the first coolant 4.

  During the operation of the nuclear reactor 10, the annular reflector 2 gradually moves at a very low speed from the lower part to the upper part of the side surface (circumferential surface) of the core 1. Thereby, combustion (fission) of the core 1 is maintained over a long period of time.

After the operation of the nuclear reactor 10 is stopped, the spent metal fuel is taken out from the nuclear reactor 10. The taken-out spent metal fuel is reprocessed. Specifically, the spent metal fuel is reprocessed, for example, by the following steps.
First, the used metal fuel is taken out from the used fuel pin taken out from the core 1. Next, the spent metal fuel is sheared and immersed in the molten salt in a state of being put in an iron (Fe) container. The molten salt is, for example, a liquid in which a lithium chloride (LiCl) solution and a potassium chloride (KCl) solution at 500 ° C. are mixed at a ratio of 1: 1.

  Subsequently, according to the principle of electrolysis, a spent metal fuel is set as the anode, and an iron (Fe) rod installed in the molten salt is set as the cathode, and a voltage of, for example, 2 volts is applied. The time for which the voltage is applied is, for example, 10 to 12 hours. Then, the metal in the spent metal fuel is dissolved as chloride ions in the molten salt. And uranium deposits on the surface of the cathode iron bar. Thereafter, the iron bar is taken out from the molten salt, and the iron bar and uranium adhering to the surface are separated. Through the above steps, uranium is recovered from the spent metal fuel.

  Subsequently, a crucible containing liquid cadmium (Cd) is charged into the molten salt, and a voltage is applied with the spent metal fuel set as the anode and liquid cadmium (Cd) set as the cathode. The voltage is 2 volts, for example, and the voltage is applied for 10 to 12 hours, for example. Then, a plutonium-cadmium alloy (PuCd6) is formed inside the crucible. Thereafter, the plutonium-cadmium alloy is taken out from the molten salt and heated to 1300 ° C., for example. As a result, cadmium is evaporated and separated from the plutonium-cadmium alloy, and the plutonium remains. Through the above steps, plutonium is recovered from the spent metal fuel.

  When the metal fuel has uranium 238 as in the present embodiment, plutonium 239 is formed in the used metal fuel, so that the plutonium 239 and uranium 238 are recovered from the used metal fuel, If mixed at a ratio, the metal fuel can be formed again. In addition, when reprocessing gold spent metal fuel using the dry reprocessing method described above, wet reprocessing such as separating and purifying uranium and plutonium after dissolving the metal of the metal fuel in an aqueous solution such as nitric acid. Compared to the case where the method is used, the cost can be reduced to about 1/16. Further, according to the dry reprocessing method described above, since no aqueous solution is used in the reprocessing step, the amount of waste liquid generated by reprocessing is extremely small compared to the wet reprocessing method, and the volume of radioactive waste is 1 / 100th. There is an advantage that it can be suppressed to the extent.

  According to the configuration of the nuclear reactor 10 described above, the core 1 has a slender shape with a diameter D set to 1 meter or less, so that in addition to the relatively small amount of nuclear energy held by the core 1, Even if an abnormal temperature rise occurs in the core 1 due to the accident, the fuel density in the core 1 is reduced and neutrons are likely to leak to the outside, so the number of neutrons inside the core 1 is reduced and the core is reduced. The fission chain of 1 disappears naturally. Therefore, a safer nuclear reactor 10 can be provided.

  Further, by using a metal fuel having a higher thermal expansion coefficient than that of the oxide fuel as the fuel of the core 1, the fuel of the core 1 is rapidly expanded due to a rapid temperature rise of the core 1, and the fuel density is increased. Since it decreases immediately, the fission chain of the core 1 can be eliminated more quickly and reliably. In addition, since the fuel in the core 1 includes a metal fuel, the fuel in the core 1 is maintained for a long period of time as compared with the case of oxide fuel combustion, so that frequent replacement of the fuel in the reactor 10 becomes unnecessary. . In addition, when the metal fuel reaches about 1000 ° C., the fuel itself softens rapidly, and the gaseous fission product contained in the metal in the fuel expands into bubbles and expands to reduce the fuel density to about 1100 ° C. Then, the metal fuel itself becomes a foam and the fission reaction cannot be continued. Therefore, even if the temperature of the core 1 is increased due to an accident, the reactor 10 can be stopped more safely and reliably.

  Further, as described above, by ensuring the safety of the core 1 accommodated in the reactor vessel 3, the configuration of the reactor vessel 3 can be simplified, such as adopting a single-wall structure. This makes it possible to reduce the cost associated with the installation and maintenance of the nuclear reactor 10.

  Furthermore, according to the structure of the nuclear reactor 10, facilities such as a control rod and a control rod driving device for safely stopping the fission reaction of the core 1 from the outside, and an emergency core for cooling the core 1 in an emergency. There is no need to install equipment such as a cooling pump or emergency power supply. In addition, operators and monitoring personnel for these facilities are not required. Therefore, the cost for installation and operation of the reactor 10 can be reduced, and the risk of failure of the reactor 10 as a whole can be reduced. Therefore, according to such a nuclear reactor 10, a highly safe nuclear reactor can be provided at low cost.

Second Embodiment
Next, the structure of the electric power generation system concerning 2nd Embodiment of this invention is demonstrated. In the following description, the same or equivalent components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted or simplified.
FIG. 2 is a schematic configuration diagram illustrating an example of a power generation system according to the second embodiment. As shown in FIG. 2, the power generation system 100 includes a nuclear reactor 10, first coolant pipes 21 and 22, a heat exchanger 30, a turbine generator (power generation facility) 40, a second coolant pipe 41, 42 and a heat radiator 50. The power generation system 100 is, for example, a nuclear power plant.

  The nuclear reactor 10 is buried underground. Thereby, compared with the case where the nuclear reactor 10 is installed on the ground, the earthquake resistance and sealing performance of the nuclear reactor 10 can be improved.

  The first coolant pipes 21 and 22 connect the reactor vessel 3 of the nuclear reactor 10 and the heat exchanger 30. The first coolant pipe 21 connects the upper side surface of the reactor vessel 3 and the upper side surface of the heat exchanger 30. The high temperature first coolant 4 heated in the reactor vessel 3 flows through the first coolant piping 21. Further, the first coolant pipe 22 connects the lower side surface of the reactor vessel 3 and the lower side surface of the heat exchanger 30. The low temperature first coolant 4 that has passed through the heat exchanger 30 flows through the first coolant pipe 22. An electromagnetic pump P is provided in the first coolant pipe 22.

  The heat exchanger 30 performs heat exchange between the first coolant 4 and the second coolant 6. A plurality of heat transfer tubes 31 through which the first coolant 4 passes are installed inside the heat exchanger 30. The heat exchanger 30 is installed on the ground.

The second coolant 6 receives thermal energy from the first coolant 4 in the heat exchanger 30, thereby driving the turbine generator 40. The second coolant 6 is supercritical carbon dioxide gas (CO ₂ ), but may be water or steam (H ₂ O).

  The turbine generator 40 includes, for example, a gas turbine 40a having a rotating shaft and a plurality of blades attached to the side surface of the rotating shaft. The gas turbine 40 a is driven by the fluid energy of the second coolant 6. Electricity generated in the turbine generator 40 is transmitted via a transmission line and a substation (not shown) and used as a power source for home use and business use.

  The second coolant pipes 41 and 42 connect the heat exchanger 30 and the turbine generator 40. The second coolant pipe 41 is drawn from the upper part of the side surface of the heat exchanger 30. The second coolant pipe 42 is connected to the lower part of the side surface of the heat exchanger 30 and is provided with an injector (not shown).

  The radiator 50 is installed to release heat generated in the nuclear reactor 10 to the outside in an emergency. It is not used during normal operation of the power generation system 100. The radiator 50 is installed on the ground and includes a large number of radiator plates 51.

Next, the operation of the power generation system 100 will be described.
First, the metal fuel in the core 1 burns (fission). Then, the metal fuel generates heat and the temperature of the core 1 rises. Then, the heat of the core 1 is transmitted to the first coolant 4. The first coolant 4 that has reached a high temperature rises inside the reactor vessel 30 and is sent to the heat exchanger 30 via the first coolant piping 21.

  In the heat exchanger 30, the heat of the first coolant 4 is transferred to the second coolant 6 through the heat transfer tube 31. The 1st coolant 4 used as high temperature flows into the turbine generator 40 via the 2nd coolant piping 41, and drives the gas turbine 40a. As a result, electricity is generated in the turbine generator 40.

  During normal operation of the power generation system 100, the valve 23 installed in the first coolant pipes 21 and 22 is opened. When the electromagnetic pump P is operated, the first coolant 4 is changed in the order of the reactor vessel 3, the first coolant pipe 21, the heat exchanger 30, the first coolant pipe 22, and the reactor vessel 3. Circulate with. The second coolant 6 circulates in the order of the heat exchanger 30, the second coolant pipe 41, the turbine generator 40, the second coolant pipe 42, and the heat exchanger 30. The second coolant 6 in the second coolant pipe 42 flows into the heat exchanger 30 via the injector. Further, during normal operation, the radiator 50 is not used, and the valve 52 installed in the pipe connecting the reactor vessel 3 and the radiator 50 is closed.

  In the power generation system 100, when the output of the turbine generator 40 increases due to an increase in power demand, the amount of energy transferred from the reactor 10 to the turbine generator 40 via the first and second coolants 4 and 6 increases. Therefore, the temperature of the core 1 decreases, and in the thin core 1 having a diameter D of 1 meter or less, the density increases and the nuclear reaction in the core 1 increases. Conversely, when the output of the turbine generator 40 decreases due to a decrease in power demand, the amount of energy transferred from the nuclear reactor 10 to the turbine generator 40 decreases. Therefore, the temperature of the core 1 rises, and in the thin core 1 having a diameter D of 1 meter or less, the density is lowered and the nuclear reaction in the core 1 is reduced. As described above, the power generation system 100 has the property that the nuclear fission reaction of the core 1 follows in accordance with the increase or decrease of the power demand in the turbine generator 40, that is, the load followability. Since the power generation system 100 employs a metal fuel that rapidly and greatly changes in volume due to a heat change as the nuclear fuel of the core 1, the load follow-up response speed described above is fast and has a remarkable effect. .

  In an emergency such as when an accident occurs in the nuclear reactor 10, the valve 23 provided in the first coolant pipes 21 and 22 is closed and provided in the pipe connecting the reactor vessel 3 and the radiator 50. The valve 52 is opened. Then, the first coolant 4 circulates through the reactor vessel 3 and the radiator 50, whereby heat inside the reactor 10 is released to the outside through the first coolant 4 and the radiator 50, so that the core The temperature rise of 1 is suppressed.

  Thus, in the power generation system 100, the output of the nuclear reactor 10 is automatically controlled according to the power demand in the turbine generator 40. Therefore, since it is not necessary to adjust the output according to the electric power demand in the nuclear reactor 10, a control device for adjusting the output of the nuclear reactor 10 is not necessary. Therefore, according to the power generation system 100, in the nuclear reactor 10, it is possible to supply power at a low cost by omitting installation of devices for stopping the nuclear fission reaction of the core 1 and adjusting the output.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the description mentioned above, A various change is possible in the range which does not deviate from the summary of this invention. For example, the core 1 may be installed in the reactor vessel 3 such that the length direction is inclined with respect to the vertical direction. Further, the core 1 is not limited to a substantially cylindrical shape, and may be a prismatic shape or the like. Further, the number of the cores 1 in the reactor vessel 3 is not limited to one, and a plurality of cores 1 may be arranged at intervals. When a plurality of cores 1 are installed in the reactor vessel 3 as described above, the number of outputs of the reactor is obtained by multiplying the number of outputs of the core 1 by the number of installations. According to the reactor in this case, Safety is ensured and high output can be achieved. Further, the core 1 (fuel pin) is not limited to a configuration having a metal fuel, and may have an oxide fuel or the like instead of the metal fuel. Further, the reactor vessel 3 may have a shape having a square tube instead of a cylinder, and a multiple wall structure may be adopted instead of a single wall structure.

  In addition, the power generation equipment connected to the nuclear reactor 10 of the present invention is not limited to the turbine generator 40, and finally converts energy generated due to heat generated in the nuclear reactor 10 into electric energy. If it is. Further, the gas turbine 40a in the turbine generator 40 may be driven by the first coolant 4 instead of the second coolant 6. In this case, the power generation system includes the second coolant 6 and the heat exchanger 30. In addition, the turbine generator 40 may be connected to the coolant pipes 21 and 22 without providing the second coolant pipes 41 and 42.

DESCRIPTION OF SYMBOLS 1 ... Core 3 ... Reactor vessel 10 ... Reactor 40 ... Turbine generator (power generation equipment)

Claims (5)

A nuclear reactor with a core,
A nuclear reactor characterized in that leakage of neutrons from the core increases due to a rise in temperature of the core, and the nuclear fission chain naturally disappears. Connected to a power generation facility for supplying electric power by converting energy generated by heat generated in the core into electric energy;
The nuclear reactor according to claim 1, wherein the reactor uses the property that the temperature of the core changes and the fission reaction follows in accordance with an increase or decrease in demand for electric power in the power generation facility.   The nuclear reactor according to claim 1, wherein the fuel in the core is a metal fuel. The metal fuel has uranium and plutonium,
The uranium is
The spent metal fuel is immersed in a molten salt, the spent metal fuel is set as an anode, an iron bar installed in the molten salt is set as a cathode, and a voltage is applied to the spent metal fuel. With uranium recovered from
The plutonium is
Charging a crucible containing liquid cadmium into the molten salt, applying the voltage by setting the spent fuel as an anode and the liquid cadmium as a cathode;
Heating the alloy formed inside the crucible;
The nuclear reactor according to claim 3, comprising plutonium recovered by a process including Comprising a reactor vessel containing the core;
The nuclear reactor according to any one of claims 1 to 4, wherein the nuclear reactor vessel has a single-wall structure.

Images