JP2002181976A - Nuclear reactor and nuclear plant equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively use nuclear fuel resources without reprocessing spent fuel. SOLUTION: The spent fuel and auxiliary metal fuel which offsets a deficiency in reactivity resulting from the use of the spent fuel to maintain fission chain reaction are loaded in a core 4 and a gas is used as a cooling material 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nuclear reactor and a nuclear power plant provided with the same. More specifically, the present invention relates to a nuclear reactor that uses spent fuel, depleted uranium, and recovered uranium, which have been difficult to treat and dispose as fuel, and is suitable for utilizing recycled fuel resources, and a nuclear power plant including the same. is there.

[0002]

2. Description of the Related Art Conventionally, spent fuel used in a nuclear reactor is:
They have been disposed of as radioactive waste, or have been reprocessed to separate and recover plutonium and uranium (recovered uranium) and reprocessed into nuclear fuel.

[0003]

However, when the spent fuel is discarded as it is, a large amount of uranium and plutonium remaining in the spent fuel are also discarded, and the fuel can be effectively used as nuclear fuel. Resources are wasted in large quantities. In addition, since a large amount of uranium and plutonium that are originally reusable are discarded, radioactive waste is generated more by that amount.

When reprocessing spent fuel,
Although the effective use of uranium and plutonium remaining in spent fuel is possible, reprocessing leads to other problems,
For example, special equipment and radiation control for reprocessing are required, and problems specific to reprocessing such as generation of new high-level radioactive waste in the reprocessing step occur. Also,
In the present situation where the nuclear fuel cycle has not been realized, separated uranium and plutonium must be stored for a long period of time, and it is necessary to reuse uranium and plutonium in a method that can be realized early and separately from the nuclear fuel cycle.

[0005] On the other hand, there is also a demand for effective utilization of depleted uranium, which is a by-product when enriching uranium 235 from natural uranium.

[0006] The present invention provides a nuclear reactor capable of effectively utilizing nuclear fuel resources without reprocessing spent fuel,
An object of the present invention is to provide a nuclear power plant using this nuclear reactor.

[0007]

In order to achieve the above object, a nuclear reactor according to the first aspect of the present invention comprises a spent fuel and an auxiliary for maintaining the fission chain reaction by supplementing the lack of reactivity caused by the use of the spent fuel. Metal fuel is loaded into a reactor core, and gas is used as a coolant.

For example, the spent fuel of a light water reactor is uranium 235
Is contained, and contains fission products that are poisons. Therefore, even if only spent fuel is loaded into the core, the effective multiplication factor cannot be increased to 1 or more, and the reactivity becomes 0.
It is difficult to do this. However, the lack of reactivity, that is, the reactivity required to bring the reactivity to zero or to a value above zero, can be compensated for by loading the auxiliary metal fuel. That is, in the nuclear reactor of the present invention, an auxiliary metal fuel is loaded in addition to the spent fuel to maintain the fission chain reaction. In addition, a gas that does not slow down neutrons compared to liquid metals and water is used as a coolant, and an auxiliary metal fuel that is a metal fuel that does not slow down neutrons compared to oxide fuels or nitride fuels is used. The conversion of uranium 238 remaining in the spent fuel to plutonium is efficiently performed.
The converted plutonium contributes to maintaining the fission chain reaction.

Further, the nuclear reactor according to the present invention uses any of depleted uranium, recovered uranium, enriched uranium, natural uranium and uranium mixed with plutonium as an auxiliary metal fuel. When depleted uranium or recovered uranium is used as the auxiliary metal fuel, depleted uranium, a by-product of enrichment of uranium 235, or recovered uranium (depleted uranium) recovered by reprocessing the fuel can be effectively used. When uranium enriched with uranium, natural uranium, or plutonium is used as an auxiliary metal fuel,
Compared with depleted uranium and recovered uranium, it is easier to maintain a fission chain reaction in the early stage of burning spent fuel.

[0010] The nuclear reactor according to claim 3 uses uranium enriched with uranium or a mixture of plutonium in the early stage of combustion of the spent fuel as an auxiliary metal fuel, and responds to the accumulation of plutonium due to the combustion of the spent fuel. Depleted uranium or recovered uranium. Therefore, it is easy to maintain the fission chain reaction in the early stage of the combustion of the spent fuel, and the depleted uranium and recovered uranium can be effectively used.

Further, a nuclear power plant according to a fourth aspect is provided with the nuclear reactor according to any one of the first to third aspects. Therefore, a nuclear power plant that effectively utilizes uranium resources is provided.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail based on the best mode shown in the drawings.

FIG. 1 shows an example of an embodiment of a nuclear power plant having a nuclear reactor to which the present invention is applied, FIG. 2 shows an example of spent fuel, and FIG. 3 shows an example of an auxiliary metal fuel. A reactor 1 in which a core 4 is loaded with a spent fuel 2 and an auxiliary metal fuel 3 which compensates for a lack of reactivity due to the use of the spent fuel 2 and maintains a fission chain reaction, and uses a gas as a coolant 5 It is.

The spent fuel 2 that can be burned in the nuclear reactor 1 may be generated in any of a light water reactor, a heavy water reactor, a fast reactor, a gas reactor and the like. Spent fuel 2 is
It is possible to use the fuel taken out of the reactor that was first burned as new fuel after fuel processing. That is, the reactor that was first burned as fuel (hereinafter
The used fuel assemblies taken out of the first reactor are disassembled, and the separated fuel rods 12 are put together to form the fuel assembly 6 for the reactor 1 of the present invention. However, the fuel assembly taken out of the first reactor 1 may be loaded as it is as the fuel assembly 6 of the reactor 1 of the present invention.

The cladding tube 13 of the spent fuel 2 is somewhat fragile due to irradiation with neutrons or the like during the first use in the nuclear reactor. For this reason, in the nuclear reactor 1 of the present invention, the power density of the reactor is, for example, about 1/10 or less of that of the light water reactor, that is, the linear power density is, for example, 30 W / cm or less, thereby preventing the cladding tube from being damaged. For example, when the spent fuel 2 generated in the light water reactor is used, the temperature inside the reactor vessel 7 is set to, for example, about 300 ° C. or less in consideration of the high-temperature creep characteristics of Zircaloy, which is the material of the cladding tube 13.

As the auxiliary metal fuel 3, uranium metal such as depleted uranium, recovered uranium, enriched uranium of uranium 235, natural uranium, uranium mixed with plutonium, etc. can be used. Selected. For example, when the ratio of uranium 235 and plutonium 239 contained in the spent fuel 2 is small and the effective multiplication factor of the spent fuel 2 alone is much less than 1, the enriched uranium or plutonium of the uranium 235 is used as the auxiliary metal fuel 3. Increase the effective multiplication factor to one or more using mixed uranium. On the other hand, the ratio of uranium 235 and plutonium 239 contained in the spent fuel 2 becomes larger than the above case, and the effective multiplication factor becomes 1 or more even when depleted uranium or recovered uranium is used as the auxiliary metal fuel 3. If it can be increased, depleted uranium or recovered uranium is used as the auxiliary metal fuel 3. If the effective multiplication factor can be increased to 1 or more by using natural uranium as the auxiliary metal fuel 3, natural uranium may be used.

Further, since plutonium is accumulated in the spent fuel 2 and the auxiliary metal fuel 3 by combustion and changes the reactivity, even if the auxiliary metal fuel 3 used is changed in accordance with the combustion of the spent fuel 2, good. For example, in the early stage of operation of the nuclear reactor 1, that is, in the early stage of combustion of the spent fuel 2, uranium obtained by enriching the uranium 235 to about 10% is used. Alternatively, recovered uranium may be used.

The auxiliary metal fuel 3 is filled in a cladding tube 14 and processed into a fuel rod 15 for use. For example, the auxiliary metal fuel 3 is formed into granules, and the granulated fuel is
Is loaded into the reactor core 4. Although the fuel expands due to swelling or the like, there is a gap between the granular fuels, so that the expansion of the fuel can be absorbed. The cladding tube 14 may be filled with a heat transfer medium together with the fuel, or the heat generated by the fuel may be directly transmitted to the cladding tube 14 by contact without filling the heat transfer medium. It is preferable to use the same substance as the coolant 5 as the heat transfer medium filled in the cladding tube 14. As the material of the cladding tube 14, in addition to stainless steel, a zirconium alloy such as Zircaloy, an aluminum alloy, a magnesium alloy such as Magnox, or the like can be used.

The uranium fuel contains, for example, 10% Zr.
The fuel properties may be stabilized by mixing to a certain degree. Further, the shape of the fuel filled in the cladding tube 14 is not limited to a granular shape, and may be, for example, a cylindrical shape having a hole at the center. The cylindrical shape makes it possible to absorb the expansion of the fuel at the central hole.

A fuel assembly 6 comprising fuel rods 12 for spent fuel 2 and a fuel rod 15 for auxiliary metal fuel 3 are provided in the core 4.
Is loaded. However, one fuel assembly may be constituted by the fuel rod of the spent fuel 2 and the fuel rod 15 of the auxiliary metal fuel 3, and this fuel assembly may be loaded into the core 4.

As the gas coolant 5, for example, helium gas, carbon dioxide gas or the like can be used. The gas coolant 5
It does not slow down the neutrons as compared with the liquid metal or the coolant 5 of light water or heavy water.

A nuclear power plant can be configured by including the reactor 1 configured as described above. The nuclear power plant is, for example, a power generation plant. In the reactor vessel 7, a steam generator 9, a control mechanism 10, and the like are installed in addition to the reactor core 4 and the coolant 5. The steam generated by the steam generator 9 is supplied to the reactor vessel 7
Is supplied to a power generation turbine 11 installed outside the power generator.

The control mechanism 10 controls the reactivity by, for example, installing a neutron reflector outside the core 4 and moving the neutron reflector to increase or decrease the amount of leakage of fast neutrons that contribute to the fission chain reaction. Things. However, the control mechanism 1
The value of 0 is not limited to this. For example, by moving a fast neutron absorbing material such as boron or tantalum closer to or away from the reactor core 4, the number of fast neutrons contributing to the fission chain reaction is increased or decreased to control the reactivity. May be. Since the reactivity of the reactor 1 of the present invention has a small surplus, a small control mechanism 10 is sufficient.

Although not shown in FIG. 1, it is a matter of course that a reflector, a shielding material, an emergency core stop device, an emergency core cooling device, and the like are installed in the reactor vessel 7.

The fuel assembly 6 composed of the fuel rods 12 of the spent fuel 2 and the fuel assembly 8 composed of the fuel rods 15 of the auxiliary metal fuel 3 are loaded into the core 4 and the operation is started.
Is transmitted to the steam generator 9 by natural convection of the gas coolant 5. In other words, the gas coolant 5 becomes high temperature while flowing upward from the bottom of the reactor core 4, and the reactor vessel 7
And flows to the steam generator 9 along the ceiling. Then, by performing heat exchange in the steam generator 9, it descends while being cooled, and flows into the core 4 from below. As described above, the coolant 5 can be circulated by natural convection, and in this case, power is not required unlike the case where the coolant 5 is forcedly circulated by using a pump or the like. Incidentally, it is also possible to forcibly circulate the coolant 5 using a pump or the like to perform forced cooling.

The steam generated by the heat of the coolant 5 in the steam generator 9 returns the water to the steam generator 9 after rotating the power generation turbine 11 and circulates to the steam generator 9. Power generation turbine 11
By rotating, power is generated. In addition, instead of providing the power generation turbine 11, steam may be supplied to a place where heat is used, and heat generated in the reactor 1 may be used for heat supply such as heating.

The reactor core 4 is loaded with spent fuel 2 as a nuclear fuel which has an effective multiplication factor of less than 1 and cannot have a reactivity of 0 or more, but is insufficient for a critical or supercritical state. The reactivity is supplemented by the auxiliary metal fuel 3. Therefore, the fission chain reaction can be maintained.

In addition, a gas that does not slow down neutrons as compared with liquid metal or water is used as the coolant 5, and an auxiliary metal fuel 3 that is a metal fuel that does not slow down neutrons as compared to oxide fuel or nitride fuel is used. Since it is used, uranium 238 in the spent fuel 2 and the auxiliary metal fuel 3 is efficiently converted to plutonium using fast neutrons.
The plutonium produced in the core 4 in this way contributes to the fission chain reaction.

For example, in the spent fuel 2 generated in the light water reactor, uranium 238 remains, for example, about 95% of the uranium portion. Uranium 238 is converted to plutonium by the combustion of spent fuel 2, and contributes to the fission chain reaction. Also,
In the spent fuel 2 generated in the fast reactor, about 75% of uranium 235 and about 10% of plutonium remain, for example. The uranium 235 and plutonium remaining in the spent fuel 2 and the newly converted plutonium contribute to the fission chain reaction.

FIG. 4 shows the relationship between the burnup of fuel and the infinite multiplication factor. When the spent fuel 2 and the auxiliary metal fuel 3 burn, plutonium is accumulated in the fuels 2 and 3, so that the infinite multiplication factor increases. Here, the curve a in the figure shows the case where the auxiliary metal fuel 3 using depleted uranium and the spent fuel 2 are loaded in the core, and the curve b in the figure shows the auxiliary metal fuel 3 in which uranium 235 is enriched to about 10%. Metal fuel 3 and spent fuel 2
Is loaded in the core. In any case, the infinite multiplication factor can be set to 1 or more to maintain the fission chain reaction.

However, in the case of the curve a, in the initial stage of combustion, for example, in the portion where the burn-up is less than 40 GWd / t, the fission chain reaction cannot be maintained because plutonium is not sufficiently produced in the reactor core, and The multiplication factor is less than 1. On the other hand, in the case of the curve b, the infinite multiplication factor can be set to 1 or more from the beginning of combustion. On the other hand, from the viewpoint of effective utilization of uranium resources and reduction of energy and cost required for uranium enrichment, it is preferable to use depleted uranium or recovered uranium rather than using enriched uranium as auxiliary metal fuel 3. For this reason, it is conceivable that the auxiliary metal fuel 3 and the spent fuel 2 of the curve b are burned at the beginning of the combustion, and then the auxiliary metal fuel 3 and the spent fuel 2 of the curve a are burned. That is, uranium enriched with uranium or plutonium mixed in the initial stage of combustion is used as the auxiliary metal fuel 3, and depleted uranium or recovered uranium is used according to the accumulation of spent fuel 2 or plutonium due to combustion of the auxiliary metal fuel 3. Thus, the fission chain reaction can be maintained by always maintaining the reactivity at 0 or more, and the uranium resources can be effectively used. The auxiliary metal fuel 3 is changed from fuel that uses enriched uranium or uranium mixed with plutonium to fuel that uses depleted uranium or recovered uranium in order at the time of refueling.

The spent fuel 2 loaded in the core 4 is burned until the burnup becomes about 250 GWd / t, for example.
The spent fuel 2 burned in the core 4 is, for example, disposed of. However, the spent fuel 2 burned in the core 4
Can be reprocessed.

As described above, in the nuclear reactor 1 of the present invention, the spent fuel 2 can be loaded into the reactor core 4 and burned, so that uranium resources can be effectively utilized and
Radioactive waste can be reduced. In addition, since it is not necessary to reprocess the spent fuel 2, special equipment for reprocessing and radiation management can be eliminated, and no new radioactive waste is generated by the reprocessing. Further, it is not necessary to store uranium and plutonium in a separated state as in the case of reprocessing spent fuel generated in a light water reactor. In addition, since depleted uranium and recovered uranium, which have conventionally been difficult to utilize effectively, can be burned, uranium resources can be more effectively utilized.

The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, in the above description, the spent fuel 2 is taken out of the first reactor, and the fuel rods 12 are burned as it is in the reactor 1 of the present invention. However, the present invention is not limited to this. For example, the fuel rods 12 taken out of the first reactor may be annealed at a high temperature, for example, about 500 ° C., and then burned in the reactor 1 of the present invention. By doing so, it is possible to mitigate the effects of radiation irradiation in the first reactor, and to prevent damage during use in the reactor 1 of the present invention.

As shown in FIG. 5, the fuel rods 12 of the spent fuel 2 taken out of the first reactor may be sealed in the overpack 16 and loaded on the reactor 1 of the present invention. By doing so, even if the cladding tube 13 of the fuel rod 12 is broken, fuel leakage can be prevented. The overpack 16 is, for example, a stainless tube. Since the fuel rods 12 are slightly deformed by use, it is preferable to form the overpack 16 slightly larger than the size of the fuel rods 12. It is preferable that a heat transfer medium 17 such as He gas is sealed in the overpack 16.

Further, the amount of fuel to be loaded on the reactor 1 may be changed. For example, in the early stage of operation of the nuclear reactor 1, the loading of the spent fuel 2 and the auxiliary metal fuel 3 is reduced to form a small core 4, and the loading is gradually increased at the time of refueling to enlarge the core 4. You may do it. By doing so, the amount of enriched uranium required in the early stage of operation of the nuclear reactor 1 can be reduced.

[0037]

As described above, in the nuclear reactor according to the first aspect of the present invention, the spent fuel and the auxiliary metal fuel that compensates for the lack of reactivity due to the use of the spent fuel and maintains the fission chain reaction are loaded in the reactor core. Since the gas is used as the coolant, the fission chain reaction can be maintained while burning the spent fuel. For this reason, uranium resources can be effectively used without performing fuel reprocessing, and generation of radioactive waste can be suppressed. In addition, since there is no need to reprocess spent fuel, special equipment and radiation control required for reprocessing are not required, and the generation of new radioactive waste can be prevented. There is no need to store waste uranium or plutonium. Further, since the spent fuel can be effectively used without simply storing and storing, it is possible to promote the nuclear fuel cycle.

Further, in the nuclear reactor according to the second aspect, as the auxiliary metal fuel, depleted uranium, recovered uranium, enriched uranium,
Either natural uranium or uranium mixed with plutonium is used, and among them, when depleted uranium or recovered uranium is used, conventionally, it is possible to burn depleted uranium or recovered uranium, which has been difficult to use, Utilization of uranium resources can be more effectively utilized and the nuclear fuel cycle can be further promoted. In addition, when uranium mixed with enriched uranium, natural uranium, and plutonium is used as an auxiliary metal fuel, the fission chain reaction is maintained even in the early stage of the combustion of spent fuel, compared to the case where depleted uranium or recovered uranium is used. Is easy.

In the nuclear reactor according to the third aspect, uranium enriched with uranium or a mixture of plutonium is used as an auxiliary metal fuel in the early stage of combustion of the spent fuel, and the amount of plutonium accumulated by the combustion of the spent fuel is increased. Since depleted uranium or recovered uranium is used, it is easy to maintain a fission chain reaction in the early stage of the combustion of spent fuel, and moreover, depleted uranium or recovered uranium can be effectively used.

Further, the nuclear reactor according to the fourth aspect is provided with the nuclear reactor according to any one of the first to third aspects, so that a nuclear power plant capable of effectively utilizing uranium resources can be provided.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of an embodiment of a nuclear power plant including a nuclear reactor to which the present invention is applied.

FIG. 2 is a front view showing a spent fuel partially cut away.

FIG. 3 is a front view showing the auxiliary metal fuel with a part cut away.

FIG. 4 is a diagram showing a relationship between burnup and infinite multiplication factor.

FIG. 5 is a sectional view conceptually showing a state in which a fuel rod of spent fuel is sealed in an overpack.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nuclear reactor 2 Spent fuel 3 Auxiliary metal fuel 4 Core 5 Coolant

Claims (4)

[Claims] Claims: 1. A nuclear reactor characterized in that a spent fuel and an auxiliary metal fuel for supplementing a lack of reactivity due to the use of the spent fuel and maintaining a fission chain reaction are loaded in a reactor core, and gas is used as a coolant. Furnace. 2. The depleted uranium as the auxiliary metal fuel,
2. The nuclear reactor according to claim 1, wherein one of recovered uranium, enriched uranium, natural uranium and uranium mixed with plutonium is used. 3. Uranium mixed with enriched uranium or plutonium is used as the auxiliary metal fuel in the initial stage of combustion of the spent fuel, and depleted uranium or recovered uranium is stored in accordance with the accumulation of plutonium due to the combustion of the spent fuel. The nuclear reactor according to claim 1, wherein: 4. A nuclear power plant comprising the nuclear reactor according to claim 1.