JP2959980B2 - Subcritical reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention combines an accelerator and a subcritical reactor, controls the generation of neutrons in the reactor by an externally installed accelerator, and generates a fission reaction in the reactor using the generated neutrons. The present invention relates to a nuclear reactor that safely burns fuel loaded in a reactor core.

[0002]

2. Description of the Related Art A nuclear power generation system is a system in which uranium or the like is used as nuclear fuel, and energy released by the fission reaction is converted into electric energy to obtain electric power. The nuclear fission reaction is a reaction that occurs when neutrons are absorbed by nuclear fuel, and a conventional nuclear reactor utilizes neutrons generated simultaneously with energy during the nuclear fission reaction as neutrons to cause this reaction. In other words, the neutrons necessary for the fission reaction are obtained from the fission reaction (this is called a fission chain reaction) in a stable manner, so that a constant energy is always obtained. The state in which the fission chain reaction occurs stably (the number of fission is constant with respect to time) is called critical.

For a nuclear reactor to become critical, a certain amount of fissile material is required in the core. Conversely, if the amount is less than this certain amount, no fission chain reaction occurs and energy cannot be extracted. Conventional reactors are devices that can load fissionable material in the reactor core in an amount larger than that required for criticality and control the fission reaction so that the critical state can be maintained by neutron absorbers such as control rods. Yes,
This is a system that can take out constant energy with respect to time.

[0004]

As described above, when the nuclear reactor is brought into a subcritical state, a fission chain reaction does not occur and energy cannot be taken out. Therefore, it is necessary to completely burn nuclear fuel like oil or coal. Can not. In order to secure a certain amount of fissile material, for example, when uranium is used as fuel in light water reactors, a process called enrichment is necessary, and in reactor operation, periodic replenishment of fissile material is necessary. Refueling is required.

Further, in the operation of the conventional nuclear reactor, since it is necessary to continuously extract energy for a certain period of time (the refueling operation is uneconomical because it is necessary to shut down the reactor), a certain degree of supercriticality is required. That is, the supercriticality is suppressed by a control rod or the like. This contributes to a decrease in safety. That is, if the control rods and the like are lost from the core, the safety of the reactor is significantly impaired.

[0006] In order to maintain the criticality of the reactor, it is necessary to remove the fuel with reduced criticality from the reactor. However, since the removed fuel contains substances that can become nuclear fuel, the once-through method of discarding this as it is,
The utilization rate of natural uranium resources will be low. For example, in a light water reactor once-through system, it is about 0.5%. Therefore, a process of reprocessing spent fuel is required to improve the efficiency of natural uranium utilization. Since this treatment involves the transfer of nuclear material and the single treatment of plutonium, it has the potential to enhance nuclear proliferation. In addition, high radioactive waste generated by reprocessing contains transuranium elements and fission products (FPs) with a long half-life, so that it is necessary to sufficiently consider the environmental impact.

An object of the present invention is to provide a nuclear reactor system capable of satisfying the requirements of increasing the utilization efficiency of natural uranium as an energy source, always keeping the core in a subcritical state and having high safety. It is.

[0008]

According to the present invention, there is provided a combination of an accelerator for producing protons or deuterons and a subcritical core, wherein the subcritical core is provided with neutrons by protons or deuterons supplied from the accelerator. A subcritical reactor having a target material that generates heat, a core part that has a solid nuclear fuel and generates heat by a fission reaction using neutrons generated from the target material, and a neutron reflector surrounding them is there. As the solid nuclear fuel, a pin type fuel or a particle fuel is used. For pin type fuel,
Use liquid sodium for the coolant, and for particulate fuel,
Helium gas is preferably used as the coolant. As the nuclear fuel, natural uranium or plutonium-enriched fuel is used.

[0009]

In a nuclear power generation system, power is generated using energy generated by a fission reaction of uranium or the like.
Since the fission reaction is caused by the absorption of neutrons by uranium or the like, neutrons are required to cause this reaction. A feature of the nuclear reactor of the present invention is that the neutrons necessary to cause a fission reaction are not obtained only by the fission reaction. When protons or deuterons generated by the accelerator collide with the target material, neutrons are generated, and the neutrons contribute to the fission reaction. For this reason, the concept of criticality is not required in the nuclear reactor of the present invention, and the nuclear fuel in the nuclear reactor may be a subcritical amount. Also, no process such as uranium enrichment is required.

[0010]

FIG. 1 is an overall structural view showing an embodiment of a subcritical nuclear reactor according to the present invention, which is an example in the case of using a pin type fuel. The reactor system includes an accelerator 10 for producing protons or deuterons, and a subcritical core 12 using solid fuel. As shown in FIG. 2, the configuration of the subcritical core 12 is a target material 1 that generates neutrons by protons or deuterons supplied from the accelerator 10.
4, a core 18 having a fuel assembly 16 that generates a heat by performing a fission reaction by neutrons generated from the target material 14, and a neutron reflector 20 surrounding the core 18
Having.

As shown in FIG. 3, for example, a plurality of pin-type fuels 22 are supplied to the fuel assembly 16 by the entrance nozzle 2.
4. A ductless structure (a structure without a trumpet tube) supported by the grid 26 and the handling head 28 to minimize waste of neutrons due to the structural material.

As shown in FIG. 1, the primary sodium coolant heated by the fission reaction in the subcritical core 12 passes through the intermediate heat exchanger 32 to exchange heat with the secondary sodium.
It is cooled and returns to the subcritical core 12 by the primary circulation pump 34. The secondary sodium heated in the intermediate heat exchanger 32 is
The heat is exchanged with water through the steam generator 36, cooled, and returned to the intermediate heat exchanger 32 by the secondary circulation pump 38. The steam heated by the steam generator 36 turns the generator 42 by the turbine 40, turns into water, and returns to the steam generator 36 by the pump 44.

Neutrons for causing a fission reaction are specifically obtained by a combination of an accelerator 10 and a target material 14 such as uranium, bismuth, lead, and tungsten. That is, protons or deuterons are produced by a proton synchrotron or a linac accelerator. Then, these protons or deuterons are guided to a target material 14 arranged in a reactor core through a proton conduit and irradiated, and neutrons are generated by a nuclear fragmentation reaction. The reason that the protons or deuterons are guided to the core to generate neutrons is that neutrons have no electric charge, so that neutrons cannot be directly guided to the core by a magnetic method.

The neutrons generated from the target material 14 irradiate the nuclear fuel in the core to produce a parent material (U-238).
) Into fissile material (such as Pu-239) or cause a fission reaction. In this way, in principle, all nuclear fuel in the reactor can undergo a nuclear reaction, and a natural uranium utilization efficiency of almost 100% can be achieved.

FIG. 4 is an overall configuration diagram showing another embodiment of the subcritical reactor according to the present invention, in which a particulate fuel is used. This reactor system includes an accelerator 50 for producing protons or deuterons, and a subcritical core 52 using solid fuel. The configuration of the subcritical core 52 is as follows.
As shown in FIG. 5, a target material 54 for generating neutrons by protons or deuterons supplied from the accelerator.
And a reactor core 58 having a fuel assembly 56 that generates heat by performing a nuclear fission reaction by neutrons generated from the target material 54, and a neutron reflector 60 surrounding the reactor core 58.

As shown in FIG. 6, for example, the fuel assembly 56 has a structure in which a particulate basket 62 containing nuclear fuel material contained in carbon is filled in a cylindrical basket 64. Try to avoid eating. Then, the coolant can freely flow in the vicinity of the particulate fuel 62 through the hole 65 provided in the basket 64.

As shown in FIG. 4, the coolant helium gas heated by the nuclear fission reaction in the subcritical core 52 passes through a heat exchanger 72 to exchange heat with air, and is cooled and circulated by a circulation pump 74. To return to the subcritical core 52. Heat exchanger 62
Is heated by the turbine 76 to turn the generator 78, cooled, and returned to the heat exchanger 72 by the pump 79.

Since the structure of the accelerator 50 may be the same as that of the above-described embodiment, a description thereof will be omitted.
The advantage of using particulate fuel is that only particulate fuel can be removed from the fuel assembly. The reactor of the present invention operates for a very long time. Therefore, it is expected that the structural members of the nuclear reactor will be degraded by irradiation. Attempts to use nuclear fuel beyond the life of the structural material will require removal of the fuel. For the reasons set forth above, particulate fuel can only be transferred to a new reactor system, ensuring long-term sound operation.

FIG. 7 is a half RZ sectional view of the subcritical core used for the simulation. The described core dimensions assume a prototype reactor class with an output of about 400 MW. FIG.
As shown in the figure, the subcritical core 82 is a target material 8 that generates neutrons by protons or deuterons from the accelerator.
4. A core portion 88 having a solid nuclear fuel that generates heat by a fission reaction composed of nuclear fuel, and a target material 84
And a neutron reflector 90 such as stainless steel surrounding the core portion 88. The target material at the center is cylindrical, and the target material around is cylindrical. The neutron reflector 90 returns the neutrons to the core 88, reduces the load on the accelerator, and functions as a shield.

In the core dimensions shown in FIG.
FIG. 8 shows the aging of the neutron source intensity required to obtain 0 MW (constant). To obtain a constant output, it is necessary relatively high neutron source strength at the start of operation, then the neutron source strength may be ^{10 13 ~10 14 n / cm 3} / sec approximately. However, at the end of operation, a fairly high neutron source intensity is required. This is because neutrons are absorbed by fission products generated during the operation of the reactor, so that extra neutrons are required. For reference, the neutron source intensity required when fission products (FP) generated during operation are removed is also shown.

In the core shown in FIG. 7, it is assumed that the volume of the target material for supplying neutrons from the outside is about 5 × 10 ⁵ cm ³ . Using known data that when one 1.5 GeV proton collides with a target material (lead / bismuth), about 40 neutrons are generated, the number of protons required to obtain the above neutron source intensity is obtained. Is from 2.5 × 10 ¹²
10 ¹³ n / cm ³ / sec. From these facts, the current value required for the accelerator is (5 × 10 ⁵ ) × (2.5 × 10 5
¹² to 10 ¹³ ) × (1.6 × 10 ⁻¹⁹ ) = 200 to 200
It becomes 0 mA. A current value of several hundred mA is sufficiently feasible. At present, the upper limit is considered to be somewhat difficult to realize, but in such a case, when one proton collides with the target by increasing the energy of the proton or increasing the target density. The problem can be solved by increasing the neutron generation amount or reducing the reactor power.

As described above, in the present invention, the number of neutrons generated from the target material 84 is controlled by controlling the concentration of accelerating particles from an accelerator installed outside the reactor, and the output of the reactor is controlled. . That is, the intensity of the external neutron source is controlled by the current value of the accelerator. Therefore, if the operation of the accelerator stops for any reason, neutrons will not be supplied, and the operation of the reactor will naturally stop.

In FIG. 8, in the nuclear reactor, nuclear fuel material is concentrated in the initial stage of operation (less than 5 to 10 years), and thereafter reprocessing and fuel processing are performed.
After the year), it can be seen that the waste is being treated. At the end of operation, the neutron source intensity may be low if the reactor power is reduced due to waste disposal. When the plutonium-enriched fuel is used, the neutron source intensity at the beginning of the operation can be kept low. Therefore, if there is surplus plutonium produced in a reactor system other than the reactor of the present invention, it can be used.

FIG. 9 and FIG. 10 show the criticality and the secular change of the fuel material when the neutrons having the neutron source strength shown in FIG. 8 are supplied to the core configured as described above (only natural uranium is used as fuel). Shown respectively. As can be seen from FIG. 9, the core is always in a subcritical state (effective multiplication factor is less than 1) during the combustion period. As shown in FIG.
U-238 loaded with 0000 kg will be reduced to about 30 kg after 70 years, and can be burned almost completely (up to 99.7%). In other words, if the operation can be continued for about 70 years, the natural uranium utilization efficiency will be almost 100%.

Incidentally, it is preferable that the nuclear reactor of the present invention be continuously operated for a long period of several decades. As a result, the core material is subjected to a large amount of neutron irradiation, and swelling and strength deterioration due to irradiation damage are expected to occur. Therefore, it is necessary to develop and use a core structure material with excellent durability, and also to consider a backup system that can be easily replaced. For this purpose, for example, reactor power and core size (fuel inventory)
It is conceivable that the number of operating days is adjusted to the life of the plant equipment by appropriately designing. In this case, the furnace can be decommissioned when the operation is completed. Alternatively, a reactor vessel equipped with a target material and a neutron reflector, and a plurality of cooling systems are installed, and before the life of the structural materials and plant equipment of the reactor system in use is over, the reactor system in use is terminated. It is necessary to take measures to refill the particulate fuel into another new basket, introduce it into the reactor vessel and continue operation.

[0026]

According to the present invention, as described above, neutrons required for fission reactions are not obtained from fission reactions, but neutrons are generated by irradiating a target material in the reactor core with protons or deuterons introduced from the outside. Since it is configured to cause a fission reaction, the following effects can be obtained. Natural uranium can be used as nuclear fuel. Fissile material undergoes fission as it is, and the parent material absorbs neutrons and converts to fissile material to fission. Therefore, if the operation is continued for a long period of time, nuclear fuel can be burned almost completely in the nuclear reactor, and it is possible to achieve a natural uranium utilization efficiency of almost 100%. The enrichment process becomes unnecessary, and the nuclear fuel cycle can be simplified. Further, if the operation is continued for a long period, a reprocessing process is not required. In that case, since there is no transfer of nuclear material or single treatment of plutonium,
Nuclear proliferation resistance can be improved. Since the reactor is always operated in a subcritical state, there is no danger of nuclear runaway and safety is significantly improved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing one embodiment of a subcritical reactor system according to the present invention.

FIG. 2 is an explanatory diagram showing an example of the core configuration.

FIG. 3 is an explanatory view showing an example of a fuel assembly used for the fuel assembly.

FIG. 4 is an overall configuration diagram showing another embodiment of the subcritical reactor system according to the present invention.

FIG. 5 is an explanatory view showing an example of the core configuration.

FIG. 6 is an explanatory view showing an example of a fuel assembly used for the fuel assembly.

FIG. 7 is a sectional view of a nuclear reactor used for the simulation.

FIG. 8 is a diagram showing the aging of the neutron source intensity at a constant reactor power.

FIG. 9 is a diagram showing the aging of criticality at a constant reactor power.

FIG. 10 is a graph showing the secular change of the weight of fuel nuclides in a reactor at a constant reactor power.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Accelerator 12 Subcritical core 14 Target material 16 Fuel assembly 18 Core 20 Neutron reflector 32 Intermediate heat exchanger 36 Steam generator 40 Turbine

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-60-117177 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G21C 1/30 G21C 1/02 GDF G21C 3 / 62 GDR G21G 1/10 G21G 4/02 JICST file (JOIS)

Claims (4)

(57) [Claims] An accelerator for producing protons or deuterons is combined with a subcritical core, wherein the subcritical core comprises a target material for generating neutrons by protons or deuterons supplied from the accelerator, and a solid material. A core part having nuclear fuel and generating heat by fission reaction using neutrons generated from the target material,
Comprising a neutron reflector surrounding them, the solid nuclear fuel
Using pin-type fuel as the coolant and liquid metal as the coolant
A subcritical nuclear reactor characterized by being used . 2. An accelerator for producing protons or deuterons.
And a sub-critical core, wherein the sub-critical core includes protons or protons supplied from the accelerator.
Is a target material that generates neutrons by deuterons,
Neutrons generated from the target material having a body nuclear fuel
A core that generates heat by fission reaction using
A neutron reflector surrounding them;
Use particulate fuel as a fuel and gas as a coolant
A subcritical reactor. 3. The use of natural uranium as nuclear fuel.
Or a subcritical reactor according to 2. 4. A sub-critical reactor of claim 1, wherein using the plutonium enrichment fuel in the nuclear fuel.