JPH0886893A - Complete combustion type nuclear reactor - Google Patents

Abstract

PURPOSE: To heighten the natural uranium utilization efficiency by making enrichment and reprocessing facilities unnecessary for simplification of a nuclear fuel cycle facility, improve the resistance to nuclear proliferation and heighten the safety. CONSTITUTION: The complete combustion type reactor has an accelerator 10 for producing protons or deuterons and a subcritical core 12 for using fluid-like molten salt fuel. Preferably, a fuel processor 14 for removing fission products is provided in a cooling system. A subcritical core is provided with a target substance 16 for producing neutrons by the protons and the deuterons supplied from the accelerator, a core part 18 for performing nuclear fission reaction by the neutrons produced from the target substance 16 and producing heat, and a neutron reflector 20 for surrounding the core part 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides means for supplying neutrons from the outside to a subcritical core, and uses the neutrons to cause a fission reaction in the reactor to burn the fuel loaded in the core almost completely. It relates to a nuclear reactor that can be turned off.

[0002]

2. Description of the Related Art A nuclear power generation system is a system for obtaining electric power by using uranium or the like as a nuclear fuel and converting the energy released by the fission reaction into electric energy. A fission reaction is a reaction that occurs when neutrons are absorbed by nuclear fuel, and conventional nuclear reactors use neutrons that are generated at the same time as energy during a fission reaction as neutrons for causing this reaction. In other words, a stable energy is always obtained by stably causing a process of obtaining neutrons necessary for fission reaction from fission reaction (this is called fission chain reaction). The state where this fission chain reaction occurs stably (the number of fission is constant over time) is called critical.

In order for a nuclear reactor to become critical, a certain amount of fissile material is required in the core. On the other hand, if the amount is less than this fixed amount, the fission chain reaction does not occur and the energy cannot be extracted. A conventional nuclear reactor is a device that can control the fission reaction so that a neutron absorber such as a control rod can maintain a critical state by loading a larger amount of fissile material than that required for criticality into the core. Yes,
This is a system that makes it possible to extract a certain amount of energy with respect to time.

[0004]

As described above, when the nuclear reactor is in a subcritical state, no fission chain reaction occurs and energy cannot be taken out. Therefore, it is necessary to completely burn nuclear fuel like oil and coal. I can't. In order to secure a “fixed amount” of fissile material, for example, when using uranium as a fuel in a light water reactor, a process called enrichment is necessary, and in the operation of a nuclear reactor, periodical replenishment of fissile material is necessary. Refueling is required.

Further, in the operation of the conventional nuclear reactor, since it is necessary to continuously take out energy for a certain period of time (the above-mentioned refueling work is uneconomical because the reactor must be stopped), the supercriticality is set to some extent. The design is different, that is, the control rod is used to suppress the supercriticality. This is one of the factors that reduce safety. That is, when the control rods and the like are lost from the core, the safety of the nuclear reactor is significantly impaired.

In order to maintain the criticality of the nuclear reactor, it is necessary to take out the fuel with the lowered criticality from the nuclear reactor. However, since the extracted fuel contains substances that can be nuclear fuel, the once-through method of discarding this as it is,
The utilization rate of natural uranium resources is low. For example, in the light water reactor once through system, it is about 0.5%. Therefore, in order to improve the utilization efficiency of natural uranium, a process of reprocessing spent fuel is required. This process has the potential to enhance nuclear diffusivity, as it involves the transfer of nuclear material and plutonium alone. Further, the high radioactive level waste generated by the reprocessing contains transuranium elements and fission products (FP) having a long half-life, so it is necessary to fully consider the environmental impact.

The object of the present invention is to increase the utilization efficiency of natural uranium as an energy source, to eliminate the need for enrichment and reprocessing facilities as a simplification of nuclear fuel cycle facilities, and to use nuclear materials to enhance nuclear proliferation resistance. It is an object of the present invention to provide a reactor system capable of satisfying the requirements such as not taking out a certain plutonium to the outside of the reactor system, keeping the core in a subcritical state at all times and having high safety.

[0008]

The present invention comprises an accelerator for producing protons or deuterons, and a subcritical core using a fluid molten salt fuel, the subcritical core being supplied from the accelerator. A target material that generates neutrons by the protons or deuterons that are generated, and a core part that generates heat by fission reaction by the neutrons generated from the target material,
It is a complete combustion type nuclear reactor provided with a neutron reflector that surrounds the core. Here, it is preferable to provide a fuel processing device for removing fission products in the cooling system. Natural uranium or plutonium-rich fuel is used as nuclear fuel.

In order to operate such a complete combustion reactor, a plurality of reactor vessels equipped with a target material and a neutron reflector and capable of holding molten salt fuel, and a plurality of cooling systems capable of circulating molten salt fuel are installed. Then, before the life of the structural material of the reactor system in use and the plant equipment is exhausted, the molten salt fuel of the reactor system in use is introduced into another reactor system to continue the operation.

[0010]

[Operation] In the nuclear power generation system, the energy generated by the fission reaction of uranium or the like is used to generate electricity.
Since the fission reaction occurs when neutrons are absorbed by uranium or the like, neutrons are necessary to cause this reaction. A feature of the nuclear reactor of the present invention is that the neutrons necessary for causing a fission reaction are not obtained only by the fission reaction. The protons or deuterons generated in the accelerator collide with the target material to generate neutrons, which contribute to the fission reaction. From this, the reactor of the present invention does not require the concept of criticality, the nuclear fuel in the reactor may be a subcritical amount, the loaded nuclear fuel can be burned almost completely, and the process such as uranium enrichment is also possible. do not need.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an overall configuration diagram showing an embodiment of a complete combustion reactor according to the present invention. This nuclear reactor system
An accelerator 10 that produces protons or deuterons, a subcritical core 12 that uses a molten salt fuel in a fluid state, and a fuel processor 1 that is provided in a primary cooling system thereof to remove fission products 1
4 and. The subcritical core 12 is the accelerator 10
A target material 16 for generating neutrons by protons or deuterons supplied from the reactor, a core part 18 for generating heat by fission reaction by neutrons generated from the target material 16, and a neutron reflector 20 surrounding the core part 18. Have.

The high temperature molten salt fuel heated by the nuclear fission reaction in the subcritical core 12 exchanges heat with water through the steam generator 22 of the cooling system and is cooled and returned to the subcritical core 12 by the circulation pump 24. . That is, in the case of molten salt fuel, the fuel substance also functions as a coolant. The steam heated in the steam generator 22 turns the generator 28 in the turbine 26, becomes water, and returns to the steam generator 22 in the pump 30.

The neutrons for causing the fission reaction are specifically obtained by combining the accelerator 10 and the target material 16 such as uranium, bismuth, lead or tungsten. That is, protons or deuterons are produced by the proton synchrotron or linac accelerator. Then, these protons or deuterons are guided to a target material 16 arranged in the core through a proton conduit and irradiated, and neutrons are generated by a nuclear fragmentation reaction. The reason why neutrons are generated by introducing protons or deuterons into the core is that neutrons cannot be directly introduced into the core by a magnetic method because they have no electric charge.

By irradiating the nuclear fuel in the core with neutrons generated from the target material 16, the parent material (U-238
Etc.) into fissionable substances (Pu-239 etc.) or cause fission reaction. In this way, in principle, all nuclear fuels can undergo a nuclear reaction, and natural uranium utilization efficiency of almost 100% can be achieved. It also does not require the process of reprocessing nuclear fuel. The elimination of the need for these processes simplifies the nuclear fuel cycle and improves proliferation resistance.

Molten salt fuel is a fluid fuel containing a nuclear fuel material such as chloride or fluoride. As a fuel processing method in the fuel processing apparatus 14 attached to the primary cooling system, when chloride is used as a molten salt, a chloride volatilization method, which is one of dry reprocessing methods, can be used. In the chloride volatilization method, there are differences in the volatility of uranium, plutonium, and chlorides in fission products, and selective adsorption / adsorption on solid chloride.
These are separated using a desorption reaction or the like. Since the molten salt fuel circulates outside the core as a cooling system, the fission products are removed by the fuel processor while operating the reactor.

The removal of fission products is intended to reduce the burden on the accelerator. Therefore, a fission product that has a large reaction cross-section with neutrons and that does not pose a problem even when exposed to the environment may be taken out.

FIG. 2 is a 1 / 2RZ sectional view of the subcritical core used in the simulation. The described core dimensions are based on the prototype reactor class with an output of about 400 MW. Figure 2
As shown in Fig. 1, the subcritical core 12 is a target material 1 that produces neutrons by protons or deuterons from an accelerator.
6, a core portion 18 that generates heat due to a nuclear fission reaction composed of nuclear fuel, and a neutron reflector 20 such as stainless steel that surrounds the target material 16 and the core portion 18. The target material in the center has a cylindrical shape, and the target material in the periphery has a cylindrical shape. The neutron reflector returns neutrons to the nuclear reactor, reduces the burden on the accelerator, and functions as a shield.

In the core size shown in FIG. 2, the reactor power 40
FIG. 3 shows the secular change in the neutron source intensity required to obtain 0 MW (constant). In order to obtain a constant output, a relatively high neutron source intensity is required at the start of operation, but thereafter, the neutron source intensity may be about 10 ¹³ to 10 ¹⁴ n / cm ³ / sec. However, a considerably high neutron source intensity is required at the end of operation. In any case, the fission products generated during the reactor operation absorb neutrons, so if the fission products generated during the reactor operation are removed by the fuel processor as in the present invention, the effective neutron Since it can be utilized, the intensity of the neutron source can be lowered as shown in FIG.

In the core shown in FIG. 2, it is assumed that the volume of the target material for supplying neutrons from the outside is about 5 × 10 ⁵ cm ³ . Using the 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 used. Is 2.5 × 10 ¹² ~
It becomes 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 ~10 13) × (1.6 ×} 10 -19) = 200~200
It becomes 0 mA. A current value of several hundred mA can be sufficiently realized. Regarding the upper limit, it is considered that it is difficult to realize at present, but in such a case, when one proton is collided 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 decreasing the reactor power.

As described above, in the present invention, the number of neutrons generated from the target material 16 is controlled by controlling the concentration of accelerating particles from the accelerator installed outside the nuclear reactor, and the output of the nuclear reactor is controlled. be able to. 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 is stopped for some reason, neutrons are not supplied and the operation of the reactor is naturally stopped.

In FIG. 3, in the reactor, the 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, and the final stage of operation (60 to
It can be seen that waste treatment is being carried out after 1965). Since the final stage of operation is waste treatment, the neutron source strength may be small if the reactor power is reduced. If plutonium-enriched fuel is used, the neutron source strength at the initial stage of operation can be kept low. Therefore, any surplus plutonium produced in a reactor system other than the reactor of the present invention can be utilized.

FIGS. 4 and 5 show the criticality and the secular change of the fuel material when neutrons having the neutron source intensity shown in FIG. 3 are supplied to the core (only natural uranium is used as a fuel) thus constructed. Shown respectively. As shown in FIG. 4, the core is always subcritical (effective multiplication factor is less than 1) during the combustion period. As shown in Fig. 5, U-238 loaded with 10000 kg at the start of operation will decrease to about 30 kg after 70 years, and can burn out almost completely (up to 99.7%). it can. That is, the utilization efficiency of natural uranium is almost 100%.

By the way, in the nuclear reactor of the present invention, FIGS.
As can be seen from the above, the vehicle will continue to operate for a long period of time, for example, 70 years. Therefore, the core structural material will receive a large amount of neutron irradiation, and it is expected that swelling and strength deterioration due to irradiation damage will occur.
Therefore, it is necessary to develop and use core structure materials with excellent durability, and to consider the need for a backup system that allows easy replacement. For that purpose, for example, by appropriately designing the reactor power and the core size (fuel inventory), it is possible to match the number of operating days with the life of the plant equipment. In this case, the reactor can be decommissioned when the operation ends. Alternatively, a reactor vessel capable of holding a molten salt fuel having a target material and a neutron reflector, and a plurality of cooling systems in which molten salt fuel can circulate are installed, and structural materials and plant equipment of the reactor system in use. It is necessary to take measures to introduce the molten salt fuel of the reactor system in use into another reactor system and continue the operation before the end of its life.

[0024]

INDUSTRIAL APPLICABILITY As described above, the present invention does not obtain the neutrons necessary for the fission reaction from the fission reaction, but emits neutrons by irradiating the target material in the 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 the nuclear fuel, and the nuclear fuel can be burned almost completely in the nuclear reactor. The fissile material undergoes fission as it is, and the parent material absorbs neutrons and transforms into fissile material to undergo fission. Therefore, the utilization efficiency of natural uranium can be almost 100%. No enrichment and reprocessing processes are required, and the nuclear fuel cycle can be simplified. Further, since nuclear material is not transferred and plutonium alone is not treated, nuclear diffusion resistance can be improved. Since the nuclear reactor is always operated in a subcritical state, there is no danger of nuclear runaway and safety is significantly improved.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of a complete combustion reactor according to the present invention.

FIG. 2 is a cross-sectional view of a nuclear reactor used for simulation.

FIG. 3 is a diagram showing a secular change in neutron source intensity with a constant reactor output.

FIG. 4 is a diagram showing the secular change in criticality at a constant reactor output.

FIG. 5 is a diagram showing a secular change in the weight of fuel nuclides in the reactor at a constant reactor output.

[Explanation of symbols]

 10 accelerator 12 subcritical core 14 fuel processor 16 target material 18 core 20 neutron reflector

Claims (5)

[Claims] 1. An accelerator for producing a proton or a deuteron, and a subcritical core using a fluid molten salt fuel, wherein the subcritical core is a neutron produced by a proton or a deuteron supplied from the accelerator. A target substance that generates
A complete-burning nuclear reactor comprising: a core portion that undergoes a nuclear fission reaction by neutrons generated from the target material to generate heat; and a neutron reflector that surrounds the core portion. 2. An accelerator for producing protons or deuterons, a subcritical core using a fluid molten salt fuel, and a fuel processor provided in a cooling system for removing fission products, The subcritical core is a target material that generates neutrons by protons or deuterons supplied from the accelerator,
A complete-burning nuclear reactor comprising: a core portion that undergoes a nuclear fission reaction by neutrons generated from the target material to generate heat; and a neutron reflector that surrounds the core portion. 3. A natural uranium is used as a nuclear fuel.
Alternatively, the complete combustion reactor according to the item 2. 4. The complete combustion nuclear reactor according to claim 1, wherein plutonium-enriched fuel is used as the nuclear fuel. 5. A structural material of a reactor system in use, comprising a plurality of reactor vessels equipped with a target material and a neutron reflector capable of holding a molten salt fuel, and a plurality of cooling systems capable of circulating the molten salt fuel. 3. The method for operating a complete combustion reactor according to claim 1, wherein the molten salt fuel of the reactor system in use is introduced into another reactor system and the operation is continued before the life of the plant equipment is exhausted.