JP3407037B2 - Direct cycle fast reactor - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD This invention relates to direct cycle fast reactors.

[0002]

Uranium accounts for 99.3% of uranium.
It consists of 238 and uranium-235, which accounts for the remaining 0.7%. In light water reactors such as pressurized water reactors and boiling water reactors, which currently dominate nuclear power generation, uranium-
A fuel enriched with 235 to 3-4% is used. According to the evaluation of the International Atomic Energy Agency (IAEA), the economically minable uranium resources are 2070 to 2100 AD.
It is expected to be exhausted by about age.

On the other hand, in the fast reactor, uranium-238, which accounts for 99.3% of uranium, is plutonium-239 in the reactor.
To generate electricity by burning this plutonium-239. Therefore, the uranium resource can be effectively used about 60 times that of the light water reactor, and the fast reactor allows humankind to use the uranium resource as an energy source for thousands of years. Therefore, developed countries have been competing to develop this fast reactor.

In fast reactors, uranium-238 in the core
To plutonium-239 conversion efficiency (growth ratio), the pitch of fuel rods is much smaller than that of light water reactors so that neutrons generated by fission do not collide with other substances and slow down as much as possible. It is suppressed. As a result, the power density of the fast reactor is about 4 to 7 times that of the light water reactor. In order to obtain high cooling efficiency in such a dense core, liquid metal sodium having a high heat transfer characteristic is generally used as a coolant at present.

[0005]

[Problems to be Solved by the Invention] However, (1)
When liquid metal sodium leaks from the cooling system to the outside and reacts violently when it comes into contact with air or water, it damages the cooling system and peripheral equipment. (2) When the core overheats and liquid metal sodium boils during an accident, If bubbles enter and void, positive reactivity (sodium void reactivity) is inserted and the core further advances in the direction of overheating,
(3) A cooling system such as a primary cooling system, a secondary cooling system, and a steam system using liquid metal sodium as a coolant,
Furthermore, there are problems such as preheating equipment for freeze prevention, sodium cleaning equipment, and sodium leakage countermeasure equipment, which increases construction costs. For this reason, most advanced countries that were developing fast reactors are slowing down development.

For this reason, it has been considered to form the coolant from a gas such as helium, but the cooling capacity was low, and the power density of the nuclear reactor had to be reduced. Therefore, in order to obtain the same amount of power generation output, it is necessary to increase the core volume, which causes a problem of an increase in construction cost due to an increase in the amount of plant material.

It is an object of the present invention to provide a novel direct cycle fast reactor in which a novel coolant replacing liquid metal sodium is used, and the coolant directly rotates a turbine to generate electricity. .

[0008]

[Means for Solving the Problems] In order to achieve the above object,
The present invention comprises a nuclear reactor, a turbine, and a generator, and heats a coolant in the nuclear reactor by heat generated by burning plutonium obtained by converting uranium-238, and heating the coolant. A fast reactor in which the turbine is driven by a coolant and the generator is driven to generate electric power, and the coolant is composed of supercritical carbon dioxide, and the coolant is directly supplied to the turbine. The present invention relates to a direct cycle fast reactor, which is characterized by being introduced into.

Supercritical carbon dioxide has a cooling performance (heat transfer coefficient and heat transport capacity) that is 2-3 times higher than that of a gas such as helium. Further, since carbon dioxide is condensed by lowering the temperature, Rankine cycle with high thermal efficiency can be adopted. Therefore, the turbine can be rotated with high thermal efficiency equivalent to that of the conventional light water reactor, and thus high power generation efficiency can be obtained.

Further, since carbon dioxide is chemically inert to air and water, it does not react violently with air or water even if it leaks from the cooling system to the outside. Therefore, it is possible to avoid the problem that the cooling system and peripheral equipment are damaged due to the leakage of the coolant.

Further, since the carbon dioxide used in the present invention is in a supercritical state in the core, the generation of voids due to boiling can be avoided. Therefore, the problem of core overheating due to the insertion of positive reactivity can be avoided.

Further, since the cooling medium heated in the nuclear reactor is used to directly drive the turbine to drive the generator, the secondary cooling system and the secondary cooling system can be used as compared with the case where liquid metal sodium is used as the cooling medium. No steam system is required. Therefore, the plant structure can be simplified, and as a result, the plant operation can be facilitated, and the man-hours for inspection and maintenance can be reduced and reduced.

Further, since carbon dioxide having a supercritical pressure has a lower coolant density than liquid metal sodium, the neutron moderating effect is reduced and the proportion of high energy neutrons is increased. As a result, the production efficiency (breeding ratio) of fissile materials such as plutonium-239 in the reactor is increased, and the deterioration of the reactivity of the reactor due to combustion is reduced, so that the refueling interval is extended. You can also Furthermore, due to the increase in high-energy neutrons, the minor actinide elements (such as neptinium, americium, and cucumber) that have been the target of deep-sea disposal as long-lived radioactive waste can be efficiently burned. As a result, the long-term storage management burden of these elements can be reduced.

The "supercritical carbon dioxide" in the present invention means carbon dioxide in a pressure state of a critical pressure (7.375 MPa) or higher.

In the direct cycle fast reactor of the present invention, the coolant may be composed of ammonia instead of the supercritical carbon dioxide. Furthermore, in the direct cycle fast reactor of the present invention, the coolant may be composed of nitrogen dioxide instead of the supercritical carbon dioxide.

Like supercritical carbon dioxide, ammonia and nitrogen dioxide are chemically inert to air and water and do not react with them. Furthermore, the generation of voids due to boiling does not occur. Moreover, since the cooling efficiency is also high, it is possible to achieve high power generation efficiency based on high heat efficiency. Therefore, the object of the present invention can be sufficiently achieved even when ammonia or nitrogen dioxide is used as the coolant. Furthermore, the additional effect described above due to the increase in the proportion of high-energy neutrons can be obtained.

In a preferred embodiment of the invention, when ammonia and nitrogen dioxide are used as coolants, these are composed of nitrogen isotopically enriched with nitrogen-15. As a result, the ¹⁴ N (n, p) ¹⁴ C reaction can be reduced, and the generation of radiocarbon-14 can be suppressed. The term "nitrogen dioxide" as used in the present invention means that nitrogen 1 is combined with oxygen 2 and N ₂ in addition to NO _2.
It also includes ₂ O _{4 and the} like, and further includes a mixture thereof.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments of the invention. FIG. 1 is a configuration diagram showing a preferred embodiment of the direct cycle fast reactor of the present invention. The direct cycle fast reactor shown in FIG. 1 includes a reactor 1 and a turbine 2.
And a generator 3. Further, the regenerative heat exchanger 4 is provided between the outlet side of the turbine 2 and the inlet side of the reactor 1.
And a condenser 5 and a pump 6. The arrow in the figure indicates the direction in which the coolant flows in the direct cycle fast reactor.

The coolant heated in the core of the nuclear reactor 1 is directly guided to the turbine 2 to rotate the turbine 2, thereby driving the generator 3. The coolant discharged from the turbine 2 is introduced into the condenser 5 via the regenerative heat exchanger 4. Cooling water such as seawater or cold heat when vaporizing liquefied natural gas can be introduced into the condenser 5 from the outside, whereby the coolant is cooled and liquefied.

The liquefied coolant is sent to the regenerative heat exchanger 4 by the pump 6, and the heat exchange with the coolant discharged from the turbine 2 pressurizes it to a pressure higher than the critical pressure and raises it to the inlet temperature of the reactor 1. To be made. The coolant pressurized above the supercritical pressure reaches the core of the nuclear reactor 1 where it is heated again. Then, by going through the above-mentioned steps again, the generator is continuously driven to generate power.

In the direct cycle fast reactor shown in FIG. 1, a regenerative heat exchanger 4 and a condenser 5 are provided between the outlet side of the turbine 2 and the inlet side of the reactor 1 to condense the coolant into a liquid. The so-called Rankine heat cycle is used to shrink the volume. For this reason, a compressor for volumetrically compressing the coolant and a compression power for driving the compressor are unnecessary, so that the structure of the fast reactor can be simplified and downsized. Furthermore, by liquefying, the pump efficiency can be improved and the pump power can be reduced. Therefore, the power generation efficiency of the fast reactor can be improved.

Further, by using the vaporized cold heat of the liquefied natural gas for cooling in the condenser 5, it is possible to effectively utilize the vaporized cold heat which was conventionally wasted.
The coolant in the direct cycle fast reactor shown in FIG. 1 comprises supercritical carbon dioxide, ammonia, or nitrogen dioxide according to the present invention. When ammonia or nitrogen dioxide is used as the coolant, it is preferably nitrogen-isotopically enriched with nitrogen-15 in order to suppress the generation of radiocarbon-14 as described above.

In the direct cycle fast reactor shown in FIG.
The operation when supercritical carbon dioxide is used as the coolant is specifically carried out as follows. The supercritical carbon dioxide is heated to about 530 ° C. in the reactor 1 and has a pressure of about 15.5 MPa. The heated supercritical carbon dioxide reaches the turbine 2 to drive the turbine 2 and drive the generator 3 to generate electric power. After driving the turbine 2, the carbon dioxide reaching the turbine outlet has a temperature of about 420 ° C. and a pressure of about 6 MPa. Next, the carbon dioxide is guided to the condenser 5 by passing through the regenerative heat exchanger 4 and liquefied as a cooling liquid. As a result, the carbon dioxide becomes liquid carbon dioxide in the condenser 5 at a pressure of about 6 MPa and a temperature of about 25 ° C.

Next, this liquid carbon dioxide is sent to the regenerative heat exchanger 4 by the pump 6 and exchanges heat with the carbon dioxide discharged from the turbine 2 and having a temperature of about 420 ° C., so that the liquid carbon dioxide is pressurized above the supercritical pressure. At the same time, the temperature is raised to about 260 ° C., which is the inlet temperature of the reactor, and the temperature is again introduced into the reactor 1. Then, by repeating the above steps, continuous power generation is performed. It should be noted that the above shows one embodiment of the specific example, and the heating temperature and the like differ depending on the specific configuration and size of the fast reactor, the amount of power generation, and the like.

FIG. 2 is a schematic diagram showing another preferred embodiment of the direct cycle fast reactor of the present invention. The direct cycle fast reactor shown in FIG. 2 has the same structure as the direct cycle fast reactor shown in FIG. 1 except that a coolant storage tank 7 is provided between the regenerative heat exchanger 4 and the condenser 5. There is. By providing such a coolant storage tank 7, even in the unlikely event that a pipe breaks between the reactor 1 and the turbine 2, the pressure drop on the reactor 1 side causes the coolant to drop. The coolant stored in the storage tank 7 is automatically vaporized and supplied into the reactor. Therefore, it is possible to prevent the supply of the coolant into the reactor from being stopped due to the breakage of the pipe.

In the above description, the case of burning plutonium obtained by converting uranium-238 has been described, but it can also be used when burning uranium-235 or uranium-233 due to the constitution and characteristics of the present invention.

Although the present invention has been described in detail based on the embodiments of the invention with reference to specific examples, the present invention is not limited to the above contents and does not depart from the scope of the present invention. All modifications and changes are possible.

[0028]

As described above, according to the present invention,
Unlike liquid metal sodium, the coolant is composed of supercritical carbon dioxide, which is chemically inert to air and water. Therefore, even if the coolant leaks from the cooling system to the outside, it does not react with air, water, etc., so that damage to the cooling system and peripheral equipment can be prevented. Furthermore, since supercritical carbon dioxide does not boil during the operation of the fast reactor, the problem of core overheating due to the insertion of positive reactivity due to the generation of voids does not occur.

Further, since the turbine is directly rotated by the coolant heated in the nuclear reactor to drive the generator, the intermediate cooling system is not required and the structure itself of the fast reactor can be simplified. Further, since the structure of the fast reactor is simplified, the maintenance and operation of the fast reactor can also be simplified. Also, since the proportion of high-energy neutrons increases,
The production efficiency (growth ratio) of fissile substances such as plutonium-239 is increased, and minor actinide nuclides, which are long-lived radioactive wastes, can also be burned and reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a preferred embodiment of a direct cycle fast reactor of the present invention.

FIG. 2 is a structural diagram showing another preferred embodiment of the direct cycle fast reactor of the present invention.

[Explanation of symbols]

1 reactor 2 turbine 3 generator 4 Regenerative heat exchanger 5 condenser 6 pumps 7 Coolant storage tank

Continuation of front page (56) References JP-A-8-313664 (JP, A) JP-A-2000-2790 (JP, A) Yasushio KATO and Yoshi YOZAHIZAWA A, Direct Cycle Fast Reactor, Bull. Re s. Lab. Nucl. React. , Japan, October 31, 2000, Volume 24, pp. 85-86 (58) Fields investigated (Int.Cl. ⁷ , DB name) G21C 1/02 GDF G21C 15/00 GDF G21C 15/28 G21D 5/06

Claims (10)

(57) [Claims] 1. A reactor, a turbine, and a generator, which heat the coolant in the reactor by heat generated by burning plutonium obtained by converting uranium-238, and heating the coolant. A fast reactor in which the turbine is driven by a coolant, and the generator is driven to generate electric power, and the coolant is composed of supercritical carbon dioxide, and the coolant is directly supplied to the turbine. Direct cycle fast reactor, which is characterized in that 2. The direct cycle fast reactor according to claim 1, wherein a minor actinide nuclide is added to the plutonium and burned. 3. Uranium-2 in place of plutonium
The direct cycle fast reactor according to claim 1, wherein 35 is burned. 4. Uranium-2 in place of the plutonium
The direct cycle fast reactor according to claim 1, wherein 33 is burned. 5. The direct cycle fast reactor according to claim 1, wherein the coolant is composed of ammonia instead of the supercritical carbon dioxide. 6. The direct cycle fast reactor according to claim 5, wherein the ammonia is composed of nitrogen obtained by isotopically enriching nitrogen-15. 7. The direct cycle fast reactor according to claim 1, wherein the coolant is composed of nitrogen dioxide instead of the supercritical carbon dioxide. 8. The direct cycle fast reactor according to claim 7, wherein the nitrogen dioxide is composed of nitrogen obtained by isotopically enriching nitrogen-15. 9. A regenerative heat exchanger and a condenser are provided between an outlet side of the turbine and an inlet side of the reactor, and the coolant discharged from the turbine is passed through the regenerative heat exchanger. And then liquefied by being introduced into the condenser to be cooled, and the liquefied coolant is introduced into the regenerative heat exchanger to exchange heat with the coolant discharged from the turbine to achieve supercritical pressure or higher. The direct cycle fast reactor according to any one of claims 1 to 8, characterized in that the pressure is applied to the reactor and the temperature is raised to the inlet temperature of the reactor before being introduced into the reactor. 10. A coolant storage tank is provided between the regenerative heat exchanger and the condenser.
Direct cycle fast reactor described in.