JP3950392B2 - Reactor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure of a nuclear reactor, and more particularly to a structure of a nuclear reactor that does not require operations for controlling the reactivity of a core.
[0002]
[Prior art]
In a conventional nuclear reactor, in order to suppress the excessive reactivity of the core and maintain the effective multiplication factor of the core at 1.0, the control rod including the neutron absorber is inserted and pulled, or the neutron absorber is included in the primary coolant. Reactivity control operations such as changing the neutron absorber concentration by dissolving the neutrons are performed.
Such an operation for controlling the reactivity of the core is one of the most important technologies for safely operating the nuclear reactor, and at present, automatic operation by computer control is achieved.
[0003]
[Problems to be solved by the invention]
However, while carrying out automated operation of such a reactor, in the event of a failure of the reactor equipment, multiple operators with skilled technology and knowledge constantly monitor the operating state of the reactor 24 hours a day In addition, if necessary, the reactor must be operated manually. For this reason, it is necessary to respond to the facility so that manual operation is possible, and to train operators for manual operation.
Reactor monitoring work by operators for reactivity control accounts for a major part of the cost required for reactor operation.
[0004]
On the other hand, the change in reactivity during normal operation is very small, and in order to detect this constantly and perform delicate reactivity control operations, there is a demand for equipment with highly reliable and precise structure and function. In addition, in order to make a highly reliable nuclear reactor, it is necessary to assume that the reactivity input or the loss of reactivity occurs due to the abnormality of the reactivity control system. In such a situation, it is necessary to multiplex the facilities independently, for example, by providing a plurality of control rods for controlling the reactivity independently so that the reactor can be safely shut down. The introduction of such precise reactivity control and equipment for dealing with abnormalities in the reactivity control system accounts for a major part of the reactor construction cost.
[0005]
The present invention has been made to solve such problems, and does not require a reactor monitoring operation for reactivity control, and is equipped with equipment for precise reactivity control and reactivity control system abnormality handling. The purpose is to provide an unnecessary nuclear reactor.
[0006]
[Means for Solving the Problems]
The nuclear reactor according to the present invention is composed of a sub-core in which the core is divided into a plurality of cores , each of the sub-cores has a pressure tube and a fuel body inside the pressure tube, and is included in at least two of the sub-cores. The amount of flammable poisons to be loaded is different.
Further, the plurality of sub-cores are divided into one central sub-core and a plurality of peripheral sub-cores arranged radially around the central sub-core, and the amount of combustible poison contained in the central sub-core is The amount of combustible poison contained in the peripheral sub-core can be reduced.
A control rod is provided between the sub-cores, and this control rod can be used in a drawn state during normal operation.
Sub core is in the interior of the pressure tube may consist of nuclear steam supply cassette having a steam generator.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an elevational sectional view of a nuclear reactor 20 according to an embodiment of the present invention, and FIG.
As shown in FIG. 2, seven nuclear steam supply cassettes 21 are arranged radially from the center in a moderator tank 31 filled with a moderator 30 of light water, heavy water, or graphite.
As shown in FIG. 1, the nuclear steam supply cassette 21 includes a pressure pipe 22 and a steam generator 23 arranged circumferentially from the center to the top of the inner wall thereof. Is provided with an in-cassette core 24 constituting a fuel assembly.
The pressure tube 22 is an elongated cylindrical tube having a diameter of about 50 cm and a length of several meters, for example, a pressure tube liner 25 made of a metal material such as stainless steel, and a carbon fiber on the outer peripheral surface thereof. And a reinforcing fiber layer 26 reinforced with strength. Between the pressure tube 22 and the core 24 in the cassette, a downcomer portion 27 in which the primary coolant 28 enclosed in the pressure tube 22 flows downward is formed. Further, a riser 29 is formed above the core 24 in the cassette to raise the primary coolant 28 heated by the core 24 in the cassette, so that the primary coolant 28 is indicated by an arrow in the pressure tube 22. It is configured to circulate.
[0008]
As shown in FIG. 2, among the in-cassette cores 24 of the nuclear steam supply cassettes 21 arranged radially, the in-cassette core 24 at the center constitutes the central in-cassette core 24 c and has a circumference around it. The in-cassette core 24 constitutes a peripheral cassette in-core 24d, and the reactor 20 as a whole constitutes an in-package core in which a plurality of in-cassette cores 24 are combined.
That is, in this nuclear reactor 20, the core of the entire nuclear reactor is divided and arranged in a plurality of nuclear steam supply cassettes 21, the central cassette core 24c is the central sub-core, and the peripheral cassette core 24d is the peripheral sub-core. Multi-sub core structure.
[0009]
Here, the core 24c in the central cassette includes a flammable fuel such as uranium and plutonium having a loading amount c1, and a flammable poison such as boron having a loading amount c2. Further, the core 24d in the peripheral cassette includes a fissile fuel having a loading amount d1 and a combustible poison having a loading amount d2. The ratio of the flammable poison loading amount between the core 24c in the central cassette and the core 24d in the peripheral cassette has a relationship of c2 <d2, and the flammable poison loading amount d2 in the core 24d in the peripheral cassette is the center cassette. The combustible poison loading amount c2 of the inner core 24c is increased.
[0010]
Further, as shown in FIG. 2, around the nuclear steam supply cassette 21 in the center, six control rods 32 are arranged on the circumference so as to cover the core 24 in the center cassette. The control rod 32 is composed of three plate-like members extending between adjacent nuclear steam supply cassettes 21 and extends in the vertical direction along the core 24 in the cassette as shown in FIG. Are connected to the control rod drive 33. The control rod driving device 33 moves the control rod 32 up and down.
Here, the control rod 32 in the nuclear reactor 20 is used as an emergency stop system facility for the nuclear reactor. During the normal operation of the nuclear reactor 20, the reactor 20 is fully pulled out. At the time of reactor scram, which is when an abnormality occurs in the reactor 20, or when the reactor is shut down, the control rod 32 is inserted downward so that the core in the package can always be subcritical.
[0011]
A heat insulating material 34 is wound around the outer peripheral surface of the moderator material tank 31, and a water shielding tank 35 is provided outside the heat insulating material 34. The water shielding tank 35 is filled with shielding water 36, and the shielding water 36 shields neutrons and gamma rays emitted from the respective cores 24 in the cassette from the outside.
[0012]
Before the reactor 20 is started up, the liquid level of the primary coolant 28 stored in the pressure pipe 22 is at the position H1, and the steam generator 23 is submerged, and is placed in the upper part 21b of the nuclear steam supply cassette 21. Is formed with a gas phase portion 28a. Further, as a supply / discharge path for the secondary coolant 43 of the steam generator 23, a secondary coolant pipe 44 provided with an on-off valve 41 is disposed on the way, and is connected to a turbine and a pump (not shown). Further, a pipe 39 is disposed through the upper portion 21 b of the nuclear steam supply cassette 21 and connected to the pressure reducing valve 40 in the storage container 42.
[0013]
On the other hand, a piping 37 is disposed through the bottom 21a of the nuclear steam supply cassette 21 and passes through the bottom surface of the moderator tank 31 and is connected to an emergency cooling water supply valve 38 provided in the water shielding tank 35. Has been.
When the heat generation function of the nuclear steam supply cassette 21 is lost, such as when heat exchange cannot be performed in the steam generator 23, the shield water 36 in the water shield tank 35 is transferred from the emergency cooling water supply valve 38 to the nuclear steam supply cassette 21. The core 24 in the cassette is cooled, and the steam generated in the nuclear steam supply cassette 21 is decompressed by the pressure reducing valve 40 and discharged to the outside of the nuclear steam supply cassette 21.
In addition, an air flow path 45 for air-cooling the storage container 42 is formed on the outer periphery of the storage container 42.
[0014]
Next, the operation of the nuclear reactor according to the embodiment of the present invention will be described.
As shown in FIG. 1, before starting the nuclear reactor 20, the control rod 32 is inserted by the control rod driving device 33 to the lower part of the moderator tank 31 so as to cover the core 24 c in the central cassette from the surroundings. Is in a subcritical state. Thereafter, the operation of the nuclear reactor 20 is started, the control rod 32 is pulled upward, and combustion is started when the fully pulled state is reached.
FIG. 3 shows a graph of the change over time of the reactivity associated with the combustion of the core in the central cassette 24c, the core in the peripheral cassette 24d, and the core in the package combining these after the start of combustion.
At the beginning of combustion, the fission chain reaction is maintained only in the core 24c in the central cassette, and the reactivity of the core 24 in the central cassette is positive. However, since the amount c2 of combustible poisons in the central cassette core 24c is small and neutrons are small, neutrons generated in the central cassette core 24c are supplied to the peripheral cassette core 24d.
[0015]
Since the peripheral cassette core 24d has a large amount of combustible poison loading c2, the reactivity of the peripheral cassette core 24d is negative. However, as the neutron is supplied, the combustible poison reacts with the neutron and disappears. Go. As the flammable poison loading c2 decreases, the reactivity of the core 24d in the peripheral cassette increases, and the peripheral cassette core 24d alone can maintain the fission chain reaction. Further, as the combustion proceeds, the reactivity of the core 24c in the central cassette alone decreases, but the fission chain reaction in the core 24d in the peripheral cassette is maintained.
[0016]
Next, looking at changes in the reactivity of the entire core in the package over time, even if the heat generation amount of the entire core in the package is constant, it is maintained near 0%, and the reactivity can be controlled only by self-controllability. Is in range.
Here, self-controllability refers to the Doppler effect that causes a negative reactivity change when the reactivity increases and the temperature of the core in the package reactor rises, and when the reactivity increases and the temperature of the moderator 30 increases, the moderator By the moderator density coefficient effect that changes the density of 30 and causes a negative reactivity change, the reactivity can be maintained in the vicinity of 0% without exceeding the allowable range, which is also called the reactivity feedback effect.
In this way, by shifting the timing of the fission chain reaction of the core 24 in the cassette and maintaining the reactivity within a range not exceeding the allowable range, the calorific value of the entire core in the package does not change greatly, and the self-control inherent to the core The reactivity can be controlled only by the property, and the reactivity control by inserting and pulling out the control rod and the reactivity control by changing the concentration of the neutron absorber in the primary coolant become unnecessary.
[0017]
FIG. 4 shows an evaluation example of a change in surplus reactivity over time associated with combustion of the nuclear reactor according to this embodiment when the heat generation amount of the entire core in the package is constant.
In the plurality of nuclear steam supply cassettes 21 used for this evaluation, the core 24c in the central cassette contains 10 wt% enriched uranium corresponding to about 860 fuel rods as the loading amount c1, and the loading of the flammable poison The quantity c2 is 0 and no flammable poison is loaded. The peripheral cassette core 24d contains 10 wt% enriched uranium corresponding to about 770 fuel rods (about 90% of the loaded quantity c1) as the loaded quantity d1. Furthermore, the peripheral cassette core 24d contains natural boron corresponding to about 90 combustible poison rods as a combustible poison with a loading amount d2.
[0018]
As shown in the solid line in FIG. 4, the maximum surplus reaction of the core in the package is achieved when the entire combustion of the nuclear reactor 20 configured as described above achieves a high burnup with an extraction average burnup of 70 GWd / t. The degree is about 5%, and the surplus reactivity change rate is 0.1% / (GWd / t). Therefore, these values are about 1/5 or less of the core of a normal nuclear reactor indicated by a broken line, and are very small.
Thus, by making the flammable poison loadings of the central cassette core 24c and the peripheral cassette core 24d different, the time when each of the cassette cores 24 can maintain the fission chain reaction independently is shifted. The surplus reactivity of the core in the package can be maintained at almost 0% only by the inherent self-controllability.
[0019]
As described above, for example, the amount of combustible poisons loaded in each cassette core 24 is adjusted, and for several years from the start of operation of the reactor 20, the fission chain reaction is maintained independently for the core cassette core 24c. For several years, the nuclear reactor 20 can be operated for a long time without refueling by maintaining the fission chain reaction independently for the plurality of peripheral cassette cores 24d.
Further, since the divided sub-cores can be provided in the nuclear steam supply cassette 21, it is easy to make the amount of combustible poisons loaded for each sub-core different. Furthermore, a desired power generation amount can be obtained according to the number of nuclear steam supply cassettes 21.
[0020]
The present invention described above is not limited to the above, and can be implemented with appropriate modifications.
For example, in the above-described embodiment, a plurality of nuclear steam supply cassettes 21 are used to divide the entire reactor into a plurality of cores. However, the present invention is not limited to this, and there is one core in the reactor vessel. In a conventional nuclear reactor that only exists, the core may be divided into a plurality of parts, and the amount of combustible poison contained in the divided core may be different. That is, such a multi-sub core structure can be applied to a conventional nuclear reactor.
Further, as shown in FIG. 1, the liquid level of the primary coolant 28 filled in the nuclear steam supply cassette 21 was at the position H1, but the liquid level was set at the position H3, All of the generator 23 may be exposed. In this case, heat exchange with the secondary coolant 43 is performed by the primary coolant 28 that has become boiling steam. That is, by using the coolant boiling in the nuclear steam supply cassette 21 as in the conventional boiling water light water reactor, the reactivity control only by the self-controllability inherent in the core is further facilitated.
[0021]
【The invention's effect】
As described above, according to the present invention, the core of the entire nuclear reactor is composed of a plurality of sub-cores , each sub-core having a pressure tube and a fuel body inside the pressure tube, At least because the amount of combustible poisons contained in the two sub-cores is different, the allowable range in which the reactivity of the entire nuclear reactor can be controlled only by self-control by shifting the time when the fission chain reaction can be maintained in the sub-core alone Can be maintained. Therefore, reactor monitoring work for reactivity control, precise reactivity control, and equipment for dealing with abnormalities in the reactivity control system can be eliminated.
[Brief description of the drawings]
FIG. 1 is an elevational sectional view showing a structure of a nuclear reactor according to an embodiment of the present invention.
FIG. 2 is a cross-sectional plan view of the nuclear reactor shown in FIG.
FIG. 3 is a graph showing a concept of a change in reactivity of a core accompanying combustion of a nuclear reactor according to an embodiment.
FIG. 4 is a graph showing an evaluation example of a change in the excess reactivity of the core accompanying combustion of the nuclear reactor according to the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 20 ... Package type nuclear reactor, 21 ... Nuclear steam supply cassette, 22 ... Pressure pipe, 23 ... Steam generator, 24 ... Core in cassette, 24c ... Core in core, 24d ... Core in peripheral cassette, 32 ... Control rod.

Claims (4)

The core is composed of sub-cores that are divided into multiple parts.
Each of the sub-cores has a pressure tube and a fuel body inside the pressure tube,
At least nuclear reactors having different flammable poison loadings contained in the two sub-cores. The plurality of sub-cores are divided into one central sub-core and a plurality of peripheral sub-cores arranged radially around the central sub-core,
The nuclear reactor according to claim 1, wherein a combustible poison loading amount contained in the central sub-core is smaller than a combustible poison loading amount contained in the peripheral sub-core. A control rod is provided between the sub-cores,
The nuclear reactor according to claim 1, wherein the control rod is used in a pulled-out state during normal operation. The sub-core is in the interior of the pressure tube reactor according to claim 1 consisting of a nuclear steam supply cassettes having a steam generator.

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