JPS59196497A - Pwr type reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressurized water nuclear reactor characterized by an output control device that can respond to rapid output changes and can control output distribution.

Conventionally, a control rod made of a neutron absorbing material has been used as a means of output control in a nuclear reactor, and the neutron absorbing material of the control rod is usually set evenly in the axial direction from the upper end to the lower end.

In addition, when controlling the exit direction of the reactor using the control rods, the power distribution within the reactor changes by vertically moving the control rods, and the reactor-specific reactivity feedback due to changes in the exit direction. The output distribution changes due to
On the other hand, in order to operate a nuclear reactor safely and efficiently, it is necessary to limit the output distribution within a certain range. (For example, if the reactor power becomes excessive, the fuel in that area will be damaged.) In other words, reactor power control requires control of neutron flux, that is, control of reactivity, and control of power distribution. For example, Japanese Patent Publication No. 43-20225 proposes a control rod in which elements with different neutron absorption capacities are arranged in a track shape in descending order of neutron absorption capacity. The distribution of neutron absorption capacity has not been clarified, and the track-shaped control rods cannot be applied to current pressurized water reactors.

Furthermore, as a power distribution control means currently adopted, there is a constant axial neutron flux operation method. The power distribution tends to be biased toward the upper part of the core, but this is because the moderator temperature coefficient of the reactor is negative, so a decrease in power causes the moderator temperature in the upper part of the core to decrease, which causes positive reactivity in the upper part of the core. This is because it is added. Control rods are inserted into the reactor core from above in order to correct the distortion in the power distribution and to perform plate stress control necessary to reduce the power.

However, control rod insertion at this time is mainly for power distribution control, and inserting control rods to the point where sufficient reactivity is compensated for the output drop is not allowed from the perspective of power distribution control (abnormal distribution occurs).

Therefore, another method of reaction control is performed, namely control of the neutron absorber concentration in the primary coolant. In this control method, since the neutron absorbing material is uniformly distributed within the reactor, changes in the power distribution that pose a problem in power distribution control do not occur. Furthermore, when returning from a low output state to the rated output, the above-mentioned operation is generally reversed. However, this method has a weakness in that it also uses reactivity control by adjusting the concentration of neutron absorber in the coolant. Further, fluoric acid is usually used as a neutron absorbing material in the coolant, and the two methods described below are currently used alone or in combination to adjust its concentration. One of the methods is to dilute the concentration of acrylic acid by extracting the secondary coolant and simultaneously injecting an equal amount of pure water, and to concentrate it, the same amount of pure water is injected. This is done by injecting high-concentration boric acid water instead of pure water to adjust the boric acid concentration in the entire secondary system, but because the amount of injection is limited compared to the amount of coolant in the secondary system, there is a time delay. There is a drawback.

t. Other methods iii. Using an ion exchange resin, the difference in the adsorption of boron depending on the temperature of the resin is utilized. In this case as well, the entire primary coolant is brought into contact with the resin and the temperature of the resin is controlled. Because of this, it is impossible to avoid time delays, and it is not possible to respond as quickly as with control rods, making it impossible to respond to rapid changes in the direction of deployment. That is, the rate of change in output is limited by the ability to control the concentration of neutron absorber in the primary coolant.

Furthermore, as an operating method to reduce the degree of insertion of control rods into the reactor core, which causes a large change in the distribution of the rods, as in Japanese Patent Publication No. 51-47837, a large number of control assemblies are arranged in the same structure and in the same manner of use. A system has been developed in which the output is varied by three types of control banks: an output control bank, a Doppler control bank, and a xenon control bank. It controls only the Doppler effect reactivity due to
K is designed so that it is used as a full drawer at the rated output. However, in this method, all the reaction production necessary for output control is performed by control rods, so it is thought that it can cope with rapid output changes, but it ignores reactivity changes due to moderator temperature changes, and , no consideration has been given to output distribution control.

The present invention was developed in view of the above-mentioned actual situation, and the neutron absorption capacity of control rods inserted into a reactor core composed of a large number of nuclear fuel assemblies is set evenly in the vertical direction. A control rod assembly group that can be freely moved in the vertical direction, and a control rod assembly group inserted into the reactor core, whose neutron absorption capacity is set to be small in the lower part and large in the upper part, and that can be freely moved in the vertical direction, and when operating at rated power, the control rods are inserted into the reactor core. It is characterized by being equipped with a power control device consisting of a group of control rods for power distribution control that are arranged on the outside. The object of the present invention is to provide a pressurized water nuclear reactor that has a quick reactivity control function and eliminates the above-mentioned drawbacks.

The present invention has the above-mentioned configuration, and includes a control rod assembly group that can be freely moved in the vertical direction in which the neutron absorption capacity of the control rods is set equally in the vertical and vertical directions, and a group of control rods that can be freely moved in the vertical direction and the neutron absorption capacity of the control rods is set to be equal in the vertical direction. The control rod assembly group is provided with a control rod assembly group for power distribution control that is set to a large value and can be freely moved in the vertical direction and is placed outside the reactor core during rated power operation. It is possible to control the low power of a pressurized water reactor by fully inserting the control rod assembly group for power distribution control, and it is possible to perform low power control of a pressurized water reactor by fully inserting the control rod assembly group for power distribution control.In addition to controlling the power of only the control rods, the neutron absorption capacity is set to be small at the bottom and large at the top. By fully inserting all control rods, it is possible to respond to rapid output changes and control output distribution, resulting in safety and
It has a high-efficiency, quick reactivity control function with little distortion in power distribution, and significantly improves the power control performance and reliability of pressurized water reactors.

Embodiments of the present invention will be described below with reference to the drawings.

To explain a pressurized water reactor with a thermal output class of 2.7 million KW and a standard 3-loop system, as shown in Figure 4, its core is composed of 157 fuel assemblies, as well as cluster-type control rod assemblies. A power control device in which 48 control rod assemblies are arranged and further 13 backup control rod assemblies can be attached is attached to the core.

The above-mentioned 48 control rod assemblies are arranged so that they can be freely moved in the vertical direction with equal neutron absorption capacity in the vertical axis direction, and the 6 control rod assemblies are used in the same manner of use, that is, for the same mission. groups or banks, stop banks (SA), (S
B) and control banks (Al, (B), and (C)), all of the banks are for output control, and the control bank (DJ) is used during normal operation.

Furthermore, in this embodiment, in addition to the control bank, a group of control rod assemblies for power distribution control consisting of five control rod assemblies, that is, an output control bank (D) is provided. Each control rod assembly has a structure in which its neutron absorption capacity is set to be small in the lower part and large in the upper part, and the power control bank (PJ) provides the negative reactivity necessary for reducing the output, and also In order to correct the distortion in the power distribution caused by this, the configuration is adjusted as described above, and at low power, the control pin is inserted over the entire length of the top and bottom of the core, and at rated power, it is pulled out and placed outside the core. It has an output distribution control function as well as a normal output control function, and is configured to be freely movable in the vertical direction.

Further, it is also possible to compensate for some correction of reactivity and output distribution using the control bank (D) in the conventional manner.

The embodiment of the present invention has the above-mentioned configuration, and has the above-mentioned control rod assembly groups, that is, control banks (AJ, OUT, (Q,
(D), and the effectiveness and practicality of controlling the output of a pressurized water reactor using a power control device consisting of the aforementioned control rod assembly group for power distribution control, that is, the power control bank (8). To explain using computer simulation results, at a certain time T, the output is rapidly reduced from the rated output state to 50% output at a rate of 5%/minute, and after maintaining that 50% output state for up to 6 hours. ,next,
Similarly, the main parameters when carrying out daily load follow-up cycle operation in which the output is increased to the rated output at a rate of 5% and 100% and maintained 24 hours a day are shown in Figures 1 and 2. The figure shows a control rod assembly group, or control bank (AJ,
(B), (c+, only a part of (D) is used (stop bank (SA), (SB) and (N, (B), (part of q is fully drawn), and the curve (1) is the relative power of the reactor, curve (2) is the control bank (A) (or (B)
, (C) and curve (3) are the relative positions in the core of the control bank (D), where 1.0 and 0.0 indicate their fully withdrawn and fully inserted positions, and FIG. , a control rod assembly group for power distribution control in which the neutron absorption capacity of the control rods is set to be small in the lower part and large in the upper part, that is, the power control bank (B) and the control bank (Di), and the curve (2
) indicates the output control bank (8), and the 1.2
Curves (4) and (4) in the figure show the respective axial neutron flux deviations (Δ
The deviation (∆mechanism) is expressed by the following formula.

P: Relative power of the core (Also, the dotted line (5) in the same figure indicates a certain tolerance range, that is, a tolerance range, in order to provide flexibility in operation in constant axial neutron flux operation. In the case of Fig. 1, the control bank (A) (or (
The control bank (D) is fully inserted, and the lack of reactivity is supplemented by the control bank (D).
) is also inserted to keep the axial neutron flux deviation (Δc) within the permissible range. However, if this state continues, the power distribution will shift in the negative direction due to changes in the concentration of xenon (which absorbs neutrons but has a short half-life) among the fission products, that is, in the lower half of the core. The output of the upper half of the reactor increases, and conversely the output of the upper half decreases, increasing the unbalance of the Shimoda force above the core. The deviation (Δwork) is controlled within the allowable range (within the dotted line (5)).

However, in order to return to the rated output, the control bank was pulled out (and the output distribution was changed so that the deviation (Δwork) was outside the negative tolerance range, and the deviation (Δwork) was controlled by control rod operation. I can do it,
In other words, even if the control rods are inserted in this state, the power distribution will further increase the power in the lower half of the core, decrease the power in the upper half, and the deviation (Δwork) will become even more negative. to move to. Operation with constant axial neutron flux becomes impossible.

In order for the above-mentioned operation to be possible, all operations must be possible within the allowable range of the above-mentioned deviation (Δ machining).

In addition, in Figure 2, since the output bank (8) is used, the output distribution change at low output is extremely small (so that even after the rated output is restored, the deviation (Δwork) is within the allowable range. At the 17th hour from the time ('If), a control bank is inserted a little to prevent the deviation (Δwork) from deviating to the positive side, and after 2 hours, the deviation (Δwork) becomes negative. Although it is pulled back to its original position to prevent it from deviating to the side, the deviation (Δwork) is well controlled.

In addition, in FIGS. 1 and 2, the control bank (DJ
The fact that it is not fully withdrawn is in accordance with the requirements established by operational necessity.

Further, FIG. 3 shows the axial neutron absorption capacity of the output control bank (P), and the curve (6) is expressed by taking the control bank peak as a reference trap and setting its absorption capacity as 1.0, Curve (7) is the output control bank (8'P) used in the simulation of FIG. That is,
As is clear from the figure, by using only the control rods and fully inserting the output control bank (P), it is possible to respond to rapid output changes and control the output distribution, ensuring safe and highly efficient output distribution. It has a quick reactivity control function with little distortion,
The power control performance and reliability of pressurized water reactors are significantly improved.

Although the present invention has been described above with reference to embodiments, it goes without saying that the present invention is not limited to these embodiments, and that various design changes can be made without departing from the spirit of the invention. be.

[Brief explanation of the drawing]

Figure 1 is a diagram of the main parameters in power control of a pressurized water reactor using only a group of control rod assemblies in which the neutron absorption capacity of the control rods is set equally in the upper and lower axial directions, and Figure 2 is a group of control rod assemblies for power distribution control. Figure 3 is a diagram of the neutron absorption capacity of the control rod assembly group for power distribution control, and Figure 4 is a structural layout diagram of the core and control rods of a pressurized water reactor. A.8. C, D: Control rod assembly group (control bank) SA
, SB: Group of control rod assemblies (stop bank) P: Group of control rod assemblies for power distribution control (output control bank) Sub-agent Patent attorney Shige Okamoto 2 outsiders (%lct禾eE114'IIJ) Qζ, 11dl11
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('/,) Continuation of page 1 of 117 ■Applicant: Kansai Electric Power Co., Inc., 3-3-22 Nakanoshima, Kita-ku, Osaka ■Applicant: Shikoku Electric Power Co., Inc., No. 2-5, Takamatsu Seijinouchi ■Applicant: Kyushu Electric Power Co., Ltd. 2-1-82 Watanabe-dori, Chuo-ku, Fukuoka ■Applicant Japan Atomic Power Co., Ltd. 1-6-1 Otemachi, Chiyoda-ku, Tokyo Applicant Mitsubishi Heavy Industries, Ltd. Chiyoda, Tokyo 2-5-1 Marunouchi Ward

Claims (1)

[Claims] A group of control rod assemblies that can be freely moved in the vertical direction, with the neutron absorption capacity of the control rods inserted into a reactor core made up of a large number of nuclear fuel assemblies set equally in the vertical axial direction, and a control rod assembly that is inserted into the reactor core. The neutron absorption capacity of the rods is set to be small in the lower part and large in the upper part, and is movable in the vertical direction, and is equipped with a power control device consisting of a group of control rod assemblies for power distribution control placed outside the core during rated power operation. A pressurized water reactor characterized by: