JPH01299495A - Operation control of nuclear reactor - Google Patents

Abstract

PURPOSE:To keep a load following capability with a rather small number of control rods, by providing both low absorption control rods and high absorption control rods and by selecting one of both kinds of the rods according to a received signal of an averaged temperature deviation of a nuclear reactor coolant with a consideration of a deviation signal of an axial output distribution. CONSTITUTION:By this particular method, a low absorption control rod GR is selected by a deviation signal from a standard value of an averaged temperature of a primary coolant, otherwise, a high absorption control rod D is selected according to a deviation DELTAI of an axial output distribution shown as an equation I. In case that a deviation from a standard value of an averaged primary coolant temperature, that is, a temperature deviation DELTAT, is negative, which means a case of a withdrawal demand, the deviation DELTAI of an axial output distribution moves towards a positive side. With this reason, in case that the DELTAI is more negative than a certain value compared to a control target, the high absorption control rod D is selected and otherwise the low absorption control rod GR is selected, alternatively. With this sort of procedure, the reactor can be controlled, neglecting a meaningless movement of control rods and a mutual interfere of both kinds of the control rods.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the operation of a nuclear reactor, which is applied to operations involving changes in output, for example, in a pressurized water nuclear reactor.

[Prior art] For example, in a pressurized water reactor, operation that involves changes in reactor output in response to changes in load can be divided into the following three basic modes, and these modes can be operated singly or in combination. be done.

(1) Operation mode based on a predetermined output change pattern (2) Operation mode that randomly changes output according to external requests (3) Frequency adjustment, etc. due to external requests or load changes This is an operation mode that automatically changes output according to changes.

In general, the requirements for the power variation range of a nuclear reactor are as follows (1)
), (2), and (3), and the frequency of requests for output changes is highest in the order of (3), (2), and (1).

Conventionally, reactivity was adjusted for these operations by moving one type of control rod group with multiple groups and manually adjusting the boron concentration in the secondary coolant. When the output change rate is large, the output change width is limited to a small one from the viewpoint of keeping the output distribution and distortion within the limit values, and restrictions are added to the operation mode (1).

Therefore, in order to solve this problem, a method has been proposed that uses two types of control rod groups that have different degrees of influence on the output distribution.

As a specific example of this, as shown in Japanese Patent Publication No. 58-34795, the degree of insertion of the control rod group that has a smaller effect on the power distribution (hereinafter referred to as weak absorption control rods) is determined as a function of the required turbine output. The control rod group (
The strong absorption control rod (hereinafter referred to as a strong absorption control rod) moves according to the deviation of the average temperature of the -order coolant from the reference value, and changes the average temperature by adjusting the boron according to the deviation of the axial power distribution. This is a method (hereinafter referred to as F method) of keeping the axial power distribution deviation within a predetermined range.

In addition to this F method, as shown in Japanese Patent Application No. 61-206836, strong absorption control rods are used to adjust the control rods to control rods when the output changes or according to the deviation of the average temperature of the primary coolant from the reference value that occurs along with the change in output. The weak absorption control rod is moved according to the axial power distribution deviation, and the strong absorption control rod is moved through the resulting average temperature deviation to keep the axial power distribution deviation within a predetermined range. The adjustment of the intensity is a method (hereinafter referred to as the M method) that is mainly used as an auxiliary for weak absorption control rods.

The F method and M method described above have the following differences in performance. Generally, the performance for the operations (1) to (3) above is evaluated mainly based on the following points.

(4) Arbitrarity with load patterns, that is, ability to follow sudden load changes and unplanned random load changes. (5) Water treatment amount: Although it is necessary to treat wastewater associated with desert level adjustment,
The amount of water treated by the plant increases as the range of adjustment of the degree of desertification increases. Further, even if the adjustment range is the same, the amount of water treated increases as the degree of desertification in the secondary coolant decreases.

Therefore, in the case of an operating method that is highly dependent on crawling degree adjustment, load following operation is limited at the end of the core life.

(6) Burden on equipment The number of operations of each control equipment increases due to various parameter fluctuations accompanied by changes in output, but the control rod drive mechanism in particular is difficult to replace, so the amount of control rod movement must not become excessive. is necessary.

(7) Equipment costs This is the equipment cost required to perform load following operation.

[Issues to be Solved by the Invention] However, in the operation of a nuclear reactor that includes changes in output as described in (1) to (3) above, control elements such as control rods and boron generally do not control the combustion of fuel. In addition to the accompanying long-term adjustment of core reactivity, it is necessary to compensate for the following two reaction changes.

(8) Changes in reactivity caused by temperature changes in the moderator and fuel accompanying changes in output (hereinafter referred to as output loss).

(9) Changes in reactivity (hereinafter referred to as Xe) due to changes in the amount of xenon (hereinafter referred to as
(referred to as e-deficiency).

In method F, the weak absorption control rod is inserted to substantially compensate only for the output loss, so full output can be quickly restored at any time, and as in (2) above,
While it is adaptable to random output change requests, compensation for the Xe deficiency is essentially only by adjusting the degree of desertification, so the amount of water to be treated as described in (5) increases, which is preferable. do not have. In addition, when performing the operation described in (3) above, there are very frequent changes in output, but when the weak absorption control rod position is controlled as a unique function of output as in this method, ) operation will be compensated for only by the weakly absorbing control rods, and due to their small reactivity value, the control rod movement will be excessive, resulting in the above (6)
There are problems like this.

Method M can solve the problems of method F described above, but it does not require a relationship in which the axial power distribution deviation is corrected by a strong absorption control rod through a change in the average primary coolant temperature caused by the movement of the weak absorption control rod. First, in order to avoid mutual interference between the control rods of both groups, it is necessary to significantly reduce the influence on the power distribution of the weakly absorbing control rods compared to method F above, which inevitably reduces the number of control rods required. increases, and the gap point in (7) above occurs.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a nuclear reactor operation control method that can ensure the required load following ability with a relatively small number of control rods and can reduce the amount of water to be treated.

[Means for Solving the Problem] In order to achieve the above object, the present invention has a weak absorption control rod and a strong absorption control rod as control rods inserted into and removed from the core of a reactor vessel, and has a reactor coolant. When operating a nuclear reactor equipped with a thermal desertification control device connected to the circulation system, an average temperature deviation signal of the reactor coolant is received, and an axial power distribution deviation signal (
This is a nuclear reactor operation control method in which one of the two control rods is selected taking into account ΔI) and the in-reactor reactivity is adjusted.

[Function] As described above, by selecting and moving either the strong absorption control rod or the weak absorption control rod according to the deviation of the average temperature, the load following ability required by a relatively small number of control rods can be achieved. can be secured, and the amount of water to be treated can be reduced.

[Example 7] Examples of the present invention will be described below with reference to the drawings. First, the concept of the operation control method of the present invention will be explained with reference to FIG. - Weak absorption control rod GR or strong absorption depending on the deviation signal of the average coolant temperature from the reference value! The control rod is selected and driven according to the axial power distribution deviation ΔI shown by the following equation. This selection means that the deviation of the axial output distribution deviation ΔI from the control target value at that point is
If the control rod movement is performed by a strongly absorbing control rod,
If the temperature deviation is corrected at the same time, the strong absorption control rod is selected; otherwise, or if the deviation from the target value becomes larger when the strong absorption control rod is moved.
Axial output distribution deviation Δ! This is done so that the weak absorption control rod GR that has less influence on the control rod GR is selected.

ΔI-mP, -P8 PT: Ratio of the power of the upper half of the core to the core rated power (%
) PB: Ratio of the power of the lower half of the core to the core rated power (%
) Next, the concept of drive control rod selection based on the axial power distribution deviation ΔI will be explained with reference to FIG. - If the deviation of the average temperature of the next coolant from the reference value, that is, the temperature deviation ΔT, is negative, that is, in the case of a withdrawal request, when the strong absorption control rod is withdrawn, the axial power distribution deviation Δ■ shifts to the positive side. Therefore, as shown in Fig. 2(a), if ΔI is on the negative side to a certain extent (for example, 2%) or more with respect to the control target [second
The strong absorption control rod is selected in the shaded area in Figure (a), and the weak absorption control rod GR is selected in other cases. Similarly, when the temperature deviation ΔT is positive and a control rod is inserted, the opposite is true, and as shown in Figure 2 (b), ΔI has a positive deviation of more than a certain degree (for example, 2%) from the control target. If the strong absorption control rod is present [the shaded area in Fig. 2 (b)], the strong absorption control rod is selected and inserted; otherwise, the weak absorption control rod GR is selected and inserted. be done.

With this method, the movement of the control rods is driven by the best option considering the power distribution at that time, ignoring unnecessary movement of the control rods, and controlling the interaction between the two types of control rods. Can be controlled by ignoring interference. In addition, in the case of the selection index as shown in FIG. 2, the weak absorption control rod GR is often selectively driven during the operation in (3) above, and as a result, the amount of movement of the weak absorption control rod GR increases. If the above problem (6) occurs, it can be dealt with by changing the position of the control rod selection boundary line (solid line in the figure) with respect to the control target in FIG. 2, for example, by changing the set value.

In other words, as the boundary line is shifted to the positive side of ΔI (to the right side of the diagram) for Figure 2 (a), and to the negative side of Δ■ (to the left side of the diagram) for Figure 2 (b), , the weak absorption control rod movement decreases and the strong absorption control rod movement increases.

In this case, due to the difference in control rod values, the amount of increase in the amount of movement of the strong absorption control rod is smaller than the amount of decrease in the amount of movement of the weak absorption control rod. Figure 3 shows a case where the boundary lines in Figure 2 have been shifted to reduce the amount of movement of the weak absorption control rods.
FIG. 3(a) shows a case where the temperature deviation is negative, that is, a withdrawal request is made, and FIG. 3(b) shows a case where the temperature deviation is positive, that is, an insertion request.

Next, an embodiment of the present invention will be described, but the control target here is a four-loop pressurized water reactor, and as a weak absorption control rod, its neutron absorption capacity is in the vertical axis direction. The lower half is small and the upper half is large, and each group consists of four lenses, and is used in a two-group configuration.

FIG. 4 shows an example of the weak absorption control rod movement range, where the horizontal axis shows the relative output and the vertical axis shows the degree of insertion of the weak absorption control rod. Within the range surrounded by the withdrawal limit shown by the solid line and the insertion limit shown by the broken line in the figure, the weak absorption control rod will be able to:
It is activated when a weak absorption control rod is selected, and reduces the amount of water to be treated by compensating for part or all of the Xe deficiency as well as the output loss. That is, the typical movement of a weak absorption control rod is as follows.

(a) When the output decreases, the average temperature is sequentially inserted due to an increase in the positive deviation of the temperature - (b) After the output decrease is completed, it is withdrawn due to the negative temperature deviation due to the accumulation of Xe - (c) When it is pulled out to the withdrawal limit is stopped → (d) If the partial output state is long,
Inserted due to the temperature deviation on the positive side due to the collapse of c - (e) Withdrawal due to the temperature deviation on the negative side when the output increases.

In general, the insertion limit shown in Figure 4 can be set as necessary from the viewpoint of core safety, such as securing shutdown margin, and the withdrawal limit can be set based on the partial power state required for the plant for operation. Determined by rapid output recovery ability.

That is, if the withdrawal limit line in FIG. 4 is set at the lower part of the figure, the rapid output return ability will be improved, and if it is set at the upper part, the amount required for the crawling degree, that is, the amount of water to be treated will be reduced.

FIG. 5 shows simulation calculation results for the operation (1) above using the weak absorption control rod movement range shown in FIG. 4. In the figure, Gl and G2 are the first group of weak absorption control rods, respectively.
It is the second group, and the second group G2 is allowed to be fully withdrawn at 50% output, and D is a strong absorption control rod. As is clear from this figure, the output decreased from full output to 50% output in 1 hour, and after maintaining 50% output for 8 hours, returned to full output in 1 hour. The weak absorption control rod moves as described above, and the variation in ΔI is controlled within a small range.

FIG. 6 shows the calculation results for the case where the insertion degree of the weak absorption control rod is made a function of the output in order to clarify the effect on the change in the degree of crawling.

It can be seen that by the operation control method according to the present invention shown in FIG. 5, the range of variation in the degree of desertification, that is, the amount of water to be treated is significantly reduced.

FIG. 7 shows the basic configuration of the control system according to the present invention.
Control rod drive request signal ■, control rod drive system based on selection signal ΔI■, request for change in heading vagueness due to ΔI deviation■, request for change in heading vagueness when the control rod position reaches its limit■ It is controlled by the distance control system.

According to the embodiment of the present invention described above, a range in which the weak absorption control rod GR can freely move even under a constant output is set, and within this range, the temperature deviation ΔT of the average primary coolant temperature from the reference value By moving the weak absorption control rod GR in accordance with the above, it is possible to compensate for not only the output loss but also at least a portion of the Xe loss. In addition, a method is adopted in which either the strong absorption control rod or the weak absorption control rod GR is selected and moved according to the deviation of the average temperature, and good control of the axial power distribution is used as an indicator for the selection. , and uses an axial power distribution deviation signal to prevent the travel amount of only one control rod from increasing, so it is possible to secure the required load following ability with a relatively small number of control rods, and reduce the amount of water treated. can.

[Effects of the Invention] According to the present invention described above, it is possible to provide a nuclear reactor operation control method that can ensure the required load following ability with a relatively small number of control rods and can reduce the amount of water to be treated.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the concept of the nuclear reactor operation control method of the present invention, FIG. 2 is a diagram for explaining the concept of control rod selection based on the axial power distribution deviation ΔI in FIG. 3 is a diagram for explaining a method for reducing the amount of movement of the weak absorption control rod in FIG. 2, FIG. 4 is a diagram showing an example of setting the movement range of the weak absorption control rod according to the present invention, and FIG. Figure 6 is a diagram showing parameter changes during load value follow-up operation when using the operation control method according to the present invention, Figure 6 is a diagram showing parameter changes during load follow-up operation using the conventional operation method, and Figure 7 is a diagram showing the control system according to the present invention. It is a figure showing the basic composition of. GR...Weak absorption control rod, D...Strong absorption control rod, Δ■
...Axial power distribution deviation, Δ■...-Next coolant average temperature deviation. Applicant's agent Patent attorney Takehiko Suzue ■ Figure 1 Control target Second control target (a) Second control target (b) Figure 2 Figure 3 0.5 0.6 0.7 0R
Ojt. Relative output figure 4

Claims (1)

[Claims] When operating a nuclear reactor that has weak absorption control rods and strong absorption control rods as control rods that are inserted into and removed from the core of the reactor vessel, and has a boron concentration control device connected to the reactor coolant circulation system, it is necessary to A nuclear reactor operation control method that receives an average temperature deviation signal of a reactor coolant, selects one of the control rods in consideration of an axial power distribution deviation signal (ΔI), and adjusts the reactivity in the reactor.