JPS5827090A - Method of controlling power of bwr 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 provides a boiling water aim sub-reactor (hereinafter referred to as BWR).
Output control method (: related.

Generally, in an EWR power plant, the reactor output is adjusted by individually controlling the control rod position and core flow rate. However, when performing multi-load follow-up operation using such conventional control methods: : had a problem in that it was difficult to adjust output in accordance with large load changes due to the influence of the so-called toxic effect of xenon. Xenon (hereinafter referred to as
!・18w) is generated and neutrons are absorbed,
As a result, the reactivity decreases, and its zeta
The process of creation and disappearance of g is as follows.

G, l@chi) To explain this simply, zetag is one time of nuclear fission, directly o, 03 o, indirectly 0. # It is known to occur at the opening of -. In the indirect case,
First, Te@ljl is produced by nuclear fission, and that is! 6 pss due to collapse], and more! This occurs due to the collapse of z and 181.

The generated X-111 is even more! Collapse (1, Ill
On the other hand, +n neutron rIk is collected and z@1m
m and disappears. Note that 7hr and hr are the half-lives (hours) of the x-
(2) has the property of absorbing neutrons well, leading to a decrease in reactivity and, as a result, a decrease in reactor output.

By the way, in load following operation of a nuclear reactor, Figure 1 (IL)
As shown in , operation is performed in a cycle of initial high output operation → low output operation → high output operation again.

When such operation is performed, the conventional control method
, the linear power density of the fuel rod under the influence of the poisonous effect of Ill!
A problem arises in that when 'a (1!ff%a) returns from low output operation to high output operation, it becomes smaller than the linear output density during the initial high output operation.

To explain the aspect of this change in linear power density in more detail,
As shown in Figure 1 (0), during the high power return maintenance period TI after returning to high power C2, the linear power density P at the top of the core (Figure 1, ■) is immediately after returning to high power in IU. It increases slightly and then decreases, and after a long time it settles to the same value as the initial high output period (1). The linear power density Pυ in the middle part of the core (Fig. 2) is almost the same as the initial high power.
The linear power density P(17,) in the lower part of the core (L in Figure 1) increases significantly from the initial high power.What is particularly problematic about this transition is the linear power density P(LL
This is an increase in The reason for this is that such an increase in the linear power density Pa in the lower part of the core may cause POX damage.

Here, Pa let C1ad Int@r
aotion) is a cladding tube (01a) that constitutes a fuel rod.
d) and the fuel pellets inserted inside it) (P.11
・This is an interaction caused by the difference in the respective expansion coefficients with t). The coefficient of expansion of the mold cladding tube is smaller than that of the fuel pellets, so if the reaction of the fuel pellets is suddenly increased, tardage will occur in the cladding tube, this is called POI failure.

In order to prevent this PO process damage, conventionally the output is increased below a predetermined linear output density increase rate at a linear output density higher than a threshold value, and after holding the reached output for a predetermined time,
The output was once lowered, and then the control rod position butter y was changed and the above operation was repeated to gradually expand the POI/velope (hereinafter referred to as fuel leveling operation).

However, this fuel run-in operation temporarily lowers the output, which lowers the operating rate of the IWR power plant. Furthermore, if the fuel run-in operation is insufficient, it is necessary to take measures to prevent the occurrence of PCI damage in advance, so it is necessary to perform an operation that follows the target output change curve (Figure 1 (lLJ, P)).
The problem arises that it becomes difficult to

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an output control method that enables operation that accurately follows a target output change curve without causing POI damage during the high output return maintenance period.

The feature of the present invention is that control rod and core flow rates are finely coordinated and controlled during the low power period so that the linear power density at the time of high power return does not exceed the linear power density allowed for preventing Ami-X damage. be.

Hereinafter, the present invention will be described in detail based on illustrated embodiments.

<Principle> [Definition of permissible linear power density] First, the permissible linear power density (hereinafter referred to as permissible linear power density) from the viewpoint of preventing paI damage is defined as follows.

Assuming the linear power density distribution of the fuel rods when the fuel run-in operation is performed as described above, the fuel run-in operation is performed multiple times with changing the control rod position as appropriate. ..., L), the linear output density when performing
) (1 duck') (1-r,,)Po
ljk=Pijk υ Pijk
−−−−°υ Let Pijk be the PO envelope.

If it is within the AC envelope Pa1jk defined in this way, the rate of increase in output is unlimited and POI damage will not occur.In addition, if the output is to be increased beyond this A/C envelope Pa1jk, the output must be increased within a predetermined line. Below the output density increase rate (:
If it is kept in check, damage to the PO will not occur. Therefore, the allowable linear power density is a function of time and is defined as linear.

Po1jk(t)=Poijk+a t=
(/1 (hr)) Also, depending on the degree of fuel improvement, the linear power density increase rate α
It is also possible to increase the allowable linear power density, or it is also possible to add a certain value l to the allowable linear power density. In that case, it is defined as linear.

Po1jk(t)=Foijk +a t+β ---
--- (2J [Control Principle]) Next, the principle of the control method according to the present invention will be explained. Namely, 1. The power control according to the present invention controls the control rod operation and the core flow rate under certain conditions during the low power period 'rz. This is based on slow cooperative operation.What are the certain conditions?

During the high-output return supply period TI, the linear power density PiJk(t) at each fuel rod position is determined to be the linear power density allowable for Pct damage of the fuel rod, that is, Po1jk(t)...
1) Condition J is such that the value obtained by subtracting the formula is a negative value and the absolute value of its maximum value is the minimum. Expressing this as a formula, Jta( pgk(t) −pot, +h(t))
...Track (J)aX.To sum up, the low output period TL
In this case, the control rods are operated under the condition that the linear power density after operation of the control rods does not exceed the PO envelope Po1jk, and the core flow rate is operated in a coordinated manner in conjunction with the operation.

As shown in FIG. 3, the control rod is operated by inserting the deep control rod Oil and withdrawing the shallow control rod OR-. In FIG. 3, the solid line IIB indicates the case where the control rod is operated, and the broken line IIB indicates the case where it is not operated.

Here, we will discuss @inserted control rods OR- and shallowly inserted control rods 6 Normally, in a nuclear reactor, there are control rods (i.e., deeply inserted control rods (i.e., (deeply inserted control rods) and loosely inserted control rods (that is, shallowly inserted control rods) are used to adjust the linear power density in the lower part of the core (lower part of the fuel rods). When the deep insertion control rod 0RII is inserted, the bottom peak (
Bottom P@ak) occurs, and when the shallowly inserted control rod OR, is withdrawn, a bottom peak similarly occurs. And the low power period? If a bottom peak is produced at L, a phenomenon occurs in which the linear power density in the lower part of the reactor core becomes smaller at a high power return period.

Next, the first explanatory diagram shows the case of multi-load follow-up operation using the cooperative interlock control according to the present invention. The broken line B shows the case where the same control is not performed.

That is, when operating by following a predetermined target output change curve r as shown in the first part (a), the deeply inserted control rod O
The control rods are operated by inserting R& and withdrawing the shallowly inserted control rod OR-, but in general, the deep-inserted control rod OR4 has a greater reaction flow effect than the shallowly-inserted control rod OR-, so deep insertion control rod Since the reactivity of the reactor core decreases due to the insertion of the rod ORd, the core flow rate when the control rods are operated (A) is higher than when the control rods are not operated (BJ l = In addition, during the low power period TL, just before the return from low power to high power begins, the control rods 0RIL and OR- are gradually returned to their original control rod positions, and the core flow rate is adjusted accordingly. Then, the core flow rate when the control rods are operated (A) will show almost the same transition as when the control rods are not operated (B).

On the other hand, control rod operation 1: As shown in Figure 5, the linear power density moves significantly compared to the initial linear power density (as well as the period). Output period? 1
．． A large bottom peak occurs in the first time (
As shown in 0), the increase in power during the high power return holding period TE is relaxed compared to the case without control rod operation (19). This means that the output density during the high output recovery maintenance period 〒- was suppressed within the allowable linear output density Po1jk by the cooperative operation.What is obtained as a result is that occurrence of POI damage can be prevented.

The above-mentioned matter can be further physically explained using the diagram as follows. In other words, Figure 1 shows the low output period〒L
When the control rods are operated at
Regarding B), at the core position where the output increased due to control rod operation!・This shows the time course of the concentration of No. 11. As can be seen from the 1llJ diagram, when the control rods are operated (when the control rods are not ejected (during a period of low power compared to the case where the power is low! In the core position where the power increases during L), there is a lot of nuclear fission. The concentration of pal, which is a substance, is larger), and at the time of returning to high output, 1.ta is reduced due to I decay.
s, so high output recovery maintenance period! When it becomes -, z@II
The concentration of I becomes even greater. Hence the low power period! L
The part where the output increases is the period during which high output is maintained!
-, the negative reactivity of X@$81 increases, w
This means that the increase in p'th force writing level is suppressed.

[Optimum Control Rod Operation] Since the control rod operation method described above cannot be uniquely determined, an example of an optimal control rod operation method will be described below.

First, in order to compare the control rod operation and cooperative control according to the present invention, a case where the break-in operation is insufficient and the cooperative control according to the present invention is not performed will be described below with reference to Figs. .

Before starting the load following operation, a fuel break-in operation is performed to obtain a predetermined P (j/perop P61Jk), as mentioned above.However, this break-in operation is insufficient. A) If the expansion of PA/Perope Po1jk is locally insufficient, the following will occur. wife)
, from the end of the break-in operation to the start of the load following operation, the combustion of the working elements progresses and a change in the core condition occurs, and this is the case where the output is adjusted by controlling the control rod position or the core flow rate.

The linear output density distribution Pijk immediately before the start of load following operation changes, resulting in a high output recovery maintenance period during load following! The linear power density at − is the allowable linear power density PO1jk(t)
There is a good chance that it will exceed locally. An example of the control rod position when such a situation occurs is shown in Fig. 97.

Figure 7 shows 100,07K”tilB W!1 power generationff
F2 is the control rod position during 4t high output operation and 'P
A typical example of the control rod position when the C-velope Pa1jk is insufficiently expanded is shown. In Figure 7, the numbers in the figure indicate the control rod positions in the core height direction.

When the total core height is divided into 50 parts, O is the top of the core.

The bottom of the core is represented by 0, for example, O represents full insertion, and the blank represents full withdrawal, and an intermediate value, for example, indicates the position of gate 6. The same applies to other intermediate values. Also, the shaded area is p.

It shows a region where the envelope Po1Jk is insufficiently expanded.

Figure 1 shows (IL), (kl), the change in linear power density with respect to the target output change - IIP when the cooperative control of the present invention is not performed during the low output period, #I7
This is an example in which the target position is the 〃th position in the core height direction at the core mid-radial position shown in a in the figure. According to this figure, it can be seen that the predicted linear power density at the 24th position exceeds the permissible linear power density 6.

d indicates PC/Perop Pa1jk.

The figure below shows the target output change in figure (IL) - the 7th at each time point t ``II + tC in the follow-up operation of IIP.
The figure shows the axial linear power density distribution at position a. This figure shows that in the lower part of the core, the linear power density (tC) is higher than the PO envelope Pc1jk...d during the high power return maintenance period T-.
It can be seen that the driving exceeds the limit.

Next, a case in which the optimum control rod operation and core flow rate are cooperatively controlled according to the present invention will be explained using Figs. 1Q to 1C.

The first OwJ shows an example of the control rod position during the low power period τL obtained by optimal control rod operation according to the first invention.

By positioning the control rods in this manner, it is possible to fully insert the control rods around the periphery of the PO envelope;
By withdrawing the shallowly inserted control rod near the area where the PO envelope is insufficiently expanded, the output of the area where the PO envelope is insufficiently expanded can be made sufficiently large during low output operation. As a result, as shown in FIG. 1, the linear power density during the high power return sustaining period TH1 is suppressed to below the allowable linear power density C and the PO envelope d. That is, #! /1 Figure (a), (1)l is,
This figure shows the change in linear power density to t with respect to the target power change 11111P when the optimal control rod operation according to the present invention I is carried out.

FIG. 1 shows an example of the axial linear power density distribution during the low output period t when operating at the control rod position shown in FIG. 10, and when the control rod is operated by t.

1 shows the case where the control rod is operated.

This figure shows that the linear power density at the lower core increases during the low power period Tl.

<Cooperative control device> Next, an example of the configuration of a control rod operation/core flow rate control cooperative control device (hereinafter referred to as a cooperative control device) for implementing the output control method of the present invention will be presented! No. 7 in relation to power plants
Shown in Figure 3.

First, an overview of the BY-R power plant will be described. Steam generated from the nuclear reactor is sent to the turbine, which rotates and does work. A generator as the turbine rotates!
converts rotational energy into electrical energy and outputs it. On the other hand, the steam that has done work in the turbine is returned to water by the condenser l and sent to the feed water heater t as feed water. After being heated by the bleed air from the turbine/co in the feed water heater t.

(by the water supply bong 7) is returned to the reactor l.

In the BWR power plant described above, the output of the reactor l is adjusted by the positional manipulation of the control rods/l and the control of the core flow rate.As mentioned above, the control of the core flow rate is The recirculation flow rate controller t performs the recirculation through the recirculation pump D. The positioning of the control rods // is performed by the control rod drive 10.

Next, a cooperative control device/f according to the present invention will be explained. First, I will give an overview. Process signals from each device within the BllR power plant are input to a process computer. The process computer /J monitors the status of each device based on each process amount, while the process computer /J monitors the status of each device based on each process amount.
The black signal is collected and sent to the cooperative control device /f. The cooperative control device f19 receives the process collection data I and various command data from the terminal device 1g, and calculates and determines the optimum control rod operating position and core flow rate based on these data, and then calculates the control rod drive device 10. It also outputs a control signal to the recirculation flow rate control device I to control the output of the reactor I.

The details will be explained next. The calculation algorithm within the cooperative control device f/de is as shown in the flowchart shown in Figure 1111LtIi.

[Step/] First, the allowable linear power density calculator 13
Run the fuel run-in multiple times (while changing the control rod position as appropriate).
1 = /, Ko,! , ..., L), each linear power density Pijk"""" is taken in through the process computer 12, and each of these plurality of linear power densities Pijk(1"=/°
4a), i.e. po/velope Pc
Get 1jk. Here.

a. 1jk=Pijk(1=/)(1=λ) (
1=L) LIPijk, . . .U Pijk. Next, based on the obtained PC envelope Po1jk, the allowable linear power density PO1 is calculated based on equation (1) or equation (1).
Calculate jk(t). Calculated allowable linear power density Po
1jk(t) is sent to the next optimum control rod operation/core flow rate control computing unit (hereinafter referred to as the optimum control computing unit) 13.

[Stepco] The optimum control calculator/j calculates low output at a certain control rod position that is different from the control rod position during high output operation under low output operating condition L (see Figure (a)). Changes in the core flow rate for each control rod position during operation are measured from the input/output controller/? to calculate the transition of core flow rate. The calculated core flow rate is sent to the next linear power density prediction calculation. Note that 1=/ indicates the setting of the initial value of the number of control rod position changes.

[Step J) # In the output level prediction calculator/q, when performing an operation that follows the target output change curve P, the low output operating condition in the step controller, that is, the control rod position different from the high output operation When low power operation is performed with a certain control rod position d = ζ:, high power return maintenance period 〒i,
(Secondly, the correlation between the reactor core flow rate and control rod operation control determined by the step controller (relationship for keeping the reactor output constant) is calculated to predict what the linear power density will be at the time of ejection, and the predicted line The output density Pijk(t) is calculated.This predicted line output density Pijk(t) is calculated by the optimum control calculator 13.
C”-Sent.

[Stepping] The optimum control calculator 15 calculates the calculated allowable linear power density PO1jk(t) and predicted linear power density Pij
Using k(t), p evaluation function J1 is determined by equation (J).

J1=(Pijlc(t)−Poljk(t))
・・・・・・(3) aX 7 times or multiple times until this evaluation function J1 becomes the minimum (
Number of times + 1) While changing the control rod position during the low power operation period TL, calculate the linear power density Pij for each control rod position.
k(t) is calculated by the predicted line power density calculator. Note that the control rod operation is performed via the control rod operation control device 14. That is, after it is determined whether J≧0, the calculated evaluation function 11 is stored in the memory together with the control rod position information at that time if J≧0. 1=14
The -/ function is a counting operation to determine the number of control rod position changes. 0 indicates that the count value is incremented by 11' for each position change.
Next, it is determined whether the evaluation function J stored in the memory is the minimum value, and if it is the minimum value, the control rod position at that time is selected and determined as the optimum position. If the minimum value does not exist, the process returns to step 1 again and the same calculation operations as described above are repeated until the minimum value is determined.

Here, it is determined whether the evaluation function J1 is the minimum.

In practice this is done with an approximation of 0, for example.

The number of times is truncated k(
x > 1 s) to find the minimum value empirically.

A possible method is to set a certain standard value (W/hr) for the purpose of aging ('l<JO life).

The minimum evaluation function described above is compatible with the first condition of the cooperative interlock control described in the explanation of the principle, and the control rod is adjusted during the low output period Tt so that this minimum condition is satisfied. By controlling the position information and core flow rate in a coordinated manner as described above, the high power return maintenance period TI,
can suppress the linear power density at P
This can be achieved by preventing the occurrence of O-work damage and performing operation that follows the target output change curve. <Effects> As described above, according to the present invention, xenon (z, 1 = / )
By compensating for the increase in reactor power due to the effects of poisonous effects during the low power period through coordinated control of control rod operation and core flow rate, the linear power during the high power return maintenance period, which has been a problem in the past, can be improved. It is possible to prevent damage to the PO process due to increase in density, and to perform operation that follows the target output change direction, H=.

[Brief explanation of the drawings] Figure 1 shows the time course of the main process quantities in the reactor in the conventional control method, where (a) is the target power change curve, and (b) is the core flow rate adjustment curve. curve, (Q) is an explanatory diagram showing the power density change curve, Figure 2 is a diagram to explain the upper, middle, and lower part of the reactor core, and Figure 3 is an explanation showing the relationship between control rod insertion and withdrawal. figure. Figure 1 shows the time course of the main process quantities in the reactor according to the output control method of the invention, where -J is the target output change curve, (b) is the core flow rate change curve, ((1) is An explanatory diagram showing the power density change curve. Figure 1 is an explanatory diagram showing the linear power density distribution at the axial position of the fuel rod. Figure 4 is z, DI with and without control rod operation.
An explanatory diagram showing the temporal change in concentration. FIG. 7 is an explanatory diagram showing control rod positions during high power operation when the PO envelope is insufficiently expanded. Figure 2 is an explanatory diagram showing the change in linear power density for the target output change curve 1 when operating at the control rod position shown in Figure 7. Figure 2 is an illustration showing the change in linear power density when operating at the control rod position shown in Figure 7. (Explanatory diagram showing the axial linear power density distribution at -). Figure 70 is an explanatory diagram showing an example of the optimal control rod position obtained by the control method of the present invention. An explanatory diagram showing the change in linear power density with respect to the target output change curve during operation at the control rod position shown in Fig. 10. Fig. 1 is an axial linear power density distribution during operation at the control rod position shown in Fig. io. FIG. 13 is an explanatory diagram showing the present invention H.
A block diagram showing a configuration example of such a cooperative interlocking control device and its relationship with the B'WR power plant, and FIG. Space (hr) 7th figure hanging 8th figure procedure correction writing method) 1. Display of the case First patent application in Kaku Showa era! ! $1s91 No. 2, Title of the invention: Output control method for boiling wood reactor 3, Person making the amendment Relationship to the case Patent applicant (307) Tokyo Shibaura Electric Co., Ltd. Drawing 8, Contents of the amendment Drawing, Figure 4 , Add the drawing number r(c)J as written in red on the attached drawing copy. Figure 4 (1)

Claims (1)

[Claims] 1. Based on the control goal of switching the output of the boiling edema reactor from high output to low output and then returning to high output again,
In the method of controlling the output of the nuclear reactor to follow the control target by controlling the recirculation flow rate and manipulating the control rods. At each point in the high power return maintenance period during which the reactor power is returned to high power and maintained, the value obtained by subtracting the linear power density allowable for preventing damage to the fuel rods from the linear power density at each fuel rod position is negative. - under the condition that the absolute value of its maximum value is the minimum. 411& is an output control method for a boiling water reactor, which includes cooperative interlocking control of recirculation flow rate control and control rod operation so as to increase the output of the lower part of the core during the low-output operation period of the reactor. (1) The cooperative interlocking control includes: calculating an allowable linear power density based on a distribution aperture that encompasses the linear power density of the rod for each control position change during fuel break-in operation; During the period of low power operation of the reactor, the control rod position is different from that during high power operation of the reactor, provided that the power is kept constant: 2. High power la during low power operation
[Step of predicting and calculating the linear power density during the return maintenance period. An evaluation function (based on the allowable linear power density and predicted linear power density) is determined, and the control rod position is changed one or more times during the reactor low power period until the evaluation function is minimized for each control position. The boiling point according to claim 1, further comprising the step of determining the linear power density of the control rod by the predictive calculation and determining the control rod position when the evaluation function becomes the minimum as the optimum position. Output control method for water reactors.