JPH07140290A - Axial xenon vibration suppressing method - Google Patents

Abstract

PURPOSE:To suppress axial xenon vibration effectively and easily by making the relative difference of xenon quantity and iodine quantity between the upper half and lower half of a reactor core respectively DELTAx and DELTAII, displaying them on X-Y coordinates, and operating a control rod in the direction of reducing each relative difference. CONSTITUTION:DELTAIX represents the relative difference between the quantity of xenon produced with iodine, a fission product, as a parent nucleus in the upper half of a reactor core, and the quantity of xenon produced in the same way in the lower half of the reactor core. DELTAII represents the relative difference between the iodine quantity in the upper half of the reactor core and the iodine quantity in the lower half. In the case of placing DELTAIX on an X-axis coordinate and DELTAII on a Y-axis coordinate, axial xenon vibration describes a curve corresponding to the vibration stability. On this coordinates, the change of xenon vibration with the lapse of time is displayed by a clockwise elliptic orbit, and in order to stabilize the vibration, it is understood that the ellipse has to be made small so as to approach a zero point, that is, a control rod is operated in the direction of reducing the variation of DELTAIX, DELTAII. Xenon vibration can be thereby suppressed even by an inexperienced operator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for suppressing axial xenon vibration which is carried out during operation of a pressurized water reactor.

[0002]

2. Description of the Related Art In a conventional pressurized water reactor, the neutron detector outside the reactor is divided into two in the axial direction, and the axial neutron flux defined by the difference between the output in the upper half of the reactor and the relative output in the lower half. A deviation (hereinafter referred to as ΔI) is used as an operation index, and this axial offset constant value control operation method is to maintain this ΔI within a certain target range (usually ± 5%) on the positive and negative sides from the target value. Has been adopted.

Further, even when the xenon vibration in the axial direction is generated, ΔI is used as an index for driving, and ΔI is suppressed within its original target range by operating the control rod.
Further, since only ΔI is used as such an operation index, it is not sufficient to grasp the essential tendency of the xenon vibration characteristic, and the xenon vibration suppression depends on the experience of the operator.

[0004]

Since the conventional method for suppressing the axial xenon vibration is carried out as described above, the timing of the operation of the control rod or the like is unclear only with the current ΔI information. However, if the operator is inexperienced, there was a problem that it could not be operated properly.

The present invention has been made in view of the above problems, and an object thereof is to provide an axial xenon vibration suppressing method which can extremely effectively and easily suppress axial xenon vibration. .

[0006]

In the axial xenon oscillation suppressing method according to the present invention, the relative difference between the upper half and the lower half of the core of the xenon is ΔI ^X, and the relative difference between the upper half and the lower half of the core of the iodine is set. as [Delta] I ^I, and displays each X, on the Y-coordinate, illustrates the change over time in each of these relative differences, is to manipulate the control rod in a direction to decrease the respective relative difference.

[0007]

In the axial xenon oscillation suppressing method according to the present invention, the axial xenon oscillation is generated by the fluctuation of xenon produced by using iodine produced by fission as a parent nucleus, and the above-mentioned upper half and lower half of the core of the amount of iodine and xenon are produced. A clearer control method is created by constantly converting half of the relative difference into ΔI ^I and ΔI ^X. That is, ΔI ^X , ΔI ^I
The xenon oscillation is controlled by operating the control rod at a point where ΔI ^I crosses the zero point on the coordinates and bringing it closer to the zero point on the ΔI ^X and ΔI ^I coordinates.

[0008]

【Example】

Example 1. Embodiments of the present invention will be described below with reference to the drawings. Now, in addition to the axial neutron flux deviation ΔI used in the operation of a conventional pressurized water reactor, the amount of xenon that is produced in the upper half of the core as the parent nucleus of iodine produced by fission and the lower half is similar xenon. the relative difference between the amount and [Delta] I ^X,
Similarly, if the relative difference between the amount of iodine in the core half and the amount of iodine in the lower half is ΔI ^I and these are introduced, ΔI ^X is on the X axis,
When ΔI ^I is taken on each coordinate of the Y axis, the xenon vibration in the axial direction becomes as shown in FIGS. 1 to 3 depending on the vibration stability.

In this case, when the xenon vibration is a constant vibration, as shown in FIG. 1, the stability index = 0.
0, and in the case of convergence, as shown in FIG.
Stability index _{= (1 / T) l n} (a / b) <0 , and the in the case of divergent, as shown in FIG. 3, stability index =
A _{(1 / T) l n (} a / b)> 0. However, T is the period of vibration.

From the above FIGS. 1 to 3, ΔI ^I ,
On the ΔI ^X coordinate, the xenon vibration is displayed in a clockwise elliptical orbit, and it can be seen that in order to stabilize the vibration, it is necessary to reduce the ellipse so that it approaches the zero point. That is, the control rod is operated in a direction to reduce the amount of change in ΔI ^X , ΔI ^I.

Embodiment 2. Next, in order to suppress the xenon vibration by operating the control rod, ΔI ^X , ΔI ^{I on the} coordinates ΔI
When ^{the I} crosses the zero point, by pulling out to the original position to a few hours after [Delta] I ^X by inserting the control rod until the [Delta] I is returned to its steady state value becomes zero when [Delta] I ^X is negative, and [Delta] I
^{If X} is positive, insert a control rod until ΔI returns to its steady value, and pull out to its original position several hours after ΔI ^X becomes zero, stabilize both ΔI ^I and ΔI ^X at the zero point. Can be done.

FIG. 4 shows an example of the operation of this control rod as a time change of ΔI, and FIG. 5 shows the xenon vibration locus on the ΔI ^X and ΔI ^I coordinates at this time. According to this, it is understood that the xenon oscillation is well controlled and stabilized by returning the control rod to the original position 4 hours after the insertion of the control rod as described above.

Similarly, when the control rod is inserted to the original position several hours after the control rod is pulled out, the loci of ΔI ^X and ΔI ^I are as shown in FIG. 6, and both ΔI ^X and ΔI ^I return to the zero point. It turns out that it stabilizes.

Example 3. On the other hand, ΔI ^I during xenon oscillation
When the time derivative of ΔI ^X is Δ # ^I and the time derivative of ΔI ^X is Δ # ^X , and K ₀ is a constant coefficient, K ₀ Δ # ^I +
Delta # ^X becomes amount is linearly changed as shown in FIG. 7 with respect to [Delta] I (%). Since ΔI at which K ₀ Δ # ^I + Δ # ^X becomes zero is an original steady value, the vibration suppressing operation of xenon is performed by K ₀ Δ
It is necessary to operate the control rod so that # ^I + Δ # ^X becomes zero.

For example, when the control rod is inserted and withdrawn as shown in FIG. 8, the K ₀ Δ # ^I + Δ # ^X straight line moves parallel to ΔI as shown in FIG. At an appropriate timing, K ₀ Δ # ^I + Δ #
Xenon oscillation can be stabilized by setting ^X to zero and returning ΔI to a steady value.

Example 4. Next, a case where the vibration is stabilized t hours after the middle of the axial xenon vibration will be described.
In this case, first, ΔI from the present time to t hours later
Estimate and predict the ^I curve and create it.

This stabilizes the xenon oscillation in the axial direction Δ
The I curve is ΔI = (λ _I / K _I ) Δ from the ΔI ^I curve
It is calculated by I ^I + (1 / K _I ) Δ # ^I. Here, λ _I and K _I are constants. When the ΔI curve is created in this way, the control rod is operated as shown in FIG. 10A so that this ΔI curve is obtained, and ΔI is brought to a constant value by the time t. According to FIG.
As shown in (b), xenon vibration can be stabilized.

However, if the ΔI prediction curve cannot be achieved by operating the control rod as described above, the first ΔI
^{Since the I-} curve prediction was not valid, the procedure is to re-create the possible ΔI curve by re-performing the ΔI ^I- curve prediction.

[0019]

As is evident from the foregoing description, according to the present invention, the relative difference between the lower half and the upper half of the core xenon weight and [Delta] I ^X, a relative difference between the lower half and the upper half of the core iodine amount as [Delta] I ^I, Each of them is displayed on the X and Y coordinates, the change over time of each relative difference between them is illustrated, and the control rod is operated in the direction of decreasing each relative difference. It is possible to obtain the effect that the xenon vibration can be suppressed easily and surely without requiring

Further, ΔI ^X , ΔI ^I coordinates and K ₀ Δ
# ^I + Δ # ^X vs. Δ ^I By adopting an intuitively easy-to-understand graphical display, the xenon vibration behavior can be easily understood, and a predictive control method based on the Δ ^{I I} curve, which is a method that is easily predicted in advance. By controlling the xenon vibration and displaying it on the on-site computer of the power plant, it is possible to obtain an effect that the operator can deal with it with a margin.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a xenon vibration locus during constant vibration showing an axial xenon vibration suppressing method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a xenon vibration locus at the time of convergence, showing an axial direction xenon vibration suppressing method according to an embodiment of the present invention.

FIG. 3 is an explanatory view showing a xenon vibration locus at the time of divergence showing an axial direction xenon vibration suppressing method according to an embodiment of the present invention.

FIG. 4 is a ΔI characteristic diagram showing a change in ΔI during xenon vibration.

FIG. 5 is an explanatory view showing a locus of xenon vibration at the time of pulling out after inserting the control rod in the present invention.

FIG. 6 is an explanatory view showing a locus of xenon vibration when the control rod is inserted after withdrawal in the present invention.

FIG. 7 is a characteristic diagram of K ₀ Δ # ^I + Δ # ^X vs. ΔI in the present invention.

FIG. 8 is an explanatory diagram showing a method of suppressing xenon vibration according to the present invention.

9 is a K ₀ Δ # ^I + Δ # ^X vs. ΔI characteristic diagram corresponding to FIG. 8;

FIG. 10 is an explanatory diagram showing a xenon vibration control method by a ΔI ^I prediction method.

Claims (4)

[Claims] 1. A relative difference between the upper half and the lower half of the xenon amount is ΔI ^X, and a relative difference between the upper half and the lower half of the iodine amount is ΔI ^I , which are displayed on X and Y coordinates, respectively. A method for suppressing axial xenon vibration, in which a change over time of each of these relative differences is illustrated and the control rod is operated in a direction of decreasing each of the relative differences. 2. When the relative difference ΔI ^I becomes zero, when the relative difference ΔI ^X is negative, the axial neutron flux deviation Δ
I inserts the control rod to return to the steady-state value, then, after the relative difference [Delta] I ^X is held in a few hours at the same position until the zero point,
Pull out the control rod to its original position, while moving the relative difference ΔI
^{When X} is positive, the control rod is pulled out until the axial neutron flux deviation ΔI returns to a steady value, and then the relative difference ΔI
^The method for suppressing axial xenon vibration according to claim 1, wherein after holding the same position for several hours until ^X becomes zero, the control rod is inserted to the original position. 3. A value K ₀ Δ # ^I + Δ when the time differential amount of the relative difference ΔI ^I is Δ # ^I , the time differential amount of the relative difference ΔI ^X is Δ # ^X, and K ₀ is a constant coefficient. Using the fact that # ^X linearly changes with respect to the axial neutron flux deviation ΔI at the same control rod position, operate the control rod so that the above K ₀ Δ # ^I + Δ # ^X converges to zero. Item 1. A method for suppressing axial xenon vibration according to Item 1. 4. An estimated curve of a relative difference ΔI ^I from the time of setting the axial xenon vibration to a predetermined time is estimated and created,
When K _I and λ _I are constants, the prediction curve of the axial neutron flux deviation ΔI required to stabilize the axial xenon oscillation is ΔI = (λ _I / K _I ) ΔI ^I + (1 / K _I ) Δ #
^The method of suppressing axial xenon vibration according to claim 1, wherein the control rod is operated so as to obtain a prediction curve of the axial neutron flux deviation ΔI by utilizing the calculation from ^I.