JPH07128484A - Operation monitoring and protection method for reactor - Google Patents

Abstract

PURPOSE:To protect DNBR, maximum linear power or heat flux hot-channel factor by defining axial offset with a specific equation using the power of neutron detectors arranged outside a reactor splitted in quarter in core axial direction and calculating the departure from nucleate boiling ratio (DNBR). CONSTITUTION:When the outputs of out-of-core neutron detectors 2a, 2b, 2c, 2d splitted in four in core 1 axial direction are let q1, q2, q3, q4, respectively, three kinds of axial offsets AO are defined with an equation. Where, A. OC, A. OT. A. OB, are axial offsets for core average, core upper half and core lower half, respectively. By normalizing the output signals to q1+q2+q3+q4=1, the DNBR is indicated, by using the axial offsets A, OC, A. OT, A. OB, DNBR is calculated, and by limiting the DNBR and the heat flux hot-channel factor, perimittable operation range is ensured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a core monitoring and protecting method for limiting an allowable operating range of a pressurized water reactor.

[0002]

2. Description of the Related Art In a conventional pressurized water reactor operation monitoring method, when the out-of-core neutron detector used for monitoring is divided into two in the axial direction, the axial offset of the core average regarding the axial power distribution is used. , The operating range of the reactor is displayed as its function form. In its typical example, the axial offset target value within a predetermined target range of the positive and negative sides with respect to the axial offset of the rated power operating conditions A.O ^C. A so-called constant axial offset constant value control operation method for maintaining the above is adopted (for example, refer to JP-A-62-299792).

[0003] integrity of the core and fuel (i.e. nucleate boiling ratio and maximum linear output limit) for protection, axial offset target value A.O ^C. A protection system is installed in the reactor to limit the range to a certain range, and when the target value deviates from this range, the reactor is finally tripped.
All this method, such as an axial offset A.O ^C. Since the power deviation of the upper half and the lower half of the core is used,
As illustrated in FIG. 1 (a) and (b), axial offset A.O ^C of the same value. In there is a problem that it is impossible to determine the very different power distribution distribution shape even, also, the core average axial offset A.O ^C.
There is also a problem that the operating range is narrowed because the protection function is determined by the envelope.

In order to solve the above-mentioned problems, it has been proposed to use a neutron detector which is divided into four axial directions as shown in FIG. 2. However, when such a neutron detector is used, it has been conventionally known. , The output distribution of about 60 points in the axial direction is reproduced and calculated based on the four output signals from these neutron detectors, and the maximum line power of the core and the nuclear boiling limit ratio (DNBR) are directly calculated from this calculation result. It employs the method of evaluating it.

[0005]

In this case, although there is an advantage that a detailed axial power distribution can be obtained, in order to guarantee the accuracy, the result of the power distribution measurement inside the furnace once a month and the outside of the furnace are measured. The neutron detector needs to be calibrated at every 60 points so that the reproduced output distribution from the output signal of the four-division neutron detector is matched, and maintenance of the neutron detector is troublesome. . In addition, there is a problem that it is difficult to intuitively understand the relationship with the control rod operation if the shape of the axial power distribution is unchanged.

Therefore, the present invention reduces the labor and frequency of changing the protection system setting when using the above-mentioned four-part neutron detector outside the reactor, and at the same time, uses the same easy-to-understand index as the conventional axial offset. It is an object of the present invention to provide a reactor operation monitoring and protection method for protecting the boiling limit ratio and the maximum line output or heat flux hydrothermal channel coefficient.

[0007]

In order to achieve the above object, in the operation monitoring and protecting method for a nuclear reactor according to the present invention, neutrons which are axially divided into four parts and which are arranged vertically outside the reactor are provided. When the output signal of the detector is q ₁ , q ₂ , q ₃ , q ₄ from the one above the neutron detector, the axial average of the core average is obtained by the output signals q ₁ , q ₂ , q ₃ , q _4. offset A.O ^C. , The core upper half axial offset A.O ^T., The reactor core lower half axial offset A.O ^B., Respectively

[Equation 2] Is defined as, the output signal _{q 1 + q 2 + q 3} + q 4 = 1 normalized to display the nucleate boiling ratio DNBR than the output signal, said nucleic boiling limit ratio DNBR axial offset A.O ^C. , A.O ^T. And A.O ^B. Use calculates, A.O the same nucleate boiling ratio DNBR ^C. And A.O ^T. Relationships and A.O ^C. And A.O ^B _The heat flux heat channel coefficient F _Q is displayed by the output signals q ₁ , q ₂ , q ₃ and q ₄ and the heat flux heat channel coefficient F _Q is indicated by the axial offset. A.O ^C., A.O ^T. and A.O ^B. use calculated, the same heat flow Tabanetsu waterways factor F _Q A.O ^C. and A.O ^T. relationships and A. O ^C. and A.O ^B. , The nucleate boiling limit ratio DNBR and the heat flux heat channel coefficient F _Q , which are the thermal limit values of the core, are limited from the respective graphic representations to determine the allowable operating range. Limit nucleate boiling ratio DNBR and heat flow Tabanetsu waterways factor F _Q is A.O ^C. , A.O ^T. And A.
When configured as a functional form of O ^B. It is suitable.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the present invention will be described with reference to the drawings. In FIG. 2, the out-of-core neutron detectors 2a, 2b, 2 are divided into four in the axial direction of the core 1.
When the output signals of c and 2d are q ₁ , q ₂ , q ₃ and q ₄ , respectively, the following three types of axial offset AO are defined.

[Equation 3]

[0009] Here, A.O ^C. The reactor core average axial offset, A.O ^T. The core upper half axial offset and A.O ^B. Is the axial offset in the lower half of the core. Generally, the nucleate boiling limit ratio (hereinafter referred to as DNBR) at a certain axial position is inversely proportional to the product of the output integrated value up to the axial position and the output at the coaxial position. Displaying the DNBR using the output signals q ₁ , q ₂ , q ₃ , q ₄ of

[Equation 4] Becomes This relationship is a clear linear relationship as shown in FIG.

On the other hand, detector output signals q ₁ , q ₂ , q ₃ , q ₄
The axial offset of the (1) formula A.O ^C., A.
From O ^T. , A. O ^B. , It can be calculated as follows.

[Equation 5]

However, the output signal of each detector is q ₁ + q ₂
It is standardized as + q ₃ + q ₄ = 1.0. That is, the above (2)
From the formula and (3), DNBR is axial offset A.O ^C. , A.O ^T., Can be calculated using the A.O ^B.. 4 and 5 are graphical representations of these results,
In FIG. 4, a combination of (A.O ^C. And A.O ^T.), Are represented the value of the DNBR in combination (A.O ^C. And A.O ^B.) In FIG. 5 because, can be limited to a certain allowable range of the DNBR if limiting the scope of each combination (A.O ^C. and A.O ^T.) and (A.O ^C. and A.O ^B.).

On the other hand, the highest line output is obtained by multiplying the heat flux heat channel coefficient F _Q of the core by the average line output, and is proportional to the detector output signals q ₁ , q ₂ , q ₃ , q _4. It has been known. That is,

[Equation 6]

Therefore, the heat flux heat channel coefficient F _Q and the maximum line output are the same as the axial offset A.
^{O C., A.O T.,} A.O B. Can be calculated using 6 and 7 are graphical representations of these results.
The combination of (A.O ^C. And A.O ^T.) In FIG. 7
In is expressed heat flow Tabanetsu waterways factor F _Q in combination (A.O ^C. And A.O ^B.). Now, each combination (A.O ^C. And A.O ^T.) And (A.O ^C. And A.O ^B.)
If the range is limited, the heat flux heat channel coefficient F _Q can be limited to a certain allowable range.

When the present invention is used for core protection, it is carried out as follows. Conventionally, consider factors axial power distribution distortion in overtemperature ΔT trip and over power ΔT trip system which is installed in a pressurized water nuclear reactor, which is a function of the axial offset A.O ^C. F
While using (A.O ^C.) That Is, as an alternative to this, in the present ^{invention, f (A.O C., A.O} T., A.O
^B. ) will be used.

The function f (A.O ^C.) In the axial offset A.O ^C. Only functions compared to being protected by f (A.
^{O C., A.O T.,} A.O B.) In A.O ^C. In addition to A.O ^T.,
Since A.O ^B. Even classifies and displays the scope of protection, f (A.
O ^C.) Than A.O ^T., An advantage of operating margin spreads in accordance with the value of A.O ^B..

[0016] Functions of the present embodiment in FIG. 11 f (A.O ^C.,
A.O ^T., Are illustrated the ^{A.O B.), A.O T.} , A.O
^Since the value of this function changes according to the value of ^B., f (A.
O ^C.) Wider A.O ^C than in the case of. It can be seen that the range can be used and the operating margin expands.

[0017]

As described above, according to the present invention, the present invention, axial offset A.O ^C. Can be displayed in is always calculated screen reactor plant computer, A.O ^T.,
A.O ^B. A.O ^C using conventionally by three indicators DNBR, it is possible to view the limited range with F _Q. There is an advantage that even the operator who is familiar with it can express the protection range with an index that is intuitively understandable. In addition, the axial offset A.O ^C. , A.O ^T., A.O ^B. 4 split the output signal of the detector _{q 1, q 2, q 3} , q 4 only can be calculated using the signal to be used in the protection system is the detector output Since only the signals q ₁ , q ₂ , q ₃ , and q ₄ are required, there is an advantage that the calibration work for ensuring the accuracy is simple and the frequency thereof is small. Further, as an index when the operator is a control rod operation, shown in FIG. 8 (A.O ^C. And A.O ^T.) The diagram to modify the limit range deviation by the control rod insertion, Figure 9
As shown in (A.O ^C. And A.O ^B.) In diagram, an advantage that readily seen how to operate and so to modify the limit range deviation by the control rod withdrawal. (A.
O ^C. And A.O ^T.) The drawing shows the change in axial offset from the core of the beginning of life to the end. Conventionally,
Axial offset A.O ^C used in pressurized water reactors. When determining the DNBR protection function only, A.O ^T shown in FIG. 10. Since the end of life is the most severe in terms of DNBR, the allowable axial offset A.O.
Is the range. Even when the allowable axial offset AO is wider on the positive side as in the beginning of the life, the allowable axial offset AO at the end of the life is uniformly limited, so the allowable axial offset AO range is narrow. there was a problem that, if the method of the present invention described above, A.O ^T at that time. There is an advantage that the allowable axial offset AO range can be widened according to the above.

[0018] In addition, the function ^{f (A.O C., A.O T} ., A.
O ^B.) A is shown in Figure 11, A.O ^T., The value of the function depending on the value of A.O ^B. Has changed f (A.O ^C.)
Broader A.O ^C than in the case of. The range can be used and the operational margin can be expanded.

[Brief description of drawings]

[1] (a) and (b) are the same A.O ^C. Examples of different axial power distributions that appear for

FIG. 2 is a layout explanatory view of an axial quadrant neutron detector.

FIG. 3 is an explanatory diagram showing that the minimum DNBR and 4max.q have a linear relationship.

[4] (A.O ^C. And A.O ^T.) DNB in relation
An example of a curve displaying a constant R value.

[5] (A.O ^C. And A.O ^B.) DNB in relation
An example of a curve displaying a constant R value.

[6] (A.O ^C. And A.O ^T.) Curve example displays F _Q constant value in relation to.

[7] (A.O ^C. And A.O ^B.) Curve example displays F _Q constant value in relation to.

[8] (A.O ^C. And A.O ^T.) Shows a change curve of the control rod operation in relation.

[9] (A.O ^C. And A.O ^B.) Shows a change curve of the control operations in relation to.

[10] (A.O ^C. And A.O ^T.) Shows a change curve by combustion from beginning of life to the end of life in relation to.

FIG. 11 shows a function f (A.
O ^C. , A. O ^T. , A. O ^B.) And shows a A.O ^C. Relations.

[Explanation of Codes] 1 ... Reactor core, 2a, 2b, 2c, 2d ...

Claims (2)

[Claims] 1. The output signals of neutron detectors which are axially divided into four parts with respect to the core and which are arranged vertically above and below the reactor are output as q ₁ , q ₂ , q ₃ , q ₄ from those above the neutron detector. , The output signals q ₁ , q ₂ , q ₃ and q _{4 are used} to determine the axial offset A.O ^C. , Of the core on the half-axial offset A.O ^T. And the core lower half axial offset A.O ^B. Respectively, Is defined as, the output signal _{q 1 + q 2 + q 3} + q 4 = 1 normalized to display the nucleate boiling ratio DNBR than the output signal, said nucleic boiling limit ratio DNBR axial offset A.O ^C. , A.O ^T. And A.O ^B. Use calculates, A.O the same nucleate boiling ratio DNBR ^C. And A.O ^T. Relationships and A.O ^C. And A.O ^B The heat flux heat channel coefficient F _Q is displayed by the output signals q ₁ , q ₂ , q ₃ and q ₄ and the heat flux heat channel coefficient F _Q is indicated by the axial offset. A.O ^C., A.O ^T. and A.O ^B. use calculated, the same heat flow Tabanetsu waterways factor F _Q A.O ^C. and A.O ^T. relationships and A. O ^C. and A.O ^B. Atoms of the graphical display and in relation, to determine the nucleate boiling ratio DNBR and acceptable operating range by limiting the heat flow Tabanetsu waterways factor F _Q is a thermal limit of the reactor core from the respective graphical display Furnace operation monitoring and protection method. Wherein said nucleate boiling ratio DNBR and heat flow Tabanetsu waterways factor F _Q of the limit A.O ^C. , A.O ^T. And A.O ^B.
The reactor operation monitoring and protection method according to claim 1, which is configured as a function form of