JPH04258791A - Nuclear reactor output control method and device thereof - Google Patents

Abstract

PURPOSE:To prevent the damage of fuel rods by setting a limit line where a boiling transition occurs by an analysis in advance, and automatically performing a scram when the operation enters the operation region in which the boiling transition occurs. CONSTITUTION:A selective control rod inserting device 5 and a comparing device 6 are connected to a control rod driving device 4. A limit curve calculating device 7 and an operation state judging device 8 are connected to the device 6, and the nuclear reactor output and core flow quantity which are plant data are inputted to the device 7. The device 7 sets the BT limit curve where a boiling transition(BT) causing the damage of fuel rods occurs and the stable limit curve 32 where the fluctuation of the output and flow quantity occurs during the operation of a boiling-water type nuclear reactor by an analysis in advance. The device 8 judges the operation state from the plant data. The device 6 judges whether the operation state is included in the limit region or not, and a scram is automatically performed by the device 4 if the operation state enters the scram region.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling the power of a boiling water reactor, which controls the operating range so as not to impair fuel integrity during the operation of a boiling water reactor.

0002

BACKGROUND OF THE INVENTION Boiling transition development has been used in boiling water nuclear reactors (B
This is an important development that should be considered when designing WR). A boiling transition is caused by a sudden deterioration in heat transfer. There are various names for this point of origin, but BW
Regarding R, boiling transition
ion:BT).

[0003] In the operation of BWR, a standard is adopted that does not impair the integrity of the fuel, but in actual application, the standard that BT does not occur is used to determine the operating range and evaluate transient development at abnormal times. is being carried out. Many studies have been conducted on the prediction of BT, and a correlation formula giving the critical heat flux at which BT is generated has been created based on steady experimental data.

However, the current BWR design employs GE's GEXL system. In the GEXL formula, the critical power is given instead of the critical heat flux, and the margin to BT is evaluated by the critical power ratio (CPR), which is defined as the ratio of the critical power to the actual bundle power. Stability is also an important consideration in BWR design. This is because in an unstable state, output and flow rate fluctuations may occur, and in some cases, BT may occur.

[0005] In general, the coolant passing through the fuel bundle provided in the core of a boiling water reactor forms a two-phase flow of water and steam to remove heat generated in the core. It is known that there is a possibility of thermo-hydraulic oscillations based on feedback between voids, pressure drop, and flow rate.

[0006] There are a large number of fuel channels in the reactor core, which form parallel flow paths. Therefore, for each fuel bundle, its thermo-hydraulic oscillations occur under the condition of a constant differential pressure between the inlet and the outlet. It can be considered that this occurs independently from other fuel channels. Furthermore, due to the locality of vibrations, feedback via nuclear properties is considered to be secondary.
As a first approximation, this can be ignored.

[0007] Such a vibration mode is called channel stability, while a vibration mode in which the core characteristics of the core and the dynamic characteristics of the recirculation flow path are related to the feedback development of the two-phase flow of the fuel bundle is called core stability. It is called.

[0008] Furthermore, in recent years, output vibrations in a spatially opposite phase mode, which is thought to be caused by the mutual influence of the above two modes, have been observed in BWR plants overseas. This type of vibration mode is called regional stability.

Core stability during operation of an actual nuclear power plant can be monitored by global signals such as core average neutron flux signal, recirculation flow rate, etc., but channel stability can be monitored locally. Since this is a typical development process, it is not expected that it can always be monitored solely by the readings from the in-reactor neutron detector.

[0010] Also, regarding regional stability, since one half of the core produces output oscillations that are in the opposite phase to the other half, the core average neutron flux cancels each other out, resulting in fluctuations in the core average neutron flux signal. are small and cannot be expected to be constantly monitored.

[0011] The communication operation range of BWR is analyzed at the design stage to prevent the occurrence of BT and unstable vibrations, but most of the previous research on stability has focused on determining the limit conditions where unstable conditions occur. The focus was on this, and there was little consideration in relation to BT.

However, from the perspective of fuel health,
An unstable state is a problem because it can cause BT due to fluctuations in output and flow rate, and although it is not a desirable state if BT does not occur, it is a state that should be absolutely avoided. It is inconceivable that this is the case. Therefore, the relationship between the region where an unstable state appears and the region where BT occurs in BWR operation will be described below.

Generally speaking, the stability of the nuclear reactor core decreases as the core flow rate decreases and as the reactor output increases, and on the flow rate control curve, the lower the flow rate, the lower the stability. Therefore, on the same flow rate control curve, the natural circulation state is the least stable.

[0014] Furthermore, in such a state of low flow rate and high output, an unstable state is more likely to occur than in BT. This relationship
Shown in Figure 3. Both the steady BT curve 34 and the stability limit curve 32 in the figure indicate that BT and unstable vibration occur in a region where the output is higher and the flow rate is lower (upper left side of the curve) than these curves.

Now, considering the case where the output increases on the natural circulation curve 31, the natural circulation curve 31 and the stability limit curve 3
Unstable vibration occurs at the intersection point 33 (indicated by a black circle in the figure) of 2. Furthermore, when the output is increased, flow rate oscillations occur, so although the average flow rate is the natural circulation flow rate, its amplitude (indicated by △W in the figure) increases, so the flow rate takes into account the amplitude. A point 35 (
It is thought that BT occurs at points (indicated by white circles in the figure). Therefore, the output at this point is generally smaller than the BT generated output when there is no vibration. In addition, 36 in the figure
37 is the flow control curve, and minimum pump speed curve 38 is the excessive BT.

[0016] In the above explanation, in order to clearly show the relationship between the unstable state and BT, only the flow rate oscillation was considered, but in reality both the output and the flow rate oscillate, so the relationship is complicated. The basic relationship remains unchanged.

[0017] Therefore, from the viewpoint of fuel integrity, it is desirable to limit the BT generation range, including the above-mentioned points. Further, even if there is no problem in terms of fuel integrity, the unstable region is not a desirable state, so if the unstable region falls into that region, it is desirable to take measures to deviate from that region.

[0018]

SUMMARY OF THE INVENTION In response to such demands, in the current BWR, no operational control curve has been established that takes into account unstable conditions. Also, depending on the plant type, there are controls such as setting a constant output value (above the rated output) or a curve with high output parallel to the flow rate control curve, and causing a scram when the output exceeds these values.
It is not clearly defined from the BT conditions.

The present invention has been made to solve these conventional problems, and its purpose is to eliminate the possibility of fuel damage in order to maintain the integrity of the fuel during operation of a boiling water reactor. An object of the present invention is to provide a method and apparatus for controlling the output of a nuclear reactor, which determines the region where boiling transitions and unstable vibrations occur and controls the operating region. [Structure of the invention]

[0020]

[Means for Solving the Problems] A method for controlling nuclear reactor power according to the present invention provides a method for controlling the power output of a nuclear reactor at a limit line at which boiling displacement that may cause damage to fuel rods occurs during operation of a boiling water reactor.
The stability limit line where output and flow rate oscillations occur is determined in advance by analysis, and when the operating region enters the operating region where boiling transition occurs, it is automatically scrammed, and the stability limit line where boiling transition does not occur is determined in advance. If it exceeds and enters the unstable region,
By selectively inserting control rods, the output is reduced to below the output on the 80% output flow rate control curve.

The reactor power control device according to the present invention includes a pressure vessel, a reactor core disposed within the pressure vessel, a control rod communicating with the reactor core, and a control rod communicating with the control rod. A rod drive device, a selective control rod insertion device that operates the control rod drive device, a comparison device that communicates with the selective control rod insertion device and the control rod drive device, and a limit curve calculation device that communicates with the comparison device. , and a driving status determination device communicating with the comparator.

[0022]

[Operation] In the present invention, from the viewpoint of maintaining the fuel integrity of the BWR, the operating range is limited from the BT and stability limits that affect it, and in the current case, the operating range is automatically set to the range where BT occurs. When scramming and entering an area where BT does not occur but is in an unstable state, select control rod insertion (S
RI) to a sufficiently stable region to avoid damage to the fuel rods.

[0023]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. FIG. 1 shows a control device used in the method for controlling the reactor output according to the present invention, and 1 represents a pressure vessel.

A nuclear reactor core 2 is arranged in this pressure vessel 1, and a control rod 3 is connected to this reactor core 2. This control rod 3 is driven by a control rod drive device 4. A selective control rod insertion device 5 and a comparison device 6 are connected to the control rod drive device 4 . Comparison device 6
A limit curve calculation device 7 and an operating state determination device 8 are in communication with each other. The operating state determination device 7 is configured to receive the reactor output and core flow rate from the plant data.

In the present invention, as shown in FIG. 2, the limit curve calculation device 7 calculates the BT limit curve and output power at which a boiling transition that may cause fuel rod damage occurs during operation of a boiling water reactor. The stability limit curve 32 at which vibrations and flow rate oscillations occur is determined in advance by analysis. In this case, the stability limit curve 32 is determined to encompass all the unstable regions controlled by the limit curves for each of core stability, channel stability, and region stability.

Then, the operating state determining device 8 determines the operating state from the plant data. In this state,
The comparison device 6 determines whether the operating state is included in the restricted region or not, and determines whether the operating state is included in the restricted region, that is, the operating region in which boiling transition occurs, that is,
When entering the scram area, the control rod drive device 4 automatically scrams.

Further, if the comparator 6 determines that the operating state does not cause a boiling transition but exceeds the stability limit and enters the unstable region, that is, the SRI region, the selective control rod insertion device 5 selects a preselected control rod. The control rod 3 is inserted to reduce the output to below the output on the 80% output flow rate control curve and deviate from the control region.

[0028]

[Effects of the Invention] As described above, in the present invention, when operating a boiling water reactor, the limit line where a boiling transition that may cause damage to the fuel rods occurs, and the stability line where fluctuations in output and flow rate occur, are solved. The limit line is determined in advance through analysis, and when the operation enters an operating region where a boiling transition occurs, it is automatically scrammed.Also, when a boiling transition does not occur but the stability limit is exceeded and the operation enters an unstable region, By inserting the selective control rod, 8
Since the output is reduced below the output on the 0% output flow rate control curve, damage to the fuel rods can be avoided.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a control device used in a method for controlling nuclear reactor output according to the present invention.

FIG. 2 is a diagram showing an operation control area of a BWR in the present invention.

FIG. 3 is a diagram showing the relationship between the BWR operating range and constraint conditions from the viewpoint of fuel integrity.

[Explanation of symbols]

1......Pressure vessel 2... Nuclear reactor core ３……Control rod 4......Control rod drive device 5...Selective control rod device 6……Comparator 7... Limit curve calculation device 8...Operating state determination device

Claims (2)

[Claims] [Claim 1] A limit line where boiling transition occurs that may cause fuel rod damage during operation of a boiling water reactor, and a stability limit line where fluctuations in output and flow rate occur are determined in advance by analysis. , automatically scrams when entering an operating region where a boiling transition occurs, and when a boiling transition does not occur but exceeds the stability limit and enters an unstable region, the output is reduced to 80% by selective control rod insertion. A nuclear reactor power control method characterized by reducing the power below the power on the flow rate control curve. 2. A pressure vessel, a nuclear reactor core disposed within the pressure vessel, and a control rod communicating with the reactor core;
a control rod drive device that communicates with the control rod, a selective control rod insertion device that operates the control rod drive device, and a comparison device that communicates with the selective control rod insertion device and the control rod drive device;
A nuclear reactor power control device comprising a limit curve calculation device connected to the comparison device and an operating status determination device connected to the comparator.