JP3080726B2 - Control rod removal prevention monitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control rod withdrawal prevention monitor for a boiling water reactor, and more particularly to a control rod withdrawal that allows a minimum control rod operation even during a control rod withdrawal inhibition operation. It relates to an inhibition monitor device.

[0002]

2. Description of the Related Art In a boiling water reactor, since reactor water boils in the reactor core and voids are generated, it is very important to maintain fuel rod cooling efficiency in maintaining the fuel rod integrity. It is.

The boiling state is roughly classified into a nucleate boiling state and a film boiling state. In the nucleate boiling state, voids are repeatedly generated and disappear on the surface of the fuel rod, so that the cooling efficiency is high and the soundness of the fuel rod is high. Can be secured. On the other hand, the film boiling state occurs when the fuel rod surface temperature (fuel rod output) is higher than the nucleate boiling state. When the fuel rod output is increased, a vapor layer is rapidly formed on the entire fuel rod surface, resulting in cooling efficiency. Refers to a state in which is greatly reduced. In this state, the cooling efficiency deteriorates, so that the surface temperature further increases, and eventually the fuel rods are damaged.

As described above, the state rapidly changes from the nucleate boiling state to the film boiling state. At this time, the calorific value of the fuel rod is called a limit output, and the ratio of the limit output to the current output is a limit output ratio ( = Limit output / current output). The critical power ratio can be obtained for each fuel in the reactor core, and is a value of 1 or more in a normal operating state (nuclear boiling state). The smaller the value, the closer the output to film boiling is. ing. In particular, the minimum critical power ratio in the core is called a minimum critical power ratio (hereinafter, referred to as MCPR), and is one of the most important parameters to be monitored in the operation of the core.

However, in a boiling state of the fuel rod, it is necessary to avoid a film boiling state in any event as well as in a normal operation state. For this reason, on the operation side of the reactor, it is not more than 1.0, but on the safe side (more than 1.0)
Has two levels for monitoring.

One of them is determined in consideration of the certainty of the limit power ratio calculated by the computer, and is called a minimum safety limit power ratio (hereinafter, referred to as SLMCPR).
No event should fall below this value. Below this value indicates an increased likelihood of a transition to film boiling in the core.

Another one is a value called a minimum operating power ratio (hereinafter referred to as OLMCPR), which is a SLMCP.
It is provided on the safer side than R. Among the various events that can be considered in a nuclear reactor, MC
In some cases, it is worse than PR. The difference between the initial MCPR and the smallest MCPR is called ΔMCPR,
It is necessary to add the maximum ΔMCPR among various events to the SLMCPR to obtain a monitoring level during normal operation. This value is OLMCPR.

[0008] One of the events in which the MCPR transiently deteriorates during the rated output operation is erroneous removal of the insertion control rod. Assuming that the control rod is completely removed from all insertions, depending on the state of the core at that time, the worst case is ΔM more than other events.
CPR may increase. in this case,
The OLMCPR value is high, which hinders the core operation plan.

[0009] Therefore, conventionally, ΔMCP of control rod erroneous withdrawal
In order to reduce R, a control rod removal prevention monitor device (hereinafter, referred to as an RBM device) is provided.

[0010] The RBM device has two to four parts surrounding the pull-out control rod.
The LPRM signals in the LPRM strings are averaged, and the gain is adjusted to match the APRM instruction before the extraction (this signal is referred to as an RBM signal). When the output locally increases with the removal and the RBM signal reaches a preset control rod removal prevention set level, as shown in FIG. 3, the RBM device 1 outputs the RBM removal prevention signal to the control rod removal prevention signal. It is sent to the control rod operation system 2 as a pull-out prevention signal to prevent pull-out. Since ΔMCPR due to control rod withdrawal is almost directly proportional to the local output increase, RBM before withdrawal is used.
The difference between the signal and the extraction prevention set level substantially corresponds to ΔMCPR on a one-to-one basis.

At present, in a 1100 MWe-class boiling water reactor, the set level of withdrawal inhibition can be represented by a line on the power-flow diagram shown in FIG. Is above these lines, the control rod is prevented from pulling out.

That is, as shown in FIG. 4, three levels of the pull-out prevention setting level are set: a low position level 3, a middle position level 4 and a normal position level 5. Of these levels, the low position level 3 and the low position level 3 are set. The middle position level 4 can be bypassed by the operator after reaching the set value. On the other hand, the normal position level 5 has no bypass function.

Each of these levels 3, 4, and 5 is set at an 8% output interval, so that the RBM signal is allowed to withdraw only a maximum of 8% in one extraction. . Δ corresponding to 8% of RBM signal
The MCPR is kept small to the extent that it is less than the largest ΔMCPR among the other events except for control rod mispulling.

As described above, the RBM device is a device that reduces ΔMCPR at the time of erroneous withdrawal of the control rod so that the erroneous withdrawal event does not become the most severe event.

When the RBM signal reaches the normal position level 5, the bypass cannot be performed as described above, and the control rod cannot be further pulled out. This limits the OLMCPR so that it does not fall below the lower limit of the OLMCPR in the initial fuel characteristics.

[0016]

However, improvements have been made to the fuel design of nuclear reactors, and both core characteristics and economics have been improved compared to the initial fuel. Accordingly, there is an increasing demand for operating the reactor in a reactor core operating range that is as wide as possible in the rated operating state of the reactor. Hereinafter, a specific description will be given with reference to FIG.

FIG. 4 shows the reactor operating state as points on the graph, with the horizontal axis representing the core flow rate and the vertical axis representing the reactor power, and represents the trajectory of the reactor state when the reactor is started. ing. In the figure, reference numeral 6 is a typical reactor startup curve due to an increase in core flow rate, and reference numeral 7 is a typical reactor startup curve due to control rod withdrawal.

Here, the rated power state can take a state between the point A and the point B. In order to improve the economy, the reactor operation range at the rated power indicated by reference numeral 8 is set. , The operating range of the reactor indicated by reference numeral 9 needs to be increased.

However, since the levels 3, 4, and 5 of the RBM withdrawal prevention setting decrease as the recirculation flow rate decreases, at the operating point B 'where the core flow rate is low, unlike the case of the operating point B, at the operating point B' where the core flow rate is low. Above the normal position level 5. Normally, the operation by the control rod operation during the rated output operation is not performed, but in the surveillance test for confirming the soundness of the control rod, it is necessary to insert and withdraw one notch of the control rod. Since the RBM prevents the control rod from being pulled out, the control rod surveillance test cannot be performed.

In order to reduce the core flow rate at the time of reaching the rated power even at the time of starting the reactor, the target control rod pattern is in a state in which the target control rod pattern is pulled out more than in the conventional case. As shown by C ', when creating the target pattern,
The possibility of exceeding the normal position level 5 increases.

In order to solve this, it is conceivable to review the set value of the RBM and raise the normal position level 5, but it is preferable to change the current set value because it changes to the non-safety side. Absent. Therefore, the current normal position level 5
It is sufficient to add a new setting line above the setting line, but this method has a problem that the change of the RBM becomes large.

The present invention has been made in view of the above points, and has as its object to provide a control rod withdrawal prevention monitor device capable of extending the operation range in which the control rod can be operated with only a slight change. I do.

[0023]

According to the present invention, as a means for achieving the above object, a control rod withdrawal prevention monitor is provided with a discriminating means, and the discriminating means is turned on simultaneously with the control rod withdrawing switch during continuous withdrawal. Of continuous pulling switch
A neutron flux high control rod withdrawal setting level is set to allow the control rod to be pulled out by one notch when the reactor power exceeds the continuous withdrawal allowable level by providing a withdrawal inhibition signal to the control rod operating system under the condition of F. Further, the control rod is prevented from being pulled out to the high reactor output side.

[0024]

According to the present invention, the control rod withdrawal prevention monitor is provided with a discriminating means, and provided that the continuous withdrawal switch is turned off.
Since the control rod withdrawal prevention signal is given to the control rod operation system,
Even if the reactor power exceeds the set value, the control rod can be pulled out by one notch. For this reason, there is an effect that the surveillance test of the control rod which can not be freely performed conventionally can be freely performed. Further, a neutron flux high control rod withdrawal prevention setting level for preventing control rod withdrawal is provided at a level exceeding this one-notch withdrawable level. At the reactor power level that may impair the performance, the withdrawal of the control rod can be prevented.

[0025]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a control rod withdrawal prevention monitor device according to the present invention. In the figure, reference numeral 1 denotes an RBM device, and reference numeral 2 denotes a control rod operation system. The pull-out prevention signal from the RBM device 1 is given to the control rod operation system 2 as a control rod pull-out prevention signal via the determination means 11.

The discriminating means 11 is provided with an O of a continuous pulling push button switch (hereinafter referred to as a continuous pulling PB) from the control rod operating system 2.
Under the condition of FF, a pull-out prevention signal is given to the control rod operation system 2. This continuous drawing PB is turned on at the same time as the control rod pulling push button switch when performing continuous drawing.

Next, the operation of the present embodiment will be described.

The pull-out prevention signal from the RBM device 1 is given to the control rod operating system 2 as a control rod pull-out prevention signal via the determination means 11, but the determination means 11
Under the condition of FF, a pull-out prevention signal is given to the control rod operation system 2. That is, the pull-out prevention signal of the RBM device 1 is valid only when continuous pulling is to be performed, and one-notch pull-out can be performed freely without being prevented from being pulled out by the RBM device 1.

This will be described in detail with reference to FIG.

FIG. 2 (a) shows a conventional operating range of a nuclear reactor. In FIG. 2 (a), reference numeral 5 indicates a normal position level of control rod withdrawal prevention. ,
The continuous notch pull-out allowable range is 12.

On the other hand, FIG. 2 (b) shows the operating range of the reactor according to the present invention. The notch withdrawal allowable range 14 is between the position level 5 and the neutron flux high control rod withdrawal prevention setting level 13 above it. Therefore, the range up to the neutron high control rod withdrawal prevention set level 13 is within the range in which the neutron can be withdrawn.

As described above, the operation range in which the control rod can be operated can be expanded, and accordingly, the operation in the rated output state can be performed. As a result, a surveillance test for confirming the soundness of the control rod, which has been impossible in the past, becomes possible, and the operating range can be expanded.

[0034]

As described above, according to the present invention, the operating range in which the control rod can be operated can be expanded with only a slight change of providing the determination means. In addition, at a level that exceeds this one-notch withdrawable level, a set level for preventing withdrawal of the control rod is provided.
Even with one notch withdrawal, control rod withdrawal can be prevented at the reactor power level where fuel integrity may be compromised.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a control rod withdrawal prevention monitor device according to an embodiment of the present invention.

FIG. 2A is an output-flow rate diagram showing an operation range of a nuclear reactor in a conventional apparatus. (B) is an output-flow diagram showing a reactor operation range in the RBM device according to the present invention.

FIG. 3 is a configuration diagram showing a conventional control rod withdrawal prevention monitor device.

FIG. 4 is an output-flow rate diagram showing a relationship between a set level of RBM control rod withdrawal prevention and a reactor operation range when an operation region is expanded.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 RBM apparatus 2 Control rod operation system 11 Judgment means

Claims (1)

(57) [Claims] 1. A control rod withdrawal prevention monitor device for providing a control rod withdrawal prevention signal to a control rod operation system when a reactor power reaches a preset set value. The determination means is provided to provide the pull-out prevention signal to the control rod operation system on the condition that the continuous pull-out switch is turned on simultaneously with the control rod pull-out switch when the continuous pull-out is performed, and the reactor exceeds the continuous pull-out allowable level. A neutron flux high control rod withdrawal setting level that allows one notch withdrawal of the control rod at the time of output is provided to prevent the control rod from being withdrawn to the high reactor output side beyond the set level. Characteristic control rod withdrawal prevention monitor device.