JPS59112281A - Control system of control rod - 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] [Technical Field of the Invention] The present invention relates to a control rod control system number for a brine type nuclear reactor.
related.

[Technical Background of the Invention and Problems Therewith] In water reactors, a control rod withdrawal monitoring device is provided to monitor the power increase caused by control rod withdrawal during power operation. In order to increase output power, when a certain control rod is selected, a plurality of fixed in-reactor neutron detectors (hereinafter referred to as LPRM) are placed around the selected control rod. Furthermore, the average value of the signals from the selected LPRM is taken, and when the average value exceeds the average value before withdrawal by a predetermined value, a control rod withdrawal prevention function is set to prevent control rod withdrawal. It has the function of suppressing the increase in output below a predetermined level by sending a signal and preventing the control rods from being withdrawn.

FIG. 1 is a diagram showing an example of the arrangement of LPRM in a conventional device.
2. LPRM, i.e., fixed type in-reactor neutron detection, marked with a circle 2 and a triangle 3 around the selected withdrawn control rod 1 (IA in the view shows the state of the fully withdrawn control rod at the time of scram). There are 16 vessels arranged in a grid. (Except for the periphery of the core, they are arranged like this.) This L
The PRM is divided into two systems, for example, an A system and a B system, and eight LPRMs are assigned to each system. And the A system and B system are the 21st Q+ (a), (b
), they have different signal strength-control rod withdrawal position characteristics. In addition, the vertical axis in Figure 2 shows the signal strength of LPRM, and the horizontal axis shows the control rod withdrawal position (with the withdrawal distance of the selected control rod, 0 point indicates the full insertion position, When all LPRMs are normal and both A and B systems are operating, the characteristics are shown in 21st FI (a).
As shown by the solid lines Al and Bl in (b), the responses of both systems are fast. (The signal strength is higher than in the case of dotted lines A2 and B2, which will be described later.) From the intersection of the characteristic curves of solid lines AI and Bl and the preset pull-out prevention level HL (indicated by a two-dot chain line) When the perpendicular line is lowered, the control rod withdrawal position &a1. b1 is fired. Therefore, A system, B
The control rod withdrawal prevention signal described above is sent from the system that reaches the above-mentioned intersection first among the systems.

By the way, there are variations in the output of the LPRM as the control rods are withdrawn. Among these variations, there are some that are undesirable from the viewpoint of preventing control rod withdrawal. For example, due to a malfunction or the like, an output extremely 52 higher than the average value or an output lower than the average value may cause the control rod to be pulled out.

Therefore, LPR, which is undesirable from the viewpoint of preventing control rod withdrawal,
Bypassing or disabling M, the preferred LPR
A control rod withdrawal prevention signal is output based only on the output signal from M.

Therefore, in some cases, C2 may completely bypass either system A or system B. A described in Table 1
It means system bypass or B system bypass.

When the Table 1 system is bypassed, the response of the system is generally 6 more confusing than when it is normal, ie, when no bypass is performed. In addition, among the LPRMs in the system,
Second, the LP with a good response of about 1g of withdrawn control rod
The response also deteriorates when RM2 or Fi3 is bypassed. This case is called worst-case bypass. Table 1 shows pull-out prevention positions in various cases, and in this table, min (al l bl )'? "Rui mtn(a2.ba)" means that it takes the smaller value of al and bl, or the smaller value of a2+b2.

Figure 2(a), point #51A2 of (1:+). The characteristic curve indicated by B2 shows the characteristics of each group at the worst bypass. As can be seen from FIG. 2, in the worst bypass case, when the control rod withdrawal position is in the A system, it moves to #b2 in the case of the aBIB system, resulting in a considerably worse response state than in the normal state (1).

In this way, in the conventional device, each group and ≦2 specific L
When the PRM is bypassed, the response deteriorates, and there is little hope for improvement. Further, in a nuclear reactor where high safety is required, the above-described deterioration in response due to bypass l2 is undesirable because it reduces the safety margin.

Furthermore, in the case of operation in which a plurality of control rods are operated at the same time, the number of LPRMs to be detected increases.

For example, when operating four control rods at the same time, 16X4=
Detection of 64 LFRMs is required for control rod withdrawal monitoring, and the configuration of the monitoring device becomes complicated. The purpose is to improve (a) and (b).

(a) If each group or specific LPRM is bypassed, the response will deteriorate and the amount of output increase will increase.

(b) When performing C2 operation (withdrawal) on multiple control rods at the same time,
The circuit for detecting changes in core status becomes complicated. Therefore, the monitoring system becomes complicated.

In other words, by not using the detection of % core state (station 9 [output] change) to set the control rod withdrawal prevention position (control rod withdrawal length), a stable and reliable withdrawal prevention function can be ensured. be.

Specifically, C2 is a control rod withdrawal monitoring device whose purpose is to prevent control rod withdrawal based on an allowable control rod withdrawal length that is appropriately determined in advance from safety and operational considerations.

In order to stably limit the amount of local power increase, the length of the withdrawal is determined as a function of the control rod position before the start of withdrawal.
This determines the length of the permit withdrawal.

[Summary of the Invention] The present invention relates to a core of a nuclear reactor, a control rod that is pulled out and inserted into the core, a control rod drive mechanism for the control rod, and a control rod for the control rod.
A control rod control device that controls the drive mechanism, a control rod axial position detection device for the control rod, and a control rod withdrawal prevention position signal that receives signals from the control rod axial position detection device and the control rod control device. A control rod control system comprising: a control rod withdrawal monitoring device that inputs the information into the control rod control device;
The control rod withdrawal monitoring device includes a target control rod selection circuit into which a control rod axial position signal from a control rod axial position detection device and a control rod selection signal from the control rod control device are input, and a target control rod selection circuit. Extraction control rod axial position signal from the circuit (2) If the initial axial position of the extraction control rod is in the center of the reactor core, the allowable extraction length is decreased. The control rod control is characterized by a control rod withdrawal prevention position setting circuit that outputs a control rod withdrawal prevention position signal to a control rod control device, which is determined by a characteristic curve inputted in advance to increase the allowable withdrawal length. system (there are two)

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows a control S drive system for a boiling water reactor using the control rod withdrawal monitoring device 4 according to the present invention.

Inside the core 5 shown in FIG.
A large number of extraction control rods 1 such as L and T are stored.

In the figure, the control rods that are not pulled out are omitted and not shown. The extraction control rod 1 is extracted and inserted by a control m drive mechanism 6 which is bifurcated below the core 5. This control rod drive mechanism 6 is controlled by a control rod control device 7. This control rod control device 7 inputs a control rod operation signal S1 and a control rod withdrawal prevention position signal 82, and receives a control rod drive signal S3.
and a control rod selection signal S4. control rod drive signal s
3 is sent to the control rod drive mechanism 6, and a control rod selection signal S
4 is sent to the control rod withdrawal monitoring device 4. The control rod axial position signal s5 sent from the four control rod axial position detection devices 10 of the control rod withdrawal monitoring device is inputted, and the control rod withdrawal prevention position signal s2 is outputted to the control rod control device 7.

FIG. 4 shows in detail the configuration of the control rod withdrawal monitoring device 4 according to the present invention shown in FIG. 3.

In FIG. 4, the target control rod selection circuit 8 selects the withdrawal control rod 1 in response to the control rod selection number S4, and sends the selected withdrawal control rod axial position signal S5A to the control rod withdrawal prevention position setting circuit. Send on 9th. This control rod withdrawal prevention position setting circuit 9C incorporates the relationship between the control rod initial axial position p and the allowable withdrawal length ΔL, and uses this relationship to signal the initial control rod withdrawal axial position. 85A to find the allowable pull-out length ΔL. A withdrawal prevention position is set from the withdrawal restriction '#1 initial axial position signal S5A and this allowable withdrawal length ΔL, and this is sent to the control rod control device k7 as a withdrawal prevention position signal S2.

The relationship between the initial axial position of the control rod and the allowable withdrawal length in the control rod withdrawal prevention position setting circuit 9C is shown in FIG. Fifth
The vertical axis of the figure indicates the allowable pull-out length ΔL of the pull-out control rod 1, and the horizontal 4
ill indicates the control rod initial axial position P of the withdrawn control rod 1. When the control rod initial axial position PX is at the top and bottom of the core, the allowable pull-out length is large, and when the control rod initial axial position fufPx is at the center of the core, the allowable pull-out length △L is set to be small. The ceremony has been held.

The pullout prevention position is set as a value obtained by subtracting the allowable pullout length obtained from the 1yl relationship between the control rod initial axial position PI and the allowable pullout length ΔL described above from the initial axial position. That is, if the initial axial position of the control rod 1b'' is PI + this PIl2 and the corresponding allowable pull-out length is △L, then the pull-out prevention position pB
is set so that pB = P, -ΔL.

In the system of the present invention configured as described above, during output operation (when the second withdrawal control rod 1 is selected and the control rod operation signal S1 is input to the control rod control device 7, the control rod withdrawal monitoring 4U
A control rod selection signal S4 is sent to the target control rod selection circuit 8 of flt4.
will be sent. The target control rod selection circuit 8 selects the necessary extraction control rod 1 based on the control rod selection signal S4, and sets the initial axial position 1Mi J4S 5 of the extraction control rod 1 to the control rod extraction prevention position setting circuit 9. send.

In this control rod withdrawal prevention position setting circuit 9, based on the initial axial position signal 85, an allowable withdrawal length ΔL corresponding to the initial axial position fPIl2 is set, and from the allowable withdrawal length to the initial axial rotation. Set the control rod withdrawal prevention position pB. This position is sent to the control rod control 1 device 7 as the control rod withdrawal prevention position (No. g 8B).

For example, if the initial axial position of the selected control rod is 0.6 m from the top of the core, and the allowable withdrawal length corresponding to this position is 0.4 m, then the control rod withdrawal prevention position is 1.6 m from the top of the core. It is set to 0 m, and this becomes the control rod withdrawal prevention position signal S2. Also, if the initial axial position of the selected control rod is approximately half the height of the core (approximately 2 m from the top of the core), about this much? ! Since the initial position is at the center of the core, the allowable pull-out length for 1'-1 is shorter than the previous example of 0.4 m, for example 0.3, and the control rod pull-out monitoring position fRt-t is 23 m from the top of the core. Set.

In the control rod control device 7, when the control rod operation signal Sl instructs the withdrawal of the control rod beyond the withdrawal prevention position inputted by the control rod withdrawal prevention position signal s2, g2 is the control rod withdrawal position at the prevention position of the withdrawal prevention position signal S2. Control is performed to prevent withdrawal.

FIG. 6 shows the output increase characteristics when using the device of the present invention in comparison with the case of a conventional device. In the figure, -PI indicates the initial axial position of the withdrawal control rod; indicates the pull-out prevention position when all LPRMs are normal, and the output increase amount at that time is Δ
0 and P2, which is Pi, indicate the pull-out blocking position when the conventional system and a specific LPPM are bypassed, and the output increase amount at that time is ΔF9.

Therefore, the output increase iFi when using the device of the present invention,
Total LPR of conventional equipment regardless of detector bypass status
As in the case where M is normal, it is certain (20 minutes low view [2) can be suppressed.

Two effects of changing the allowable pull-out length depending on the initial axial position, which is one of the features of the present invention, will be explained below. (Characteristic diagram in FIG. 5) In the core 52 of a boiling water reactor, the power distribution in the axial direction is small at the top and bottom of the core, and large at the center of the core. For this reason, as shown in Fig. 7, the local power increase in the control rods is increased in the center of the core where the power is high, and the power increase in the upper and lower parts of the core where the power is low is increased. is a small characteristic. Therefore, when using the system of the present invention, the control rods are pulled out in such a way that the allowable pull-out length is small in the central part of the core, and the allowable pull-out length is large in the upper and lower parts of the core, as shown in Figure 5 f-2. Therefore, as shown in FIG. 8C, a constant increase in output can be suppressed regardless of the initial axial position of the control rod.

Furthermore, by adopting the system of the present invention, when multiple control rods are withdrawn at the same time, even if the control rods are accidentally withdrawn during power operation, the core detection system is not used, so the control rods are always in the same position and easily removed. The control rod is prevented from being pulled out, and an excessive increase in output can be prevented.

[Effects of the Invention] As described in detail above, the control rod withdrawal is prevented using the relationship between the initial control rod position and the allowable withdrawal length provided in the system of the present invention, so that the #pau bypass state , regardless of the number of withdrawal control frames and the initial control rod position g1. It is possible to restrict the power to an appropriate number of digits, maintain a thermal margin for the fuel, and improve the reliability and safety of boiling water reactors.

[Brief explanation of drawings]

Fig. 1 is a layout diagram of a withdrawn control rod and a fixed in-reactor neutron detector, Fig. 2 is a signal strength-control rod withdrawn position characteristic diagram of a conventional device, and Fig. 3 is a diagram of a boiling water reactor according to the present invention. FIG. 4 is a block diagram showing the configuration of a control rod withdrawal monitoring device according to the present invention, and FIG. 5 is a diagram showing the control rod drive system according to the present invention. Figure 6 is a characteristic diagram of the allowable pull-out length vs. control rod axial position; Figure 6 is a characteristic diagram of output increase when using the device of the present invention vs. control rod axial same position @ characteristic diagram; Figure 7 is a characteristic diagram of the same length of control rod. FIG. 8 is a characteristic diagram of the amount of increase in output when the rod is pulled out versus the initial position of the control rod. FIG. 1... Extraction control rod 2.3... Fixed type in-reactor neutron detector (LPRM) 4.
... Control rod withdrawal monitoring device 5 ... Core 6 ... Control rod drive mechanism 7 ... Control rod control device 8 ... Target control rod selection circuit 9 ... Control rod withdrawal prevention position setting circuit. ... Control rod axial position detection device S1 ... Control rod operation signal S2 ... Control rod withdrawal prevention position signal S3 ... Control rod drive signal S4 ... Control rod selection signal S5 ... Control rod axis Directional position signal S5A... Extracted control rod axial position signal Agent Patent attorney Nori Chikazoe Tasuku (1 person) 65 Figure 1 Broom 2 Figure (α) Cb body 11λ modified ■ 1 throat, 51 I l deficiency 4 present
Body 11 Yh'j1 Friends 1-Nails 4
Fig. 5 Fig. 6 PI FIβ2 Control focus axial gradient 1 654- Fig. 7 Fig. 8

Claims (1)

[Claims] (1) The reactor core, the control rods that are pulled out and inserted into the core, the control rod drive mechanism of the control rods, and the control rods.
A control rod control device that controls the JIA dynamic mechanism, a control rod axial position detection device for the control rod, and a control rod axial position detection device! ! A control rod control system 52 includes a control rod withdrawal monitoring device that receives a signal from the control rod control device and inputs a control rod withdrawal prevention position signal to the control rod control device. The device performs target control +1 to which a control rod axial position signal from a control rod axial position detection device and a control rod selection signal from a control rod control device are input. The selection circuit and the control rod axial position signal from this target control rod selection circuit determine the control rod withdrawal prevention position 1i/1', and if the initial axial position of the withdrawal control rod is in the center of the core, the allowable withdrawal length. If it is small and located at the top and bottom of the core, increase the allowable pull-out length.Determine based on the pre-input characteristic curve,
A control rod control system comprising a control rod withdrawal prevention position setting circuit that outputs a control rod withdrawal prevention position signal to a control rod control device C. The control rod control system 0 according to claim 1, characterized in that