JPS60249094A - Monitor device for drawing 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 withdrawal monitoring device for preventing an excessive increase in power due to erroneous control rod withdrawal during power operation of a nuclear reactor.

[Technical Background of the Invention] A boiling water reactor (BWR), as shown in Fig. 4, has nuclear fuel loaded in a reactor pressure vessel 1 and control rods 2 with neutron absorption capacity arranged between the fuel. A reactor core 3 is constructed, and a coolant (soft water) 4 is housed inside the pressure vessel 1 . Further, a control rod drive mechanism 5 is installed at the bottom of the pressure vessel 1 in correspondence with each control rod 2, and the control rod drive mechanism 5 controls the core output by inserting and withdrawing the control rods 2. There is.

On the other hand, a plurality of jet pumps 6 are installed around the reactor core 3, and a recirculation system is constituted by these diene pumps 1 to 6 and a recirculation pump 7 provided outside the pressure vessel 1. The coolant 4 inside the reactor core 3 is forced to circulate from below to above.

There, the coolant 4 is heated by the reaction heat of the nuclear fuel loaded in the reactor core 3, and the resulting high temperature and high pressure steam is sent to the turbine 9 via the main steam pipe 8, which drives the generator 10. be done. Further, the steam that has passed through the turbine 9 is cooled and liquefied in a condenser 11 and returned to the pressure vessel 1 by a water supply pump 12.

By the way, in such a WR, a control l1tI withdrawal monitoring device 113 is provided in order to monitor the power increase accompanying control rod withdrawal during reactor power operation.

The configuration of the control rod withdrawal monitoring device 13 is as follows. That is, the reactor core 3 has a large number of fixed in-core neutron detectors (LP).
RM) 14 is installed, and the signal (LPPM signal) d output from each detector 14 is sent to the neutron detector selection circuit (
The LPPM selection circuit 15 selects the control rod to be extracted from among all the LPRM signals d based on the control rod selection signal (signal e) indicating which control rod is to be extracted. specific III
The PRM14 was installed around the control rod.
Select only the LPRM signal d' from .

The LPRM signal d' selected in this way is sent to the averaging circuit 1.
6 is input. Then, the average 111I (four-part average value signal) f of the plurality of LPRM signals d' is calculated,
This local average value signal f is input to the gain adjustment circuit 17. The LPRM signals d from all the LPRMs 14 in the core 3 are also input to another averaging circuit 18-, where the average value (core average value signal, or APRM signal) q of all the PRM signals d is calculated. , are input to the gain adjustment circuit 17. Therefore, the gain adjustment circuit 17 uses the local average value signal f input from the averaging circuit 16 and the APR.
By comparing the M signal and the q signal, the gain of the averaging circuit 16 is adjusted until the local average value signal f becomes larger than the APRM signal Q.

On the other hand, a recirculation pump flow rate signal is input to one withdrawal prevention level setting circuit, and the control rod withdrawal prevention level A is set based on this signal.

This control rod withdrawal closure level A is input to the determination circuit 20, where the local average value signal @i adjusted by the gain adjustment circuit 17 is compared with the control rod withdrawal closure level A, and the local average value When the signal i exceeds the control rod withdrawal prevention level A, the determination circuit 20 outputs the control rod withdrawal prevention signal j, thereby suppressing the reactor output below a certain level.

The reason why the gain of the local average value signal is adjusted is that the local average value signal If f is used as it is as a comparison standard for generating a control rod withdrawal prevention signal, even if a control rod is erroneously withdrawn, it will take time to generate the control rod withdrawal prevention signal, and the detection of erroneous operation will be delayed. The average value for the entire reactor core has been increased, which is a significant improvement.

[Problems with Background Art] As described above, in the conventional control rod withdrawal monitoring device, the control rod withdrawal prevention level Δ is set in the withdrawal prevention level setting circuit 19 as a function only of the recirculation pump flow rate.
If the recirculation pump flow rate is constant, the control rod withdrawal prevention level A is also constant, and the generation of the control rod withdrawal prevention signal is delayed at times when the reactor output is low, such as at the beginning of the control rod withdrawal operation.

Therefore, in the event that a control rod is erroneously withdrawn, the rate of increase in reactor power associated with it will be greater as the reactor output is lower, and the effect on the fuel will be greater until the control rod withdrawal prevention signal is generated. There was a problem that the thermal influence became large.

[Object of the invention] The present invention was made based on the above circumstances, and
The purpose of this is to suppress the rate of increase in reactor power at the time of pullout, even if a control rod is accidentally pulled out during low-power reactor operation, and to reduce the thermal effect on the fuel. An object of the present invention is to provide a control rod withdrawal monitoring device that can easily maintain the integrity of a control rod.

[Summary of the Invention] In order to achieve the above object, the present invention inputs detection signals from a plurality of fixed neutron detectors that detect the in-reactor neutron output, and detects a control rod around a withdrawn control rod based on a control rod selection signal. A neutron detector selection circuit that selects detection signals from a plurality of installed in-core neutron detectors, an averaging circuit that calculates the average value of the plurality of signals output from the neutron detector selection circuit, and at least a A signal related to the output is input and the control rod withdrawal prevention level is fixed as a function of the core output.The output of the averaging circuit is compared with the control rod withdrawal prevention level and the control rod withdrawal prevention level is set as a function of the core output. and a determination circuit that outputs a control rod withdrawal closing signal when the output of the control rod withdrawal prevention level exceeds the control rod withdrawal prevention level.

In other words, the control rod withdrawal prevention level is set as a function of the reactor core power, so that even during low power operation, the rate of increase in reactor power when control rods are withdrawn can be suppressed to a small level. This is what we do.

[Embodiments of the Invention] First, a first embodiment of the present invention will be described with reference to FIG. In FIG. 1, the parts other than the control rod withdrawal monitoring device 21 have the same configuration as in FIG. 4, and therefore are given the same reference numerals.

The control rod withdrawal monitoring device 21 is configured as follows.

That is, the LPRM signal d signal from a large number of fixed in-core neutron detectors (LPRM) 14 installed in the reactor core 3 is input to the in-core neutron detector selection circuit 22, and this in-core neutron detector selection circuit 22 selects all From among the LPPM signals d, based on the control rod selection signal e, select the LPRM signal d from the LPRMi4 installed around the specific control rod (extraction control rod) selected for extraction operation. .

The LPPM signal d' selected in this way is sent to the averaging circuit 2.
3 is input. Here, an average value (local average value signal) f of the plurality of LPPM signals d- is calculated, and this local average value signal f is input to the gain adjustment circuit 24. Also, all LFs in the core 3! The LPRM signal d from the RM14 is also input to another averaging circuit 25, where the average value of all LPRM signals d (APRM signal) is
g is calculated, and this APRM signal Q is input to the gain adjustment circuit 24 and the pull-out prevention level setting circuit 26.

Therefore, the gain adjustment circuit 24 compares the local average value signal f input from the averaging circuit 23 with the APRM signal Q signal.
The gain of the averaging circuit 23 is adjusted until the local average value signal f becomes larger than the APRM signal q.

On the other hand, the pull iH[1 stop bell setting circuit 26 inputs the recirculation pump flow rate signal to the APRM signal Q signal ratio, and based on these signals a and h, the control rod withdrawal prevention level A is set as a function of these signals. be done.

This control rod withdrawal prevention level A is input to the determination circuit 27, where the local average value signal i adjusted by the gain adjustment circuit 24 is compared with the control rod withdrawal prevention level A, and the local average value signal i When exceeds the control rod withdrawal prevention level A, the determination circuit 27 outputs a control rod withdrawal prevention signal j, whereby the reactor output is always suppressed below the control rod withdrawal prevention level A.

Here, in the pull-out prevention level setting circuit 26, the control t[I
II withdrawal prevention level A is set as a function of average core power (APRM power) and recirculation pump flow rate by the following equation.

A=aw+bp+c... (1) However, A: Control rod retraction fill level: Recirculation pump flow rate 1): APRM output a, b, c: constants Indicate by inserting specific numbers into the above formula (1) and becomes as follows.

(Case 1) a=0.11. b=0.8. Let c=16. At this time, the relationship among the recirculation pump flow 1w, the ARPM output p, and the control rod withdrawal prevention level A is as shown in the following table.

(Case 2) a=0.22. b=0.6. c=25 and η. At this time, the relationship among the recirculation pump flow rate w, the ARPM output p, and the control rod pull 1 inhibition level A is as shown in the following table.

(Case 3) a=Q, 33. b=0.4. c=34. At this time, the relationship among the recirculation pump flow rate w, the ARPM output p, and the control rod withdrawal prevention level A is as shown in the following table.

As described above, even if the recirculation pump flow 1w is constant, when the reactor output is low, the control rod withdrawal prevention level A becomes low, and the control rods are withdrawn earlier than before.

By setting constants a, b, and c appropriately, it is possible to adjust the dependence of the control rod withdrawal prevention level A on the recirculation pump flow rate W and reactor power, and to adjust the control rod withdrawal appropriate for the situation. 172 inhibition level A can be set.

Further, in the configuration shown in FIG. 2, the control rod withdrawal prevention level A may be set as the smaller value of the following Al and A2.

A1=aw+bp+c・(2>A2=xw+y...(3) However, x, y
: Constant, for example, 50, as at the beginning of the control rod withdrawal operation.
% or less, if the control rod withdrawal prevention level A is set as a function of only the core average power, it will take too much time to generate the control rod withdrawal prevention level. On the other hand, at such low output, there is no problem even if the control rod withdrawal prevention level is set as a function only of the recirculation pump flow rate.

Therefore, At obtained from the above formulas (2) and <3>.

The smaller value of A2 is always set as the control rod withdrawal/closing level A.
By doing so, A2, which is a function only of the recirculation pump flow rate, becomes the control rod withdrawal prevention level A at low output such as at the beginning of the control rod withdrawal operation, and as the output increases, the APRM output and the recirculation pump flow rate change. The function A1 becomes the control rod withdrawal prevention level A.

Note that a certain output level α is determined in advance, and when the output level is below α, A2 in equation (3) is set as the control rod withdrawal prevention level A, and when the output level exceeds α, (2)
AI based on the formula may be used as a stop bell A for erroneous control rod removal.

Furthermore, in the configuration shown in FIG. 2, the control rod withdrawal prevention level A may be set as the smaller value of the following A+ and A2.

A1-bp+c...(4) A2=XW+V...(5) In this way, A1, A obtained from the above formulas (4) and (5)
By always setting the smaller value of 2 as the control rod withdrawal prevention level A, A2, which is a function only of the recirculation pump flow rate, becomes the control rod withdrawal prevention level A at low output such as at the beginning of the control rod withdrawal operation. As the output increases, Ar, which is a function only of the APRM output, becomes the control rod withdrawal prevention level A, and even at a low output level such as at the beginning of the control rod withdrawal operation, it takes time until the control rod withdrawal prevention level occurs. It is possible to solve the problem of taking too much time.

Next, a second embodiment of the present invention will be explained.

The control rod withdrawal monitoring device 31 of this embodiment has the configuration shown in FIG. 2, and the withdrawal prevention level setting circuit 36 sets the Mill rod withdrawal prevention level as a function of only the APRM output using the following equation.

A=bD+C...(6) In this case, regardless of the recirculation pump flow rate, when the reactor power is low, the control rod withdrawal prevention level A will be low, and the control rods will be withdrawn faster than before. It turns out.

Next, FIG. 3 shows a third embodiment of the present invention, in which a control rod withdrawal monitoring device 41 sets the generator output signal k of the nuclear power plant as a signal related to the core output to a withdrawal prevention level. The signal k is input to a circuit 46, and the circuit 46 sets a control rod withdrawal prevention level A as a function of the generator output based on this signal k.

Even in this case, when the reactor power is low, the control rod withdrawal prevention level A becomes low, and the control rods are withdrawn faster than before.

[Effects of the Invention] As described above, according to the present invention, even if a control rod is erroneously pulled out during low power operation of the reactor, the rate of increase in the reactor power at the time of the pullout can be suppressed to a small level. , it is possible to easily maintain the health of the fuel by reducing the thermal influence on the fuel.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the first embodiment of the present invention, FIG. 2 is a schematic diagram showing the second embodiment of the invention, and FIG. 3 is a schematic diagram showing the third embodiment of the invention. , FIG. 4 is a schematic configuration diagram showing a conventional example. 21.31.41...Control rod withdrawal monitoring device, 221.
...Neutron detector selection circuit, 23...Averaging circuit, 2
4...gain adjustment circuit, 26.36. ．． 46... Pull-out prevention level setting circuit, 27... Judgment circuit, A...
Control rod withdrawal prevention level, 0... APRM signal, h...
・Recirculation pump flow rate signal, i...Local average value signal, j
...Control rod withdrawal prevention signal. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (7)

[Claims] (1) Multiple fixed types that detect in-core neutron output/Input detection signals from neutron detectors and detect signals from multiple in-core neutron detectors installed around extracted control rods based on control rod selection signals. a neutron detector selection circuit that selects a detection signal; an averaging circuit that calculates the average value of a plurality of signals output from the neutron detector selection circuit; Compare the output of the control rod withdrawal prevention level with the control rod withdrawal prevention level setting circuit and the output of the averaging circuit to determine whether the output of the averaging circuit exceeds the control rod withdrawal prevention level. What is claimed is: 1. A method of viewing a control rod, comprising: a determination circuit that outputs a control rod withdrawal prevention signal. (2) The control according to claim 1, wherein the control rod usage prevention level set by the withdrawal prevention level setting circuit increases in accordance with an increase in the recirculation pump flow rate (ζ). Rod withdrawal monitoring device. (3) The control rod withdrawal prevention level A is A=aw+bp
+c However, W: recirculation pump flow rate p: core average power a, b, c: set as constants Claim 1
Control rod withdrawal monitoring device described in Section 1. (4) The control rod withdrawal prevention level A is A1=aw+b
p+c A2 = xw+y where W: recirculation pump flow rate p: average core power output a, b, c, x, y: set as the smaller value of constants. Control rod withdrawal monitoring device described in Section 1. (5) The control rod withdrawal prevention level A is A, = b
p 10c, where p: core average power, c: constant, etc.
Control rod withdrawal monitoring device described in Section 2. (6) The control rod withdrawal prevention level A is A1=bp+-
c A2=xw-+-y where W: recirculation pump flow rate p: average core power output, c, x, y: set as the smaller value of constants. Control rod withdrawal monitoring device according to item 1. (7) The control rod withdrawal monitoring device according to claim 1, wherein a generator output signal of a nuclear power plant is used as the signal related to the core output.