JPH05346488A - Reactor startup region monitor - Google Patents

Abstract

PURPOSE:To make possible ensuring on operable state of a standby SRNM detector by monitoring the output of startup region neutron (SRNM) detector in power operation on the basis of normal characteristics with using a detector diagnosis device. CONSTITUTION:The output of an SRNM detector 1 is measured with a startup region measurement device 2 for the output pulse generation rate, square mean of alternating current output and direct current value. An irradiation dose evaluation device 4 measures the output of a local output monitor system (LPRM) detector 6 placed at a symmetrical position to the detector 1 across the center of a core 8 with an output region measurement device 7 and using the value, evaluates the irradiated neutron flux to the detector 1. By measuring the detector 1 output vs. irradiated neutron flux and storing it in a characteristic storage device 5, or calculating normal time output in real time with the device 5, small variation is judged with a detector diagnostic device 3. That is, the device 3 obtains the detector 1 output in normal time from the device 5 and compares it with the present value to judge whether any abnormality exists.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor start-up area monitoring device for measuring and monitoring a wide range of neutron flux or γ-ray flux in a reactor pressure vessel of a boiling water reactor (hereinafter referred to as BWR). ..

[0002]

2. Description of the Related Art In general, a neutron flux or a γ-ray flux in a reactor pressure vessel has a wide measurement range (for example, an 11-digit measurement range in BWR), and it is technically possible to measure with one measurement means. Have difficulty. Therefore, conventionally, measurement is performed by combining three measuring means.

The first measuring means relates to the low neutron flux range (neutron source region). In this region, since the reactor output is proportional to the number of output pulses of the detector, the low range 6 digits are measured by the pulse counting method. To do.

The second measuring means relates to an intermediate neutron flux range (intermediate region), and in this region, the reactor power is measured by focusing on the fact that it is proportional to the root mean square value of the fluctuation components of the detector output signal. It is called Campbell method or MSV method.

The third measuring means relates to the high neutron flux range (output region), and in this region, the direct current of the detector is measured by paying attention to the fact that the reactor output is proportional to the direct current component of the detector output signal. To do.

Conventionally, different detectors are used for these measuring methods. That is, the first measuring means has 4 to 6 neutron source region neutron detectors (SRM detectors), and the second measuring means has 6 to 8 intermediate region neutron detectors (IRM detectors). In the third measurement method, 100 to 200 neutron detectors for local power range (LPRM detectors) arranged in the core are used.

In the reactor neutron instrumentation monitoring device thus constructed, the SRM detector is inserted into the reactor at the time of startup of the reactor, its output is monitored, and the reactor output rises.
If the measurement range of the RM detector is about to be exceeded, then the IRM
The detector is inserted in the furnace instead of the SRM detector and its output is monitored. When the output further rises and the reactor reaches 100% of its rated operation, the LPR fixed inside the reactor
The neutron flux is monitored by the output of the M detector.

Since the reactor will continue to operate at 100% for several months,
The neutron flux of a normal reactor core is monitored by this LPRM detector and its measuring device, but 100 to 200 of this LPRM detectors are arranged in the core, and some abnormalities in the core can be found instantly. It is configured to do.

The neutron instrumentation system configured as described above has been improved recently, and a start-up area monitor has been developed which is configured to continuously measure neutron levels in a neutron source area and an intermediate area.

In this start-up area monitor, the output signals of 6 to 8 start-up area neutron detectors (hereinafter referred to as SRNM detectors) fixed in the reactor are measured by a first measurement method (hereinafter referred to as a pulse measurement method). Note) and the second measurement method (hereinafter referred to as Campbell measurement method) depending on the level of the neutron flux so that the neutron flux in the neutron source region and the intermediate region can be continuously monitored.

[0011]

However, since the SRNM detector used for this is fixed in the reactor, the neutron flux level becomes the output region and high neutron flux is maintained during 100% rated operation for several months. Is irradiated. Moreover, when the neutron flux drops sharply, such as when the reactor scrums, and the neutron flux level shifts to the start-up region, the neutron flux must always be in a measurable state so that it can be monitored. ..

Thus, the SRNM detector during output operation is always in a measurable state, but the neutron flux is high, the output current is large, and the detector is used to protect the power supply and prevent disconnection of cables and the like. The output current is limited by lowering the voltage applied to the voltage below the level at which it normally operates.

In the region where the current is limited, the state of the detector can be always confirmed by monitoring the lowered applied voltage to the detector. However, with this voltage monitoring alone, the irradiation neutron flux is different for each detector and the output is in a saturated state, so there is a problem that early detection of minute abnormal signs is difficult.

The present invention has been made in order to solve the above-mentioned problems, and the SRNM detector in the standby state is in operation during the rated operation for several months when the reactor output shifts to the output region and the SRNM detector is in the standby state. It is an object of the present invention to provide a reactor start-up area monitoring device capable of quantitatively confirming that is in an operable state, and capable of detecting an abnormal sign of a detector at an early stage.

[0015]

SUMMARY OF THE INVENTION The present invention is a start-up area detector for measuring neutron flux or γ-ray flux in the start-up area of a nuclear reactor, a start-up area measuring device for processing an output signal of the detector, and the detector. Irradiation dose evaluation device to evaluate the neutron flux or γ-ray flux at the installation position of, the relationship between the irradiation neutron flux or γ-ray flux of the detector and the output of the detector connected to the irradiation amount evaluation device and the activation area measurement device Calculate
A characteristic storage device for storing the information, and a detector diagnostic device connected to the characteristic storage device and the dose evaluation device for diagnosing the soundness of the detector are provided.

[0016]

The output signal of the SRNM detector is measured by the activation area measuring device. SR evaluated by the dose evaluation device
With respect to the neutron flux or the γ-ray flux at the installation position of the NM detector, the output characteristic of the SRNM detector at the normal time is calculated by the characteristic storage device. The output of the SRNM detector during the reactor power operation is monitored by the detector diagnostic device on the basis of the normal characteristic obtained from the characteristic storage device to detect an early abnormality of the SRNM detector.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a reactor starting area monitoring apparatus according to the present invention will be described with reference to FIGS.

In FIG. 1, reference numeral 1 is an SRNM detector,
The output side of the SRNM detector 1 is connected to the activation area measuring device 2. Reference numeral 3 is a detector diagnostic device, and the detector diagnostic device 3 is connected to the activation area measuring device 2 and the characteristic storage device 5. The characteristic storage device 5 is connected to the activation area measuring device 2, the dose evaluation device 4 and the detector diagnostic device 3.

FIG. 2 (a) shows a state in which the apparatus having the configuration shown in FIG. 1 is connected to the SRNM detector 1 and the LPRM detector 6 in the reactor core 8, and FIG. 2 (b) is shown in FIG. The arrangement state of each said detector 1,6 installed in the reactor core 8 of (a) is shown.

In the reactor start-up area monitoring apparatus configured as described above, the output of the SRNM detector 1 is the output pulse generation rate (counting rate), the mean square value of the AC output (Campbell output), and the DC current value. Is measured by the activation area measuring device 2.

As shown in FIG. 2 (b), for example, the dose evaluation device 4 includes a local power monitor system detector 6 provided at a position symmetrical to the SRNM detector 1 with respect to the center of the reactor core 8.
The output (hereinafter referred to as a symmetric LPRM detector) is measured by the output area measuring device 7, and the SRNM detector 1 is measured from the measured value.
Evaluate the neutron flux irradiated to.

This is because the nuclear reactor is operated so that the neutron distribution in the nuclear reactor core 8 is symmetrical with respect to the center of the nuclear reactor core 8, so the axial position is the axial position of the SRNM detector 1. Is almost equal to, and the output of the symmetrical LPRM detector 6 arranged at the position of rotational symmetry or point symmetry with respect to the core center in the radial direction of the reactor core 8 is approximately proportional to the irradiation neutron flux of the SRNM detector 1. I use what I think to be.

FIG. 3 (a) shows the output current value of the SRNM detector 1 with respect to the irradiation neutron flux measured at the time of starting or shutting down the reactor. The output current of the SRNM detector 1 is proportional to the irradiation neutron flux (that is, the indicated value of the symmetrical LPRM detector 6) in the measurement range of the SRNM detector 1 (FIG. 3).
(A) Middle, proportional region).

When the reactor output rises and the irradiation neutron flux increases, the output current of the SRNM detector 1 saturates and is no longer proportional (saturation region in FIG. 3 (a)). When the irradiation neutron flux further increases, the voltage applied to the detector is reduced to limit the output current to a certain constant value in order to protect the power source of the detector and the measurement device as described above.

FIG. 3 (b) shows changes in the applied voltage to the detector with respect to the symmetric LPRM indication value. Normally, when the reactor is operating at about 100% power, SR as shown in Fig. 3 (b)
The applied voltage of the NM detector is lower than the operating voltage of the detector.

Such an output characteristic is different from the normal characteristic when the SRNM detector is normal, but when an abnormality occurs in the detector such as when the insulation resistance of the detector is lowered. Becomes

The SRNM detector 1 comprises an anode 11, a cathode 13 and an insulating material 12, as shown in FIG. A voltage is applied to the anode 11 and the cathode 13 by the power supply 15, and the anode 11
A charge proportional to the neutron flux generated between the cathode 13 and the cathode 13 is collected. The current Is flowing by this charge collection is measured by a pulse measuring method when the irradiation neutron flux level is low, and by a Campbell measuring method when the neutron flux level is high.
Measure with.

FIG. 5 shows changes in the output current when the insulation resistance of the SRNM detector is lowered. In the figure, i _l is the leakage current i _s is the neutron current. Since these measurements are not performed accurately in the output region, the soundness of the detector is confirmed by measuring the direct current, but this measured current passes through the current ls due to neutrons and the insulating material 12. It is a total current ld (ld = ls + ll) together with the flowing leakage current ll.

One possible cause of the abnormality of the SRNM detector 1 which is placed in a high neutron flux field for a long time is an increase in leakage current due to the deterioration of the insulation resistance. In this case, the leakage current ll is added to the output current ls, and it can be measured as an increase in the measured current. However, when the output is high, the leakage current is smaller than the output current, and it is difficult to determine the leakage current by the output fluctuation of the reactor.

However, in the reactor start-up area monitoring apparatus according to the present embodiment, the output of the SRNM detector 1 with respect to the irradiation neutron flux for each of the detectors inserted in the reactor at the time of starting or shutting down the reactor. Is detected and stored in the characteristic storage device 5 in advance, or the output of the normal state is calculated in real time by the characteristic storage device 5, and the detector diagnostic device 3 determines this slight variation. You can

That is, in the detector diagnostic device 3, based on the irradiation neutron flux of the SRNM detector 1 at that time, that is, the irradiation neutron flux obtained from the indicated value of the symmetrical LPRM detector 6 from the irradiation amount evaluation device 4, The normal output of the SRNM detector 1 for the irradiated neutron flux is acquired from the characteristic storage device 5 and compared with the current output of the SRNM detector 1 to determine whether there is any abnormality.

FIG. 6 shows changes in the output current (a), changes in the applied voltage to the detector (b), and Campbell output with respect to the indicated value of the symmetrical LPRM detector when the detector is normal and when the insulation is degraded and abnormal. The changes (c) are shown respectively.

As shown in FIG. 5, the measured current increases as the insulation resistance decreases, but as shown in FIG. 6 (a), the current is limited by the current limiter at 100% reactor output for circuit protection. This increase in current cannot be detected. Instead, when the insulation resistance decreases, the current limiter decreases the applied voltage by the increase in the current as shown in FIG. 6B.

In other words, this decrease detects an abnormality in the detector due to a decrease in insulation resistance. At the same time, the characteristics of the Campbell output change in the abnormal state due to the decrease of the insulation resistance as shown in FIG. 6C as compared with the normal state. Therefore, the change can be measured in the abnormal state like the change of the applied voltage.

As described above, according to the reactor start-up area monitoring apparatus according to the present embodiment, the detector output characteristics under normal conditions with respect to the irradiated neutron flux at the time of reactor startup or shutdown are measured and stored. By doing so, the soundness of the SRNM detector can be quantitatively confirmed even at the rated output of the reactor in which the SRNM detector is in the standby state, that is, 100% output, and the sign of abnormality can be detected early.

That is, since the operating state of the reactor can be confirmed before the reactor enters the shutdown operation and the neutron flux falls within the measurement range of the SRNM detector, it is not necessary to perform recovery work or the like during the shutdown operation, and reliability is improved. Will be further improved.

Next, another embodiment of the present invention will be described with reference to FIG. The present embodiment is different from the embodiment of FIG. 1 in that a core performance calculation device 9 is connected to the dose evaluation device 4, and a characteristic restoration device 10 is connected to the starting region measurement device 2 and the detector diagnostic device 3. is there. Since the other parts are the same as those in FIG. 1, description of the overlapping parts will be omitted.

In this embodiment, the irradiation performance neutron flux of the SRNM detector 1 during the rated operation of the nuclear reactor is calculated by the core performance calculation device 9. The core performance calculation device 9
The neutron flux distribution of the reactor can be calculated from various characteristics such as the burnup of the fuel, the reactor pressure, and the heat output. From the calculation result, the irradiation neutron flux of the SRNM detector 1 is calculated in the dose evaluation device 4.

Further, when an abnormal sign of the SRNM detector is detected during the operation of the reactor, the SRNM detector is in a standby state, and the characteristic restoration device 10 selects an appropriate restoration work based on the diagnosis result and the restoration is performed. Carry out the work.

In particular, when the insulation resistance is lowered, for example, when a protrusion is formed on the electrode surface and the resistance is lowered, the voltage applied to the detector is increased to generate a small discharge between the electrodes to eliminate the protrusion. Restores resistance. Since such a recovery work can be automatically performed in this embodiment, a system with higher reliability and simple maintenance work can be realized.

The present invention can take the following embodiments. (1) Neutron flux or γ-ray flux at the installation position of the starting area detector is evaluated by the output of the detector for output area arranged at the detector in a point symmetric or 90 degree rotational symmetry position with respect to the reactor center. Equipped with an output evaluation device. (2) An output device for evaluating the neutron flux or γ-ray flux at the position of the start-up area detector from the reactor performance calculation shall be provided. (3) Provide a recovery device that restores the detector to its normal characteristics when an abnormality is detected by the detector diagnostic device.

[0042]

According to the present invention, the soundness of the SRNM detector can be quantitatively evaluated at the rated output of the reactor in which the SRNM detector is in the standby state, that is, 100% output, and the output of the reactor can be quantitatively evaluated. It can be confirmed that an accurate measurement can be performed when the value falls within the measurement range of the SRNM detector.

Further, since abnormal signs of the SRNM detector can be detected at an early stage, and the diagnostic function can formulate countermeasures and automatically perform restoration work, the SRNM detector can always be kept in a healthy state. It is possible to provide a reactor start-up area monitoring device that is reliable, has high reliability, and is easy to maintain.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a reactor starting area monitoring apparatus according to the present invention.

2 (a) is a system diagram showing a state in which the apparatus in FIG. 1 is connected to a detector in a nuclear reactor core, and FIG. 2 (b) is a schematic diagram showing the arrangement state of detectors in a nuclear reactor core in FIG. 2 (a). FIG.

3 (a) is a characteristic diagram showing changes in detector output current with respect to irradiation neutron flux of the SRNM detector in FIG. 1,
FIG. 7B is a characteristic diagram showing a change in the detector applied voltage in FIG.

FIG. 4 is a vertical sectional view schematically showing the structure of the SRNM detector in FIG.

5 is a curve diagram showing a change in output current when the insulation resistance of the SRNM detector in FIG. 1 is lowered.

6 (a) is a characteristic diagram showing changes in detector output current with respect to irradiation neutron flux of the SRNM detector in FIG. 1,
(B) is a characteristic diagram showing a change in detector applied voltage,
FIG. 6C is a characteristic diagram similarly showing a change in detector Campbell output.

FIG. 7 is a block diagram showing another embodiment of the reactor starting area monitoring apparatus according to the present invention.

[Explanation of symbols]

1 ... SRNM detector, 2 ... starting area measuring device, 3 ... detector diagnostic device, 4 ... dose evaluation device, 5 ... characteristic storage device,
6 ... Symmetric LPRM detector, 7 ... Output area measuring device, 8 ...
Reactor core, 9 ... Core performance calculation device, 10 ... Characteristic restoration device, 11 ... Anode, 12 ... Insulation material, 13 ... Cathode, 14 ... Measuring device,
15 ... power.

Claims (1)

[Claims] 1. A start-up area detector for measuring neutron flux or γ-ray flux in a start-up area of a nuclear reactor, a start-up area measuring device for processing an output signal of the detector, and a neutron flux at an installation position of the detector or A dose evaluation device for evaluating a γ-ray flux, and a characteristic memory which is connected to the dose evaluation device and the activation region measurement device to calculate and store the relationship between the irradiation neutron flux of the detector or the γ-ray flux and the output of the detector. A device,
A reactor start-up area monitoring device comprising: the characteristic storage device; and a detector diagnostic device that is connected to the dose evaluation device and diagnoses the soundness of the detector.