JP2003057382A - Testing device of existence of cable disconnection and test method of existence of cable disconnection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a testing device of existence of cable disconnection and a test method of existence of the cable disconnection capable of testing with high reliability on a neutron detector and a test of existence of the cable disconnection. SOLUTION: In this device for monitoring the output of a nuclear reactor by installing the neutron detector 31 in the reactor core 1 and measuring neutrons, characteristic deterioration or the like of the neutron detector 31 is inspected periodically, and the connection state of a connection line positioned in the nuclear reactor of the neutron detector 31 is confirmed. In the confirmation, γ rays are detected by the neutron detector 31, and the detection signal is amplified by a γ ray signal amplifier 7, and it is determined whether a plateau characteristic exists or a resistance characteristic exists from the signal by a cable connection determination circuit 8, to thereby determine existence of the disconnection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable disconnection presence / absence test device and a cable disconnection presence / absence test method effective for monitoring reactor power output.

[0002]

2. Description of the Related Art In a nuclear power plant, a large number of neutron detectors are arranged in order to obtain a stable and uniform reactor output, and the operating state of the reactor is monitored and controlled. That is, in the 1.1 million class BWR type reactor core,
About 200 neutron detectors are arranged to monitor and control to obtain a uniform neutron flux distribution.

In this monitoring system, as shown in FIG. 11, the output of each neutron detector 31 is wired by a cable 32, and the neutron output is installed in the control room in the radiation nonexistence region outside the nuclear reactor. It is connected to the measuring circuit 33. The neutron output measurement circuit 33 outputs the detection signal of the neutron detector 31. The cable 32 is connected to the cable 35 and the cable 36 by the connector 34 at the exit position of the nuclear reactor. This is because the temperature inside the reactor is as high as about 300 ° C., so that the connector 34 and the neutron detector 31 are connected by a special heat resistant coaxial cable (MI cable) output cable 35. . That is, the output cable 35 located in the reactor containment vessel of the neutron detector 31 is heat-resistant. A coaxial cable 36 for normal temperature is connected to the neutron measuring device 33 side cable from the connector 34.

However, the characteristics of each of the neutron detectors 31 and the output cable 35 are deteriorated due to the cumulative irradiation amount of radiation, causing disconnection, connection failure, and the like. For this reason, about 200 neutron detectors 31, in order to obtain stable reactor output, the neutron detectors 31 and peripheral circuits are checked for soundness at a frequency of about once a month for a long time. It is being carried out. This confirmation test is performed as shown in FIG.
A neutron detector tester 37 is connected to each coaxial cable 36 for zero neutron detectors 31.

As the confirmation test item, a plateau characteristic, a breakdown voltage (VBD), a state of connection of the neutron detector and a cable, and the like are tested. Plateau characteristic, VB
D is tested by the neutron detector tester 37, and the connection state of each neutron detector 31 and each cable 35, 36 is tested by connecting a tester for presence or absence of breakage of a dedicated cable, respectively.

All the tests for the presence or absence of disconnection are carried out one by one during a periodic inspection during which the operation of the nuclear reactor is stopped.

[0007]

However, at the time of periodic inspection of the reactor, it is necessary to temporarily lift the connection of the connector 34 in order to confirm the soundness of the output cable 35 alone and to carry out auxiliary work of the reactor body. . The connector 34 is reconnected after the completion of the operation of the reactor main body, but the connection state of the connector 34 was confirmed only by visual inspection and appearance check, and it could not be confirmed whether or not it was completely electrically connected. Therefore, when the neutron signal is abnormal after the reactor is started, it is not possible to determine whether the neutron detector 31 is abnormal or the connection portion of the connector 34 is abnormal.

Further, the operator lifts the connector 34 lifted during the periodic inspection of the nuclear reactor, but the operator confirms the restoration only by the operator's judgment and visual inspection.
There are many cases, poor workability, and the possibility that external force may be applied after restoration. In some cases, the connection may be incomplete and electrical confirmation technology was required.

Further, in the test using the tester dedicated to the presence / absence of cable breakage, if a breakage or a defect occurs in the connection between each neutron detector 31 and each cable 35, the leak current increases in proportion to the increase in voltage, and It was difficult to judge good or bad. Further, in this test method, when a disconnection or a defective portion occurs, a reflection signal is generated from the location, and the disconnection position is determined by the reception time of the reflection signal. In this test method, there are reflections due to changes in the characteristic impedance of the signal transmission system in addition to disconnection and defective points.Therefore, if a reflected signal is received, it will be judged as disconnection, and after maintenance, disconnection may not occur, so the test There was a problem with the method.

As a result of detailed examination of this problem, it was found that this erroneous determination was made even if the cable 35 was not broken.
It was found that when there is a bent portion, a reflected signal is generated from the bent portion, which is indistinguishable from the reflected signal at the time of disconnection, and an erroneous determination is made. As described above, the neutron detector 31
With respect to the test of whether the cable 35 and the cable 35 are connected without any problem, it is required to develop a highly reliable test.

The present invention has been made to solve the above-mentioned conventional problems, and a cable disconnection presence / absence test device and a cable disconnection presence / absence test capable of performing a highly reliable test for a disconnection presence / absence of a neutron detector and a cable. The purpose is to provide a method.

[0012]

SUMMARY OF THE INVENTION The present invention provides a neutron detector for monitoring the output of a reactor, which has an order of magnitude lower sensitivity than the neutron detection sensitivity during reactor operation with respect to gamma rays when the reactor is shut down. That the neutron detector detects γ-rays, the voltage to the neutron detector shows a saturation characteristic (plateau characteristic), and the voltage of the neutron detector at the time of disconnection
The current characteristics are based on such features that the leak current increases as the applied voltage rises.

The present invention is to detect γ-rays while the reactor is out of operation by a neutron detector and to test for the presence or absence of disconnection. The disconnection test is to confirm the connection state of the connection line (cable, connector) located inside the reactor of the neutron detector.

In order to achieve the above object, the present invention provides a neutron detector test apparatus, a neutron detector test method, and a reactor output measuring apparatus having the following configurations.

That is, the cable disconnection presence / absence testing device according to claim 1 is a cable disconnection presence / absence testing device for testing the output cable disconnection of a neutron detector installed in a nuclear reactor, wherein the neutron detector detects A γ-ray detection signal amplifier connected to the output cable for amplifying the γ-ray detection signal, and a disconnection presence / absence determining means for determining that there is no disconnection when the γ-ray detection signal amplifier outputs the γ-ray detection signal. It is characterized by comprising.

A cable disconnection presence / absence testing device according to claim 2 is a cable disconnection presence / absence testing device for testing the presence / absence of a disconnection of an output cable of a neutron detector installed in a nuclear reactor. A neutron measurement device for measuring, a presence or absence test device for testing the presence or absence of a disconnection of the output cable of the neutron detector, a selection circuit for selecting and switching the neutron measurement device and the presence or absence test device for the disconnection, When the γ-ray detection signal amplifier connected to the disconnection presence / absence testing device and the selection circuit select the disconnection presence / absence testing device and the γ-ray detection signal amplifier outputs a γ-ray detection signal, it is determined that there is no disconnection. A disconnection presence / absence determining means is provided.

According to the first and second aspects of the present invention, it is possible to perform a highly reliable test for the presence or absence of disconnection of the output cable of the neutron detector.

A cable disconnection presence / absence test device according to claim 3 is the cable disconnection presence / absence test device according to claim 1 or 2, wherein the neutron detection means that the γ-ray detection signal amplifier outputs a γ-ray detection signal. It is characterized in that there is a plateau characteristic in the output current waveform of the γ-ray detection signal amplifier by sequentially changing the voltage applied to the container to a high voltage.

According to the third aspect of the present invention, it is possible to determine whether or not the neutron detector is disconnected from the cable based on the presence or absence of the plateau characteristic, so that a highly reliable test can be performed.

According to a fourth aspect of the present invention, there is provided a cable breakage presence / absence test device, comprising:
The voltage applied to the neutron detector is a ramp-shaped DC voltage.

According to the invention of claim 4, it is possible to determine whether or not the output cable of the neutron detector is broken, so that a highly reliable test can be performed.

A cable disconnection presence / absence testing device according to claim 5 is the cable disconnection presence / absence testing device according to claim 1, 2 or 3, wherein the signal current input to the γ-ray detection signal amplifier is a current of the order of μA. It is characterized by

According to the invention of claim 5, the γ-ray detection sensitivity is incomparable to that of the neutron detection sensitivity, so that a highly reliable test can be performed for determining whether or not the output cable of the neutron detector is broken.

According to a sixth aspect of the present invention, there is provided a test method for presence / absence of cable breakage, which is a test method for testing the presence / absence of breakage of a cable connecting a neutron detector and a neutron measurement circuit connected to the neutron detector. Γ-ray detection step of detecting γ-rays by
And a judgment step of judging that there is no disconnection when a line is detected.

According to the sixth aspect of the present invention, it is possible to detect the presence or absence of disconnection of the cable with high reliability because it is determined that there is no disconnection when γ-rays with relatively low sensitivity are detected.
In particular, it is suitable to be used for a reactor power control system that requires reliability.

In the method for testing the presence / absence of a cable breakage according to claim 7, the neutron detector of a neutron measuring system for detecting neutrons by a neutron detector and measuring the amount of neutrons produced by a neutron measuring device is connected to the neutron measuring device. In the test method for testing the presence or absence of a cable disconnection, the neutron detector detects the γ-ray detection signal detected by switching to the γ-ray detection signal amplifier and amplifying, and the DC voltage applied to the neutron detector in order. It is characterized by comprising a determination step of determining a normal connection when a plateau waveform exists in the current waveform output by the γ-ray detection signal amplifier by changing to a high voltage.

According to the seventh aspect of the present invention, the presence or absence of a break in the output cable of the neutron detector can be determined by the presence or absence of a plateau waveform, so a highly reliable test can be performed.

The cable subjected to the disconnection test is the output circuit of the neutron detector from the output terminal of the neutron detector to the input circuit of the γ-ray detection signal amplifier, and the circuit components such as connectors and switches connected to this circuit. It also includes connected circuits. The ramp-like voltage is to gradually change to a high voltage.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a cable break presence / absence test device and a cable break presence / absence test method according to the present invention will be described with reference to FIG. The same parts as those in FIGS. 8 and 9 are designated by the same reference numerals, and detailed description thereof will be omitted. Figure 1
FIG. 3 is a system configuration diagram showing a neutron detection system 2 for one neutron detector 31 out of about 200 neutron detectors 31 arranged in the reactor 1 for monitoring the output of the reactor. Therefore, since the other neutron detection system 2 has the same configuration, the description thereof will be omitted.

Since the neutron detection system 2 is a sensor (neutron detector 31) that mainly detects neutrons, the amount of neutrons detected during the operation of the reactor is on the order of mA, and when the operation of the reactor is stopped. The amount of γ-rays detected is on the order of μA. The neutron detection system 2 is a circuit in which an output cable 35, a connector 34, a coaxial cable 36, a neutron measuring device 33 and the like are connected in series to a neutron detector 31. The neutron measuring device 33 converts the reactor output into a neutron amount,
It is a device for monitoring the operating state of a nuclear reactor.

The output of the neutron detector 31 is further connected to a neutron detector tester 37 and a cable break presence / absence testing device 3 for measuring changes in the detection characteristics of the neutron detector 31 and related circuits. . The neutron detector tester 37 and the cable breakage presence / absence testing device 3 are connected so that the output of the neutron detector 31 can be switched by the selection circuit 4 and used. The selection circuit 4 selects the tester 37 of the neutron detector when the reactor is operating, and selects the cable disconnection presence / absence testing device 3 when the reactor is stopped.

The neutron detector tester 37 is connected with a neutron signal amplifier 5 for amplifying the output signal of the neutron detector 31 of the mA order, and the neutron plateau characteristic measuring circuit 6 is connected to the output circuit of the neutron signal amplifier 5. Is configured. The neutron detector tester 37 supplies the neutron signal amplified by the neutron signal amplifier 5 to the neutron plateau characteristic measuring circuit 6 to measure the plateau characteristic, breakdown voltage (VBD), etc., and the soundness of the neutron detector 31. To confirm. The neutron signal amplifier 5 is a circuit that amplifies a neutron signal of the mA order output by the neutron detector 31 during the operation of the reactor.

The cable breakage presence / absence test device 3 electrically tests the connection state of the output cable 35 and the connector 34 of the neutron detector 31 to confirm the presence / absence of a wire breakage. That is, the disconnection presence / absence test is to confirm the connection state of the connection point of the neutron detector 31 with the output cable 35 located in the reactor containment vessel.

The connection state of the output cable 35, the connector 34, and the coaxial cable 36 of the neutron detector 31 is such that the neutron detector 31 detects the γ-dose generated in the reactor,
The presence or absence of disconnection is confirmed from the characteristics of this detection signal. The configuration of the cable disconnection presence / absence testing device 3 is the neutron detector 31.
A γ-ray signal amplifier 7 and a cable connection determination circuit 8 are connected in series to the output via the selection circuit 4. The γ-ray detection current detected by the neutron detector 31 is a γ-ray dose while the reactor is not in operation, and is a detection amount of, for example, μA at a minute current. The γ-ray signal amplifier 7 is a circuit that amplifies a γ-ray detection signal current on the order of μA.

The cable connection determination circuit 8 confirms the connection state of the cable 35 and the connector 34 from the waveform of the output signal of the γ-ray signal amplifier 7. The waveform for confirming the connection state of the output cable 35 is the same as the current characteristic curve shown in FIG. 2 when the DC voltage applied between the electrodes of the neutron detector 31 is sequentially increased to a high voltage (ramp DC voltage). -It is judged whether or not it has the characteristic P. The presence of the plate-characteristic P indicates a normal connection state, and the absence of the plate-characteristic P indicates a disconnection state.

In FIG. 2, curve-a is a waveform in a normal connection state without disconnection. That is, the detected value of the γ dose detected by the neutron detector 31 is output to the output of the γ-ray signal amplifier 7. This characteristic curve flows between the electrodes 10 and 12 when the DC voltage 13 applied between the electrodes 10 and 12 of the neutron detector 31 shown in FIG. 3 is sequentially changed to a high voltage (when ramped DC voltage is used). It is the figure which plotted the electric current value, and shows a saturation characteristic (plateau characteristic) when the amount of γ-rays is increased during the initial period.

The curve-b is the output cable 35 and the connector 3
4 is a waveform when there is a circuit break in any of the coaxial cables 36. When the DC voltage applied between the electrodes 10 and 12 of the neutron detector 31 is gradually changed to a high voltage (ramp DC voltage), the leak characteristic increases proportionally. That is, the neutron detector 31
Since the circuit between the γ-ray signal amplifier 7 and the γ-ray signal amplifier 7 is disconnected, a leak current flowing in the input circuit of the γ-ray signal amplifier 7 is output. In this way, the presence or absence of disconnection can be determined from the detected current waveform of γ-ray. The disconnection refers to the case where the cable 35 and the coaxial cable 36 are disconnected, or the case where the connection state of the connector 34 is incomplete.

The cable connection judging circuit 8 is a logic circuit for judging whether the output signal of the γ-ray signal amplifier 7 is a plate-characteristic or a resistance characteristic. As a specific example of sequentially increasing the DC voltage applied between the electrodes of the neutron detector 31, about 10
The output current of the neutron detector 31 when the direct current voltage is increased from 0 V to 1000 V per second (ramp direct current voltage) is as follows. In the case of normal connection, the γ ray detection current value is about 0.6 μA, and in the case of disconnection, the leak current linearly increases to about 0.2 μA at 1000 V.

An example of the structure of the neutron detector 31 described above is shown in FIG. 3, and is of a small size capable of withstanding high temperature, high pressure and high radiation for a long time. It is composed of a metal airtight container 10, an insulator stem 11 is formed on one end side of the metal container 10, and a rod-shaped electrode 12 is attached to penetrate the stem 11 airtightly. It is filled with Ar gas. The DC voltage between the airtight container (electrode) 10 and the rod-shaped electrode 12 of the neutron detector 31 is changed from 0 V to 1000 V (ramp DC voltage).
A DC power supply 13 capable of being connected is connected. By applying a DC voltage of 0 V to 1000 V (lamp-shaped DC voltage) to the neutron detector 31, when neutrons and γ rays are generated, the current changes and can be detected as a radiation dose.

In addition, as the neutron detector 31, the BF
_{There are 3} proportional counters, ¹⁰ B proportional counters, fission counters, etc. The temperature inside the reactor is about 3 for light and heavy water reactors.
00 ° C., 500 to 6 for sodium cooled fast reactor
It is 50 ° C.

A configuration example of the γ-ray signal amplifier 7 for amplifying the γ-ray detection current of the order of μA is shown in FIG. 4, and a part of the amplified output signal of the operational amplifier 15 is fed back through the feedback resistor 16 to the operational amplifier 15. It is an amplifier that is fed back to the input of.

The configuration example of the cable connection determination circuit 8 for determining the presence / absence of disconnection from the γ-ray detection signal is determined by the soft logic shown in FIG. That is, the presence / absence 18 of the flat characteristic portion is determined from the γ-ray detection current waveform 17 output from the γ-ray signal amplifier 7.
Do. When the flat characteristic is present, there is no disconnection and a normal connection state 19 is shown. If not, disconnection or connector 35
20 shows a state 20 of poor contact.

Since such a judgment is made by a waveform which is largely different from the normal connection state and the broken connection state, it has a feature that a highly reliable judgment with few errors can be made. The determination result can be displayed on the monitor as the characteristic curve diagram of FIG. 2, or can be printed and output. Further, the determination result can be stored in a memory such as a personal computer together with the address of each neutron detector 31 and the determination date.

Next, when it is determined by the circuit of FIG. 1 that the connection is broken, the insulation resistance of the cable 35 and the connector 34 can be measured. This embodiment will be described with reference to FIG. The same parts as those in FIGS. 1 to 5, 8 and 9 are designated by the same reference numerals, and detailed description thereof will be omitted. The output of the γ-ray signal amplifier 7 is branched and the cable insulation resistance measuring circuit 22 is connected. At the output of the γ-ray signal amplifier 7, a current-voltage as shown by the curve-b in FIG. 2 is generated. Therefore, the cable insulation resistance measuring circuit 22 can obtain the insulation resistance of the coaxial cables 35, 36 and the connector 34. That is,
Assuming that the insulation resistance of the cable 32 is R, the applied voltage is V, and the signal current is I, the insulation resistance R when it is determined that the wire is broken can be obtained from the following equation R = V / I. This insulation resistance R is shown in Figure 2
It corresponds to the inclination of b.

Next, an embodiment in which the neutron detector tester 37 and the cable disconnection presence / absence testing device 3 are configured by one circuit will be described with reference to FIG. This embodiment is an example in which the neutron signal amplifier 5 and the γ-ray signal amplifier 7 of FIG. 1 are amplified by one wide range amplifier 24. The wide-range amplifier 24 has a neutron detection signal in the mA order,
Since the line detection signal is in the order of μA, it has a function of amplifying an input signal in a wide range of about 3 digits.

Further, the circuits of the neutron plateau characteristic measuring circuit 6 and the cable connection judging circuit 8 are constituted by the measuring judgment circuit 25. The measurement / determination circuit 25 is provided with a circuit for measuring the plateau characteristic and VBD in order to confirm the presence or absence of characteristic deterioration of the neutron detector 31 during the operation of the reactor. Further, the measurement determination circuit 25 incorporates a circuit for detecting the presence / absence of disconnection of the output cable 35 and the coaxial cable 36 at the time of periodic inspection while the reactor is stopped, and the presence / absence of contact failure of the connector 34. With this configuration, the measuring device can be unified, and the switching operation by the selection circuit 4 is also unnecessary.

In order to obtain a stable reactor output, it is necessary to periodically check the characteristics of the neutron detector 31 which is irradiated with radiation and deteriorates in sensitivity and the like. Next, an example of this confirmation method will be described with reference to FIGS.

In the embodiment shown in FIG. 8, a neutron measuring device 33, a neutron detector tester 37, and a cable disconnection presence / absence testing device are provided on a coaxial cable 36 outside the connector 34 connected to the output cable 35 of the neutron detector 31. This is an example in which a selection circuit 4 for selecting 3 circuits such as 3 is connected. That is,
During the reactor operation, the neutron measuring device 33 is selected and the reactor is controlled based on the neutron detection amount measured by the neutron detector 31.

Neutron detector 31 exposed to radiation for a long period of time
Must be regularly checked because the characteristics deteriorate.
The characteristics of the neutron detector 31 are confirmed by selecting the neutron detector tester 37 in the operating state of the reactor. Immediately after the measurement, the neutron measuring device 33 is returned to the selected state and the reactor is controlled.

Further, at the time of periodic inspection with the nuclear reactor stopped, the selection circuit 4 selects the cable disconnection presence / absence testing device 3 to determine the connection state of the output cable 35, the coaxial cable 36, and the connector 34 of the neutron detector 31 as described above. Check according to the procedure.

FIG. 8 shows one neutron detection system 2 and all neutron detection systems 2 have the same circuit configuration. Therefore, the selection circuits 4 of all the neutron detection systems 2 are configured to be interlocked and switch-controlled.

Further, the neutron measuring device 33 and the neutron detector tester 37 are operated commonly during the operation of the nuclear reactor and are commonly connected to the selection circuit 4 as shown in FIG. 9 for measurement and testing. You may. In this case, many neutron detection systems 2
When switching control is automatically performed by interlocking the selection circuit 4 of
This has the effect of simplifying the control circuit.

In the embodiments shown in FIGS. 8 and 9, the neutron detector tester 37 and the cable breakage presence / absence testing device 3 are connected to each neutron detection system 2 in a circuit, and automatic control is performed. A person may manually connect and switch.
An example of this manual operation is shown in FIG.

That is, the neutron detector tester 37 and / or
Alternatively, the cable breakage presence / absence testing device 3 is provided as one device or as a single device. An operator can manually connect a large number of neutron detection systems 2 one by one in order and perform a test of the neutron detector 31 and confirm the presence or absence of cable breakage. In this case, there is an effect that the equipment cost becomes low.

[0055]

As described above, according to the present invention, it is possible to perform a highly reliable test for the presence / absence of disconnection of the neutron detector and the output cable.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram for explaining an embodiment of the present invention.

FIG. 2 is a current characteristic curve diagram with respect to voltage for explaining a γ-ray detection waveform by the neutron detector of FIG.

FIG. 3 is a diagram for explaining an embodiment of the neutron detector of FIG.

FIG. 4 is a circuit wiring diagram for explaining an embodiment of the γ-ray signal amplifier of FIG.

5 is a flowchart for explaining an embodiment of the cable connection determination circuit of FIG.

FIG. 6 is a circuit configuration diagram for explaining another embodiment of FIG. 1.

7 is a circuit configuration diagram for explaining another embodiment of FIG.

FIG. 8 is a circuit configuration diagram for explaining a specific example of the neutron detector test of FIG.

9 is a circuit configuration diagram for explaining another embodiment of FIG.

FIG. 10 is a circuit configuration diagram for explaining another embodiment of FIG.

FIG. 11 is a circuit configuration diagram for explaining a neutron measurement system in a conventional nuclear reactor.

FIG. 12 is a circuit configuration diagram for explaining a conventional neutron detector tester.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor, 2 ... Neutron detection system, 3 ... Cable breakage presence / absence testing device, 4 ... Selection circuit, 5 ... Neutron signal amplifier, 6
... Plateau characteristic measuring circuit, 7 ... γ-ray signal amplifier, 8 ... Cable connection determination circuit, 10, 12 ... Electrode, 11 ... Stem, 13 ... DC power supply, 15 ... Operational amplifier, 16 ... Feedback resistor, 17 ... γ-ray Detection current waveform, 18 ... Presence / absence judgment of flat characteristic portion, 19 ... Normal connection state, 22 ... Cable insulation resistance measuring circuit, 24 ... Wide range amplifier, 25 ... Measurement judging circuit, 31 ... Neutron detector, 32 ... Cable, 33
... Neutron measuring device, 34 ... Connector, 35 ... Output cable, 36 ... Coaxial cable.

Claims (7)

[Claims] 1. A cable breakage presence / absence testing device for testing the presence or absence of a breakage in an output cable of a neutron detector installed in a nuclear reactor, wherein the output is provided for amplifying a γ-ray detection signal detected by the neutron detector. A cable disconnection comprising: a γ-ray detection signal amplifier connected to the cable; and a disconnection presence / absence determining unit that determines that there is no disconnection when the γ-ray detection signal amplifier outputs the γ-ray detection signal. Presence / absence test device. 2. A cable disconnection presence / absence testing device for testing the presence / absence of disconnection of an output cable of a neutron detector installed in a nuclear reactor, comprising: a neutron measuring device for measuring neutrons generated from the reactor; A disconnection presence / absence test device for testing the presence / absence of disconnection of the output cable of the detector, a selection circuit for selecting and switching the neutron measurement device and the presence / absence test device for disconnection, and the presence / absence test device connected to the disconnection test device. a γ-ray detection signal amplifier, and the selection circuit selects the disconnection presence / absence testing device
A cable disconnection presence / absence testing device comprising: a disconnection presence / absence determining unit that determines that there is no disconnection when the line detection signal amplifier outputs a γ-ray detection signal. 3. The output current waveform of the γ-ray detection signal amplifier when the γ-ray detection signal amplifier outputs the γ-ray detection signal when the voltage applied to the neutron detector is sequentially changed to a high voltage. 3. The cable disconnection presence / absence testing device according to claim 1, wherein the plateau characteristic is present in. 4. The cable breakage presence / absence test apparatus according to claim 3, wherein the voltage applied to the neutron detector is a lamp-like DC voltage. 5. The cable disconnection presence / absence testing device according to claim 1, wherein a current of the order of μA flows as a signal current input to the γ-ray detection signal amplifier. 6. A γ-ray detecting step of detecting γ-rays by the neutron detector in a test method for testing whether or not a cable connecting between a neutron detector and a neutron measuring circuit connected to the neutron detector is disconnected. And a judgment step of judging whether or not there is a disconnection when the γ-ray is detected in this γ-ray detection step. 7. A test for testing the presence or absence of disconnection of a cable connecting the neutron detector and the neutron measuring device of a neutron measuring system for detecting neutrons with a neutron detector and measuring a neutron generation amount with a neutron measuring device. In the method, a switching step of amplifying the γ-ray detection signal detected by the neutron detector by switching to a γ-ray detection signal amplifier, and the γ-ray by sequentially changing the DC voltage applied to the neutron detector to a high voltage. A method for testing the presence / absence of a cable break, which comprises a determination step of determining a normal connection when a plateau waveform is present in the current waveform output by the detection signal amplifier.