JPH0363595A - Thunderbolt-resistance type neutron measuring instrument - Google Patents

Abstract

PURPOSE:To preclude a noise at the time of lightning by grounding exclusively only the ground side of an output signal as to a neutron detector protection tube which contains a neutron detector for measuring neutron flux and a neutron detector conduit for calibration as a cooling gas passage. CONSTITUTION:The neutron detector 1 in the neutron detector protection tube 15 is insulated electrically from the neutron detector protection pipe 15 and neutron detector conduit 16 for calibration by an insulating support 17 and cooling gas 21. The neutron detector protection pipe 15 is connected to a building ground line 9 and the ground side of the neutron detector 1, an MI cable 2, and a cable 4 is led out to a signal processor 7 outside a unclear reactor container 6 while insulated from the periphery and then grounded at one point of an exclusive ground line 10 having large grounding effect. Therefore, no potential difference is generated on the ground line and no circulating current is generated, so no noise is generated. Consequently, neither a wrong alarm nor a wrong scram signal due to lightning is prevented from being generated.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention aims to reduce the total amount of in-reactor neutrons in the power range of a nuclear reactor to A+.
The present invention relates to a neutron measuring device that is ++, and particularly relates to a lightning-proof neutron measuring device that prevents noise from being received during a lightning strike.

(Prior Art) In nuclear couplants, a neutron needle 11111 device is installed to monitor the output of the nuclear reactor. This neutron measurement device has a range of approximately 9 digits (approximately 10
-7% to 100%), there are generally three types of measuring devices: a neutron source region measuring device, an intermediate region measuring device, and an output head-mounted weighing device. It monitors a wide range of about 9 digits. Among these, the output range measuring device is approximately LO of the rated value.
It monitors the neutron flux level from % to LOG%, and the DC signal from the neutron detector is processed by a signal processing device in the control room. Conventionally, the signal from the neutron detector is 1
It is a direct current of about 00 μA, and since this current value is large, the signal from the MI cable 2 drawn out from the neutron detector 1 is connected to the connector 3 and the cable 4, as shown in the circuit diagram of
Then, through electrical penetration 5, the signal is introduced into a signal processing device 7 provided in a control room outside the reactor containment vessel 6. The ground side of this signal is connected to a building grounding wire 9 laid in the building in the reactor containment vessel 6 together with the neutron detector protection tube 8 housing the neutron detector 1, thereby grounding the building.

Furthermore, in addition to grounding the circuit within the signal processing device 7, the signal processing device 7 is also connected to a dedicated grounding wire 10, which has a higher grounding effect than the building grounding wire 9 laid at the foundation of the nuclear power plant. Two-point grounding is implemented.

In addition, inside the neutron detector protection tube 8, as shown in the enlarged sectional view of the main part of the neutron detector in FIG. accommodated and supported by a metal support 12,
Reactor water 14 is allowed to flow in the direction of the arrow through a hole 13 made in this support 12 to cool down the heat generated by the gamma rays of the neutron detector 1.

(Problems to be Solved by the Invention) In the above power range measuring device, the signal cable of the neutron detector 1 is connected to the building grounding wire 9 in the reactor containment vessel 6, and the dedicated grounding wire lO in the signal processing device 7. Since the circuit is configured to be grounded at two points, in the event of a lightning strike, a potential difference occurs due to the difference in the grounding effect between the building grounding wire 9 and the dedicated grounding wire 10, causing a circulating current to flow, which generates noise and interferes with measurement. There were problems with the mZ value and the possibility of issuing a false scram alarm.

The present invention has been made in view of the above, and its purpose is to electrically insulate a neutron detector within a neutron detector protective tube, and to ground the cable at one point to prevent noise generation even during lightning strikes. The purpose of the present invention is to provide a demand-resistant neutron measuring device that has never been available before.

[Structure of the invention] (Means for solving the problem) A neutron detector that measures a neutron flux with its surroundings electrically insulated and a neutron detector conduit for calibration that are housed together and isolated from reactor water. A protection tube, and the inside of this neutron detector protection tube and the inside of the calibration neutron detector conduit are used as a circulation path for an insulating cooling gas that insulates and cools the neutron detector, and the output signal cable of the neutron detector is grounded. A side of the neutron detector is grounded at one point in the signal processing device, and a cooling device is further provided for supplying the cooling gas into the neutron detector protection tube.

(Function) The neutron detector is electrically insulated by reactor water and insulating cooling gas within the neutron detector protection tube, and the ground side of the output signal cable is grounded at one point, so it is safe to use in the event of a lightning strike. Even in this case, there is no potential difference on the ground side of the cable, so there is no circulating current and associated noise.

This can prevent false alarms and false scram signals from occurring due to false outputs from the neutron detector.

(Example) An embodiment of the present invention will be described with reference to the drawings.

As shown in the circuit diagram of FIG. 1, the signal from the MI cable 2 drawn out from the neutron detector 1 is sent to the control room outside the reactor containment vessel 6 via the connector 3, the cable 4, and the electrical penetration 5. The signal is introduced into the processing device 7, in which the signal is processed by the LPRM processing circuit 7a, and further subjected to averaging processing by the APRM processing circuit 7b. This result is transmitted to a meter 7c and a trip circuit 7d, and a scram signal 7e is generated for display and in the event of an abnormality.

The neutron detector protection tube 15 is grounded to the building grounding wire 9 in the reactor containment vessel 6, but the ground side of the cable for the output signal of the neutron detector 1 remains insulated from the neutron detector protection tube ■5. In addition to grounding the circuit within the signal processing device 7, the signal processing device 7 is connected to and grounded to a dedicated grounding wire 10 laid in the foundation of the nuclear power plant.

FIG. 2 is an enlarged cross-sectional view of the main parts of a neutron detector, in which a plurality of neutron detectors 1 and a neutron detector conduit 16 for calibration of the neutron detectors 1 are supported by a plurality of insulating supports 17, and a neutron detector protection tube ( The neutron detector protection tube 15 is a sealed tube that isolates the reactor water 14 in the reactor from the neutron detector 1 and the calibration neutron detector conduit 16 inside.

Further, a hole 18 is made in the insulating support 17, and a hole 19 is also made in the upper part of the calibration neutron detector conduit 16.
As a cooling gas passage, an insulating cooling gas 2k such as N2 gas from the cooling device 20 is passed through the calibration neutron detector conduit 1G as shown by the arrow to cool down the heat generated by γ rays in the neutron detector 1. . The cooling gas 21 that has been circulated and cooled within the neutron detector protection tube 15 is discharged into the reactor containment vessel 6 via the trap 22.

Furthermore, a neutron detector protection tube (5 is a reactor pressure vessel installed in the reactor containment vessel 6 as shown in the cross-sectional view of the overall configuration in FIG. 23 is set in the reactor core 24, and the electrical signal from the neutron detector 1 is extracted to the outside via a cable 2, connected to a cable 4 with a connector 3, and is connected to the reactor containment vessel 6 through electrical penetration 5. The neutron detector conduit 16 for calibration is connected to the guide tube 25 outside the neutron detector protective tube 15, and is connected to any neutron detector conduit 1B for calibration. It is connected to a drive device 29 via an indexer 26, an isolation valve 27, and a shielding container 28.

A calibration neutron detector 30 is housed in the shielding container 28, and is inserted into a predetermined calibration neutron detector conduit 16 via the indexer 26 and the guide tube 25 by a drive device 29 at predetermined time intervals. It is inserted to calibrate a plurality of neutron detectors 1. Further, the guide pipe 25 is connected to a cooling device 20 by a gas pipe 32 via an isolation valve 31, and normally a cooling gas 21 is supplied from the cooling device 20 to the calibration neutron detector conduit 16 and the neutron detector protection pipe 15. The structure is such that the neutron detector 1 is cooled.

Next, the effect of the above configuration will be explained. The neutron detector 1 in the neutron detector protection tube 15 has an insulating support 17
is electrically insulated from the neutron detector protection tube 15 and the calibration neutron detector conduit 1B by the cooling gas 21, and
The heat generated from the wire is cooled down.

The neutron detector protection pipe 15 is connected to the building ground wire 9 on the spot, but the ground sides of the neutron detector 1, MI cable 2, and cable 4 are connected to the outside of the reactor containment vessel 6 while being insulated from the surroundings. It is led out to the signal processing device 7 and is grounded at one point on a dedicated grounding line lO, which has a greater grounding effect than the building grounding line 9. Therefore, even if there is a lightning strike during operation, the electrical circuit of the neutron measurement device is grounded at only one point, and the dedicated grounding wire IO has a large grounding effect, so no potential difference will occur in the grounding wire and circulating current will flow. There is no noise, so no noise is generated. This can prevent false alarms and false scram signals from occurring.

[Effects of the Invention] According to the present invention, noise caused by lightning strikes is prevented from occurring in the output signal of a neutron measuring device, so false alarms and scrams at the time of lightning strikes are prevented, and the safety of nuclear power plants is improved. This has the effect of improving driving efficiency.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is an enlarged sectional view of essential parts of a neutron detector of an embodiment of the invention, Fig. 3 is a sectional view of the overall configuration, and Fig. 4 is a conventional neutron detector. Circuit diagram of the measuring device,
FIG. 5 is an enlarged sectional view of the main part of a conventional neutron detector. 1...Neutron detector, 2...Ml cable, 4
... Cable, 7... Signal processing device, 1
0... Dedicated grounding wire, 15... Neutron detector protection tube, 16... Neutron detector conduit for calibration, 17... Insulation support, 18.19... Hole, 2
0... Cooling device, 21... Cooling gas.

Claims (1)

[Claims] a neutron detector that is electrically insulated from the surroundings and measures neutron flux in the power range of the reactor; a neutron detector protection tube that houses the neutron detector and a calibration neutron detector conduit that also serves as a cooling gas passage; A lightning-resistant neutron measuring device comprising: a cooling gas cooling device connected to the cooling gas passage of the calibration neutron detector conduit; and a grounding side of a cable for output signal of the neutron detector connected to a dedicated grounding wire. .