JPH0212093A - Structure for fitting neutron flux detector - Google Patents

Abstract

PURPOSE:To improve exchanging works so that the necessary time for periodical inspections can be shortened and quantity of radiation exposure can be reduced by fixing a hollow in-core nut to a flange for neutron flux monitor after screwing the nut into the lower end section of a neutron flux monitor main body. CONSTITUTION:A neutron flux monitor main body 35 has a long tubular form and its lower end side is extended downward through a neutron flux monitor housing 36 to a flange 37 for neutron flux monitor supporting the main body 35. The housing 36 is fixed to the bottom plate of a reactor pressure vessel and provided with a flange section 36a at its lower end. The flange 37 is fixed to the flange section 36a with a fastening bolt 38. Therefore, an in-core nut 40 can be easily fitted to and removed from the neutron flux monitor main body 35 without removing the motor section 32 of a control rod driving mechanism 30 around a neutron flux detector 33 when the detector 33 is fitted or exchanged.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a neutron flux detector used in a *m water reactor equipped with an electric type control rod drive mechanism, and particularly relates to a neutron flux detector used in a water reactor equipped with an electric type control rod drive mechanism. Attach to the mounting structure of the bundle detector.

(Prior art) Since the output of a nuclear reactor such as a boiling water reactor is proportional to the neutron flux, the neutron flux of the reactor is measured by a neutron flux detector (neutron (bundle monitor). The neutron flux detector has a
RNM) and power range monitors (LPRM, APRM, etc.), each of which is arranged in plural in the core of a nuclear reactor. Among these, SRN M 4.1 is used for measurements of neutron multiplication while approaching criticality, measurements while increasing reactor power, etc.

Neutron east detection humidity 1 of SRNM etc. is sent to boiling water reactor No. 7
Mounted as schematically shown in the figure.

A reactor core 3 is accommodated in the reactor pressure vessel 2 as shown by the broken line, and this reactor core 3 is defined by a core support plate 4, an upper grid plate 5, and a core shroud 6. A plurality of neutron flux monitor bodies 7 are installed to guide insertion. In the illustrated example, one neutron flux monitor main body 7 is shown for the sake of simplification.

The neutron flux monitor main body 7 is formed into a long elongated shape, and its upper end is connected to the support hole 5a formed in the lower surface of the upper grid plate 5.
Its lower part protrudes downward from the reactor pressure vessel 2 via the neutron flux monitor guide tube 8 and the neutron flux monitor housing (in-core housing) 9, and its lower end is connected to the neutron flux r monitor flange. (Inner lower flange) is abutted and supported by 10. Neutron flux monitor body 7
is fixed to the neutron flux monitor flange 10 with an installation nut 11. The neutron flux monitor flange 10 is fixed to the lower end outer circumferential flange 9a of the neutron flux monitor housing 9 with tightening holes 1-12.

When installing the neutron flux monitor main body 7 in the reactor core 3, it is suspended from the core 3J into the neutron flux monitor guide tube 8, and the lower end of the neutron flux monitor main body 7 is attached to the neutron flux monitor flange 10. It is brought into contact with and supported by the Taper receiving surface 10a.

The upper part of the neutron flux monitor main body 7 pushes down the plunger 13 against the spring force of the coil spring 14, and the locking part 13a at the upper end of the plunger 13 is inserted into the support hole 5a of the upper grid plate 5.
to engage. As a result, the plunger 13 is biased and fixed toward the upper grid plate 5 by the spring force of the coil spring 14.

After installing the neutron flux monitor main body 7 in the reactor core 3,
Tighten the neutron flux monitor installation nut 11 to fix it.

On the other hand, when removing the neutron flux monitor body 7 from the core 3, remove the installation nut 11 for fixing the lower end, contrary to the installation process, and then attach the plunger 13 for fixing the upper end to the spring of the coil spring 14. Push down against the force, remove the plunger 13 from the support hole 5a of the upper grid plate 5, grasp the grip ring 13b with a handling jig (not shown), etc., and lift it upward.

Incidentally, a sensor cable 15 extends from the lower end of the neutron flux monitor main body 7, as shown in FIG. The sensor pull 15 is guided within a cable guard 16 and is connected to a signal cable 18 via a cable connector 17. The signal cable 18 is extended from the lower end of the cable guard 16 to a room III (not shown), and is configured to send a neutron flux detection signal to this control room. The cable guard 16 is removably screwed to the lower end of the neutron beam main body 7, and protects the cable connector 17 from water leakage by a seal 19 inserted therein.

Note that the reference numeral 20 is a gas injection port for injecting an inert gas such as helium gas, and the gas is injected into the neutron flux monitor main body 7 from this gas injection port 20.
The internal environment is well maintained.

(Problem to be solved by the invention) In a boiling water reactor, a 10th
As shown in the figure, a large number of control rod drive mechanisms (hereinafter referred to as CRD) 21 are vertically installed in a forest, and a neutron flux monitor housing (in-core housing) protrudes downward from the bottom of the reactor pressure vessel 2. ) around 9! ;t
A CRD housing 22 is provided. Some boiling water reactors, like improved boiling water reactors, have motor-driven υ
There are plans to use the 1111 rod drive mechanism (hereinafter referred to as FMCRD).

In this FMCRD, an axially long motor section 23 is attached to the lower part of the CRD housing 22. Each motor part 23.2
The space between the three rooms is small and the working environment is poor. For this reason, various operations such as a connector connection operation for connecting the sensor cable from the neutron flux monitor main body 7 to the signal cable 18 cannot be performed using the narrow working space between the motor sections 23.

This connector connection work is performed when replacing the neutron flux monitor main body 7 such as an LPRM or SRNM, and this replacement work is performed for a plurality of monitors, for example, about 10 monitors at a time, during a periodic inspection of a nuclear reactor. When replacing the neutron flux monitor main body 7,
Each time each neutron flux monitor body 7 is replaced, it is necessary to remove the CRD motor 23 around the neutron flux monitor housing 22.
It actually takes several hours.

For this reason, it takes a long time to replace the neutron flux monitor body 7, which is carried out during periodic inspections of the nuclear reactor, and as a result, there is a risk that the period of periodic inspections will become longer and the amount of radiation exposure will increase.

The present invention has been made in consideration of the above-mentioned circumstances, and is a neutron flux detector that can improve the workability of replacing the neutron flux monitor main body, shorten the regular inspection period, and reduce the amount of radiation exposure. It provides a mounting structure.

[Structure of the invention]

(Means for Solving the Problems) In the mounting structure of the neutron flux detector according to the present invention, the upper end of the neutron flux monitor main body is elastically supported by the upper grid plate, and the neutron flux detector is passed through the lower end side into the neutron flux monitor housing. In the mounting structure of a neutron flux detector supported by a flux monitor flange, a hollow cylindrical incore nut is screwed to the lower end of the neutron flux monitor body to connect the lower end of the neutron flux monitor body to the neutron flux monitor flange. The nut part of the in-core nut is positioned near the lower part of the motor of the control rod drive mechanism.

Further, in the mounting structure of the neutron flux detector of the present invention, the neutron flux monitor main body projects downward from the in-core nut, a cable guard is provided at the lower end of the neutron flux monitor main body, and a cable connector is housed within the cable guard, This cable connector connects the sensor cable from the neutron flux monitor main body to the signal cable.

In the mounting structure of the neutron flux detector of the present invention, the neutron flux monitor body further has a rotation preventing surface formed on the outer surface of the protrusion that protrudes downward from the Incore nut, so that when the Incore nut is attached to and detached from the neutron flux monitor body, neutron flux This prevents the bundle monitor main body from running late.

(Function) The mounting structure of this neutron flux detector is such that the lower end of the neutron flux monitor main body is passed through the neutron flux monitor housing and supported by the neutron flux monitor flange, and the lower end is fixed to the hollow cylindrical Incore Analyzer 1. . This in-core nut is screwed to the lower end of the neutron flux monitor main body, and the nut part of the in-core nut is located near the bottom of the lateral drive mechanism of the IIJID rod drive machine, so when installing or replacing the neutron flux detector, it can be The in-core nut can be easily removed from the neutron flux monitor body without removing the motor part of the II-III rod drive mechanism.

Therefore, it is possible to improve the workability of replacing the neutron flux detector and to significantly shorten the replacement work time, thereby shortening the regular inspection period and reducing radiation waves III.

In addition, the mounting structure of this neutron flux detector is such that the neutron flux monitor main body protrudes downward from the in-core nut, and a cable guard is provided at the lower end to accommodate the cable connector, and the sensor cable from the neutron flux monitor main body is connected by the cable connector. Since it is connected to the signal cable, the connection work is done by the control rod! RFJ can be performed simply, easily, and in a short time in a relatively wide working space without being hindered by the j+ mechanism motor section.

The mounting structure of this neutron flux detector further includes a rotation preventing surface formed on the outer surface of the protruding part of the neutron flux monitor body that protrudes downward from the Incore nut, and when the neutron flux monitor body is attached to the Incore Analyzer 1- or the cable guard during 1JIIR. Since it is possible to effectively prevent the neutron flux monitor main body from rotating, f1 damage to the sensor cable and the like can be effectively prevented.

(Implementation M) Hereinafter, an embodiment of the mounting structure for a neutron flux detector according to the present invention will be described with reference to the accompanying drawings.

The mounting structure of this neutron flux detector basically has a major feature in the lower mounting structure of the neutron flux detector, and the upper mounting structure is different from the conventional neutron flux detector shown in FIGS. 7 and 8. Since they are basically the same, they will be given the same reference numerals and their explanation will be omitted.

At the bottom of the reactor pressure vessel 2 of the boiling water reactor, there is a motor-driven control rod drive mechanism (FMCRD) 30 that moves control rods (not shown) into and out of the reactor core as shown in FIG. A large number of these trees are vertically installed in standing forests. This 1NI
The IIl rod drive mechanism 30 has an FMCR at the bottom of a control rod drive mechanism housing (hereinafter referred to as CRD housing) 31.
A motor section 32 of D is provided. This motor section 32 is
For example, it has an axial length of about 1.5 m.

Further, the neutron flux of the nuclear reactor is monitored by a neutron flux detector 33 such as a SRNM and a power range monitor (LPRM, APRM, etc.) in order to display the output of the reactor and evaluate the burnup. This neutron flux detector 33 is installed in an appropriate space between each FMCRD 30, and is located on the right side of a long neutron flux monitor main body 35. This neutron flux monitor main body 35 accommodates a neutron detection'; , so the explanation will be omitted.

The neutron flux monitor main body 35 has an elongated tubular shape, and its lower end extends downward through the neutron flux monitor housing 36, as shown in FIG. It is supported in contact with. The neutron flux monitor housing 37 is fixed to the bottom plate (lower mirror plate) of the reactor pressure vessel 2, and has a flange 36a at its lower end. A neutron flux monitor flange 3 is attached to this flange portion 36a.
7 is fixed by a tightening bolt 38.

For example, a tapered stepped support hole 39 is bored through the seven neutron flux monitor langes 37.
The large-diameter sleeve portion 35a of the neutron flux monitor main body 35 is in contact with and supported by the tapered stepped portion that also serves as a seal portion. The neutron flux monitor main body 35 has a neutron flux monitor flange 37
It protrudes further downward. Neutron flux monitor body 3
A male threaded portion 35b is formed below the large diameter sleeve portion 35a of No. 5, and a hollow cylindrical elongated incore nut 40 is screwed to this male threaded portion 35b.

By screwing the in-core nut 40, the lower end of the neutron flux monitor main body 35 is tightened and fixed to the neutron flux monitor flange 37.

At the lower end of the incore nut 40, as shown in FIG.
A hollow portion 40a is formed, and the in-core nut 40 is attached and removed via this nut portion 40a.

As shown in FIG.
A disk-shaped support member 41 is provided inside, and the lower part of the incore nut 40 is supported by the neutron flux monitor main body 35 via the support member 41, and a sealing member 42 such as an O-ring is provided.
42 to keep it liquid-tight.

The dry tube 44 of the neutron flux monitor main body 35 is inserted into the incore nut 4o and protrudes downward, and a vibrator-like cable guard 45 is attached to the lower end of the dry tube 44 of the neutron flux monitor main body 35.
Freely screwed together. A cable connector 46 is accommodated within the cable guard 45, and this cable connector 4
6, a sensor cable 47 from the neutron flux monitor main body 35 is connected to a signal cable 48. The signal cable 48 extends into rooms f, II and III (not shown), and monitors the neutron flux in the reactor within this control room.

On the other hand, on the outer surface of the protrusion of the neutron flux monitor main body 35 that protrudes downward from the in-core nut 40, a quench stopper 50 is provided as shown in FIGS. 5(A) and 5(B). At least two of the rotation stopping surfaces 50 facing each other in the diametrical direction are formed in a planar shape, and stop the neutron flux monitor main body 35 from rotating when the incore nut 40 is tightened or the cable guard 45 is attached. . The rotation stopper surface 50 is formed at a position where it will not interfere with the lower end of the Incore nut 40 even if the Incore nut 40 is lowered too far after the Incore nut 40 is loosened and removed.

By the way, C/L of the neutron flux monitor main body 35, part 3
9 is damaged for some reason and the reactor water in the reactor pressure vessel 2 leaks and flows up through the neutron flux monitor main body 35, the sealing material 42 attached to the support member 41 of the incore nut 4o .42 can stop water leakage. The stopped leakage is drained to Incore Nut 4 through the drain port 52.
0 is discharged to the outside.

By interposing the sealing materials 42 and 42 on the support member 41 of the in-core nut 40, it is possible to reliably prevent water leakage from penetrating through the neutron flux monitor main body 35 and into the cable guard 45. This allows cable guard 4
This prevents electrical insulation failure of the cable connector 46 housed in the cable connector 5 and improves the reliability of neutron flux measurement. The support member 41 may be fixed within the in-core nut 40 by screwing, as shown in FIG. 3, or by welding or the like.

Next, the replacement work of the neutron flux detector will be explained.

When installing the neutron flux detector 33 in a boiling water reactor, the neutron flux monitor body 35 of the neutron flux detector 33 is suspended from above the reactor core, and the neutron flux monitor guide tube (see Figure 7) is installed. ) 8 and neutron bundles are guided into the chive housing 36, and the lower end portion thereof is brought into contact with the tapered stepped portion (sealed portion) of the support hole 39 of the neutral single bundle monitor flange 37 to be supported.

Thereafter, the upper end of the neutron flux monitor main body 35 is elastically supported by the support hole of the upper grid plate, and an incore nut 40 is screwed and tightened to the male threaded part 35b formed at the lower end of the neutron flux monitor main body 35, and the neutron The lower end of the bundle monitor main body 35 is fixed to the seven neutron flux monitor flange 37. Then, a sensor cable 47 protruding downward from the neutron flux monitor main body 35 is connected to the signal cable 4 via a cable connector 46, and a cable guard 4 is arranged to accommodate the cable connector 46.
5 is screwed to the lower end of the neutron flux monitor main body 35.

On the other hand, the upper part of the neutron flux monitor main body 35 is operated in the same manner as the conventional neutron flux monitor main body, engages with the support hole of the upper grid plate, and is elastically supported by the upper grid plate.

In order to remove the neutron flux monitor main body 35 from the core of the nuclear reactor, the operation may be performed in the reverse order to that used during installation. At that time, the in-core nut 40 is removed from the neutron flux monitor water body 35, the neutron flux monitor 45 is also removed from the monitor body 35, and the sensor cable 47 is removed by operating the cable connector 46. It is disconnected from the signal cable 48.

When removing the incore nut 40 from the neutron flux monitor main body 35, the nut part 40a of the incore nut 40 is
Since it is located near the bottom of the motor of the RD30, there is no need to remove the motor part 32 of the FMCRD30 located around the neutron flux monitor housing 36, as shown in FIG. , the in-core nut 40 can be easily removed from the neutron flux monitor main body 35 in a short time. At that time, the neutron flux monitor main body 35
Since the rotation stop surface 50 is formed on the rotation stop surface 50, this rotation stop surface 50
By holding down and operating the incore nut 40, it is possible to reliably prevent the neutron flux monitor main body 35 from rotating when the incore nut 40 is operated, and damage to the sensor cable 47 can be prevented.

In addition, since the cable guard 45 and the cable connector 46 are located below the inner nut 40, the cable guard 45 and the cable connector 46 can be operated in a relatively wide operating space.
This can greatly improve workability and operability.

Since these operations are performed in a space far below and away from the cladding adhered to the neutron flux monitor housing 36 and easy to operate, the amount of radiation exposure due to the cladding inside the neutron flux monitor housing 36 can be reduced.

Furthermore, at the stage of developing the mounting structure for this neutron flux detector, the neutron flux monitor housing was extended to the vicinity of the Tanabata lower part of the FMCRD, the 7 langes for the neutron flux monitor were fixed near the lower part of this motor, and the neutron flux A plan was proposed to support the lower end of the neutron flux monitor main body with a monitor flange, but in this case, the flange of the neutron flux monitor housing and the neutron flux monitor flange would interfere with the FMCRD, so maintenance and inspection of the FMCRD would be difficult. There are some problems with the work and it is not desirable.

〔Effect of the invention〕

As described above, in the mounting structure of the neutron flux detector according to the present invention, the lower end and side of the neutron flux monitor body are passed through the neutron flux monitor housing and supported by the neutron flux monitor 7 langes, and the lower end portion is hollowed out. While it is fixed with a cylindrical Incore nut, the Incore nut is screwed to the lower end of the neutron flux monitor main body, and the nut part of the Incore nut is located near the bottom of the motor of the control rod drive mechanism, making it easy to install the neutron flux detector. During replacement, the in-core nut can be easily attached and detached from the neutron flux monitor body without removing the motor part of the control rod drive mechanism.
This improves work efficiency and significantly reduces work time.

Therefore, it is possible to shorten the regular inspection period and reliably reduce the amount of radiation exposure.

In addition, the mounting structure of the neutron flux detector of the present invention is such that the neutron flux monitor body is protruded downward from the incore analyzer i, and a cable guard is provided at the lower end of the neutron flux monitor body.
A cable connector is housed inside this cable guard, and the sensor cable from the neutron flux monitor body is connected to the signal cable using this cable connector, so the connection work is not hindered by the motor part of the control rod drive vJR structure. This can be done simply and easily in a relatively large work space and in a short time.

This neutron flux detector mounting structure further includes a rotation stopping surface formed on the outer surface of the protruding part of the neutron flux monitor body that protrudes downward from the incore nut, and at 1ff12 when the incore nut or cable guard is attached to the neutron flux D monitor body. It is possible to effectively prevent the neutron flux monitor main body from rotating, and damage to the sensor cable and the like can be effectively prevented.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the mounting structure of the neutron flux detector according to the present invention, FIG. 2 is an overall layout diagram showing the lower mounting structure of the neutron flux detector, and FIG. A partial cross-sectional view of the in-core nut fixed to the neutron flux monitor body of the flux detector, FIG. 4 shows the lower end of the neutron flux detector and i,
II II A diagram showing the arrangement relationship of the rod drive mechanism, Figure 5 (
A) is a diagram showing a rotation stopping surface formed on the neutron flux monitor main body of a neutron flux detector, FIG. 5(B) is a sectional view taken along line 8-8 of FIG. 5(A), and FIG. Neutron flux detector and control rod layer! A diagram showing the arrangement relationship with the l1 mechanism, FIG. 7 is a diagram schematically showing the mounting structure of a conventional neutron flux detector, and FIG. 8 is a detailed sectional view showing the mounting structure of the conventional neutron flux detector.
FIG. 9 is a diagram showing a lower mounting structure of a conventional neutron flux detector, and FIG. 10 is an overall layout diagram showing the lower mounting structure of a conventional neutron flux detector. Container, 3... Core, 4... Core support plate, 5... Upper grid plate, 6... Core shroud, 30... Control rod section! ! ! 1 mechanism, 31... control rod drive mechanism housing, 32... motor section, 33... neutron flux detector, 3
5... Neutron flux monitor main body, 36... Neutron flux monitor housing, 37... Flange for neutron flux monitor,
40... Incore nut, 40a... Nut part, 4
DESCRIPTION OF SYMBOLS 1... Support member, 42... Seal material, 44... Dry tube, 45... Cable guard, 46...
Cable connector, 47...sensor cable, 48...
... Signal cable, 50... Rotating surface. Applicant's agent Hisashi Hatano 1.30...
Neutron flux detector, 2...Reactor pressure 1st tea vice certain episode

Claims (1)

[Claims] 1. Mounting structure for a neutron flux detector in which the upper end of the neutron flux monitor main body is elastically supported by an upper grid plate, and the lower end thereof is supported by a neutron flux monitor flange that passes through the neutron flux monitor housing. In this step, a hollow cylindrical in-core nut is screwed to the lower end of the neutron flux monitor body to fix the lower end of the neutron flux monitor body to the neutron flux monitor flange, and the nut portion of the in-core nut is driven by a control rod. A mounting structure for a neutron flux detector, characterized in that it is located near the bottom of a motor of a mechanism. 2. The neutron flux monitor main body is made to protrude downward from the in-core nut, a cable guard is provided at the lower end of the neutron flux monitor main body, a cable connector is accommodated in this cable guard, and the sensor from the neutron flux monitor main body is connected to the neutron flux monitor main body by this cable connector. Claim 1: The cable is connected to a signal cable.
Mounting structure of the described neutron flux detector. 3. The neutron flux monitor body has a rotation preventing surface formed on the outer surface of the protrusion that protrudes downward from the in-core nut to prevent the neutron flux monitor body from rotating when the in-core nut is attached to and removed from the neutron flux monitor body. Mounting structure of the neutron flux detector described in Item 1.