JP2011153831A - Device for monitoring radiation in discharge canal of nuclear power plant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the upsizing of a radiation monitoring device placed in a discharge canal of a nuclear power plant. <P>SOLUTION: The device for monitoring radiation in a discharge canal of a nuclear power plant placed in a discharge canal where the sea water discharged from a nuclear power plant flows includes a detector which detects radiation in the sea water, a first cylindrical protection tube which accommodates the detector at its end and keeps the detector located below the seawater level, a second protection tube placed outside around the first protection tube to cover the part of it below the seawater level and a support structure for fixing the second protection tube onto a fixed structure. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a water discharge radiation monitoring apparatus for a nuclear power plant.

  Nuclear power plants take in seawater, cool various facilities, and discharge seawater after use from the spillway to the sea. At this time, a water discharge radiation monitor device is attached to the side wall of the water discharge channel that discharges seawater as an underwater device for measuring the radiation coefficient rate.

  Here, Japanese Patent Laid-Open No. 2001-151474 proposes a lifting device for underwater equipment using buoyancy.

JP 2001-151474 A

  This lifting device is a device for moving an underwater device by generating a buoyancy larger than the gravity acting on the underwater device or using an external force. Therefore, Patent Document 1 does not disclose any installation structure of the discharge channel radiation monitor device.

  Moreover, the full length of the protective tube which protects a water discharge radiation monitor apparatus becomes long with about 7-10m. Therefore, in order to ensure the strength of the discharge channel radiation monitor device, it is necessary to enlarge the device.

  Then, this invention aims at suppressing the enlargement of the radiation monitor apparatus provided in the water discharge channel of a nuclear power plant.

  The present invention includes a detector that detects radiation in seawater, a cylindrical first protective tube that houses the detector at the end, and is disposed below the seawater surface, and an outer periphery of the first protective tube And a support structure for fixing the second protection tube to the fixed structure. The second protection tube is provided on the side and covers the first protection tube below the seawater surface.

  ADVANTAGE OF THE INVENTION According to this invention, the enlargement of the radiation monitor apparatus provided in the water discharge channel of a nuclear power plant can be suppressed.

It is an Example of a discharge channel radiation monitor apparatus. It is a comparative example of a water discharge radiation monitor apparatus. It is detail drawing of the 2nd protective tube of a present Example.

  Generally, when various devices such as a measuring instrument or a transmitter are held in water, a protective tube for protecting the surroundings and a supporting structure for supporting the device are attached. Further, the support structure has sufficient mechanical strength so as not to drop off or be damaged, and is bonded to the fixed structure. At this time, it is necessary to strengthen the support structure as the total mass of the various underwater devices and the support structure increases. Therefore, the support structure tends to be excessive or excessively heavy.

  In addition, when a device is provided in water to measure the temperature and electromagnetic waves in water, it is necessary to open the measuring instrument body or the surroundings of the measuring instrument in water depending on the type of measurement method.

  In the following embodiments, a discharge channel radiation monitoring device in a nuclear power plant is cited. The nuclear power plant discharges seawater taken in to cool various facilities from the discharge channel to the sea. At this time, in order to measure the radiation coefficient rate of the seawater discharged from the nuclear power plant, a discharge channel radiation monitor device is attached to the discharge channel.

  FIG. 2 shows a comparative example of the discharge channel radiation monitoring device. The monitor device of the comparative example includes a first protective tube 5 that protects the detector 4, a second protective tube 8 provided on the outer peripheral side of the first protective tube 5, and a support structure 9 that fixes the second protective tube. Is provided. The cylindrical second protective tube 8 is opened in seawater. Therefore, the front-end | tip part of the 1st protective tube 5 is a structure exposed in seawater.

  In the case of the comparative example, since importance is attached to the accuracy of the measurement result, seawater is in direct contact with the first protective tube, and the end portion is exposed. Therefore, many marine organisms adhere around the first protective tube, and the marine organisms are removed during maintenance and inspection.

  Moreover, since there is a possibility that the underwater equipment is fouled by seawater corrosion, a protection tube having corrosion resistance is required. However, the wall thickness of the protective tube is about 7.1 mm. Therefore, when a metal material having corrosion resistance such as stainless steel is used for the protective tube, the stainless steel becomes a large shielding material.

  Therefore, it is necessary to use an aluminum material or the like having a small shielding effect for the discharge channel radiation monitoring device as well as the protective tube used for the main steam radiation monitoring device. The main steam radiation monitoring device is a system that continuously monitors the radiation concentration of steam supplied to the steam turbine of the nuclear power plant. The protection tube of the main vapor radiation monitoring device is a structure having a total length of about 2 to 3 m, and is a metal tube that mechanically and chemically protects the surroundings of the monitoring instrument. This main vapor radiation monitor protective tube uses a corrosion-resistant aluminum material.

  On the other hand, the overall length of the protective tube of the discharge channel radiation monitoring device is about 7 to 10 m. If the thickness of the aluminum material (protection tube) is increased in order to ensure sufficient strength, the thickness of the aluminum material needs to be larger than 7.1 mm, and the manufacturing cost and workability are reduced. In addition, when aluminum material is applied to the discharge channel radiation monitor protective tube, the weight of the monitor device is increased, resulting in a problem of insufficient strength. As described above, in order to maintain the strength, there is a problem that the monitor device is enlarged.

  Example 1 will be described below. The present embodiment is an example in the case of a discharge channel radiation monitor device including a radiation coefficient rate detector.

  FIG. 1 shows a monitor device of this embodiment. Seawater 1 taken in as a coolant for equipment in the plant is discharged from the main flow path 2. In the upper part of the main flow path, a joining tank composed of a concrete side wall 3 having a space is installed.

  The discharge channel radiation monitor device includes a detector 4 that detects a radiation coefficient rate, two protective tubes that protect the detector, and a support structure 9 that fixes the device to the side wall 3. Inside the detector 4, a scintillator 7 for detecting the radiation coefficient rate is provided. Further, the detector 4 is attached with a connector 12 by a cable 11 for transmitting the measurement result. An amplifier 13 for amplifying the transmitted signal is connected to the other end of the cable 11, and a radiation monitor 19 is further connected via the cable 14.

  The detector 4 is protected by a cylindrical first protective tube 5 and a second protective tube 15. The first protective tube 5 is a cylindrical structure in which one end is closed and the other end is opened. The cable 11 is drawn out from the opening of the first protective tube 5. Moreover, the 1st protection pipe 5 is installed in the orthogonal | vertical direction with respect to the seawater surface, and the closed edge part is located below the seawater surface. The detector 4 is located at the closed end of the first protective tube 5.

  And the 2nd protective tube 15 is provided so that the circumference | surroundings of the 1st protective tube 5 and the detector 4 may also be covered. FIG. 3 shows the structure of the second protective tube 15. The second protective tube 15 has a bottom plate 15b welded to a strength reinforcing cylindrical steel material 15a. A thin cylindrical steel material 15d having an inner diameter equivalent to the hole 15c opened in the center of the bottom plate 15b and a bottom plate 15e are welded. Thus, the second protective tube 15 is manufactured by combining two cylinders having different inner diameters.

  Further, the first protective tube 5 and the second protective tube 15 are fastened at the upper portion thereof by a first protective tube side flange 16, a second protective tube side flange 17 and a bolt 18.

  The support structure 9 is a metal member for supporting and fixing a set such as the second protection tube 15 and supports the entire weight of the protection tube set. The support structure 9 is welded to the hardware plate 10 and the second protective tube 15 embedded in the side wall 3. In addition, a plurality of support structures 9 may be installed, or the dimensions and attachment methods may be changed in order to maintain the strength corresponding to the total load of the protective tube set.

  Thus, in the discharge channel radiation monitor apparatus of the present embodiment (FIG. 1), the second protective tube 15 provided on the outer peripheral side of the first protective tube 5 has the first protective tube 5 below the seawater surface. It is fixed to cover.

  When the second protective tube 15 covers the first protective tube 5 below the seawater surface, the device volume below the seawater surface increases. Specifically, the apparatus volume under the surface of the water in the comparative example is determined by the first protective tube 5, whereas in the present embodiment, it is determined by the second protective tube 15. Therefore, the buoyancy acting on the monitor device increases as the device volume below the surface of the water increases compared to the comparative example, and the load applied to the fixed portion of the support structure 9 is reduced. Therefore, the strength of the monitor device can be maintained without increasing the weight of the support structure or increasing the number of support structures installed, and the size of the radiation monitor device can be suppressed. And installation in a narrow part is also possible, and cost reduction is possible.

  Specifically, as shown in the first embodiment, the second protective tube 15 located on the outermost side of the radiation monitor device does not form a water entrance in a range in contact with water (below the water surface), and the buoyancy due to the internal volume. And reducing the load difference between the radiation monitor device. In this case, the actual load applied to the support structure is obtained by subtracting the product of the inner volume, water density, and gravity acceleration from the total load of the radiation monitor device.

  Moreover, the main flow path 2 in which the discharge channel radiation monitor apparatus is installed flows seawater at a fast flow rate of about 4 m / s. Therefore, considering the case where the first protective tube 5 is longer than 10 m, the strength of the protective tube shaft in the normal direction is reduced in the structure of the comparative example. In the comparative example, since the contact point of the first protective tube and the second protective tube is only the uppermost flange, it is difficult to ensure sufficient strength of the device. The reason why the strength of the device cannot be ensured is that the first protective tube 5 is directly affected by the flow velocity because the tip (around the detector) of the first protective tube 5 is open to the water. .

Therefore, in this embodiment, the second protective tube 15 is fixed so as to cover the first protective tube 5 below the seawater surface, so that the first protective tube is a thin member having an outer diameter of about 80 mm and a thickness of about 4 mm. Even 5 can avoid the lack of strength. By suppressing the thickness of the first protective tube 5 to about 4 mm, the shielding effect on the scintillator 7 for the purpose of detecting the radiation coefficient rate stored in the detector 4 is reduced, and k-40 is set to 3. It is possible to satisfy the required sensitivity of detecting predominantly in units of 7 × 10 ⁻² [Bq / cm ³ ]. As described above, the first protective tube 5 is covered with the second protective tube 15 made of a steel material such as stainless steel having a strength higher than that of aluminum around the first protective tube 5 so that the first protective tube 5 is covered with the strength. Is reinforced.

  However, the above is premised on not obstructing the installation purpose of the detector. In the case of Example 1, the cylindrical second protective tube is formed so that the thickness of the portion covering the detector (thin cylindrical steel material 15d) is thinner than that of the other portion (strength reinforcing cylindrical steel material 15a). Has been. Thus, by reducing the thickness of the second protective tube (thin cylindrical steel material 15d) around the measuring instrument from the conventional thickness of 7.1 mm to 5.5 mm, the shielding effect in the radiation coefficient rate measurement can be reduced. .

  In the monitoring apparatus of this embodiment, the second protective tube 15 covers the first protective tube 5 below the seawater surface, so that seawater flows between the first protective tube 5 and the second protective tube 15. Can be prevented. Therefore, it is possible to prevent underwater organisms from adhering to the first protective tube 5 and corroding the underwater equipment. In addition, invasion and growth of underwater organisms are prevented, and the concern about metal corrosion caused by contact with water and oxygen can be eliminated.

  Furthermore, as shown in FIG. 3, the second protective tube 15 of the present embodiment has a lower inner diameter that is smaller than the upper inner diameter. The first protective tube 5 is formed by arranging a plurality of tubes in the central axis direction and joining them with bolts or the like. At this time, if the inner diameter is determined so that the lower inner diameter of the second protective tube 15 is smaller than the upper inner diameter, the first protective tube 5 is fixed at the lower end of the second protective tube 15 while the first protective tube 5 is fixed. The joint portion of the protective tube 5 can be provided on the outer peripheral side of the first protective tube 5. Thus, by providing the joint portion of the first protective tube 5 on the outer peripheral side of the first protective tube 5, the first protective tube 5 can be easily manufactured and disassembled.

DESCRIPTION OF SYMBOLS 1 Seawater 2 Main flow path 3 Side wall 4 Detector 5 1st protective tube 7 Scintillator 8, 15 2nd protective tube 11, 14 Cable 12 Connector 13 Amplifier 19 Radiation monitor

Claims (3)

A nuclear power plant radiation monitoring device provided in a water discharge channel through which seawater discharged from the nuclear power plant flows,
A detector for detecting radiation in the seawater;
A cylindrical first protective tube that houses the detector at an end, and disposes the detector below the seawater surface;
A second protective tube provided on an outer peripheral side of the first protective tube and covering the first protective tube below the seawater surface;
A water discharge radiation monitoring apparatus for a nuclear power plant, comprising a support structure for fixing the second protective tube to a fixed structure. The discharge channel radiation monitoring device according to claim 1,
The water discharge radiation monitoring apparatus, wherein the lower inner diameter of the second protective tube is smaller than the upper inner diameter. The discharge channel radiation monitoring device according to claim 1,
The cylindrical second protective tube is a discharge channel radiation monitoring device characterized in that the thickness of the portion covering the detector is thinner than the other portions.

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