JP2010190644A - Structure of neutron detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure of a neutron detector that regulates output signals of the neutron detector and is assembled accurately. <P>SOLUTION: The structure includes a columnar neutron detector 1 whose outer wall is electrically conductive and extends in its longitudinal direction, cables which are connected to the neutron detector 1 and applies voltage to take out detection signals, neutron moderators 2 which comprise dielectrics where through holes 2a are formed and moderate neutrons incident from surroundings by piling up the dielectrics to cover the outer wall including the shorter direction of the neutron detector 1, a conductive external cylinder 3 which covers the longitudinal outer periphery of the neutron moderators 2, a conductive lid 4 which seals one end of the external cylinder 3 that is opened and pulls the cables that have passed through the neutron moderators 2 outside of the holes 2a, a conductive lid 5 which seals the other end of the external cylinder 3 that is opened and a tightening means 7 which couples and fixes individual neutron moderators 2 by inserting a rod 6 into the through holes 2a of the piled neutron moderators 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a neutron detector structure that converts thermal neutrons into electrical signals.

In neutron detectors that measure thermal neutrons (average energy 0.025 eV), medium and fast neutrons with higher energy than thermal neutrons are more likely to penetrate the neutron detectors and are difficult to measure. In order to measure medium and fast neutrons, it is necessary to attenuate the energy to the thermal neutron level before the neutrons enter the neutron detector.

At nuclear power plants that employ pressurized water reactors, neutron detectors that measure thermal neutrons are used inside and outside the reactor. Neutron detectors installed outside the reactor need to measure thermal neutrons over a wide range from when the reactor is shut down (low thermal neutrons) to full power operation (high thermal neutrons). The measurement range is divided into three, each using a different neutron detector. The three measurement ranges are called a radiation source region, an intermediate region, and an output region in order from a range with few thermal neutrons, and are set to overlap each measurement range.

The neutron detector for the source region and the intermediate region adopts a structure using a neutron moderator. This is because there are few thermal neutrons on the lower side of the source region and the intermediate region, and the output signal is small only with the signal from the thermal neutron, so the medium and fast neutrons are decelerated with a neutron moderator and converted into thermal neutrons for output. This is to increase the signal.

As the neutron moderator, an organic substance containing a large amount of hydrogen, such as polyethylene, is used, and is disposed around the neutron detector for the source region and the intermediate region. Since there are many thermal neutrons released outside the reactor in the power region, neutron moderators are usually not used, and medium and fast neutrons are usually not measured.

As for the neutron detector for the output region, there are many thermal neutrons in the past, so the application of the moderator has not been confirmed so far, but considering the economics of the neutron amount in the reactor in the future, adopting a neutron reflector etc. The emitted thermal neutrons may be reduced. In that case, it is considered that measures to increase the output signal of the neutron detector for the output region are required.

As a neutron detector, for example, Japanese Patent Application Laid-Open No. 2003-240862 FIG. 1 (see Patent Document 1) discloses a mode in which sensitivity adjusting holes 22 and 24 are provided in the rear side end portion 14A of the moderator 14. Yes.

  FIG. 4 (see Patent Document 2) of Japanese Patent Laid-Open No. 5-134049 discloses a detector that detects thermal neutrons, epithermal neutrons, and fast neutrons using the first moderator 24a and the second moderator 24b. Is disclosed.

Japanese Patent Laying-Open No. 2003-240862 (FIG. 1)

Japanese Patent Laid-Open No. 5-134049 (FIG. 4)

However, since the thing of patent document 1 is providing the sensitivity adjustment holes 22 and 24 in the back side edge part 14A of the moderator 14, the subject that there is little adjustment effect with respect to the neutron which injects from various directions. was there.
The structure described in Patent Document 2 is complicated because the moderator 24 is divided into a hollow cylindrical first moderator and a second moderator that is detachably attached to the hollow cylindrical portion. There was a problem.

The present invention has been made to solve the above-described problems. A neutron detector structure that can be assembled with high accuracy while adjusting the output signal of a neutron detector used outside the furnace, such as a pressurized water reactor, is provided. The purpose is to provide.

The neutron detector structure according to claim 1 has a cylindrical neutron detector whose outer wall has electrical conductivity and extends in the longitudinal direction, and is connected to the neutron detector and applies a voltage to extract a detection signal. A neutron moderator that decelerates neutrons incident from the surroundings by covering the outer wall including the cable and the outer wall including the short direction of the neutron detector by being concentrically overlapped in the longitudinal direction, and comprising a cable and a dielectric having a through hole portion The conductive outer cylinder covering the outer periphery in the longitudinal direction of the neutron moderator and the one open end of the outer cylinder are sealed, and the cable that has passed through the neutron moderator is pulled out from the hole. A conductive first lid, a conductive second lid that seals the other open end of the outer cylinder, and a rod inserted into the through-hole portion of the stacked neutron moderator, Tightening means to connect and fix neutron moderator It is those with a.

The neutron detector assembly according to claim 2 includes a plurality of adjustment holes for adjusting a neutron moderation amount so as to surround the central axis in the longitudinal direction at a dielectric installation position spaced from the central axis in the longitudinal direction of the neutron moderator. It is a thing of Claim 1 provided.

According to the first aspect of the invention, since a plurality of moderators are arranged along the outer periphery of the neutron detector, the amount of neutrons incident on the neutron detector can be changed by changing the type of moderator. Even if the neutron detector is long and bent or distorted by the neutron detector, the divided moderator can absorb the bent or distorted material, so that there is an effect of obtaining a neutron detector structure that can be easily assembled.

According to the invention of claim 2, since the adjustment hole is provided so as to surround the central axis of the moderator, the output signal of the neutron detector can be adjusted by changing the diameter of the adjustment hole and the like, and from different directions This has the effect of detecting incident neutrons with high accuracy.

Embodiment 1 FIG.
The neutron detector structure of the present invention will be described with reference to FIG. FIG. 1 is a structural diagram of a neutron detector structure according to Embodiment 1 of the present invention. In Figure 1, 1 using boron ^{(10 B)} neutron sensible substances, in the ionization chamber of cylindrical shape using a metal such as aluminum to the outer wall (outer circumference) that is hermetically sealed enclosing therein ionized gas A neutron detector constructed.

Reference numeral 2 denotes a neutron moderator (moderator), which is formed of an organic dielectric having a through hole 2a containing a large amount of hydrogen, such as polyethylene, and has a hollow cylindrical shape except for the end of the neutron detector 1 and has a total length. This is a combination of a plurality of parts that are divided and shortened so as to be superposed one after another in a concentric manner. Further, the neutron moderator 2 covers the periphery of the outer wall of the neutron detector 1 including the short-side end region of the neutron detector 1 and serves to decelerate neutrons incident from the periphery.

3 is made of an aluminum material and the like, and an outer cylinder configured in a hollow cylindrical shape so as to cover the outer periphery of the neutron moderator 2 along the longitudinal direction of the neutron detector 1, and 4 is one short side of the neutron moderator 2. A disc-shaped upper lid made of aluminum or the like that covers the surface in the hand direction and is sealed, and 5 is a bottom of the disk that is made of aluminum or the like that covers the other short-side surface of the neutron moderator 2 and is sealed. The lid 6 is made of a metal such as stainless steel and has an elongated cylindrical shape with both ends screwed. The lid 6 penetrates through a through hole 2a provided in the longitudinal direction of the neutron moderator 2 and the neutron moderator 2 Rods (rods) 7 for attaching them to each other are nuts (tightening means) for inserting the rods 6 and connecting and fixing the individual neutron moderators 2.

Reference numeral 8 denotes a high voltage cable for supplying (applying) a high voltage to the detector 1, and 9 is a signal cable for taking out a signal detected by the detector by applying a high voltage (voltage). Reference numeral 10 denotes an insulator made of an organic substance containing a large amount of hydrogen, such as polyethylene, having a hollow cylinder cut in half and sandwiching the high-voltage cable 8 and the signal cable 9 therebetween. Reference numeral 11 denotes a screw for fixing the cables 8 and 9 sandwiched between the insulators 10 through the upper lid 4. Reference numeral 12 denotes a screw for fixing the outer cylinder 3 and the upper lid 4, and reference numeral 13 denotes a screw for fixing the outer cylinder 3 and the lower lid 5. Further, the upper lid 4 is provided with a hole 4a through which the high voltage cable 8 and the signal cable 9 of the neutron detector 1 that have passed through the neutron moderator 2 are drawn out. The neutron detector 1 and the neutron moderator 2 are fixed by a cylindrical outer cylinder 3, a disc-shaped upper lid 4 and a lower lid 5. In the drawings, the same reference numerals indicate the same or corresponding parts.

FIG. 2 is an enlarged view of the vicinity of the cable outlet provided in the upper cover 4 of the neutron detector structure shown in FIG. In FIG. 2, the high-voltage cable 8 and the signal cable 9 are connected to the detector 1, pass through the neutron moderator 2, and are drawn out. In the figure, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

FIG. 3 is an external view of a neutron moderator used in the neutron detector structure according to Embodiment 1 of the present invention. In FIG. 3, the through-hole portion 2 a is provided inside the neutron moderator 2, and is provided at two locations parallel to the length direction so as to face the central axis of the neutron moderator 2. The neutron moderator 2 has a hollow part diameter of 80 mm, an outer diameter (outer diameter) of 140 mm, and a length of 200 mm to 400 mm. After a plurality of neutron moderators 2 are stacked in the length direction, the rods 6 are put together in the through-hole part 2a. Inserted and fixed with nut 7 (tightening means). In the figure, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

Next, the overall configuration will be described with reference to FIGS. The total length of the neutron detector structure is about 4500 mm and the outer diameter is 150 mm, excluding the protrusion, and the total length of the neutron detector 1 is about 4000 mm and the outer diameter is 80 mm. Moreover, each length of the neutron moderator 2 attached in piles is 200 to 400 mm, and the outer diameter is 140 mm.

The length of the neutron moderator 2 covering the outer circumference in the short direction of the neutron detector 1 is 100 to 200 mm, the outer diameter is 140 mm on both the upper lid 4 side and the lower lid 5 side, and the neutron detector 1 of the upper lid 4 and the lower lid 5 The thickness in the longitudinal direction is about 40 mm. For example, when the length of the neutron moderator 2 is 400 mm, ten neutron moderators 2 are overlapped, and one on each of the upper lid 4 side and the lower lid 5 side is added. Accordingly, twelve neutron moderators 2 are provided. Further, when the length of the neutron moderator 2 is 200 mm, 20 neutron moderators 2 are stacked, and one each of the upper lid 4 side and the lower lid 5 side is added. Accordingly, 22 neutron moderators 2 are provided. The total length of the high voltage cable 8 and the signal cable 9 of the neutron detector 1 is about 16000 mm.

Next, the operation will be described. FIG. 4 is an equivalent circuit diagram for explaining the relationship between the neutron detector structure according to Embodiment 1 of the present invention and its measurement system. In FIG. 4, a power source capable of applying a voltage of, for example, 1 kilovolt is connected to the high voltage cable 8 of the neutron detector structure, and a current capable of measuring a current of, for example, several picoamperes is connected to the signal cable 9. Connect the meter. The neutron detector 1 and the outer cylinder 3 are insulated by a neutron moderator 2.

FIG. 5 is a block diagram illustrating the relationship between the neutron detector assembly and the neutron source according to Embodiment 1 of the present invention. Medium and fast neutrons incident on the neutron detector structure are decelerated by the neutron moderator 2, converted into thermal neutrons, and detected by the neutron detector 1. Thermal neutrons incident on the neutron detector structure are decelerated as are medium and fast neutrons. When the diameter of the neutron moderator 2 is thick or when the hydrogen content contained in the neutron moderator 2 is large, the thermal neutron loses energy and does not enter the neutron detector 1. Therefore, in order to increase the output signal, the thickness of the neutron moderator 2 is reduced so that the thermal neutrons incident on the neutron detector 1 are increased, and the hydrogen content of polyethylene in the neutron moderator 2 is adjusted to be reduced. This will increase the output signal for thermal neutron detection.

Conversely, if there are fewer thermal neutrons than medium and fast neutrons in advance, the neutron moderator 2 material is changed to one with a high hydrogen content to enhance the moderation effect of medium and fast neutrons, and a neutron detector Increase the output signal.

  As described above, since a plurality of neutron moderators 2 are arranged along the outer periphery of the neutron detector 1, the amount of neutrons incident on the neutron detector 1 can be changed and the neutron detection can be performed by changing the type of the neutron moderator 2. Even if the device 1 is long and bent or distorted due to it, the divided neutron moderator 2 can absorb the bent or distorted material, so that there is an effect of obtaining an easily assembled neutron detector structure.

Embodiment 2. FIG.
A method for increasing the output signal from the neutron detector when there are fewer fast neutrons than thermal neutrons and medium neutrons will be described with reference to FIG. FIG. 6 is an external view of a neutron moderator used in the neutron detector structure according to Embodiment 2 of the present invention. In FIG. 6, 14 is provided inside the neutron moderator 2, and a plurality of them are provided parallel to the central axis of the neutron moderator 2 in the longitudinal direction between the hollow portion and the outer periphery of the neutron moderator 2. This is a through hole (adjustment hole) for neutron moderation. The neutron moderator 2 has a hollow portion diameter of 80 mm, an outer shape of 140 mm, and a length of 200 to 400 mm. After a plurality of neutron moderators 2 are stacked in the length direction, a rod 6 is inserted into the through-hole portion 2a and a nut 7 ( Fastened by fastening means). In the figure, the same reference numerals as those in FIG. 3 denote the same or corresponding parts. Since other configurations and operations are the same as those described in the first embodiment, the description thereof is omitted.

The neutron moderator 2 is provided with a large number of adjustment holes 14 to weaken the effect of slowing down fast neutrons, thereby promoting thermal neutronization of medium speed neutrons and suppressing reduction of thermal neutrons. The diameter of the adjustment hole 14 is 10 mm, and the number of holes is adjusted so that the output signal is increased. In the example shown in FIG. 6, ten adjustment holes 14 are arranged circumferentially. In addition, as shown in FIG. 6, by arranging the adjustment holes 14 evenly around the neutron detector 1, there is an effect that a stable output signal can be detected regardless of the incident direction from the neutron source.

In addition, since the neutron moderator 2 is also installed in the short direction of the neutron detector 1, the detection signal from the neutron source can be properly detected even if the incident direction enters the detector 1 from any direction. There is.

The present invention can be used for a power region neutron detector used outside a pressurized water reactor.

1 is a structural diagram of a neutron detector structure according to Embodiment 1 of the present invention. It is an enlarged view of the cable outlet opening periphery provided in the upper cover of the neutron detector structure by Embodiment 1 of this invention. It is an external view of the neutron moderator used for the neutron detector structure by Embodiment 1 of this invention. It is an equivalent circuit diagram explaining the relationship between the neutron detector structure by Embodiment 1 of this invention and its measuring system. It is a block diagram explaining the relationship between the neutron detector structure by Embodiment 1 of this invention, and a neutron source. It is an external view of the neutron moderator used for the neutron detector structure by Embodiment 2 of this invention.

1 .. Neutron detector 2. Neutron moderator (moderator) 2a ... Through hole (through hole)
3. ・ Outer cylinder 4. ・ Upper lid (first lid) 4a ・ ・ Hole 5 ・ ・ Lower lid (second lid)
6. ・ Rod (rod) 7 ・ ・ Nut (tightening means)
8. High voltage cable (cable) 9. Signal cable (cable)
10..Insulator, 11..Screw 12..Screw 13..Screw 14 .... Adjustment hole (adjustment hole)

Claims (2)

A cylindrical neutron detector whose outer wall is conductive and extending in the longitudinal direction, a cable connected to the neutron detector and applying a voltage to take out a detection signal, and a dielectric provided with a through hole A neutron moderator that decelerates neutrons incident from the surroundings by concentrically overlapping the longitudinal direction and covering the outer wall including the short direction of the neutron detector, and covering the outer circumference in the longitudinal direction of the neutron moderator A conductive outer cylinder, a closed first end of the outer cylinder, and a conductive first lid that draws the cable that has passed through the neutron moderator to the outside from the hole; and A conductive second lid for sealing the other open end of the tube, and a clamping means for inserting and connecting individual neutron moderators by inserting rods into the through-hole portions of the stacked neutron moderators And a neutron detector structure. 2. The neutron detector according to claim 1, wherein a plurality of adjustment holes for adjusting a neutron moderation amount are provided so as to surround the central axis in the longitudinal direction at a dielectric installation position spaced from the central axis in the longitudinal direction of the neutron moderator. Structure.

Images