JP4829052B2 - Manufacturing method of neutron detector - Google Patents

Description

Was inserted into the reactor core relates to the production how neutron detector for measuring the neutron in the core.

  In a nuclear reactor, the reactor power is monitored by measuring the neutron flux with a sensor installed in the core.

  For example, in a boiling water reactor (BWR), the reactor is monitored by a local power range monitor (LPRM), which is a neutron detector installed in the reactor core. The operation is stopped (see Patent Document 1).

  This LPRM sensor is a detector that measures radiation by separating a cathode and an anode with an insulator, applying a voltage to the two, and collecting ionized ions therebetween.

  Specifically, a neutron conversion material that reacts with neutrons to release charged particles is applied to the inner surface of the cathode, the gas between the electrodes is ionized by the charged particles released from the neutron conversion material, and the amount of ionization is measured. (See Patent Document 2).

Normally, this LPRM sensor is a reactor with 1.1 million kW output, and about 43 LPRM detector assemblies in which four sensors are stored along the fuel axis direction are arranged in the core. To monitor.
JP 2001-228282 A Japanese Patent No. 3719748

  It is desired to install such a neutron detector in a gap that is narrower than that of the currently installed reactor fuel. To that end, the diameter of the neutron detector, that is, the diameter of the cathode is further reduced. There is a need to.

  However, when the cathode has a small diameter, it becomes difficult to stably apply the neutron conversion substance to the inner surface of the cathode.

  For example, when the PVD method is used in which plasma is generated in a vacuum, the neutron conversion layer is sputtered with the plasma, and the neutron conversion layer is applied to the inner surface of the anode, reducing the cathode diameter is sufficient to generate the plasma. There was a problem that it was difficult to secure space.

  Usually, a case is provided outside the cathode in order to enclose the ionizing gas in the neutron detector, and the ionizing gas is enclosed in the case. However, in order to reduce the diameter of the neutron detector, it is difficult to adopt such a double cylindrical structure.

The present invention has been made in view of the above problems, and an object thereof is to provide a way to produce a small-diameter neutron detectors.

  In order to solve the above problems, a method for manufacturing a neutron detector according to the present invention includes a cylindrical cathode housed in a body case, a rod-shaped anode disposed in the cathode, and a filling gas inside the body case. In the method of manufacturing a neutron detector, in which a neutron conversion layer that emits charged particles in response to neutrons is provided on the inner peripheral wall of the cathode, the neutron sensitive material is included instead of the anode, and the tip is pointed A discharge electrode having a portion is inserted into the cathode, a voltage is applied to the discharge electrode and the cathode, plasma is generated between the tip of the discharge electrode and the cathode, and the neutron sensitive material of the discharge electrode is sputtered by this plasma. A neutron conversion layer is provided by vapor deposition on the inner peripheral wall of the cathode.

According to the manufacturing how neutron detector according to the present invention, it is possible to manufacture the thin neutron detector.

An embodiment of a method for manufacturing a neutron detector according to the present invention will be described with reference to the accompanying drawings.

[First Embodiment]
First, the manufacturing method of the neutron detector which concerns on this invention, and 1st Embodiment of the neutron detector manufactured by this manufacturing method are described in detail based on FIGS.

  FIG. 1 is a configuration diagram showing a neutron detector 1 of the first embodiment.

  The neutron detector 1 is a neutron detector that is composed of a fission ionization chamber and is generally called a local output region monitor (LPRM).

  As shown in FIG. 1, the neutron detector 1 has a cylindrical main body case 2, and a rod-shaped anode 3 is arranged in the axial direction at the center of the main body case 2, and is cylindrical so as to surround the anode 3. A cathode 4 is arranged. Both ends of the anode 3 are fixed to the cathode 4 by a circumferential positioning insulator 5 so that the circumferential position in the cathode 4 is not shifted. The circumferential positioning insulator 5 also serves as a spacer for the anode 3 and the cathode 4.

  One end of the main body case 2 is closed with a metal end plug 6, and an axial positioning insulator 7 is accommodated between the end plug 6, the anode 3, and the cathode 4. It is fixed so that the position in the axial direction does not shift.

  The main body case 2 is filled with a filling gas 8 such as argon and kept at a high pressure of about several atmospheres in order to shorten the range of particles.

  A signal cable element 9 is inserted into the other end of the main body case 2 and electrically connected to the anode 3 and the cathode 4. A weld 10 is provided between one end of the main body case 2 and the signal cable element 9 so that the filling gas 8 in the main body case 2 does not leak to the outside of the main body case 2.

  The inner peripheral wall 11 of the cylindrical cathode 4 is provided with a neutron conversion layer 12 made of a neutron sensitive material such as uranium that reacts with neutrons to cause a nuclear reaction and releases charged particles.

  When neutrons generated in the core enter the neutron conversion layer 12 of the neutron detector 1, the neutrons are converted into charged particles. The neutron detector 1 measures the neutrons by detecting the charged particles A with the anode 3 and the cathode 4.

  A method for applying the neutron conversion layer 12 to the inner peripheral wall 11 of the cathode 4 in the neutron detector 1 will be described.

  FIG. 2 is a configuration diagram of a neutron conversion layer coating apparatus 13 for coating the neutron detector 1 with the neutron conversion layer 12.

  The neutron conversion layer coating apparatus 13 includes an elongated rod-shaped or pencil-shaped discharge electrode 15 having a protruding tip 14 at the tip, and a cylindrical or sleeve-shaped insulator that electrically insulates the discharge electrode 15 and the cathode 4. 16, voltage applying means 17 for applying a voltage between the discharge electrode 15 and the cathode 4, and when the discharge electrode 15 is inserted into the cathode 4 of the neutron detector 1, the discharge electrode 15 and the insulator 16 are connected to the cathode 4. It is comprised from the electrode moving means 18 which moves to an axial direction inside. In addition, the periphery of the discharge electrode 15 is covered with the insulator 16, and only the tip portion 14 of the discharge electrode 15 is exposed from the insulator 16.

  The discharge electrode 15 may be formed by coating the entire surface or a part of the surface with a neutron sensitive substance B such as boron or lithium that reacts with neutrons to generate charged particles A or uranium that causes fission. The whole may be made of these materials. The material of the insulating material is alumina, silica, or the like.

  In the neutron conversion layer coating apparatus 13, when the atmosphere or the distance between the tip 14 of the discharge electrode 15 and the cathode 4 satisfies the plasma generation conditions, the gas between the tip 14 of the discharge electrode 15 and the cathode 4 is plasma. Turn into. The neutron sensitive material B of the discharge electrode 15 is sputtered by the plasma P, and the neutron conversion layer 12 is applied to the inner surface of the cathode 4.

  FIG. 3 is an operation explanatory diagram when the neutron conversion layer 12 is applied to the cathode 4 of the neutron detector 1.

  As shown in FIG. 3, a rod-shaped discharge electrode 15 having a conical or polygonal conical tip 14 at the tip is inserted into the cathode 4. If there is a space where the plasma P can be stably generated between the cathode 4 and the discharge electrode 15, the plasma P is generated and the accelerated charged electrons A collide with the discharge electrode 15 and are applied to the material or the surface thereof. The neutron sensitive material B is sputtered, and the sputtered neutron sensitive material B is deposited on the inner peripheral wall 11 of the cathode 4 to generate the neutron conversion layer 12.

  At this time, since the plasma P is generated only around the tip portion 14 not covered with the insulator 16 of the discharge electrode 15, the discharge electrode 15 is scanned in the cathode 4 in the axial direction by the electrode moving means 18. The neutron conversion layer 12 can be applied to an arbitrary position in the cathode 4.

  By providing the tip portion 14 at one end of the discharge electrode 15 in this way, it becomes possible to secure a gap between the tip portion 14 of the discharge electrode 15 and the cathode 4 even if the cathode 4 has a small diameter. A stable plasma P can be generated between the electrode 15 and the cathode 4 to generate a stable neutron conversion layer 12.

  FIG. 4 is an operation explanatory diagram when a conventional cylindrical discharge electrode 15 </ b> A that does not have the tip portion 14 is used. In FIG. 4, when the inner diameter of the cathode 4 becomes narrower, a space for stably generating the plasma P cannot be secured, whereas in FIG. 3 corresponding to the present invention, it is necessary to always generate the plasma P stably. A plasma space can be secured.

  That is, the conventional neutron conversion layer coating method (FIG. 4) could not be applied unless the inner diameter of the cathode is 5 mm or more, but according to the neutron conversion layer coating method of the first embodiment (FIG. 3), Even when the inner diameter of the cathode is 4 mm or less, a stable neutron conversion layer can be applied.

  Further, instead of using the discharge electrode 15 itself as a sputtering target, the neutron sensitive material B may be separately installed in the plasma P portion.

  That is, as shown in FIG. 5, in the neutron conversion layer coating apparatus 13A, the discharge electrode 15 is not produced by a neutron sensitive substance B such as uranium, or the discharge electrode 15 is not coated with the neutron sensitive substance B. The neutron conversion material 19 containing the neutron sensitive substance B and the neutron conversion material moving means 20 for moving the neutron conversion material 19 in the cathode 4 together with the discharge electrode 15 in the axial direction may be provided separately.

  Further, as shown in FIG. 6, when applying the neutron sensitive substance B in the neutron conversion layer coating apparatus 13B, particles are injected into the cathode 4 from the particle generating apparatus 21 that generates particles such as ions and electrons. May be. By causing the particles to directly collide with the discharge electrode 15 using the particle generator 21, the frequency of sputtering can be improved and the time required for applying the neutron conversion layer 12 can be shortened.

  According to the first embodiment, even if the cathode 4 has a small diameter, the neutron conversion layer 12 can be applied to the inner peripheral wall 11 of the cathode 4, and a small neutron detector 1 can be provided. .

[Second Embodiment]
Next, a second embodiment of the neutron detector 1 and the manufacturing method thereof according to the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the structure same as 1st Embodiment, and the overlapping description is abbreviate | omitted.

  FIG. 7 is a configuration diagram showing a neutron detector 1A of the second embodiment.

  In the neutron detector 1A of the second embodiment, the main body case 2 used in the neutron detector 1 of the first embodiment is omitted by making the cathode 4A have a pressure resistant structure.

  That is, as shown in FIG. 7, the neutron detector 1A has a cylindrical or sleeve-like cathode 4A having pressure resistance, and a rod-like anode 3 is disposed in the center of the cathode 4A. Both ends of the anode 3 are fixed to the cathode 4A by a circumferential positioning insulator 5 so that the circumferential position in the cathode 4A is not shifted.

  One end of the cathode 4A is closely sealed by welding with a metal end plug 6, and an axial positioning insulator 7 is accommodated between the end plug 6, the anode 3 and the cathode 4A, whereby the anode 3 and the cathode It is fixed so that the axial position of 4A does not shift.

  A filling gas 8 such as argon is sealed inside the cathode 4A, and is kept at a high pressure of about several atmospheres in order to shorten the range of particles.

  A signal cable element 9 is inserted into the other end of the cathode 4A, and is electrically connected to the anode 3 and the cathode 4A. A welding portion 10 is provided between the cathode 4 </ b> A and the signal cable element 9 so that the filling gas 8 in the main body case 2 does not leak to the outside of the main body case 2.

  A neutron conversion layer 12 is provided on the inner peripheral wall 11 of the cylindrical cathode 4A.

  In a conventional neutron detector having a main body case, the outer diameter is 8 mm or more. However, according to the second embodiment, the outer diameter can be reduced by the amount of the main body case. It becomes possible to make the outer diameter of the detector 1A 6 mm or less.

  According to the second embodiment, the diameter of the neutron detector 1A can be further reduced by the amount of the main body case 2.

[Third Embodiment]
Next, a third embodiment of the neutron detector 1 and the manufacturing method thereof according to the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the structure same as 1st Embodiment and 2nd Embodiment, and the overlapping description is abbreviate | omitted.

  FIG. 8 is a configuration diagram showing a neutron detector 1B of the third embodiment.

  The neutron detector 1B of the third embodiment is formed by separating a plurality of neutron conversion layers 12a to 12c in the axial direction in the neutron detector 1A of the second embodiment and using the optical fiber 22 instead of the anode 3. Is.

  That is, as shown in FIG. 8, the neutron detector 1B has a cylindrical cathode 4A having pressure resistance, and the optical fiber 22 is disposed so as to penetrate both ends of the cathode 4A in the central portion of the cathode 4A. The

  The optical fiber 22 is welded and fixed at both ends of the cathode 4A, and the welded portion 10 prevents leakage of the internal filling gas 8 to the outside.

  A plurality of neutron conversion layers 12a to 12c are provided on the inner peripheral wall 11 of the cylindrical cathode 4A.

  When the neutron conversion layer coating apparatus 13 of the first embodiment is used, the inner peripheral wall of the cathode 4A is obtained by applying a voltage at an arbitrary axial position while moving the discharge electrode 15 in the axial direction in the cathode 4A. Any number of neutron conversion layers 12a to 12c can be provided at any one of 11 positions.

  FIG. 8 shows an example in which three neutron conversion layers 12a to 12c are applied to the inner peripheral wall 11 of the cathode 4A at intervals.

  The neutron detector 1 can measure the neutron distribution by distributing the neutron conversion layers 12a to 12c at multiple points and identifying and reading a signal due to a neutron reaction from each position.

  That is, it installs so that the scintillation light may generate | occur | produce in the optical fiber 22 with the charged particle which reacted with the neutron in the neutron conversion layers 12a-12c and was discharge | released. From this difference in detection time of the scintillation light, the generation position of the scintillation light can be specified, and finally the neutron reaction position can be identified.

  In the third embodiment, the method of detecting the position with light using the optical fiber 22 has been described. However, a method of measuring with gas scintillation light of a gas sealed in a tube, or a plurality of electrical electrodes (anode electrodes) ), And a method using signal processing for identifying each position may be substituted.

  According to the third embodiment, it is possible to provide a neutron detector 1B having a small-diameter distribution measurement type by applying the neutron conversion layers 12a to 12c separately at arbitrary positions in the cathode 4A. .

The block diagram which shows 1st Embodiment of the neutron detector which concerns on this invention. The lineblock diagram showing the neutron conversion layer coating device of a 1st embodiment. Operation | movement explanatory drawing which shows the neutron detector of 1st Embodiment. Operation | movement explanatory drawing which shows the neutron detector of 1st Embodiment. The block diagram which shows the other Example of 1st Embodiment. The block diagram which shows the other Example of 1st Embodiment. The block diagram which shows 2nd Embodiment of the neutron detector which concerns on this invention. The block diagram which shows 3rd Embodiment of the neutron detector which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1A, 1B Neutron detector 2 Main body case 3 Anode 4, 4A Cathode 5 Circumferential positioning insulator 6 End plug 7 Axial positioning insulator 8 Filling gas 9 Signal cable element 10 Welding part 11 Inner peripheral walls 12, 12a-12c Neutron conversion layer 13 Neutron conversion layer coating device 14 Pointed portion 15, 15A Discharge electrode 16 Insulator 17 Voltage applying means 18 Electrode moving means 19 Neutron converting material 20 Neutron converting material moving means 21 Particle generator 22 Optical fiber A Charged particle B Neutron Sensitive substance P plasma

Claims (3)

A cylindrical cathode is housed in the main body case, and a rod-shaped anode is axially arranged in the cathode. The main body case is filled with a filling gas, and the inner peripheral wall of the cathode is charged by reacting with neutrons. In the method of manufacturing a neutron detector provided with a neutron conversion layer that emits particles,
Instead of the anode, a discharge electrode containing a neutron sensitive material and having a tip at the tip is inserted into the cathode,
A voltage is applied to the discharge electrode and the cathode to generate plasma between the tip of the discharge electrode and the cathode,
A method for producing a neutron detector, characterized in that a neutron conversion layer is provided by sputtering a neutron sensitive substance of a discharge electrode by this plasma and depositing it on an inner peripheral wall of a cathode.   The neutron detector manufacturing method according to claim 1, wherein when applying a voltage to the discharge electrode and the cathode, the periphery of the anode is covered with an insulator, and only the tip of the anode is exposed from the insulator. A cylindrical cathode is housed in the main body case, and a rod-shaped anode is axially arranged in the cathode. The main body case is filled with a filling gas, and the inner peripheral wall of the cathode is charged by reacting with neutrons. In the method of manufacturing a neutron detector provided with a neutron conversion layer that emits particles,
Instead of the anode, a discharge electrode containing a neutron sensitive material and having a tip at the tip is inserted into the cathode,
A method for producing a neutron detector, comprising: providing a neutron conversion layer by discharging charged particles toward the discharge electrode, sputtering the neutron sensitive material of the discharge electrode, and depositing the neutron sensitive material on the inner peripheral wall of the cathode.

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