JPH06235771A - Multiple-element type neutron detector - Google Patents

Abstract

PURPOSE:To enhance operating efficiency of a reactor by improving reliability for monitoring the reactor and then relaxing the restriction im terms of operation of the reactor due to the limitation in the number of allowable bypasses and then reinforce monitoring by achieving the abnormality diagnosis function of a neutron detection element. CONSTITUTION:A plurality of neutron detection positions are set at different positions in axial direction within a protection tube 12 and then a plurality of neutron detection elements 14 are incorporated and multiplexed, which can be applied to a local output detector. Also, the neutron detection positions can also be applied to a detector for starting and that for increasing output. A neutron detection element is in ionization box format with a column-shaped anode 16 and a cylindrical cathode 18 surrounding it and a plurality of neutron detection elements are laid out vertically in one piece or they may be laid out in parallel in one piece. By comparing the signals of the multiplexed neutron detection elements, abnormality diagnosis can be made.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a neutron detector used in various nuclear reactors. More specifically, it is a multi-element neutron detector in which a plurality of neutron detector elements are incorporated and multiplexed at one neutron detector position. It relates to the device. Currently, the boiling water reactor (BWR) and the new converter Fugen power plant are the nuclear reactors that use the neutron detector in the reactor. There are various types of neutron detectors, such as a startup detector (SUM), an output increase detector (PUM), and a local output detector (LPM) according to the purpose of use. It can be applied to a detection device and a system using the same.

[0002]

2. Description of the Related Art A new converter Fugen power plant is a pressure tube type nuclear reactor, which uses light water as a coolant and heavy water as a moderator. The thermal neutron flux in the reactor can be detected by inserting a neutron detector into the heavy water from the upper part of the calandria tank.

The local output detector used here sets four neutron detection positions at different axial positions in the protective tube near the tip (from the top, A, B, C and D are distinguished from each other). ), And one neutron detector is incorporated at each neutron detection position to form an integrated structure. The region in the nuclear reactor is divided into four, and four local output detector assemblies having such a structure are distributed in each region at a suitable position in the radial direction, four in total in each region. Therefore, a total of 16 (4 x
There will be a local output neutron detector of 4).
Its purpose is to monitor the neutron flux (equivalent to reactor power) during operation.

Further, the starting detector and the output increasing detector each have a structure in which one neutron detector is incorporated. The former has four and the latter has six, and these are also radial in the reactor. Are distributed at appropriate positions.

Each of the neutron detectors used for these has an anode in the center and a cathode in the periphery, and the neutron-sensitive substance (UO) is attached to the electrodes.
It is a small ionization chamber type coated with ₂ ), and the inside is filled with ionized gas. These are composed of materials that can be used at high temperatures and have little radiation damage.

For example, detection signals from a total of 16 (4 × 4) local output detectors distributed in each region of the reactor are connected to a region output detector (RPM) of each region. There is. The indication value of this area output detection device is obtained by multiplying the average value of the detection signals from the 16 local output detectors by a necessary coefficient. The coefficient to be multiplied is regularly calibrated and is a numerical value that accurately represents the output of the area. In the reactor protection circuit, a limit value is set for the area output of each area, and in the case of the Fugen power plant, 120% at rated operation.
Is.

[0007]

However, since the neutron detector is exposed to the high radiation environment in the reactor, no matter how carefully it is designed and manufactured, defects will occur during use. Is not nothing. If it becomes unusable due to a failure during operation, it will be bypassed (the signal will be cut off). When a certain neutron detector is bypassed, it becomes impossible to locally monitor the neutron flux in the reactor at the neutron detection position. Therefore, the allowable number of bypasses has a certain limit. This is because the integrity of the fuel may not be guaranteed at the time of an accident depending on the bypassing method or when the thermal limitation of the fuel is severe.

Therefore, when bypassing beyond the allowable number, it is necessary to take measures such as lowering the scrum setting value of the area output detecting device. However, lowering the scrum set value of the area output detection device means that there is no operational margin, and even if a small amount of disturbance is applied, the reactor may shut down without being necessary. This is not desirable.

Also, regarding the start-up detection device or the output increase detection device, the allowable number of bypasses due to a failure is determined, and if even one of them fails, it is necessary to take measures such as replacement.

It is an object of the present invention to improve the reliability of reactor monitoring and to alleviate the restrictions on the operation of the reactor caused by the limitation on the allowable number of bypasses, thereby increasing the operating efficiency of the reactor. It is to provide a neutron detector capable of Another object of the present invention is to provide a method of using the neutron detection device, having a function of diagnosing an abnormality of a neutron detection element, and enhancing monitoring.

[0011]

The present invention provides a detector assembly in which a plurality of neutron detection positions are set at different axial positions in a protection tube, and a neutron detector is installed at each neutron detection position. It is a multi-element type neutron detection device in which a plurality of neutron detection elements are incorporated and multiplexed at neutron detection positions at or above locations. This can be applied to a local output detection device. When there is only one neutron detection position, a plurality of neutron detection elements are incorporated and multiplexed at the neutron detection position. This can be applied to the activation detection device and the output increase detection device.

In these multi-element type neutron detecting devices, each neutron detecting element is of an ionization chamber type having a cylindrical anode located at the center and a cylindrical cathode facing it, and the neutron detecting element is A plurality of columns may be arranged in a row to be integrated, or a plurality of columns may be juxtaposed to form a columnar bundle. In addition, each neutron detection element has a fan-shaped cross section (including a semi-circular cross section), a small ionization chamber type with a central anode and a fan-shaped cylindrical cathode facing it, and multiple neutron detection elements are arranged side by side. It is also possible to adopt a structure integrated in a cylindrical shape.

Further, the present invention is a multi-element type neutron which compares signals from a plurality of multiplexed neutron detection elements with each other to diagnose normality / abnormality and issues an alarm when one of the indicated values indicates abnormality. This is a method for diagnosing an abnormality in a detection device. Furthermore, the present invention inputs the signals from the multiple neutron detection elements that have been multiplexed to each input terminal of the averaging processing device and performs averaging processing, and the average value is used as an instruction signal of the neutron detector, and an abnormality occurs. At that time, the signal from the neutron detection element in which the abnormality has occurred is blocked, and the signal from the normal neutron detection element remains input to the original input end of the averaging processing device, from the neutron detection element in which the abnormality has occurred. It is a bypass processing method of a multi-element type neutron detection apparatus which supplies the averaging processing apparatus instead of a signal.

[0014]

Function: A detection signal is output from a plurality of neutron detection elements provided at the same neutron detection position. For example, in the case of a local output detection device, the detection signal from each neutron detection element is input to the area output detection device. Therefore, when the detection signals of a plurality of neutron detection elements at the same neutron detection position are compared, if all are normal, the same detection signal should be output. Therefore, the abnormality can be diagnosed by comparing the detection signals. If an abnormality occurs in one neutron detection element, it will be bypassed, but by using another normal neutron detection element, it is possible to detect the neutron flux at that position and continue to properly monitor the reactor output. it can.

[0015]

1 shows an embodiment of a multi-element type neutron detector according to the present invention, which is an example applied to a detector assembly of a local output detector. This is a structure to be inserted into the calandria tank of the new type converter from above, and four neutron detection positions are arranged at different positions in the axial direction inside the protection tube 12 below the guide tube 10 (A to D) is set, and two neutron detection elements 14 are arranged in a row and integrated with each other at their neutron detection positions. Each neutron detection element 14
Is a small ionization chamber type having a cylindrical anode 16 located in the center and a cylindrical cathode 18 surrounding the anode 16 at a distance so as to face it. The opposing surfaces of the anode 16 and the cathode 18 are coated with uranium (UO ₂ ) which is a neutron-sensitive substance, and the space 19 between them is filled with ionized gas.

FIG. 2 shows another embodiment of the present invention.
Since the basic configuration of each neutron detection element 14 may be the same as that in FIG. 1, corresponding members are designated by the same reference numerals, and description thereof will be omitted. This embodiment is an example in which n neutron detecting elements 14 (n is an integer of 3 or more) are arranged in series and integrated.

FIG. 3 shows still another embodiment of the present invention. (A) shows its appearance, and its X ₁ -X ₁ cross section is shown in (b). This is a configuration in which two neutron detection elements 24 are arranged side by side. The neutron detection element 24 has a semicircular cross section, a semicylindrical anode 26 located in the center, and a semicylindrical cathode 28 surrounding the semicylindrical anode 26. This is a structure in which (UO ₂ ) is coated, and the space 29 between them is filled with ionized gas. Two of them are combined back-to-back and integrated into a columnar shape as a whole.

FIG. 4 shows another embodiment of the present invention.
(A) shows its appearance, the X ₂ -X ₂ section (b)
Shown in. This is a configuration in which n neutron detection elements 34 are juxtaposed. The neutron detection element 34 has a fan-shaped cross section, and an anode 36 at the center thereof and a fan-shaped cylindrical cathode 3 surrounding the anode 36.
Eight. It is the same that the opposing surface was coated with uranium (UO ₂ ) which is a neutron-sensitive substance, and the space 39 between them was filled with an ionized gas. N pieces of them are combined so that the required positions are matched, and are integrated so as to form a columnar shape as a whole.

Next, an example of system configuration in the case of using a local output detection device incorporating a two-element type neutron detection element is shown in FIG.
Shown in. Two neutron detectors (LPM ₁ , LPM ₂ )
The detection signals from 50a and 50b are guided to the abnormality diagnosis processing device 52, respectively. Both detection signals are input to the area output detection device (RPM ₁ ) 58 via the bypass processing device 54 and the averaging processing device 56. The bypass processor 54 normally connects the detection signals to the input terminals of the averaging processor 56 corresponding to the straight lines by switches S ₁ and S ₁ .
₂ and a switch S ₁₂ separating the two signal lines. The output from each area output detection device 58 is input to the entire area output detection device (TPM) 60, and a trip signal is generated when an abnormality occurs. The abnormality diagnosis processing device 52 may be connected in parallel to the system as shown in the figure, or may be connected in series to the system.

In the abnormality diagnosis processing device 52, the detection signals from the two neutron detection elements 50a and 50b are constantly monitored,
The two are compared, and if they are almost the same, it is determined that they are operating normally. Both detection signals are averaged by the averaging processor 56. In the abnormality diagnosis processing device 52, when both detection signals are compared, if one of the indicated values indicates abnormality, an alarm is issued. Then, in the bypass processing device 54, the switch S ₁ of the signal line in which the abnormality has occurred (for example, if there is an abnormality in the neutron detection element 50a, that signal line) is opened,
The switch S ₁₂ is closed. As a result, the normal detection signal is also connected to the signal line in which the abnormality has occurred and is applied to both input terminals of the averaging processing device 56. This is to prevent the value indicated by the area output detection device 58 from fluctuating excessively when one of them is bypassed. Switch S ₁₂
Opening and closing may be performed manually or automatically. In the automatic case, the abnormality detection signal from the abnormality diagnosis processing device 52 is used.

The above is the case where the neutron detection element is doubled, but the case where the number of the neutron detection elements is three or more (when it is three or more) can be similarly configured. In any case, even if the indicated value of each neutron detection element suddenly changes due to a failure or the like by averaging by the averaging processing device in this way, the influence is 1
/ N.

Although the above-mentioned example is the case of the local output detecting device, it goes without saying that the present invention can be applied to the starting detecting device and the output increasing detecting device. When the local output detection device is multiplexed, it is not always necessary to multiplex the neutron detectors at all detection positions. For example, only one set at the top may be used, or two sets may be used. Only the positions important for safety may be multiplexed.

[0023]

As described above, the present invention has a configuration in which a plurality of neutron detection elements are incorporated at the neutron detection position and is multiplexed. Therefore, for example, in the case of a local output detection device, the operation is caused by the limitation on the allowable bypass number. It is possible to significantly relax the constraint of. For example, conventionally, since four local output detectors were used in the axial direction, when one local output detector failed, local output was not monitored for that part. The invention allows one fault to be covered by another neutron detection element. By multiplexing such neutron detection elements, the reliability of neutron flux (corresponding to reactor output) monitoring can be improved.

By this multiplexing, the allowable number of bypasses of the local output detector can be increased more than ever, and the scrum set value of the area output detector can be relaxed more than ever. Further, even when the thermal limit value of the fuel during operation is severe, it is not necessary to change the scrum setting value, and the operating margin can be increased.

If the present invention is also used for the start-up detector and the output-increasing detector, even if the detector is bypassed due to a failure or the like, it is not necessary to replace it immediately and the operation efficiency can be improved.

In the present invention, the abnormality diagnosis is automatic (online) by comparing the indicated values by a plurality of neutron detection elements.
Can be done with. Further, since the detection signals from the plurality of neutron detection elements are processed by the averaging processing device, the influence at the time of failure of the neutron detection elements can be reduced to 1 / n of the conventional one. Further, in the case of bypassing one neutron detection element, by inputting a normal signal to the bypass detector side, it is possible to eliminate the influence when the detection element is bypassed.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of a multi-element type neutron detection device according to the present invention.

FIG. 2 is an explanatory diagram of a main part showing another embodiment of the present invention.

FIG. 3 is an explanatory diagram of a main part showing still another embodiment of the present invention.

FIG. 4 is an explanatory diagram of a main part showing another embodiment of the present invention.

FIG. 5 is an explanatory diagram of a processing system according to the present invention.

[Explanation of symbols]

 12 Protective tube 14 Neutron detection element 16 Anode 18 Cathode

Claims (6)

[Claims] 1. A detector assembly in which a plurality of neutron detection positions are set at different axial positions in a protective tube, and a local output detector is installed at each neutron detection position, and at least one or more neutron detection positions are provided. , A multi-element neutron detector characterized in that a plurality of neutron detection elements are incorporated and multiplexed. 2. A neutron detection device having a detector for starting or increasing output at a neutron detection position in a protection tube, wherein multiple neutron detection elements are incorporated at the neutron detection position and multiplexed. Type neutron detector. 3. The neutron detection element according to claim 1 or 2, wherein each neutron detection element is an ionization chamber type having a cylindrical anode located at the center and a cylindrical cathode facing the anode, and a plurality of neutron detection elements are provided. A multi-element type neutron detector that has a structure in which individual tandems are arranged in a row. 4. The ionization chamber according to claim 1 or 2, wherein each neutron detection element has a circular cross section, a semicircular cross section, or a fan shape, and each has a central anode and a cylindrical or fan-shaped cylindrical cathode facing it. A multi-element type neutron detection device having a structure in which a plurality of neutron detection elements are juxtaposed and combined in a cylindrical shape to be integrated. 5. A multi-element for diagnosing normality / abnormality by comparing signals from a plurality of multiplexed neutron detection elements according to claim 1 or 2 and issuing an alarm when one of the indicated values indicates abnormality. Type neutron detector abnormality diagnosis method. 6. The signals from the multiple neutron detection elements according to claim 1 or 2 are input to the respective input terminals of the averaging processing device to perform averaging processing, and the average value thereof is measured by the neutron detector. As an instruction signal, when an abnormality occurs, the signal from the neutron detection element in which the abnormality has occurred is interrupted, and the signal from the normal neutron detection element is input to the original input end of the averaging processing device, and an abnormality occurs. A bypass processing method for a multi-element type neutron detector, which is supplied to the averaging processor as a substitute for a signal from the neutron detector.