JP2013217811A - Internal state observation method and internal state observation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately observe an internal state inside a hard-to-approach object from the outer side.SOLUTION: An internal state observation device 10 includes: a plurality of muon detectors 11a and 11b disposed at positions facing each other across an object on the outside of the object; a coincidence counting circuit for counting coincidence of muon strength detected in the muon detectors 11a and 11b on both side faces of the object; a straight line calculation unit for calculating a straight line connecting the muon detectors that supply a coincidence count result on the basis of an installation position relationship of the respective muon detectors 11a and 11b; a strength correction unit for correcting the coincidence count result of the muon strength by an angle to the horizontal direction of the straight line; and a density distribution calculation unit for calculating the density distribution of an inherent object inside the object by performing tomography three-dimensional reconstruction using the muon strength counted in the coincidence count circuit and the straight line calculated in the straight line calculation unit.

Description

  The present invention relates to an internal state observation method and an internal state observation device.

  If the reactor is damaged due to a serious accident and the core melts, the melted core fuel may reach the bottom of the reactor pressure vessel, or may elute outside the reactor pressure vessel and reach the containment vessel. . In such a case, the radiation dose in the reactor building increases, making it difficult for workers to approach and easily observe the inside.

  Observing the conditions inside the reactor pressure vessel or the containment vessel is important information for the purpose of converging the accident. However, it takes a very long period of time for the conditions for observing the internal state to be met by gradually decontaminating the reactor building and proceeding with shielding measures.

  Meanwhile, the means for monitoring the state of the reactor containment vessel and further the reactor pressure vessel is based on the monitoring of the ambient temperature and radiation dose, but the number of observation points for such information is limited.

  For this reason, as a means of observing the internal state of a large structure such as a nuclear reactor, a particle beam such as a highly permeable muon is observed, the direction of transmission is specified and the amount of transmission is measured. A method of performing density distribution and tomographic image reconstruction is conceivable.

  Patent Document 1 discloses a technique for observing an internal structure by arranging a plurality of position sensitive detectors on the side of a large structure and measuring muons penetrating the large structure.

  Non-Patent Document 1 also shows an example in which the amount of wear of bricks inside a blast furnace is evaluated by a similar measuring device.

Japanese Patent No. 4106445

Internal estimation of huge structures using cosmic ray muons, Journal of the Japan Society of Mechanical Engineers, Vol. 114, p4

  As mentioned above, when a serious accident occurs in the reactor and it is necessary to observe the internal state of the reactor containment vessel or reactor pressure vessel, the inside of the containment vessel that requires observation is relatively wide, and In the inside, a portion where the structure can be almost specified and a portion where the structure is not substantially overlapped.

  Thus, for example, when observing the internal state of an object such as a reactor containment vessel or a reactor pressure vessel, it is necessary to specify the transmission direction of muons with high accuracy. A detector that specifies the muon transmission direction, such as the position sensitive detector in the above-mentioned document example, is useful. For example, in order to observe the structure inside the reactor building, the transmission direction should be specified with higher accuracy. Is required.

  Therefore, an object of the present invention is to provide an internal state observation method and an internal state observation device that can accurately observe an internal state in an object from the outside.

  In order to achieve the above-described object, the present invention is an internal state observation device for observing an internal object in an object from the outside of the object, and is disposed outside the object and at positions facing each other with the object interposed therebetween. A plurality of muon detectors installed, a coincidence counting circuit for simultaneously counting muon intensities detected by the muon detectors on both sides of the object, and the simultaneous positions based on the installation positional relationship of the muon detectors. The line calculation unit that calculates a straight line connecting the muon detectors that gives the counting result, the intensity correction unit that corrects the coincidence result of the muon intensity according to the angle of the line with respect to the horizontal direction, and the coincidence counting circuit By performing tomography three-dimensional reconstruction using the muon intensity obtained and the straight line calculated by the straight line calculation unit, the density distribution of the inherent object in the object A calculation for the density distribution calculation unit, characterized in that it comprises a.

  The present invention also provides a correction data maintenance step for collecting a relationship between an incident angle and an incident intensity of a muon, and an external side surface of the object in an internal state observation method for observing an internal object in the object from the outside of the object. A detector installation step for installing muon detectors at positions facing each other, a counting step for performing coincidence measurement by each muon detector, and a straight line connecting the muon detectors that give the coincidence result is calculated. A straight line calculating step, an intensity correcting step for correcting the coincidence result of the muon intensity according to an angle of the straight line with respect to a horizontal direction, a muon intensity counted by the coincidence circuit, and a straight line calculated by the straight line calculating unit. And the tomographic three-dimensional reconstruction is used to calculate the density distribution for calculating the density distribution of the inherent object in the object. A calculation step, and having a.

  According to the present invention, it is possible to accurately observe the internal state of an object from the outside.

It is an elevation sectional view showing the state where the 1st embodiment of the internal state observation device concerning the present invention was arranged outside the reactor building. It is a perspective view which shows arrangement | positioning of the muon detector of 1st Embodiment of the internal state observation apparatus which concerns on this invention. It is a block diagram which shows the structure of the muon detection circuit of 1st Embodiment of the internal state observation apparatus which concerns on this invention. It is a block diagram which shows the whole structure containing the signal processing of 1st Embodiment of the internal state observation apparatus which concerns on this invention. It is a flowchart which shows the internal state observation method using 1st Embodiment of the internal state observation apparatus which concerns on this invention. It is a perspective view of the muon detector panel in 2nd Embodiment of the internal state observation apparatus which concerns on this invention. It is an elevation sectional view showing the state where the 3rd embodiment of the internal state observation device concerning the present invention was arranged outside the reactor building. It is an elevation sectional view showing the state where the 4th embodiment of the internal state observation device concerning the present invention was arranged outside the reactor building.

  Hereinafter, embodiments of an internal state observation method and an internal state observation device according to the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

[First embodiment]
FIG. 1 is an elevational sectional view showing a state in which the first embodiment of the internal state observation apparatus according to the present invention is arranged outside the reactor building. FIG. 2 is a perspective view showing the arrangement of the muon detector of the present embodiment.

  In the reactor pressure vessel 1, there are a core 3 and other inclusions 3. The reactor pressure vessel 1 is stored in a reactor containment vessel 2. Further, the reactor containment vessel 2 is accommodated in the reactor building 4. Further, the reactor building 4 is covered with a reactor building cover 5 around the reactor building 4.

  The internal state observation device 10 includes a first internal state observation device 10a and a second internal state observation device 10b. The first internal state observation device 10a includes a first muon detector 11a and a first muon detector installation unit 15a. The second internal state observation device 10b includes a second muon detector 11b and a second muon detector installation unit 15b.

  A first muon detector installation part 15a is provided in the vicinity of one side surface of the reactor building cover 5, and a first muon detector 11a is provided in the first muon detector installation part 15a. In addition, a second muon detector installation portion 15b is provided in the vicinity of the opposite side surface across the reactor building cover 5, and the second muon detector installation portion 15b has a second muon detector. 11b is arranged.

  The first muon detector 11a and the second muon detector 11b are preferably plural as shown in FIGS. However, the number of the first muon detector 11a and the second muon detector 11b need not be the same.

  The first muon detector 11a and the second muon detector 11b are installed for the purpose of detecting muon particles. As the first muon detector 11a and the second muon detector 11b, a plastic scintillator or the like is suitable.

  Muon particles are highly permeable particle beams that react with the atmosphere after high-energy primary cosmic rays reach the atmosphere and then drop to the ground. Unlike neutrinos, detection is relatively easy because of the charge. Also, the amount of particle beam and the average energy, that is, the transmission power, gradually change depending on the incident angle formed between the horizontal direction and the horizontal direction when the muon falls on the ground.

  The reactor building 4 is several tens of meters in both width and height. Now, the distance between the first muon detector 11a and the second muon detector 11b placed on both sides of the reactor building cover 5 is 40 m, and the first muon detector 11a and the second muon detector 11b If one side of the sensitive part is 20 cm, the width of the muon incident direction detected by the first muon detector 11a and the second muon detector 11b on both sides is about 0.3 degrees. Thus, by arranging the first muon detector 11a and the second muon detector 11b on both side surfaces outside the reactor building 4, the incident direction can be specified with very high accuracy.

  FIG. 3 is a block diagram showing the configuration of the muon detection circuit 30 of the present embodiment.

  The muon detection circuit 30 includes a first delay circuit 31a, a second delay circuit 31b, a first coincidence circuit 32a, and a second coincidence circuit 32b.

  The first delay circuit 31a receives the output of the first muon detector 11a as an input, and outputs the input signal with a predetermined delay time. Similarly, the second delay circuit 31b receives the output of the second muon detector 11b and outputs the input signal with a predetermined delay time.

  The first coincidence circuit 32a receives the output signal of the first muon detector 11a and the output signal of the second delay circuit 31b as inputs, and receives these inputs within a predetermined time difference that can be regarded as simultaneous. Simultaneous counting is performed as a simultaneous signal. The second coincidence circuit 32b receives the output signal of the second muon detector 11b and the output signal of the first delay circuit 31a as inputs, and receives these inputs within a predetermined time difference that can be regarded as simultaneous. In addition, simultaneous counting is performed as a simultaneous signal.

  Here, the delay time is a time shorter than the predetermined time difference that can be regarded as simultaneous, and the two signals input to the first coincidence circuit 32a and the second coincidence circuit 32b are different signals. It is set to a time longer than the shortest time that can be discriminated as a circuit.

  In order to prevent a situation in which simultaneously generated signals are not detected in a circuit when a delay time is not set, one of them is artificially delayed and received as two signals to ensure detection. effective.

  FIG. 4 is a block diagram showing an overall configuration including signal processing according to the present embodiment.

  The outputs of the first muon detector 11 a and the second muon detector 11 b are input to the muon detection circuit 30. The contents of the processing in the muon detection circuit 30 are as described in the explanation of FIG.

  The first muon detector 11a is disposed on the first muon detector panel 20a, and the second muon detector 11b is disposed on the second muon detector panel 20b. Position signals of the instrument panel 20a and the second muon detector panel 20b are input to the straight line calculation unit 40.

  The straight line calculation unit 40 is based on position signals from the first muon detector panel 20a and the second muon detector panel 20b in which the first muon detector 11a and the second muon detector 11b are arranged. Based on the positional relationship between the specified first muon detector panel 20a and the second muon detector panel 20b, the first muon detector 11a and the second muon detector 11b that give the coincidence count result are connected. Calculate the straight line.

  The intensity correction unit 50 was measured by the angle of the straight line connecting the first muon detector 11a and the second muon detector 11b giving the coincidence result with respect to the horizontal direction calculated by the straight line calculation unit 40. Correct the coincidence result of muon intensity.

  Now, since the intensity of the muon that does not pass through any object and is not attenuated depends on the angle θ with respect to the horizontal direction, the intensity of this muon is represented by M (θ). Since the muon intensity at the reference angle Θ is M (Θ), if the muon intensity at the angle θ is expressed as r (θ) as a ratio to the muon intensity at the reference angle Θ, the value of r (θ) is M (θ ) / M (Θ). The intensity of the muon incident on the object changes to r (θ) with respect to the reference value according to θ.

  Now, assuming that the intensity of the muon that has passed through the object at an angle θ with respect to the horizontal direction is m (θ), the attenuation rate d (θ) is expressed by d (θ) = m (θ) / M (θ). .

  However, since the intensity of the incident muon depends on the incident angle θ, the attenuation rate d (θ) is an attenuation rate that does not depend on θ, that is, an attenuation rate of attenuation caused only by being transmitted through the target portion. It is necessary to correct.

  The numbers of the first muon detector 11a and the second muon detector 11b are i and j, respectively, and the intensity of the muon that has passed through the object in the combination of i and j is mij (θ), attenuation independent of θ. Let the rate be Dij. Here, since mij (θ) is incident at an angle θ and the incident intensity depends on θ, correction for normalization is performed so that the incident intensity does not depend on the angle. The corrected attenuation rate Dij is expressed by the following equation.

Dij = d (θ) · r (θ)
= [Mij (θ) / M (θ)] · [(M (θ) / M (Θ)]
= Mij (θ) · M (Θ)
The density distribution calculation unit 60 uses the muon intensity counted by the coincidence circuit 32 and the straight line calculated by the straight line calculation unit 40 based on each coincidence result Dij corrected by the intensity correction unit 50 tomography 3. Perform dimension reconstruction. As a result, the density distribution of the inclusion 3 in the reactor containment vessel 2 is obtained.

  FIG. 5 is a flowchart showing an internal state observation method using this embodiment.

  First, prior to measurement, the relationship between the incident angle of muon and the incident intensity is sampled to obtain r (θ) (S01).

  The first muon detector 11a and the second muon detector 11b are installed at positions facing each other on the side surface of the reactor building cover 5 (S02).

  After step S02, the coincidence measurement is performed by the first muon detector 11a and the second muon detector 11b (S03).

  The straight line calculation unit 40 calculates a straight line connecting the first muon detector 11a and the second muon detector 11b that gives the coincidence result (S04).

  The intensity correction unit 50 corrects the coincidence result of the muon intensity by the angle θ with respect to the horizontal direction of the straight line (S05).

  The density distribution calculation unit 60 performs tomography three-dimensional reconstruction using the muon intensity counted by the coincidence counting circuit and the straight line calculated by the straight line calculation unit 40, so that the internal density in the reactor containment vessel 2 is increased. The density distribution of the object 3 is calculated (S06).

  With the internal state observation device and the internal state observation method according to the present embodiment configured as described above, the internal state in the object can be accurately observed from the outside.

[Second Embodiment]
FIG. 6 is a perspective view of a muon detector panel in the second embodiment of the internal state observation device according to the present invention.

  Here, the first muon detector panel 20a and the second muon detector panel 20b in the first embodiment are shown as a muon detector panel 20 as a representative. Further, the first muon detector 11a and the second muon detector 11b in the first embodiment are shown as the muon detector 11 as a representative.

  The muon detector panel 20 includes a moving panel 24 and a muon detector 11 provided on the moving panel 24 in the center. The movable panel 24 can be moved in the vertical and horizontal directions by the horizontal direction detector driving unit 21 and the vertical direction detector driving unit 22.

  The left-right direction detector drive unit 21 is attached to the external frame 25 and is movable along the external frame 25. The vertical direction detector drive unit 22 is attached to the inner frame 26 and is movable along the inner frame 26.

  The plurality of muon detectors 11 mounted on the moving panel 24 of the muon detector panel 20 configured as described above are movable as a unit.

  Further, one or both of the first muon detector panel 20a and the second muon detector panel 20b (FIG. 4) are movable as shown in FIG.

  For this reason, it is possible to measure at various positions at various angles θ and also in the horizontal circumferential direction centering on the inclusion 3.

  For this reason, the internal state in the object can be observed from the outside with higher accuracy.

[Third embodiment]
FIG. 7 is an elevational sectional view showing a state in which the third embodiment of the internal state observation apparatus according to the present invention is arranged outside the reactor building.

  On the incident side, a direction detection type muon detector 12 having a known incident angle is provided.

  The direction detection type muon detector 12 arranges two muon detectors 11 at a distance and measures them simultaneously, thereby selectively detecting only the muons in the direction toward the muon detector 11.

  The direction detection type muon detector 12 is tilted in the angle δ direction with respect to the horizontal direction. Muons are scattered by the inclusion 3 and enter the muon detector 11 installed on the opposite side of the reactor building cover 5.

  Here, the time T during which the muon passes between the direction detection type muon detector 12 and the muon detector 11 is measured.

  The distance L1 between the direction detection type muon detector 12 and the inherent object 3 and the distance L2 between the muon detector 11 and the inherent object 3 can be expressed by the following equations.

L1 + √ ((S−L1) ² + M ² ) = C · T
(Where C is the muon speed, S and M are known values determined from the installation position of the muon detector)
By obtaining L1 using this equation, the position of the structure can be specified. The time T is a time when the muon detector 11 reacts between √ (S ² + M ² ) ÷ C and (S + M) ÷ C from the time when it reacts with the direction detection type muon detector 12.

  By changing the angle δ of the direction detection type muon detector 12 with respect to the horizontal direction and specifying the position of the inclusion 3 in the vertical direction by the above method for each angle δ, the entire interior of the reactor building 4 is obtained. The position of the intrinsic 3 structure can be specified.

  It should be noted that a plurality of direction detection type muon detectors 12 are arranged by changing the direction δ, a plurality of muon detectors 11 are arranged, and a combination of a plurality of direction detection type muon detectors 12 and a plurality of muon detectors 11 is inherent. The position of the object 3 may be specified.

  As described above, by adding a method for measuring time in a detection system in which the incident angle and the angle after scattering are known, the internal state in the object can be observed from the outside with higher accuracy.

[Fourth Embodiment]
FIG. 8 is an elevational sectional view showing a state in which the fourth embodiment of the internal state observation apparatus according to the present invention is arranged outside the reactor building.

  This embodiment is a modification of the third embodiment, and the direction detection type muon detector 12 is provided on both sides of the reactor building cover 5. Simultaneous counting is performed by setting the angle of one direction detection type muon detector 12 with respect to the horizontal to δ and the other direction detection type muon detector 12 with respect to the horizontal.

  In the present embodiment, an intersection of a straight line having a δ direction with respect to the horizontal passing through one direction detection type muon detector 12 and a straight line having an angle with respect to the horizontal passing through the other direction detection type muon detector 12. Since there is a muon scattering position, the muon scattering position can be specified.

  By changing each of δ and ε, the entire position of the structure in the building can be specified. In the coincidence counting, the time (L1 + L2) / C that passes between the first direction detection type muon detector 12a and the second direction detection type muon detector 12b is calculated from the time when the first direction detection type muon detector 12a reacts. After the elapse of time, it is counted simultaneously with the muon detector 12b.

  As described above, by adding a method for evaluating attenuation in a detection system in which the incident angle and the angle after scattering are known, the internal state in the object can be observed from the outside with higher accuracy.

[Other Embodiments]
As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. Moreover, you may combine the characteristic of each embodiment. Furthermore, these embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention.

  These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 2 ... Reactor containment vessel, 3 ... Contained matter, 4 ... Reactor building, 5 ... Reactor building cover, 10 ... Internal state observation apparatus, 10a ... 1st internal state observation apparatus, 10b DESCRIPTION OF SYMBOLS 2nd internal state observation apparatus, 11 ... Muon detector, 11a ... 1st muon detector, 11b ... 2nd muon detector, 12 ... Direction detection type muon detector, 12a ... 1st direction detection type Muon detector, 12b ... second direction detection type muon detector, 15a ... first muon detector installation unit, 15b ... second muon detector installation unit, 20 ... muon detector panel, 20a ... first Muon detector panel, 20b ... second muon detector panel, 21 ... horizontal direction detector drive unit, 22 ... vertical direction detector drive unit, 24 ... moving panel, 25 ... external frame, 26 ... Part frame, 30 ... muon detection circuit, 31a ... first delay circuit, 31b ... second delay circuit, 32 ... coincidence counting circuit, 32a ... first coincidence circuit, 32b ... second coincidence circuit, 40 ... Linear calculation unit, 50 ... Intensity correction unit, 60 ... Density distribution calculation unit

Claims (6)

In the internal state observation device that observes the internal objects in the object from the outside of the object,
A plurality of muon detectors arranged outside the object and facing each other across the object;
A coincidence circuit for simultaneously counting muon intensities detected by muon detectors on both sides of the object;
Based on the installation positional relationship of each of the muon detectors, a straight line calculating unit that calculates a straight line connecting the muon detectors that gives the coincidence result,
An intensity correction unit that corrects the coincidence result of the muon intensity according to an angle with respect to the horizontal direction of the straight line;
Density distribution for calculating the density distribution of the inherent object in the object by performing tomography three-dimensional reconstruction using the muon intensity counted by the coincidence circuit and the straight line calculated by the straight line calculation unit A calculation unit;
An internal state observation apparatus comprising:   The internal state observation apparatus according to claim 1, further comprising a muon detector panel to which a plurality of the muon detectors are attached and which can move so as to change a direction with respect to an object. The plurality of muon detectors include a first muon detector and a second muon detector that is a direction detection type muon detector having a known incident angle;
The scatter location specifying part which specifies the scatter location of a muon from the detection time difference with the 2nd muon detector which carried out coincidence with the 1st muon detector is further provided. 2. The internal state observation apparatus according to 2. The plurality of muon detectors include a first muon detector that is a direction detection type muon detector having a known incident angle, and a second muon detector that is a direction detection type muon detector having a known incident angle. And including
The scatter location specifying part which specifies the scatter location of a muon from each direction of the 2nd muon detector with which the 1st muon detector and simultaneous counting were made is further provided. Item 3. The internal state observation device according to Item 2.   5. The interior according to claim 1, further comprising a circulation device that circulates around an object, wherein the muon detector is disposed in the circulation device. 6. State observation device. In the internal state observation method of observing the internal objects in the object from the outside of the object,
Correction data maintenance step for collecting the relationship between the incident angle and the incident intensity of the muon,
A detector installation step of installing muon detectors at positions facing each other on the outer side surface of the object;
A counting step for performing simultaneous counting measurement by each of the muon detectors;
A straight line calculating step for calculating a straight line connecting the muon detectors giving the coincidence result;
An intensity correction step for correcting the coincidence result of the muon intensity according to an angle of the straight line with respect to a horizontal direction;
Density distribution for calculating the density distribution of the inherent object in the object by performing tomography three-dimensional reconstruction using the muon intensity counted by the coincidence circuit and the straight line calculated by the straight line calculation unit A calculation step;
An internal state observation method characterized by comprising:

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