JP5347102B2 - Predictive diagnosis of irradiation induced stress corrosion cracking of austenitic stainless steel by neutron irradiation - Google Patents

Description

  The present invention relates to an IASCC predictive diagnostic method and apparatus for monitoring a predictive sign of an irradiation-induced stress corrosion cracking (IASCC) occurring in a structural material such as a nuclear reactor or a particle accelerator before the occurrence of a crack.

Austenitic stainless steel is used as the structural material of reactor internals such as nuclear reactors, but the austenitic stainless steel undergoes repeated neutron irradiation to change the Cr concentration at grain boundaries, and as a result, Increases the possibility of stress corrosion cracking. For this reason, conventionally, IASCC diagnosis of the metal material of the reactor internal structure has been carried out by various methods from the viewpoint of ensuring the safety of the nuclear reactor and the like and predicting the lifetime (for example, Patent Document 1 and Patent Document). 2).
JP-A-6-331784 JP 2002-148383 A

  However, all of the conventional IASCC diagnostic techniques are diagnostic methods that can be detected after damage such as a microcrack has already occurred in a structural material. Diagnosis at the floor before the occurrence of damage such as cracks was difficult. (Takashi Sugaya, Hisashi Endo, Tetsuya Uchiichi, Toshiyuki Takagi “Quantitative Crack Growth Evaluation Using Eddy Current Monitoring System” Transactions of the Japan Society of Mechanical Engineers, Volume 72, No. 714 (2006), pp. 20-25

  An object of the present invention is to provide an IASCC predictive diagnostic method and an apparatus therefor capable of monitoring a sign of a structural material such as a nuclear reactor or a particle accelerator before the occurrence of a crack due to irradiation-induced stress corrosion cracking (IASCC). There is to do.

  As a result of repeated research and experiments on measures against irradiation-induced stress corrosion cracking (IASCC) of austenitic stainless steel, the present inventors have found that the change in the third harmonic voltage value from the specimen obtained by the alternating current magnetization method is IASCC. I found that there was a very linear correspondence with the degree of sensitivity.

  As a result, the IASCC predictive diagnosis method according to one aspect of the present invention measures the third harmonic voltage value of the subject by the alternating current magnetization method, and obtains the third harmonic voltage value obtained in advance. The method includes a step of obtaining a degree of IASCC sensitivity of a subject with reference to a database showing a correlation between the change and the degree of IASCC sensitivity.

  Furthermore, the present inventors have found that a change in probe voltage obtained when measuring an object by an eddy current method also shows a very linear correspondence with the degree of IASCC sensitivity.

  As a result, the IASCC predictive diagnosis method according to another aspect of the present invention is based on the previously described eddy current method probe by further measuring the eddy current method probe voltage of the subject. Referring to a database indicating the correlation between the change in voltage value and the degree of IASCC sensitivity, the degree of IASCC sensitivity of the subject is obtained, and the obtained degree of IASCC sensitivity is the change in the third harmonic voltage value. From the degree of IASCC susceptibility obtained from step (1) to determine whether or not it is within a predetermined error range. By taking such a configuration, a more reliable IASCC predictive diagnosis can be performed.

  According to one aspect of the present invention, the method described above is obtained in advance by a sensor probe including an excitation coil that AC magnetizes the wall surface of the structure, and a detection coil that detects magnetic flux from the wall surface of the structure. A memory storing data indicating a correlation between the magnitude of the change of the third harmonic voltage value being measured and the degree of IASCC sensitivity, and based on the third harmonic voltage value obtained by the sensor probe, The present invention can also be implemented by an IASCC predictive diagnosis device configured to refer to the memory and obtain the degree of IASCC sensitivity corresponding to the voltage value change.

  In the aforementioned IASCC predictive diagnosis apparatus, when the structure is a nuclear reactor structure, the sensor probe is a ferrite in which the excitation coil and the detection coil covered with a radiation-resistant member are high permeability materials. It is preferably an I-type core sensor wound on a core and supported by a radiation-resistant member molded body bobbin. More preferably, the radiation-resistant member is preferably a polyether ether ketone material or a polyimide material. By covering the periphery of the I-type core sensor with a radiation-resistant member, the environment resistance against radiation and the like can be greatly improved.

  More preferably, the aforementioned IASCC sign diagnostic apparatus further includes a positioning device for positioning the sensor probe on the wall surface of the structure, and the axial driving of the positioning device is performed by an ultrasonic motor. preferable. This is because, in the case of a stepping motor used for positioning in nondestructive inspection, electromagnetic noise adversely affects the detection signal of the measurement probe.

  By using the present invention during the maintenance of equipment such as nuclear reactors and particle accelerators that use structural materials, it is possible to evaluate the signs of irradiation-induced stress corrosion cracking (IASCC) before the occurrence of cracks. Can be evaluated, and the safety of the equipment can be improved. Moreover, since an efficient maintenance plan can be made, it becomes possible to improve economy.

  First, a schematic configuration of an irradiation induced stress corrosion cracking (IASCC) predictive diagnosis apparatus performed in a hot cell according to an embodiment of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 10 indicates the inside of the hot cell, and 20 indicates the outside of the hot cell. In addition to the I-type core sensor 13 which is an AC magnetic sensor, an FG sensor 11 and an MI sensor 12 which are DC magnetic sensors for measuring a static and weak leakage magnetic flux density are attached to the hot cell interior 10. In the present invention, only the I-type core sensor 13 is used to measure the third harmonic voltage value of the subject by the AC magnetization method and the probe voltage value by the eddy current method. Further, as a positioning means for determining a diagnosis position, a uniaxial ball screw driving mechanism and an ultrasonic motor 16 for moving the stage on which the CCD camera 14 and the test piece are placed to a desired position are provided. Further, a detachable magnetic excitation coil 15 for magnetizing and demagnetizing the subject for measurement by the DC magnetic sensor is provided at a position sufficiently away from the magnetic sensor so as not to adversely affect the magnetic sensor. .

  On the other hand, the hot cell exterior 20 includes a sensor amplifier 21 for amplifying detection signals from various sensors 11, 12, 13, a signal processing unit 22 for processing signals from the sensor amplifier 21, and an ultrasonic motor for positioning. An ultrasonic motor driver 24 for driving 16, a power unit / stage control unit 23 for supplying a drive control signal to the ultrasonic motor driver 24, and a display device 25 for displaying a signal processing result are provided.

  In the above apparatus configuration, the basic operation of the entire apparatus other than those described above is the same as the operation of the well-known nondestructive inspection apparatus in the reactor so far, and the details are omitted. In this embodiment, the diagnosis is performed by observing the test piece in the hot cell. However, in the actual machine, for example, a rail is directly laid on the structural material of the nuclear reactor, and the remote operation is performed. The above-mentioned I-type core sensor 13 is moved on the rail to perform positioning. As for remote operation, it was confirmed by experiments that remote operation up to 10 m was possible without signal attenuation.

  A schematic configuration of the I-type core sensor 13 is shown in FIG. The I-type core sensor 13 includes a sensor probe 131 and a bobbin 132 that supports the sensor probe 131. A bobbin 132 extending to the center of the sensor probe 131 is embedded with a ferrite core 133 which is a high permeability material having a diameter of 1.2 mmφ at the center to increase the magnetic flux density excited by the excitation coil 134 and to detect the upper and lower detection coils. It plays the role which raises the detection sensitivity of 135,136. The bobbin 132 is formed of a polyether ether ketone (PEEK) material, which is a material with high radiation resistance, and ensures radiation resistance. In addition, the excitation coil 134 and the upper and lower detection coils 135 and 136 are covered with a polyimide (PI) material, which is a material with high radiation resistance, to ensure radiation resistance. The bobbin 132 may be formed of a polyimide (PI) material, and the excitation coil 134 and the upper and lower detection coils 135 and 136 may be covered with a polyether ether ketone (PEEK) material, or the bobbin 132 and the excitation coil 134 may be Only the polyether ether ketone (PEEK) material may be used for covering the detection coils 135 and 136, or only the polyimide (PI) material may be used.

  Next, the procedure of the IASCC predictive diagnosis method for an actual machine will be described with reference to FIG. In the flowchart of FIG. 3, in order to obtain reference data first, non-irradiated stainless steel having 0 IASCC sensitivity outside the furnace is used to measure the third harmonic voltage value by the AC magnetization method and to the eddy current method. The zero point adjustment of the measuring apparatus to be used is performed (step 200). Next, at the time of maintenance of the nuclear reactor such as periodic inspection, the I-type core sensor probe 13 is inserted into the nuclear reactor by remote control, positioned, and brought into close contact with the surface of the structural material (step 300). Next, the measurement of the third harmonic voltage value by the alternating current magnetization method and the probe voltage value by the eddy current method are performed for the structural material (step 400). Next, the IASCC sensitivity is evaluated by referring to a database of IASCC sensitivity / third harmonic voltage value change prepared in advance using a sample piece and stored in a memory (not shown) of the signal processing unit 22. (Step 500). Similarly, the reliability of the IASCC sensitivity obtained in step 500 is evaluated with reference to the IASCC sensitivity / eddy current method probe voltage value change database previously stored in the memory (step 600). If both IASCC sensitivities are not substantially equal, it is determined that there is a problem in the measurement environment, and the process returns to step 300, and the procedure up to step 600 is executed again. On the other hand, if both sensitivities are substantially the same, the process proceeds to the previous step, and after moving the probe position, the procedure from step 300 to step 600 is repeated to obtain the IASCC susceptibility map of the in-furnace structural material. It is created (step 700) and stored in the memory of the signal processing unit 22. Here, that both IASCC sensitivities are substantially equivalent means that both IASCC sensitivities are within 20%.

  As described above, by preparing an IASCC sensitivity map of the in-furnace structural material, maintenance is efficiently and accurately performed at the next maintenance by particularly inspecting a portion with high IASCC sensitivity. It becomes possible.

  Next, referring to FIG. 4 to FIG. 9, the relationship between IASCC sensitivity (%) and third harmonic intensity (dB) (ratio to the reference voltage), and IASCC sensitivity (%) and probe voltage, which are the principles of the present invention. The relationship (au) will be described. In each figure, HP304, HP316, HP304 / C, HP304 / Si, HP304 / P, and HP304 / S are all high-purity model austenitic stainless alloys. These alloys are prepared by individually adding elements such as Mo, C, Si, P, and S based on HP304 prepared so that the impurity element concentration of SUS304 is minimized. Then, the test piece was cut out and predetermined neutron irradiation was performed. The diameter of the grip part of the test piece is 11 mmφ, and this end is subjected to a magnetic measurement, and subjected to SSRT test (Slow Strain Rate Technique) in high temperature water under light water reactor conditions. ) Was evaluated.

  FIG. 4 shows the relationship between the measurement result of the third harmonic intensity (dB) obtained by the AC magnetization method and the evaluation result of IASCC sensitivity (%) obtained for the high purity model austenitic stainless alloy irradiated material such as HP304. In this embodiment, the excitation frequency is 10 kHz, and the voltage values detected by the detection coils 135 and 136 are Fourier-transformed to determine the fundamental voltage value and the third harmonic voltage value component. From FIG. 4, it can be seen that there is a positive correlation in which the third harmonic intensity (dB) increases almost linearly as IASCC sensitivity (%) increases. Here, the third harmonic voltage 1V is converted to 0 dB as the third harmonic intensity (dB). That is, the change in the third harmonic voltage value and the IASCC sensitivity (%) indicate that there is a one-to-one correspondence. FIG. 5 shows the evaluation results on the phase plane (Vx, Vy) of the same irradiated material by the eddy current method. Here, the measurement was performed based on the 1 dpa irradiated material of HP316 whose IASCC sensitivity was O in the previous studies.

FIG. 6 shows a graph in which the relationship between the relative value (au) of the probe voltage obtained from the evaluation result on the phase plane and the IASCC sensitivity (%) is plotted. Here, the relative value (au) of the probe voltage was defined as √ (Vx ² + Vy ² ). Although the variation was larger than the result obtained by the AC magnetization method, a positive correlation was obtained in which the probe voltage increased with an increase in IASCC sensitivity (%). The variation in the dependence data on the IASCC sensitivity (%) of the third harmonic intensity obtained by the AC magnetization method shown in FIG. ) To the same extent. In the case of the AC magnetization method, information based on a change in depth can be acquired by adjusting the excitation frequency as compared with the leakage magnetic flux density. Therefore, the AC magnetization method can separate and evaluate the influence of the oxide layer generated on the surface of the test piece and the surface roughness, and has higher applicability to an actual machine than the leakage magnetic flux density measurement.

  The above evaluation by the alternating current magnetization method and the eddy current method can be performed using the same sensor probe and the same measuring device. For this reason, even when applied to actual equipment, the AC magnetizing method and the eddy current method are evaluated in parallel for the same measurement location of the structural material, and by comparing the results, appropriate IASCC predictive diagnosis can be performed. Can be done. In addition, since a test piece having a grip diameter of 11 mmφ was evaluated and magnetic data correlated with IASCC sensitivity could be obtained, a part having a relatively complicated shape such as a wall surface of an actual machine structural material was obtained. In addition, by performing appropriate alignment or the like, IASCC predictive diagnosis can be performed by an AC magnetization method or an eddy current method.

  Next, FIG. 7 shows a graph plotting the relationship between the measurement result of the third harmonic intensity (dB) of the SUS316L irradiated material by the alternating current magnetization method and the evaluation result of IASCC sensitivity (%) obtained so far. A positive correlation was obtained in which the third harmonic intensity increased with an increase in IASCC sensitivity (%).

  Moreover, the evaluation result on the phase plane by the eddy current method of the same irradiation material is shown in FIG. Here, the measurement was performed based on the 0.12 dpa irradiated material whose IASCC sensitivity (%) was 0 in the previous studies. FIG. 9 is a graph plotting the relationship between the relative value of the probe voltage obtained from the evaluation result on the phase plane (Vx, Vy) and IASCC sensitivity (%). A positive correlation was obtained in which the probe voltage increased with increasing IASCC sensitivity.

  The present invention is not limited to the above-described embodiments, and is included in the claims of the present application without departing from the scope of the technical idea of the present invention. For example, in the embodiment of the present application, the third harmonic voltage value is used. However, if the detection sensitivity is improved, the fifth harmonic voltage or the seventh harmonic voltage can be used. In the above-described embodiment, the single-axis ball screw drive mechanism is used to increase the positioning accuracy. However, in the inspection of a large structural member, a conventional positioning device that can move in the biaxial direction of XY is used. Efficient.

1 is a schematic configuration diagram of an irradiation induced stress corrosion cracking (IASCC) predictive diagnosis apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration of an I-type core sensor 13. It is a flowchart which shows the procedure of the IASCC sign diagnostic method. It is a figure which shows the relationship between the measurement result of the 3rd harmonic intensity | strength (dB) by an alternating current magnetization method, and the evaluation result of IASCC sensitivity (%). It is a figure which shows the probe voltage distribution on the phase plane by an eddy current method (Vx, Vy). It is a figure which shows the relationship between an eddy current method probe voltage value measurement result, and the evaluation result of IASCC sensitivity (%). It is a figure which shows the relationship between the measurement result of the 3rd harmonic intensity | strength (dB) by an alternating current magnetization method, and the evaluation result of IASCC sensitivity (%). It is a figure which shows the probe voltage distribution on the phase plane by an eddy current method (Vx, Vy). It is a figure which shows the relationship between an eddy current method probe voltage value measurement result, and the evaluation result of IASCC sensitivity (%).

Explanation of symbols

11, 12 DC magnetic sensor 13 I-type core sensor 14 CCD camera 15 Detachable magnetic excitation coil 16 Ultrasonic motor 21 Sensor amplifier 22 Signal processing unit 23 Power unit / stage control unit 24 Ultrasonic motor driver 25 Display device 131 Sensor probe 132 Bobbin 133 Ferrite Core 134 Excitation coil 135, 136 Detection coil

Claims (1)

In the predictive diagnostic method for irradiation induced stress corrosion cracking of austenitic stainless steel by neutron irradiation,
A sensor probe is brought into close contact with the surface of an austenitic stainless steel specimen, and the third harmonic voltage value of the specimen is measured by an alternating current magnetization method. By the change in the third harmonic voltage value obtained in advance and neutron irradiation Referring to the database showing the correlation with the degree of irradiation-induced stress corrosion cracking susceptibility, determine the degree of irradiation-induced stress corrosion cracking susceptibility due to neutron irradiation of the specimen,
Further, the probe voltage of the subject is measured by the eddy current method using the same sensor probe as the sensor probe used in the AC magnetization method, and the eddy current method probe voltage value obtained in advance and irradiation by neutron irradiation Referring to the database showing the correlation with the degree of susceptibility to induced stress corrosion cracking, the degree of susceptibility to irradiation induced stress corrosion cracking due to neutron irradiation of the specimen is determined,
It is determined whether or not the degree of the susceptibility to the radiation induced stress corrosion cracking obtained is within a predetermined error range from the degree of the susceptibility to the radiation induced stress corrosion cracking obtained from the third harmonic voltage value. A method for predicting radiation-induced stress corrosion cracking of austenitic stainless steel by neutron irradiation.

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