JP2736955B2 - Method and apparatus for measuring hydrogen content in metal materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the amount of hydrogen contained in a metal material such as steel.

[0002]

2. Description of the Related Art Hydrogen embrittlement is one of the causes of deterioration of metal materials such as steel materials. The total amount of hydrogen contained in steel, such as hydrogen atoms dispersed in steel and hydrogen constituting hydrocarbons, is considered to be a direct indicator of steel deterioration due to hydrogen. For example, in a reactor that handles high-temperature and high-pressure hydrogen, nondestructive quantitative measurement of the amount of hydrogen in steel constituting the reactor is required to prevent destruction due to hydrogen embrittlement.

However, in the prior art, it is impossible to nondestructively quantitatively measure the amount of hydrogen in steel.
For example, in order to prevent the destruction of the reactor due to hydrogen embrittlement, only a Nelson diagram or the like indicating the use environment limit of steel is used.

[0004]

In view of such a problem,
An object of the present invention is to provide a measuring method and a measuring device for nondestructively quantitatively measuring the amount of hydrogen contained in a metal material.

[0005]

In order to achieve the above object, a first characteristic configuration of the method for measuring the amount of hydrogen in a metal material according to the present invention is to irradiate neutrons to the metal material from a neutron irradiation device, Providing a neutron detector to measure the amount of thermal neutrons out of the neutrons decelerated by irradiation to, arranging the sensor portion of the neutron detector on the irradiation axis of neutrons irradiated from the neutron irradiation device, the metal material The amount of hydrogen contained in the metal material is determined by measuring the amount of the thermal neutrons by making neutrons reflected from the laser beam incident on the sensor unit.

A second feature of the method for measuring the amount of hydrogen according to the present invention is that, in addition to the first feature of the above method, the neutrons are decelerated by a moderator and passed through a thermal neutron removal filter. The object of the present invention is to irradiate a metal material and measure the amount of thermal neutrons among the neutrons decelerated by the irradiation of the metal material by a BF ₃ counter.

On the other hand, a first characteristic configuration of the apparatus for measuring the amount of hydrogen in a metal material according to the present invention is that a neutron irradiation device for irradiating the metal material with neutrons, A neutron detector for measuring the amount of thermal neutrons is provided, and the sensor unit of the neutron detector is arranged on an irradiation axis of neutrons irradiated from the neutron irradiation device, and neutrons reflected from the metal material are disposed. The configuration is such that the light is incident on the sensor unit.

[0008] A second characteristic configuration of the hydrogen amount measuring apparatus according to the present invention, in addition to the first characteristic configuration of the above-described apparatus, is a moderator for decelerating neutrons generated from a radiation source of the neutron irradiation device. And a thermal neutron removal filter for removing thermal neutrons from the neutrons passing through the moderator, and the neutron detector is provided with a BF ₃ counter.

[0009]

[0010]

[0011]

For example, neutrons generated at the time of spontaneous fission such as ²⁵² Cf are called fast neutrons having high energy of about 2 MeV, and neutrons transmitted through or scattered by a substance collide with atoms in the substance. , And eventually becomes a thermal neutron having a low energy of about 0.5 eV or less, which is in equilibrium with room temperature. The deceleration effect due to the collision varies depending on the material. The average number of collisions with atoms required for neutrons generated from ²⁵² Cf to become thermal neutrons is as follows:
In the case of an iron atom, it takes 515 times, whereas in the case of a hydrogen atom, 1
There is a big gap with eight times. Therefore, as the amount of hydrogen contained in the metal material increases, neutrons that pass through or are scattered by the metal material are more strongly decelerated, and the probability of becoming a thermal neutron increases.

According to the first characteristic configuration of the measuring method and the measuring apparatus, the neutrons are irradiated on the metal material, and the neutrons are decelerated by colliding with hydrogen atoms in the metal material. Occurs. According to the above-described principle, the amount of generated thermal neutrons increases as the amount of hydrogen in the metal increases. In fact, according to experiments performed by the inventors, it was confirmed that the frequency of thermal neutrons decreases as the number of hydrogen atoms charged to the steel material by the electrolytic charging method decreases, as described later. Therefore, the amount of thermal neutrons among the neutrons decelerated by irradiation on the metal material is measured by a neutron detector,
By converting the measurement results using the correlation between the amount of thermal neutrons generated in advance and the amount of neutrons in the metal material,
It is possible to quantitatively determine the amount of hydrogen contained in the metal material. Moreover, since the sensor section of the neutron detector is arranged on the irradiation axis of the neutrons irradiated from the neutron irradiation device, the neutrons irradiated on the metal material pass through the sensor section and are irradiated on the metal material. At this time, the ratio of thermal neutrons to the transmitted neutrons is low, and the adverse effect on the measurement is small. In addition, since the thermal neutrons reflected from the metal material are configured to be incident on the sensor unit, the transmitted neutrons collide with hydrogen in the metal material and become thermal neutrons,
Part of the light is reflected and detected by the sensor unit. According to this configuration, the incident angle of the neutrons can be set to 90 degrees with respect to the surface of the metal material, and the reflected thermal neutrons can be captured most efficiently. Further, since the sensor unit can be brought close to the surface of the metal material, it is possible to capture thermal neutrons reflected over a wide angle by the sensor unit.

The probability that neutrons collide with atoms in a substance increases as the energy of neutrons decreases. Therefore, according to the second characteristic configuration of the measurement method and the measurement device, by irradiating the metal material after neutrons are decelerated by the moderator, the probability of neutrons colliding with hydrogen in the metal material is improved, This allows more neutrons to be reduced to thermal neutrons by collisions with hydrogen. In addition, by irradiating the metal material after passing through a thermal neutron removal filter in advance, it is possible to reduce background noise by removing thermal neutrons that have been caused by the moderator. Also,
Since the BF ₃ counter has high sensitivity to low-speed neutrons, the use of the BF ₃ counter makes it possible to measure the amount of thermal neutrons more efficiently.

[0014]

[0015]

As described above, according to the first characteristic configuration of the method and the apparatus for measuring the amount of hydrogen in a metal material according to the present invention, the amount of hydrogen contained in the metal material is quantitatively measured nondestructively. It has become possible to nondestructively inspect the progress of hydrogen embrittlement of reactors and other structures. In particular, by efficiently capturing the reflected thermal neutrons, the radiation source can be effectively used, and more accurate measurement of the amount of hydrogen can be performed from one side of a structure or the like.

According to the second feature of the method and the apparatus for measuring the amount of hydrogen in a metal material according to the present invention,
It is possible to improve the sensitivity of neutron detector relative amount of hydrogen by the use of moderator and BF ₃ counter, and by thermal neutrons removal filter is reduced background noise, it is possible to reduce a measurement error Was.

[0017]

[0018]

Next, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram of an apparatus for measuring the amount of hydrogen according to the present invention. This measuring apparatus 1 includes a collimator 20 functioning as a neutron irradiation apparatus for irradiating neutrons to a test body 5. A neutron detector 30 is provided for measuring the amount of thermal neutrons out of the neutrons N2 transmitted through the body 5 as the number of thermal neutrons detected per unit time. In this embodiment, a steel material, which is an example of a metal material, is measured as a test body 5. Support base 40
In the figure, the collimator 20, the sensor tube 32 of the neutron detector 30, and the test body 5 are arranged at regular intervals. In this embodiment, the test piece 5 is a small piece and is mounted on a common mounting table with the mounting table of the collimator 20 and the sensor tube 32. However, the collimator is provided inside and outside the pressure vessel. When the -20 and the neutron detector 30 are respectively mounted, separate test stands may be provided.

In the collimator 20, a neutron irradiation hole 23 is formed on one side of a radiation source container 22 molded into a cubic shape from polyethylene, and a neutron source 24 is provided behind the irradiation hole 23. At the same time, a cadmium plate 25 is wound around the source container 22. Of the neutrons generated from the radiation source 24, those directed to the right side in FIG. 1 become neutron beams via the irradiation holes 23 and are irradiated to the specimen 5. Those traveling in the other direction are decelerated by hydrogen in the polyethylene constituting the source container 22 to become thermal neutrons, and further,
The cadmium plate 25 for removing thermal neutrons prevents leakage to the outside. The moderator 26 is formed of polyethylene similarly to the source container 22, and serves to reduce the speed of fast neutrons to a level not reaching thermal neutrons as described later. The thickness is smaller than the thickness of the source container 22. Some of the neutrons that pass through the moderator 26 reach thermal neutrons.
First thermal neutron removal filter 28 for removing this
Is provided at the exit of the irradiation hole 23.

The neutron detector 30 includes a sensor tube 32 as a sensor, which is a tubular body in which BF ₃ gas is sealed, and a BF ₃ counter-35 comprising a control device 34, and the number of times thermal neutrons are detected by the sensor tube 32. And a scaler 36 for counting. BF ₃ counter-35
Counter for detecting neutrons utilizing nuclear reactions of BF ₃ - a, energy - sensitivity is higher with respect to the low thermal neutrons. The scaler 36 has a flip-flop circuit to enable decimal counting and incorporate a timer capable of changing the time constant. By resetting the flip-flop according to the start of the timer, the number of thermal neutrons reaching the sensor tube 32 within a certain time can be integrated and displayed. The amount of neutrons is measured based on the number of thermal neutrons.

In this embodiment, the radiation source 24 is ²⁵² Cf · 2
0 μCi is used. The neutrons N1 generated from the radiation source 24 are fast neutrons. In the present embodiment, neutrons having smaller energy than fast neutrons and larger energy than thermal neutrons are stochastically present. The speed is reduced by using the moderator 26. FIG. 2 shows a state in which fast neutrons generated from a radiation source become thermal neutrons having low energy by colliding with hydrogen atoms or the like. The neutrons generated from the radiation source 24 are decelerated by colliding with hydrogen atoms in the test specimen 5, and those that have become thermal neutrons are detected by the sensor tube 32. Here, in the state of fast neutrons, the collision cross section with hydrogen is small, and therefore, the probability that fast neutrons will collide with hydrogen atoms in the specimen 5 and become thermal neutrons is low. Rather than irradiating the test specimen 5 with neutrons as fast neutrons, as shown in FIG. 3, fast neutrons having high energy E1 are converted to energy -E2 up to energy E3 which reaches thermal neutrons. By reducing the speed by the moderator 26, the probability of collision with hydrogen atoms in the test body 5 is improved, and the probability of thermal neutron generation by hydrogen contained in the test body 5 is improved. Also,
The first thermal neutron removal filter 28 reduces noise on the sensor tube 32 by removing the thermal neutrons that have been decelerated by the moderator 26.

FIG. 3 shows the results obtained by subjecting a steel material made of SS41C to hydrogen charging by the electrolytic charging method and using this as a test body 5 using the apparatus shown in FIG. The horizontal axis is time, and the vertical axis is the number of thermal neutrons counted per hour. It is known that hydrogen charged by an electrolytic charger is separated from steel material with the passage of time. Also in the experimental results of FIG. 3, the scale display of the scaler decreases with the passage of time, and it is understood from the experimental results that the effect of the present invention is appropriate.

The following procedure may be used to quantitatively measure the amount of hydrogen in a steel material using the above measuring device. (1) First, using test pieces having different thicknesses and hydrogen contents, measurement was performed by the test apparatus 1 of FIG.
First, the correlation between the indicated value of No. 6 and the actual hydrogen content is determined. The hydrogen content of the test piece can be determined by a destructive test. It is desirable that the correlation graph also includes parameters such as temperature and humidity.

(2) The part to be measured and the peripheral part of the steel material as the test piece 5 are rusted over the front and back, and are dried and well-moistened.

(3) Using a reference piece having a low hydrogen content as a test body, measurement is performed by the measuring apparatus 1 of FIG. 1 to obtain a background value of the measuring apparatus 1.

(4) The actual test object is inserted as the test piece 5, the background value is offset from the measured value of the scaler 36, and a correction is made to obtain the hydrogen content in the test piece 5. Find the quantity. The hydrogen content is determined by comparing the corrected display value of the scaler 36 with a correlation graph and by converting the display value of the scaler in accordance with the above correlation. The circuit may be provided in the scaler 36.

Next, a second embodiment of the present invention will be described. In the first embodiment, the test piece 5 is
As shown in FIG. 4, a neutron N1 is irradiated from the collimator 20 to the specimen 5 and neutrons N2 reflected and scattered by the specimen 5 are captured by the sensor tube 32 as shown in FIG. It may be configured to measure. In the second embodiment, the test body 5 is a steel plate constituting a pressure vessel of a reactor, and the collimator 20 and the neutron detector 30 are each inclined 45 degrees with respect to the perpendicular to the steel surface from the steel. is there. That is, the thermal neutrons of the neutrons N2 which collide with the hydrogen element in the steel material due to the oblique irradiation from the collimator 20, are decelerated and reflected and scattered are converted into the sensor tube 3.
2 to catch. At this time, in order to prevent the influence of disturbance on the sensor tube 32, a second thermal neutron removal filter 37 made of the same cadmium material as the first thermal neutron removal filter 28 is provided around the sensor tube 32 except for the entrance 32a.
Is provided. By providing the second thermal neutron removal filter 37 around the sensor tube 32, thermal neutrons that reach the sensor tube 32 as noise can be removed, and neutrons with high energy that do not reach thermal neutrons can be removed from the sensor tube 32.
There is no problem because it is hard to count even if passing.

Further, the neutrons N reflected by the specimen 5
5 when the sensor 2 is captured by the sensor tube 32 and measured.
The third embodiment shown in FIG. In the third embodiment, a sensor tube 32 is arranged on a straight line of an irradiation hole 23 in a collimator 20 via a first thermal neutron removal filter 28. Since the neutrons N1 generated from the radiation source 24 are decelerated by the moderator 26 and the thermal neutrons are removed by the first thermal neutron removal filter 28, the sensor tube 32 hardly reacts to the neutrons N1, The neutron beam N1 passes through the sensor tube 32 and reaches the specimen 5. Of the neutrons N2 reflected and scattered by the test body 5, those that have become thermal neutrons reach the sensor tube 32 and are counted. By arranging in this manner, the sensor tube 32 can be brought close to the surface of the steel material, and at the same time, the collimator 20 can be brought close to the surface of the test body 5, so that the radiation efficiency of neutrons can be further improved. . Further, by bringing the sensor tube 32 close to the steel material surface, even thermal neutrons having a large scattering angle can be captured, and the detection accuracy of thermal neutrons can be further improved.

Further, other embodiments of the present invention will be listed.
In each of the above embodiments, the BF ₃ counter-35 is used as the neutron detector 30, but another type of detector having high sensitivity to thermal neutrons can be used as the neutron detector.

In each of the above embodiments, ²⁵² Cf ·
Although 20 μCi was used, other sources, such as ²⁴¹
Am-Be or the like may be used.

The present invention relates to carbon steel, 1 1/4 Cr-0.5
Mo steel, 2 1/4 Cr-1Mo steel, 3.0 Cr-0.5
In addition to being particularly suitable for steel materials such as Mo steel,
The present invention is also applicable to other metal materials. In the present invention, the purpose of determining the amount of hydrogen in the metal material is not limited to prevention of hydrogen embrittlement.

The first and second moderators include hydrocarbons such as paraffin and polypropylene, in addition to polyethylene,
Graphite, beryllium oxide, or the like may be used. Further, a filter other than cadmium may be used as the neutron removal filter.

In each of the above embodiments, the first thermal neutron removing filter 28 is provided to remove thermal neutrons. However, the measurement may be performed without providing the first thermal neutron removing filter. However, when the first thermal neutron removal filter is not provided, it is necessary to cancel background noise due to thermal neutrons.

Note that fast neutrons are neutrons having an energy of 500 KeV or more, and thermal neutrons are 0.5 neutrons.
Although neutrons having an energy of eV or less may be referred to, specific numerical values in the present specification show an example of an embodiment of the present invention, and fast neutrons and thermal neutrons referred to in the present invention are not necessarily those neutrons. However, the present invention is not limited to the specific numerical values. In addition, the moderator 26 in each of the above embodiments is ²⁵² C
Neutrons having a high energy of about 2 MeV generated at the time of spontaneous fission of f
The thickness of the measuring device 1 may be kept small enough to reduce the energy to KeV or more. However, in order to improve the sensitivity of the measuring apparatus 1, the degree of deceleration by the moderator 26 may be appropriately increased.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an apparatus for measuring the amount of hydrogen in a metal material.

FIG. 2 is a graph showing a state in which a high-energy neutron loses energy due to collision with a hydrogen atom or the like.

FIG. 3 is a graph showing a state in which hydrogen charged to a steel material is reduced with the passage of time by a BF ₃ counter.

FIG. 4 is a schematic sectional view showing a second embodiment of the measuring method and the measuring apparatus according to the present invention.

5A and 5B show a third embodiment of the measuring method and the measuring apparatus according to the present invention, wherein FIG. 5A is a longitudinal sectional view in a plane perpendicular to the central axis of the sensor tube, and FIG. 5B is a plane perpendicular to FIG. FIG.

[Explanation of symbols]

N1 Neutron 5 Metal material N2 Decelerated neutron 30 Neutron detector 26 Moderator 28 Thermal neutron removal filter 24 Source 35 BF ₃ counter. .

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takuichi Imanaka 1-18-14 Kitahorie, Nishi-ku, Osaka-shi Non-destructive Inspection Co., Ltd. (56) References JP-A-4-23247 (JP, A) JP-A-59-114447 (JP, A) JP-A-62-85849 (JP, A) JP-A-57-17437 (JP, U) JP-B-49-7518 (JP, B1) WILLIAM H. MILLER, ROBERT BRUGGER & W ALTER MEYER, "MODIFIED NOTCHED FILTER TECHNIQUE FOR DET ERMINING HYDROGEN IN METALS," TRANS. AM. NUCL. SOC. , (1990), VOL. 61, p. 102−103

Claims (4)

(57) [Claims] 1. A neutron irradiator (20) receives neutrons (N
1) irradiating the metal material (5) with the neutron detector (30) for measuring the amount of thermal neutrons among the neutrons (N2) decelerated by the irradiation of the metal material (5); The sensor section (32) of the neutron detector (30) is arranged on the irradiation axis of the neutrons (N1) irradiated from the element (20), and the neutrons (N2) reflected from the metal material (5) are reflected by the sensor section ( 32) A method for measuring the amount of hydrogen in a metal material by determining the amount of hydrogen contained in the metal material (5) by measuring the amount of the thermal neutrons by entering the metal material. 2. The neutron (N1) is decelerated by a moderator (26) and passed through a thermal neutron removal filter (28), and then irradiates the metal material (5) to irradiate the metal material (5). hydrogen amount measuring method of the metal material according to claim 1 for determining the amount of out heat neutron BF ₃ by a counter (35) of neutrons (N2) which is decelerated by. 3. A neutron irradiation device (20) for irradiating a neutron (N1) to a metal material (5), and a metal material (5).
A neutron detector (30) for measuring the amount of thermal neutrons out of the neutrons (N2) decelerated by irradiation of the neutrons (N2), and the irradiation axis of the neutrons (N1) irradiated from the neutron irradiation device (20) A sensor unit (32) of the neutron detector (30) is arranged on a line, and neutrons (N2) reflected from the metal material (5) are incident on the sensor unit (32). Hydrogen measuring device. 4. A radiation source (2) for the neutron irradiation device (20).
A moderator (26) for moderating neutrons (N1) generated from 4) and a thermal neutron removal filter (28) for removing thermal neutrons from the neutrons (N1) passing through the moderator (26) are provided. , The neutron detector (30) has BF ₃
The apparatus for measuring the amount of hydrogen in a metal material according to claim 3, further comprising a counter (35).