Surface corrosion analyzer and surface corrosion analyzer

Abstract

This invention provides a surface corrosion analysis technique for analyzing the compositional distribution of metal corrosion products accumulated on the surface of structures. [Solution] The surface corrosion analyzer comprises a transmitting unit 11 that transmits a light emission command 12 to a light source that irradiates the surface of a metal member with light and reflects the reflected light; a receiving unit 15 that receives a first image signal 16a and a second image signal 16b from an imaging unit that images the surface with at least two types of first and second wavelength components of the reflected light; a brightness setting unit 17 that sets a first brightness 13a and a second brightness 13b of pixels constituting the surface image based on the first image signal 16a and the second image signal 16b; and an analysis unit 18 that analyzes the compositional distribution of metal corrosion products accumulated on the surface based on the first brightness 13a and the second brightness 13b.

Description

Technical Field

[0001] Embodiments of the present invention relate to a surface corrosion analysis technique for analyzing metal corrosion products deposited on the surface of a structure.

Background Art

[0002] A closed circuit in which cooling water is circulated to extract the thermal energy generated in the core of a nuclear reactor to the outside is called a nuclear reactor cooling system. In a nuclear reactor, during the operation period after the start of commercial operation, insoluble metal oxides (hereinafter referred to as metal corrosion products) accumulate on the surface of the in-vessel structures of the nuclear reactor cooling system that come into contact with the cooling water.

[0003] The origin of the formation of this metal corrosion product may be the oxide film of the structural material at the deposition position, or may be a product that is deposited on the surface of the fuel rod in the core, for example, different from the deposition position, is activated by radiation, and a part of it is peeled off or eluted. If the accumulation of metal corrosion products in the nuclear reactor cooling system continues, problems such as deposition on the fuel cladding tube and reduction of the heat transfer coefficient, deposition on the pipe surface and increase of the pressure loss of the cooling water, and increase of the exposure dose due to radioactive accumulation will occur.

[0004] On the other hand, in nuclear power plants, in order to detect abnormalities such as friction, cracks, corrosion, and erosion on the surface of in-vessel structures, a remote visual inspection using an underwater camera is regularly carried out during the operation period.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The remote visual inspection using the underwater camera described above involved visually inspecting the internal reactor structure through camera photography. Therefore, the assessment of metal corrosion products was limited to confirming their accumulation state from the images. Consequently, detailed analysis of metal corrosion products accumulated on the surface of the structure was not carried out.

[0007] Embodiments of the present invention have been made in consideration of these circumstances, and aim to provide a surface corrosion analysis technique for analyzing the compositional distribution of metal corrosion products accumulated on the surface of a structure. [Means for solving the problem]

[0008] A surface corrosion analyzer according to an embodiment is characterized by comprising: a transmitting unit that transmits a light emission command to a light source that irradiates the surface of a metal member with irradiation light and reflects the reflected light; a receiving unit that receives a first image signal and a second image signal from an imaging unit that images the surface with at least two types of first wavelength components and second wavelength components of the reflected light; a brightness setting unit that sets a first brightness and a second brightness of pixels constituting the image of the surface based on the first image signal and the second image signal; and an analysis unit that analyzes the compositional distribution of metal corrosion products accumulated on the surface based on the first brightness and the second brightness. [Effects of the Invention]

[0009] Embodiments of the present invention provide a surface corrosion analysis technique for analyzing the compositional distribution of metal corrosion products accumulated on the surface of a structure. [Brief explanation of the drawing]

[0010] [Figure 1] A longitudinal cross-sectional view of a reactor pressure vessel to which the surface corrosion analysis apparatus according to each embodiment is applied. [Figure 2] A block diagram showing the control circuit of a surface corrosion analyzer according to the first embodiment. [Figure 3]The probe (light source, imaging unit) of a surface corrosion analyzer is shown as follows: (A1) is a front view of Example 1, (A2) is a side view of Example 1, (B1) is a front view of Example 2, (B2) is a side view of Example 2, (C1) is a front view of Example 3, and (C2) is a side view of Example 3. [Figure 4] This graph shows the reflectance (%) of reflected light against the wavelength (nm) of irradiated light for typical metal corrosion products (Cr2O3, Fe2O3, Fe3O4) that accumulate on the surface of in-core structures in the reactor cooling system. [Figure 5] A block diagram showing the control circuit of the surface corrosion analyzer according to the second embodiment. [Modes for carrying out the invention]

[0011] (First Embodiment) Embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 is a longitudinal cross-sectional view of a reactor pressure vessel 30 to which a surface corrosion analyzer according to each embodiment is applied. The surface corrosion analyzer consists of a control circuit 10 (Figure 2) and a probe 20 (Figure 3; light source 21 and imaging unit 22).

[0012] In this embodiment, the probe 20 (light source 21 and imaging unit 22) is suspended from the upper opening of the reactor pressure vessel 30 by a suspension member 25 and supported in the cooling water 26 contained within. This allows the surface corrosion analyzer to remotely analyze the corrosion state of the internal surface 33 of the reactor pressure vessel 30 that is in contact with the cooling water 26.

[0013] In Figure 1, the reactor pressure vessel 30 is shown with the shroud 31 present as an example of an internal reactor structure after the removal of the upper lid (not shown), steam dryer (not shown), steam-water separator (not shown), fuel assemblies (not shown), etc. This shroud 31 is a stainless steel cylinder that separates the upward flow of cooling water 26 inside where the fuel assemblies are housed from the downward flow of cooling water 26 in the annular region outside.

[0014] Furthermore, the inner surface of the reactor pressure vessel 30 is lined with stainless steel to maintain the airtightness of the vessel and contain radioactive materials. In addition, a heat-resistant and corrosion-resistant nickel-based alloy (Inconel®) buildup is formed at the welded joints on the inner surface of the reactor pressure vessel 30.

[0015] The composition of metal corrosion products generated in the reactor cooling system (primary reactor system) varies significantly even within light water reactors, depending on whether it is a boiling water reactor (BWR) or a pressurized water reactor (PWR), and also depending on the location. Here, metal corrosion products include not only water-insoluble and dispersed metal oxides (also called "cladding," such as hematite (Fe2O3) and magnetite (Fe3O4)), but also oxide films formed on the surface of in-reactor structures (such as the oxide film of Inconel, Cr2O3).

[0016] A movable body 32, located at the top of the reactor pressure vessel 30, allows a probe 20 suspended from the tip of a suspension member 25 to be arbitrarily positioned and directed within the cooling water 26. In this embodiment, surface analysis of an in-core structure in contact with the cooling water 26 of the reactor pressure vessel 30 in a boiling water reactor (BWR) is illustrated. However, the application of the surface corrosion analyzer is not limited to this, and it can also be applied to corrosion analysis of in-core structures in contact with cooling water in a pressurized water reactor (PWR), and to metal surfaces in contact with the gas phase.

[0017] FIG. 2 is a block diagram showing a control circuit 10a(10) of the surface corrosion analyzer according to the first embodiment. As described above, the surface corrosion analyzer of the first embodiment includes a transmitter 11 that transmits a light emission command 12 to a light source 21 that irradiates the surface 33 of a metal member (the in-vessel structure of the reactor pressure vessel 30 in the drawing) with irradiation light 23 (FIG. 3) and reflects reflected light 24 (FIG. 3), a receiver 15 that receives a first image signal 16a and a second image signal 16b from an imaging unit 22 that images the surface 33 with at least two types of first wavelength components 41 (FIG. 4) and second wavelength components 42 (FIG. 4) of the reflected light 24, a luminance setting unit 17 that sets a first luminance 13a and a second luminance 13b of pixels that constitute an image of the surface 33 based on the first image signal 16a and the second image signal 16b, and an analysis unit 18 that analyzes the composition distribution of metal corrosion products deposited on the surface 33 based on the first luminance 13a and the second luminance 13b.

[0018] Each of FIGS. 3(A1) and (A2) shows a front view and a side view of a probe 20a (light source 21a, imaging unit 22a) of Example 1. As described above, in the probe 20a of Example 1, a plurality of light sources 21 are arranged in an annular shape at the center position of the imaging unit 22. Thereby, the composition distribution can be analyzed without being affected by halation (reflection) due to the unevenness of the surface 33.

[0019] Each of FIGS. 3(B1) and (B2) shows a front view and a side view of a probe 20b (light source 21b, imaging unit 22b) of Example 2. As described above, in the probe 20b of Example 2, the optical axes 27, 27 of a pair of light sources 21b, 21b arranged on both sides sandwiching the imaging unit 22b intersect the optical axis 28 of the imaging unit 22b at the same angle. Thereby, when the first wavelength component 41 and the second wavelength component 42 of the irradiation lights 23, 23 are output from separate light sources 21b, 21b (such as light emitting diodes) (described later), the reflected light 24 can be efficiently incident on the imaging unit 22b.

[0020] Each of FIGS. 3(C1) and (C2) shows a front view and a side view of the probe 20c (light source 21c, imaging unit 22c) of Example 3. As such, the probe 20c of Example 3 is arranged such that the optical axis 27 of the light source 21 and the optical axis 28 of the imaging unit 22 intersect at the same angle with respect to the normal line 29 of the surface 33. Thereby, when outputting the irradiation light 23 from the light source 21 (such as an incandescent lamp) including both the first wavelength component 41 and the second wavelength component 42 (described later), the reflected light 24 can be efficiently incident on the imaging unit 22b.

[0021] In FIG. 1, the imaging unit 22 and the light source 21 are configured as an integrated probe 20, but they may be separately configured.

[0022] FIG. 4 is a graph showing the reflectance (%) of the reflected light 24 with respect to the wavelength (nm) of the irradiation light 23 for typical compositional metal corrosion products (Cr2O3, Fe2O3, Fe3O4) deposited on the surface of the in-vessel structure of the reactor coolant system. Here, the reflectance represents the ratio of the intensity of the irradiation light 23 and the intensity of the reflected light 24 for each wavelength.

[0023] As shown in FIG. 4, the metal corrosion products of the above composition have a characteristic that a significant difference in reflectance is observed in the wavelength range 40 of 550 nm to 900 nm. Also, in this wavelength range 40, there are metal corrosion products (for example, Cr2O3, Fe2O3) with large fluctuations in reflectance and metal corrosion products (for example, Fe3O4) with small fluctuations.

[0024] Utilizing this feature, based on the first wavelength component 41 and the second wavelength component 42 selected from the wavelength range 40 of 550 nm to 900 nm, the composition of the metal corrosion product deposited on the reflected surface 33 can be identified. Specifically, for the difference or ratio of the intensities of both, the first wavelength component 41 and the second wavelength component 42 are experimentally found so as to have unique determination values for various compositions of the metal corrosion product. Note that the wavelength components used to derive such determination values are not limited to the above two types, and more may be used.

[0025] Returning to Figure 1, we continue the explanation. The transmitting unit 11 transmits a light emission command 12 to the light source 21 to emit illumination light 23 containing a first wavelength component 41 and / or a second wavelength component 42. Here, the light source 21 may either include both the first wavelength component 41 and the second wavelength component 42 in the illumination light 23, or include either the first wavelength component 41 or the second wavelength component 42.

[0026] In the former case, the light emission command 12 causes the imaging unit 22 to output the illumination light 23 for a period of time sufficient to discriminate and detect the first wavelength component 41 or the second wavelength component 42. In the latter case, the light emission command 12 causes the illumination light 23 containing the first wavelength component 41 and the illumination light 23 containing the second wavelength component 42 to be output separately with a time difference.

[0027] The receiving unit 15 receives a first image signal 16a, which images the surface 33 with the first wavelength component 41 of the reflected light 24, and a second image signal 16b, which images the surface 33 with the second wavelength component 42. Here, each of the first image signal 16a and the second image signal 16b contains intensity information of the first wavelength component 41 and the second wavelength component 42 for each pixel constituting the image of the surface 33. Note that the wavelength components 41, 42 and the image signals 16a, 16b are not limited to two types, but may be more than two.

[0028] The brightness setting unit 17 sets the first brightness 13a of the pixels constituting the image of the surface 33 based on the first image signal 16a. Furthermore, the brightness setting unit 17 sets the second brightness 13b of the pixels constituting the image of the surface 33 based on the second image signal 16b. Here, the first brightness 13a and the second brightness 13b correspond to the intensities of the first wavelength component 41 and the second wavelength component 42, respectively. In this way, two types of images are obtained separately for the surface 33: an image of the first wavelength component 41 and an image of the second wavelength component 42.

[0029] The analysis unit 18 analyzes the compositional distribution of metal corrosion products accumulated on the surface 33 based on the first brightness 13a and the second brightness 13b. Here, assuming for illustrative purposes that the spectrum of the irradiated light 23 is flat, the spectrum of the reflected light 24 from the surface 33 where the metal corrosion products (Cr2O3, Fe2O3, Fe3O4) are accumulated will draw the same curve as in Figure 4.

[0030] For each pixel of interest in the image of surface 33, if "first brightness 13a < second brightness 13b", it is suggested that the composition of the metal corrosion product is Fe2O3; if "first brightness 13a > second brightness 13b", it is suggested that the composition of the metal corrosion product is Cr2O3; if "first brightness 13a ≈ second brightness 13b" and the value is small, it is suggested that the composition of the metal corrosion product is Cr2O3; and if "first brightness 13a ≈ second brightness 13b" and the value is large (considered to be total internal reflection), it is suggested that there is no accumulation of metal corrosion products.

[0031] The attribute information base 14 stores information that has been experimentally obtained in advance from images of known metal corrosion products, specifically the first brightness 13a and the second brightness 13b, and links the resulting judgment values ​​with the composition of the metal corrosion products. The analysis unit 18, upon receiving the first brightness 13a and the second brightness 13b as input, accesses the attribute information base 14 and outputs the attribute information of the surface 33 (composition of the metal corrosion products or composition of the base metal). Attribute information is then assigned to each pixel, and by making each pixel emit light at the brightness associated with this attribute information, an image 19 showing the compositional distribution of the metal corrosion products is obtained.

[0032] (Second Embodiment) Next, a second embodiment of the present invention will be described with reference to Figure 5. Figure 5 is a block diagram showing the control circuit 10b(10) of the surface corrosion analyzer according to the second embodiment. The control circuit 10b in the second embodiment has a configuration that adds a switching unit 35(35a,35b), a distance measuring unit 36, a correction unit 37, and a modification unit 38 to the configuration of the control circuit 10a of the first embodiment described above. In Figure 5, parts that have the same configuration or function as those in Figure 1 are indicated by the same reference numerals, and redundant explanations are omitted.

[0033] When using light-emitting diodes as the light source 21 (Figure 3), the irradiation light 23, which has a single spectrum containing the first wavelength component 41 and the second wavelength component 42 separately, is irradiated from separate light-emitting diodes (light sources 21). In this case, the first switching unit 35a switches between the separate light-emitting diodes (light sources 21) to irradiate each irradiation light 23 separately.

[0034] The light source 21 used preferably outputs irradiation light 23 having a single spectrum in the wavelength range 40 of 550 nm to 900 nm. When using a highly directional light source 21, such as a semiconductor laser, it is preferable to use a lens that uniformly spreads the irradiation light 23.

[0035] Furthermore, when an incandescent lamp is used as the light source 21 (Figure 3), continuous spectrum light 23 including the first wavelength component 41 and the second wavelength component 42 is irradiated from a single incandescent lamp (light source 21). In this case, the second switching unit 35b switches a filter (not shown) to allow the first wavelength component 41 and the second wavelength component 42 to pass through the continuous spectrum separately.

[0036] The correction unit 37 corrects the intensity of the first wavelength component 41 and the second wavelength component 42, taking into account the attenuation of the irradiated light 23 and reflected light 24 propagating through the water. To this end, the distance measuring unit 36 ​​determines the distance from the position of the surface 33 corresponding to the pixel to the light source 21 based on the first image signal 16a and the second image signal 16b. Then, according to this determined distance, it determines the amount of attenuation of the intensity of the first wavelength component 41 and the second wavelength component 42, and corrects the first brightness 13a and the second brightness 13b of the pixel.

[0037] The correction unit 38 outputs a corrected image 39 in which the pixels of the image obtained by the first wavelength component 41 and the image obtained by the second wavelength component do not match, and the compositional distribution is corrected. As shown in Figure 1, the probe 20 (light source 21 and imaging unit 22) is supported in the cooling water 26 and can be in both a stationary and moving state. When in a moving state, the first image signal 16a and the second image signal 16b, received with a time difference, will be images of different areas of the surface 33.

[0038] Consequently, the first brightness 13a and second brightness 13b set in the brightness setting unit 17 may correspond to pixels at different locations on the surface 33. As a result, the analysis unit 18 may incorrectly analyze the attribute information of the metal corrosion products on the surface 33. The correction unit 38 corrects the composition distribution image 19 output based on such incorrect attribute information and outputs it as a corrected image 39.

[0039] According to the surface corrosion analyzer of at least one embodiment described above, it is possible to analyze the compositional distribution of metal corrosion products accumulated on the surface of a structure by capturing an image based on the first and second wavelength components of the reflected light from the light source.

[0040] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, modifications, and combinations are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0041] 10 (10a, 10b)... Control circuit of surface corrosion analyzer, 11... Transmitter, 12... Light emission command, 13a... First brightness, 13b... Second brightness, 14... Attribute information base, 15... Receiving unit, 16a... First image signal, 16b... Second image signal, 17... Brightness setting unit, 18... Analysis unit, 19... Image of composition distribution, 20 (20a, 20b, 20c)... Probe, 21 (21a, 21b, 21c)... Light source, 22 ( 22a, 22b, 22c)...imaging unit, 23...irradiated light, 24...reflected light, 25...suspension member, 26...cooling water, 27, 28...optical axis, 29...normal, 30...reactor pressure vessel, 31...shroud, 32...moving body, 33...surface, 35 (35a, 35b)...switching unit, 36...distance measurement unit, 37...correction unit, 38...correction unit, 39...corrected image, 40...wavelength range, 41...first wavelength component, 42...second wavelength component.

Claims

1. A transmitting unit that transmits a light emission command to a light source that irradiates light onto the surface of a metal component and reflects the reflected light, A receiving unit receives a first image signal and a second image signal from an imaging unit that images the surface with at least two types of first and second wavelength components of the reflected light, A brightness setting unit sets a first brightness and a second brightness of pixels constituting the image on the surface based on the first image signal and the second image signal, A surface corrosion analyzer comprising: an analysis unit that analyzes the compositional distribution of metal corrosion products accumulated on the surface based on the first brightness and the second brightness.

2. In the surface corrosion analyzer according to claim 1, The surface, the light source, and the imaging unit are a surface corrosion analysis device that is submerged in water.

3. In the surface corrosion analyzer according to claim 2, The aforementioned surface is the contact surface with the water contained in the reactor pressure vessel. The light source and the imaging unit are suspended and supported from the upper opening of the reactor pressure vessel in a surface corrosion analysis apparatus.

4. In the surface corrosion analyzer according to claim 2 or claim 3, A surface corrosion analyzer comprising a correction unit that corrects the first brightness and second brightness of the pixel according to the distance from the position of the surface corresponding to the pixel to the light source.

5. In the surface corrosion analyzer according to any one of claims 1 to 3, The first wavelength component and the second wavelength component are selected from a wavelength range of 550 nm to 900 nm in a surface corrosion analyzer.

6. In the surface corrosion analyzer according to any one of claims 1 to 3, The light source emits the irradiation light, which comprises a single spectrum containing the first wavelength component and the second wavelength component separately, from separate light sources. A surface corrosion analyzer comprising a first switching unit that switches between separate light sources to irradiate each light source separately.

7. In the surface corrosion analyzer according to any one of claims 1 to 3, The light source emits the irradiation light, which has a continuous spectrum including the first wavelength component and the second wavelength component, by itself. A surface corrosion analyzer comprising a second switching unit that separates the first wavelength component and the second wavelength component from the continuous spectrum by switching filters.

8. In the surface corrosion analyzer according to any one of claims 1 to 3, A surface corrosion analyzer comprising the light source and the imaging unit, wherein a plurality of the light sources are arranged in a ring shape at the center of the imaging unit, or the optical axes of a pair of light sources arranged on either side of the imaging unit intersect the optical axis of the imaging unit at the same angle, or the optical axes of the light sources and the optical axis of the imaging unit intersect the normal to the surface at the same angle.

9. In the surface corrosion analyzer according to any one of claims 1 to 3, A surface corrosion analyzer comprising a correction unit that, when the image obtained by the first wavelength component and the image obtained by the second wavelength component do not match, matches the pixels of both and outputs a corrected image with the composition distribution corrected.

10. The process involves transmitting a light emission command to a light source that emits light onto the surface of a metal component and reflects the reflected light, The steps include receiving a first image signal and a second image signal from an imaging unit that has imaged the surface with at least two types of first and second wavelength components of the reflected light, A step of setting a first brightness and a second brightness of pixels constituting the image on the surface based on the first image signal and the second image signal, A surface corrosion analysis method comprising the step of analyzing the compositional distribution of metal corrosion products accumulated on the surface based on the first brightness and the second brightness.

Images