JP2672613B2 - Surface treatment method for reactor internal structures and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a surface treatment method for a reactor internal structure and equipment installed in reactor water in a reactor pressure vessel.

(Prior Art) The configuration of a conventional boiling water reactor will be described with reference to the schematic diagram of FIG. At the center of the reactor pressure vessel 1, hundreds of fuel assemblies 2 are arranged. Further, hundreds and ten control rods 3 are arranged at a rate of one for every four fuel assemblies 2. These fuel assemblies 2 and control rods 3 etc.
Is formed. The upper part of the fuel assembly 2 is supported by the upper lattice plate 5, and the lower part thereof is supported by the core support plate 6 at predetermined positions. The upper lattice plate 5 and the core support plate 6 are fixed to a cylindrical shroud 7 that surrounds the core portion 4. Above the shroud 7, a dish-shaped shroud head 8 is installed. Hundreds of steam separators 9 are planted on the upper part of the shroud head 8, and a steam dryer 10 is arranged further above. On the other hand, below the shroud 7, a shroud support 11 is installed. In addition, dozens of jet pumps 12 are arranged in the gap between the shroud 7 and the reactor pressure vessel 1, and cooling water is forcedly circulated in the core to adjust the reactor output. A guide tube 13 of a control rod drive mechanism (not shown) is arranged at the bottom of the reactor pressure vessel 1. In addition, equipment such as a feed water sparger, a core spray line, and a spray sparger are installed in the reactor pressure vessel.

As described above, there are various nuclear reactor internal structures and equipment in the reactor pressure vessel 1, and austenitic stainless steel is used.

(Problems to be Solved by the Invention) Austenitic stainless steel may cause intergranular stress corrosion cracking (IGSCC) in high temperature pure water.

The major material-side factor of IGSCC is the formation of grain boundary carbides in the heat-affected zone of the weld due to the heat cycle such as welding and the accompanying formation of a Cr-deficient layer near the grain boundaries, that is, the welding sensitivity. It is becoming.

Furthermore, the equipment and structures installed in the radiation irradiation field
Irradiation-induced segregation caused by irradiation may cause impurities to segregate at the grain boundaries, resulting in reduced corrosion resistance at the grain boundaries.

An object of the present invention is to eliminate a chromium deficient layer or a grain boundary segregation portion in a region having low intergranular corrosion cracking resistance on a surface of an austenitic stainless steel in contact with reactor water (hereinafter referred to as a liquid contact portion) in a reactor pressure vessel. Another object of the present invention is to provide a surface treatment method for reactor internals and equipment that can change the surface texture to have excellent intergranular corrosion cracking resistance.

[Configuration of the invention]

(Means for Solving the Problems) In order to achieve the above object, in the present invention, the surface of a welded portion of an austenitic stainless steel reactor internal structure and equipment installed in reactor water in a reactor pressure vessel And a surface treatment method for a reactor internal structure and equipment, which comprises a melting step of melting a molten steel with a laser in reactor water, and a quenching step of rapidly cooling the surface of the melted welded portion with the reactor water. To do.

(Operation) The surface of the internal structure of the reactor installed in the reactor water in the reactor pressure vessel, which has poor corrosion resistance, is affected by welding heat-affected zone and the grain boundary segregation zone caused by irradiation etc. is melted by laser. This molten surface is rapidly cooled by the surrounding reactor water, ferrite is generated, and two phases are formed. This makes it possible to improve the corrosion resistance.

(Embodiment) An embodiment of the surface treatment method for reactor internals and equipment according to the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 is a cross-sectional view of a nuclear reactor and the periphery of the nuclear reactor. This FIG. 1 shows a periodic inspection, and the reactor water 1 is filled with reactor water 29. The surface treatment device includes a laser oscillator 20, a driving device 21, and a laser emitting section 22. The laser oscillator 20 is installed on the operation floor surface 23 and has a remote control panel 24 for operating the drive unit 21. The drive unit 21 is installed on the flange surface 25 of the nuclear reactor 1, and is configured so that the laser emitting unit 22 can be moved to any place in the nuclear reactor 1. The drive device 21 and the laser oscillator 20 are connected by a control line 26, and the laser oscillator 20 supplies power to the drive device 21 and transmits a drive signal. In addition, the control line 26 transmits an image signal from an image input unit (not shown) installed in the vicinity of the laser emission unit 22 from the drive device 21 to the laser oscillator 20. The laser oscillator 20 and the laser emission unit 22 are connected by a laser guide tube 27, and the laser light generated by the laser oscillator 20 is reflected by a mirror in the laser guide tube 27 while being welded to a heat-affected zone which is a melting target section. Equivalent to 28.

FIG. 2 is an enlarged sectional view showing a portion A of FIG. 1, and FIG. 3 is a front view of the surface of the shroud 7 as seen from the direction B of FIG.

As shown in FIG. 2, a laser beam 30 is applied to the portion of the welding heat affected zone 28 of the austenitic stainless steel (shroud 7) in contact with the reactor water 29. It melts the surface of the wetted part, which is a problem of corrosion resistance. As for the melting depth, only the surface needs to have corrosion resistance, and therefore, a depth of 20 to 100 μm is melted from the surface of the liquid contact portion. This molten surface is the same as the surrounding reactor water 29.
And then the surface treatment is completed. The part where the surface treatment is completed is the two-phase conversion part 31. The portion indicated by reference numeral 32 in FIGS. 2 and 3 is a welded metal portion.

Fig. 4 shows the structure when the welded portion was surface-treated, cut in the cross-sectional direction and etched with 10% oxalic acid. Cr carbide 41 is precipitated in the weld heat affected zone 28 of the stainless steel base material 40, and a Cr deficient layer is formed around it. On the other hand, after being melted by the laser, the portion rapidly cooled has ferrite 42 formed up to a depth of about 80 μm, and has a two-phase structure. That is, in the member with segregated grain boundaries, the liquid contact portion is melted by a laser and then rapidly cooled, so that the segregated impurities diffuse and the segregated portion disappears, and that portion becomes a two-phase stainless steel containing ferrite.

Table 1 shows the results of the SCC test performed on the test piece taken from the joint including the weld heat affected zone of SUS304 steel and the test piece taken from the duplex stainless steel containing about 6% of ferrite.

The test conditions were 8 ppm of dissolved oxygen and high temperature pure water of 288 ° C. As a test method, a test piece 51 is attached to a test jig 50 shown in FIG. 5 and immersed for 500 hours. Reference numeral 53 in FIG. 5 is a bolt, and reference numeral 52 is graphite wool. As shown in Table 1, intergranular cracking occurred in the weld heat affected zone of the joint including the weld heat affected zone, but no crack occurred in the duplex stainless steel containing ferrite.

A technique such as a plasma method may be used instead of the laser method.

〔The invention's effect〕

According to the present invention, since the welded heat-affected zone having poor corrosion resistance or the welded portion in the segregation zone is melted by a surface treatment technique such as laser and then rapidly cooled to be two-phased, the corrosion resistance can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view around a nuclear reactor showing a surface treatment method according to the present invention, FIG. 2 is a cross-sectional view showing an enlarged part A of FIG. 1,
3 is a front view of the surface of the shroud 7 as seen from the direction B in FIG. 2, FIG. 4 is a structural diagram according to the present invention, FIG. 5 is a front view of a test jig according to the present invention, and FIG. FIG. 1 is a schematic diagram of a boiling water reactor according to the present invention. 1 …… Reactor, 7 …… Shroud 28 …… Welding heat affected zone, 29 …… Reactor water 30 …… Laser light

Claims (1)

(57) [Claims] 1. A melting step of melting a surface of a welded portion of an austenitic stainless steel reactor internal structure and equipment installed in reactor water in a reactor pressure vessel by laser in reactor water, and the melted welding. And a surface cooling method for rapidly cooling the surface of a part with the reactor water.