JPS59192995A - Method and device for exchanging reactor pressure vessel safety end - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for replacing a safe end connected to a nuclear reactor pressure vessel (abbreviated as RPV) and a device therefor. .

[Background of the invention]

In recent years, in boiling water reactors, there have been cases of stress corrosion cracking occurring in piping made of austenitic stainless steel such as high carbon stainless steel 5US304 and RPV safe ends, and various measures have been taken to prevent stress corrosion cracking. Action is being taken.

Weld heat affected zone of austenitic stainless steel (hereinafter referred to as
Intergranular stress corrosion cracking that occurs in HAZ (abbreviated as HAZ) is
The following three problems occur: the generation of high tensile stress that exceeds the yield strength of the material by 0.2%, the formation of a chromium-deficient layer (this is called sensitization) along the grain boundaries in the AZ region, and a corrosive environment such as dissolved oxygen. Stress corrosion cracking occurs when conditions are superimposed.If even one of the three conditions mentioned above is absent, stress corrosion cracking will not occur.

Taking the case of piping as an example, high-carbon SUS 304 piping, etc., is bath-welded using conventional natural cooling welding (no forced cooling such as filling water inside the piping during welding). As shown in Fig. 1, in stainless steel piping containing carbon dioxide, tens of tens of 90% of the inside surface of the piping 1 is damaged due to thermal stress due to the temperature difference between the inside and outside in the thickness direction of the piping 1 during welding and shrinkage of the piping 1 due to heat. A high tensile residual stress of up to v==2 is generated in the weld 2 as shown by curve 4 (5 indicates 0.2% yield strength) and in the HAZ area near the weld 2 (3 in the figure). ), and if this is combined with a corrosive environment, there is a risk of stress corrosion cracking occurring here.

Since the safe end that is welded to the RPV of a boiling water reactor is usually made of SUS 304 forged steel, the three conditions mentioned above combine to cause stress corrosion cracking to occur near the weld to the RPV. There is a risk.

As a countermeasure to this problem, consideration is being given to replacing the safe end made of 5US304 forged steel with a low carbon stainless steel forged product before stress corrosion cracking occurs. In particular, early measures are being considered for plants where stress corrosion cracking has recently occurred as described above.

Replacement of such safe ends must be completed within a short period of time since there is a risk of radiation exposure to workers.

[Purpose of the invention]

SUMMARY OF THE INVENTION In order to meet the above-mentioned needs, it is an object of the present invention to provide a method and apparatus for quickly replacing a safe end welded to an RPV.

[Summary of the invention]

The method of replacing a reactor pressure vessel safe end according to the present invention is to cut the piping welded to the safe end, and further cut the thermal sleeve from the safe end near the base, and to replace the nozzle part of the reactor pressure vessel with the safe end. Cut the welded part with the end.

The weld heat affected zone (HAZ) of the nozzle after cutting is removed, and then a new safe end made of low carbon stainless steel is welded to the nozzle, and the inside and end of the new safe end and the above This method is characterized by welding the cut remaining thermal sleeve and external piping.

Further, the device used in the method for replacing the reactor pressure vessel safe end according to the present invention is capable of being suspended along the inner circumferential surface of the reactor pressure vessel, and is connected to the main body, and is connected to the reactor pressure vessel and is connected to the reactor pressure vessel. a gripping device that removably grips a jet pump riser pipe in the vessel and is held by being stretched from a shroud in the reactor pressure vessel; A sealing mechanism that is stretched from the shroud and is in liquid-tight pressure contact with the inner circumferential surface of the reactor pressure vessel; and means for flowing air and pack purge gas through the sealing mechanism. It is.

[Embodiments of the invention]

Examples of the method according to the invention will be described below.

In this example, the jet pump nozzle is
``-'' safe end will be explained.

FIG. 2 is an elevational sectional view showing the configuration of the RPV, safe end, thermal sleeve, and jet pump riser pipe to which the present invention relates, and FIG. 3 is a plan sectional view thereof.

In Figures 2 and 3, 6 is RPV, 7 is RPV
6 (7) Nozzle 6 of i RPV 5 installed on the outer periphery
8 is a thermal sleeve, 9 is a jet pump riser pipe attached to the thermal sleeve 8, and 10 is a pipe connected to the safe end 7. 16 indicates a shroud provided within the RPV 6.

Figure 4 shows the details. 10 shows a pipe welded and connected to the safe end 7. RPV 6 nozzle 6
', safe end 7, thermal sleeve 8, riser pipe 9, piping 10, etc. are connected by a welded structure shown in black in the figure. These welded structures are determined by ease of manufacture and installation during plant construction. In particular, the welding part 11 between the safe end 7 and the pipe 10 and the welding part 1 between the nozzle 6' of the RPV 6 and the safe end 7, where the three-line stress corrosion cracking described above is superimposed and stress corrosion cracking has occurred in the past.
In the HAZ part near 2, there is a high possibility that stress 1 side corrosion cracking will occur, and if this occurs, the RP will be removed from there.
This is the part that requires the most attention as the coolant inside the V6 will leak.

According to an embodiment of the method of the invention, stress corrosion 1 as described above
The work of replacing the safe end 7, which has been subject to wear and tear, with a new safe end made of low carbon stainless steel forging is carried out in accordance with the process described below with reference to FIGS. 5 to 7.

As shown in Figure 5, the coolant inside the RPV 6 is drained in advance to just below the jet pump main body nozzle, and then
Cut 0. This cutting is carried out using a porta-pull which is attached and fixed to the outer periphery of the nozzle 6' of the RPV 6 and a part of the piping 10 and is held by an equipment holding device 13 supported by the access floor 15 and driven to revolve around the axis of the piping 10. This is done by using a suitable cutting machine or fusing machine 14.

After this cutting is completed, the thermal sleeve 8 is cut as shown in FIG. Before this cutting, the suet pump riser pipe 9 is welded to the thermal sleeve 8.
was released by the cutting and deformed or moved to the side opposite to the inner surface of the RPV 6, causing problems in installing and welding the new safe end and thermal sleeve, or resulting in an increase in work time. It is necessary to take measures to prevent this from happening. Therefore, a fixing device 17 is installed between the riser pipe 9 and the shroud 16 to prevent it from moving, and pressurized air is also installed to prevent foreign matter such as chips from entering the RPV S when the thermal sleeve 8 is cut. A sealing mechanism 18 ejecting toward the outside of the RPV 6 is brought into close contact with the inner surface of the RPV 6. Then, a portable cutting machine (separated from 19 and 19' in FIG. 6) is held by the equipment holding device 13 to cut the welded portion near the base of the thermal sleeve 8 as shown in FIG.

Next, the old safe end 7 connected to the nozzle 6' is cut and removed, and then a new safe end 20 is welded and installed as shown in FIG. 7, and the thermal sleeve 8 and piping 10 are welded to this. Connect and restore. This is done as follows.

When cutting the safe end 7, use the thermal sleeve 8 mentioned above.
Similarly to cutting, the pressurized air from the sealing mechanism 18 is
The welded portion 12 is cut by the porta-pull cutter 14 while preventing foreign matter from entering the RPV 6 by spouting it outward from the PV 6 . After cutting the safe end 7, replace the cutting machine 14 with a portable processing machine, support it on the equipment holding device 13, and cut the distance including the HAZ part on the RPV side of the welding part 12 (approximately more than the plate thickness of the safe end). Cut the nozzle part 6' of the RPV 6 to a position that is closer to the RPV side from the welded part 12 by (as a guide). This process is the final finish for installing a new safe end, so
In particular, it is necessary to reduce the feeding speed and rotational speed of the processing machine below the rated speed, and to carefully control the processing machine so that high-precision surface finishing can be achieved at low speeds. After the machining is completed, as shown in Fig. 7, the processing machine is replaced with a porta-pull welding machine 14, and considering that the material of the RPV 6 is carbon steel, the nozzle 6' is first overlaid, and then the beveling is performed. Repeat processing as described above. After completion of this processing, low carbon content (C less than 0.020%)
A new safe end 20 (having a root for connecting the thermal sleeve), which is a stainless steel forged product, is newly welded to the nozzle portion 6' of the RPV 6. During this welding, pack gas (argon gas, etc.) is supplied and exhausted from the sealing mechanism 18 in view of the construction method and welding quality. Note that the gas is supplied from the upper part of the sealing mechanism 18 and exhausted from the lower part according to the characteristics of the gas and the specifications of the back part. Next, the remaining round sleeve main body 8 after the cutting is welded to the base of the new low carbon stainless steel forging. Since this welding involves welding residual SUS 304 material that has not yet been treated with stress corrosion cracking and new material, from the perspective of stress corrosion cracking prevention, the specified cooling water is supplied from the gas supply port of the sealing mechanism 18 to complete the first layer welding. Water-cooled welding is then performed by running water to reduce residual stress caused by welding. Similarly, piping 1
Weld 0 to the end of the new safe end. After construction, radiographic tests and liquid penetrant flaw tests will be conducted to confirm the integrity of the welded areas in accordance with standards and regulations.

Replacement is carried out using the method described above, but in cases where the radiation exposure to workers is high due to the water shielding effect in the RPV, further processing and installation of equipment for installing cutting and welding machines may be necessary. It is desirable to provide the device 13 with a lead shielding plate and to operate it remotely as much as possible.

Next, an example of an apparatus used in the method of the present invention will be described.

FIG. 8 shows a mechanism for preventing displacement of the jet pump riser pipe 9 in the process (corresponding to 17 above), and RP during cutting and welding of the safe end.
It serves both as a supply of air to prevent foreign matter from entering the V-circle and a supply of pack gas during welding, and also to the upper part of the RPV nozzle (to the area directly below the nozzle part of the jet pump body) to reduce radiation exposure during the above work. FIG. 9 is a side view showing a sealing mechanism (corresponding to 18 above) that allows water to fill in, and FIG. 9 is a plan view thereof.

In Figures 8 and 9, 21 is Jet Bongra f.
22 is a support rod that is integrally attached to the grip device 21 and has a buckle structure; 23 is a seal portion that covers the horizontal portion of the riser tube 9 and is pressed against the inner surface of the RPV 6; 24 is a riser The seal part 25, which can be attached to the horizontal part of the tube 9 and is in close contact with the seal part 23, indicates a pair of support rods for properly pressing the seal parts 23 and 24. 26 is the gripping device 21 and the sealing part 23゜2
4 is shown.

The gripping device 21 is attached to a main body 26, and has a mechanism in which a two-part claw grips and releases the silizer tube 9 so that it can be gripped horizontally by rotating a socket provided in the main body 26. . An elastic rubber plate is attached to this claw portion so as not to damage the existing riser pipe 9. Further, a support rod 22 integrally attached to the claw portion of the gripping device 21 engages the outer circumference of the shroud 16 to prevent the riser pipe 9 from moving toward the shroud 16 due to the safe end of the RPV 6 and the cutting release of the thermal sleeve. contact,
The buckle portion 27 provides tension. The buckle part 27, which will be described in detail later, can be adjusted to maintain the distance between the riser pipe 9 and the shroud 16 by operating it with a general-purpose pole prepared in advance from the flange surface of the RPV 6 or from the fuel exchange trolley. It has become.

The seal portion 23 has connection ports 28 and 29 that serve both to supply air to prevent foreign matter from entering the RPV during cutting and to supply and exhaust back gas during welding. Furthermore, in order to reduce exposure to radiation, the seal part 23 is designed so that the contact part with the inner surface of the RPV and the joint part with the seal part 24 can be completely sealed with an O-ring 31 etc. so that water can be filled as described above. riser pipe 9
The gripping devices 2 and 1 can be attached from above to the horizontal part of the
It also has a two-part structure. Further, the seal portion 23 is
Uniform and fixed surface pressure (approximately 4 kg/crn) on the inside of RPV
As mentioned above, the shroud 1 is attached by the buckle 27 so that it can be sealed while maintaining the surface pressure (to withstand 2G of water pressure).
It is pressed against the 6th side.

The seal part 24 has a two-part structure like the above-mentioned gripping device 21, and like the seal part 23, even when filled with water as described above, the joint part with the riser pipe 9 and the seal part 23.
The connecting part has a sealing property that can withstand the aforementioned water pressure.

FIG. 10 is a view taken along line AA in FIG. 8.

As can be seen from this figure and FIGS. 8 and 9, the shape and structure of the two-split claw portion of the gripping device 21 and the seal portion 23
, 24 has a structure that can be rotated relative to each other by the illustrated bottle joint, and the connection ports 28 and 29 for air supply and gas supply and discharge of the seal part 23 are designed to allow for relative rotation during welding. Due to the characteristics of the gas pump/e-duke, the supply connection port is located at the top and the exhaust connection port is located at the bottom, as shown in the figure. The reason why the support rods 25 of the seal portion are arranged as a pair is to bring the seal portion 23 into uniform contact with the inner surface of the RPV 6.

FIG. 11 shows a detailed cross-section of the seal portions 23 and 24. As shown in the figure, the structure is such that a plurality of Q IJ rings 31 improve sealing performance. RPV 6 and Safe End 7
When cutting the welded part 12 of the new safe end 20, air is supplied under pressure to the outside of the RPV 6 through the connection ports 28 and 29 in order to prevent chips and the like from entering the RPV 6 as foreign matter. In such cases, connect the back
No gas is supplied and the gas is exhausted from the connection port 29.

Note that gas and air will be supplied from the top of RPV 6 and the fuel exchange truck.

12, 13, and 14 are front views showing the structure of the buckle 27 as cross-sectional views, respectively.

FIG. 2 is a plan view and a side view. The buckle 27 is the support rod 22.
25 has opposed right-hand and left-hand threads cut at the ends thereof, and by rotating the shaft 32 with the aforementioned general-purpose pole, a geared nut 34 that is screwed into the above-mentioned screws is rotated via a gear 33. and this rotation causes the support rod 22.2 to
5 toward or away from each other.

The operation of the above device as a whole will be explained below.

The gripping device 21, sealing portions 23, and + 24 connected to each other are integrally connected to the RPV 6 by the gripper 30 of the main body 26 using a general-purpose pole or rope prepared in advance.
After lowering the gripping device 21 from above to the position shown in FIG.
4 to the horizontal part of the riser pipe 9. The seal portion 23 is mounted and fixed so as to cover the seal portion 24, and is supported by the support rod 25 against the sea loud 16. In this state, the gripping device #21 is fixed to the sea loud 16 and the riser pipe 9, the main body 26 is set in an immovable position and does not move, and the seal portion 23 is pressed against the inner surface of the RPV 6 by the support rod 25. and the seal part 23
．． 24 and between the seal portion 23 and the RPV inner surface.
The ring 31 provides a complete seal. In this state, the above-described cutting and welding of the new safe end are performed.

〔Effect of the invention〕

The RPV safe end replacement method according to the present invention has a systematic operating procedure, so the safe end can be replaced in a short time, reducing worker exposure to radiation, and the welding heat of the RPV nozzle. Since the affected zone (HAZ zone) is removed, the risk of stress corrosion cracking can be minimized.

Furthermore, according to the device used for replacing the RPV safe end according to the present invention, during the replacement work, the Noenoto pump riser pipe in the RPV and the thermal sleeve connected thereto can be held so that they are not unnecessarily displaced from their original positions. The work becomes significantly easier, and an air jet is applied during cutting to prevent foreign matter from entering the RPV, and a back part gas flow is applied during welding to improve welding quality. It is possible to work with water filled directly below the nozzle of the suet pump body, which has the effect of reducing radiation exposure for workers.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the occurrence of leg force corrosion cracking, Fig. 2 is a view of the branch centering around the safe end of the RPV, Fig. 3 is its plan cross-sectional view, and Fig. 4 is the vicinity of the safe end of the RPV. 5 to 7 show the process in an embodiment of the method of the present invention, in which FIG. 5 shows the cutting of the piping, FIG. 6 shows the cutting of the thermal sleeve, and FIG. 7 shows the cutting of the safe end. FIG. 3 is a diagram showing disconnection and restoration. Fig. 8 is a side view of the entire embodiment of the device of the present invention, Fig. 9 is a plan view thereof, Fig. 10 is an elevational view taken from A-A in Fig. 8, and Fig. 11 is the device of the above embodiment. 12, 13 and 14 are front, top and side sectional views, respectively, of the buckle 27 in the device. 6: Reactor Pressure Vessel, 7: Safe End, 8: Thermal Sleeve, 9 Rainbow Engineering Row? pump riser pipe, 10: external piping, 11, 12: welded part, 13:
Equipment mounting device, 14: Cutting machine, 16: Shroud, 17: Riser pipe displacement prevention mechanism, 18: Seal mechanism, 19.19': Cutting machine, 21
: Gripping device, 22: Support rod, 23: Seal part,
24. Seal part, 25: Support rod, 26
: Main body, 27: Buckle, 28: Air/gas outlet, 31: 0 ring, 34: Nut with gear. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8\ Figure 10 Figure 12 C) Figure 18 3μ

Claims (1)

[Claims] 1. A safe end of a reactor pressure vessel which has a thermal sleeve inside, is welded to the outer nozzle part of the reactor pressure vessel, and has external piping welded to the end. The replacement method includes cutting the piping welded to the safe end, cutting near the base of the thermal sleeve, and cutting the weld between the nozzle part of the reactor pressure vessel and the safe end, The welded heat-affected zone of the nozzle part of the cut reactor pressure vessel is removed, and then a new safe end made of low carbon stainless steel is welded to the nozzle part of the reactor pressure vessel. A method for replacing a safe end of a nuclear reactor pressure vessel, comprising welding the cut remaining thermal sleeve and external piping to the inside and end of the reactor pressure vessel, respectively. 2. A reactor pressure vessel safe-end replacement method that has a thermal sleeve inside, is welded to the outer nozzle of the reactor pressure vessel, and has external piping welded to the end. A device that can be suspended along the inner circumferential surface of a reactor pressure vessel, comprising a suspended main body; a gripping device that is held by being stretched from a shroud in the reactor pressure vessel; a gripping device that is detachably and liquid-tightly attached to a jet pump riser pipe and that is held by being stretched from the shroud against the inner circumferential surface of the reactor pressure vessel; 1. A device comprising: a sealing mechanism that is brought into liquid-tight pressure contact; and means for flowing air and pack gas through the sealing mechanism.