JP3692289B2 - Method for cleaning steam generator inside nuclear power plant - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cleaning the inside of a large shell tube heat exchanger, and more particularly to a method for cleaning the inside of a steam generator in a nuclear power plant.
[0002]
[Prior art]
The pressurized water reactor currently widely used for power generation generally uses 2 to 4 steam generators. Although this steam generator has a different structure in detail, a shell tube type heat exchanger is used as the steam generator. That is, a high-temperature primary fluid, that is, a reactor coolant, is caused to flow inside a large number of heat transfer tubes, and a secondary fluid, that is, feed water, is caused to flow to the trunk side space outside the heat transfer tubes, and this feed water is evaporated to become main steam. Thus, in the trunk side space (hereinafter referred to as the secondary side space), the water supply repeatedly evaporates, so the impurities contained therein are scaled on the outer surface of the heat transfer tube and the surface of the secondary side space part device. Adhere to. Since such a scale promotes corrosion and the like, it is not preferable for maintaining the soundness of the heat transfer tube and the like, and cleaning for removing the scale is performed periodically or as necessary.
[0003]
From the above situation , an example of a conventional steam generator internal cleaning method will be described with reference to FIG . In the figure, the structure of the steam generator 10 is conceptually shown, but the lower side of the saddle-shaped body 11 is integrally connected to a thick tube plate 13 and accommodates a brackish water separator (not shown). The enlarged portion 11 a communicates with a main steam pipe provided with a main steam valve 15. The lower side of the tube plate 13 is surrounded by the end plate 17, and the water chambers 19 and 21 are formed therein by being separated by a partition wall 23. An inverted U-shaped heat transfer tube 25, conceptually shown only one, is provided in the barrel 11, and both ends thereof are inserted into holes in the tube plate 13 and open to the water chambers 19 and 21, respectively. . The heat transfer tube 25 is a thin thin tube and is arranged at a very narrow interval to form a heat transfer tube bundle, and an iron oxide scale 27 adheres to the outer surface thereof. Further, iron oxide scales are also attached to the secondary equipment surface such as the inner surface of the body 11 and the surface of the tube sheet 13. Washing is intended to remove the iron oxide scale 27. During normal operation, the reactor coolant sequentially flows through the water chamber 21, the heat transfer tube 25, and the water chamber 19 to heat the secondary side water supply.
[0004]
In order to clean the inside of the steam generator having such a structure, as shown in FIG. 4A, a chemical cleaning liquid 29 is put into the body 11 and the portion to be cleaned is immersed. Then, the main steam valve 15 is closed, the internal temperature is set to 170 ° C., and the pressure is set to 10 ata. In order to maintain the chemical cleaning liquid 27 at this temperature, the heat of the primary fluid flowing in the heat transfer tube 25 may be used. In this state, natural convection occurs due to a temperature difference in the chemical cleaning liquid 29, and the chemical cleaning liquid 29 flows. Then, the main steam valve 15 is fully opened as shown in FIG. That is, when the main steam valve 15 is fully opened, the internal pressure becomes atmospheric pressure, so that boiling occurs everywhere in the chemical cleaning liquid 29, the bubbles rise, and the chemical cleaning liquid 29 is vigorously fluidized or stirred. Such boiling action promotes the dissolving action of the iron oxide scale 27 and promotes cleaning. Such cleaning is based on the dissolution reaction of the iron oxide scale 27 by the chemical cleaning solution 29, and the progress thereof is regulated by the diffusion of the dissolved matter, so that it is greatly promoted by the above-described boiling stirring.
[0005]
[Problems to be solved by the invention]
As described above, the conventional steam generator internal cleaning method has a problem that the cleaning operation time becomes longer because the cleaning liquid stirring that largely restricts the progress of the cleaning operation relies on the boiling under reduced pressure. This also has the effect that the steam generator is provided inside a narrow, shielded compartment and it is difficult to use a normal stirring accelerator. Further, as described above, since a plurality of steam generators are provided, the cleaning method performed for each unit necessitates a long-time cleaning operation.
Accordingly, an object of the present invention is to provide a method for efficiently cleaning the inside of a plurality of steam generators in a nuclear power plant in a short time.
[0006]
[Means for Solving the Problems]
To solve the problems described above, the steam generator inside the cleaning method of the nuclear power plant that by the present invention, the bottom portion of the body-side space of the steam generator of the at least two groups is communicated with each other by transfer pipe, one steam generator A predetermined amount of the cleaning liquid is supplied to the body side space of the cylinder, and then the cleaning liquid is transferred to the other steam generator via the transfer pipe by applying an inert gas pressure to the cleaning liquid. a manner, the cleaning liquid to the reverse transfer to one of the steam generator from said the other of the steam generator, is to supply and discharge alternately into a plurality of steam generators. As a driving source for the cleaning liquid, the pressure of pressurized inert gas via the main steam valve of the steam generator may be used, or a transfer pump provided in the transfer pipe may be used in combination. Further, according to another aspect of the present invention, in the steam generator internal cleaning method of a nuclear power plant , the upper parts are communicated with each other by the upper connecting pipe in the trunk side space of at least two steam generators, and the lower parts are connected to each other by U communicated respectively by shaped tube, by injecting the cleaning liquid to the other leg while injecting nitrogen gas into one leg of the U-shaped tube, through the U-tube and the upper connecting pipe between a plurality of steam generators to form a circulating flow of the cleaning liquid, then switched to inject nitrogen gas into the other leg portion with injecting a cleaning liquid to the one leg, characterized in that to form a reverse circulation flow in the flow direction Is . In this way, cleaning liquid circulates, while reversing the direction of flow, and successively flow into non-dissolution reaction of the iron oxide scale on the outer surface of the heat transfer tube, the diffusion of the melt is accelerated dissolution reaction or washing Is promoted. According to a preferred embodiment, the flow direction of the circulating flow is reversed as appropriate, also be Ru further promote diffusion by thermal evaporation by passing the reactor coolant in the heat transfer tube.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the same part over all drawings including drawing regarding a prior art, and it helps a quick and accurate understanding of invention.
First, as shown in FIG. 1, the blowdown pipes 31 of the two steam generators 10 are connected by the transfer pipe 33. The blow-down pipe 31 is originally provided in the vicinity of the tube plate 13 of the steam generator 10, and the original purpose is to discharge the water supply inside the barrel 11. The transfer pipe 33 is provided with the transfer pump 35. However, when the installation space cannot be secured in the nuclear power plant, the transfer pump 35 may not be attached. The two steam generators 10 connected by the transfer pipe 33 have the same structure, but in the following description of the cleaning operation, the reference numerals are denoted by 10a and 10b, respectively, in order to distinguish them. First, the cleaning liquid 29 is put into the steam generator 10a to a predetermined water level. Next, pressurized nitrogen gas is supplied via the main steam valve 15 and the transfer pump 35 is operated. As a result, the cleaning liquid 29 passes through the blow-down pipe 31 and the transfer pipe 33 of the steam generator 10a and the blow-down pipe 31 of the steam generator 10b and is transferred into the steam generator 10b. At this time, the main steam valve 15 of the steam generator 10b is opened, and the air in the steam generator 10b is pushed out through the main steam valve 15 into the atmosphere. After a predetermined time, the cleaning liquid in the steam generator 10b is reversely transferred into the steam generator 10a through the transfer pump 353 by the same operation. This transfer operation and reverse transfer operation are repeated as appropriate.
[0008]
In the steam generator 10a where the cleaning liquid 29 is pushed out by the above-described cleaning liquid transfer operation, the cleaning liquid flows downward along the outer surface of the heat transfer tube 25, while in the steam generator 10b into which the cleaning liquid flows, the level of the cleaning liquid As the temperature rises, the cleaning liquid 29 collides and contacts the iron oxide scale 27 on the outer surface of the heat transfer tube 25 one after another. Due to the flow of the cleaning liquid and the contact action with the iron oxide scale, dissolution of the iron oxide scale 27 is promoted, and cleaning is performed effectively. Further, since the cleaning operation is simultaneously performed on at least two steam generators, the cleaning time is reduced from this aspect and the amount of cleaning liquid required is one volume, which leads to a reduction in materials and later. The cleaning liquid processing operation to be performed is halved and the waste liquid processing cost is reduced.
[0009]
In order to demonstrate the effect of the cleaning action by stirring, the following comparative test was conducted. As the object to be cleaned, magnetite (Fe ₃ O ₄ ), which is a typical iron oxide, was used. As the cleaning liquid, a liquid containing 7% malonic acid and 3% ascorbic acid was used. The test temperature is 60 ° C. The result is shown in FIG. In the graph of FIG. 2, curve I shows the time-dependent change of the eluted iron ion when stirring, and curve II shows the time-dependent change of the eluted iron ion when not stirred. Here, the results of two cases of a case where the magnetite is stationary in the cleaning liquid and a case where the water level up-and-down vibration by periodic stirring is actively performed and stirred are shown. As can be seen from the graph of FIG. 2, the time required to dissolve 10 g of magnetite was about 5 hours when stirring was performed, but when stirring was not performed, stirring was performed even after 25 hours had elapsed. In some cases no dissolution is obtained.
[0010]
Next, another embodiment will be described with reference to FIG. First, as shown in the figure, the upper part of the upper body 11 of the body 11 of the two steam generators 10 (these are also of the same structure but are distinguished by adding reference numerals 10a and 10b for convenience of explanation). To communicate with each other. Specifically, the upper connecting pipe 41 is easily attached by attaching flanges having the same shape as the manhole cover at the both ends of the upper connecting pipe 41. Next, the blow-down piping 31 under the steam generators 10 a and 10 b is connected by a U-shaped tube 43. The lower legs of the U-shaped tube 43 are provided with joints 43a and 43b at corresponding positions, and these can be detachably connected to a nitrogen gas injection line 45 and a cleaning liquid injection line 47 as described later. Obviously, the attachment of the upper connecting pipe 41 and the U-shaped pipe 43 is a preparatory work for cleaning, and thus may be performed simultaneously or may be performed after the replacement.
[0011]
When the preparation is completed as described above, the nitrogen gas supply line 45 is connected to the joint 43a, the cleaning liquid injection line 47 is connected to the joint 43b, and nitrogen gas and cleaning liquid are injected into the U-shaped tube 43, respectively. If it does in this way, nitrogen gas will flow upwards as it is, and will flow in into steam generator 10a, but cleaning fluid will also be led to this flow and will flow into steam generator 10a. At this time, the main steam valve 15 of the steam generator 10a is opened and the nitrogen gas escapes into the atmosphere, so that the nitrogen gas flow is suitably maintained. When the water level of the cleaning liquid reaches the position of the upper connecting pipe 41, a clockwise cleaning liquid circulating flow through the steam generators 10a and 10b, the upper connecting pipe 41 and the U-shaped pipe 43 is generated. This cleaning liquid circulation flow is continued for a predetermined time, and thereafter, the connection relationship between the nitrogen gas supply line 45 and the cleaning liquid injection line 47 is switched to perform nitrogen gas injection and cleaning liquid injection. Then, the direction of the cleaning liquid circulation flow is switched counterclockwise. By such a circulating flow of the cleaning liquid, the dissolution reaction between the iron oxide scale 27 on the outer surface of the heat transfer tube 25 and the cleaning liquid is promoted because the solution in the reaction section is quickly replaced.
[0012]
Although it is a selective operation, a relatively high-temperature reactor coolant is caused to flow through the heat transfer tube 25 in accordance with the maintenance of the above-described cleaning liquid circulation flow. If it does in this way, cleaning fluid will be heated and it will heat up and generate | occur | produce a vapor | steam. In order to effectively generate such steam, the main steam valve 15 of the steam generator 10 on the nitrogen gas inflow side is opened and closed. In this way, pressurization and depressurization are repeated, boiling or steam generation is repeated, and stirring is performed. The main steam valve 15 of the steam generator 10 on the side where the nitrogen gas does not flow is closed. In this way, the flow of the cleaning liquid circulation flow due to the circulation flow and the generation of steam occurs on the outer surface of the iron oxide scale on the outer surface of the heat transfer tube 25, and the dissolution reaction or cleaning is promoted.
[0013]
【The invention's effect】
As described above, according to the present invention, at least two steam generators communicate with each other, and a cleaning liquid in an amount necessary for cleaning only the steam generator is reciprocated or circulated by changing the flow direction. Since the washing is performed while flowing, stirring is promoted by the flow, and many steam generators can be washed efficiently in a short time. When the cleaning liquid is reciprocated between the two steam generators, the amount of the cleaning liquid used may be one, so that there is little waste liquid and the waste liquid processing cost can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of the present invention.
FIG. 2 is a graph showing test results for explaining the operational effects of the embodiment.
FIG. 3 is a system diagram showing another embodiment of the present invention.
FIG. 4 is a system diagram for explaining the prior art.
[Explanation of symbols]
10, 10a, 10b Steam generator 11 Body 13 Tube plate 15 Main steam valve 17 End plate 19, 21 Water chamber 23 Partition 25 Heat transfer tube 27 Iron oxide scale 29 Cleaning liquid 31 Blowdown piping 33 Transfer piping 35 Transfer pump 41 Upper connecting tube 43 U-tube 45 Nitrogen gas supply line 47 Cleaning liquid injection line

Claims (3)

Communicated with each other by a transfer pipe bottom of the body-side space of the steam generator of the at least two groups, the washing liquid a predetermined amount supplied to the shell side space of one of the steam generator, after which action the inert gas pressure in the cleaning solution by, and through the transfer pipe transferring the cleaning fluid to the other of the steam generator, after a predetermined time, in the same manner, inversely transferring the cleaning fluid from the other steam generator to one of the steam generator wherein A method for cleaning a steam generator inside a nuclear power plant. 2. The method of cleaning a steam generator inside a nuclear power plant according to claim 1 , wherein a transfer pump is provided in the transfer pipe in order to promote transfer and reverse transfer of the cleaning liquid. In the trunk side space of at least two steam generators , the upper parts communicate with each other by an upper connecting pipe, the lower parts communicate with each other by a U-shaped pipe, and nitrogen gas is injected into one leg of the U-shaped pipe. the wash was injected into the other leg, via the U-tube and the upper connecting pipe to form a circulating flow of the cleaning liquid between the plurality of steam generator, the other leg along with then injecting washing liquid into one leg A method for cleaning the inside of a steam generator of a nuclear power plant, characterized in that a nitrogen flow is switched to be injected into a section to form a circulating flow having a reverse flow direction .

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