Fuel debris retrieval method

Abstract

To provide a fuel debris retrieval method that allows fuel debris to be retrieved from inside a reactor pressure vessel without installing a structure that straddles a reactor building.SOLUTION: A fuel debris retrieval method for retrieving fuel debris at a boiling water nuclear power plant is provided, comprising opening piping connected to a reactor pressure vessel inside a reactor containment vessel to introduce a remote device into the reactor pressure vessel from the opened piping, and performing survey of the inside of the reactor pressure vessel, sampling, removal of obstacles, and treatment and retrieval of fuel debris.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for retrieving fuel debris through a nozzle of a reactor pressure vessel. [Background technology]

[0002] Regarding the removal of fuel debris, in order to access and remove the fuel debris from inside the reactor pressure vessel from above, it will be necessary to install large-scale equipment such as lifting equipment and shielding structures on top of the reactor building.

[0003] An example of such a method for retrieving fuel debris is the method described in Patent Document 1. In this retrieval method, a fuel debris retrieval facility with a shielding function is installed on the top of the reactor building, and the reactor internal structures are dismantled and removed in order from the top, after which the fuel debris is accessed, processed, and retrieved. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-114486 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method described in Patent Document 1 requires installing large-scale equipment on top of the reactor building. If the reactor building is damaged, it will be difficult to support the full load of the equipment. Therefore, a framework for supporting the equipment needs to be installed across the reactor building, which will lengthen the preparatory work period before fuel debris removal can begin.

[0006] In view of the above, an object of the present invention is to provide a fuel debris retrieval method that can remove fuel debris from inside a reactor pressure vessel without installing a framework spanning the reactor building. [Means for solving the problem]

[0007] In view of the above, this invention is a "fuel debris retrieval method for removing fuel debris from a boiling water nuclear power plant, in which piping connected to the reactor pressure vessel is opened inside the reactor containment vessel, and entry is made into the reactor pressure vessel through the opened piping to investigate the inside of the reactor pressure vessel, perform sampling, remove obstacles, and process and recover the fuel debris."

[0008] The present invention is also described as "a fuel debris retrieval method for removing fuel debris from a boiling water nuclear power plant, in which an opening is constructed in the reactor pressure vessel within the reactor containment vessel, and entry is made into the reactor pressure vessel from the constructed opening to investigate the inside of the reactor pressure vessel, perform sampling, remove obstacles, and process and recover the fuel debris." Effect of the Invention

[0009] According to the present invention, it is possible to remove fuel debris from inside a reactor pressure vessel without installing a framework spanning the reactor building. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a diagram showing a method of intrusion into a reactor pressure vessel via a main steam connection pipe connection nozzle when there is no fuel debris in the core. [Diagram 2] This is the workflow for removing fuel debris from the reactor pressure vessel via the reactor pressure vessel connecting piping, in the case where there is no fuel debris in the reactor core. [Diagram 3] A diagram showing a method for investigating the annulus when there is no fuel debris in the core. [Figure 4] FIG. 13 is a diagram showing a method for partially removing the upper part of the steam dryer when there is no fuel debris in the core area. [Diagram 5] FIG. 1 is a diagram showing a method for investigating the core when there is no fuel debris in the core. [Figure 6]FIG. 2 is a diagram showing a method of entering a reactor pressure vessel from an open reactor recirculation system piping when there is no fuel debris in the core. [Figure 7] FIG. 2 is a diagram showing a method of filling the reactor bottom with fuel debris when there is no fuel debris in the core. [Figure 8] FIG. 1 shows the route for removing fuel debris from the bottom of the reactor and transporting it from the reactor pressure vessel when there is no fuel debris in the core. [Figure 9] FIG. 2 is a diagram showing a method of intrusion into a reactor pressure vessel via a main steam connection pipe connection nozzle when fuel debris remains in the core. [Figure 10] This is the workflow for removing fuel debris from the reactor pressure vessel via the reactor pressure vessel connecting piping when fuel debris remains in the core. [Figure 11] FIG. 1 shows a method for investigating the annulus when fuel debris remains in the core. [Figure 12] FIG. 13 is a diagram showing a method for partially removing the upper part of the steam dryer when fuel debris remains in the core area. [Figure 13] FIG. 1 is a diagram showing a method for investigating the core when fuel debris remains in the core. [Figure 14] FIG. 2 is a diagram showing a method of filling fuel debris when fuel debris remains in the core portion. [Figure 15] FIG. 1 is a diagram showing a method for constructing an evacuation route from the reactor recirculation system piping when fuel debris remains in the reactor core. [Figure 16] A diagram showing the method of removing the lower part of the steam dryer and the steam-water separator using a platform, and the route for transporting the dismantled pieces. [Figure 17] FIG. 1 is a diagram showing a method for removing fuel debris from the bottom of the reactor and a route for carrying it out when fuel debris remains in the reactor core. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. EXAMPLES

[0012] Fig. 1 and Fig. 3 to Fig. 8 are diagrams showing the states of each process in Example 1 of the present invention, and Fig. 2 is a diagram showing the workflow in Example 1. Since Fig. 1 and Fig. 3 to Fig. 8 show the states at each stage of the workflow in Fig. 2, the following explanation will be made by comparing these.

[0013] First, Fig. 1 is a diagram showing a method of entering a reactor pressure vessel via a main steam connection pipe connection nozzle when there is no fuel debris in the reactor core. As shown in Fig. 1, a remote device 4 is inserted through a penetration hole 3 in a reactor containment vessel 1 (processing step S100 in Fig. 2), and then travels by itself through existing stairs 20 and ladders 21 in the reactor containment vessel 1 to reach a main steam pipe connection nozzle 5 at a high place (processing step S101 in Fig. 2). After reaching the location, the remote device 4 enters the reactor pressure vessel 2 by cutting and opening the main steam pipe (processing step S102 in Fig. 2).

[0014] Fig. 3 is a diagram showing a method for investigating the annulus when there is no fuel debris in the core. After entering the reactor pressure vessel 2, as shown in Fig. 3, an annulus investigation camera 6 is lowered from a remote device 4 to investigate the annulus (processing step S103 in Fig. 2).

[0015] Fig. 4 is a diagram showing a method for partially removing the upper part of the steam dryer when there is no fuel debris in the core. After the investigation, as shown in Fig. 4, the steam dryer 7 is partially cut off by a remote device 60 having a cutting tool 22. After cutting, a simple lifting device 23 is attached to the steam dryer 7, and then the cutting tool is lowered to create an opening in the shroud head (processing step S104 in Fig. 2).

[0016] Fig. 5 is a diagram showing a method for investigating the core section when there is no fuel debris in the core section. As shown in Fig. 5, a core section investigation camera 24 is attached to a simple lifting machine 23, and the core section is investigated (processing step S105 in Fig. 2) through the constructed opening. Subsequent implementation details change depending on the presence / absence and amount of remaining fuel debris confirmed as a result of the investigation. Example 1 covers the case where there is no fuel debris in the core section. If fuel debris remains in the core section, the second implementation details shown in Example 2 will be taken.

[0017] After confirming that no fuel debris remains in the reactor core as a result of the core investigation, preparations will begin for the removal of the fuel debris 8 from the reactor bottom. The reactor recirculation system piping connection nozzle 9 will be used to remove the fuel debris 8 from the reactor bottom.

[0018] Fig. 6 is a diagram showing a method of entering the reactor pressure vessel from the open reactor recirculation system piping when there is no fuel debris in the reactor core. As shown in Fig. 6, the remote device 4 is moved to the reactor recirculation system piping connection nozzle 9 via the existing stairs 20 inside the containment vessel 1. After reaching the vicinity of the reactor recirculation system piping connection nozzle 9, the reactor recirculation system piping is cut and opened (processing step S106 in Fig. 2), making it possible to enter the reactor pressure vessel 2.

[0019] After it becomes possible to enter the reactor pressure vessel from the reactor recirculation system piping connection nozzle 9, an in-RPV lifting machine 26 is installed on the reactor recirculation system piping (processing step S107 in Fig. 2). The remote device 4 is inserted into the reactor pressure vessel 2, and obstructions such as the shroud 10 are cut out to a size large enough for the remote device 4 to enter, thereby constructing an access route to the fuel debris 8 at the reactor bottom. After it becomes possible to access the fuel debris 8 at the reactor bottom, measures are taken to prevent the fuel debris 8 at the reactor bottom from falling.

[0020] Fig. 7 is a diagram showing a method for filling fuel debris at the reactor bottom when there is no fuel debris in the reactor core. As shown in Fig. 7, a filling hose 12 is inserted into the reactor pressure vessel 2 from the reactor recirculation system piping connection nozzle 9, and a filling material 30 is spread on the surface of the fuel debris 8 at the reactor bottom (processing step S108 in Fig. 2) and solidified to prevent it from falling. After the filling work is completed, the work of removing the fuel debris 8 from the reactor bottom is started.

[0021] Fig. 8 is a diagram showing the route for removing fuel debris from the reactor bottom and carrying it out from the reactor pressure vessel when there is no fuel debris in the reactor core. As shown in Fig. 8, a remote device 4 is inserted through the reactor recirculation system piping connection nozzle 9 to process and collect the fuel debris 8 from the reactor bottom (processing step S109 in Fig. 2).

[0022] The collected fuel debris is transported from inside the reactor pressure vessel 2 to the first floor inside the reactor pressure vessel 1, via the reactor recirculation system piping, using the lifting machine 26 inside the RPV. A PLR lifting machine 25 is used to transport the container inside the reactor recirculation system piping. Then, the container 16 containing the fuel debris is transported through the containment vessel penetration hole 3. This series of processing, recovery and transport operations for the reactor bottom fuel debris 8 is repeated until the removal of the fuel debris from inside the reactor pressure vessel 2 is completed. EXAMPLES

[0023] Figures 9 and 11 to 17 are diagrams showing the states of each step in embodiment 2 of the present invention, and Figure 10 is a diagram showing the workflow in embodiment 1. Figures 9 and 11 to 17 show the states at each stage of the workflow in Figure 10, so the following explanation will be made by comparing these. As mentioned above, embodiment 2 is a method intended for the case where the presence or absence of remaining fuel debris in the core is confirmed as a result of an investigation.

[0024] Therefore, the only difference between Figures 1 and 9, Figures 3 and 11, and Figures 4 and 12 is whether or not fuel debris remains in the core, and the other process contents are the same, so explanations in the drawings will be omitted. Also, since process steps S100-S103 in the flow of Figure 2 correspond to process steps S200-S203 in the flow of Figure 11, this flow will also be omitted. Incidentally, Figure 9 shows a method of entering the reactor pressure vessel via the main steam connection piping connection nozzle when fuel debris remains in the core, Figure 11 shows a method of investigating the annulus when fuel debris remains in the core, and Figure 12 shows a method of removing a part of the upper part of the steam dryer when fuel debris remains in the core.

[0025] Fig. 13 is a diagram showing a method for investigating the core when fuel debris remains in the core. Example 2 is a method intended for cases where the presence or absence of remaining fuel debris in the core is confirmed as a result of investigating the presence or absence of remaining fuel debris in the core using the method shown in Fig. 13. Here, a core investigation camera 24 is attached to a simple lifting machine 23, and the core is investigated through a constructed opening.

[0026] FIG. 14 is a diagram showing a method of filling fuel debris when fuel debris remains in the core. In the second embodiment, as shown in FIG. 14, after the investigation of the core, all remaining parts of the upper part of the steam dryer 7 are dismantled, and then the removal platform 13 is constructed on the lower part 28 of the steam dryer (processing step S206 in FIG. 10). This platform 13 is equipped with a lifting machine 27. Parts of this platform 13 and the lifting machine 27 are carried in from outside the containment vessel 1 using a remote device 4, and assembled on the lower part 28 of the steam dryer. After the construction of the platform 13 is completed, as shown in FIG. 14, the core filling hose 14 is lowered from the platform 13, and a filling material is spread on the surface of the core fuel debris 15 (processing step S207 in FIG. 10) to take measures against falling. After the fall prevention work is completed, the work proceeds to the construction of a carry-out route from the reactor recirculation system piping connection nozzle 9.

[0027] Fig. 15 is a diagram showing a method for constructing a carry-out route from the reactor recirculation system piping when fuel debris remains in the core. As shown in Fig. 15, a remote device 60 holding a cutting tool is lowered from a platform lift 27 to the annulus, and after dismantling the reactor recirculation pump, the shroud 10 is cut out to a size large enough for the remote device 4 to enter, and an opening into the shroud 10 is constructed (processing step S208 in Fig. 10). Outside the reactor pressure vessel 2, as a parallel operation, the reactor recirculation system piping is cut and opened, and then a PLR lift 25 is installed (processing step S209 in Fig. 10), making it possible to carry out the vessel via the reactor recirculation system piping.

[0028] FIG. 16 is a diagram showing a method for removing the lower part of the steam dryer and the steam-water separator using a platform, and a route for carrying out the dismantled pieces. Next, as shown in FIG. 16, the lower part 28 of the steam dryer and the steam-water separator are dismantled from the top (processing step S210 in FIG. 10). The container 17 containing the dismantled pieces is carried out from the reactor recirculation system piping connection nozzle 9, and then carried out to the outside of the reactor containment vessel 1 via the reactor recirculation system piping. After repeating this dismantling work, the fuel debris 15 from the core is also removed in a similar manner. After the removal of the fuel debris 15 from the core (processing step S211 in FIG. 10) is completed, the fuel debris 8 from the reactor bottom is removed (processing step S212 in FIG. 10).

[0029] FIG. 17 is a diagram showing a method for removing fuel debris from the reactor bottom and a route for carrying it out when fuel debris remains in the reactor core. As shown in FIG. 17, a remote device 4 is lowered onto the fuel debris 8 at the reactor bottom using a platform 13, and processing and recovery are performed. The recovered fuel debris 8 at the reactor bottom is lowered through the reactor recirculation system piping from the reactor recirculation system piping connection nozzle 9 using a PLR lifting machine 25, and transported to the first floor inside the reactor containment vessel 1. After that, the container 16 containing the fuel debris is carried out of the reactor containment vessel 1 via the reactor containment vessel penetration hole 3. This processing, recovery, and carrying out work is repeated to complete the removal of the fuel debris from the reactor pressure vessel 2.

[0030] The above-mentioned first and second embodiments can be modified as follows, and can be implemented as appropriate. First, the filling operation of the reactor bottom fuel debris 8 performed in the first embodiment may be omitted. The filling operation of the core fuel debris 15 performed in the second embodiment may be omitted. The intrusion route into the reactor pressure vessel 2 used in the first and second embodiments may use a nozzle other than the main steam pipe connection nozzle and the reactor recirculation system pipe connection nozzle. The intrusion route into the reactor pressure vessel 2 used in the first and second embodiments may be constructed by drilling a hole in the reactor pressure vessel 2 itself, and the constructed hole may be used as an access route.

[0031] According to the present invention described above, after a remote device is brought in through the penetration hole in the reactor containment vessel, the piping connected to the reactor pressure vessel inside the reactor containment vessel is cut and opened to access the inside of the reactor pressure vessel, whereby the fuel debris inside the reactor pressure vessel is processed and collected. This eliminates the need to install equipment for fuel debris removal on the top of the reactor building, and therefore eliminates the need for a framework to support such equipment, making it possible to remove the fuel debris inside the reactor pressure vessel without dismantling the buildings around the reactor building. This makes it possible to start removing the fuel debris inside the reactor pressure vessel with a relatively short preparatory work period. [Explanation of symbols]

[0032] 1: Nuclear containment vessel 2: Reactor pressure vessel 3: Reactor containment vessel penetration hole 4: Remote device 5: Main steam pipe connection nozzle 6: Annulus inspection camera 7: Steam dryer 8: Fuel debris at the bottom of the reactor 9: Reactor recirculation system piping connection nozzle 10: Shroud 11: Removal device 12: Filling hose 13: Extraction platform 14: Core filling hose 15: Core fuel debris 16: Container containing fuel debris 17: Container containing dismantled pieces 20: Existing stairs inside the reactor containment vessel 21: Existing ladder inside the reactor containment vessel 22: Cutting tool 23: Simple lifting machine 24: Camera for investigating the core 25:PLR lifting machine 26: RPV internal lifting machine 27: Platform lifting machine 28: Lower part of steam dryer 30: Filling material 50: Open main steam connection pipe 51: Open reactor recirculation piping 60: Remote device holding a cutting tool

Claims

1. A fuel debris retrieval method for removing fuel debris from a boiling water nuclear power plant. This involves opening the piping connected to the reactor pressure vessel inside the containment vessel, allowing access into the reactor pressure vessel through the opened piping to investigate the inside of the reactor pressure vessel, take samples, remove obstacles, and process and collect the fuel debris.

2. A fuel debris retrieval method for removing fuel debris from a boiling water nuclear power plant. An opening is made in the reactor pressure vessel inside the containment vessel, and entry is made into the reactor pressure vessel through the opening to investigate the inside of the reactor pressure vessel, take samples, remove obstacles, and process and collect the fuel debris.

3. The fuel debris retrieval method according to claim 1 or 2, A fuel debris retrieval method characterized by assembling equipment inside the reactor pressure vessel.

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