JPH01307695A - Internal pump - Google Patents

Abstract

PURPOSE:To prevent the infiltration of activated clads by providing primary sealing devices forming slight gaps with the inner peripheral face of a sleeve near the top end of a pump shaft. CONSTITUTION:The sealing device 25 in the circumferential direction forming the slight gap 24 by reacting with the top end face of the sleeve 14 is also provided to the rear surface of an impeller 12 exiting at the outflow point of purging water in a reactor pressure vessel 1. Further, the sealing device 27 forming the slight gap 26 with the tapered surface of the inside peripheral face at the top end of the sleeve 14 is also provided to the top end of the pump shaft 6. Three pieces of the slight gaps 23, 26, 24 exist in the flow passage of the purging water with such internal pump and, therefore, the flow rates of the purging water in the respective gaps increase and the infiltration of the clads near the top end of the pump shaft 6, i.e., the position furthest from a motor section 4 is prevented.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to an internal pump installed in the lower part of a nuclear reactor pressure vessel, which recirculates coolant in a sub-reactor pressure vessel. Related.

(Prior Art) An internal pump is installed in the lower part of a nuclear reactor pressure vessel and is used to recirculate the coolant contained therein.

Figure 3 is a vertical cross-sectional view of an example of a conventional internal pump.
FIG. 4 is an enlarged longitudinal cross-sectional view of the main part (the part surrounded by the tank circle B in FIG. 3). In FIG. 3, the bottom of the reactor pressure vessel 1 is provided with a plurality of bosses 2 (only one is shown) that are equally distributed in the circumferential direction and penetrate the bottom of the vessel, and each boss 2 has an interface. A casing 5 of a motor section 4 of the null pump 3 is fixed by welding or the like. Motor part 4
A rotor and a stator (not shown) are installed inside, and a pump shaft 6 integrated with the rotor passes through the boss portion 2 and projects into the pressure vessel 1 . Further, the pump shaft 6 is supported with respect to the casing 5 by journal bearings 7.8 near the upper and lower ends of the casing 5. Also,
A thrust disk 9 is provided at the lower end of the pump shaft 6, and the axial position of the pump shaft 6 is regulated by a pair of thrust bearings 10.11 that sandwich the thrust disk 9.

Further, an impeller 12 for circulating coolant is attached to the upper end of the pump shaft 6, that is, the end protruding into the pressure vessel 1. A diffuser 13 is provided to surround the impeller 12 and rectify the coolant, and a stepped portion 15 on the inner surface of the lower end of the sleeve 14 of the diffuser 13 engages the upper end of the stretch tube 16 inserted into the boss portion 2. The mating portion 17 is engaged, and the diffuser 14 is thereby fixed and supported on the upper end surface of the boss portion 2.

In addition, in the figure, 18 and 19 are piping for cooling water that cools the inside of the casing 5, and 20 is a piping provided on the upper part of the casing 5, which is used to collect the activated sludge from inside the pressure vessel 1.
The purge water piping to prevent infiltration is shown in each figure.

(Problems to be Solved by the Invention) In the conventional internal pump having the above configuration, purge water is supplied to the reactor pressure vessel 1 as shown by arrow 21 in FIG.
flows towards. As shown in an enlarged view in FIG. 4, the purge water flow path has a wide gap between the sleeve 14 of the diffuser 13 and the primary sealing means of the pump shaft 6. In the wide part of the gap, it is difficult to obtain a flow velocity sufficient to prevent the inflow of crud from the reactor pressure vessel.

Therefore, there is a possibility that the cladding may enter the motor section 4, and as a result, the radiation dose within the motor section 4 may increase. The motor section 4 needs to be removed, disassembled, and inspected during periodic inspections, but an increase in the radiation dose inside the motor section 4 as described above will lead to an increase in the radiation exposure of workers, which is preferable in terms of exposure control. do not have.

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide an internal pump that can prevent crud from entering the motor section from the reactor pressure vessel.

[Structure of the Invention] (Means for Solving the Problems) The internal pump of the present invention includes a motor section that is located below the bottom surface of the reactor pressure vessel and includes a casing, and a motor section that connects the bottom surface of the reactor pressure vessel from the motor section. a pump shaft extending into the container through the boss portion and having an impeller at its inner end; a diffuser provided surrounding the impeller; and a diffuser interposed between the boss portion and the pump shaft. A stretch tube that engages with a sleeve at the bottom of the diffuser to fix the diffuser to the reactor pressure vessel, a cooling water pipe that supplies cooling water into the casing, and a cladding pipe that connects the reactor pressure vessel to the inside of the motor section. A primary sealing device is provided near the upper end of the pump shaft to form a minute gap between the inner peripheral surface of the sleeve and a lower end surface of the impeller. It is characterized by providing a sealing device that forms a minute gap with the upper end surface.

(Function) In the internal pump of the present invention having the above configuration, at least two small gaps are provided in series in a part of the purge water flow path near the upper end of the pump shaft, that is, a part farthest from the motor part. Since the purge water is given a large flow velocity in the gap, crud is prevented from flowing into the motor section from the reactor pressure vessel.

(Example) The same parts as in FIGS. 3 and 4 are given the same reference numerals. FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, and FIG. FIG. 2 is an enlarged vertical cross-sectional view of the portion surrounded by A. In the present invention, as shown in FIG.
A primary sealing device 22 is provided which cooperates with the inner circumferential surface of the sleeve 14 of No. 3. The gap 23 between the secondary sealing device 22 and the inner peripheral surface of the sleeve 14 is made as narrow as possible without interfering with the rotation of the pump shaft 6.

Further, a circumferential sealing device 25 is provided on the lower surface of the impeller 12, which is the outflow point of the purge water into the reactor pressure vessel 1, and opposes the upper end surface of the sleeve 14 to form a small gap 24.

Furthermore, the upper end of the pump shaft 6 also has a tapered circumferential surface 6a corresponding to the taper of the inner circumferential surface of the upper end of the sleeve 14, and a minute gap 2 is formed between the taper and the inner circumferential surface of the sleeve 14.
A sealing device 27 forming 6 is provided.

In the embodiment of the present invention having the above configuration, there are three small gaps 23, 26, and 24 in the purge water flow path, so the flow rate of the purge water in each of these gaps is large. Infiltration of the cladding can be prevented near the upper end of the pump shaft 6, that is, at the farthest position from the motor section 4.

[Effects of the Invention] As is clear from the above, in the internal pump of the present invention, as long as purge water is supplied, the intrusion of activated crud from the reactor pressure vessel into the motor section is minimized. This can be prevented at a remote location. In this way, by preventing the crud from penetrating into the motor section.

It is possible to minimize the radiation exposure of workers when disassembling and inspecting the motor section during periodic inspections and the like.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of the main part of an embodiment of the present invention, and Fig.
An enlarged vertical cross-sectional view of the part surrounded by tank circle A in the figure. FIG. 3 is a vertical cross-sectional view of a conventional internal pump, and FIG. 4 is an enlarged vertical cross-sectional view of the portion surrounded by a tank circle B in FIG.

Claims (1)

[Claims] a motor section located below the bottom of the reactor pressure vessel and provided with a casing; and a pump shaft extending from the motor section into the vessel through a boss section on the bottom of the reactor pressure vessel and provided with an impeller at its inner end. a diffuser that surrounds the impeller; and a stretch tube that is interposed between the boss portion and the pump shaft and that engages with the sleeve at the bottom of the diffuser to fix the diffuser to the reactor pressure vessel. and a cooling water pipe that supplies cooling water into the casing, and a purge water pipe that prevents crud from flowing into the motor section from the reactor pressure vessel, wherein the sleeve is located near the upper end of the pump shaft. A primary sealing device is provided to form a minute gap between the impeller and the inner circumferential surface, and a sealing device is further provided at the lower end surface of the impeller to form a minute gap with the upper end surface of the sleeve. internal pump.