JPH01219596A - Internal pump for nuclear reactor - Google Patents

Abstract

PURPOSE:To prevent falling of clads to a motor casing side by providing a clad fall preventive mechanism which prevents the fall of the clads from a reactor pressure vessel between a pump shaft and a diffuser. CONSTITUTION:The clad fall preventive mechanism 101 is installed between the pump shaft 26 and the diffuser 24. The mechanism 101 is constituted of an annular member 102 which is projected outward in a radial direction from the shaft 26 and an annular member 103 which exists in the position below the member 102 and is projected inward in the radial direction from the diffuser 24. The fluid between the shaft 26 and the diffuser 24 is swirled to push the clads outward in the radial direction by centrifugal force so that the clads are captured at the base end of the member 103 when the pump is under operation. The fall of the clads to the motor casing side is, therefore, prevented.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an internal pump boiling water reactor (hereinafter referred to as A
The present invention relates to an internal pump for a nuclear reactor used in a nuclear reactor (hereinafter referred to as "BWR"), and particularly to one having a configuration for trapping crud that enters the internal pump from inside the reactor pressure vessel.

(Prior Art) A conventional example will be described below with reference to FIGS. 7 to 9. FIG. 7 is a vertical sectional view showing a schematic configuration of the A-BWR, and reference numeral 1 in the figure is a reactor pressure vessel. A coolant 2 and a reactor core 3 are housed within the reactor pressure vessel 1 . The reactor core 3 is composed of a plurality of fuel assemblies and control rods (not shown), and is supported by a shroud 5, a core support plate 6, and an upper grid plate 7 installed in the reactor pressure vessel 1. . The control rod 4 is driven by a control rod drive mechanism 8.

A steam separator 9 is installed above the core 3, and a steam dryer 10 is installed above it. A water supply pipe 11 is connected to the reactor pressure vessel 1 located below the steam-water separator 9, and this water supply pipe 11 is connected to a water supply sparger 12 disposed within the reactor pressure vessel 1. .

A plurality of internal pumps 14 are installed at equal intervals in the circumferential direction at the lower part of the downcomer section 13 between the shroud 5 and the reactor pressure vessel 1. The internal pump 14 forcibly circulates the coolant 2 into the reactor core 3 . Note that the reference numeral 15 in the figure is a main steam pipe.

The internal pump 14 has a configuration as shown in FIG. The internal pump 14 is connected to the pump section 2
1 and a motor section 22. The pump section 21 includes an impeller 23, a diffuser 24 installed on the outflow side of the impeller 23, and a diffuser ring 2.
The impeller 23 is connected to the motor section 22 via a pump shaft 26.

A nozzle 1a is provided on the lower mirror portion of the reactor pressure vessel 1 to protrude upward, and the fuser 24 described above is fixed to this nozzle 1a by a stretch tube 27.

On the other hand, the motor section 22 is composed of a rotor 30, a stator 31, etc., which integrally accommodate the pump shaft 26,
Each of these components is housed within a casing 32. The casing 32 is welded with its tip inserted into the nozzle 1a, and cooling water is circulated inside the casing 32 through a pipe 33, thereby preventing burnout. An auxiliary impeller 34 is fixed to the lower end of the rotor 30. Also, the above stretch tube 27
The lower end of the casing 32 engages with a stepped portion formed on the upper part of the casing 32.

A purge water flow port 41 is provided in the upper part of the casing 32, and purge water is supplied into the casing 32 via this purge water flow port 41. As shown in FIG. 9, the purge water supplied into the casing 32 passes through the gap A between the pump shaft 26 and the stretch tube 27, and then flows into the gap B between the pump shaft 26 and the diffuser 24.
flows into. By supplying purge water in this manner, contaminant particles within the reactor pressure vessel 1 are removed from the casing 32.
This prevents the liquid from flowing into the interior of the casing 32 and cools the upper part of the casing 32. Furthermore, due to the cooling effect of the purge water, even though the high temperature reactor water in the reactor pressure vessel 1 is at about 300°C, the inside of the casing 32 is suppressed to about 40°C, and the winding insulation material of the stator 31 or This prevents high-temperature deterioration of polymer materials such as the seal rubber material of the secondary seal.

The above configuration has the following problems. In other words, when trying to prevent the intrusion of ruds with particularly high specific gravity among claddings, it is necessary to increase the flow rate of purge water. Alternatively, a large thermal stress may be applied to the stretch tube 24, and its integrity may be impaired.

(Problem to be Solved by the Invention) In this conventional configuration, in order to prevent rads with large specific gravity from entering, it is necessary to increase the flow rate of purge water. In this case, there is a problem in that large thermal stress is generated in the pump shaft or stretch tube, which may damage its integrity.

The present invention has been made based on these points, and its purpose is to provide a nuclear reactor internal that can prevent the intrusion of rads with large specific gravity without increasing the flow rate of purge water. Our goal is to provide pumps.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the internal pump for a nuclear reactor according to the present invention connects its tip end to the reactor pressure vessel through the lower mirror part of the reactor pressure vessel. a motor casing inserted into a pressure vessel; a pump shaft housed within the motor casing and having its upper end disposed within the reactor pressure vessel;
The impeller fixed to the tip of the pump shaft, the diffuser placed on the outflow side of the impeller, and the pump shaft are arranged with a gap between them, and the upper end of the diffuser is connected to the reactor pressure. A stretch tube fixed to the vessel is connected to the motor casing, and purge water is supplied between the pump shaft and the diffuser via the stretch tube and the stretch tube to prevent crud from entering from the reactor pressure vessel side. and a crud fall prevention mechanism that is provided between the pump shaft and the diffuser to trap crud from the reactor pressure vessel side and prevent the crud from falling. It is something to do.

As the above-mentioned clad fall prevention mechanism, first, an annular member is provided protruding from either the pump shaft or the diffuser,
It is conceivable to trap crud falling from the reactor pressure vessel side on the upper surface side of this annular member.

Next, a configuration can be considered in which annular members are respectively provided protruding from the pump shaft and the diffuser so that the tips of the annular members are overlapped with each other. In this case, a bypass path is formed, and the crud from the reactor pressure vessel side is trapped in two stages.

Next, in the above structure, there is a structure in which the tip end of at least one of the annular members is bent in the direction of the annular member to which it faces, and in this case, the tip ends of the bent portions are overlapped with each other, or the tip portions of the bent portions are A configuration in which a valve is provided between the annular member and the opposing annular member is also considered.

Furthermore, there is also a configuration in which the bent portions of the respective annular members are bent toward each other in a direction to narrow the passage, and it goes without saying that all of these are within the scope of the present invention, and in the examples, representative examples thereof are shown. Let me explain using an example.

(Function) In other words, there is a crud fall prevention mechanism between the pump shaft and the diffuser that traps crud falling from the reactor pressure vessel side, and the crud is collected by this crud fall prevention mechanism. , it will not fall into the motor casing. In addition, it can achieve the same effect even when the flow rate of purge water is low, so there is no need to increase the flow rate of purge water to purge rads with large specific gravity as in the past. , it is possible to eliminate various problems caused by an increase in the flow rate of purge water.

(Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. 1 to 3. Incidentally, the same parts as in the prior art are denoted by the same reference numerals, and the explanation thereof will be omitted.

As shown in FIG. 1, the pump shaft 26 and the diffuser 24
A cladding fall prevention mechanism 101 is installed between the two. This clad fall prevention mechanism 101 has a pump shaft 26
An annular member 102 protruding radially outward from the side
and an annular member 103 located below the annular member 102 and protruding radially inward from the diffuser 24. The amount of protrusion of the annular member 102 is pi, the amount of protrusion of the annular member 103 is p2,
When g is the distance between the pump shaft 26 and the diffuser 24, the following relationship exists between them.

pl+p2>g (1) That is, the tips of the two annular members 102 and 103 are in a state where they overlap in the radial direction. Further, the vertical distance between the two annular members 102 and 103 is h.

The operation will be explained based on the above configuration.

First, we will explain the case when the pump is stopped.

In this case, as shown in FIG. 2, the rad 108, which has a higher specific gravity than the purge water, is deposited on the upper surfaces of the annular members 102 and 103, and is prevented from falling downward. At this time, since the tips of the annular members 102 and 103 are in an overlapping state, the cladding 10g is trapped over the entire range of the gap between the pump shaft 26 and the diffuser 24.

Also, it goes without saying that a flow path for purge water is ensured.

Next, a case where the pump is in operation will be explained. In this case, the fluid flow between the pump shaft 26 and the diffuser 24 becomes a swirling flow, and the Cla-Rad 108 is forced outward in the radial direction by centrifugal force, and the proximal end of the annular member 103 as shown in the figure. collected by the department. In this case as well, the cladding 108 does not fall downward and is reliably collected by the annular member 103.

According to this embodiment, the following effects can be achieved.

First, a crud fall prevention mechanism 101 is provided between the pump shaft 26 and the diffuser 24 to collect the crud 108 falling from the reactor pressure vessel 1 side, so that no further crud 108 falls. It does not enter the motor casing 32. In addition, there is no need to increase the flow rate of the purge water as in the past in order to prevent the rad 108, which has a higher specific gravity than the purge water, from falling, and various problems associated with an increase in the flow rate of the purge water can be solved. .

Further, the clad drop prevention mechanism 101 of this embodiment includes annular members 102 and 103 that protrude from the pump shaft 26 and the diffuser 24, respectively, and these two annular members 102 and 103 have their tips radially It is provided by polymerization. Therefore, the crud collection function can be exhibited at least over the entire range of the gap between the pump shaft 26 and the diffuser 24. Therefore, it is possible to prevent the cladding from falling with a high probability.

Furthermore, in the case of this embodiment, simply a pair of annular members 102
It is possible to realize a configuration that exhibits the desired function simply by protruding the parts 103 and 103, and therefore it can be easily applied to existing equipment.

Next, a second embodiment will be described with reference to FIG. This corresponds to the annular members 102 and 103 in the first embodiment.
The tips of the two are bent in the vertical direction so that they are close to each other. When the amount of vertical protrusion of each of the bent portions 102a and 103a is ql and q2, these have the following relationship with the spacing between the annular members 102 and 103.

ql +q2 >h...(n) According to the second embodiment, not only can the same effects as the first embodiment be achieved, but also more effectively prevent the cladding 108 from falling. can do. This is because the bent portions 102a and 103a are provided at the tips of the annular members 102 and 103, and especially when the cladding 108 has a higher specific gravity than the purge water, it cannot overcome the bent portions 103a. Therefore, even if the pump is in operation and the flow condition in the purge water flow path B is disturbed, the cladding 108
will definitely be captured.

Further, since the bent portions 102a and 103a are configured such that their tip portions overlap each other, the above effect is further ensured.

Next, a third embodiment will be described with reference to FIG.

This is because in the configuration of the second embodiment, each bent portion 10
Check valves 109 and 110 are provided between the annular members 103 and 102 opposite to the tips of 2a and 103a. The check valves 109 and 110 are connected to the flow of purge water (
Flow in the direction indicated by the arrow in the figure) is allowed, but flow in the opposite direction, for example, movement of the cladding 108, is restricted.

Therefore, not only can the same functions and effects as in the second embodiment be achieved, but also the falling of the cladding 108 can be more reliably prevented.

Next, a fourth embodiment will be described with reference to FIG. This corresponds to each bent portion 102a and 103 in the second embodiment.
The distal end portion of a is further bent in the radial direction, and the area of the flow path 111 is narrowed down by each bent portion 102b and 103b.

According to the above configuration, the flow rate of the purge water increases, thereby more effectively preventing the cladding 108 from falling.

According to the third and fourth embodiments, it is possible to more reliably prevent the cladding 108 from falling, so that, for example, if the flow of the purge water flow path B is disturbed and the cladding 108 is
This can effectively deal with cases where the centrifugal force acting on the 08 cannot be expected to be sufficient or where the amount of 10g of cladding is extremely large.

As already mentioned, the present invention is not limited to the above-mentioned embodiments, and the point is to prevent the cladding from falling while interposing it between the pump shaft and the diffuser to ensure a flow path for the purge water. Anything that can be done is fine. Further, in the second and third embodiments, a configuration in which a bending portion or a check valve is provided on either one is also conceivable.

[Effects of the Invention] As detailed above, according to the internal pump for a nuclear reactor according to the present invention, it is possible to effectively prevent the cladding from falling from the reactor pressure vessel side to the motor casing side, and in this case, Unlike the conventional method, there is no need to increase the flow rate of purge water, and therefore various problems caused by an increase in the flow rate of purge water can be solved, and other effects are great.

[Brief explanation of the drawing]

1 to 3 are diagrams showing a first embodiment of the present invention,
Fig. 1 is a sectional view showing the structure of the upper part of the internal pump, Figs. 2 and 3 are sectional views showing the structure and operation of the cladding fall prevention mechanism, and Fig. 4 is the cladding fall prevention mechanism according to the second embodiment. 5 is a sectional view of the cladding fall prevention mechanism according to the third embodiment; FIG. 6 is a sectional view of the cladding fall prevention mechanism according to the fourth embodiment; FIGS. 7 to 9
The figures are used to explain the conventional example. Figure 7 is a sectional view showing the schematic configuration of an internal pump boiling water reactor, Figure 8 is a sectional view showing the configuration of the internal pump, and Figure 9. 8 is an enlarged cross-sectional view of a part of FIG. 8. FIG. 1... Reactor pressure vessel, 23... Impeller, 24...
... Diffuser, 26... Pump shaft, 27... Stretch tube, 101... Clad fall prevention mechanism. Figure 131 / Figure 2 Figure 3 @ Figure 7 Figure 8 Figure 9

Claims (2)

[Claims] (1) A motor casing whose tip end is inserted into the reactor pressure vessel through the lower mirror part of the reactor pressure vessel, and a motor casing which is accommodated in the motor casing and whose upper end is inserted into the reactor pressure vessel. The disposed pump shaft, the impeller fixed to the tip of the pump shaft, the diffuser disposed on the outflow side of the impeller, and the pump shaft are disposed with a gap between them, and the upper end thereof a stretch tube that fixes the diffuser to the reactor pressure vessel;
a purge water supply port connected to the motor casing and configured to supply purge water between the pump shaft and the diffuser through between the pump shaft and the stretch tube to prevent crud from entering from the reactor pressure vessel side; An internal pump for a nuclear reactor, comprising: a crud fall prevention mechanism provided between the pump shaft and the diffuser to trap crud from the reactor pressure vessel side and prevent the crud from falling. (2) The cladding fall prevention mechanism is an annular member protruding from at least one of the pump shaft and the diffuser, and traps the cladding on the upper surface side of the annular member. Internal pump for furnace.