JP2695826B2 - Internal pump for nuclear reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an internal pump for a nuclear reactor used in an internal pump type boiling water reactor (hereinafter referred to as A-BWR). In particular, the present invention relates to an apparatus having a configuration for trapping a clad entering a side of an internal pump from a reactor pressure vessel.

(Prior Art) A conventional example will be described below with reference to FIGS. 11 to 13. FIG.
FIG. 11 is a longitudinal sectional view showing a schematic configuration of the A-BWR, and reference numeral 1 in the figure is a reactor pressure vessel. The reactor pressure vessel 1 contains a coolant 2 and a reactor core 3. The core 3 includes 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 lattice plate 7 installed in the reactor pressure vessel 1. . The control rod 4 is driven by a control rod drive mechanism 8.

A steam / water separator 9 is provided above the core 3 and a steam dryer 10 is provided further above the steam / water separator 9. A water supply pipe 11 is connected to the reactor pressure vessel 1 at a position below the steam separator 9, and the water supply pipe 11 is connected to a water supply sparger 12 disposed in the reactor pressure vessel 1. .

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

The internal pump 14 has a configuration as shown in FIG. The internal pump 14 has a pump section 21
And a motor unit 22. Pump section 21
Is composed of an impeller 23, a diffuser 24 installed on the outflow side of the impeller 23, a diffuser ring 25, and the like. The impeller 23 is connected to the motor section 22 via a pump shaft 26.

A nozzle 1a projects upward from the lower mirror portion of the reactor pressure vessel 1, and the diffuser 24 is provided with the nozzle 1a.
Is fixed by a stretch tube 27.

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

A purge water inlet 41 is provided at the upper part of the casing 32, and the casing water is supplied through the purge water inlet 41.
Purge water is supplied into 32. The purge water supplied into the casing 32 passes through the gap A between the pump shaft 26 and the stretch tube 27 and into the gap B between the pump shaft 26 and the diffuser 24, as shown in FIG. Inflow. By supplying the purge water in this manner, the contamination particles in the reactor pressure vessel 1 are prevented from flowing into the casing 32, and the upper part of the casing 32 is cooled. Also, the cooling action of the purge water suppresses the inside of the casing 32 to about 40 ° C. despite the high-temperature reactor water in the reactor pressure vessel 1 being about 300 ° C. High-temperature deterioration of a polymer material such as a seal rubber material of the next seal is prevented.

The above configuration has the following problem. That is, in order to prevent the intrusion of the clad having a large specific gravity among the clads, it is necessary to increase the flow rate of the purge water, and when the flow rate of the purge water is increased in this manner, the pump shaft 26 or A large thermal stress acts on the stretch tube 24, which may impair its soundness.

(Problems to be Solved by the Invention) As described above, in the conventional configuration, it is necessary to increase the flow rate of the purge water in order to prevent the intrusion of the clad having a large specific gravity. In such a case, a large thermal stress is generated in the pump shaft or the stretch tube, and there is a problem that its soundness may be impaired.

The present invention has been made based on such a point, and an object of the present invention is to provide an internal pump for a nuclear reactor capable of preventing the penetration of a clad having a large specific gravity without increasing the flow rate of purge water. Is to provide.

[Configuration of the invention]

(Means for Solving the Problems) In order to achieve the above object, an internal pump for a nuclear reactor according to the present invention has its tip inserted into the reactor pressure vessel via a lower mirror section of the reactor pressure vessel. A motor shaft, a pump shaft housed and disposed in the motor casing and having an upper end disposed in the reactor pressure vessel, an impeller fixed to a tip portion of the pump shaft, and an outflow side of the impeller. A diffuser arranged, a stretch tube arranged with a gap between the pump shaft and fixing the diffuser to a reactor pressure vessel at an upper end thereof, and purge water connected to the motor casing. A pump is provided between the pump shaft and the diffuser through the space between the pump shaft and the stretch tube to prevent cladding from entering the reactor pressure vessel. A plurality of small-diameter through-holes are provided in a cylindrical diffuser wall located above the stretch tube, and the cladding extends from the inside of the purge water passage to the inside of the pressure vessel outside the diffuser wall. The outlet is set, and the shape of the through hole is sufficiently small in the range larger than the size of the clad, and the through hole is inclined so that the flow path from the inside to the outside of the diffuser is horizontal or downward toward the outside of the diffuser. The clad in the passage is discharged to the outside of the diffuser wall by the rotation of the pump shaft through the through hole, thereby preventing the clad from falling into the motor casing.

Further, in the through hole, in order to enhance the function of discharging the clad in the purge water passage to the outside of the diffuser, an uneven portion is provided on the diffuser inner wall near the diffuser inside entrance of the through hole, and the clad in the passage is formed in the uneven portion. And improved cladding discharge capacity.

In the above-mentioned through-hole, the through-hole is distributed only on the core side, so that a large pressure difference can be obtained between the inside and outside of the diffuser wall of the through-hole, so that the cladding discharge capability is enhanced.

Further, in order to increase the clad accumulation ability of the uneven portion provided near the diffuser inside entrance of the through hole, the protrusion is held on the pump shaft side above the uneven portion and protrudes into the purge water passage between the pump shaft and the diffuser. It is characterized by having a ring-shaped projection.

(Operation) In other words, in the above-described structure, the diffuser has a clad discharging means for discharging the clad falling into the diffuser from the reactor pressure vessel side to the outside of the diffuser. Is discharged out of the diffuser by the clad discharging means, so that it does not fall into the motor casing. In addition, even if the flow rate of purge water is small,
This makes it possible to achieve the effect, so that it is not necessary to increase the flow rate of the purge water in order to purge the clad having a large specific gravity unlike the related art, and it is possible to solve various problems caused by the increase in the flow rate of the purge water.

(Embodiment) Hereinafter, an embodiment of an internal pump for a nuclear reactor according to the present invention will be described with reference to FIGS. 1 to 10 in which the same members as those in FIGS. 11 to 13 are denoted by the same reference numerals. explain.

FIG. 1 illustrates a mounting portion of a cladding discharge mechanism according to the present invention. An impeller 23 is fixed to an upper end of a pump shaft 26 protruding inside the reactor pressure vessel 1, and a downstream side of the impeller 23. Is provided with a diffuser 24. The lower end of the diffuser 24 is fixed to the reactor pressure vessel 1 by the upper end 27a of the stretch tube 27. A purge water passage B is formed between the pump shaft 26 and the diffuser 24. Diffuser
The diffuser 24 is provided with a plurality of small-diameter through-holes 51 at a portion where the stretch tube 24 is fixed to the upper end 27a of the stretch tube 27. The details of the through hole 51 are shown in FIG. The lower end of the inside of the diffuser 24 of the through hole 51 is the contact point between the upper end 27a of the stretch tube and the diffuser 24,
The upper end of the stretch tube 27a is provided in a region C having a horizontal plane as an upper limit, and the inner diameter of the through hole 51 is, for example, in a range of 0.1 mm or more and 5.0 mm or more. The through hole 51 is formed so as to be inclined horizontally or downward from the passage B to the outside of the diffuser 24 in the diffuser 24 wall. FIG. 3 shows an example of the distribution of the through-holes 51 in the circumferential direction of the diffuser 24. The number of the through-holes 51 is, for example, 20 or more at equal intervals in the circumferential direction of the diffuser 24 (accordingly, at an angle of 18 ° or less). ) Is provided.

Next, the operation of the device according to the invention will be described. Cladding 53 in reactor pressure vessel 1 penetrating into purge water flow path B
Is larger than the liquid in the purge water flow path B, and is deposited on the upper end 27a of the stretch tube when the pump is stopped, as shown in FIG. The deposited clad 53 is blown toward the diffuser 24 by the circumferential flow around the pump shaft 26 generated in the purge water flow path B due to the high speed rotation of the pump shaft 26 when the pump rotates, as shown in FIG.
Since the pressure in the purge water flow path B is higher than that in the reactor pressure vessel 1 outside the diffuser 24, the clad blown toward the diffuser 24 is blown into the through hole 51 as shown in FIG. It is discharged outside. The clad 53 that has thus entered the purge water flow path B is discharged to the outside of the diffuser 24 through the through hole 51 when the pump rotates, so that the clad 53 is formed in the gap A between the stretch tube 27 and the pump shaft 26 and the casing under the same. It does not invade 32.

FIG. 7 shows a second embodiment of the present invention, in which the effect of discharging the clad 53 to the outside of the diffuser 24 during rotation of the pump is enhanced, and the diffuser 24 of the through hole 51 is shown. A ring-shaped recess 55 is provided at the inner entrance. The height h of the concave portion 55 is larger than the diameter d of the through hole 51 and is, for example, 1 mm or more. Other configurations are the same as those of the first embodiment. With this configuration, the clad blown to the diffuser 24 when the pump is rotating
53 are integrated in the concave portion 55, and the clad 53 can be more effectively discharged from the through hole 51.

FIG. 8 shows a third embodiment different from the second embodiment shown in FIG.
In this embodiment, the position of the through-hole 51a is set to be higher than the upper end 27a of the stretch tube.
On the four walls, the same ring-shaped concave portion 55a as in FIG. 7 is provided at the entrance of the through hole 51a inside the diffuser 24, and a ring-shaped convex portion 56 protruding into the purge water flow path B is provided below the ring-shaped concave portion 55a. Provided. A ring-shaped protrusion 57 projecting into the purge water flow path B is also provided above the ring-shaped recess 55a.
Is provided on the pump shaft 26 side, and the width x of the ring-shaped protrusion 56 provided on the diffuser 24 side and the width y of the ring-shaped protrusion 57 provided on the pump shaft 26 side are equal to the width of the purge water flow path B. Then, the configuration is such that the relationship x + y> z is satisfied.
Other configurations such as the shape of the through hole 51a and the distribution in the circumferential direction are the same as those of the first embodiment. With this configuration, as shown in FIG. 9, the clad 53 having a large specific gravity penetrating into the purge water flow path B has the ring-shaped convex portion 56 and the
When the pump is operated, the deposited clad 53 is blown toward the diffuser 24 side of the ring-shaped convex portion 56, is collected in the ring-shaped concave portion 55a, and is discharged through the through-hole 51a, so that the through-hole 51a is stretched. Even if it is not provided in contact with the upper end 27a of the tube 27, the same effect as the cladding discharge capability of the through hole 51 configured as in the first embodiment can be obtained, and further the degree of freedom in design can be increased. . Also,
The through-hole 51a shown in FIG.
It may be provided in combination with the through hole 51 shown in the first and second embodiments provided near 7a.

FIG. 10 is a modification of the present invention in which the distribution of the through holes 51 in the circumferential direction of the diffuser 24 is provided only in the direction of the center of the reactor pressure vessel 1, and the distribution of the through holes 51 in the circumferential direction of the diffuser 24 is different. Except for this, the other configuration is the same as the configuration shown in the first embodiment, the second embodiment, or the third embodiment. In FIG. 10, since the through holes 51 are provided at equal intervals only in the semicircular portion of the diffuser 24 facing the core 3 direction, the number of the through holes 51 is About half. The differential pressure between the purge water flow path B and the outside of the diffuser 24 is
The discharge flow rate from the pump outside 24 is greatest in the direction of the core center where the flow velocity is large. Therefore, the through hole 51 formed in the diffuser 24 has the highest cladding discharge capability in the through hole facing the core direction. For this reason, even if the through-hole 51 is provided only in the semicircular portion of the diffuser 24 facing the center of the core as shown in FIG. 10, a sufficient cladding discharge capability can be obtained.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, even when the flow rate of the purge water is small, or even when the flow rate of the purge water becomes zero, the clad having a larger specific gravity than the liquid in the purge water flow path is rotated during pump rotation. Is discharged outside the diffuser and does not flow into the motor case. As a result, contamination in the motor case due to the activated material in the reactor pressure vessel can be prevented, and the reliability and safety of the internal pump can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a first embodiment of an internal pump for a nuclear reactor according to the present invention, FIG. 2 is an explanatory view illustrating a through hole (cladding discharge means) according to the present invention, and FIG. FIGS. 4 to 6 are cross-sectional views showing the distribution of through holes (cladding discharge means) in the diffuser circumferential direction. FIGS. 4 to 6 are explanatory views illustrating the function of the internal pump according to the present invention.
FIG. 10 to FIG. 10 are vertical and horizontal sectional views showing second and third embodiments of the internal pump according to the present invention.
The figure is a sectional view showing the schematic configuration of an internal pump type boiling water reactor, FIG. 12 is a longitudinal sectional view showing a conventional internal pump, and FIG. 13 is an enlarged view of the vicinity of a stretch tube in FIG. 1 is a reactor pressure vessel, 23 is an impeller 24 is a diffuser, 26 is a pump shaft 27 is a stretch tube 51, 51a is a through hole (cladding discharge means) 53 is a clad.

Claims (1)

(57) [Claims] A motor casing having a distal end inserted into the reactor pressure vessel via a lower mirror portion of the reactor pressure vessel; a motor casing housed and disposed in the motor casing; A pump shaft disposed in a vessel, an impeller fixed to a tip end of the pump shaft, and a diffuser disposed on an outflow side of the impeller and having a through hole, wherein the diffuser has a through hole from the reactor pressure vessel side. The internal pump for a nuclear reactor, wherein the clad flowing into the diffuser is discharged from the through hole provided in a circumferential direction of the diffuser to the outside of the diffuser by rotation of the pump shaft.