JPH01178792A - Recycle pump - Google Patents

Abstract

PURPOSE:To prevent occurrence of any crack on a pump shaft, a casing cover and the like by placing the lower ends of plural cylindrical cavities provided for a casing cover above a purge water outlet at a predetermined distance. CONSTITUTION:A pump shaft 1 is fitted with an impeller 2 concentrically, and the impeller 2 is surrounded by a casing 3. And a casing cover 4 is fixed on the upper surface of the casing 3. The lower ends of cylindrical cavities 13 where cooling water flows are located above a purge water outlet at a predetermined distance. Then the cooling of purge water is moderated, so that the temperature of the purge water is, to some extent, raised during its flow. Consequently, the influence of a temperature variation caused by the mixture of the purge water with primary cooling water, on thermal fatigue can be moderated.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION Field of Industrial Application The present invention relates to recirculation pumps used in boiling water nuclear reactors.

(Prior Art) In a boiling water nuclear reactor, primary cooling water is forcibly circulated within the reactor in order to increase the thermal efficiency of the reactor.

In order to perform this circulation, the primary cooling water in the pressure vessel is extracted through a first pipe communicating with the reactor pressure vessel, the pressure is increased by a pump communicating with this pipe, and the water is sent to the pump discharge port. Returning the water into the pressure vessel through a connected second pipe, the pressure water drives a jet pump installed in the vessel to perform recirculation;
A mechanical pump is installed inside the reactor pressure vessel, its drive shaft is made to protrude watertightly outside the pressure vessel, and this drive shaft is driven by a motor installed outside the pressure vessel to pump the coolant under pressure. There are some that allow recirculation without extracting anything outside the container. Therefore, the present invention relates to a recirculation pump used in the former recirculation system.

FIG. 4 is a longitudinal sectional view of an example of a conventional recirculation pump. In this figure, an impeller 2 is fixed concentrically to the pump shirt (-), and the impeller 2 is surrounded by a casing 3. Furthermore, a casing cover 4 is fixed to the upper surface of the casing 3.

The pump shirt I~]- passes through the center of the casing cover 4 with a slight clearance, and the casing cover 4 penetration part -1 of the pump shirt I~1;
A mechanical seal 5 is installed between the pump shirt I- and the casing cover.

On the other hand, a cylindrical pump bearing 6 is installed between the casing 3 and the pump shaft 1. This pump bearing 6 is fixed to the casing cover 4, and a plurality of through holes 7 are bored at approximately the middle position in the axial direction and equally spaced in the circumferential direction. Incidentally, a journal 8 is provided on the upper surface of the impeller 2 and is integral with the impeller 2 and is concentric with the pump bearing 6. Further, the casing cover 4 is held between the casing 3 and the support base 9. Further, a wear ring 10 is installed in the suction portion of the casing 3. A seal chamber 11 is provided below the mechanical seal 5.

In the configuration described in item 1, the mechanical seals 5 prevent fluid from flowing into the motor (not shown), and are usually installed in a plurality of locations distributed in the axial direction of the pump shaft 1. This mechanical seal often needs to be replaced and is cooled by injecting clean cooling water from the outside in order to extend the life of the seal and reduce radiation exposure during replacement work.

A part of this injection water (mechanical seal purge water (hereinafter simply referred to as purge water)) 12 is discharged to the outside in order to adjust the pressure in each mechanical seal chamber 11.
The other part flows down along the pump shaft 1 and into the casing 3.

By the way, as shown in FIG. 5, the casing cover 4 has a plurality of axially cylindrical cavities whose lower ends are connected to each other by passages 1.3a, which are equally spaced in the circumferential direction. One of the two adjacent cylindrical cavities 13 is connected to a cooling water supply passage 14a bored in the casing cover 4, and the other one is connected to a similar cooling water discharge passage 14b. ing. The passage 13a, the cylindrical cavity 13
constitutes a cooling jacket, and the cooling water flowing inside this cooling jacket 1 is supplied to the pump shaft 71 of the casing cover 4.
This is to cool the purge 12 flowing down along the penetration part and the pump shirt 1-1, but when the purge water]2 is shut off, this shut-off causes the rising high-temperature primary water to flow toward the mechanical seal chamber 11-1. It has the function of cooling the cooling water and protecting the mechanical seal 5.

Note that the purge water is about 30°C to 50°C, but since it is cooled by the cooling water (about 30°C to 50'C) flowing through the cooling jacket while passing through the clearance,
The temperature upon entry into the casing is also maintained at approximately 30°C to 50°C.

On the other hand, the temperature of the primary cooling water 15 during reactor operation is approximately 270°C to 280°C, and temperature fluctuations (third (dashed line in the figure), and fluctuating thermal stress is generated on the pump shaft surface and the casing cover surface facing it.

In addition, the purge water is cooled by the cooling water flowing inside the cooling jacket 1- and flows down at a low temperature of about 30°C to 50°C, so that the part of the pump shaft 1 inside the casing 3 and the casing cover 4 static thermal stress occurs.

Figures 6A and B show the axial distance and static thermal stress with the horizontal axis representing the axial distance from the purge water outlet (in the negative direction on the impeller side) and the vertical axis representing the stress generated (the tensile side is the forward direction). FIG. In this figure, the dashed line shows this relationship] in a conventional recirculation pump. From this figure, static thermal stress becomes zero in the pump shirt at a position slightly closer to the impeller 2 side from the purge water outlet of the casing cover 4, and compressive stress at a position closer to the impeller 2 than the above position, and It can be seen that tensile stress is generated at the position on the opposite side of the impeller.

By the way, in the frequency of water temperature fluctuation when the purge water and the primary cooling water are mixed, the rotational frequency component of the pump shaft is predominant. In other words, if the rated rotation speed of the pump is 1
395r, p, m (23,5I(z), the dominant frequency of water temperature fluctuation is 23°5. The heat transfer coefficient between the fluid flowing through the gap between the double pipes and the rotating body is: It is a function of the Reynolds number and Nusselt number, which are hydrodynamic parameters, and recent research shows that h is 5,0OOca1℃/m
It has been revealed that it is about o1~10,000 cal/mo1.

The heat transfer coefficient function is f (h), and the water temperature fluctuation l] is Δ
If Tw, ΔTm during surface temperature fluctuation of the pump shaft 1 or casing cover 4 is expressed as follows.

ΔT m =ΔTw−f(h) Here, f (h) is 5. ○0Oca1℃/mol-1
0.

000 cal/mo1, and may be approximately 0.45. Therefore, ΔTm=0.45−ΔTw.

On the other hand, if the stress fluctuation 1J of the pump shaft 1 and the casing cover 4 is Δσ, then Δσ=EαΔTm/(1−ν) where E is Young's modulus, α is the coefficient of thermal expansion, ν is Poisson's ratio, and the pump For the stainless steel that constitutes the shaft 1 and the casing cover 4, E=18. ○OOkg
/nun'' α=17×10′+nm/′C乍=0.3, so Δσ during stress fluctuation is given by Δa=0 and 44ΔTm=0.2ΔTw.

If the rate at which static stress contributes to equipment damage due to fluctuating stresses such as thermal stress is Q, static stress is σθ, and the tensile strength of the target material is ση, then Q=1/ (1−σθ/ση ) becomes.

In other words, when the static stress σ0 is a tensile stress, the fluctuating stress needs to be estimated larger than when σm is O,
If σm is a compressive stress, the fluctuating stress may be expressed in small quantities.

(Problems to be Solved by the Invention) As described above, in the conventional recirculation pump, the casing cover 4 and the pump shaft 1 near the purge water outlet of the casing cover 4 are subject to high static tensile stress. is present and is superimposed with fluctuating stress due to temperature fluctuations, so there is a risk that either or both of the pump shaft and the casing cover will crack due to the temperature fluctuations.

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a recirculation pump that is free from the possibility of cracks occurring in the pump shaft, casing cover, etc. due to temperature fluctuations caused by injection of purge water.

[Configuration of the Invention (Means for Solving Problems)] The recirculation pump of the present invention includes a pump shirt 1-, an impeller fixed to the pump shaft, a casing surrounding the impeller, and a casing attached to the casing. A fixed casing cover, a mechanical seal installed between the pump shirt l~ and the casing cover, a pump bearing attached to the casing cover, and a pump bearing formed integrally with the impeller through a clearance. a cooling jacket consisting of a plurality of cylindrical cavities provided in the casing cover to concentrically surround the pump shaft penetration portion and whose upper and lower ends are communicated by passages; In the mechanical seal that supplies purge water, the lower end of the cylindrical cavity is located a predetermined distance above the outlet of the purge water.

(Function) In the recirculation pump of the present invention having the above configuration, the cooling of the purge water is eased by the amount that the cooling journal is shortened, and temperature fluctuations at the time of mixing with the primary cooling water at the purge water outlet are alleviated. Therefore, the generation of fluctuating stress due to temperature fluctuations is suppressed, and cracks are prevented from occurring in the pump shirt 1 to the casing cover located near the purge water outlet.

(Embodiment) FIG. 1, in which the same parts as in FIG. 4 are denoted by the same reference numerals, shows an embodiment of the present invention. In this figure, explanations of the parts designated by the same reference numerals and which are the same as those of the conventional recirculation pump will be omitted. Accordingly, in the present invention, the lower end of the cylindrical cavity 13 through which the cooling water flows is set at a predetermined distance above the purge water outlet. As will be clear from the description below, the distance between the lower end of the cavity and the purge water outlet needs to be appropriately set so as to be sufficient to moderate the cooling of the purge water.

By arranging the lower end of the cylindrical cavity 13 above the purge water outlet as described above, the cooling of the purge water is relaxed and the temperature of the purge water is increased to a certain extent while flowing down the interval. In this way, the temperature at position 10 near the purge water outlet is raised to a temperature slightly lower than that of the secondary cooling water. Here, if 30 mm is taken as the Mij interval, the circumferential stress σO of the pump shaft 1 and casing cover 4 located near the purge water outlet will be on the compression side, and the mixing of the purge water and the primary cooling water near the outlet will be The effect of temperature fluctuations on thermal fatigue can be alleviated.

Furthermore, since the purge water is heated and flows in as described above, the temperature fluctuation (solid line in FIG. 3) during mixing itself is reduced to a fraction of that of the conventional method, and thermal fatigue is significantly reduced. In addition, as mentioned above, the temperature fluctuation IJ due to mixing, the temperature fluctuation 1] of the pump shaft near the purge water outlet, and the casing cover surface are reduced, so the stress fluctuation 1] of each member is reduced by several times compared to the conventional one. is reduced to -.

Furthermore, in conventional recirculation pumps, the circumferential stress in the pump shaft and casing cover appears as a large tensile stress near the outlet of the purge water, but in the present invention, the maximum tensile stress is It appears near the lower end of the shaped cavity 13, and its value is several times lower than the conventional value. Thereby, the stress acting on the pump shirt 1-1 and the casing cover 4 near the purge water outlet can both be on the compression side. Said stresses acting on the recirculation pump of the present invention are shown by solid lines in FIG. 6A. In addition, in FIG. 6B, the dashed-dotted curve shows the stress in the circumferential direction of the casing cover in the conventional recirculation pump, and the dashed-double curve shows the stress in the recirculation pump of the present invention.

In addition, in the present invention, the backup function of the conventional recirculation pump when the purge water is shut off is not impaired in any way, and the safety of the nuclear reactor is not impaired.

[Effects of the Invention] As is clear from the above, in the recirculation pump of the present invention, the temperature fluctuation caused by the mixing of the purge water and the primary cooling water near the mechanical seal purge water outlet is reduced. The occurrence of fluctuating stress in the pump shaft and casing cover can be significantly reduced, and the occurrence of cracks in these members can be prevented. Therefore, the present invention can be said to be extremely useful for maintaining the integrity of a nuclear reactor.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of an embodiment of the present invention, FIG. 2 is a vertical cross-sectional view showing an enlarged main part thereof, and FIG. 3 is a diagram showing temperature fluctuations near the purge water outlet of the recirculation pump of the present invention and conventional Figure 4 is a vertical sectional view of a conventional recirculation pump, Figure 5 is a schematic perspective view of its cooling jacket, and Figure 6A is a diagram showing a non-dimensional diagram comparing it with that of a conventional recirculation pump. A diagram showing the static stress of the casing cover on the pump shirt 1 near the purge water outlet of the recirculation pump of the invention in comparison with that of a conventional recirculation pump, FIG. 6B is a circle of the pump shaft and the casing cover. FIG. 3 is a diagram showing a comparison of circumferential stress with that of a conventional one.

Claims (1)

[Claims] A pump shaft, an impeller fixed to the pump shaft, a casing surrounding the impeller, a casing cover fixed to the casing, a mechanical seal installed between the pump shaft and the casing cover, and the casing cover. a pump bearing attached to the impeller; a journal integrally formed with the impeller and surrounding the pump bearing via a clearance; ,
a cooling jacket consisting of a plurality of cylindrical cavities whose lower ends communicate with each other through passages, and which supplies purge water to the mechanical seal, wherein the lower end of the cylindrical cavity is located at a predetermined distance from the outlet of the purge water. A recirculation pump characterized by having a distance upwards.