JPH03295499A - Nuclear reactor recirculation pump - Google Patents

Abstract

PURPOSE:To relieve thermal stress by providing a labyrinth seal part with many labyrinth grooves and mixing grooves which have larger spaces at least either of a casing cover and a pump shaft. CONSTITUTION:Many labyrinth grooves 14 for obtaining specific flow passage resistance are formed in the inner peripheral part of a casing cover 4 and several mixing grooves 15 which have larger spaces than the labyrinth grooves 14 are arranged at equal intervals. When the mixing grooves 15 are formed, the flow rate increases and purging water which enters a cylindrical flow passage 13 flows the 1st mixing groove 15 and stays therein, so that cold water and hot water are mixed. Consequently, the temperature of the purging water approximates to the temperature before the flow rate increase speedily and their temperature difference decreases greatly as compared with a conventional temperature difference DELTAT1. Therefore, thermal stress generated in the structure material of the labyrinth part is relieved and the safety is improved.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a reactor recirculation pump provided in a reactor recirculation system of a boiling water reactor, and particularly relates to a seal structural material. The present invention relates to a nuclear reactor recirculation pump designed to alleviate generated thermal stress.

(Prior art) In a boiling water reactor, a primary coolant circulation system that circulates the primary coolant is used as a reactor recirculation system. Built-in circulation pump.

The reactor recirculation pump a is constructed as shown in FIGS. 9 and 10, and an impeller (pump impeller) C for pumping up the primary coolant is housed in the pump casing b. This impeller C is connected to a pump shaft d that is rotationally driven by a motor (not shown). This pump shaft d is supported in a liquid-tight manner by a shaft sealing device f housed in the cylindrical outer body of the casing cover e.

The shaft sealing device f of the reactor recirculation pump a has multi-stage mechanical seals f, f to enhance the resealing function and improve reliability. In addition, clean cooling water (purge water) is injected into the seal chamber g from the outside to prevent exposure to radiation during disassembly and inspection of the mechanical seals f and f.

Purge water injected from the seal purge port is forced to circulate by the pump action of a circulation vane i provided in the seal chamber g, thereby forming a shaft sealing water (purge water) circulation cooling system j. This circulation cooling system j has seal chambers g, for example, 6
A heat exchanger k is provided to maintain the temperature at about 0°C. The heat exchanger has one spirally wound heat exchange coil.
is arranged on the outer periphery of the cylindrical outer body part e1 of the casing cover e.

When the cooling water passes through this heat exchange coil kl, the cooling water exchanges heat with the heat exchanger cooling water 7 and is cooled.

The heat exchanger cooling water is injected from the cooling port 11, cools the shaft seal cooling water, and then is extracted to the outside from the cooling water outlet 12.

On the other hand, the purge water injected from the seal purge port is
The shaft sealing water circulation cooling system j is forced to circulate, but part of the purge water is discharged to the outside (control bleed off) to adjust the pressure in the sealing chamber g, and the rest is pumped between the pump shaft d and the casing cover e. is pushed into the pump casing b through the gap (labyrinth seal part m),
This prevents high-temperature, high-pressure reactor water from entering the seal chamber g.

In addition, if the purge water is cut off for some reason, high-temperature reactor water of about 280°C, for example, may enter the seal chamber g through the labyrinth seal part m, and the shaft seal water rises due to the intrusion of high-temperature reactor water. There is a risk of overheating. For this reason,
A cooler jacket n is provided on the outer periphery of the labyrinth seal part m of the casing cover e, and jacket cooling water is injected into this cooler jacket n from a jacket cooling water population O through the water cooling jacket p to cool the water passing through the labyrinth seal part m. , lowering the temperature. This jacket cooling system q is configured independently from the shaft sealing water circulation cooling system j.

(Problem to be solved by the invention) In conventional nuclear reactor recirculation pumps, the temperature of high-temperature reactor water is approximately 2
80°C1 The temperature of the shaft sealing water in the seal chamber g is approximately 60°C, and due to this large temperature difference, when the flow rate of purge water changes, the temperature of the purge water in the labyrinth seal part m, which is the boundary part, changes. However, a large thermal stress is generated on the outer circumference of the pump shaft d and the inner circumference of the casing cover e, which are in contact with the pump shaft d. Therefore, it is required to keep the flow rate of purge water constant.

However, it is difficult to accurately maintain a constant flow rate of purge water. Therefore, the labyrinth seal part m can absorb some fluctuations in the flow rate of the purge water, and by stabilizing the temperature of the purge water, it can relieve the thermal stress generated on the pump shaft d and the casing cover e.
structure is required.

The present invention was made in consideration of the above circumstances, and stabilizes the temperature of the purge water by absorbing slight fluctuations in the flow rate of the purge water, thereby reducing the thermal stress generated in the structural materials of the labyrinth section and the loop section. The objective is to provide a nuclear reactor recirculation pump that can improve reliability and safety.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the invention according to claim 1 provides that the labyrinth seal portion has a plurality of labyrinth grooves in at least one of the casing cover and the pump shaft, and that the labyrinth grooves are larger than the labyrinth grooves. and one or more mixing grooves having a large space.

In the invention as claimed in claim 2, the labyrinth seal portion has a large number of labyrinth grooves in at least one of the casing cover and the pump shaft, and a temperature gradient of 2 to 2b is formed.

In the invention according to claim 3, the labyrinth seal part has a labyrinth part equipped with a large number of labyrinth grooves, and a mixing part equipped with a plurality of mixing grooves having a larger space than the labyrinth grooves, and A groove is formed in at least one of the casing cover and the pump shaft.

(Function) In the invention according to claim 1, since the mixing groove has a larger space than the labyrinth groove, it absorbs changes in the flow rate of the purge water, and this buffering action stabilizes the temperature of the purge water, and the labyrinth seal portion In the invention according to claim 2, the length of the labyrinth seal portion is long, so that the temperature gradient is gentle, and even if the flow rate of the purge water fluctuates, the temperature of the purge water remains constant. Changes will be gradual.

In the invention according to claim 3, in order to absorb fluctuations in the flow rate of purge water in the mixing section and sufficiently mix cold and hot water,
The temperature in the labyrinth becomes stable.

(Embodiments) Hereinafter, embodiments of the nuclear reactor recirculation pump according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of the present invention, in which an impeller (pump impeller) 2 for pumping up a primary coolant is housed in a pump casing 1 constituting a pressure-resistant part. This impeller 2 is connected to a pump shaft 3 that is rotationally driven by a motor (not shown). This pump shaft 3
is rotatably supported by an underwater bearing 5 attached to a casing cover 4. The casing cover 4 constitutes a pressure-resistant part together with the pump casing 1, while sealing high temperature reactor water in the pump casing 1 by a shaft sealing device i6 housed in its cylindrical outer body 4a.

The shaft seal device I6 is a multistage mechanical seal 6a.

6b enhances the sealing function and improves reliability. In addition, mechanical seal 6a
, 6b, to prevent exposure to radiation during disassembly and inspection.
Clean cooling water (purge water) is injected from the outside.

The purge water injected from the seal purge port 8 is forced to circulate by the pump action of a circulation vane 9 provided in the seal chamber 7, thereby forming a shaft sealing water (purge water) circulation cooling system 10. This circulation cooling system 10 has a seal chamber 7, for example, 6
A heat exchanger 11 is provided to maintain the temperature at about 0°C. A part of the purge water in the seal chamber 7 is injected into the pump casing 1 through the labyrinth seal section (secondary seal section) 12, and high temperature, high pressure, and radioactive reactor water mixes into the seal chamber 7. It prevents you from doing so.

The labyrinth seal portion 12 is provided on the impeller 2 side of the seal chamber 7, as shown in FIGS. 2 and 3. The labyrinth seal portion 12 is formed by the outer circumference of the pump shaft 3 and the inner circumference of the casing cover 4, and a cylindrical flow path]3 is formed therebetween. A large number of labyrinth grooves 1 are formed on the outer circumference of the pump shaft 3 in order to provide a predetermined flow path resistance.
4 is formed. A large number of labyrinth grooves 14 are formed in the inner peripheral part of the casing cover 4 to provide a predetermined flow path resistance, and several mixing grooves 1-5 having a larger space than the labyrinth grooves 14 are formed evenly. They are arranged at intervals. The stiff groove 1415 is formed in a ring shape along the inner circumference of the casing cover 4 and the outer circumference of the pump shaft 3. The mixing groove 15 is a cylindrical channel 1
Even if there is some fluctuation in the flow rate of purge water flowing through the
It has a size (width, depth) that can absorb it, and when the amount of cold purge water increases, the cold water and hot water are mixed inside.

Next, the effect will be explained.

Generally, the thermal stress on the surface of a structural material is obtained by the following formula.

Here, σa: η α ΔT : p R TSEAL' Fluctuation stress correction coefficient Longitudinal elastic modulus Linear expansion coefficient Metal surface temperature fluctuation rate PLR Pump internal reactor water temperature − room water temperature It turns out that it is best to reduce the temperature fluctuation range.

In the embodiment described above, purge water flows from the seal chamber 7 through the cylindrical channel 13 into the pump casing 1 below. When the flow rate of this purge water increases, the increased purge water flows into the first mixing groove 15, where low temperature purge water (cold water) and high temperature purge water (warm water) are mixed. Then, the mixed purge water whose temperature is stable flows through the cylindrical flow path 13.

In the conventional structure in which the mixing groove 15 is not provided, the temperature of the purge water when the flow rate increases is significantly higher than the temperature of the purge water before the increase, as shown by the solid line, as shown by the two-dot chain line in Figure 4. decreases to That is, before the flow rate is increased, the temperature of the purge water entering the cylindrical flow path 13 at the inlet temperature T+ gradually increases as it moves through the cylindrical flow path 13, as shown by the solid line, and the outlet temperature increases. becomes T2. On the other hand, after the flow rate is increased, the temperature of the purge water is indicated by the two-dot chain line a
As shown in , the temperature does not rise much and the outlet temperature reaches T2'. As a result, the temperature decreases by a maximum of ΔT1, and a large thermal stress is generated in the pump shaft 3 and the casing cover 4.

On the other hand, in the case of the above embodiment in which the mixing grooves] and 5 are provided, the purge water that has increased in flow rate and entered the cylindrical flow path 13 at the inlet temperature T1 flows into the first mixing groove 15, where it flows into the first mixing groove 15. The cold water and hot water are mixed together.

As a result, the temperature of the purge water rapidly approaches and matches the temperature before the flow rate increase, as shown by the broken line C.

Therefore, the maximum temperature drop is ΔT before entering the mixing groove 15.
2, which is significantly smaller than the conventional temperature difference ΔT1. If the flow rate is further increased, the temperature drop of the purge water extends to the second mixing groove 15, but the temperature drop is still much smaller than in the conventional case. Note that the symbol d indicates the position of the mixing groove 15. Furthermore, even when the flow rate of purge water is reduced, the temperature rise is significantly smaller than before, as described above.

In this way, according to the above embodiment, fluctuations in the flow rate of purge water can be absorbed by the mixing groove 15 and temperature changes can be suppressed. relieve,
Reliability and safety can be improved.

FIG. 5 shows a second embodiment of the present invention, in which a labyrinth seal portion 12A has mixing grooves 15 arranged near the inlet and outlet of the purge water. According to this embodiment, the influence of temperature changes of purge water due to fluctuations in purge water flow rate can be limited to the inlet or outlet portion.

FIG. 6 shows a third embodiment of the present invention, in which the conventional temperature was approximately 5°C.
In order to reduce the temperature gradient from /an to 2 to b degrees, the axial length of the labyrinth seal part]2B was
It is about twice as long. According to this embodiment, since the temperature gradient is small, even if the flow rate of the purge water fluctuates, the temperature change is moderated.

7 and 8 show a fourth embodiment of the present invention, in which a labyrinth seal portion 12C has a large number of labyrinth grooves 14.
The mixing section 18 includes a labyrinth section 17 having a plurality of mixing grooves 15 and a mixing section 18 having a plurality of mixing grooves 15. In the labyrinth portion 1 - 7 , a large number of labyrinth grooves 14 are formed on the outer circumference of the pump shaft 3 and on the inner circumference of the casing cover 4 . Mixing section 1
8, as shown in FIG. 8, the outer circumference of the pump shaft 3 is formed smoothly, and the inner circumference of the casing cover 4 is provided with a plurality of mixing grooves 15. The mixing section 18 is provided upstream of the labyrinth section 17.

According to this embodiment, since the purge water that has been sufficiently warmed in the mixing section 18 flows into the labyrinth section 17, cold water and hot water are not mixed in the labyrinth section 1.7, and the temperature of the purge water remains stable. do. In addition, since the outer circumference of the pump shaft 3 of the mixing section 18 is formed smoothly, a fluid boundary layer develops on the structural surface 2, which reduces the effect of temperature changes on the metal. Further, by forming the corners of the mixing grooves 1-5 smoothly, thermal stress at the corners can be alleviated.

〔Effect of the invention〕

As explained above, the present invention can suppress the temperature change of the purge water passing through the labyrinth seal, thereby alleviating the thermal stress generated in the structural material of the labyrinth seal, thereby improving reliability and safety. It is possible to direct the

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing the first embodiment of the present invention, FIG. 2 is a longitudinal sectional view showing the labyrinth seal portion in the above embodiment, and FIG. 3 is an enlarged sectional view showing the labyrinth seal portion in the above embodiment. , FIG. 4 is a diagram showing the temperature of the purge water in the labyrinth seal portion, FIG. 5 is an enlarged cross-sectional view showing the second embodiment of the present invention, and FIG. 6 is a longitudinal cross-sectional view showing the third embodiment of the present invention. , FIG. 7 is a longitudinal sectional view showing a fourth embodiment of the present invention,
FIG. 8 is an enlarged sectional view showing the mixing section of the above embodiment, FIG. 9 is a cutaway perspective view showing the conventional example, and FIG. 1-0 is a longitudinal sectional view showing the sealing section of the above conventional example. 1... Pump casing, 2... Impeller, 3...
Pump shaft, 4...Casing cover, 5...
Underwater bearing, 6... Shaft sealing device, 7... Seal chamber, 9.
...Circulation vane, 12.12A, 12B, 12C...Labyrinth seal part, 14...Labyrinth groove, 15...
- Mixing groove, 17... Labyrinth part, Co-8... Mixing part.

Claims (1)

[Claims] 1. An impeller connected to a pump shaft is housed in a pump casing, the pump shaft is fluid-tightly supported by a shaft sealing device provided in a sealing chamber of a casing cover, and the sealing chamber is In the reactor recirculation pump, a labyrinth seal part is provided on the impeller side of the pump for adjusting purge water into the pump casing. , and one or more mixing grooves having a larger space than the labyrinth groove. 2. The impeller connected to the pump shaft is housed in the pump casing, the pump shaft is fluid-tightly supported by a shaft sealing device provided in the sealing chamber of the casing cover, and the pump is connected to the impeller side of the sealing chamber. In a nuclear reactor recirculation pump provided with a labyrinth seal section for regulating purge water into the casing, the labyrinth seal section has a large number of labyrinth grooves in at least one of the casing cover and the pump shaft, and the temperature gradient is 2. ~3℃/cm
A nuclear reactor recirculation pump characterized by having a long axial length so that the pump has a long axial length. 3. The impeller connected to the pump shaft is housed in the pump casing, the pump shaft is fluid-tightly supported by a shaft seal device provided in the seal chamber of the casing cover, and the pump is connected to the impeller side of the seal chamber. In a reactor recirculation pump that is provided with a labyrinth seal portion that adjusts purge water into the casing, the labyrinth seal portion includes a labyrinth portion having a large number of labyrinth grooves, and a plurality of labyrinth portions having a larger space than the labyrinth grooves. 1. A nuclear reactor recirculation pump, comprising: a mixing section having a mixing groove, the labyrinth groove and the mixing groove being formed in at least one of a casing cover and a pump shaft.