JPS644160B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is characterized in that cold water injected into a mechanical seal of a nuclear reactor recirculation pump flows along the pump shaft.
The present invention relates to a recirculation pump having a thermal barrier to reduce shaft thermal stress caused by mixing with high temperature reactor water near the top of the impeller.

Reactor recirculation pumps for primary coolant circulation used in boiling water reactors have mechanical seals as shaft seals. This mechanical seal needs to be replaced frequently, and clean cold water is injected from the outside in order to reduce the amount of radiation exposure during replacement work and to prevent foreign matter from getting into the mechanical seal and shortening the seal's lifespan. are doing. A portion of this injection water (mechanical seal purge water) flows out to the outside to adjust the pressure in each of the plurality of seal chambers, but a portion flows into the casing along the pump shaft.

A portion of the purge water that has flowed into the casing mixes with high-temperature reactor water around the pump shaft above the pump impeller. The water temperature in the sealing chamber is approximately 30-50℃.
Since reactor water is approximately 270 to 280°C, temperature fluctuations occur near the mixing of the two, resulting in thermal stress on the pump shaft surface and the inner surface of the pump casing cover that faces it, causing temperature fluctuations and fluctuations. Depending on the cycle, cracks may occur on the pump shaft surface and the inner surface of the casing cover.

The present invention has been made to solve the above problems, and eliminates mixing of low temperature purge water and high temperature reactor water near the pump shaft surface and casing cover surface.
The purpose of the present invention is to provide a nuclear reactor recirculation pump that can prevent cracks from occurring due to thermal stress.

The present invention will be described below with reference to drawings of embodiments. FIG. 1 is a cross-sectional view of a nuclear reactor recirculation pump. An impeller 2 is fixed to a pump shaft 1 at the center of the pump. A casing 3 is installed on the outer periphery of the impeller 2 to form a flow path, and a casing cover 4 is fixed to the upper part of the casing 3. This casing cover 4 and the pump shaft 1 have a gap 5, and a mechanical seal 6 is further arranged. A cylindrical pump bearing 5 is provided between the casing 3 and the pump shaft 1. The pump bearing 5 is fixed to the casing cover 4, and a plurality of holes 7 are bored in the radial direction approximately in the middle of the cylindrical axis. Further, inside the pump bearing 5, a journal 8, which is a cylindrical member, is arranged concentrically with the pump bearing 5. This journal 8 forms a part of the impeller 2. Furthermore, inside the journal 8 and concentrically with the journal 8, a casing cover 4 is provided.
A cylindrical thermal barrier 10 is provided which is attached to the.

In addition, the lower gap 1 between the circulating water suction part 9 and the thermal barrier 10
A plurality of holes 12 are bored in the impeller 2 to communicate with the impeller 2. Gaps 13 and 14 are provided inside and outside the thermal barrier 10.
is formed. Further, the casing cover 4 is held and supported by a support stand 15. A wear ring 16 is installed in the suction portion of the casing 3 near the lower end of the impeller 2 . Mechanical seal 6
A seal chamber 17 is installed in the lower part of.

Next, the effect will be explained.

Purge water 18 injected into the seal chamber 17 of the reactor recirculation pump passes through the gap 5 between the pump shaft 1 and the casing cover 2 and enters the gap 13 between the pump shaft 1 and the thermal barrier 10 above the impeller 2 . Reactor water 19 pressurized by the impeller 2 flows from the pump bearing 5 through the gap 20 between the pump bearing 5 and the casing 3.
through the gap 21 between journal 8 and journal 8.
and enters the gap 14 of the thermal barrier 10. On the other hand, the cold purge water 18 flowing into the gap 13 reaches the pump shaft 1 and the thermal barrier 10 by the time it reaches the lower region 1 of the thermal barrier 10.
Reactor water 19 is heated in region 11 by heat inflow from
It flows into the suction part 9 of the impeller 2 through the flow path 12 provided in the impeller 2.

The thermal barrier 10 is attached to the casing cover 4 , and the lower area 11 of the thermal barrier 10 is attached to the casing cover 4 so that the purge water 18 and the reactor water 19 exchange heat through the thermal barrier 10 .
In this case, the temperature fluctuation when the purge water 18 and the reactor water 19 are mixed becomes small. Furthermore, purge water 18 and reactor water 19
Since the mixing is performed at a position away from the inner surface of the pump shaft 1 and the casing cover 4, the problem of thermal stress on the outer surface of the pump shaft 1 and the inner surface of the casing cover 4 is eliminated.

Figure 2 shows the case where the thermal barrier 10a is attached to the pump shaft 1, and the purge water 18 and reactor water 19 are connected to the thermal barrier 1.
0a and the gap 14a between the journal 8. Since the thermal barrier 10a rotates together with the pump shaft 1, the purge water 18 flowing into the gap 14a is sufficiently stirred and mixed with the reactor water 19 quickly.

FIG. 3 shows the heat barrier 10 attached to the casing cover 4,
This is a case where the thermal barrier 10a is attached to the pump shaft 1, and the purge water 18 is in the gap 13b between the thermal barriers 10 and 10a.
Then, the reactor water 19 flows into the gap 14b between the thermal barrier 10 and the journal 8. In this case, purge water 18 is warmed within gap 13b, and reactor water 19 is cooled within gap 14b. In addition, the flow paths for purge water 18 and reactor water 19 are separated, and mixing of purge water 18 and reactor water 19 is performed in the area below the thermal barriers 10 and 10a, so the outer surface of the pump shaft 1 and the inner surface of the casing cover And the problem of thermal stress on the surface of the journal 8 is eliminated.

The shape of the thermal barrier according to the present invention is generally considered to be cylindrical, but in order to increase heat exchange efficiency, the surface shape may be waveform, or it may have a shape with unevenness or protrusions to create turbulence in the flow. becomes more effective.

FIG. 4 shows an example of changing the shape of the thermal barrier in order to increase the amount of heat exchange between the purge water 18 and the reactor water 19. Purge water 18 and reactor water 19 exchange heat through a sufficient gap 13c between the thermal barriers.

FIG. 5 shows an example in which the surface of the thermal barrier 10b is corrugated, which gives turbulence to the purge water 18 and the reactor water 19, thereby increasing the heat exchange efficiency.

FIG. 6 shows an example in which holes 22 are provided in the thermal barrier 10c in order to more effectively mix the purge water 18 and the reactor water 19. Purge water 18 in gap 13 is jetted out from hole 22 into gap 14 by centrifugal force and mixes with reactor water 19.

As explained above, according to the present invention, low-temperature purge water and high-temperature reactor water do not mix directly and near the pump shaft and casing cover surface, so it is possible to prevent cracks from occurring due to thermal stress.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a nuclear reactor recirculation pump according to one embodiment of the present invention, and FIGS. 2 to 6 are state diagrams showing other embodiments of the thermal barrier of FIG. 1... Pump shaft, 2... Impeller, 3... Casing, 4... Casing cover, 5... Pump bearing, 6... Mechanical seal, 8... Journal, 10... Thermal barrier.

Claims (1)

[Claims] 1. An impeller fixed to the end of the pump shaft, a casing forming a circulating water flow path, a casing cover fixed to the casing, and a mechanical seal installed between the casing cover and the pump shaft, A nuclear reactor recirculation pump comprising a pump bearing attached to the casing cover, a journal formed in the impeller through a gap from the pump bearing, and a thermal barrier provided inside the journal.