JPH04246286A - Mechanical pump for sodium - Google Patents

Abstract

PURPOSE:To obviate the need of externally installing an overflow system, reduce the material cost, eliminate cause of the temperature distribution nonuniformity in the peripheral direction and prevent the bending and galling of a driving shaft. CONSTITUTION:A hollow driving shaft 42 is inserted into a vertical casing 40 having a sodium free liquid surface chamber 48, and supported in free revolution by a static pressure bearing 44, and sodium is sucked from an inlet nozzle 54 by the revolution of a main impeller 46 at the lower edge of the driving shaft, and discharged from an outlet nozzle 56. A sodium returning impeller 62 is installed in the vicinity of the free liquid surface of the hollow driving shaft, and sucks sodium, which is allowed to flow down in a sodium returning hole 66 in the hollow part of the driving shaft and the bearing part on the revolution side and is returned to a pump suction side, and the liquid surface is controlled to a constant level.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical free liquid level centrifugal pump having a sodium liquid level within a casing and a cover gas sealed above the sodium liquid level. More specifically, the present invention relates to a mechanical pump for sodium in which sodium in a free liquid level chamber is returned to the pump suction side using a hollow portion of the drive shaft. This pump is used, for example, as a main circulation pump for the primary cooling system of a sodium-cooled fast breeder reactor.

0002

2. Description of the Related Art Primary main cooling system circulation pumps used in sodium-cooled fast breeder reactors are usually mechanical pumps with a free sodium liquid level within a vertical casing. For example, if the reactor structure is a loop type, the pump 10 is installed in a dedicated guard vessel 12, as shown in FIG. It is sucked in through the inlet nozzle 14, discharged through the outlet nozzle 16, and sent to the reactor vessel via the primary main cooling system check valve 18 and flow meter 19. Sodium heated in the reactor core in the reactor vessel is sent to the primary main cooling system intermediate heat exchanger, where heat exchange is performed. A primary sodium coolant circulates in such a loop.

[0003] Details of the main parts of the mechanical pump (section A in Figure 2)
is shown in Figure 3. The pump 10 is constructed by inserting a hollow drive shaft 24 into a double-structured vertical casing 22 having a sodium free liquid level chamber 20 therein, and rotating an impeller 26 attached to the lower end of the drive shaft 24 to open an inlet nozzle 14. This is a type in which sodium is sucked in from the tank and discharged from an outlet nozzle 16. By the way, since the pump 10 is used at high temperatures, a hydrostatic bearing 28 having a structure as shown in FIG. 3 is used as the bearing. In the static pressure bearing 28, a rotating side bearing part 28a provided on the drive shaft 24 and a cylindrical fixed side bearing part 28b provided on the casing side are coaxially located with a slight gap therebetween, and the fixed side bearing part 28b has a cylindrical fixed side bearing part 28b. It has a structure in which a plurality of sodium supply holes 30 are formed in the radial direction.

[0004] Such a hydrostatic bearing 28 uses the discharge pressure of the pump to lubricate itself with sodium, and a portion of the sodium on the pump discharge side is sent into the bearing gap through the sodium supply hole 30. The fed sodium finally enters the free liquid level chamber 20. Therefore, during pump operation, sodium always enters the free liquid level chamber 20, so in conventional pumps that require a free liquid level,
As shown in FIG. 2, an overflow system piping 32 is provided near the free liquid level of the casing, and an overflow column 3
Connect to the pump inlet pipe through a tank called 4,
Overflow sodium is returned to the primary main cooling system.

[0005]

[Problems to be Solved by the Invention] As mentioned above, in conventional mechanical pumps that require a free liquid level, it is necessary to install overflow system piping and tanks outside the casing, and these piping and tanks are not connected to equipment. In addition to placing restrictions on the layout design, it also had the disadvantage of increasing the amount of material. Furthermore, due to the connection of the overflow system piping, a biased flow of sodium occurs, resulting in uneven temperature distribution in the circumferential direction of the pump, which may cause bending of the drive shaft or galling of the shaft due to bending.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, eliminate the need to externally attach an overflow system to the pump body, eliminate constraints on equipment layout and design, and reduce the amount of material. To provide a mechanical pump for sodium which can prevent bending and galling of a drive shaft by eliminating the cause of uneven temperature distribution in the circumferential direction.

[0007]

[Means for Solving the Problems] The present invention involves inserting a hollow drive shaft into the center of a vertical casing having a sodium free liquid level chamber, and rotatably rotating the drive shaft at the lower part thereof using a hydrostatic bearing. This type of pump sucks in sodium from the inlet nozzle and discharges it from the outlet nozzle by rotating an impeller supported at the lower end of the drive shaft. In order to achieve the above object, the present invention forms an opening in the vicinity of the free liquid surface of the hollow drive shaft to provide a sodium return impeller, and utilizes the hollow part of the drive shaft to form a free liquid level chamber. and the pump suction side, and the sodium in the free liquid level chamber inside the pump is returned to the pump suction side.

Specifically, a sodium return hole that communicates with the hollow part of the drive shaft is provided in the rotating side bearing part of the hydrostatic bearing, and the free liquid level chamber and the pump suction side are connected by the hollow part of the drive shaft and the sodium return hole. communicate with. Further, a sodium return hole may be formed in the drive shaft itself.

[0009]

[Operation] A portion of the sodium flows out from the hydrostatic bearing into the free level chamber. Since the sodium return impeller is located near the free liquid level, sodium near the free liquid level is sucked in from the sodium return impeller and sent to the pump suction side through the hollow portion of the drive shaft. Therefore, the liquid level in the free liquid level chamber is always kept constant only inside the pump body. Furthermore, since the impeller for returning sodium rotates together with the drive shaft, no uneven flow of sodium occurs, and the temperature distribution in the circumferential direction becomes uniform.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a mechanical pump according to the present invention. This pump is a primary main cooling system circulation pump used in sodium-cooled fast breeder reactors. A vertical casing 40 with a double structure, a hollow drive shaft 42 inserted into the center from above, a hydrostatic bearing 44 that rotatably supports the drive shaft 42 at its lower part, and a hydrostatic bearing 44 provided at the lower end of the drive shaft. A main impeller 46 is provided. A sodium free liquid level chamber 48 is formed inside the vertical casing 40, and the upper part of the chamber 48 is sealed with a cover gas. Therefore, the upper part of the drive shaft 42 is sealed with a mechanical seal 50, and the coupling 5
A drive motor (not shown) located further above via 2
is connected. When the drive shaft 42 is rotated by the drive motor, the main impeller 46 also rotates, drawing in sodium from the inlet nozzle 54 and expelling it from the outlet nozzle 56.

In the present invention, an opening 60 is formed near the free liquid level of the hollow drive shaft 42 to provide a sodium return impeller 62, and the hollow part 64 of the drive shaft is used to connect the free liquid level chamber 48 and Provide communication with the pump suction side. In addition, a sodium return hole 6 passing through the rotating side bearing portion 44a in the axial direction
6 is formed, and the free liquid level chamber 48 and the pump suction side are communicated through the drive shaft hollow part 64 and the sodium return hole 66. The basic structure of the hydrostatic bearing 44 itself may be the same as that of the prior art. A plurality of sodium supply holes 68 are formed in the fixed side bearing portion 44b in its radial direction, and sodium enters the bearing gap, lubricates it, and flows out into the free liquid level chamber 48.

Of the sodium flowing out from the static pressure bearing 44 into the free liquid level chamber 48, the sodium near the free liquid level is sucked in by the sodium return impeller 62, and the sodium is sucked into the drive shaft 4.
The sodium flows downward through the hollow portion 64 of No. 2, and is returned to the suction side of the main impeller 46 through the sodium return hole 66 of the rotating side bearing portion 44a. This point is a feature of the present invention. The sodium return impeller 62 rotates at the same rotation speed as the pump while it is operating, so there is no uneven flow of sodium in the free liquid level chamber, the temperature distribution is uniform in the circumferential direction, and the sodium is always free. The effect of returning sodium from the liquid level chamber 48 continues.

Next, the size of the impeller for sodium return (
Consider the impeller diameter D). Here, lifting height H:
20m (Sodium liquid level height: 5m + cover gas pressure:
1kg/cm2 ~ 10m with allowance)・Rotation speed N
:650 rpm (a value assuming a large furnace), the impeller diameter D is approximately 600 mm from the following formula D = 19.1 x (2 gH) 1/2 /N. Since the diameter of the drive shaft is approximately 500 to 600 mm in a large furnace, it is possible to mount an impeller for sodium return having the above-mentioned diameter. The amount of sodium returned is determined by the pump discharge flow rate.
If the flow rate is approximately 200m3/min, the amount of sodium flowing from the static pressure bearing into the free liquid level chamber is approximately 5m3/min.
n (designed to be approximately 2.5% of the discharge flow rate).

By the way, in the above embodiment, the sodium return hole 66 is formed in the rotating side bearing portion 44a and passes through in the axial direction, but the sodium return hole is provided in the drive shaft 42 itself, and the sodium return hole is The free liquid level chamber and the pump suction side may be communicated by a hole.

[0015]

Effects of the Invention As described above, the present invention eliminates the need for the overflow system piping that was conventionally attached to the outside of the pump body. ), and the temperature distribution in the circumferential direction of the pump can be made uniform. This prevents the drive shaft from bending and eliminates the causes of malfunctions such as shaft galling. Furthermore, since there is no need to externally attach overflow system piping or tanks, the amount of material can be reduced, equipment layout can be designed more easily, and the entire plant that uses mechanical pumps can be downsized.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of a mechanical pump for sodium according to the present invention.

FIG. 2 is a schematic diagram of a conventional mechanical pump for sodium.

FIG. 3 is a detailed view of section A in FIG. 2;

[Explanation of symbols]

40 Vertical casing 42 Drive shaft 44 Static pressure bearing 46 Main impeller 48 Free liquid level chamber 60 Opening 62 Sodium return impeller 64 Drive shaft hollow part 66 Sodium return hole

Claims (3)

[Claims] Claim 1: A drive shaft having a hollow structure is inserted into the center of a vertical casing having a free liquid level chamber of liquid sodium, the drive shaft is rotatably supported by a hydrostatic bearing at the lower part of the drive shaft, and the lower end of the drive shaft is In a pump of the type that sucks in sodium from an inlet nozzle and discharges it from an outlet nozzle by rotation of an impeller provided therein, an opening is formed near the free liquid surface of the drive shaft having a hollow structure, and an impeller for returning sodium is provided. A mechanical pump for sodium, characterized in that a free liquid level chamber and a pump suction side are communicated through a hollow part, and sodium in the free liquid level chamber is returned to the pump suction side inside the pump. [Claim 2] A sodium return hole communicating with the hollow part of the drive shaft is provided in the rotating side bearing part of the hydrostatic bearing, and the free liquid level chamber and the pump suction side communicate with each other through the hollow part of the drive shaft and the sodium return hole. The mechanical pump according to claim 1. 3. The machine according to claim 1, wherein the drive shaft itself has a sodium return hole that communicates with the drive shaft hollow part, and the free liquid level chamber and the pump suction side communicate with each other through the drive shaft hollow part and the sodium return hole. formula pump.