JPH0212319Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a vertical free liquid level pump, and more specifically, the invention connects a casing and a dump tank with an emergency discharge siphon pipe that is activated when the liquid level inside the casing rises abnormally. This invention relates to a mechanical pump with an emergency discharge siphon that can thereby prevent the liquid level in the pump from rising to the upper mechanical bearing in the event of damage to the cover gas system piping.

The most common main circulation pump for loop type liquid metal cooled fast breeder reactors is the vertical free liquid level type, which has a liquid metal level inside the casing and a cover gas space above it. It is a mechanical pump. An example is shown in FIG. 1A. Liquid sodium flows in from the suction nozzle 2 at the lower end of the casing 1, obtains a discharge pressure by the impeller 3, and flows out from the discharge nozzle 4. The liquid metal that has entered the overflow column 6 via the overflow pipe 5 is returned to the suction nozzle 2 again. A shaft 7 that transmits rotational force to the impeller 3 is supported by a hydrostatic bearing 8 in a fluid at a lower portion and a mechanical bearing 9 at an upper portion. Further, a mechanical seal 10 is provided on the lower side of the mechanical bearing 9 to prevent cover gas from leaking from the casing 1. By constantly flowing inert gas downward from this mechanical seal 10, liquid metal vapor is released. By preventing it from rising into the seal and at the same time providing a predetermined cover gas pressure, it is possible to set the level of free liquid level in the pump and provide the pump with the required suction head required.

In the conventional example shown in FIG. 1A, the cover gas is supplied from a gas supply pipe 11 attached to the lower part of the mechanical seal 10,
The cover gas space 13 descends through the gap between the
The gas is recycled through the gas pipe 14 connected to the overflow column 6 and recovered through the exhaust pipe 15. This cover gas pressure is higher than the atmospheric pressure in which the pump is installed, so if the above-mentioned cover gas system piping were to break, the free liquid level inside the pump would rise rapidly, and in some cases, the mechanical seal 10 and rise up to the mechanical bearing 9, causing serious damage to the pump and causing leakage of liquid metal.

The liquid level in the pump and the liquid level in the overflow column in FIG. 1A are those when the pump is in normal operation. On the other hand, Fig. 1B shows the liquid in the pump and overflow column when the gas supply pipe 11 or the exhaust pipe 15 is damaged. This shows the change in position. The vertical axis in this figure corresponds to the height in FIG. 1A, and the horizontal axis indicates the elapsed time after the gas system pipe breakage. Each line in the figure is as follows. Code 20 is the pump liquid level, code 2
1 is the overflow column liquid level, 22 is the reactor vessel cover gas pressure (represented by the liquid metal head),
Reference numeral 23 indicates the upper end position of the gas pipe 14, reference numeral 24 indicates the lower surface position of the shielding plug, and reference numeral 25 indicates the position of the gas supply pipe 11.

In this case, as shown in FIG. 2, the cover gas system piping of the pump communicates with the cover gas system of the reactor vessel 30, so if the gas system piping near the pump breaks, the gas pressure inside the pump will decrease. The pressure drops to atmospheric pressure in a short time. On the other hand, regarding the cover gas pressure on the reactor vessel side, it is known that it takes one minute or more for the gas pressure to decrease to atmospheric pressure because the volume of the gas space 31 is much larger than that in the case of a pump. During this time, a gas pressure imbalance occurs between the reactor vessel and the pump, and this differential pressure causes the liquid level in the pump to rise. That is, the liquid level in the overflow column rises at the same time as the gas system pipe breaks, and when it reaches the same level as the liquid level in the pump, both rise. However, when reaching the upper end of the gas pipe 14, the liquid level in the overflow column can hardly rise any further, and only the liquid level in the pump continues to rise. At this point, the reactor vessel cover gas pressure still has a high pressure, so the liquid level in the pump will reach the shielding plug 12, the mechanical seal 10 and the mechanical bearing 9, which will only cause serious damage to the pump. This will cause leakage of liquid metal to the outside of the pump. This risk is more significant when the pump is in a cold leg configuration due to the higher cover gas pressure during operation.

In addition, in FIG. 2, reference numeral 32 indicates an outlet pipe;
33 is a main cooling pipe, 34 is a drain valve, 35 is a drain tank, and 36 is a cover gas purification facility.

The present invention eliminates the drawbacks of the prior art as described above, and even if damage occurs to the cover gas system piping, it is possible to prevent the liquid level in the pump from rising to the mechanical bearing. Therefore, mechanical seals and mechanical bearings are not damaged by liquid metal.
Another object of the present invention is to provide a mechanical pump with a siphon for emergency release that does not cause any harm to humans or surrounding equipment since no liquid metal flows out from the mechanical seal.

In order to achieve this object, the present invention is configured to connect the casing and the dump tank with an emergency discharge siphon pipe that is activated when the liquid level in the pump casing rises abnormally.

Hereinafter, the present invention will be explained in more detail based on the drawings. FIG. 3 is an explanatory diagram showing an embodiment of the present invention. Since the basic structure is the same as the conventional one shown in FIG. 1, corresponding parts are given the same reference numerals and their description will be omitted. The present invention is significantly different from the prior art in that the pump casing 1 and the dump tank 41 are connected by an emergency discharge siphon pipe 42. This siphon tube 42 is covered with a heat insulating material and is always maintained at a temperature exceeding the freezing point of the liquid metal. Gas system piping is connected to the dump tank 41, and the cover gas in the dump tank and the pump are in communication.

The levels written in the figure are as follows.

L0...Impeller center level L1...Minimum level to prevent the hydrostatic bearing in the fluid from being exposed L2...Siphon pipe installation level for emergency release L3...Minimum level inside the pump during pump operation L4...Overflow level inside the pump L5...For emergency release Siphon operation level L6...lower surface level of pump shielding plug Also, the liquid levels in the pump and in the overflow column shown in the same figure are under normal operating conditions.

As before, the cover gas is supplied from the gas header 40 through the gas supply pipe 11 attached to the lower part of the mechanical seal 10, and the cover gas is supplied to the shielding plug 1.
2 and the shaft 7, and the cover gas space 1
3, is collected through the gas pipe 14 connected to the overflow column 6, and then through the exhaust pipe 15, thereby performing its circulation.

Now, in Figure 3, in the unlikely event that the gas system piping is marked 4
When the pump is damaged at position 3a or 43b and the liquid level in the pump rises to L5, the emergency discharge siphon pipe 42 is activated and the liquid metal in the pump is discharged into the dump tank 41. This siphon function continues until the liquid level in the pump drops to L2. Such an emergency discharge siphon device is extremely advantageous because, after activation, operation can be resumed simply by returning the liquid metal discharged into the dump tank to the loop in which the pump is installed. In order for this device to function properly, it must be activated before the liquid level in the pump reaches the level L6 of the lower surface of the shielding plug. The conditions are shown by the following equation.

L4<L5<L6 The present invention allows the pump to be quickly restored even if the cover gas system piping is damaged, so it is particularly effective when installed in a location where a high operating rate is required. For example, in the case of a pump for the secondary cooling system of a fast breeder reactor, the cover gas pressure is high (more than 1 kg/cm ² G), so when the gas system piping is damaged, atmospheric gas (air) gets mixed into the cover gas and the liquid becomes liquid. There is no need to worry too much about the damage caused by oxidizing the metal. In this case, the cover gas is
Since it is not activated, it is harmless even if it leaks outside the pipe.

In addition, in the case of a pump for the fast breeder reactor primary cooling system,
Although the cover gas pressure is not very high (around 0.5Kg/cm ² G), in this case the atmospheric gas is nitrogen, so
Even if mixed into the cover gas, the liquid metal will not be oxidized. In particular, when it is desired to increase the operating rate, it is recommended to use the pump of the present invention. Furthermore, if contamination of the atmospheric gas due to leakage of the cover gas becomes a problem, there is also a method of using a separate cover gas-based shielding device.

An example of using this pump as a main circulation pump for primary cooling in a liquid metal cooled fast breeder reactor is shown in Figure 4.

Now, in the present invention, the reason why the emergency release siphon tube 42 is specifically designated as a "siphon" is as follows. In a configuration in which a simple overflow pipe is connected to the level of L5, when the liquid level in the pump rises, this liquid level will be maintained at L5. However, the shielding plug 12 of the pump is designed to have a predetermined heat shielding function at the normal liquid level of L4, and when the liquid level is held at an abnormally high level as described above, the mechanical seal 10 and the Although not shown in , it is dangerous because the temperature of the seal at the joint between the shielding plug 12 and the casing 1 cannot be maintained below a predetermined value.
In the case of a gas system piping breakage accident assumed here, the liquid level in the pump will rise rapidly, and once the liquid level reaches L5, it will be rapidly lowered by the emergency discharge siphon device of the present invention. Therefore, in the pump of the present invention, there is no problem since the liquid level rises to L5 in a short time. Emergency release siphon tube 4
The mounting position L2 of No. 2 is strictly defined below.

L1≦L2≦L4 That is, if L2 is higher than L4, it is dangerous for the above-mentioned reason. Further, L2 may be anywhere between L1 and L4. In the case of the accident assumed here, operation cannot be resumed until repairs are made and restoration is performed.
There is no problem even if the level after activation of the emergency discharge siphon is lower than the liquid level range L3 to L4 during normal operation.

Since the present invention is constructed as described above, when the cover gas pipe breaks, the liquid level inside the pump will not rise to the mechanical seal, thereby preventing damage to mechanical bearings, mechanical seals, etc. It also has excellent effects, such as being able to prevent liquid metal from flowing out.

[Brief explanation of the drawing]

Figure 1 is an example of a conventional mechanical pump and a diagram showing the liquid level change when the cover gas system piping breaks, Figure 2 is an explanatory diagram showing an example of how the conventional pump is used, and Figure 3 is a machine according to the present invention. An explanatory diagram showing an example of a type pump,
FIG. 4 is an explanatory diagram showing an example of the usage state of the pump according to the present invention. 1...Casing, 2...Suction nozzle, 3...
Impeller, 4...Discharge nozzle, 7...Shaft, 8...
Hydrostatic pressure bearing in fluid, 9... Mechanical bearing, 10... Mechanical seal, 41... Dump tank, 42...
...Siphon tube for emergency release.

Claims (1)

[Claim for Utility Model Registration] The casing has a liquid metal surface, above which a shielding plug and a mechanical bearing are provided via a cover gas space, and below the liquid metal surface there is a static surface in the fluid. A vertical free level pump, wherein a pressure bearing is provided, and an overflow pipe is attached to the casing between the shielding plug and the hydrostatic bearing in fluid, the casing further comprising a siphon pipe for emergency release. is attached, and the siphon pipe connects the dump tank installed outside the casing with the casing, and the mounting position L2 of the siphon pipe to the casing is L1≦L2≦L4, and the operating level L5 of the siphon pipe is L4<L5<L6 (Here, L1...the lowest level to prevent the hydrostatic bearing in the fluid from being exposed, L4...the overflow level in the pump, and L6...the lower surface level of the pump shielding plug). Mechanical pump with siphon for emergency release.