JPS6360878B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid metal cooled nuclear reactor, and more particularly, to a liquid metal cooled nuclear reactor.
The present invention relates to a furnace vessel overflow pumping device.

FIG. 1 shows a schematic diagram of a furnace vessel overflow pumping device. In liquid metal cooled nuclear reactors, the liquid metal coolant (hereinafter referred to as coolant) expands and contracts due to temperature changes within the system due to changes in operating conditions such as when the reactor starts and stops. In order to eliminate fluctuations in the liquid level of the reactor vessel, an overflow pumping device as shown in FIG. 1 is provided. This device pumps up the coolant in an overflow tank 1 using a pump 2 which is an electromagnetic pump, and sends the excess coolant to an overflow nozzle 5 to raise a furnace vessel 4 to a predetermined liquid level or higher.
The liquid level in the furnace vessel is maintained at a predetermined level by recovering the liquid and returning it to the overflow tank 1 by free fall. A liquid level gauge 7 is installed in the furnace vessel 4 to monitor the coolant liquid level.

When an abnormal drop in the liquid level of the reactor vessel is detected due to damage to the cooling system piping connected to the reactor vessel 4, the reactor is scrammed and pumping of coolant to the reactor vessel 4 is temporarily stopped. The subsequent core decay heat is removed by an auxiliary core cooling system (not shown), and as a result of the contraction of the reactor vessel coolant, the reactor vessel liquid level continues to fall. When the reactor vessel liquid level falls below the minimum liquid level 9 required for core cooling, the liquid level gauge 7 detects this, resumes pumping, restores the liquid level to a safe position, and then stops pumping again. . Thereafter, this intermittent pumping is repeated until the coolant finishes shrinking. Since the pump 2 is an electromagnetic pump, the heat insulating material of the pump duct is made thin in order to improve pump efficiency. Therefore, as shown in Figure 2, when pumping is stopped, the temperature of the pump duct drops rapidly due to heat radiation to the atmosphere, while the coolant in the overflow tank has a large heat capacity and its temperature drops slowly. This results in a temperature difference between the pump duct and the pump duct. As a result, thermal shock is applied to the pumping pump duct and the pump outlet piping during intermittent pumping operation to the furnace vessel when the piping is damaged as described above, which is disadvantageous in terms of structural design.

An object of the present invention is to eliminate thermal shock that occurs in the pump duct and pump outlet piping due to intermittent operation of the pump when the pipe is damaged.

A feature of the present invention is that by providing a bypass line in the pump, even when the voltage applied to the pump is lowered and pumping of the reactor vessel is stopped, a small amount of coolant is allowed to flow into the pump duct, allowing the pump duct and overflow to flow. This is to equalize the temperature of the internal coolant.

An embodiment of the invention is shown in FIG. This embodiment differs from the prior art shown in FIG. 1 in that a bypass line 10 and a flow control valve 11 are provided.

First, the characteristics of the electromagnetic pump will be explained. Fourth
The figure shows the QH characteristics (relationship between flow rate and head) of the pump and the guide pressure drop curve. In FIG. 4, the intersection of the QH curve at voltage V ₀ and the pressure loss curve of the pumping line represents the rated operating point. At this point, the pumping flow rate to the reactor vessel and the very small amount to the bypass line are ensured. On the other hand, when the applied voltage is set to V ₁ below a certain level, the QH curve of the pump has no points of intersection with the pressure loss curve of the pumping line, and only has points of intersection with the pressure loss curve of the bypass line.
At this point, pumping into the reactor vessel is stopped and only a small flow rate in the bypass line 10 is ensured. The flow control valve 11 may be adjusted in advance so that a small amount of coolant flows through the bypass line 100, and there is no need to perform any particular control during normal operation.

If a pipe breakage or the like occurs, this is detected by the liquid level gauge 7 or the like, and the pump applied voltage is switched from V ₀ to V ₁ .
This will stop pumping to the reactor vessel as described above, but a small amount of coolant will continue to flow through the pump duct due to the presence of the bypass line.
As a result, the temperature of the pump duct becomes almost equal to the temperature of the coolant in the overflow tank, and thermal shock to the pump duct and pump outlet piping due to intermittent pumping operation when the piping is damaged is eliminated.

(i) The present invention can eliminate thermal shock not only when piping is damaged, but also when the applied voltage is lowered and then increased again due to a failure of the pump itself, using the same principle as described above.

(ii) Sump pump switching operations can be performed not only by the reactor vessel level gauge but also by the overflow tank level gauge.

(iii) Furthermore, it is equally effective when a plurality of pumping devices as described above are installed in order to improve safety and reliability.

According to the present invention, even when pumping to the furnace vessel is stopped, the temperatures of the pump duct and the coolant in the overflow tank are kept equal, and the pump duct and the pump during intermittent pumping operation are By eliminating thermal shock in the outlet piping,
The overflow pumping system is structurally sound enough not only during normal plant operation but also in the event of piping breakage, and is extremely important for safety from the perspective of securing the reactor vessel liquid level necessary for core cooling. The reliability can be made sufficiently high.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a conventional overflow pumping device, Fig. 2 is a diagram showing temperature changes in the coolant in the overflow tank and the pump duct after pumping is stopped, and Fig. 3 is an overflow pumping device of the present invention. FIG. 4 is a diagram showing the QH characteristics of the pump and the pressure drop curve of the system. 1... Overflow tank, 2... Sump pump,
4...Reactor vessel, 7...Level gauge, 10...Bypass line, 11...Flow control valve.

Claims (1)

[Claims] 1. In a reactor volume overflow pumping device for a liquid metal cooled nuclear reactor where the reactor vessel is located at a high position and the overflow tank is located at a low position, the reactor vessel pumping piping returns from the pumping pump discharge side to the overflow tank side. An overflow pumping device for a nuclear reactor, characterized in that a line bypassing a container is provided, a flow rate control valve is provided in this line, and a small amount of coolant always flows through this line.