JPH06105315B2 - Method of restarting liquid metal cooled reactor in case of emergency shutdown - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for early restarting a liquid metal cooled nuclear reactor such as an emergency shutdown fast breeder reactor.

[Background of the Invention] A liquid metal cooling type reactor has a liquid metal coolant (hereinafter referred to as a coolant) contained in a reactor vessel accommodating a core, and an inert gas is provided between the coolant and the upper surface of the reactor vessel. It is a gas space. In order to secure this inert gas space, a reactor vessel overflow pumping device is provided so as to eliminate the change in the coolant liquid level due to the expansion and contraction of the coolant due to the change in the coolant temperature in the furnace vessel. . In this furnace vessel overflow pumping device, an overflow tank is installed outside the furnace vessel so that the coolant in the overflow tank can be pumped up to the furnace vessel by an electromagnetic pump, and the excess cooling in the furnace vessel can be performed. By returning the material to the overflow tank, the liquid level of the coolant in the furnace vessel can be kept constant. In such a reactor, the rate of temperature increase / decrease of the coolant temperature in the reactor vessel is set to about 15 ° C / hr during normal reactor startup / shutdown, and the reactor vessel overflow pumping device It continues to operate. Therefore, the temperature of the overflow tank and the temperature of the pipe connecting the overflow tank and the furnace vessel rise and fall while following the coolant temperature without causing a large difference from the temperature of the coolant in the furnace vessel.

However, when the nuclear reactor is shut down for some reason, as shown in FIG. 1, a significant temperature difference occurs between the temperature of the coolant in the reactor vessel and the temperature of the coolant in the overflow tank. That is, when the reactor emergency stop signal is generated, the control rod is inserted into the core to rapidly reduce the reactor output, and the core coolant flow rate and the reactor vessel coolant temperature are rapidly reduced. I'm drawing. Then, the coolant in the furnace vessel whose temperature has dropped rapidly is kept at a constant temperature of about 200 ° C. in order to prevent solidification as shown in FIG. on the other hand,
The coolant in the overflow tank is gradually cooled by the heat dissipated from the surface of the heat insulating material of the overflow tank into the atmosphere. For this reason, a large temperature difference occurs between the coolant in the overflow tank and the furnace container. Therefore, when the pumping of the coolant from the overflow tank to the furnace vessel is continued, thermal stress is generated due to a large temperature difference in the furnace vessel attachment portion of the coolant pumping pipe. In particular, as shown in FIG. 2, thermal stress due to a large temperature difference between the nozzle tip portion 14 of the pumping pipe 12 attached to the furnace vessel 10 and the nozzle root portion 16 of the inside 15 of the furnace vessel 10 becomes severe, and thermal fatigue is caused. Therefore, the pumping operation of the coolant into the reactor vessel is immediately stopped at the time of an emergency shutdown of the reactor. By stopping the pumping operation of this coolant,
The temperature of the coolant pumping pipe and the coolant return pipe rapidly decreases due to heat radiation into the atmosphere, as shown by the chain double-dashed line in FIG. The temperature of each pipe is adjusted to T _H (approximately 230 ° C) and T _L by controlling the preheating heater installed in the pipe to ON / OFF control in order to prevent the solidification of the coolant remaining in the pipe. (About 270 ℃).

On the other hand, a decrease in the temperature of the coolant in the furnace container causes the coolant to contract, and the liquid level of the coolant in the furnace container falls below a normal level. Therefore, when the nuclear reactor is restarted, it is necessary to restart pumping of the coolant from the overflow tank and restore the reactor vessel liquid level to a normal level. However, if the pumping of the coolant is restarted early at the time of the emergency shutdown of the reactor, the following inconvenience occurs.

(1) Since the temperature of the coolant in the overflow tank is much higher than the temperature of the coolant in the furnace vessel, large thermal stress is generated in the pumping nozzle portion.

(2) Since the coolant temperature in the overflow tank is much higher than the preheating temperature of the coolant pumping pipe, a large thermal stress is generated in the coolant pumping pipe.

(3) Since the coolant in the high temperature overflow tank pumped into the furnace vessel overflows into the coolant return pipe having a low preheating temperature, a large thermal stress is generated in the coolant return pipe.

Therefore, when restarting a conventional liquid metal cooling reactor during an emergency shutdown, pumping of coolant from the overflow tank to the reactor vessel should be performed after the coolant in the overflow tank has cooled to a temperature that does not cause the above-mentioned inconvenience. However, there is a drawback that it takes time to restart after an emergency shutdown of the reactor.

[Object of the Invention]

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and it is an object of the present invention to provide a restart method for an emergency shutdown of a liquid metal cooled nuclear reactor capable of restarting an emergency shutdown reactor early. And

[Outline of Invention]

In order to achieve the above object, the present invention provides a return pipe for returning excess cooling liquid metal in a reactor vessel of a nuclear reactor to an overflow tank and a pumping for replenishing cooling liquid metal lacking in the reactor vessel from the overflow tank. With piping,
When the operation is stopped, the cooling liquid metal in the overflow tank is pumped up to the reference height in the reactor vessel, and then the operation is restarted. In the event of an emergency stop, the reactor vessel is temporarily held at a temperature higher than the pumping restart temperature at the time of normal shutdown of the reactor, and the return pipe and pumping pipe are temporarily centered on the high holding temperature in the reactor vessel. Maintaining the temperature within the specified range, gradually lowering the temperature of the liquid metal in the overflow tank and approaching the allowable temperature difference below the high holding temperature in the furnace vessel, the liquid from the overflow tank into the furnace vessel The pumping of metal is restarted, the injection of the cooling liquid metal to the reference height in the reactor vessel by the pumping pipe is completed, and the emergency stop of the reactor is caused. There is to propose a re-starting the emergency stop of the liquid metal-cooled nuclear reactor to start the restarting of the reactor while being eliminated.

[Action]

In the present invention, during the emergency shutdown of the reactor, the return pipe, the pumping pipe, and the inside of the reactor vessel are temporarily held at a temperature higher than the pumping restart temperature at the time of the normal shutdown of the reactor, so the temperature gradually decreases. In the overflow tank, the difference between the temperature of the liquid metal in the overflow tank and the temperature at which the pumping is restarted during a normal stop is reduced to a predetermined value or less. The difference from the temperature of the liquid metal in the tank becomes less than the allowable temperature difference, and the pumping of the liquid metal from the overflow tank into the reactor vessel and the subsequent restart of the reactor can be performed early.

Even if the pumping of the liquid metal from the overflow tank into the furnace vessel is restarted at an early stage, the difference between the high holding temperature and the temperature of the liquid metal in the overflow tank that has gradually decreased at the restart is the allowable temperature difference. Because of the following, no large thermal stress is generated in any of the pumping nozzle portion, the coolant pumping pipe, and the coolant return pipe.

Example of Invention

A preferred embodiment of a restart method for an emergency shutdown of a liquid metal cooled nuclear reactor according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 shows an example of an apparatus for implementing the restart method according to the present invention. In FIG. 3, the core 20
An overflow weir 22 is provided in the furnace vessel 10 in which is stored. The overflow weir 22 is connected to one end of a return pipe 24, and the other end of the return pipe 24 is connected to an overflow tank 26. Further, the overflow tank 26 is connected with a pumping pipe 28 communicating with the furnace vessel 10,
Coolant 32 in the overflow tank by the electromagnetic pump 30
Can be pumped to the furnace vessel 10.

The return pipe 24 and the pumping pipe 28 are each equipped with a preheating heater.
34, 36 are provided, and these preheater 34, 36 are connected to the contact 3
It is connected to the power supply 42 via 8,40. Also, return piping
Temperature detectors 44 and 46 are attached to the 24 and the pumping pipe 28, and the controllers 48 and 50 open and close the contacts 38 and 40 according to the detection signals of the temperature detectors 44 and 46. The controllers 48 and 50 have the sequence control circuit shown in FIG. 4 incorporated therein, and the return pipe 24 and the pumping pipe are respectively provided during an emergency shutdown of the reactor and during a normal shutdown.
The preheating temperature of 28 can be changed.

The normal operation of a nuclear reactor by the device configured as described above is
The coolant 32 in the overflow tank 26 is drawn up by the electromagnetic pump 30 and supplied to the furnace vessel 10 through the drawing pipe 28. Then, the excess coolant 32 in the furnace vessel 10 flows into the overflow weir 22 and is returned to the overflow tank 26 via the return pipe 24. When a normal nuclear reactor is shut down,
Coolant in the reactor vessel 10 while continuing to pump coolant 32
The temperature of the furnace is lowered to about 200 ℃ at a small cooling rate of about 15 ℃ / hr, and the inside of the furnace vessel is maintained at about 200 ℃. Then, the return pipe 24 and the pumping pipe 28 are maintained in a constant temperature range by the preheat heaters 34, 36 via the controllers 48, 50. That is, as shown in FIG. 4, the controllers 48 and 50 receive the detection signals from the temperature detectors 44 and 46 when the reactor emergency stop signal is not received (during normal shutdown), and the pipe temperature T _L1 ( About 170
℃), close the contacts 38, 40 and turn on the preheater 34, 36.
Turn on. And the temperature of the pipe does not receive the reactor emergency stop signal.
When it is T _H1 (about 230 ℃), open the contacts 38, 40,
Turn off the preheater heaters 34 and 36.

On the other hand, when the nuclear reactor is brought to an emergency stop, the control rod is inserted into the core 20 and the coolant 32 in the reactor vessel 10 is rapidly cooled, as described above. Then, the electromagnetic pump 30 is set to a low voltage and the pumping of the coolant into the furnace vessel 10 is stopped. Therefore, the return pipe 24 and the pumping pipe 28 radiate heat into the atmosphere and are rapidly cooled. At this time, the controller 48,5
0 receives a reactor emergency stop signal as shown in FIG.
Moreover, the detection signals from the temperature detectors 44 and 46 are the pipe temperature T.
Turns on the preheat heaters 34 and 36 when _L2 (about 350 ℃) is reached
Then, the preheat heaters 34 and 36 are turned off when the pipe temperature becomes _TH2 (about 430 ° C). In addition, the coolant temperature in the furnace vessel 10 is 40
When the temperature drops to approximately 0 ° C, the temperature of the coolant inside the furnace vessel is maintained at approximately 400 ° C by using a heat source such as a cooling system. The temperature of the coolant inside the furnace vessel 10 is kept in the low temperature stop state (20
If the temperature is lowered to about 0 ° C), the difference between the temperature of the coolant in the overflow tank and the gradually decreasing temperature becomes large, and this temperature difference is within a predetermined value, that is, the allowable temperature difference ΔT _A (about 100 ° C). The pumping of the coolant into the reactor vessel 10 cannot be restarted for a long period until the time becomes within the range. Therefore, in this embodiment, in order to prevent the difference from the temperature of the coolant in the overflow tank, which gradually decreases, from becoming too large from the beginning, as shown in FIG. The coolant temperature is temporarily maintained at a high temperature of about 350 ° C., and when the temperature of the overflow tank 26 drops to about 450 ° C., the electromagnetic pump 30 is operated and pumping of the coolant 32 in the overflow tank 26 is restarted. . As a result, the temperature difference between the coolant 32 in the overflow tank 26 and the temperature inside the furnace container 10, the return pipe 24 and the pumping pipe 28 is within the allowable temperature difference ΔT _A , so the furnace container 10 and the return pipe 24 Therefore, large thermal stress is not applied to the pumping pipe 28.

When the pumping of the coolant by the electromagnetic pump 30 is restarted in this way, the temperature of the coolant 32 in the overflow tank 26 rapidly approaches the temperature of the furnace vessel 10 as shown in FIG. Therefore, after restarting the pumping of the coolant, the high temperature constant holding command for the coolant in the reactor vessel was released, and the coolant in the reactor vessel was cooled to about 200 ° C with an appropriate cooling rate (about 15 ° C / hr). Let At this time, the reactor emergency stop signal given to the controllers 48 and 50 was released at the same time as the cooling of the temperature of the coolant in the reactor vessel was started, the pipe preheat temperature control was switched to normal, and the return pipe 24 and the pumping pipe 28 were turned to T Control the pipe temperature in the temperature range between _H1 and _TL1 . On the other hand, the coolant 32 in the overflow tank 26 mixes with the coolant in the furnace vessel 10 returning to the overflow tank 26, and cools down following the temperature of the coolant in the furnace vessel. Therefore, the temperatures of the return pipe 24 and the pumping pipe 28 become substantially equal to the temperature of the coolant flowing in the pipes, without giving a large temperature difference to the nozzle mounting portion 14 and the nozzle base portion 16 shown in FIG. , The health of the reactor can be improved. Moreover, the coolant liquid level in the reactor vessel 10 is maintained at a normal level even while the temperature of the coolant in the reactor vessel is being lowered, so the reactor is promptly restarted after recovering the cause of the reactor emergency shutdown. Therefore, it is possible to provide a plant with a high operating rate without the need for a large increase in equipment.

In addition, although the case where the pipe preheating temperature setting is switched by the sequence circuit at the time of the emergency stop of the reactor has been described in the above-described embodiment, the operation may be manually performed by the operator.

[Effects of the Invention] As described above, according to the present invention, it is possible to quickly restart an emergency stopped liquid metal cooled nuclear reactor.

[Brief description of drawings]

FIG. 1 is a diagram showing a state of temperature drop between a coolant temperature in a reactor vessel and a coolant temperature in an overflow tank at the time of an emergency stop in a conventional liquid metal cooling reactor, and FIG. 2 is a nozzle attached to the reactor vessel. FIG. 3 is a partial sectional view of FIG. 3, FIG. 3 is a block diagram showing an example of an apparatus for carrying out a restart method according to the present invention, FIG. 4 is a sequence control diagram of the controller shown in FIG. 3, and FIG. It is a figure which shows the state of the temperature fall of the coolant temperature in a furnace container and the coolant temperature in an overflow tank by the Example which concerns on this invention. 10 …… Furnace vessel, 24 …… Return pipe, 26 …… Overflow tank, 28 …… Pumping pipe, 30 …… Electromagnetic pump, 32 ……
Coolant, 34,36 …… Preheater, 42 …… Power supply, 48,50 ……
controller.

Claims (1)

[Claims] 1. A return pipe for returning excess liquid metal for cooling in a reactor vessel of a nuclear reactor to an overflow tank, and a pumping pipe for replenishing the liquid metal for cooling shortage in the reactor vessel from the overflow tank. In the restart method at the time of an emergency stop of the liquid metal cooling reactor to restart the operation after injecting the cooling liquid metal in the overflow tank to the reference height in the reactor vessel by the pumping pipe when stopping the above, During the emergency shutdown of the reactor, the inside of the reactor vessel is temporarily held at a temperature higher than the pumping restart temperature at the time of the normal shutdown of the reactor, and the return pipe and the pumping pipe are temporarily raised in the reactor vessel. The temperature of the liquid metal in the overflow tank is gradually reduced by maintaining the temperature within a predetermined range around the holding temperature. For restarting the pumping of the liquid metal from the overflow tank into the furnace vessel in the state of approaching the allowable temperature difference or less with respect to the high holding temperature, for cooling to the reference height in the furnace vessel by the pumping pipe. A method of restarting an emergency shutdown of a liquid metal cooled reactor, characterized in that the restart of the reactor is started in a state where the injection of the liquid metal is completed and the cause of the emergency shutdown of the reactor is eliminated. .