Patent Description:
When the reactor is shut down, control rods inserted downward will immediately terminate the fission heat of the fuel rods, but the fission products of the core contain a large number of decayable radioactive elements, so that a large amount of decay heat is still generated in the core after the reactor is shut down. In order to realize reactor cooling and depressurization after the shutdown, a waste heat discharge system must be set to continuously export the waste heat out of the reactor. During the cooling process, if the heat transfer power is low and the condensate water does not fill the return pipe, there will be an obvious gas-liquid interface in the return pipe, the condensate water flows down along the return pipe to impact on the gas-liquid interface, making the interface fluctuate, which results in fluctuation of the flow rate of the condensate water. This can easily cause a large load force on the pipe, so that the pipe has the risk of rupture. When the temperature of the condensate water at an outlet of the condenser is not uniform and fluctuates greatly, the downstream pipe can be subjected to a great thermal fatigue impact, which likewise makes the pipe have the risk of rupture.

Publications <CIT>, <NPL>, and <CIT> are considered to be relevant to this application.

The technical problem to be solved by the present invention is to provide a waste heat discharge system and a flow stabilization method. This problem is solved by a waste heat discharge system having the features of claim <NUM> and by a flow stabilization method having the features of claim <NUM>.

The technical solution adopted by the present invention to solve its technical problem is:.

Preferably, the temperature buffer tank is filled with a liquid, comprises an inlet connected to the first pipeline, and is connected to the main feedwater line via the second pipeline, so as to be fluidly connected to the steam generator.

Preferably, a vertical distance between the heat exchange device and the temperature buffer tank is less than a vertical distance between the temperature buffer tank and the steam generator, the first pressure sensor is provided close to an outlet of the heat exchange device, and the second pressure sensor is provided adjacent the flow control valve.

Preferably, the temperature sensor, the second pressure sensor and the flow control valve are provided sequentially on the second pipeline along a flow direction of the liquid, and an outlet isolation valve for intercepting the liquid is further provided between the flow control valve and the main feedwater line.

Preferably, the heat exchange device is connected to the main steam line via a third pipeline, and an inlet isolation valve for intercepting steam is further provided between the heat exchange device and a main steam line.

Preferably, at least two such inlet isolation valves are provided in parallel on the third pipeline, and at least two such outlet isolation valves are provided in parallel on the second pipeline.

Preferably, the heat exchange device comprises heat exchange tubes and a heat trap water tank filled with a cooling liquid, the heat exchange tubes being submerged in the cooling liquid, and the first pipeline and the third pipeline being each connected to the heat exchange tubes.

Preferably, the heat trap water tank is further provided with an air window at a top thereof for evaporating of the cooling liquid, and the heat exchanger tubes are C-shaped heat exchange tubes.

Preferably, the liquid in the temperature buffer tank is liquid water, and the liquid water fills the temperature buffer tank when the waste heat discharge system has not yet started working.

Preferably, the first pipeline is connected to the temperature buffer tank at a top surface of the temperature buffer tank, the second pipeline is connected to the temperature buffer tank at a side surface of the temperature buffer tank, and the second pipeline is connected to a upper portion of the side surface of the temperature buffer tank.

Preferably, the first pressure sensor is provided at an outlet of the condensate liquid, and the second pressure sensor is provided adjacent the flow control valve.

Preferably, the first pressure sensor, the temperature sensor, the second pressure sensor and the flow control valve are sequentially provided on a return line of the condensate liquid along the return direction of the condensate.

The present invention further provides a flow stabilization method for a waste heat discharge system, the waste heat discharge system includes the waste heat discharge system according to any one of the above, and the method further includes the following steps:.

Preferably, the method further includes a method of adjusting the heat discharge power of the waste heat discharge system, comprising the following steps:.

The present invention has the following beneficial effects: the present invention is capable of automatically controlling the liquid level in the return line of the condensate liquid by means of a flow control device formed by the first pressure sensor, the second pressure sensor, the temperature sensor, the flow control valve and the controller; in addition, by setting the flow control device in the waste heat discharge system, the liquid level is maintained near the outlet of the heat exchanger, thereby preventing the condensate water from impacting on a gas-liquid interface, achieving the effect of eliminating the fluctuation of the flow rate of the condensate water, and realizing the flow stabilization effect of the waste heat discharge system.

The present invention will be further described below with reference to the accompanying drawings and embodiments. In the figures:.

In order to have a better understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are described in detail with reference to the accompanying drawings.

The present invention provides a flow control device which can be used as a flow stabilization device for improving operational flow stability of a passive system and reducing the probability of damage to the system piping. Specifically, with reference to <FIG>, which is not covered by the claims, the flow control device provided by the present invention, which can be used in a passive system, may specifically include a first pressure sensor <NUM>, a second pressure sensor <NUM>, a temperature sensor <NUM>, a flow control valve <NUM>, and a controller <NUM>, wherein the first pressure sensor <NUM>, the second pressure sensor <NUM>, the temperature sensor <NUM>, and the flow control valve <NUM> are all communicatively connected to the controller <NUM>.

Further, the first pressure sensor <NUM>, the second pressure sensor <NUM>, the temperature sensor <NUM>, and the flow control valve <NUM> are all disposed on a return line of condensate liquid. The first pressure sensor <NUM> and the second pressure sensor <NUM> are disposed sequentially along a return direction of the condensate liquid, and the first pressure sensor <NUM>, the second pressure sensor <NUM>, and the temperature sensor <NUM> are all disposed upstream of the flow control valve <NUM>, namely located on a pipeline on an inlet side of the flow control valve <NUM>. The first pressure sensor <NUM> may be provided close to an outlet of a condensate water source, and the second pressure sensor <NUM> may be installed close to the flow control valve <NUM>, such that the first pressure sensor <NUM> and the second pressure sensor <NUM> may measure an ambient pressure of the return line at their installation locations, and the temperature sensor <NUM> may measure the temperature of the liquid within the return line, and the first pressure sensor <NUM>, the second pressure sensor <NUM> and the temperature sensor <NUM> transmit the measurement data to the controller <NUM>, respectively.

In some embodiments, the first pressure sensor <NUM> is preferably located at the outlet of the condensate liquid, i.e., near the height at which the condensate liquid enters the return line, and the second pressure sensor <NUM> is disposed adjacent the flow control valve <NUM>, whereby the water level in the return line is always maintained at such a height that the first pressure sensor <NUM> is submerged, i.e., at the height of the condensate water source, by automatically controlling a valve opening of the flow control valve <NUM>. As such, the flow rate of the returned condensate liquid can be maintained stable.

Further, the first pressure sensor <NUM>, the temperature sensor <NUM>, the second pressure sensor <NUM>, and the flow control valve <NUM> may be sequentially disposed on the return line of the condensate liquid along the return direction of the condensate liquid.

The present invention further provides a waste heat discharge system comprising the above-described flow control device for exporting reactor waste heat. Specifically, with reference to <FIG>, the waste heat discharge system is connected between a main steam line <NUM> and a main feedwater line <NUM> of a steam generator <NUM>. A heat exchange device <NUM>, a temperature buffer tank <NUM> and the steam generator <NUM> sequentially decrease in height. In some embodiments, a vertical distance between the heat exchange device <NUM> and the temperature buffer tank <NUM> is less than a vertical distance between the temperature buffer tank <NUM> and the steam generator <NUM>.

Further, the heat exchange device <NUM> specifically includes heat exchange tubes <NUM> and a heat trap tank <NUM> containing a cooling liquid, the heat exchange tubes <NUM> being submerged in the cooling liquid for condensing the steam into a liquid. In some embodiments, the cooling liquid in the heat trap tank <NUM> is cooling water, and a gas window <NUM> is provided at a top of the heat trap tank <NUM> for evaporating of the cooling liquid. In some embodiments, the heat transfer tubes <NUM> are provided as a C-shaped heat transfer tube bundle, two ends of which are connected to the steam generator <NUM> and the temperature buffer tank <NUM>, respectively. In some embodiments, the temperature buffer tank <NUM> is filled with a liquid, specifically liquid water. The liquid water fills the temperature buffer tank <NUM> while the flow control device has not yet begun to operate. Further, the temperature buffer tank <NUM> is fluidly connected to the heat exchange tubes <NUM> via a first pipeline <NUM> and to the main feedwater line <NUM> via a second pipeline <NUM>; the heat exchange device <NUM> is connected to the main steam line <NUM> via a third pipeline <NUM>, such that the steam generator <NUM>, the heat exchange device <NUM>, and the temperature buffer tank <NUM> form a closed loop.

In order to stabilize the flow of the waste heat discharge system, in the present invention, the above-described flow control device is provided in the waste heat system. Specifically, the first pipeline <NUM> is provided with the first pressure sensor <NUM>, and the second pipeline <NUM> is provided with the second pressure sensor <NUM>. In addition, the second pipeline <NUM> is provided with the temperature sensor <NUM> for detecting the temperature of the liquid in the second pipeline <NUM>, and the flow control valve <NUM> for controlling the flow of the liquid in the second pipeline <NUM>. In the present invention, the first pressure sensor <NUM>, the second pressure sensor <NUM>, the temperature sensor <NUM>, and the flow control valve <NUM> are each communicatively connected to the controller <NUM>. Further, in some embodiments, the first pressure sensor <NUM> is disposed at an outlet of the heat exchange tubes <NUM>, and the temperature sensor <NUM>, the second pressure sensor <NUM>, and the flow control valve <NUM> are disposed sequentially on the second pipeline <NUM> along a flow direction of the liquid. Further, an outlet isolation valve <NUM> for intercepting the liquid is also provided between the flow control valve <NUM> and the main feedwater line <NUM>, and an inlet isolation valve <NUM> for intercepting the vapor is also provided on the third pipeline <NUM>. In some embodiments, at least two inlet isolation valves <NUM> are connected in parallel on the third pipeline <NUM>, and at least two outlet isolation valves <NUM> are connected in parallel on the second pipeline <NUM>, such that in the event of a failure of one of the valves where the one valve is jammed and cannot be opened, the other valve can be opened as needed, reducing the chance of system failure and improving equipment availability.

Further, the first pipeline <NUM> is fluidly connected to the temperature buffer tank <NUM> at a top surface thereof, and the second pipeline <NUM> is connected to the temperature buffer tank <NUM> at a side surface thereof. In some embodiments, the second pipeline <NUM> is connected to an upper portion of the side surface of the temperature buffer tank <NUM>, such that the water level of the temperature buffer tank <NUM> is always maintained near the height of the second pipeline <NUM>, and a certain volume of stored water is always present in the temperature buffer tank <NUM>. When the condensate water flowing down from the first pipeline <NUM> enters the temperature buffer tank <NUM>, it strikes the stored water in the temperature buffer tank <NUM>, forming a vortex inside the tank, so that the stored water inside the tank mixes sufficiently with the condensate water from the outlet of the condensate pipe, which reduces the unevenness and fluctuation of the temperature of the condensate water inside the tank, providing a temperature buffer function, thereby reducing the thermal impact of the condensate water on the second pipeline <NUM>.

Further, the present invention also provides a flow stabilization method for a waste heat discharge system, including the waste heat discharge system described above, wherein the method further includes the following steps:.

By means of the above flow stabilization method, the water level in this waste heat discharge system can be maintained near the first pressure sensor <NUM>, i.e., near the condensate pipeline outlet, which can eliminate the fluctuation of the flow rate of the condensate water in the pipeline.

Further, the flow stabilization method may also include a method of adjusting the heat discharge power of the waste heat discharge system, and may specifically include the following steps:.

By changing the length of the section of the heat exchanger tube <NUM> being submerged, which is equivalent to changing a condensing area of the heat exchanger tubes <NUM>, the purpose of controlling the heat discharge power of the waste heat discharge system can be achieved.

The waste heat discharge system and the flow stabilization method proposed in the present invention can be applied to various types of commercial pressurized water reactors to cope with various accidental working conditions and ensure the safe discharge of reactor waste heat. For example, it can be applied to the accidental condition of power failure of the whole plant, which can ensure the safety of the reactor in the event of power loss, improving the safety performance of the nuclear power plant.

Claim 1:
A waste heat discharge system, characterized in that it comprises a flow control device, a heat exchange device (<NUM>) and a temperature buffer tank (<NUM>), wherein the heat exchange device (<NUM>) and the temperature buffer tank (<NUM>) are sequentially connected in series with a steam generator (<NUM>), the heat exchange device (<NUM>), the temperature buffer tank (<NUM>), and the steam generator (<NUM>) sequentially decreasing in height;
the flow control device comprises a first pressure sensor (<NUM>), a second pressure sensor (<NUM>), a temperature sensor (<NUM>), a flow control valve (<NUM>), and a controller (<NUM>), wherein the first pressure sensor (<NUM>), the second pressure sensor (<NUM>), the temperature sensor (<NUM>), and the flow control valve (<NUM>) are disposed in a return line of a condensate liquid;
the first pressure sensor (<NUM>) and the second pressure sensor (<NUM>) are disposed sequentially along a return direction of the condensate liquid, and the first pressure sensor (<NUM>), the second pressure sensor (<NUM>), and the temperature sensor (<NUM>) are disposed upstream of the flow control valve (<NUM>);
the first pressure sensor (<NUM>), the second pressure sensor (<NUM>), the temperature sensor (<NUM>), and the flow control valve (<NUM>) are each communicatively connected to the controller (<NUM>); and
the first pressure sensor (<NUM>) is provided on a first pipeline (<NUM>) connecting the heat exchange device (<NUM>) and the temperature buffer tank (<NUM>), and the second pressure sensor (<NUM>), the temperature sensor (<NUM>), and the flow control valve (<NUM>) are all provided on a second pipeline (<NUM>) connecting the temperature buffer tank (<NUM>) and a main feedwater line (<NUM>).