An automatic water replenishment and temperature control device for the surge tank of the boric acid recirculation loop of a nuclear power unit

Abstract

The present invention belongs to the field of reactor operation technology, and specifically relates to an automatic water replenishment and temperature control device for a surge tank in a boric acid recirculation loop of a nuclear power unit. The device comprises a surge tank, a U-shaped tube, a variable frequency fan, a water replenishment pipeline, a boron addition port, and a nozzle. The boron addition port is provided at the top of the surge tank, and is connected to an inverted U-shaped tube. A heat exchange device is provided on the outside of one tube of the U-shaped tube, and a variable frequency fan is connected to the other tube of the U-shaped tube. A nozzle is provided at the lower end of the U-shaped tube, which is connected to the water replenishment pipeline. The present invention has the beneficial effects of effectively reducing the number of water replenishments required for the surge tank in the boric acid recirculation loop and effectively controlling the temperature of the surge tank in the boric acid recirculation loop by adjusting the frequency of the variable frequency fan. This device replaces the previous temperature control methods of adjusting the room damper opening, the surge tank cover opening, and adding a temporary fan, thereby avoiding the safety hazards of burns and contamination caused by steam ejection when the cover is opened.

Description

Technical Field

[0001] The invention belongs to the technical field of reactor operation, and in particular relates to an automatic water replenishing and temperature regulating device for a surge tank of a boric acid recycling loop of a nuclear power unit. Background Art

[0002] In the boric acid recirculation loop of a nuclear power unit, the concentration of the boric acid solution is adjusted accordingly as the core fuel enrichment changes during unit operation. Taking a certain plant as an example, according to the original design of the power plant, the boric acid recirculation loop should be filled with 21,000-22,500 ppm of boric acid solution to ensure that sufficient boric acid is injected into the core during injection, quickly reducing reactivity and ensuring the subcriticality of the core. However, in actual operation, if the boron concentration is maintained at 21,000-22,500 ppm, the boric acid recirculation loop needs to maintain a very high temperature, which is not conducive to system operation and maintenance, affecting the availability of the injection system and hindering the long-term stable operation of the system. After analysis by the design institute, it is feasible to appropriately reduce the boric acid concentration in this loop, so the boron concentration of the boric acid recirculation loop was modified to 9,000-10,000 ppm. With the development of nuclear power, 3G fuel has been added to the core, and its enrichment has increased from 3.25% of 2G to 3.7% of 3G, so the boron concentration has been increased from 9000-10000ppm to 12000-14000ppm. In recent years, after the unit was changed to long fuel operation, the boric acid concentration was modified again. After the modification, the boron concentration of the boric acid recirculation loop has become 17000-19000ppm, and the temperature is controlled at 73-85℃. The lower limit of 73℃ is to prevent boron crystallization, and the upper limit of 85℃ is the maximum operating temperature required by the boric acid recirculation loop surge tank.

[0003] It is precisely because the boron concentration in the boric acid recirculation loop continues to increase, coupled with the heat brought in by the continuous operation of the boric acid pump in the system, that the operating temperature in the boric acid recirculation loop is always above 80°C (the temperature can exceed 85°C when the factory ventilation is shut down). A large amount of water in the boric acid recirculation loop evaporates, causing the boric acid recirculation loop surge tank to be replenished with water very frequently.

[0004] Frequent water replenishment in the boric acid recirculation loop and high system operating temperature have currently caused many secondary problems, mainly including frequent water replenishment leading to boron crystallization in the boric acid recirculation loop system, steam overflow into the liquid level gauge causing isolation of the boric acid recirculation loop, frequent water replenishment leading to failure of valves related to water replenishment in the boric acid recirculation loop surge tank, large evaporation leading to serious boron crystallization in the boric acid recirculation loop surge tank tank, high operating temperature and large negative pressure in the room leading to scalding, pinching and contamination of on-site personnel and other problems. Summary of the Invention

[0005] The purpose of the present invention is to provide an automatic water replenishment and temperature control device for a surge tank of a boric acid recirculation loop of a nuclear power unit, mainly solving the following problems: frequent water replenishment of the boric acid recirculation loop; excessive operating temperature of the boric acid recirculation loop; the problem of boron crystallization caused by direct entry of low-temperature desalted water into the system in winter; and a series of secondary problems caused by frequent water replenishment and high system operating temperature in the boric acid recirculation loop.

[0006] The technical solution of the present invention is as follows: an automatic water replenishment and temperature control device for a surge tank of a boric acid recirculation loop of a nuclear power unit, comprising a surge tank, a U-shaped tube, a variable frequency fan, a water replenishment pipeline, a boron addition port and a nozzle. The top of the surge tank is provided with a boron addition port, which is connected to an inverted U-shaped tube, wherein a heat exchange device is provided on the outside of one tube of the U-shaped tube, and a variable frequency fan is connected to the other tube of the U-shaped tube. A nozzle is provided at the lower end of the U-shaped tube, which is connected to the variable frequency fan, and the nozzle is connected to the water replenishment pipeline.

[0007] The heat exchange device includes a heat exchanger, one end of the heat exchanger is connected to the air cooling heat exchanger through a pipeline, the air cooling heat exchanger is connected to the water tank through a pipeline, and the other end of the heat exchanger is connected to the water tank through a pipeline. A cooling water pump is also provided on the pipeline connecting the other end of the heat exchanger to the water tank.

[0008] The heat exchanger, the air cooling heat exchanger, the connecting water tank and the cooling water pump as well as the pipelines therebetween form a circulation loop.

[0009] The heat exchanger is arranged outside the U-shaped tube and has an inlet and an outlet.

[0010] The inlet and outlet of the heat exchanger are respectively provided with temperature transmitters.

[0011] The side wall surface of the surge tank is provided with a temperature transmitter and a liquid level transmitter.

[0012] The beneficial effects of the present invention are: effectively reducing the number of times the boric acid recirculation loop surge tank needs to be replenished; and effectively controlling the temperature of the boric acid recirculation loop surge tank by adjusting the frequency of the variable frequency fan. This replaces the previous temperature control methods of adjusting the room air valve opening, the surge tank cover opening, and adding a temporary fan, thereby avoiding the safety hazards of scalding and contamination caused by steam ejection when the cover is opened, avoiding the industrial safety risk of fingers being pinched when the door is opened due to increased negative pressure in the room after the room air valve is opened wide, and avoiding the defect of boric acid accumulation in the entire room due to the backflow of boron powder caused by the high negative pressure in the room when adding boron; connecting a desalted water replenishment pipe with a nozzle to the pipeline to compensate for water loss, so that the desalted water replenished into the system will increase its heat exchange with the rising steam through the nozzle, thereby increasing the temperature of the desalted water entering the boric acid recirculation loop surge tank, effectively avoiding the risk of boron crystallization caused by the low-temperature desalted water in winter directly entering the boric acid recirculation loop surge tank; and effectively preventing steam from overflowing from the cover and entering the liquid level meter, causing the liquid level meter to malfunction. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The present invention provides a schematic diagram of an automatic water replenishment and temperature control device for a surge tank of a boric acid recirculation loop in a nuclear power unit.

[0014] In the figure: 1 surge tank, 2 U-tube, 3 variable frequency fan, 4 heat exchanger, 5 air cooling heat exchanger, 6 water tank, 7 cooling water pump, 8 water supply pipe, 9 boron addition port, 10 temperature transmitter, 11 liquid level transmitter, 12 nozzle. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] The present invention provides an automatic water filling and temperature control device for a surge tank of a boric acid recirculation loop of a nuclear power unit, which aims to solve the problems existing in the operation of the boric acid recirculation loop mentioned in the background technology, optimize the operation mode of the surge tank of the boric acid recirculation loop, and completely solve the frequent water filling of the boric acid recirculation loop surge tank, excessive operating temperature, and a series of secondary problems caused by frequent water filling and high system operating temperature of the boric acid recirculation loop through the automatic water filling and temperature control device of the boric acid recirculation loop surge tank, thereby improving the reliability of the operation of the boric acid recirculation loop surge tank, which is of great significance to the long-term stable operation of the boric acid recirculation loop.

[0017] like Figure 1As shown, an automatic water replenishment and temperature control device for a surge tank of a boric acid recirculation loop of a nuclear power unit includes a surge tank 1, a U-shaped tube 2, a variable frequency fan 3, a heat exchanger 4, an air-cooled heat exchanger 5, a water tank 6, a cooling water pump 7, a water replenishment pipe 8, a boron addition port 9, a temperature transmitter 10, a liquid level transmitter 11 and a nozzle 12. A boron addition port 9 is provided on the top of the surge tank 1, and an inverted U-shaped tube 2 is connected to the boron addition port 9, wherein a heat exchanger 4 is provided outside one tube of the U-shaped tube 2, one end of the heat exchanger 4 is connected to the air-cooled heat exchanger 5 through a pipeline, the air-cooled heat exchanger 5 is connected to the water tank 6 through a pipeline, and the other end of the heat exchanger 4 is connected to the water tank 6 through a pipeline. A cooling water pump 7 is also provided on the pipeline connecting the other end of the heat exchanger 4 to the water tank 6. The heat exchanger 4, the air-cooled heat exchanger 5, the connection water tank 6 and the cooling water pump 7 and the pipelines therebetween constitute a circulation loop. The heat exchanger 4 arranged outside the U-shaped tube 2 has an inlet and an outlet, and a temperature transmitter 10 is respectively provided at the inlet and the outlet. A variable frequency fan 3 is connected to the other pipeline of the U-shaped tube 2. A nozzle 12 is installed at the lower end of the U-shaped tube 2 and the variable frequency fan 3. The nozzle 12 is connected to the water supply pipe 8. A temperature transmitter 10 and a liquid level transmitter 11 are provided on the side wall of the surge box 1.

[0018] The working principle of the present invention is as follows:

[0019] A set of automatic water replenishment and temperature control device for the boric acid recirculation loop surge tank is connected to the boron addition port of the boric acid recirculation loop surge tank. The device includes an inverted U-shaped tube, a variable frequency fan, a heat exchanger, an air-cooled heat exchanger, a water tank, a cooling water pump, a desalted water replenishment pipe, a nozzle, a temperature transmitter and other equipment as well as a control cabinet for controlling the device.

[0020] The process of this device is that the steam generated by the boric acid recirculation loop surge tank is drained by the variable frequency fan and then enters the inverted U-shaped tube. The steam is cooled into condensate by the heat exchanger in the inverted U-shaped tube and falls back to the boric acid recirculation loop surge tank. The heat exchange cooler is cooled by desalted water and the heat is taken away by the air-cooled heat exchanger.

[0021] The liquid level of the surge tank in the boric acid recirculation loop is mainly maintained by the condensate reflux. In addition, the device can automatically replenish water to the surge tank. When the liquid level is low, it automatically starts replenishing water, and when the liquid level is high, it automatically stops replenishing water. The liquid level signal is taken from the original system level gauge.

[0022] A desalted water supply pipe with a nozzle is connected to the inverted U-shaped pipe of the automatic water supply and temperature control device of the boric acid recirculation loop surge tank. In this way, the desalted water supplied to the system can increase the heat exchange with the rising steam through the action of the nozzle, thereby increasing the temperature of the desalted water entering the boric acid recirculation loop surge tank.

[0023] The input signal of the variable frequency fan is the temperature difference between the boric acid recirculation loop surge box and the inlet and outlet temperatures of the heat exchange cooler. The speed of the variable frequency fan is controlled by the temperature signal, thereby controlling the evaporation amount of the boric acid solution in the boric acid recirculation loop surge box, and then controlling the temperature of the boric acid recirculation loop surge box.

[0024] Automatic water replenishment control of the surge tank is realized on the control cabinet of the automatic water replenishment and temperature adjustment device of the boric acid recirculation loop. At the same time, the operation of equipment such as the variable frequency fan, cooling water pump, air cooling heat exchanger, etc. is controlled, and digital temperature and liquid level display instruments are configured.

[0025] The specific application of the present invention is as follows:

[0026] After the boric acid recirculation loop is shut down, the first step is to remove the original boric acid recirculation loop surge tank boron filling port and install a new boric acid recirculation loop surge tank boron filling port. Take good protection during the disassembly and assembly process to prevent the introduction of foreign matter.

[0027] The second step is to install the support bracket for fixing the automatic water replenishment and temperature control device of the boric acid recirculation loop surge tank, fix the automatic water replenishment and temperature control device of the boric acid recirculation loop surge tank on the support bracket, and terminate it with the new boron addition port, desalted water pipeline, etc.

[0028] The third step is to install the local control cabinet for the automatic water replenishment and temperature control device of the boric acid recirculation loop surge tank.

[0029] Step 4: Lay the power and control cables for the boric acid recirculation circuit surge tank's automatic water replenishment and temperature control device. Connect the power and control cables to the local control cabinet. Connect the local control cabinet to the 380V power supply. Connect the temperature transmitter and level transmitter to the local control cabinet. Ensure these connections are secure.

[0030] Step 5: Fill the boric acid recirculation circuit surge tank's automatic water supply and temperature control device with water and clean it, and check all joints for leaks. Use a 500V megohmmeter to measure the insulation of the boric acid recirculation circuit surge tank's automatic water supply and temperature control device and the control cabinet to confirm that they meet the requirements.

[0031] After the above work is completed and meets the requirements, fill water into the boric acid recirculation loop surge tank and heat it. At the same time, fill water online into the automatic water replenishment and temperature control device of the boric acid recirculation loop surge tank, power on the control cabinet, check for abnormalities, start the device for functional debugging, and confirm that the automatic water replenishment and temperature control device of the boric acid recirculation loop surge tank meets all technical requirements.

Claims

1. An automatic water replenishment and temperature control device for a surge tank in a boric acid recirculation loop of a nuclear power plant, characterized by: The system includes a surge box, a U-shaped tube, a variable frequency fan, a water supply pipe, a boron addition port and a nozzle. The top of the surge box is provided with a boron addition port, which is connected to an inverted U-shaped tube. A heat exchange device is provided outside one tube of the U-shaped tube, and a variable frequency fan is connected to the other tube of the U-shaped tube. A nozzle is provided at the lower end of the U-shaped tube and connected to the variable frequency fan, and the nozzle is connected to the water supply pipe. The heat exchange device includes a heat exchanger, one end of the heat exchanger is connected to the air cooling heat exchanger through a pipeline, the air cooling heat exchanger is connected to the water tank through a pipeline, the other end of the heat exchanger is connected to the water tank through a pipeline, and a cooling water pump is also provided on the pipeline connecting the other end of the heat exchanger to the water tank; The heat exchanger, air cooling heat exchanger, connecting water tank and cooling water pump and the pipelines therebetween constitute a circulation loop; The heat exchanger is arranged outside the U-shaped tube and has an inlet and an outlet; The inlet and outlet of the heat exchanger are respectively provided with temperature transmitters; A temperature transmitter is provided on the side wall surface of the surge box.

2. The automatic water replenishment and temperature control device for a surge tank of a boric acid recirculation loop of a nuclear power plant according to claim 1, characterized in that: A liquid level transmitter is provided on the side wall surface of the surge tank.

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