Cladding lithium-lead heat source interloop temperature maintenance system during off-period and control method

Abstract

The application provides a cladding lithium-lead heat source circuit intermittent period temperature maintenance system and a control method, and belongs to the field of fusion reactor temperature control systems. The system comprises a cladding lithium-lead heat source inlet and outlet branch, a lithium-lead heat source utilization branch, a heating branch and a control circuit. The lithium-lead heat source utilization branch and the heating branch are connected in parallel to the outlet of a lithium-lead heat source lower connection pipe of the cladding lithium-lead heat source inlet and outlet branch. The heating branch comprises a third valve, an electric heater and a second pump connected in sequence. The outlet of the second pump is connected to a first valve on the cladding lithium-lead heat source inlet and outlet branch and a second valve on the lithium-lead heat source utilization branch. The control circuit comprises a plurality of thermocouples and flow meters for monitoring the temperature and flow rate of positions for realizing the temperature maintenance of the cladding lithium-lead heat source circuit during the intermittent period. The control circuit controls the start-stop or opening degree of the first valve, the second valve, the third valve, the electric heater and the second pump. The application overcomes the solidification risk of lithium-lead medium and improves the safety of the system.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of fusion reactor temperature control system, and particularly relates to a blanket lithium lead heat source loop intermittent period temperature maintenance system and a control method. BACKGROUND

[0002] Nuclear fusion energy is considered as an important way to completely solve the energy problem in the future due to its large energy density, high safety and little greenhouse gas emission. The basic power generation principle is that deuterium and tritium are heated to become high-temperature plasma, and the reactor ignites the plasma to occur fusion. Lithium in the blanket outside the plasma reaction chamber will absorb high-energy neutrons released in the nuclear fusion reaction to produce more tritium fuel, and the blanket will also be heated by high-energy neutrons. The generated heat is transferred to a heat exchanger through a cooling loop, and finally forms a steam turbine generator for power generation.

[0003] Liquid LiPb (lithium lead) is the main medium of the fusion reactor blanket coolant, which not only can absorb and export the heat deposited in the blanket as a heat conduction medium for the power generation system of the fusion reactor, but also can promote the proliferation of tritium fuel as a tritium breeder. However, the existing fusion reactor device has intermittency, and there is no heat input during the intermittent period when the fusion device stops running or other time when it needs to be paused. Under the action of heat loss, the temperature of LiPb medium in the pipeline and equipment gradually decreases and is lower than the temperature of the inlet end of the blanket LiPb heat source. When the temperature of the LiPb medium decreases significantly, it will cause great problems. The operation of the fusion reactor blanket LiPb heat source requires that the inlet and outlet temperatures of LiPb in the blanket be consistent in each cycle. When the temperature of the LiPb medium decreases significantly, it will be lower than the inlet temperature of the blanket, resulting in a large deviation between the inlet and outlet temperatures in the next cycle, which affects the use efficiency of the LiPb heat source in the heat storage and power generation system. In addition, the liquid LiPb alloy is a eutectic of Li and Pb, and its melting point is generally around 234-239℃. When the temperature decreases close to its solidification point, it will cause great stress on the pipeline and equipment, and eventually may cause cracking of the weld or damage to the container wall, resulting in serious safety accidents.

[0004] At present, the existing fusion reactor device research does not involve the control of the medium temperature of the LiPb blanket during the pause of the fusion reactor. The method of maintaining the medium temperature by using electric heat tracing commonly used in the pipeline of solar thermal power generation and petrochemical systems is not suitable for the LiPb utilization system of the blanket. The main disadvantage is that the electric heat tracing generally maintains the temperature of the pipeline at 100-200℃, which is weak for maintaining a higher temperature. In addition, the electric heat tracing has low heat power and cannot achieve rapid and large-flow heating. When the temperature decreases, it is difficult to achieve rapid heating of all the media in the system, which increases the risk of accidents. SUMMARY

[0005] The application provides a cladding lithium-lead heat source circuit intermittent period temperature maintaining system and a control method, which are used for controlling the medium temperature in a fusion reactor cladding LiPb circuit, can realize rapid heating of the LiPb medium, solve the problem of large temperature drop of the LiPb medium, avoid the problems of instability and reduced efficiency of the heat storage and power generation system caused by large deviation of the LiPb cladding inlet and outlet temperatures, overcome the solidification risk of the LiPb medium, and improve the safety of the system.

[0006] To achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0007] A cladding lithium-lead heat source circuit intermittent period temperature maintaining system, comprising a cladding lithium-lead heat source inlet and outlet branch, a lithium-lead heat source utilization branch, a heating branch and a control circuit; the lithium-lead heat source utilization branch and the heating branch are connected in parallel at the outlet of a lithium-lead heat source lower connection pipe of the cladding lithium-lead heat source inlet and outlet branch; the heating branch comprises a third valve, an electric heater and a second pump connected in sequence, and the outlet of the second pump is connected to a first valve on the cladding lithium-lead heat source inlet and outlet branch and a second valve on the lithium-lead heat source utilization branch respectively; the control circuit comprises a plurality of thermocouples and flow meters, which are used for monitoring the temperature and flow rate of each position for realizing the cladding lithium-lead heat source circuit intermittent period temperature maintaining cooperatively, and controlling the start-stop or opening degree of the first valve, the second valve, the third valve, the electric heater and the second pump.

[0008] The application also provides a control method of the cladding lithium-lead heat source circuit intermittent period temperature maintaining system, during the stop of the tokamak device, when any two of the temperature T1 at the upper connection port of the cladding lithium-lead heat source, the temperature T2 at the lower connection port of the cladding lithium-lead heat source or the temperature T3 of the lithium-lead inside the cladding are lower than the minimum temperature limit TL, the electric heater, the second pump, the third valve and the first valve are started, so that the heated lithium-lead flows through the second pump, the first valve, the fusion reactor cladding and the third valve in sequence and then returns to the electric heater; when the temperature T1 at the upper connection port of the cladding lithium-lead heat source, the temperature T2 at the lower connection port of the cladding lithium-lead heat source or the temperature T3 of the lithium-lead inside the cladding and the medium temperature T4 at the inlet of the electric heater all rise to the minimum temperature limit TL+5℃, the electric heater, the second pump, the third valve and the first valve are closed.

[0009] Beneficial effects:

[0010] 1. The application adopts the heating branch with the electric heater, realizes rapid heating of the LiPb medium, and shortens the heating time;

[0011] 2、The application can maintain the LiPb medium temperature at the cladding inlet temperature, shorten the time for the medium temperature at the cladding outlet to reach stability in the next operation cycle, and increase the system stability. In addition, the application can realize temperature control of the medium in the lithium-lead heat source utilization circuit, so that the temperature is always higher than the minimum use temperature value, thereby avoiding the risk of equipment pipe damage caused by a large temperature drop;

[0012] 3、In the control method of the application, by setting the electric heater inlet medium temperature T4, the replacement and heating of the low-temperature medium in the pipes and equipment (cladding, heat exchanger, etc.) in each branch of the lithium-lead heat source utilization circuit can be realized, and the medium after each heating is ensured to flow through the branch before stopping heating. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a schematic diagram of the cladding lithium-lead heat source circuit intermittent temperature maintenance system of the application;

[0014] Among them, the reference signs are: 1-cladding lithium-lead heat source inlet and outlet branch, 11-lithium-lead heat source upper connecting pipe, 12-first valve, 13-fusion reactor cladding, 14-lithium-lead heat source lower connecting pipe, 2-lithium-lead heat source utilization branch, 21-second valve, 22-first pump, 23-heat exchanger, 3-heating branch, 31-electric heater, 32-second pump, 33-third valve, 4-control circuit, 41-first thermocouple, 42-second thermocouple, 43-third thermocouple, 44-fourth thermocouple, 45-fifth thermocouple, 46-sixth thermocouple, 47-seventh thermocouple, 48-first flowmeter, 49-second flowmeter. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical scheme and advantages of the application more clear and understandable, the application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application and do not limit the application. In addition, the technical features involved in each embodiment of the application described below can be combined with each other as long as they do not conflict with each other.

[0016] During the suspension of the fusion reactor, the temperature of the lithium-lead medium in the cladding lithium-lead heat source circuit needs to be maintained above the required temperature in the operation stage, so as to ensure the rapid start-up and temperature rise of the fusion reactor and improve the stability of the system operation. Based on this, as Figure 1As shown, the application provides a cladding lithium-lead heat source intermission temperature maintenance system, mainly composed of a cladding lithium-lead heat source inlet and outlet branch 1, a lithium-lead heat source utilization branch 2, a heating branch 3 and a control circuit 4. The lithium-lead heat source utilization branch 2 is connected in parallel with the heating branch 3. The lithium-lead heat source utilization branch 2 realizes the heat output of the lithium-lead heat source during the operation period, and the heating branch 3 realizes the heating of lithium-lead in the cladding lithium-lead heat source inlet and outlet branch 1 and the heating branch 3, preventing the temperature of lithium-lead from greatly reducing and solidifying during the suspension operation. The control circuit 4 realizes the start and stop of the cladding lithium-lead heat source inlet and outlet branch 1, the lithium-lead heat source utilization branch 2 and the heating branch 3 as well as the flow control through temperature monitoring.

[0017] The cladding lithium-lead heat source inlet and outlet branch 1 includes a lithium-lead heat source upper connecting pipe 11, a first valve 12, a fusion reactor cladding 13 and a lithium-lead heat source lower connecting pipe 14. The outlet of the first valve 12 is connected to the inlet of the lithium-lead heat source upper connecting pipe 11. The outlet of the lithium-lead heat source upper connecting pipe 11 is connected to the inlet of the fusion reactor cladding 13. The outlet of the fusion reactor cladding 13 is connected to the inlet of the lithium-lead heat source lower connecting pipe 14. The outlet of the lithium-lead heat source lower connecting pipe 14 is divided into two branches, which are connected to the lithium-lead heat source utilization branch 2 and the heating branch 3, respectively.

[0018] The lithium-lead heat source utilization branch 2 includes a second valve 21, a first pump 22, a heat exchanger 23 and connecting pipes. The outlet of the second valve 21 is connected to the inlet of the first pump 22. The outlet of the first pump 22 is connected to the hot side inlet of the heat exchanger 23. The hot side outlet of the heat exchanger 23 is divided into two branches, which are connected to the lithium-lead heat source lower connecting pipe 14 of the cladding lithium-lead heat source inlet and outlet branch 1 and the inlet of the third valve 33 of the heating branch 3, respectively. The cold side of the heat exchanger 23 is connected to a heat storage / power generation system.

[0019] The heating branch 3 includes an electric heater 31, a second pump 32, a third valve 33 and connecting pipes. The outlet of the third valve 33 is connected to the inlet of the electric heater 31. The outlet of the electric heater 31 is connected to the inlet of the second pump 32. The outlet of the second pump 32 is divided into two branches, which are connected to the cladding lithium-lead heat source inlet and outlet branch 1 and the lithium-lead heat source utilization branch 2 through the first valve 12 and the second valve 21, respectively.

[0020] The control loop 4 is composed of a first thermocouple 41, a second thermocouple 42, a third thermocouple 43, a fourth thermocouple 44, a fifth thermocouple 45, a sixth thermocouple 46, a seventh thermocouple 47, a first flow meter 48, a second flow meter 49 and signal lines. The first thermocouple 41 and the first flow meter 48 are installed on the upper connecting pipe 11 of the lithium-lead heat source and are used to measure the temperature at the upper connecting port of the cladding lithium-lead heat source and the flow of the inlet and outlet branch 1 of the cladding lithium-lead heat source, respectively; the second thermocouple 42 is installed on the lower connecting pipe 14 of the lithium-lead heat source and is used to measure the temperature at the lower connecting port; the third thermocouple 43 is located inside the fusion reactor and is used to measure the internal lithium-lead temperature; the fourth thermocouple 44 is arranged at the inlet of the electric heater 31 and is used to measure the medium temperature at the inlet of the electric heater; the fifth thermocouple 45 is located at the hot side inlet of the heat exchanger 23, the sixth thermocouple 46 is located at the hot side outlet of the heat exchanger 23, and the seventh thermocouple 47 is located at the middle position of the pipe section from the hot side outlet of the heat exchanger 23 to the cladding inlet, which are used to measure the temperatures at the hot side inlet and outlet of the heat exchanger 23 and the middle pipe section, respectively. The second flow meter 49 is located at the hot side inlet pipe of the heat exchanger and is used to measure the flow of the lithium-lead heat source utilization branch 2. The signal lines of the first thermocouple 41, the second thermocouple 42, the third thermocouple 43 and the fourth thermocouple 44 are connected with the controller of the first valve 12, the electric heater 31, the second pump 32 and the third valve 33. The signal lines of the fifth thermocouple 45, the sixth thermocouple 46, the seventh thermocouple 47 and the fourth thermocouple 44 are connected with the controller of the second valve 21, the electric heater 31, the second pump 32 and the third valve 33. The signal lines of the first flow meter 48 and the second flow meter 49 are connected with the controller of the second valve 21.

[0021] Preferably, the second pump 32 is an electrically controlled pump, and the start and stop of the pump are controlled according to the temperature values of the monitoring points.

[0022] Preferably, the first valve 12, the second valve 21 and the third valve 33 are electrically controlled temperature valves, and the start, stop or opening degree of the valves are controlled according to the temperature values of the monitoring points.

[0023] Preferably, the first valve 12 is a bidirectional valve, which can realize the adjustment of the flow direction of the lithium-lead medium. The second valve 21 and the third valve 33 are unidirectional valves, which control the single flow direction of the lithium-lead medium.

[0024] Preferably, the start and stop of the electric heater 31, the second pump 32 and the third valve 33 are jointly controlled by the temperature T1 (obtained by the first thermocouple) at the upper connecting port of the cladding lithium-lead heat source, the temperature T2 (obtained by the second thermocouple) at the lower connecting port of the cladding lithium-lead heat source, the internal lithium-lead temperature T3 (obtained by the third thermocouple), the medium temperature T4 (obtained by the fourth thermocouple) at the inlet of the electric heater, the temperature T5 (obtained by the fifth thermocouple) at the hot side inlet of the heat exchanger, the temperature T6 (obtained by the sixth thermocouple) at the hot side outlet of the heat exchanger and the temperature T7 (obtained by the seventh thermocouple) at the middle pipe section from the hot side outlet of the heat exchanger to the cladding inlet.

[0025] Preferably, the opening and closing of the first valve 12 is jointly controlled by the temperature T1 at the upper connection port of the cladding lithium-lead heat source, the temperature T2 at the lower connection port of the cladding lithium-lead heat source, the temperature T3 of the lithium-lead inside the cladding, and the temperature T4 of the medium at the inlet of the electric heater.

[0026] Preferably, the opening and closing of the second valve 21 is jointly controlled by the temperature T5 at the inlet of the hot side of the heat exchanger, the temperature T6 at the outlet of the hot side of the heat exchanger, the temperature T7 of the pipe segment between the outlet of the hot side of the heat exchanger and the inlet of the cladding, and the temperature T4 of the medium at the inlet of the electric heater, and the opening degree of the second valve 21 is jointly controlled by the flow rate M1 of the branch 1 between the inlet and outlet of the cladding lithium-lead heat source (obtained by the first flow meter) and the flow rate M2 of the branch 2 for use of the lithium-lead heat source (obtained by the second flow meter).

[0027] Specifically, the control method of the intermittent temperature maintaining system of the cladding lithium-lead heat source circuit of the application is as follows:

[0028] During the stop of the tokamak device, when any two of the temperature T1 at the upper connection port of the cladding lithium-lead heat source, the temperature T2 at the lower connection port of the cladding lithium-lead heat source, and the temperature T3 of the lithium-lead inside the cladding are lower than the minimum temperature limit TL, the electric heater 31 is started to heat the lithium-lead, and the temperature is raised to TL+5℃. The second pump 32, the third valve 33, and the first valve 12 are started, and the lithium-lead heated by the electric heater 31 flows through the second pump 32, the first valve 12, the upper connection pipe 11 of the lithium-lead heat source, the cladding 13 of the fusion reactor, the lower connection pipe 14 of the lithium-lead heat source, the third valve 33, and then returns to the electric heater 31.

[0029] When all of the temperature T1 at the upper connection port of the cladding lithium-lead heat source, the temperature T2 at the lower connection port of the cladding lithium-lead heat source, the temperature T3 of the lithium-lead inside the cladding, and the temperature T4 of the medium at the inlet of the electric heater are raised to TL+5℃, the electric heater 31, the second pump 32, the third valve 33, and the first valve 12 are closed, thereby realizing the control of the temperature of the lithium-lead in the branch 1 between the inlet and outlet of the cladding lithium-lead heat source.

[0030] During the stop of the tokamak device, when any two of the temperature T5 at the inlet of the hot side of the heat exchanger, the temperature T6 at the outlet of the hot side of the heat exchanger, and the temperature T7 of the pipe segment between the outlet of the hot side of the heat exchanger and the inlet of the cladding are lower than the minimum temperature limit TL, the electric heater 31 is started to heat the lithium-lead, and the temperature is raised to TL+5℃. The second pump 32, the third valve 33, and the second valve 21 are started, and the lithium-lead heated by the electric heater 31 flows through the second pump 32, the second valve 21, the first pump 22, the heat exchanger 23, the third valve 33, and then returns to the electric heater 31.

[0031] When the heat exchanger hot side inlet temperature T5, the heat exchanger hot side outlet temperature T6, the temperature T7 of the pipe segment between the heat exchanger hot side outlet and the cladding inlet, and the electric heater inlet medium temperature T4 all increase to TL+5℃, the electric heater 31, the second pump 32, the third valve 33, and the second valve 21 are closed, so as to realize the control of the lithium-lead temperature in the lithium-lead heat source utilization branch 2.

[0032] When two of the temperature measuring points (i.e. two of T1-T3 and T5-T7) in the cladding lithium-lead heat source inlet and outlet branch 1 and the lithium-lead heat source utilization branch 2 are lower than the minimum temperature limit TL, the opening of the second valve 21 is controlled according to the flow rate M1 of the cladding lithium-lead heat source inlet and outlet branch 1 and the flow rate M2 of the lithium-lead heat source utilization branch 2, so that M1=M2, and the flow rates of the cladding lithium-lead heat source inlet and outlet branch 1 and the lithium-lead heat source utilization branch 2 are consistent.

[0033] Preferably, during the intermittent period when the tokamak device is suspended, the minimum temperature limit TL is set to the temperature TL1 at the LiPb cladding inlet during stable operation. In other cases where the device is stopped and the medium is not discharged, the minimum temperature limit TL is set to TL2, which is 30℃ higher than the freezing point of the LiPb medium.

[0034] When the minimum temperature limit is set to TL2, when any one of the temperature T1 at the upper connection port of the cladding lithium-lead heat source, the temperature T2 at the lower connection port of the cladding lithium-lead heat source, and the temperature T3 inside the cladding lithium-lead heat source is lower than TL2, the heating branch 3 is started to control the lithium-lead temperature in the cladding lithium-lead heat source inlet and outlet branch 1; when any one of the heat exchanger hot side inlet temperature T5, the heat exchanger hot side outlet temperature T6, and the temperature T7 of the pipe segment between the heat exchanger hot side outlet and the cladding inlet is lower than TL2, the heating branch 3 is started to control the lithium-lead temperature in the lithium-lead heat source utilization branch 2.

[0035] Those skilled in the art will readily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A temperature maintenance system for intermittent periods in a clad lithium-lead heat source circuit, characterized in that, The system includes inlet and outlet branches of the clad lithium-lead heat source, a lithium-lead heat source utilization branch, a heating branch, and a control loop. The lithium-lead heat source utilization branch and the heating branch are connected in parallel to the inlet and outlet branches of the clad lithium-lead heat source. The heating branch includes a third valve, an electric heater, and a second pump connected in sequence. The outlet of the second pump is connected to the first valve on the inlet and outlet branches of the clad lithium-lead heat source and the second valve on the lithium-lead heat source utilization branch. The control loop includes multiple thermocouples and flow meters to monitor the temperature and flow rate at locations used to collaboratively maintain the temperature of the clad lithium-lead heat source circuit during intermittent periods, and to control the start / stop or opening degree of the first valve, second valve, third valve, electric heater, and second pump. The inlet and outlet branches of the blanket lithium-lead heat source include a first valve, an upper connecting pipe of the lithium-lead heat source, the fusion reactor blanket, and a lower connecting pipe of the lithium-lead heat source connected in sequence. The lithium-lead heat source utilization branch includes a second valve, a first pump, and a heat exchanger connected in sequence. The hot-side outlet of the heat exchanger is connected to the lower connecting pipe of the lithium-lead heat source and the third valve, respectively.

2. The temperature maintenance system for intermittent periods of a clad lithium-lead heat source circuit according to claim 1, characterized in that, The multiple thermocouples in the control loop include a first thermocouple located in the upper connecting pipe of the lithium-lead heat source, a second thermocouple located in the lower connecting pipe of the lithium-lead heat source, a third thermocouple located in the fusion reactor blanket, a fourth thermocouple located at the inlet of the electric heater, a fifth thermocouple located at the hot side inlet of the heat exchanger, a sixth thermocouple located at the hot side outlet of the heat exchanger, and a seventh thermocouple located in the middle of the pipeline from the hot side outlet of the heat exchanger to the blanket inlet.

3. The temperature maintenance system for intermittent periods in a clad lithium-lead heat source circuit according to claim 1, characterized in that, The first valve is a two-way electric temperature control valve, the second and third valves are one-way electric temperature control valves, and the second pump is an electric pump. The start and stop of the first valve, the second valve, the third valve, and the second pump are controlled by the control circuit based on the monitored temperature signal.

4. A control method for a clad lithium-lead heat source circuit intermittent temperature maintenance system according to any one of claims 1-3, characterized in that, During the shutdown of the tokamak device, when any two of the following temperatures are lower than the minimum temperature limit TL: T1 at the upper connection port of the cladding lithium-lead heat source, T2 at the lower connection port of the cladding lithium-lead heat source, or T3 inside the cladding lithium-lead, the electric heater, the second pump, the third valve, and the first valve are activated. This allows the heated lithium-lead to flow sequentially through the second pump, the first valve, the fusion reactor cladding, and the third valve before returning to the electric heater. When the temperatures T1 at the upper connection port of the cladding lithium-lead heat source, T2 at the lower connection port of the cladding lithium-lead heat source, or T3 inside the cladding lithium-lead, and the electric heater inlet medium temperature T4 all rise to the minimum temperature limit TL+5℃, the electric heater, the second pump, the third valve, and the first valve are shut down.

5. The control method according to claim 4, characterized in that, When any two of the following temperatures are lower than the minimum temperature limit TL: the inlet temperature T5 of the heat exchanger, the outlet temperature T6 of the heat exchanger, or the temperature T7 of the intermediate pipe section from the outlet of the heat exchanger to the cladding inlet, the electric heater, the second pump, the third valve, and the second valve are started, so that the heated lithium lead flows sequentially through the second pump, the second valve, the first pump, the heat exchanger, and the third valve back to the electric heater; when the inlet temperature T5 of the heat exchanger, the outlet temperature T6 of the heat exchanger, the temperature T7 of the intermediate pipe section from the outlet of the heat exchanger to the cladding inlet, and the inlet medium temperature T4 of the electric heater all rise to TL+5℃, the electric heater, the second pump, the third valve, and the second valve are shut off.

6. The control method according to claim 4 or 5, characterized in that, When two temperature measurement points in the inlet / outlet branches of the cladding lithium-lead heat source are simultaneously below the minimum temperature limit TL, the opening of the second valve is adjusted according to the flow rate M1 of the inlet / outlet branches of the cladding lithium-lead heat source and the flow rate M2 of the lithium-lead heat source utilization branch, so that the flow rate M1 of the inlet / outlet branches of the cladding lithium-lead heat source is equal to the flow rate M2 of the lithium-lead heat source utilization branch.

7. The control method according to claim 6, characterized in that, The minimum temperature limit TL is set to the cladding inlet temperature TL1 during stable operation when the tokamak device is not in operation.

8. The control method according to claim 7, characterized in that, When the system is shut down and the medium is not discharged, the minimum temperature limit TL is set to TL2, which is 30°C higher than the freezing point of LiPb. When any of the following temperatures is lower than TL2: T1 at the upper connection of the cladding lithium-lead heat source, T2 at the lower connection of the cladding lithium-lead heat source, or T3 inside the cladding lithium-lead heat source, the heating branch is activated to heat the inlet and outlet branches of the cladding lithium-lead heat source. When any of the following temperatures is lower than TL2: T5 at the hot side inlet of the heat exchanger, T6 at the hot side outlet of the heat exchanger, or T7 at the intermediate pipe section from the hot side outlet of the heat exchanger to the cladding inlet, the heating branch is activated to heat the lithium-lead heat source using the branch. LiPb represents lithium lead.

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