Fast reactor and fast reactor operating method

Abstract

The object of the present invention is to provide a fast reactor and a fast reactor operating method that can suppress the occurrence of freezing of the heat storage material used in a heat storage system connected to the fast reactor, without draining the heat storage material when the coolant of the fast reactor cools down in an operating mode such as a low-temperature shutdown. [Solution] The fast reactor of the present invention is characterized by comprising: a first heat exchanger that performs heat exchange between a primary coolant and a secondary coolant; a second heat exchanger that performs heat exchange between the secondary coolant and a heat storage material used in a heat storage system; a first pipe through which the secondary coolant flows from the first heat exchanger to the second heat exchanger; a second pipe through which the secondary coolant flows from the second heat exchanger to the first heat exchanger; and a bypass pipe provided at the inlet and outlet of the secondary coolant in the second heat exchanger and connecting the first pipe and the second pipe.

Description

[Technical Field]

[0001] The present invention relates to a fast reactor and a fast reactor operating method. [Background Art]

[0002] Renewable energy is greatly restricted by geographical constraints and weather conditions, so its power generation tends to be unstable. One effective means for stably supplying electric power including such renewable energy is an energy heat storage system provided with an energy adjustment function.

[0003] Candidates for heat sources include photovoltaic power generation, nuclear power generation and the like. As a heat storage system using photovoltaic power generation as a heat source, for example, Patent Document 1 discloses a self-consumption next-generation energy-saving heat storage system capable of converting solar energy into heat storage energy.

[0004] On the other hand, as a known example using nuclear power generation as a heat source, there is a nuclear power plant developed by TerraPower, U.S.A. This is a technology that combines a conventional fast reactor system with a heat storage system using molten salt, so that the reactor side continues operation at rated power, and heat generated in the reactor is stored or released according to the electricity market price. In a heat storage system using a fast reactor as a heat source, there are a coolant used in the fast reactor and a material that stores heat used in the heat storage system (hereinafter referred to as a heat storage material), and heat exchange between the two materials is performed in a heat exchanger that is an interface between the fast reactor and the heat storage system. [Prior Art Documents] [Patent Documents]

[0005] [Patent Document 1] Japanese National Publication of International Patent Application No. 2023-500624 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] Fast reactors have an operating mode (cold shutdown) in which the coolant temperature is lowered to around 200 degrees Celsius after a reactor scram for purposes such as nuclear fuel replacement. During rated operation, the coolant becomes hot due to the nuclear reaction, but in cold shutdown, the nuclear reaction is stopped, causing the coolant to cool down. However, depending on the combination of coolant and heat storage material (for example, sodium or something else for the coolant, and molten salt, fast reactor operating range, and the use of inexpensive materials for the heat storage material), when the coolant cools down, the temperature of the heat storage material that exchanges heat with the coolant in the heat exchanger also decreases. If this temperature falls below the freezing point, the heat storage material may solidify (freeze), potentially blocking the piping through which the heat storage material flows. Therefore, measures to prevent blockage are necessary when the heat storage material temperature drops in operating modes such as cold shutdown.

[0007] As a solution to the above problem, the inventors considered draining the heat storage material from the heat exchanger before switching from rated operation to low-temperature shutdown. However, in that case, when switching back to rated operation, it would be necessary to refill the heat exchanger with the drained heat storage material, and a preheating operation would be required before refilling, which would make the operation switching operation complicated and could reduce the plant's operating rate.

[0008] The object of the present invention is to provide a fast reactor and a fast reactor operating method that can suppress the occurrence of freezing of the heat storage material used in a heat storage system connected to the fast reactor, without draining the heat storage material when the coolant of the fast reactor cools down in an operating mode such as a low-temperature shutdown. [Means for solving the problem]

[0009] The fast reactor of the present invention is characterized by comprising: a first heat exchanger that performs heat exchange between a primary coolant and a secondary coolant; a second heat exchanger that performs heat exchange between the secondary coolant and a heat storage material used in a heat storage system; a first pipe through which the secondary coolant flows from the first heat exchanger to the second heat exchanger; a second pipe through which the secondary coolant flows from the second heat exchanger to the first heat exchanger; and a bypass pipe provided at the inlet and outlet of the secondary coolant in the second heat exchanger and connecting the first pipe and the second pipe.

[0010] The present invention relates to a fast reactor operation method comprising: a first heat exchanger for performing heat exchange between a primary coolant and a secondary coolant; a second heat exchanger for performing heat exchange between the secondary coolant and a heat storage material used in a heat storage system; a first pipe through which the secondary coolant flows from the first heat exchanger to the second heat exchanger; a second pipe through which the secondary coolant flows from the second heat exchanger to the first heat exchanger; a bypass pipe provided at the inlet and outlet of the secondary coolant in the second heat exchanger and connecting the first pipe and the second pipe; a flow-adjustable valve in the second pipe between the second heat exchanger and the connection between the bypass pipe and the second pipe; a third pipe connecting the first pipe and the second pipe; and an air cooler provided in the third pipe. The method for operating a fast reactor is characterized by stopping the operation of the fast reactor, removing heat from the secondary coolant with the air cooler, opening the valve in the bypass pipe, and operating from rated operation to low-temperature shutdown. [Effects of the Invention]

[0011] According to the present invention, when the coolant of the fast furnace cools down in an operating mode such as a low-temperature shutdown, it is possible to provide a fast furnace and a fast furnace operating method that can suppress the occurrence of freezing of the heat storage material used in a heat storage system connected to the fast furnace without draining the heat storage material.

[0012] Other issues, configurations, and effects not mentioned above will be clarified by the following description of the embodiments. [Brief explanation of the drawing]

[0013] [Figure 1] This is a diagram illustrating the configuration of a fast reactor equipped with a molten salt heat storage system for rated operation. [Figure 2] This is a perspective view of the configuration of a fast reactor equipped with a molten salt thermal storage system. [Figure 3] This is a diagram illustrating the configuration of a fast reactor equipped with a molten salt heat storage system for use during low-temperature shutdowns. [Figure 4] This flowchart shows the method for switching a fast reactor equipped with molten salt heat storage to low-temperature shutdown mode. [Figure 5] This is a diagram illustrating the configuration of a fast reactor equipped with a molten salt thermal storage system. [Modes for carrying out the invention]

[0014] The following describes embodiments with reference to the drawings. In the following description, sodium is used as the coolant for the fast reactor and a nitrate mixture, often used as a heat storage material for solar power generation, is used as the heat storage material for the heat storage system, but the present invention is not limited to this. The present invention can be applied to fast reactors equipped with a heat storage system in which freezing of the heat storage material may occur when the temperature of the coolant decreases. Furthermore, the present invention can be applied regardless of the reactor output, such as small, medium, or large, and the number of fast reactors connected to the heat storage system is not limited to one, but may be multiple. In addition, the present invention can be applied regardless of the type of nuclear fuel loaded into the fast reactor, such as MOX fuel or metallic fuel. [Examples]

[0015] Figure 1 is a diagram of the configuration of a fast reactor equipped with a molten salt thermal storage system during rated operation. Figure 2 is a perspective view of the configuration of a fast reactor equipped with a molten salt thermal storage system. For the sake of simplicity, only the main components are shown in both figures.

[0016] The arrangement of equipment and piping for a fast reactor and a molten salt heat storage system will be described. As shown in FIG. 1, a fast reactor 100 includes a core 101, an IHX 102 serving as a first heat exchanger (intermediate heat exchanger), an AC 103 serving as an air cooler, an SHX 104 serving as a second heat exchanger (sodium-molten salt heat exchanger), and a molten salt drain tank 105, and a molten salt heat storage system 200 includes a molten salt cold tank 106 and a molten salt hot tank 107. Molten salt is used as a heat storage material in the equipment of the heat storage system. When comparing oil and molten salt, molten salt has a larger heat capacity, so the required amount of heat storage material and tank capacity can be reduced compared to oil, which is advantageous in terms of cost and excellent in economic efficiency. Furthermore, molten salt also has higher thermal conductivity.

[0017] Nuclear fuel (not shown) is loaded into the core 101. During rated operation of the fast reactor, heat is generated by nuclear fission of the nuclear fuel. The generated heat is transferred to the IHX 102 side by sodium, which is the primary coolant present in the core 101.

[0018] The IHX 102 is connected to the core 101 via a flow path 160, a primary main circulation pump (not shown), and a flow path 161, and is disposed inside the reactor together with the core 101. Note that this arrangement is not limited to being inside the reactor, and an arrangement example in which the flow paths 160 and 161 are used as piping and the primary main circulation pump and the IHX 102 are connected outside the reactor is also conceivable.

[0019] The core 101, the primary main circulation pump, the flow path 160, the flow path 161, and the IHX 102 form a loop (primary loop), and the primary loop is filled with sodium as the primary coolant. Further, the IHX 102 is connected to the SHX 104 via a pipe 162 which is a first pipe and a pipe 163 which is a second pipe. As shown in FIG. 2, the SHX 104 is disposed at a position higher than the IHX 102 in the vertical direction. The IHX 102, the pipe 162, a secondary main circulation pump (not shown), the pipe 163, and the SHX 104 also form a loop (secondary loop) similarly to the primary loop, and the secondary loop is filled with sodium as the secondary coolant.

[0020] During rated operation of the fast reactor, in IHX 102, the primary coolant and the secondary coolant are in indirect contact with each other, and the heat generated in the reactor core is transferred from the primary coolant to the secondary coolant. A valve 144 is provided in the pipe 163 on the outlet side of SHX 104, a pipe 168 bypassing the valve 144 is provided, and a valve 145 is also provided in the pipe 168. The pipe 168 is narrower than the pipe 163.

[0021] AC 103 is arranged between a pipe 164 and a pipe 165, which are third pipes, in a manner bypassing the pipes 162 and 163 through which the secondary coolant flows. By providing an air cooler in the third pipe, heat removal operation by AC 103 for the purpose of decay heat removal can be achieved.

[0022] Note that, as shown in Figure 2, AC 103 is arranged at a higher position in the vertical direction than SHX 104. That is, they are arranged at increasing heights in the order of IHX 102, SHX 104, and AC 103. The connection point between the pipe 163 and the pipe 165 is located downstream in the flow direction of the secondary coolant relative to the valve 144 and the connection point between the pipe 163 and the pipe 168. A valve 142 is provided on the pipe 165 on the outlet side of AC 103, and a pipe 166 bypassing the valve 142 is provided. A valve 141 is also provided in the pipe 166. The pipe 166 is narrower than the pipe 165.

[0023] AC 103 is provided with an inlet and an outlet for external air; a duct 177 provided with a blower 181 and a damper 111 is arranged on the inlet side, and a duct 178 provided with a damper 110 is arranged on the outlet side.

[0024] Further, apart from the pipes 164 and 165 that bypass AC 103, a bypass pipe 167 that bypasses the inlet and outlet sides of SHX 104 is provided in parallel, and a bypass valve 143 is provided on the bypass pipe 167.

[0025] AC103 and bypass piping 167 may be connected in series. During normal operation, the bypass valve 143 is kept closed, and during low-temperature shutdown, the bypass valve 143 is opened and valves 142, etc., are throttled to limit the flow rate to SHX104.

[0026] In Figure 1, the bypass pipe 167 is positioned on approximately the same plane as the SHX 104. However, this is not the only possible piping arrangement; as shown in Figure 2, pipes 162 and 163 bend vertically upward at the connection point with the bypass pipe 167. It is preferable that the SHX 104 is positioned vertically higher than the secondary loop plane. By positioning the SHX 104 vertically above the bypassed pipe 164, natural circulation can be utilized, suppressing the flow of cold Na and providing an expected effect of limiting the inflow rate.

[0027] Furthermore, the piping connected to SHX104 only needs to be above the bypass piping 167, and the piping arrangement may be such that piping 162 and piping 163 do not bend at the connection point with the bypass piping 167, but instead the bypass piping 167 bends vertically downward at that connection point.As will be explained later, it is preferable for the bypass piping 167 to be thicker than the other piping when considering pressure loss.

[0028] SHX104 is connected to the molten salt cold tank 106 and the molten salt hot tank 107 via pipes 171 and 173, respectively. The heat storage material flows from the molten salt cold tank 106 to SHX104 through pipe 171 and to the molten salt hot tank 107 through pipe 173. In SHX104, the secondary coolant and the heat storage material are indirectly in contact with each other, and heat exchange occurs between them, transferring heat generated in the reactor core from the secondary coolant to the heat storage material. In other words, heat is transferred from the fast reactor 100 to the molten salt heat storage system 200, and the heat generated in the fast reactor 100 is stored in the molten salt heat storage system 200.

[0029] The molten salt cold tank 106 is connected to the steam generator (SG) via piping 176. The heat storage material, after heat is released in the SG, flows into the molten salt cold tank 106 from the SG through piping 176 and is stored there. On piping 171, a pump 132 is provided on the outlet side of the molten salt cold tank 106, and a valve 149 is provided on the inlet side of the SHX 104. In addition, a valve 152 is provided on piping 176 connecting the SG to the molten salt cold tank 106.

[0030] The molten salt hot tank 107 is connected to the SG via piping. The heat storage material, which has undergone heat exchange with the secondary coolant in the SHX 104, flows into the molten salt hot tank 107 from the SHX 104 through piping 173 and is stored there. A valve 148 is provided on the outlet side of the SHX 104, and a pump 133 and a valve 151 are provided on the piping on the outlet side of the molten salt hot tank 107.

[0031] Furthermore, pipes 174 and 175 are provided as systems for heating the heat storage material in the molten salt cold tank 106 and the molten salt hot tank 107, respectively. A valve 154 and a heater 121 are installed on pipe 174, and a valve 153 and a heater 122 are installed on pipe 175. The connection point between pipe 174 and pipe 171 is between pump 132 and valve 149 on pipe 171, and the connection point between pipe 174 and pipe 176 is downstream of valve 152. The connection point between pipe 175 and pipe 173 is downstream of valve 148, and the connection point between pipe 175 and pipe is between pump 133 and valve 151.

[0032] The molten salt drain tank 105 is connected to the SHX 104 via piping 169 and to the molten salt cold tank 106 via piping 170. The molten salt drain tank 105 allows for the draining and removal of the heat storage material from the SHX 104. The molten salt drain tank is mainly used during maintenance and upkeep work on the SHX. A valve 146 is provided on piping 169 and a valve 147 is provided on piping 171, and draining is possible by opening these valves. Subsequently, by turning on the pump 131 located on piping 170 and opening valve 150, the drained heat storage material can be transferred to the molten salt cold tank 106.

[0033] As shown in Figure 1, valves 148, 149, and 150 separate the nuclear power system (fast reactor 100) from the energy system (molten salt thermal storage system 200). This allows the radioactive controlled area to be limited to only the fast reactor 100, thereby limiting the scope of radioactive control.

[0034] This section describes the fast reactor's operation during rated operation. During rated operation, heat generated in the core 101 is transferred from the primary coolant to the secondary coolant via IHX102, and further transferred from the secondary coolant to the heat storage material via SHX104. The heated heat storage material is then stored in the molten salt hot tank 107. When the heat storage system needs to release heat due to a decrease in the amount of electricity generated from renewable energy, the discharge pressure of pump 133 is increased to increase the flow rate of the heat storage material from the molten salt hot tank 107 to the SG side, and also to increase the amount of steam generated in the SG. This increases the amount of electricity generated. Conversely, when the heat storage system needs to store heat due to an increase in the amount of electricity generated from renewable energy, the discharge pressure of pump 133 is decreased.

[0035] During rated operation, as shown in Figure 1, valves 141 and 144 are open in the fast reactor 100's piping, while valves 142, bypass valve 143, 145, 146, and 147 are closed, and the secondary coolant flows to AC103 and SHX104. In this case, piping 166, where valve 141 is located, is narrower than piping 165 and has a large pressure loss, so most of the secondary coolant flows to SHX104, and the heat generated in the core 101 is transferred to the heat storage material in the tertiary loop. A small amount of secondary coolant flows to AC103 to prevent sodium freezing, but during rated operation, there is no need to cool the secondary coolant, so the blower 181 is OFF and the damper 111 is closed. Furthermore, as shown in Figure 1, valves 148, 149, 151, and 152 of the molten salt thermal energy storage system 200's piping are open, while valves 150, 153, and 154 are closed, allowing all the thermal energy storage material to flow through the tertiary loop.

[0036] During rated operation, the inlet temperature of the secondary coolant flowing into the SHX104 is typically around 450-500 degrees Celsius, and the outlet temperature is around 300-350 degrees Celsius, while the inlet temperature of the heat storage material is around 300 degrees Celsius, and the outlet temperature is around 450-500 degrees Celsius. For example, the freezing point of Solar Salt (a mixture of potassium nitrate and sodium nitrate), which is often used as a heat storage material for solar power generation, is approximately 240 degrees Celsius, so it is usually impossible for the temperature of the heat storage material to fall below its freezing point during rated operation.

[0037] Next, we will explain the cold shutdown of a fast reactor. Figure 3 is a diagram of the configuration of a fast reactor equipped with a molten salt heat storage system during cold shutdown. Note that, for the sake of simplicity, only the main components are shown in Figure 3.

[0038] During a cold shutdown, after the reactor scram and each main circulation pump trip, if we assume that the coolant temperature is lowered to about 200 degrees Celsius while removing heat through natural circulation of the secondary coolant, then, as shown in Figure 3, valves 141 and 144, which were open during rated operation, will be closed, and valves 142 and 145 will be opened.

[0039] At this time, depending on the size of the pipe diameters of pipes 165 and 168 in which valves 142 and 145 are open, most of the secondary coolant flows to AC104, the blower 181 is turned ON, the damper 111 is opened, and the heat removal operation begins.

[0040] Here, by opening the bypass valve 143 and diverting a portion of the secondary coolant that was flowing to SHX104 to the bypass pipe 167, the amount of coolant flowing into SHX104 is reduced, thereby decreasing the amount of heat exchanged with the heat storage material in the tertiary loop. In other words, it is possible to prevent the temperature of the heat storage material from dropping below its freezing point by the secondary coolant, which has been cooled down to about 200 degrees Celsius.

[0041] The flow resistance of the SHX104 itself also contributes to the flow of more secondary coolant into the bypass pipe 167. However, as shown in Figure 2, by positioning the bypass pipe 167 lower vertically than the SHX104, the secondary coolant heated by the heat storage material within the SHX104 becomes hotter and less dense than the secondary coolant passing through the bypass pipe 167. Therefore, it is possible to cause the secondary coolant flowing through the SHX104 to stagnate at a higher position, making it more difficult to flow. Consequently, the amount of secondary coolant flowing into the SHX104 is reduced compared to a piping arrangement where the SHX104 and the bypass pipe are positioned on approximately the same plane. The inlet valve may also be throttled.

[0042] It is also conceivable to install a valve on the secondary coolant outlet side of SHX104 to prevent any secondary coolant from flowing into SHX104, and to close the valve during low-temperature shutdown to allow the secondary coolant to remain in SHX104. However, in this case, the secondary coolant remaining in SHX104 will cool down over time due to natural heat dissipation, and there is a possibility that the secondary coolant will solidify. Therefore, it is important to install a bypass pipe 167 to reduce the flow rate of secondary coolant through SHX104, but to avoid completely eliminating the sodium flow.

[0043] During this time, the molten salt thermal storage system 200 is only slightly cooled by the SHX104, so power generation is possible by continuing the circulation of the thermal storage material in the tertiary loop. However, eventually the temperature of the thermal storage material in the molten salt hot tank 107 will equalize with the temperature of the thermal storage material in the molten salt cold tank 106, making it difficult to generate steam on the SG side. Therefore, at a predetermined timing, the SG water supply is stopped, and in order to prevent temperature drops due to natural heat dissipation and freezing, valves 153 and 154 are opened, and heaters 121 and 122 are turned ON to heat the thermal storage material in both tanks.

[0044] The fast reactor of this embodiment includes a first heat exchanger that performs heat exchange between a primary coolant and a secondary coolant, a second heat exchanger that performs heat exchange between the secondary coolant and a heat storage material used in a heat storage system, a first pipe through which the secondary coolant flows from the first heat exchanger to the second heat exchanger, a second pipe through which the secondary coolant flows from the second heat exchanger to the first heat exchanger, and a bypass pipe provided at the inlet and outlet of the secondary coolant in the second heat exchanger and connecting the first pipe and the second pipe. By providing these components, it is possible to provide a fast reactor and a fast reactor operating method that can suppress the occurrence of freezing of the heat storage material used in a heat storage system connected to the fast reactor without draining the heat storage material when the coolant of the fast reactor cools down in an operating mode such as a low-temperature shutdown.

[0045] As explained above, in Example 1, a bypass pipe 167 is provided, so the heat storage material does not need to be drained into the molten salt drain tank 105, and solidification of the heat storage material in SHX104 can be prevented. Furthermore, simply by arranging the bypass route, the complicated draining operation is eliminated, and the time required for draining is reduced, which in turn improves the plant's operating rate.

[0046] Next, we will explain how to switch from rated operation to low-temperature shutdown.

[0047] Figure 4 is a flowchart showing the method for switching to a cold shutdown operation for a fast reactor equipped with molten salt heat storage. In step S301, first, control rods (not shown) inside the reactor vessel (not shown) are inserted into the core by a control rod drive mechanism (not shown), and the reactor output is gradually reduced while decreasing the flow rates of the primary and secondary main circulation pumps.

[0048] In step S302, a heat removal operation using AC103 is started for the purpose of removing decay heat. Specifically, valves 142 and 145 are opened, valves 141 and 144 are closed, blower 181 is turned ON, and damper 111 is opened. The reactor core is cooled by cooling the secondary coolant with AC103 and the primary coolant via IHX102.

[0049] In step S303, the bypass valve 143 is opened. By changing the bypass valve 143 to the open state, it is possible to minimize the flow rate of the secondary coolant flowing into the SHX104, as in the embodiment described above.

[0050] By stopping the fast reactor, removing heat from the secondary coolant with an air cooler, opening the valves on the bypass piping located on the inlet and outlet sides of the heat exchanger, and operating these functions from rated operation to low-temperature shutdown, it is possible to minimize the flow rate of the secondary coolant into the SHX104, making this a suitable method for switching from rated operation to low-temperature shutdown. [Examples]

[0051] Figure 5 is a diagram of the configuration of a fast furnace equipped with a molten salt thermal storage system in Example 2. In this modified example, there is no difference in height between the bypass piping 167 and SHX104. In other words, it is a more preferred embodiment when the bypass piping 167 and SHX104 are arranged on substantially the same plane. Only the parts that differ from Example 1 described above will be explained.

[0052] In this embodiment 2, a valve 155 with a flow rate adjustment function is provided on the pipe 163 between the connection point between the bypass pipe 167 and pipe 163 from the SHX104. In other words, a flow rate adjustment valve is provided on the second pipe between the second heat exchanger and the connection point between the bypass pipe and the second pipe. During rated operation, the valve 155 is kept open, and during low-temperature shutdown, the opening degree is adjusted to control the flow rate so that the secondary coolant does not solidify due to natural heat dissipation, thereby preventing solidification of the heat storage material.

[0053] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0054] 100...Fast reactor, 101...Core, 102...IHX, 103...AC, 104...SHX, 105...Molten salt drain tank, 106...Molten salt cold tank, 107...Molten salt hot tank, 110...Damper, 111...Damper, 121...Heater, 122...Heater, 131...Pump, 132...Pump, 133...Pump, 143...Bypass valve, 167...Bypass piping, 181...Blower, 200...Molten salt thermal storage system.

Claims

1. A first heat exchanger that performs heat exchange between a primary coolant and a secondary coolant, A second heat exchanger that performs heat exchange between the secondary coolant and the heat storage material used in the heat storage system, A first pipe through which the secondary coolant flows from the first heat exchanger toward the second heat exchanger, A second pipe through which the secondary coolant flows from the second heat exchanger toward the first heat exchanger, A fast reactor characterized by comprising a bypass pipe provided at the inlet and outlet of the secondary coolant of the second heat exchanger, and connecting the first pipe and the second pipe.

2. In the fast reactor according to claim 1, The fast reactor is characterized in that the second heat exchanger is positioned vertically above the bypass piping.

3. In the fast reactor according to claim 1, A fast reactor characterized in that a valve capable of adjusting the flow rate is provided in the second pipe between the second heat exchanger and the connection point between the bypass pipe and the second pipe.

4. In the fast reactor according to claim 1, A third pipe is provided that connects the first pipe and the second pipe. A fast reactor characterized by having an air cooler in the third piping.

5. In the fast reactor according to claim 1, The primary coolant and the secondary coolant are sodium. A fast furnace characterized in that the heat storage material is a molten salt.

6. A method for operating a fast reactor comprising: a first heat exchanger for exchanging heat between a primary coolant and a secondary coolant; a second heat exchanger for exchanging heat between the secondary coolant and a heat storage material used in a heat storage system; a first pipe through which the secondary coolant flows from the first heat exchanger to the second heat exchanger; a second pipe through which the secondary coolant flows from the second heat exchanger to the first heat exchanger; a bypass pipe provided at the inlet and outlet of the secondary coolant in the second heat exchanger and connecting the first pipe and the second pipe; a valve capable of adjusting the flow rate in the second pipe between the second heat exchanger and the connection between the bypass pipe and the second pipe; a third pipe connecting the first pipe and the second pipe; and an air cooler provided in the third pipe, The operation of the fast reactor was stopped, The secondary coolant is cooled by the air cooler, A fast reactor operating method characterized by opening the valve of the bypass piping and operating it from rated operation to low-temperature shutdown.

7. In the fast reactor operating method described in claim 6, A method for operating a fast reactor, characterized by controlling the flow rate by adjusting the opening degree of the flow-rate adjustable valve provided in the second piping.

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