JPS62127694A - Sodium cooling device in reactor vessel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a sodium cooling device in a reactor vessel such as a decay heat removal device used in a liquid metal cooled fast breeder reactor (hereinafter referred to as a fast reactor).

[The amount of invention]

The internal structure of a conventional Boulle fast reactor is explained with reference to FIG. Circulation pump, 3 is intermediate heat exchanger, 41-1: core, 5 is horizontal isolation membrane, 6 is Dobe Bu1-num, 7 is lower part] 7 renum,
8 - Putrium, 9 is secondary sodium, 10 is a heat exchanger tube. Then, the main circulation pump 2 is installed inside the furnace vessel 1.
and an intermediate heat exchanger 3 are attached to take out the heat generated in the reactor core 4 to the outside of the reactor vessel 1.

The interior of the reactor vessel 1 is vertically divided into a high-temperature upper plenum 6 and a low-temperature lower plenum 7 by a horizontal isolation membrane 5. 1 in the furnace vessel 1. During normal operation, the IJ pump 8 is driven for forced circulation by the main circulation pump 2 as shown by arrow A. 1.1'j' of sodium 8 in the lower plenum 7 is sucked in by the main circulation pump 2 and pushed out into the core 4. The sodium flow exiting from the core 4 to the upper plenum 6 enters the intermediate heat exchanger 3 and exchanges heat with the secondary system sodium 9, and then returns to the lower plenum 7 again for circulation. Inside the intermediate heat exchanger 3, there are heat exchanger tubes 10 for the heat exchanger.
is built in, and heat from the reactor core 4) is transferred to the secondary system sodium 9.

As described above, during rated operation, the heat generated within the reactor core 4 can be normally taken out of the reactor vessel 1 by forced circulation of the sodium 8. However, if the main circulation pump 2 is stopped I- due to a power outage, etc., the arrow A in the furnace vessel 1
The forced circulation flow shown in is eliminated, and the intermediate heat exchanger 3
The amount of heat removed due to this decreases. Therefore, there is a problem that the temperature of the reactor core 4 and the IJ mass 8 in the upper blemish 6 begins to rise.

In order to avoid this problem, conventionally, a reactor vessel 1 of a nuclear reactor is equipped with an in-vessel sodium cooling device as shown in FIGS. 15 and 16. 15 and 16, 11 is a heat exchanger, 12 is an air cooler, 13 is a pipe, 14 is a heat exchanger tube, 15 is a sodium inlet, 16 is a sodium outlet, 17 is a finned pipe, and 18 is a 19 is a damper, and 20 is an electromagnetic pump. Although this device does not operate during normal rated operation, the main circulation pump 2
It is designed to operate only when the temperature of the IJum 8 in the furnace vessel 1 starts to rise abnormally due to a shutdown or some other reason.

15 and 16, the main circulation pump 2 and intermediate heat exchanger 3 are omitted, and only the structure of the IJum cooling system is shown in its entirety. The IJ cooling system shown in FIG. 15 is composed of a heat exchanger 11, an air cooler 12, and piping 13 connecting the two.

The heat exchanger 11 is inserted into the upper blemish 6 and has heat transfer tubes 14 therein.

Additionally, the sodium inlet 15 and sodium outlet 16 are installed above and below. The air cooler 12 uses natural circulation heat radiation to the surrounding air, and has finned piping 17,
It is composed of a trunk 18 and a barrel 19. An electromagnetic pump 20 is installed in the pipe 13 connecting the heat exchanger 11 and the air separator 12'e to circulate an alloy sealed in liquid metal Na.

In this device, the NaK alloy in the piping 13 is constantly circulated, regardless of whether it is in rated operation or in an emergency.

During rated operation, the damper 19 of the air cooler 12
is closed, so there is no heat dissipation from the NaK in the pipe 13, and the sodium 8 in the upper blenheim 6 is not cooled either. However, in an emergency such as when the main circulation pump 2 in the furnace vessel 1 is stopped, the Danno ζ 19 opens and the circulating Na
Heat is dissipated from the K alloy to the outside. Therefore, heat exchanger 1
The temperature of the heat exchanger tube 14 in the tube 1 decreases, and heat exchange with the surrounding tube 8 occurs. As a result, the temperature of the sodium 8 in the heat exchanger 11 decreases, it becomes heavier and exits from the lower sodium outlet 16, and the hot sodium 8 in the upper plenum 6 flows into the heat exchanger 11 from the upper sodium inlet 15. It starts to come into the room.

In this way, when the damper 19 of the air cooler 12 is l<, natural circulation occurs within the upper blemish 6. In an emergency, this natural circulation lowers the temperature of the upper plenum 6 and the core 4. However, the inside of the furnace vessel of this method)
In the IJ cooling device, (1) there is a moving part called the damper 19, so the reliability of the device performance is poor.

(2) There is a possibility that local natural circulation occurs in the upper plenum 6 as shown by the dotted line C in FIG. be. In this case, there is a problem that only the upper part of the core 4 is cooled, and the entire core 4 is not cooled uniformly.

Further, another configuration of a conventionally commonly used furnace vessel sodium cooling device will be explained with reference to FIG. 16. In this example, a part of the intermediate heat exchanger 3 is used as the heat exchanger. That is, a heat exchanger tube 14 for an in-furnace sodium cooling device is wound around the upper part of the intermediate heat exchanger 3 to exchange heat with the sodium 8 in the upper brenum 6. The construction of the air cooler 12 and the piping 13 for NaK alloy circulation is the same as that shown in FIG. 15. However, even in this type of in-reactor vessel sodium cooling device, (1) there is a moving part called the damper 19, and the reliability of the device is poor.

(2) Since the intermediate heat exchanger 3 is also used as a heat exchanger, the height h of the intermediate heat exchanger 3 becomes high.

As a result, the height and size of the furnace vessel 1 become unnecessarily large, resulting in an increase in construction cost.

As this kind of sodium cooling device, 58-
No. 118989.58-35495 has been proposed.

[Purpose of the invention]

The present invention was developed in view of the above situation, and an object of the present invention is to provide a sodium cooling device in a reactor vessel that can uniformly cool the entire reactor interior and improve reliability since there are no moving parts during cooling operation. It is something.

[Summary of the invention]

The in-reactor vessel sodium cooling device of the present invention comprises: a heat exchanger disposed in the sodium in the reactor vessel of a liquid metal cooled fast breeder reactor; a cooler disposed outside the reactor vessel; The heat transfer tubes and finned piping installed in the heat exchanger and the cooler are connected to both ends, and the inside is filled with a conductive fluid to form an endless flow path, and the normal operation of the furnace. and an electromagnetic pump for driving the conductive fluid to cool the sodium in the reactor vessel when the reactor vessel is not in operation, the pump being located below a horizontal isolation membrane that divides the interior of the reactor vessel into an upper plenum and a lower plenum. an inlet outlet of the heat exchanger is opened, and a resistance element is disposed in the current circuit of the electromagnetic pump so as to be electrically conductive when the conductive fluid is in a predetermined temperature state, or The electrically conductive fluid forming part of the current circuit is configured to become conductive when the electrically conductive fluid reaches a predetermined temperature.

[Embodiments of the invention]

Hereinafter, the in-furnace vessel sodium cooling system of the present invention will be explained using embodiments, with reference to FIGS. 1 to 4, in which the same parts as those in the conventional art are denoted by the same reference numerals, and the explanation of the structure of the same parts will be omitted. Figure 1 is an explanatory diagram, Figure 2 is an explanatory diagram of the temperature characteristics of the driving force, with the horizontal axis representing the temperature of the sodium in the electromagnetic pump in Figure 4, and the vertical axis representing the driving force. 1 is a detailed perspective view of the electromagnetic pump shown in FIG. 1, and FIG. 4 is a horizontal sectional view of the central part of the pump shown in FIG. 3.

In the figure, 21 is a DC power supply, 22 is a rectangular duct, 23
24 is a permanent magnet, 24 is an electrode, 25 is a conductive fluid, 26 is a resistance element, and 27 is a current circuit.

The IJ cooling system (inside the furnace vessel) is composed of a heat exchanger 11, an air cooler 12, and piping 13.
The IJum outlet 16 is opened. The air cooler 12 is comprised only of a finned pipe 17 and a shell 18, and the damper 19 provided in the conventional FIGS. 15 and 16 has been removed. The inside of the pipe 13 is filled with a conductive fluid 25 such as NaK alloy, and an electromagnetic pump 20 is installed therein to circulate the fluid. Electromagnetic pump 2
o has a flow rate control function, and the discharge pressure of the electromagnetic pump 2o can be automatically changed depending on the temperature of the NaK alloy inside the pipe 13.

During normal rated operation of the reactor, the upper Blenheim 6
As shown in Fig. 2, the temperature of +7um8 is a constant temperature T of 540°C, for example. It is in.

Further, the temperature around the air cooler 12 is maintained at a constant temperature near room temperature. Due to this temperature difference, natural circulation occurs in the pipe 13 at a constant flow rate. Na flowing through the electromagnetic pump 20 provided near the outlet of the heat exchanger 11
The temperature of the K alloy is close to the rated temperature ToK, and at this temperature the driving force F or discharge pressure (not shown) of the electromagnetic pump 2o is set to zero. In this case, the circulation driving force in the piping 13 is due to the natural circulation force due to the temperature difference between the upper plenum 6 and the air cooler 12, so although the circulation flow rate is small, the outside air is transferred from the air cooler 12. There is some heat dissipation to the

On the other hand, if the temperature of the thorium 8 in the upper blenheim 6 rises due to some reason, such as stopping the main circulation pump 2, the temperature of the NaK alloy near the outlet of the heat exchanger 11 also begins to rise, and along with this temperature rise, The driving force F of the electromagnetic pump 2o is configured to increase along a curve shown in FIG. Therefore, when the discharge pressure of the electromagnetic pump 2o increases, the circulating flow rate within the pipe 13 increases, and therefore the amount of heat radiated from the upper plenum 6 to the outside through the air cooler 12 also increases. On the other hand, the heat exchanger 11 has a horizontal isolation membrane 5
Because it penetrates the inside of the heat exchanger 11 (C) from the inlet 15, the injector 8 is cooled and then flows through the lower plenum 7 from the outlet 16.
flows out to. Furthermore, this triwam 8 is warmed by the reactor core 4, so it rises again and returns to the upper blennium 6. In this way, a natural circulation is formed inside the reactor vessel 1, and since this natural circulation always flows through the reactor core 4 from the bottom to the top, the reactor core 4 can be reliably cooled.

FIG. 3 shows the configuration of the electromagnetic pump 20 used in the above embodiment. The electromagnetic pump 20 is composed of two permanent magnets 23 facing each other with a rectangular duct 22 in between, two electrodes 24, 24, and a DC power supply 21 applied to the electrodes 24. Then, as shown in FIG. 4, permanent magnets 23 are placed above and below.
Therefore, inside the rectangular duct 22, a DC magnetic field B is applied from top to bottom, and two electrodes 24 placed on the left and right sides are applied.
A DC power supply 21 is connected to ゜24. This causes a direct current i to flow in the conductive fluid 25 within the rectangular duct at right angles to the direct current magnetic field B. Due to the interaction of the magnetic field B1 and the current i, a driving force F acts on the RiNaK alloy fluid from the front to the back of the page.

The magnitude F of the driving force of the electromagnetic pump 20 described above is proportional to the current and the strength of the magnetic field, and the current is inversely proportional to the electrical resistance in the current circuit 27, so it can be expressed as in equation (1). can.

However, 5. C: Proportional resistance R: Resistance of the electric circuit (Ω) B: Magnetic flux density W/In2) As shown in FIG. It is incorporated in a resistive element 261 whose electrical resistance decreases as the temperature rises.Bismuth (Bi), for example, can be used as the material of this resistive element 26.This resistive element 26 has a horizontal axis f/i: l
It has a characteristic as shown by curve E in FIG. 5, where the temperature To of the sodium 8 in the hum 6 is plotted and the electric resistance R of the current circuit 27 is plotted on the vertical axis. That is, the temperature T inside the upper blemish 6 during rated reactor operation. The odor shows a very large resistance value, and the resistance value decreases rapidly when the temperature rises above U'J''o. 'l' (, -(: Vr
'di ki [IJ ro 27 vc 1:11. ), %/
The force F acting on the conductive fluid 25 does not flow.
, Therefore, the discharge pressure UO of the electromagnetic pump 2o is close to 0. However, when the temperature of the NaK alloy in the rectangular duct 22 becomes higher than To for some reason, current suddenly begins to flow through the current circuit 27, and the force F on the conductive fluid 25 begins to increase rapidly. Therefore, the N in the piping 13 shown in FIG.
The aK alloy suddenly begins to be circulated and the sodium 8 in the upper brenum 6 begins to be cooled through the air cooler 12. Therefore, the amount of cooling is controlled not by conventional mechanical means such as dampers, but by electromagnetic force that acts on the conductive fluid.

In this way, the sodium cooling system in the reactor vessel of this embodiment is configured to open the sodium outlet of the heat exchanger below the horizontal isolation membrane and to control the amount of sodium cooled. Mechanical means nyobko 11- (corresponding to the temperature of the conductive fluid, do 6!/r', L, ;+, so Q'3
The entire core can be cooled uniformly, improving electrical and electrical reliability.

Furthermore, Figure 16 (・'C shows the structure of Comparison 1)
~Construction cost total 11 (Castle 1.Improve economic efficiency'?lJru.

FIG. 6 shows another embodiment, and the difference from the above embodiment is that in the above embodiment, the heat exchanger 11 is formed of a single cylindrical body with a closed ceiling, whereas The upper end of the inner cylinder 29 is loosely fitted into the lower part of the cylinder 30.

The electromagnetic brake 28 is fixed to the lower end of the outer cylinder 30, and an annular flow forming an inlet of the heat exchanger 11 between the inner periphery of the electromagnetic brake 28 and the outer periphery of the inner cylinder 29. A path 31 is formed. The sodium hydroxide 8 in the upper plenum 6 enters the inner cylinder 29 from the annular flow path 31 as shown by the dotted line, is cooled by the heat transfer tube 14, and flows into the lower plenum 7. l) The ram 8 in the lower plenum 7 is warmed by the core 4, so it rises inside the core 4 and returns to the upper plenum 6 again.

In this way, after the main circulation pump 2 stops and the forced circulation disappears, a natural circulation flow occurs in the order of upper plenum 6 - ten heat exchangers 11 → lower plenum 7 - ÷ reactor core 4 → upper plenum 6. Moreover, since it always passes through the reactor core 4, it can be reliably cooled. However, during rated operation, some of the sodium in the upper plenum G is transferred from the upper plenum 6 to the heat exchanger 11, to the lower plenum 7, to the main circulation pump due to the discharge pressure of the main circulation pump (see Figure 14). 2
→ core 4 → upper plenum 6, and a part of the thermal energy in upper plenum 6 is transferred to heat exchanger tube 4.
4. Heat is transferred to the outside via the air cooler 12. Therefore, in order to dissipate the heat generated in the reactor core 4 to the outside (C), the economic efficiency of the reactor becomes worse.In order to prevent this, in this embodiment, the heat generated in the annular flow path 31 is
An electromagnetic brake 28 is provided as an element for controlling the inflow flow rate.

The electromagnetic pump 28 is configured so that during rated operation, the flow rate is tl and O, and the IJ pump 8 can flow into the upper plenum 6 (only when the temperature of the IJ pump 8 rises abnormally). In this way, during rated operation, the heat in the upper plenum 6 will not flow into the heat exchanger 11.
Since there is no heat exchange with the outside, unnecessary heat loss can be avoided.

Figure 7 (A) shows the electromagnetic brake 2 of the flow control element in Figure 6.
8 details are shown. A part of the outer cylinder 3o is replaced with a permanent magnet 32. The polarity of the permanent magnet 32 is N N in the axial direction.
-+ S S -+ N N-+ It is arranged so that it becomes 88-tones. A ferromagnetic material is selected as the material of the inner cylinder 29, and in this way, the space of the annular flow path 31 surrounded by the inner cylinder 29 and the outer cylinder 30 has a magnetic field as shown in FIG. 7(b). , a radial or centripetal magnetic field B is generated, indicated by the dotted line. Now, when the conductive fluid sodium 8 flows into this annular flow path 3y from the bottom to the top, a current i is generated perpendicular to the magnetic field B and the flow direction. In the case of an annular flow path, it becomes a loop current. The magnitude of this current i is, however, U: vector of separation of sodium 8 (m/s), B: magnetic flux density (W/m''), vector R: electrical resistance of the current circuit (Ω), i: loop current Density (A/m''), Vector t: Length of current circuit (crn) Furthermore, an electromagnetic braking force Fs expressed by equation (3) acts on the L linodium fluid due to the interaction between the loop current and the magnetic field.

pn = = i In the embodiment, a resistive element 26 is attached to a part of the current circuit within the annular flow path. This resistance element 26 has a resistance as shown in the curve H in FIG. 8, where the horizontal axis is the upper plenum internal temperature Tok and the vertical axis is the electrical resistance R'.The electrical resistance value of the resistance element 26 is at a certain temperature T. It's low, that's it,
- to f, it increases rapidly. Therefore, the magnitude PR of the braking force of the electromagnetic brake 28 acting on the fluid is large up to a certain temperature To', and rapidly decreases when the temperature exceeds that temperature. Now the temperature is T.

If the temperature of the IJum 8 in the upper plenum 6 during rated operation is set to 540°C, for example, in the case of Fig. 6, the conductive fluid 25 in the annular flow path 31 during rated operation Since the electromagnetic braking force acts downwardly from above, the sodium 8 in the upper plenum 6 almost flows into the heat exchanger 11, so that no heat is radiated to the outside. However, when the temperature of the sodium 8 in the upper plenum 6 increases to 540° C., the braking force decreases, so the sodium 8 in the upper plenum 6 enters the heat exchanger 11 and begins cooling. The electrical resistance elements used in this example include barium titanate (BaTits) and N1crp.
e/Az alloys can be used. This embodiment has the effect of preventing cooling of the sodium 8 in the upper plenum 6 during rated operation, and has the same effects as the above embodiments.

FIG. 9 shows still other embodiments 1 to 6. The difference from the embodiment shown in FIG. 6 is that the embodiment shown in FIG. In this embodiment, the electromagnetic brake 28 is attached to the sodium outlet 16 portion.

FIGS. 10(a) and 10(b) show details of the mounting portion of the electromagnetic brake 28. A permanent magnet 32 is incorporated in the center of the sodium outlet 16 portion of the inner cylinder 29 of the heat exchanger 11, and the polarity is set to N.
N-+S S-+NN→S 5 (7) Arranged in order.

When the polarities are aligned in this way, the magnetic field B travels 9 as shown by the dotted line.
, a loop current i is generated in the annular flow path 33 by interaction with a radial, centripetal, or centripetal magnetic field B in the annular flow path 33 formed by the inner cylinder 29 and the permanent magnet 32. Furthermore, due to the interaction between this current i and the magnetic field B,
n) Braking force F is generated in the opposite direction to the flow direction of IJum 8. This braking force F is the same as the embodiment shown in FIG. 6 and can be expressed as in equation (3). That is, the braking force F
When the strength of the magnetic field is constant, B is inversely proportional to the electrical resistance R in the circuit through which the loop current i flows.

In this embodiment as well, a resistance element 26 is attached to a part of the current circuit within the annular flow path 33, as in FIG. This resistance element 26 also has the characteristics shown in FIG.

Therefore, in Fig. 9, the inside of the upper plenum 6) IJ
If the temperature of sodium 8 is 'roK, which is the temperature during rated operation, the electromagnetic valve 1/-Kika FB acts on the sodium 8 fluid, so that the sodium 8 does not flow into the heat exchanger 11, and this Therefore, there is no heat radiation to the outside. However, when the temperature becomes higher than the rated operating temperature Tn, the electromagnetic braking force FB rapidly decreases, so that the sodium 8 in the upper plenum 6 circulates from top to bottom in the inner cylinder 29 in the heat exchanger 11. become. That is, the IJ lumen 8 in the upper plenum 6 is cooled through the air cooler 12.

FIG. 11 shows yet another embodiment, and the difference from the embodiment in FIG. 1 is that the embodiment in FIG. In the example, a conductive fluid 25, which will be described later, is used. The inner surface of the permanent magnet 23 is covered with an electrically insulating material 34, and the conductive fluid 25 is enclosed within the rectangular duct 22 surrounded by the permanent magnet 23 and the electrode 24. Inside this rectangular duct 22, a DC magnetic field B is generated vertically by the permanent magnet 23, and a DC current i flows from the outside in the left to right direction. The force F shown in equation (1) is shown perpendicular to the paper →
Occurs towards the back.

The force F is applied to the conductive fluid 25 in the rectangular duct 22,
It works in conjunction with the pump driving force and, therefore, the fluid circulation force within the piping 13.

By the way, the magnitude of the force F, and therefore the circulating force within the pipe 13, is inversely proportional to the resistance R within the current circuit 27 when the strength of the magnetic field expressed by equation (1) is constant. This current circuit 2
7 includes a conductive fluid pipe 5 within a pipe 13. In this embodiment, the conductive fluid 25 has a temperature-electrical resistance characteristic as shown by curve I in FIG. 13, where the horizontal axis represents the temperature of the sodium 8 in the upper plenum 6 and the vertical axis represents the resistance. I have chosen gold. Assuming that the resistance of the conductive fluid is R6, Qt exhibits a significantly high value up to the temperature To during rated operation of the nuclear reactor, but rapidly decreases when the temperature rises above To. When a conductive fluid 25 having such characteristics is used, the loop circulation force F is close to 0 during rated operation, and increases rapidly when the temperature becomes higher than the rated operation. Examples of conductive fluids having all of these temperature-electrical resistance characteristics include alloys such as bismuth (Bi), antimony (Sb), and indium (In). In addition, not only alloys but also pure metals,
It is known that electrical resistance rapidly changes (decreases) at a certain temperature, and it is also possible to use these molten metals.9 Therefore, in the case of the configuration shown in Figure 11, the rated During operation, the heat radiated from the upper plenum 6 to the outside through the air cooler 12 is close to O. Also,
If the sodium temperature in the upper plenum 6 increases for some reason, the circulation force F increases, and the sodium chloride 8 in the upper plenum 6 is cooled through the air cooler 12. This embodiment also has the same effect as the embodiment shown in FIG.

〔Effect of the invention〕

As described above, the IJ worm cooling device of the present invention can uniformly cool the entire inside of the furnace, and has the effect of improving reliability since there are no moving parts during cooling operation.

[Brief explanation of drawings]

Fig. 1 is a detailed perspective view of the electromagnetic pump of the sodium cooling system in the reactor vessel of the present invention, Fig. 4 is a horizontal sectional view of the central part of the pump of Fig. 3, and Fig. 5 is the current circuit of the electromagnetic pump of Fig. 3. Figure 6 is an explanatory diagram of the relationship between the electrical resistance and temperature inside the reactor vessel of the present invention. Detailed view of the part, (
B) is an explanatory diagram of the body cross section of (A) -, Figure 8 is the resistance element of Figure 7 (B), jlj ・''W resistance-temperature characteristic diagram, and Figure 9 is the diagram of the inside of the furnace vessel of the present invention. ) Explanatory diagram of still another embodiment of the IJum cooling device, 1st
Figure 0 (a) is a detailed view of the electromagnetic brake part in Figure 9, (b) is a cross-sectional explanatory view of (a), and Figure 11 is a further embodiment of the in-reactor vessel sodium cooling device of the present invention. Explanatory diagram, 1st
Figure 2 is a detailed view of the electromagnetic bomb in Figure 11, and Figure 13 is a detailed view of the electromagnetic bomb in Figure 1.
Figure 2 is an explanatory diagram of the electrical resistance-temperature characteristics of a conductive fluid driven by an electromagnetic pump, Figure 14 is an explanatory diagram of the reactor internal configuration of a conventional pool-type fast reactor, and Figures 15 and 16 are respectively diagrams of conventional pool-type fast reactors. It is an explanatory view of a sodium cooling device in a furnace vessel. 1...Furnace vessel, butt...Horizontal isolation membrane, 6...Upper plenum, 7...Lower plenum, 8...Sodium, 1
1... Heat exchanger, 12... Air cooler, 13...
Piping, 14... Heat exchanger tube, 16... Sodium outlet, 17... Piping with fins, 20... Electromagnetic pump, 2
5... Conductive fluid, 26... Resistance element, 28...
Electromagnetic brake, 32° permanent magnet.

Claims (1)

[Claims] 1. A heat exchanger disposed in sodium in a reactor vessel of a liquid metal cooled fast breeder reactor, a cooler disposed outside the reactor vessel, and the heat exchanger and piping in which heat transfer tubes and finned piping installed in the cooler are connected to both ends and are filled with conductive fluid to form an endless flow path, and the furnace is not in normal operating condition. and an electromagnetic pump that drives the conductive fluid to cool the sodium in the reactor vessel, wherein the heat is disposed below a horizontal isolation membrane that divides the inside of the reactor vessel into an upper plenum and a lower plenum. The sodium outlet of the exchanger is opened, and a resistive element configured to conduct in the case of a predetermined temperature state of the electrically conductive fluid is disposed in the current circuit of the electromagnetic pump, or is a part of the current circuit. A sodium cooling device in a reactor vessel, characterized in that the conductive fluid forming the sodium cooling device is formed to become conductive when the conductive fluid reaches a predetermined temperature state. 2. The passage for the sodium in the heat exchanger is configured to be opened and closed by an electromagnetic brake consisting of a permanent magnet and a resistance element configured to conduct when the sodium reaches a predetermined temperature. An in-furnace vessel sodium cooling device according to claim 1.