JPH0713667B2 - Tank type fast breeder reactor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a fast breeder reactor, and more particularly to an improvement of a tank type fast breeder reactor.

[Background of the Invention]

Prior to the description of the present invention, an example of the internal structure of a conventionally known tank type fast breeder reactor will be described with reference to FIG.

In FIG. 11, a reactor vessel 1 is supported by a disc-shaped roof slab 2 on the upper portion thereof, and the roof slab 2 is fixed to a reactor building wall 4 via a support cylinder 3. A reactor core 5 is located in the center of the inside of the reactor vessel 1, and the reactor core 5 has a core support structure 6 fixed to the reactor vessel 1.
Is supported through. An upper core mechanism 7 is installed above the core 5, and the upper core mechanism 7 is attached to the roof slab 2. In the upper core mechanism 7,
A control rod drive mechanism (not shown) is installed, and the output of the core 5 can be controlled by operating this control rod drive mechanism to insert or pull out the control rod from the core 5. The upper core mechanism 7 is equipped with a measuring instrument for measuring the flow rate of sodium as a coolant and the temperature of the core 5. In the peripheral part of the reactor vessel 1,
Through the roof slab 2 so as to surround the core 5,
Multiple intermediate heat exchangers 8,8 …… and main circulation pumps 9,9…
... has been inserted. The intermediate heat exchanger 8 is a shell and tube type heat exchanger that transfers the heat of the primary sodium to the sodium of the secondary cooling system (not shown). The primary sodium, which is a coolant, is heated in the core 5 and then heated.
Flows into the high temperature plenum 10 at the upper part of the heat exchanger 8 and then flows into the heat exchanger 8 through the coolant inlet 11 formed in the shell of the intermediate heat exchanger 8. Secondary sodium, which absorbs the heat of the primary sodium, flows into the heat exchanger 8 from the coolant inlet 12 of the intermediate heat exchanger 8, takes heat from the primary sodium, and flows out from the coolant outlet 13. The primary sodium that has undergone heat exchange in the intermediate heat exchanger 8 reaches a low temperature plenum 14 at a low temperature. In the tank type fast breeder reactor, a partition wall 15 is provided in the reactor vessel 1 so that the high temperature sodium in the high temperature plenum 10 and the low temperature sodium in the low temperature plenum 14 do not mix. Also,
In the intermediate plenum 16 located between the partition wall 15 and the core support structure 6, the high temperature plenum 10 and the low temperature plenum 14 are thermally shielded by stagnant sodium. The main circulation pump 9 sucks and raises the temperature of the low temperature sodium in the low temperature plenum 14 and supplies it to the lower side of the core 5 through the coolant discharge pipe 17, and the low temperature sodium supplied to the lower side of the core 5. Are distributed from the high pressure plenum 18 to the core 5. As described above, in the tank-type fast breeder reactor, the primary sodium circulates in the reactor vessel 1. However, in case of boundary breakage, the reactor vessel 1 is stored in the safety vessel 19 and The safety container 19 is fixed to the reactor building wall 4 via a support cylinder 20 by preventing leakage of the core 5 by preventing leakage. In the figure,
Reference numeral 21 denotes a fuel exchanger, and the fuel, not shown, is loaded and exchanged on the core 5 by the fuel exchanger 21.

FIG. 12 is a scram time elapsed-coolant flow rate ratio / temperature characteristic diagram at the core outlet when the tank type fast breeder reactor shown in FIG. 11 scrams.

When the nuclear reactor shown in FIG. 11 is scrammed, the control rod is inserted into the core 5, so that the output of the core 5 decreases and the temperature of sodium at the outlet of the core 5 also decreases. Then, after that, due to the decay heat of the core 5, the outlet temperature of the core 5 temporarily rises, but the outlet temperature of the core 5 falls again due to the decrease of the decay heat with the passage of time. At this time, the flow rate of sodium supplied to the main circulation pump 9 decreases at the same time as the reactor scrum, and is maintained at about 8% of the rated flow rate. In this way, in the tank type fast breeder reactor, during the reactor scrum,
When the temperature and flow rate of sodium at the outlet of the core 5 decrease, the temperature of sodium flowing out of the core 5 into the high temperature plenum 10 changes from a high temperature state to a low temperature state during reactor rated operation. , In this process, high-density sodium with a low density is at the top of the high-temperature plenum 10,
The dense low temperature sodium stays at the bottom of the high temperature plenum 10. The so-called thermal stratification phenomenon easily occurs. Therefore, the above-mentioned temperature stratification phenomenon is inserted into the high temperature plenum 10 in order to create a so-called temperature stratification interface that divides the high temperature sodium and the low temperature sodium into upper and lower parts and to generate a sharp temperature gradient in the height direction. It must be expected that thermal deformation will be applied to the core upper part mechanism 7, the intermediate heat exchanger 8, the main circulation pump 9, the reactor vessel 1, and the like. When the temperature stratification phenomenon as described above occurs, the sodium flowing out from the core 5 is not sufficiently mixed in the high temperature plenum 10 and the intermediate heat exchanger 8
Since it flows into the heat exchanger 8, excessive cold shock is added to the heat exchanger 8 and thermal stress is generated in the intermediate heat exchanger 8.

In addition, Japanese Patent Laid-Open No. 59-88687 discloses a technique of stirring the inside of a high temperature plenum by using a bypass flow from a main circulation pump.

By the way, during the reactor slam, in the low temperature plenum 14, due to the heat flux from the high temperature plenum 10, high density sodium having a low density is generated on the upper portion of the low temperature plenum 14, in other words, on the lower surface of the outer peripheral portion of the core support structure 6. The low-temperature sodium having a high density stays in the lower part of the low-temperature plenum 14 and a sharp temperature gradient is generated in the height direction as in the high-temperature plenum 10 described above, so that the core support structure 6 is thermally deformed. It must be expected that the addition and removal of the control rod makes it difficult to insert and pull out the control rod from the core 5.

In addition to this, since the partition wall 15 heated to a high temperature exists above the low temperature plenum 14, a temperature stratification phenomenon occurs in the low temperature plenum 14 even during steady operation, and the core support structure is generated. It is also necessary to consider that the object 6 may be thermally deformed.

However, heretofore, the thermal stratification phenomenon in the low temperature plenum has not been recognized.

[Object of the Invention]

The object of the present invention is not only to eliminate the temperature stratification phenomenon in the high temperature plenum, but also to the lower surface of the outer peripheral portion of the core support structure which is the upper part of the low temperature plenum due to the heat flux from the high temperature plenum during the reactor scram. High-temperature sodium with a low density stayed, and low-temperature sodium with a high density stayed at the bottom of the low-temperature plenum, and an attempt was made to generate a sharp temperature gradient in the height direction. Even if there is a partition wall and the temperature stratification phenomenon occurs in the low temperature plenum during steady operation, it can be eliminated and the thermal deformation of the core support structure can be prevented. It can be greatly reduced. It is to provide a tank type fast breeder reactor with excellent safety.

[Outline of Invention]

The above-mentioned purpose is a reactor vessel containing a coolant inside, a core installed in the reactor vessel, a core upper part mechanism attached to the reactor vessel located above the core, and located around the core. Partition wall that divides the reactor vessel into a high-temperature plenum and a low-temperature plenum, a main circulation pump that sucks the coolant in the low-temperature plenum and sends it to the core, and heat-exchanges the coolant heated in the core in the high-temperature plenum. In a tank type fast breeder reactor equipped with an intermediate heat exchanger which is then transferred to a low temperature plenum, a part of the coolant passing through the inside of the main circulation pump is branched into the high temperature plenum. Introduced,
In addition to the means for agitating the coolant in the high temperature plenum to prevent the temperature stratification phenomenon from occurring in the coolant in the plenum, it is also located on the discharge side of the main circulation pump and A part of the coolant that passes through is introduced into the low-temperature plenum, and the coolant in the low-temperature plenum is agitated to prevent the temperature-stratification phenomenon from occurring in the coolant in the plenum. Achieved by

Example of Invention

The present invention will be described below with reference to an embodiment shown in FIGS. 1 to 7. FIG. 1 is a vertical cross-sectional view around a main circulation pump, which is an essential part of the present invention. As in the conventional case, a single-stage double-blown pump is used. That is,
In FIG. 1, the main casing 9 has an outer casing.
22 and an inner casing 23 are provided, a pump rotating shaft 24 is mounted at the center of the inner casing 23, and an impeller 25 is attached to the lower end of the pump rotating shaft 24. Reference numeral 26 indicates a bearing stand attached to the inner casing 23, 27 indicates a static pressure bearing fixed on the bearing stand 26, 29 indicates a static pressure bearing fixed on the bearing stand 28, and the pump rotary shaft 24 indicates the static pressure bearing 27 and Supported by 29, impeller 25
Is located within Diff User 30. The pump rotation shaft 24 is rotated by a motor (not shown) connected to the upper end of the rotation shaft 24. When the pump rotary shaft 24 and, by extension, the impeller 25 are rotated by a motor (not shown), sodium in the low temperature plenum 14 is located at the lower end of the bearing base 26, that is, the coolant suction pipe 31 → the upper end of the bearing base 28. Coolant discharge casing in a pressurized state through the coolant suction pipe 32 → impeller 25 → differential user 30
It is discharged into the inside 33 and is then discharged into the high pressure plenum through the coolant discharge pipe 17. The above-mentioned coolant discharge pipe
17 is fixed to an outer cylinder 34 surrounding the main circulation pump 9.

Reference numeral 35 denotes a coolant supply pipe branched from the coolant discharge casing 33, and the coolant supply pipe 35 is opened at an upper portion of the low temperature plenum 14. 36 is a drawing pipe of the coolant discharge casing 33, 37
Shows a coolant flow passage switching mechanism connected to the drawing pipe 36, and this coolant flow passage switching mechanism 37 includes a coolant supply pipe 38 opening at an upper portion of the high temperature plenum 10 and a coolant discharge pipe 17. A coolant return pipe 39 that opens is connected to a control pipe 40 that opens midway in the piping system from the low temperature plenum 14 to the main circulation pump 9. A plurality of main circulation pumps 9, 9 ... Are inserted through the roof slab so as to surround the reactor core in the peripheral portion of the reactor vessel 1. Plural coolant supply pipes 35,35 connected to 9
…… and 38, 38 …… are the reactor vessels 1 respectively.
Is connected to the loop pipes 41 and 42 arranged in the circumferential direction of, and the coolant from the coolant supply pipes 35, 35 ... And 38, 38. It is jetted to the upper portions of the low temperature plenum 14 and the high temperature plenum 10 via the injection holes formed in the pipes 41 and 42, respectively.

Therefore, according to the above-described configuration, not only the temperature stratification phenomenon in the high temperature plenum 10 is eliminated, but the heat flux from the high temperature plenum 10 causes the core support structure which is the upper portion of the low temperature plenum 14 during the reactor scram. High-temperature sodium with a low density stays on the lower surface of the outer periphery of the
Even if a low-temperature sodium having a high density stays in the lower part of the tank and a steep temperature gradient is generated in the height direction, a partition wall heated to a high temperature exists above the low-temperature plenum 14.
Even if a temperature stratification phenomenon occurs in the low temperature plenum 14 during steady operation, this phenomenon can be eliminated and thermal deformation of the core support structure can be prevented.

Here, the principle of operation of the pure fluid element which is suitable for the coolant flow path switching mechanism 37 will be described with reference to FIG.

In FIG. 2 showing the OR / NOR gate, the main fluid flows in from the fluid supply port 43, and the main fluid that has passed through the main nozzle 44 is the arrow F when there is no control fluid from the control port 45. Go straight in the direction indicated by ₁ and turn to fluid output port 46
Drained from. In contrast, control fluid F ₂
, The main fluid is influenced by the control fluid F ₂ and is bent as shown by an arrow F ₃ to flow out from the output port 47. FIG. 3 is a symbolic view of the pure fluid element shown in FIG. 2, and the reference numerals shown in FIG. 2 and the reference numerals shown in FIG. 3 coincide with each other.

FIG. 4 shows a concrete example in which the pure fluidic device shown in FIG. 2 is adopted in the coolant flow path switching mechanism of the reactor of the present invention,
In FIG. 1 and FIG. 4, the coolant discharge casing 33
The withdrawal pipe 36 to the fluid supply port 43, the control pipe 40 from the cold plenum 14 to the control port 45, the fluid output port 46 to the coolant return pipe 39 opening to the coolant discharge pipe 17, and the fluid output port 47 to Coolant supply pipe 38 opening at the top of the high temperature plenum 10.
Respectively connected to.

FIG. 5 is a pressure-flow rate characteristic diagram of a fluid flowing in the pure fluid element shown in FIG. 2 to 5,
When the fluid pressure P _C of the control port 45 is small, the flow direction of sodium in the pure fluid element goes straight as shown by the arrow F ₁ in FIG. 2 and flows out from the fluid output port 46. Pressure P _C is the fluid pressure at fluid supply port 43
When it reaches α times P _S , the flow path in the pure fluid element switches and sodium flows out from the fluid output port 47. The value of α described above is 0.1 to 0.3 for a pure fluid element that has been generally used conventionally. In addition, when the flow path in the pure fluid element is switched from the output port 46 to 47,
As shown in the figure, the decrease in the sodium flow rate is indicated by the arrow in FIG. 2 in which the fluid flow is directed to the output port 46.
This is because the control fluid F ₂ is entrained from the control port 45 at the time of F ₁ . When the fluid pressure P _C of the control port 45 decreases and this fluid pressure P _C reaches β times the fluid pressure P _S of the supply port 43, the flow path in the pure fluid element is switched, and sodium is returned to the output port. Spill out of 46. The value of β and the value of α do not match, and the value is approximately 0.02 for a pure fluid element that has been generally used in the past, and the reason why the value of α does not match the value of β is This is because the wall adhesion characteristics of the fluid indicated by the symbol F ₁ and the fluid indicated by F ₃ in FIG. 2 are different. Thus, the switching of the pure fluid element shown in FIG. 2 is determined by the ratio of the fluid pressure P _S of the supply port 43 and the fluid pressure P _C of the control port 45.

FIG. 6 is a rotational speed-lift head change characteristic diagram of the main circulation pump during steady operation of the reactor and during scram.

1 to 4, and FIG. 6 showing the relationship between the number of revolutions of the main circulation pump and the dimensionless lift (P _S −P _C ) / P _S , in the steady operation of the main circulation pump 9, the pump 9 The fluid supply port 43 communicating with the coolant discharge casing 33 of the low temperature plenum 14 (on the side of the main circulation pump 9 on the suction side).
Since a pressure sufficiently higher than that of the control port 45 communicating with the fluid is applied, sodium passing through the coolant flow path switching mechanism 37 constituted by the pure fluid element flows out from the fluid output port 46. When the reactor scrams and the number of revolutions of the main circulation pump 9 decreases, the head of the pump 9 also decreases accordingly. As shown in FIG. When it is decreased to −α, the flow path in the pure fluid element is switched, and sodium flows out from the fluid pressure port 47. Therefore, the sodium flowing out from the output port 47 is jetted to the upper part of the high temperature plenum 10 through the coolant supply pipe 38 connected to the output port 47.
On the contrary, at the time of starting the reactor, when the number of revolutions of the main circulation pump 9 increases and the dimensionless head of the pump 9 reaches 1-β, the flow path in the pure fluid element is switched again. , Sodium flows out from the output port 46 and does not flow out from the output port 47, so that the sodium injection from the coolant supply pipe 38 to the upper portion of the high temperature plenum 10 is stopped.

FIG. 7 is a characteristic diagram of a time lapse of scrum-coolant temperature difference in a high temperature plenum during a reactor scram.

In Fig. 1 and Fig. 7 showing transient changes in the temperature difference between the upper and lower sides (temperature difference between the temperature stratification interface) in the high temperature plenum during the reactor scram, high temperature sodium passing through the core is called the main circulation flow. , Coolant discharge casing 33
When low temperature sodium ejected from the high temperature plenum 10 through the flow path switching mechanism 37 is referred to as a bypass flow, when the bypass flow rate is 0%, the temperature difference above and below the temperature stratification interface in the high temperature plenum 10 does not change, A constant state is maintained over a long period of time. In contrast, the coolant discharge casing
When there is a so-called bypass flow in which low temperature sodium is jetted from the 33 to the high temperature plenum 10 via the flow path switching mechanism 37, in the high temperature plenum 10, the high temperature sodium staying at the upper portion is the low temperature sodium (bypass flow). Therefore, the temperature difference between the upper and lower sides of the thermal stratification interface decreases rapidly with time. High temperature plenum during reactor scrum
When analyzing the temperature difference between the upper and lower sides within 10 as a transient change,
If the bypass flow rate and the main circulation flow rate are equal,
From Fig. 7, the time elapsed approximately 30 minutes after the reactor scrum,
It can be seen that the temperature difference above and below the thermal stratification interface in the high temperature plenum 10 is reduced to about 10%. That is, at the time of reactor scram, even in the high temperature plenum 10, low temperature sodium is ejected from above the high temperature plenum 10, sodium in the high temperature plenum 10 is forcibly stirred, and the temperature stratification interface is destroyed, Since the temperature of sodium changes gradually, the thermal stress applied to the reactor structure such as the intermediate heat exchanger 8 can be small. Further, in the present invention having the above-mentioned configuration, since the low temperature bypass flow is not injected from the outside to the high temperature main circulation flow passing through the core, the sodium inventory in the reactor vessel 1 is almost constant. Therefore, it is possible to prevent an overload from being applied to the support cylinder 20 that supports the reactor vessel 1. Moreover, as shown in the illustrated embodiment, the coolant passage switching mechanism 37 is provided on the discharge side of the main circulation pump 9 so as to bypass, and the switching operation of the passage switching mechanism 37 ensures that only during the reactor scram.
By selectively introducing the sodium flowing from the main circulation pump 9 into the coolant flow path switching mechanism 37 into the high temperature plenum 10, the heat loss of sodium circulated in the reactor vessel 1 can be minimized. In addition to this, if a pure fluid element having no mechanical operation part such as a ball, a diaphragm, or a spool is used as the coolant flow path switching mechanism 37,
It is possible to obtain the coolant flow path switching mechanism 37 which has no failure, is safe and reliable in operation, and has excellent durability.

FIG. 8 is an explanatory view of the principle of operation of the wall-adhesion type pure fluid element different from FIG. 2, and as will be apparent from the following description, the pure fluid element shown in FIG. If
Unlike the pure fluidic device shown in FIG. 2, the flow path in the fluidic device can be switched without requiring the control port 45. That is, in FIG. 8, the width of the main nozzle 44 is h, the radius of curvature of the passage surface facing the fluid output port 47 is R, the velocity of the fluid ejected from the main nozzle 44 is u, and the fluid passes through the pure fluid element. When the kinematic viscosity of the fluid is v,
Its characteristic Reynolds number R _e is defined as

In the above, when R _e becomes a turbulent flow of (1.4 to 3.5) × 10 ⁴ or more, the state of the fluid flow becomes constant regardless of R _e , and the fluid flowing from the fluid supply port 43 into the element is As shown by an arrow F ₃ in FIG. 8, the flow adheres to the wall surface of the pure fluid element and flows out from the fluid pressure port 47. In contrast,
When R _e becomes (1.4 to 3.5) × 10 ⁴ or less, the fluid flowing into the element from the supply port 43 goes straight away from the wall surface of the element and flows out from the fluid output port 46.
According to the pure fluid element shown in FIG. 8, the outflow direction of the fluid passing through the main nozzle 44 can be switched to the two output ports 46 or 47 by changing the flow rate of the fluid flowing into the supply port 43. FIG. 9 is a symbolic view of the pure fluidic device shown in FIG. 8, and the reference numerals shown in FIG. 8 and the reference numerals shown in FIG. 9 coincide with each other.

FIG. 10 shows a specific example in which the pure fluidic device shown in FIG. 8 is adopted in the coolant flow path switching mechanism of the reactor of the present invention,
In FIG. 1 and FIG. 10, the coolant discharge casing 33
Unlike the case of FIG. 4, the extraction pipe 36 of the fluid supply port 43 is different from that of FIG. Are connected to the coolant return pipes 39 opening at the respective ends. When the pure fluidic device shown in FIG. 8 is adopted for the coolant flow path switching mechanism 37, the switching of the flow path in the fluidic device is determined by the change in the flow rate of the fluid flowing into the supply port 43. However, unlike the pure fluidic device shown in FIG. 2, it does not require the control port 45,
The laying of the control pipe 40 from the low temperature plenum 14 to the control port 45 can be omitted.

〔The invention's effect〕

According to the present invention, in addition to eliminating the thermal stratification phenomenon in the high temperature plenum, the heat flux from the high temperature plenum during the reactor scram causes the lower surface of the outer periphery of the core support structure, which is the upper portion of the low temperature plenum. High-temperature sodium with a low density stayed, and low-temperature sodium with a high density stayed at the bottom of the low-temperature plenum, and an attempt was made to generate a sharp temperature gradient in the height direction. Even if the partition wall is present and the temperature stratification phenomenon occurs in the low temperature plenum during the steady operation, it can be eliminated, and the thermal deformation of the core support structure can be prevented.

That is, according to the present invention, the temperature stratification phenomenon not only in the high temperature plenum but also in the low temperature plenum, that is, the steep temperature gradient in the height direction in both the high and low temperature plenums is eliminated, and the heat for the reactor structure is eliminated. The deformation can be significantly reduced as compared with the conventional one.

[Brief description of drawings]

1 to 7 show an embodiment of a tank type fast breeder reactor according to the present invention, FIG. 1 is a longitudinal sectional view around a main circulation pump which is an essential part of the present invention, and FIG. 2 is a main circulation. FIG. 3 is a diagram for explaining the operation principle of a pure fluid element for switching a coolant flow path incorporated around a pump, FIG. 3 is a symbol diagram of the pure fluid element shown in FIG. 2, and FIG. 4 is a diagram showing the pure fluid element shown in FIG. Fig. 1 is an explanatory view of the piping system when connected around the main circulation pump, Fig. 5 is a pressure-flow rate characteristic diagram of the fluid flowing in the pure fluid element shown in Fig. 2, and Fig. 6 is during steady operation of the reactor. -Speed characteristic curve of the main circulation pump during and during scram, Fig. 7 shows the elapsed time of scrum in the high temperature plenum during reactor scram-
Coolant temperature difference characteristic diagram, FIGS. 8 to 10 show another embodiment of the present invention, and FIG. 8 is an explanation of the operating principle of the pure fluid element for switching the coolant flow path incorporated around the main circulation pump. Fig. 9 and Fig. 9 are symbolic views of the pure fluidic device shown in Fig. 8, and Fig. 10 is
Piping system explanatory diagram when the pure fluid element shown in the figure is connected around the reactor main circulation pump, FIG. 11 is a longitudinal sectional view showing an example of the internal structure of a conventionally known tank type fast breeder reactor, FIG. Is the scram time elapsed at the core outlet when the tank type fast breeder reactor shown in Fig. 11 scrums-coolant flow rate ratio
It is a temperature characteristic diagram. 1 ... Reactor vessel, 2 ... Roof slab, 3 ... Support cylinder, 4 ... Reactor building wall, 5 ... Reactor core, 6 ... Reactor support structure, 7 ... Reactor upper mechanism, 8 ... Intermediate heat exchanger, 9
...... Main circulation pump, 10 …… High temperature plenum, 11 and 12…
… Coolant inlet, 13 …… Coolant outlet, 14 …… Low temperature plenum, 15 …… Baffle, 16 …… Intermediate plenum, 17 …… Coolant discharge pipe, 18 …… High pressure plenum, 19 …… Safety container , 20 ……
Support tube, 21 …… Fuel exchanger, 22 …… Outer casing, 23
...... Inner casing, 24 …… Pump rotating shaft, 25 …… Impeller, 26 …… Bearing stand, 27 …… Hydraulic bearing, 28 …… Bearing stand,
29 …… Hydrostatic bearings, 30 …… Diff users, 31 and 32 ……
Coolant suction tube, 33 ... Coolant discharge casing, 34
…… Outer cylinder, 35 …… Coolant supply pipe, 36 …… Drawer pipe, 37 ……
Coolant flow path switching mechanism, 38 ... Coolant supply pipe, 39 ... Coolant return pipe, 40 ... Control pipe, 41 and 42 ... Loop pipe,
43 …… Fluid supply port, 44 …… Main nozzle, 45 …… Control port, 46 and 47 …… Fluid output port.

Claims (3)

[Claims] 1. A reactor vessel containing a coolant therein, a core installed in the reactor vessel, a reactor core upper mechanism located above the reactor core and attached to the reactor vessel, and located around the reactor core. To partition the inside of the reactor vessel into a high temperature plenum and a low temperature plenum, a main circulation pump that sucks the coolant in the low temperature plenum and sends it to the core, and heats the coolant heated in the core in the high temperature plenum. In a tank type fast breeder reactor equipped with an intermediate heat exchanger that is exchanged and then transferred to a low temperature plenum, a part of the coolant passing through the inside of the pump is located on the discharge side of the main circulation pump. Branch introduced,
In addition to the means for agitating the coolant in the high temperature plenum to prevent the temperature stratification phenomenon from occurring in the coolant in the plenum, it is also located on the discharge side of the main circulation pump and A part of the coolant passing through the branch is introduced into the low temperature plenum, the coolant in the low temperature plenum is agitated, and a means for preventing the temperature stratification phenomenon from occurring in the coolant in the plenum is provided. A tank type fast breeder reactor. 2. The coolant flow path according to claim 1, wherein a coolant flow path is provided on the discharge side of the main circulation pump by a change in coolant flow rate passing through the main circulation pump during steady reactor operation and scram. The coolant flow path switching mechanism for switching is provided by bypass, and by the switching operation of this flow path switching mechanism, the coolant flowing from the main circulation pump into the coolant flow path switching mechanism is cooled to a high temperature plenum only when the coolant flow rate decreases. Selectively introduced to
While stirring the coolant in the plenum to prevent the temperature stratification phenomenon from occurring in the coolant in the plenum,
A tank type equipped with means for merging the coolant flowing into the coolant flow path switching mechanism from the main circulation pump with the main circulation flow in the coolant discharge pipe opening below the core except when the flow rate of the coolant is reduced. Fast breeder reactor. 3. The tank type fast breeder reactor according to claim 2, wherein the coolant flow path switching mechanism is a pure fluid element.