JPH07209470A - Decay heat removing device for fast reactor - Google Patents

Abstract

PURPOSE:To avoid the freezing of secondary sodium in a heat transfer pipe in an air cooler, ensure the flow of the secondary sodium, and keep heat eliminating function. CONSTITUTION:A lower header 19 is connected to the lower end of a heat transfer pipe 12, and a descending pipe 10 is connected to the downstream side secondary sodium outlet port of the lower header 19. Heat transfer pipe headers 21a, 21b are connected to the upstream side heat transfer pipes 12a, 12b of the lower header 19, and bypass pipes 22a, 22b are connected between the heat transfer pipe headers 21, 21b and the descending pipe 10. The bypass pipes 22a, 22b has stop valves 23a, 23b, and heaters 24a, 24b are wound on the bypass pipes between the stop valves 23a, 23b and the descending pipe 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fast reactor decay heat removal apparatus for directly removing decay heat after a reactor shutdown in a fast breeder reactor (hereinafter referred to as "fast reactor") by a core cooling system (hereinafter referred to as "DRACS"). Regarding

[0002]

2. Description of the Related Art In order to ensure the safety of a power generation plant, it is necessary to surely stop a nuclear reactor when the plant is abnormal and to reliably remove decay heat after the reactor shutdown. DRACS cools the core with a heat exchanger that is directly immersed in the reactor vessel, and as a removal method that does not depend on dynamic equipment as much as possible, DRACS in the natural environment is drawing attention.

Regarding this DRACS, FIG.
Description will be given with reference to (b). In FIG. 5 (a), reference numeral 1 is a reactor vessel, in which a reactor core portion 2 is disposed, and an inlet pipe 4 for introducing the primary sodium 3 of the coolant into the reactor core portion 2 and a primary sodium 3 are provided. An outflow pipe 5 that flows out is connected to a side wall of the furnace vessel 1. A plug 6 for closing the upper end opening of the furnace container 1 is provided.

A heat exchanger 7 is immersed in the primary sodium 3 of the upper plenum 20 in the furnace vessel 1, and in this heat exchanger 7, an ascending pipe 9 and a descending pipe 10 through which secondary sodium flows.
One end of is connected. The other ends of the ascending pipe 9 and the descending pipe 10 are connected to a heat transfer pipe 12 in the air cooler 8.

An electromagnetic pump 11 is provided on the outer side of the rising pipe 9, and the electromagnetic pump 11 circulates secondary sodium in the heat exchanger 7 and the heat transfer pipe 12. Further, the air cooler 8 is provided with an upper damper 13 at the upper portion, a vane 14 and a damper 15 at the lower portion, and the lower damper 15 is connected to a blower 16.

The air cooler 8 has an upper header 18 and a lower header 19 connected to a housing 17 as shown in FIG. 5B, and the upper header 18 rises as shown in FIG. 1B. Tube 9
Is connected to the upper end of the heat transfer tube 12, and the lower header 19 is
And the lower end of the heat transfer tube 12 are connected.

Thus, in the decay heat removal apparatus for a fast reactor having the above structure, the primary sodium heated by the decay heat of the core 2 flows into the heat exchanger 7 at the upper plenum 20.
Heat exchange with secondary sodium. The secondary sodium flows into the air cooler 8 through the rising pipe 9 by the drive of the electromagnetic pump 11, and is heat-exchanged with the air which is the final heat sink. During normal operation, heat removal by the air cooler 8 is unnecessary, so the air flow is shut off by the dampers 13, 15.

When the nuclear reactor is stopped, the dampers 13 and 15 are opened, and air is sent by the blower 16 to remove heat, but the decay heat decays with time, so the vane 14 controls the amount of blown air. Further, even when the blower 16 is stopped, the cooling can be maintained by the natural circulation due to the temperature difference between the air cooler 8 and the upper plenum 20. Secondary sodium flows into the upper header 18 from the upper part, descends in the plurality of heat transfer tubes 12, releases heat, and flows out from the lower header 19.

[0009]

The decay heat removal device having the above-mentioned configuration is operated by opening the damper 15 and limiting the air flow rate by the vane 14, but the control function of the vane 14 is lost due to some cause. If you do, heat is removed more than needed.

Therefore, secondary sodium is contained in the air cooler 8
There is a case where the heat removal function is completely lost due to freezing in the inside and stop of the flow, which is a serious problem in reliability for the core. In order to solve these problems, the drive devices for the dampers 13 and 15 and the vanes 14, the diversification of the drive speed, and the like are being studied, but they are not the fundamental solutions to the problems.

The present invention has been made in order to solve the above-mentioned problems, and it is not to completely prevent the freezing of secondary sodium itself, but to avoid the freezing part to ensure the flow of secondary sodium. The purpose of the present invention is to maintain a heat removal function, and to provide a reliable decay heat removal device for a fast reactor that can avoid serious damage to the core by a relatively simple equipment change.

[0012]

SUMMARY OF THE INVENTION The present invention is directed to a heat exchanger immersed in primary sodium in an upper plenum in a furnace vessel, and a riser pipe having one end connected to which secondary sodium flows. A downcomer pipe, a heat transfer pipe through which the secondary sodium flows connected to the other ends of the upcomer pipe and the downcomer pipe through an upper header and a lower header, an air cooler incorporating the heat transfer pipe, and an air cooler In a decay heat removal apparatus for a fast reactor equipped with a vane and upper and lower dampers provided in, a heat transfer tube header is connected to a heat transfer tube portion upstream of the lower header, and the heat transfer tube header and the lower header are connected. A bypass pipe is provided via a valve between the secondary sodium outlet side and the downcomer pipe.

The present invention also provides a heat exchanger immersed in primary sodium of an upper plenum in a furnace vessel, and an up-and-down pipe through which secondary sodium flows, one end of which is connected to the heat exchanger, The heat transfer pipe connected to the other ends of the ascending pipe and the descending pipe through the upper header and the lower header, through which the secondary sodium flows, an air cooler including the heat transfer pipe, and the air cooler In a decay heat removal apparatus for a fast reactor comprising a vane and upper and lower dampers, a heat transfer tube header is connected to a lower portion of the heat transfer tube in the air cooler, and the heat transfer tube header and the lower header are connected to each other. It is characterized by connecting a heat transfer tube having a larger thermal resistance than the heat tube header.

Further, according to the present invention, the heat exchanger immersed in the primary sodium of the upper plenum in the furnace vessel, and the rising pipe and the descending pipe through which the secondary sodium flows, one end of which is connected to the heat exchanger, The heat transfer pipe connected to the other ends of the ascending pipe and the descending pipe through the upper header and the lower header, through which the secondary sodium flows, an air cooler including the heat transfer pipe, and the air cooler In a decay heat removal apparatus for a fast reactor comprising a vane and upper and lower dampers, a heat transfer tube header is connected to a lower part of the heat transfer tube in the air cooler, and the heat transfer tube header and the lower header are bypassed. It is characterized by connecting short tubes made of non-freezing material.

[0015]

[Function] By providing a plurality of headers and bypass pipes in the lower part of the air cooler so that the secondary sodium upstream of the freezing part can flow out through the bypass pipes, the secondary sodium descends from the inlet, The part that freezes when the temperature drops is usually the bottom of the heat transfer tube. Therefore, if the bypass flow passage can be secured from the lower header, the heat removal function at the upstream portion can be maintained.

By installing a valve in the bypass pipe in order to prevent the flow to the bypass pipe during normal operation, there is no effect on the heat removal function when no abnormality occurs. In addition, the heat resistance of a part of the heat transfer tube is increased, and a heat transfer tube that does not freeze even under the worst conditions is provided to secure the flow path. Further, it is to partially provide a heat transfer tube whose length is practically shortened.

The secondary sodium in the air cooler may freeze at temperatures below the freezing temperature (about 100 ° C.), but the most severe condition is that the temperature of the upper plenum located above the core is low This is the case when the temperature drops to about 200 ° C and forced circulation of sodium by the electromagnetic pump is not possible.

In such a case, if the secondary sodium in the air cooler freezes, the heat removal function deteriorates and the temperature of the upper plenum gradually rises. The rate of temperature rise is slow and sufficient for the operator to notice and take action.

Therefore, by opening the bypass pipe by the operator, the flow of secondary sodium can be secured and the amount of heat removed on the upstream side of the freezing part is maintained. Also, as a method not expected for operator operation, by installing a valve that automatically opens near the freezing temperature or partially installing a heat transfer tube with a large heat transfer tube with a large thermal resistance, It is also possible to ensure the flow of secondary sodium in the air cooler after freezing.

[0020]

EXAMPLE A first example of the decay heat removal apparatus for a fast reactor according to the present invention will be described with reference to FIG. In addition,
FIG. 1B shows a conventional example, which is also shown for comparison with the present example.

Since the air cooler of the decay heat removing apparatus is improved in this embodiment, only the main parts thereof are schematically shown in FIG. 1, and the other parts are omitted. Therefore, in this embodiment, only the points of improvement different from the conventional example will be mainly described.

That is, in FIG. 1A, the lower header 19 is connected to the lower end of the heat transfer tube 12 formed in a meandering shape,
The downcomer pipe 10 serving as a secondary sodium outlet is connected to the downstream side of the lower header 19.

The heat transfer tube portions 12a, 12 of the freezing predicting portion 28 where the secondary sodium on the upstream side from the lower header 19 is expected to freeze
The heat transfer tube headers 21a and 21b are connected to b respectively, and the bypass tube 22 is provided between the heat transfer tube headers 21a and 21b and the downcomer 10.
Connect a and 22b. Stop valves on the bypass pipes 22a and 22b
23a and 23b are connected, and heaters 24a and 24a are provided on the outer peripheral surfaces of the bypass pipes 22a and 22b between the stop valves 23a and 23b and the downcomer pipe 10.
24b is wound.

In the first embodiment, however, the secondary sodium flowing through the rising pipe 9 flows into the upper header 18, then descends while meandering the heat transfer pipe 12, and flows out through the lower header 19.

The inlet temperature of the secondary sodium is 200 ° C. in the lowest case, and since it flows down until it freezes at about 100 ° C., the freezing predicting portion 28 reaches the downcomer pipe 10 near the outlet of the secondary sodium on the downstream side.

According to the calculation, if the air inlet temperature is 11 ° C or higher, the result is obtained that the secondary sodium does not freeze up to 100 ° C or higher even in the natural circulation state on both the secondary sodium side and the air side. There is. Therefore, even if the air inlet temperature is further reduced, most of the sodium in the heat transfer tube will not reach the freezing temperature.

However, the frozen portion is the heat transfer tube header 21.
When it occurs between a and the lower header 19, by opening the stop valve 23a, the secondary sodium reaches the outlet from the header 21a via the bypass pipe 22a. Therefore, the amount of heat removed from the upper header 18 to the heat transfer tube header 21a can be secured.

Similarly, the heat transfer tube header 21b having a frozen portion above
And the lower heat transfer tube header 21a, the stop valve 23
Open b. Therefore, the upper header 18 heat transfer tube header 21b
It is possible to secure the heat removal amount up to.

However, in the above-mentioned operation, the heaters 24a and 24a are provided in order to prevent freezing in the bypass pipes 22a and 22b.
b must be provided and preheated before opening the stop valves 23a, 23b.

According to this embodiment, the damper of the air cooler 8 is
Loss of heat removal function caused by freezing of secondary sodium due to misopening of 13, 15 and vanes 14 etc.
It can be avoided by using a and 21b and bypass pipes 22a and 22b. Further, when the normal heat removal mode is maintained, the bypass pipes 22a and 22b are closed by the stop valves 23a and 23b, so that the normal heat removal function can be maintained.

The freezing of the secondary sodium described above can be performed by installing a flow meter in the downcomer pipe 10 or the upcomer pipe 9, and further, the heat transfer pipe header 21 described above.
It is possible to detect when the secondary sodium temperature reaches a predetermined value (for example, sodium freezing temperature) by installing a temperature detecting means in a and 21b. Then, the stop valve 23 is output by the output of the freeze signal by the sodium freeze detecting means.
By automatically opening a and 23b, the heat removal function can be reliably maintained.

Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment differs from the first embodiment in that a bimetal valve is provided at the open end of the bypass pipe 22 as shown in an enlarged view in FIG. 2 (b). Since the other parts are the same as those in the first embodiment, the description thereof will be omitted.

According to the second embodiment, the bypass pipe 22a,
Since the closing of 22b can be automatically released at the time of freezing, the valve is made by a bimetal valve 25 that deforms near the freezing temperature of 100 ° C.
By opening 25, the bypass pipe 22 is opened and the freezing part is bypassed.

As a result, there is no need for operation by the operator, and the function can be maintained during freezing. The first
In addition to the second embodiment, a plurality of heat transfer tube headers 21 and a plurality of bypass tubes 22 may be provided in consideration of the uncertainty of the freezing position.

Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment is different from the first embodiment in that the heat transfer tube header 21 is connected to the freezing predicting portion 28 of the heat transfer tube 12, but the bypass tube 22 and the stop valve 23 are not installed, and instead, the heat transfer is performed. That is, a part of the heat transfer tube 12 on the downstream side of the heat tube header 21 is replaced with a heat transfer tube 26 made of a material having a large thermal resistance. The other parts are the same as in the conventional example, and therefore the description thereof is omitted.

According to this third embodiment, another heat transfer tube 12
Since the secondary sodium in the heat transfer tube 26 made of a material having a large thermal resistance does not freeze even if it freezes, the secondary sodium in the heat transfer tube 12 upstream from the heat transfer tube header 21 will cause the heat transfer tube 26 made of a material having a large heat resistance to You can reach the lower header 19 via Therefore,
Although the amount of heat removed during normal operation is slightly reduced, there is an effect that the operation by the operator is unnecessary.

Next, a fourth embodiment of the present invention will be described with reference to FIG. The difference of the fourth embodiment from the first embodiment is that the heat transfer pipe header 21 is connected to the freezing predicting portion 28 of the heat transfer pipe 12, but the bypass pipe 22 and the stop valve 23 directly connected to the downcomer pipe 10 are not installed. Instead, heat transfer tube header 21 and lower header
That is, the non-freezing short pipe 27 that bypasses between 19 and is connected.

Since the other parts are the same as the conventional example,
The description is omitted. The material of the non-freezing short tube 27 can be arbitrarily selected as long as it has a moisture retaining property at a temperature at which secondary sodium does not freeze and does not react with sodium.

According to this fourth embodiment, the air cooler 8
The provision of the non-freezing short tube 27 can avoid the loss of the heat removal function caused by the freezing of the secondary sodium due to the erroneous opening of the dampers 13, 15 and the vanes 14 of FIG.

[0040]

According to the present invention, the secondary sodium flow is secured and the heat removal function is maintained even when the secondary sodium flowing through the heat transfer tube in the air cooler is frozen due to the accidental opening of the damper vane. it can. Therefore, the decay heat removal function is not completely lost, and serious damage to the core can be avoided.

[Brief description of drawings]

FIG. 1A is a piping system diagram schematically showing a main part of a decay heat removal system for a fast reactor according to a first embodiment of the present invention,
(B) is a piping system diagram showing a conventional example, which is also shown for comparison with (a).

FIG. 2 (a) is a longitudinal sectional view schematically showing a second embodiment of a decay heat removal apparatus for a fast reactor according to the present invention, with a part of which is cut away;
(B) is a longitudinal cross-sectional view showing an enlarged portion A of (a).

FIG. 3 (a) is a piping system diagram schematically showing a main part of a third embodiment of the decay heat removal apparatus for a fast reactor according to the present invention,
(B) is a longitudinal cross-sectional view schematically showing the device in (a).

FIG. 4 (a) is a piping system diagram schematically showing a main part of a decay heat removal system for a fast reactor according to a fourth embodiment of the present invention,
(B) is a longitudinal cross-sectional view schematically showing the device in (a).

FIG. 5 (a) is a decay heat removal system system diagram for explaining a conventional decay heat removal device for a fast reactor, and FIG.
FIG. 3 is a vertical cross-sectional view showing the decay heat removal device in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Furnace container, 2 ... Core part, 3 ... Primary sodium, 4 ... Inflow pipe, 5 ... Outflow pipe, 6 ... Plug, 7 ... Heat exchanger, 8 ... Air cooler, 9 ... Rise pipe, 10 ... Downcomer pipe , 11 ... Electromagnetic pump,
12 ... Heat transfer tube, 13 ... Upper damper, 14 ... Vane, 15 ... Lower damper, 16 ... Blower, 17 ... Housing, 18 ... Upper header, 19 ... Lower header, 20 ... Upper plenum, 21 (21a, 21b) ... Heat transfer pipe header, 22 (22a, 22b) ... Bypass pipe, 23 (23a,
23b) ... Stop valve, 24 (24a, 24b) ... Heater, 25 ... Bimetal valve, 26 ... Heat transfer tube made of material with high thermal resistance, 27 Non-freezing short tube, 28 ... Freezing prediction section.

Claims (4)

[Claims] 1. A heat exchanger immersed in primary sodium of an upper plenum in a furnace vessel, a riser pipe and a downcomer pipe, one end of which is connected to the heat exchanger, through which secondary sodium flows, and the riser pipe and A heat transfer tube through which the secondary sodium flows connected to the other end of the downcomer via an upper header and a lower header, an air cooler incorporating the heat transfer tube, a vane and upper and lower parts provided in the air cooler. In a decay heat removal apparatus for a fast reactor equipped with a damper, a heat transfer tube header is connected to a heat transfer tube portion upstream of the lower header, and the descent on the secondary sodium outlet side of the heat transfer tube header and the lower header is performed. A decay heat removal device for a fast reactor, characterized in that a bypass pipe is provided between the pipe and the pipe via a valve. 2. The decay heat removal apparatus for a fast reactor according to claim 1, wherein the bypass pipe is provided with a heater and a bimetal valve is provided between the bypass pipe and the lower header. 3. A heat exchanger immersed in primary sodium of an upper plenum in a furnace vessel, a riser pipe and a downcomer pipe, one end of which is connected to the heat exchanger, through which secondary sodium flows, and the riser pipe and A heat transfer tube through which the secondary sodium flows connected to the other end of the downcomer via an upper header and a lower header, an air cooler incorporating the heat transfer tube, a vane and upper and lower parts provided in the air cooler. In a decay heat removal apparatus for a fast reactor equipped with a damper of, a heat transfer tube header is connected to a lower part of the heat transfer tube in the air cooler, and heat is transferred from the heat transfer tube header between the heat transfer tube header and the lower header. A decay heat removal device for a fast reactor characterized by being connected with a heat transfer tube having a large resistance. 4. A heat exchanger immersed in primary sodium in an upper plenum in a furnace vessel, a riser pipe and a downcomer pipe having one end connected to the heat exchanger, through which secondary sodium flows, and the riser pipe and A heat transfer tube through which the secondary sodium flows connected to the other end of the downcomer via an upper header and a lower header, an air cooler incorporating the heat transfer tube, a vane and upper and lower parts provided in the air cooler. In a decay heat removal apparatus for a fast reactor equipped with a damper, a non-freezing material that connects a heat transfer tube header to a lower part of the heat transfer tube in the air cooler and bypasses between the heat transfer tube header and the lower header. A decay heat removal device for a fast reactor, which is characterized by connecting short tubes.