JPH0441959B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a liquid metal cooled fast breeder reactor equipped with an overflow system, and in particular to shortening the time required for starting and stopping the reactor to increase the operating rate. The present invention relates to a liquid metal cooled fast breeder reactor suitable for improving the temperature and preventing thermal shock of the overflow pumping piping nozzle section.

[Conventional technology]

Figure 10 shows a conceptual diagram of the overflow system of a liquid metal cooled fast breeder reactor.

There are two locations in the overflow system where thermal shock may occur: the overflow return pipe 4 and the overflow pumping pipe nozzle portion 6a, and the mechanisms of thermal shock occurrence are different from each other.

In overflow return piping, once the liquid level drops, the overflow is interrupted and the piping temperature drops, and then a thermal shock occurs when high-temperature refrigerant reaches the piping due to re-overflow. There are two possibilities: cold shock occurs due to low-temperature coolant flowing out.

On the other hand, in the overflow pumping piping nozzle section, if there is a difference in temperature between the coolant in the reactor vessel 1 and the coolant in the overflow tank 5, there is a risk that thermal shock will occur.

Conventional devices for suppressing these thermal shocks are disclosed in Japanese Patent Application Laid-Open No. 54-145898 for overflow return piping.
As described in the above issue, when the low-temperature coolant overflows, the overflow return pipe is forcibly cooled with atmospheric gas to prevent thermal shock on the overflow return pipe. Additionally, as described in JP-A-52-132296, consideration was given to preventing thermal shock by providing a coolant reservoir in the nozzle part of the overflow return pipe to prevent the temperature of the coolant reaching the overflow return pipe from changing rapidly. Was.

On the other hand, there is no particularly effective method for the overflow pumping piping nozzle, and the solution is to monitor the temperature of the coolant in the overflow tank and the overflow pumping piping nozzle to prevent thermal shock from occurring. Ta.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology is effective in preventing thermal shock in overflow return piping, but has no effect on overflow pumping piping. For this reason, not only during reactor scram, but also during normal startup and shutdown, if the rate of temperature rise and fall in the reactor vessel increases, the temperature difference with the coolant in the overflow tank increases, so the overflow pumping piping There is a problem in that thermal shock tends to occur in the nozzle portion. Furthermore, in order to avoid this problem, the temperature rise and fall rates of the coolant in the reactor vessel are reduced, and the temperature in the overflow tank is allowed to mix with the overflow coolant to ensure time for the temperature in the overflow tank to approach the temperature in the reactor vessel. Although this method has been adopted, it cannot be a fundamental solution and has the problem of increasing the time required for starting and stopping.

Figures 11 to 14 show system temperature rise, output rise,
It also shows the calculation results of coolant temperature changes in the reactor vessel, overflow tank, and auxiliary cooling system at each step of power reduction and system temperature reduction.
As shown in FIGS. 11 and 12, when the system temperature and output increase, the temperature of the coolant in the overflow tank rises with a lag behind the temperature of the coolant in the reactor vessel. This is because the temperature of the coolant in the overflow tank increases as it mixes with the high temperature coolant that has overflowed from the reactor vessel. Since the overflow flow rate is constant,
As the temperature increase rate of the coolant in the reactor vessel increases, the temperature difference between the two increases, making it easier for thermal shock to occur. In order to avoid thermal shock with sufficient margin, the temperature difference between the two is generally 60℃.
In actual plant operation, the temperature increase rate of the coolant in the reactor vessel should be kept within 20℃/20℃.
We have set the limit to be within hr and are careful not to deviate from the above conditions. As a result, the time required to reach the rated output after increasing the output from the system temperature is at least
It will take 14-15 hours.

On the other hand, when the output drops and the system temperature drops, the 13th
As shown in FIG. 14, the temperature change when the system temperature increases and the output increases is reversed, and the temperature of the coolant in the overflow tank is higher. In order to satisfy the above limit value of temperature difference of 60℃,
Similarly, the temperature reduction rate needs to be 20°C/hr, and the time required to shut down the reactor is also required to be 14 to 15 hours.

The purpose of the present invention is to prevent the above-mentioned thermal shock of the overflow pumping piping nozzle part, and
The aim is to shorten the time required to start and shut down a nuclear reactor.

[Means for solving problems]

The above object is achieved by installing a heat exchanger in the overflow tank and providing a coolant flow path for exchanging heat between the coolant in the reactor vessel and the coolant in the overflow tank.

[Effect]

The coolant in the overflow tank is acted on by a heat exchanger so that it approaches the temperature of the coolant in the reactor vessel, and as this temperature continues to approach, the coolant in the overflow tank flows into the reactor vessel. Thermal shock during injection is controlled.

〔Example〕

In one preferred embodiment of the invention, the auxiliary cooling system piping is simply connected to a heat exchanger installed in the overflow tank, as shown in FIG. The coolant in the reactor vessel 1 flows back through the auxiliary cooling system inlet pipe 9 and exchanges heat with the heat exchanger 13, and then flows into the reactor vessel 1 again through the auxiliary cooling system outlet pipe 8. At this time, since the auxiliary cooling system electromagnetic pump 11 is stopped, no special operation or operation is required to perform heat exchange.

Note that the amount of heat supplied or removed by the overflowing coolant is determined by the heating rate and cooling rate of 20.
In the case of °C/hr, it is approximately 100 to 200kW. For example, if a heat exchanger equivalent to this is installed, the temperature rise and fall rates can be approximately doubled, so the coolant temperature in the reactor vessel 1 and the coolant temperature in the overflow tank can be approximately doubled. The difference becomes smaller, which prevents thermal shock and reduces the time required for starting and stopping by half. The capacity of the heat exchanger to be installed should be arbitrarily determined depending on the scale of the plant and overflow system, and the time to be shortened.

From the viewpoint of cost reduction, it is most advantageous to use an auxiliary cooling system as a line for guiding the coolant in the reactor vessel to the heat exchanger. The auxiliary cooling system is
The purpose is to remove core decay heat in the event of an accident, and it is not used during normal operation. For this reason, it is known that backflow occurs in the auxiliary cooling system piping due to the pushing pressure of the main cooling pump. According to calculations, this backflow amount is approximately 21 m ³ /hr during rated operation, as shown in FIG. 15. In the present invention, this backflow is utilized as a driving force. Considering that the rated flow rate of the overflow system is 12 m ³ /hr, the above-mentioned reverse flow rate is sufficient to achieve the present invention. In addition, as shown in Figures 11 to 14, the temperature of the coolant flowing backward through the auxiliary cooling system is higher than the coolant temperature in the overflow tank when the temperature rises, and lower when the temperature falls, except for a certain range. It is fully accessible due to its age.

Examples of the present invention will be described in more detail below.

FIG. 1 is a diagram showing the system configuration of a liquid metal cooled nuclear reactor according to a first embodiment of the present invention. In the figure, 1 is a reactor vessel, 2 is a reactor core, 3 is a rotating plug, 4 is an overflow return pipe, 5 is an overflow tank, 6 is an overflow pumping pipe, and 6a is an overflow pumping pipe nozzle part. The heat exchanger 13 is connected to the reactor vessel 1 via an auxiliary cooling system outlet pipe 8 and an inlet pipe 9 thereof. The overflow system electromagnetic pump 7 is always operated, but the auxiliary cooling system electromagnetic pump 1
1 is normally in a stopped state. With this configuration, when the temperature rises, heat input from the coolant flowing in through the overflow return pipe 4 and heat input from the coolant flowing backward through the auxiliary cooling system and reaching the heat exchanger cause the inside of the overflow tank to increase. By heating the coolant, it is possible to increase the temperature increase rate. In the case of temperature reduction, the temperature reduction rate can be increased for the same reason. According to this embodiment, it is possible to reduce the temperature difference between the coolant in the reactor vessel and the coolant in the overflow tank, and not only can prevent thermal shock at the nozzle part of the overflow pumping pipe, but also This has the effect of shortening the time required to start and stop the furnace.

FIG. 2 is a diagram showing the system configuration of a liquid metal cooled nuclear reactor which is a second embodiment of the present invention. The difference from the embodiment shown in FIG.
b. In this example, valve 15
By controlling the opening and closing of a and 15b, the flow rate of the coolant flowing through the heat exchanger 13 can be adjusted. For this reason, for example, the output in Figure 12 is 85MW to 100MW.
As shown in the range, if the coolant temperature in the auxiliary cooling system and the coolant temperature in the overflow tank are reversed, heat will be removed, so to prevent this, all coolant is bypassed. It has the effect of being able to In this embodiment, as shown in FIG. 3 as a modification based on the second embodiment, a thermocouple 19, a temperature converter 20, and an arithmetic circuit 21 are added to automate the opening and closing of the valve. It is also possible to use solenoid valves 15i and 15j. The thermocouple 19 measures the coolant temperature in the auxiliary cooling system 9 and the reactor vessel 1, and the temperature converter 2
0. The opening and closing of the solenoid valves 15i and 15j can be controlled as necessary by the operation of the processing circuit of the arithmetic circuit 21. With such a configuration, the burden on the operator can be reduced and the reliability of plant control can be improved.

FIG. 4 is a diagram showing only the constituent parts of a heat exchanger and a bypass provided in an auxiliary cooling system of a liquid metal cooled nuclear reactor according to a third embodiment of the present invention. The difference from the embodiment shown in Fig. 2 is that the bypass is
Two systems, 4b and 14c, are provided, and four valves 15c, 15d, 15e, and 15f are provided. Furthermore, a heat exchanger is installed vertically. When FIG. 4 is arranged and shown, it becomes as shown in FIG. 4a. The reason for this configuration is that the coolant in the overflow tank is circulated by convection. In other words, during heating, the coolant in the overflow tank flows upward in the heat exchanger section, so
The heat exchange efficiency will be better if the flow direction of the coolant from the reactor vessel in the heat exchanger is downward. Fourth
In the figure, each valve is adjusted so that the flow normally occurs as shown by the solid line arrow, and when the flow is reversed, the flow occurs as shown by the dotted line arrow. To achieve such a flow, specifically, as shown in FIG. 5, valves 15c and 15f may be opened and valves 15d and 15e may be closed. On the other hand, during heat removal, the coolant in the overflow tank flows downward in the heat exchanger, so as shown in Figure 6, valves 15c and 15f are closed and valves 15d and 15e are opened to drain the coolant in the heat exchanger. It is better to have an upward flow in a reverse flow state. Moreover, convection is promoted by installing the heat exchanger vertically. When heat exchange is not performed, valves 15c and 15d are opened;
e, 15f may be closed. In addition, valve 15c~
The same function can be achieved by using three-way valves 15g and 15h instead of 15f, as in a modification of the third embodiment shown in FIGS. 7 and 8. According to this embodiment, since there is an effect of promoting convection, the heat exchange efficiency is improved and the time required for starting and stopping the nuclear reactor can be further shortened. In this embodiment as well, the thermocouple 19, temperature converter 20, arithmetic circuit 21, and solenoid valves 15i and 15 for automating the opening and closing of the valves shown in FIG.
It is also possible to add j.

FIG. 9 is a diagram showing the configuration of a heat exchanger and heat exchange system piping of a liquid metal cooled nuclear reactor according to a fourth embodiment of the present invention. The difference from the embodiment shown in FIG. pump 17
This is the result of the establishment of the . It is desirable that the heat exchange system piping 16 be connected to the upper part of the reactor vessel 1 as much as possible, as shown in the figure. According to this embodiment, since the coolant in the reactor vessel is driven by the electromagnetic pump 17, the amount of heat exchange can be controlled by appropriately changing the flow rate. In addition, heat exchanger 1
Since the temperature of the coolant introduced into the tube 3 is high, there is an effect that the heat exchange efficiency is good.

FIG. 16 shows a fifth embodiment in which an electromagnetic flow coupler type heat exchanger 18 is employed as the heat exchanger used in the present invention.

According to this embodiment, the coolant in the overflow tank is driven as a secondary flow in the direction of the arrow shown by the broken line in the figure by the primary flow in the piping. It is also efficient and has the effect of uniformizing the temperature inside the tank.

〔Effect of the invention〕

According to the present invention, since the difference between the coolant temperature in the overflow tank and the coolant temperature in the reactor vessel can be reduced in a short time, it is possible to prevent thermal shock from being applied to the nozzle part of the overflow pumping pipe, and to This has the effect of greatly reducing the time required to start and stop the furnace. In order to concretely demonstrate this effect, if we convert it into a monetary amount, we can expect an increase in revenue of approximately 200 million yen per cycle under the following calculation conditions, so the effect is significant.

Calculation condition (1) Plant scale: 1 million kW (2) Reduced time: 10 hours (starting 5 hours, stopping 5 hours) (3) Electricity unit price: 20 yen/kWh

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram of a liquid metal cooled fast breeder reactor showing a first embodiment of the present invention, and FIG.
FIG. 3 is a system configuration diagram of a liquid metal cooled fast breeder reactor showing a second embodiment of the present invention, and shows a modified example in which a circuit for automating the opening and closing of valves is added to the embodiment of FIG. 2. A system configuration diagram, FIG. 4 is a configuration diagram showing a third embodiment of the present invention, and FIG.
The flow path schematic diagrams in the figure, Figures 5 and 6 are
7th block diagram showing the operating method in the embodiment shown in the figure.
8 are block diagrams showing a modification of the embodiment shown in FIG. 4, FIG. 9 is a system block diagram of a liquid metal cooled fast breeder reactor showing a fourth embodiment of the present invention, Figure 10 is a system configuration diagram of a conventional liquid metal cooled fast breeder reactor, Figures 11, 12, and 13.
Figure 14 shows the reactor vessel, auxiliary cooling system piping,
This is a diagram showing changes in coolant temperature in each part of the overflow tank, in order when the system temperature rises,
Fig. 15 is a characteristic diagram showing changes in the backflow flow rate in the auxiliary cooling system during operation of the primary main cooling pump;
The figure is a fifth embodiment of the present invention, and is a diagram showing a configuration in which an electromagnetic flow coupler heat exchanger is employed as the heat exchanger. DESCRIPTION OF SYMBOLS 1...Reactor vessel, 2...Reactor core, 4...Overflow return pipe, 5...Overflow tank, 6...Overflow pumping pipe, 6a...
...Overflow pumping piping nozzle section, 7...
Overflow system electromagnetic pump, 8...Auxiliary cooling system outlet piping, 9...Auxiliary cooling system inlet piping, 11...
Auxiliary cooling system electromagnetic pump, 13... Heat exchanger, 14
... Bypass flow path, 15 ... Valve, 16 ... Heat exchange system piping, 17 ... Heat exchange system electromagnetic pump, 18 ...
Electromagnetic flow coupler heat exchanger, 19...Thermocouple, 2
0...Temperature converter, 21... Arithmetic circuit.

Claims (1)

[Scope of Claims] 1. In a liquid metal cooled fast breeder reactor in which the inside of a reactor vessel and an overflow tank are communicated with each other by an overflow return pipe and a pumping pipe, and a flow path of an auxiliary cooling system is communicated with the inside of the reactor vessel. , a heat exchanger is provided in the overflow tank, and a first
A liquid metal cooled fast breeder reactor comprising a flow path and a second flow path for returning the liquid metal from the first flow path into the reactor vessel via the heat exchanger. . 2. The liquid metal cooled fast breeder reactor according to claim 1, wherein the first channel and the second channel are channels of an auxiliary cooling system. 3 The first flow path has a path branching into a heat exchanger side flow path leading to the heat exchanger and a bypass flow path bypassing the heat exchanger and leading to the second flow path, and The liquid metal cooled fast breeder reactor according to claim 1 or 2, further comprising a flow rate regulating valve for controlling the flow rate of the heat exchanger side flow path and the bypass flow path. 4. The heat exchanger is installed in the overflow tank in such a manner that the liquid metal introduced through the first flow path flows upwardly and downwardly, and the first flow path branches into a plurality of parts in the middle of the flow path. a plurality of bypass passages that bypass the heat exchanger and connect to the second passage; a third passage that communicates the plurality of bypass passages via the heat exchanger; and the third passage and the third passage. Claim 1, comprising: each flow rate control valve provided in a portion between the third flow path and the second flow path; and each flow rate control valve provided in a portion between the third flow path and the second flow path. 1st term or 2nd term
A liquid metal cooled fast breeder reactor as described in . 5. The liquid metal cooled fast breeder reactor according to claim 1, wherein the inlet of the first flow path is provided in a portion containing high temperature liquid metal in a reactor vessel.