JPS5949478B2 - Thermal expansion absorption device for liquid metal piping - Google Patents

Description

[Detailed description of the invention] The present invention relates to a thermal expansion absorption device for liquid metal piping.

In a liquid metal cooled fast breeder reactor, liquid metal such as sodium is used as a heat medium in the primary and secondary cooling systems, and the normal operating temperature of the primary and secondary cooling systems is approximately 500°C.
and high temperature.

Conventionally, piping through which such a high-temperature heat medium flows has generally been designed to have a complicated piping layout in order to relieve stress caused by thermal expansion of the piping.

In this case, the length of the piping becomes long, which not only increases the number of hangers and snares, increases the need for heat insulating material, but also increases the pressure loss within the piping, increases the circulation pump lift, and increases the amount of building material, resulting in an increase in plant construction costs. This is a factor that leads to In recent years, attempts have been made to reduce the size of the piping system by using bellows joints in the piping system to absorb thermal expansion as a means of resolving the increase in plant construction costs.
Designing a bellows joint for use under high temperature conditions as described above has the following difficulties.

In other words, if we classify the load conditions that act on bellows joints under these conditions, we can classify them into cyclic displacement loads (secondary loads) that correspond to large humidity fluctuations when the plant starts and stops, and loads that apply after the plant reaches normal output. It can be broadly classified into primary loads such as pressure under high temperature conditions.

In the high-temperature structural design of bellows, fatigue and creep5 damage limits and strain limits must be satisfied, but secondary loads are the governing factor for fatigue damage, and pressure loads are the dominant factor for creep damage and strain limits. The bending stress of the bellows element caused by the bending stress is the dominant factor.

'0 - In general, for primary loads, it is possible to reduce the generated stress by increasing the bellows wall thickness, and conversely, for secondary loads, it is better to reduce the bellows wall thickness to reduce the generated stress. can be reduced.

It is extremely difficult to design a bellows joint that is compact enough to withstand these contradictory loads and still meet the intended purpose.

The present invention focuses on the fact that two types of loads that are contradictory to the design of bellows joints, which are difficult to design, differ between plant start-up/stop and normal operation. The load to be absorbed by
The purpose of the present invention is to provide a method that makes it easier to obtain the feasibility of the design by limiting it to only when the system is stopped.

Figure 1 simply shows the configuration of the heat transport system of a fast breeder reactor power plant, and Figure 2 shows the primary sodium and secondary sodium systems in the output operating range based on an example of a fast breeder reactor power plant. It shows the temperature versus the electrical output of the sodium system.

In the figure, when looking at curve A showing the change in inlet temperature of the intermediate heat exchanger 3 of the primary cooling system 2, the electrical output is 30% to 1
The temperature range that changes between 00% is 530℃-490℃
= 40°C, similarly looking at the curved opening indicating the outlet temperature of the intermediate heat exchanger 3 of the secondary cooling system 4, it is 505°C - 490°C =
Similarly, if we look at the curve C showing the outlet temperature of the intermediate exchanger 3 of the primary cooling system 2, 395°C - 375°C = 2.
Similarly, when looking at curve 2 showing the inlet temperature of the intermediate heat exchanger 3 of the secondary cooling system 4, 325°C - 280°C = 4
5°C, and the temperature change between 30% and 100% of electrical output is 15°C to 45°C. In other words, if the normal temperature is 30℃, the total thermal expansion from the normal temperature of 30℃ to the temperature of 100q6 of electrical output is the output operating range of 30q of electrical output.
The percentage of thermal expansion between 6 and 100% is negligible. According to a trial calculation, in the case of a curved opening, the electrical output is 30% - 100
Thermal expansion amount ΔI in %! 1-(505℃-4900C)・
α・11 On the other hand, the amount of thermal expansion from room temperature 30°C to 100% electrical output is Δ2, = (505°C - 30°C) α・l, and the ratio of that in the output operating range to the overall amount of thermal expansion is 15: 475, which is only 3.2%. Therefore, for example, the piping itself can absorb the slight thermal expansion in the high temperature range up to 30 degrees Fahrenheit (F6 to 100F), which is an electrical output of 30 degrees Fahrenheit to an electrical output of 3.
If the bellows absorbs the large thermal expansion in the low temperature range down to 0%, the amount of thermal expansion that should be absorbed by the piping is small, and the primary stress on the bellows in the high temperature range can be reduced. . (This setting of 30% electrical output varies depending on the plant conditions and is not limited to this.) Specifically, first, in order to isolate the liquid metal inside the pipe from the bellows, A bellows is fitted loosely around the outer periphery of the pipe to connect the pipes, and a liquid metal solidification part is provided between the bellows and the inside of the pipe, so that the liquid metal can be solidified or melted in the solidification part, and the inside of the pipe is While the temperature of the liquid metal flowing in the pipe is low, the liquid metal in the solidified part is melted and the bellows absorbs the thermal expansion of the pipe, and the temperature of the liquid metal flowing in the pipe rises above a certain temperature. When the liquid metal is frozen, the liquid metal in the solidified portion is solidified, and the solidified liquid metal essentially integrates the pipe, allowing the pipe itself to absorb the thermal expansion of the pipe in the high temperature range, and reducing the pressure of the liquid metal. It is also characterized by the fact that the bellows is not affected by the load and temperature, and the thermal expansion absorption mode of the piping is divided into two regions: a low temperature region and a high temperature region.

Hereinafter, details of the present invention will be explained in conjunction with an embodiment shown in the accompanying drawings. FIG. 3 shows this embodiment. In the figure, piping 1
An outer cylinder 18 is integrally provided on the outer periphery of the pipe 2, and an annular gap between the outer cylinder 18 and the pipe 12 is filled with a heat insulating material 20. On the other hand, the pipe 13 is provided with an enlarged pipe part 17 at one end thereof, and is covered with the outer periphery of the outer cylinder 18 with a certain gap therebetween.
A heat insulating material 14 is spread over a portion of the pipe 13 and the expanded tube portion 17. The flange 15 provided on the outer tube 18 and the piping 13
A bellows 9 is connected by welding to a flange 16 provided on an expanded pipe portion 17 of the pipe 1, and the bellows 9 substantially connects the pipes 12 and 13. In addition, in the figure, 21 is a heater, 22 is a cooling pipe,
23 is a cooling fin, 19 is a solidified metal portion, and 24 is a sliding contact portion between the pipes 12 and 13.

Next, the operation of this embodiment will be explained.

In this embodiment, for example, the electrical output is 30q6 to 100 (:!
The piping itself absorbs thermal expansion in the high temperature range up to 30℃ at room temperature.
The following description assumes that the bellows absorbs thermal expansion in the low temperature range from .degree. C. to 30 f1 of electrical output. First, at room temperature 30
℃ to 30% electric output, the liquid metal in the solidification section 19 is melted by the heater 21.

Note that liquid metals such as sodium melt at about 98°C. Therefore, the thermal expansion of the piping during this period is absorbed by the bellows 9 due to the melting of the liquid metal in the solidified portion and the sliding contact between the piping 12 and 13. In this low temperature range, the temperature of the liquid metal is not very high, and the bellows 9 is not exposed to high temperature conditions. Heat is also blocked by the heat insulating material 20 and the liquid metal in the solidified portion 19. Next, between the electrical outputs 30q6 and 100q1), the heater 21 is shut off and the cooling pipe 2, which flows the coolant inside, is turned off.
2 and the cooling fins 23, the liquid metal in the solidification section is cooled and solidified.

Coolant is supplied to the cooling pipe from a cold source. Due to the solidification of this liquid metal, sliding between the pipes 12 and 13 is suppressed,
It becomes essentially one pipe. Therefore, no additional stretching force acts on the bellows 9. Since the amount of thermal expansion of the piping at this time is very small, it will be absorbed by the bends of the piping, but only a small amount of piping will be required.

Further, the heat of the liquid metal is completely blocked by the heat insulating material 20 and the solidified liquid metal. As detailed above, according to the present invention, thermal expansion in a low temperature range from room temperature to a certain temperature is absorbed by the bellows, and thermal expansion in a high temperature range above a certain temperature is absorbed by solidifying the liquid metal in the solidified part. As a result, the pipe itself absorbs the water, so bellows are always used only in low temperature ranges, and there is no need to consider creep strength at high temperatures, and the expansion and contraction effect in high temperature ranges can be eliminated. This increases the fatigue life of the bellows, simplifies the design process, and minimizes the amount of thermal expansion that must be absorbed by the piping itself, making it possible to significantly shorten the length of the piping compared to conventional systems. There is something.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of a fast breeder reactor power plant; FIG. 2 is an explanatory diagram showing the relationship between electric output and heat medium temperature as an example of a fast breeder reactor power plant;
FIG. 3 shows this embodiment. 1... Nuclear reactor, 2... Primary cooling system, 3... Intermediate heat, exchanger, 3ζ... Steam generator, 4... Secondary cooling system, 1... Steam system, 5 ...Turbine, 6
ζ・Start water pump, 6...Secondary circulation pump, 7...
・Main circulation pump, 9... bellows, 12, 13...
・Piping, 19... Solidifying part, 20... Insulating material, 21... Heater, 22... Cooling pipe, 23...
・Cooling fins.

Claims (1)

[Claims] 1. At the connection part of liquid metal piping, a bellows is loosely fitted to the outer periphery of the piping, the piping is connected via the bellows, and a liquid metal condensation part is provided between the bellows and the inside of the piping. A heater and a cooler for solidifying or melting the liquid metal are installed in the solidification section, and thermal expansion is absorbed by the bellows when the liquid metal is in a molten state, and by the pipe itself when it is in a solidified state. A thermal expansion absorption device for liquid metal piping, characterized by: