JPH0119445B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to a purification unit that purifies sodium in a sodium storage tank such as a reactor vessel or a storage tank in a sodium-cooled nuclear power plant. The present invention relates to a sodium purification unit that is capable of reducing the thermal stress of component equipment and making it possible to replace the cold trap section that captures impurities, thereby extending the service life and improving the purification performance.

(Prior art and its problems) A purification unit that captures and purifies impurities in high-temperature liquid sodium, such as one in a nuclear power plant.
As shown in Figure 1, purification units used by being inserted into sodium in storage tanks such as reactor vessels in fast breeder reactors have conventionally been used mainly as cold-trace units to capture impurities in the sodium to be purified. 2, a cooler 4 for cooling the sodium with a coolant in order to obtain the optimum temperature for trapping impurities in the cold trap 2, a cooler 4 for cooling the sodium introduced into the unit from the sodium inlet 6 , an electromagnetic pump 3 for feeding sodium into the cold trap 2, an electromagnetic flowmeter 7 for measuring the flow rate of introduced sodium, sodium and coolant piping, and a shell 1 for installing the above-mentioned devices.

Impurities such as oxygen and hydrogen present in sodium in sodium storage tanks such as reactor vessels can cause blockages in coolant flow paths and cracks in equipment and piping, which can lead to problems in maintaining the functionality of nuclear plants.
In order to improve reliability, the purification unit is installed in sodium to purify it, and it is operated to maintain the impurity concentration in normal sodium below a predetermined value. To remove impurities, sodium is removed in a cooler 4 installed in the purification unit.
The purification unit is cooled to 140°C and deposited on a metal mesh _2a installed in the cold trap 2. If the purification unit is in a reactor vessel, the temperature is approximately
Since it is immersed in sodium at a high temperature of about 500 to 550°C, the shell 1 constituting the outer surface of the purification unit is also at a high temperature of about 500°C or higher.
Therefore, there is a large temperature difference between the cooler 4, cold trap 2, and _other components installed inside the shell 1. Thermal stress generated in areas such as _b was large.

As a measure to reduce these thermal stresses, the support structure of the cooler should be made into a conical shape, with the tip supporting the cooler or cold trap, and the lower end being welded to the high temperature shell. By appropriately selecting the length of the support structure, thermal stress generated in the support structure is alleviated and damage to the support structure is prevented.

However, purification units in which internal components are attached directly to the shell have had problems with the strength of the shell. Furthermore, even if the internal components of the purification unit are sound, the purification unit has a short lifespan because it must be discarded due to the loss of the impurity removal function of the cold trap.

However, in the conventional purification unit shown in FIG. 1, when purified sodium is cooled in the cooler 4 and purified by removing impurities in the cold trap 2, when it flows out from the outlet 5, the high temperature sodium in the storage tank is subject to thermal shock. Further, when the heat of the high temperature sodium in the storage tank moves to the metal mesh _2a in the cold trap 2 and the metal mesh _2a becomes high temperature, the impurity removal function of the cold trap 2 is reduced.

(Object of the Invention) The present invention has been made to solve these technical problems, and it reduces the occurrence of thermal stress in the support structure materials of internal components, increases the strength of the shell, and improves purification. It is an object of the present invention to provide a sodium purification unit that alleviates thermal shock caused by outflow of sodium and further prevents heat from high temperature sodium in a storage tank from transferring to a cold trap.

(Structure of the Invention) The present invention provides a cylindrical sodium purification unit that includes an electromagnetic pump for circulating sodium to be purified, a cooler, a cold trap, sodium and coolant piping, etc. An inner cylindrical tube is provided concentrically inside the constituent shell,
A narrow annular space is formed between the shell and the space is filled with a heat insulating material, the lower end of the filled insulating material is sealed, and impurities in the sodium are precipitated and removed inside the lower part of the inner tube. A cold trap filled with a metal mesh is removably inserted and supported, and an outer cylinder with a bottom is removably installed on the outside of the lower part of the shell at approximately the same height as the cold trap and concentrically with an appropriate gap.
A sodium cooler is installed at the upper inlet of the cold trap to set the optimum temperature conditions for impurity precipitation by heat exchange with the coolant, and the cooler is connected to the cold trap through a conical support structure. The structure is such that the sodium is supported in the inner cylinder tube in a sealed manner, and the heat insulating material filled in the annular space alleviates temperature changes in the internal components and their supporting structural materials and shells, reducing the occurrence of thermal stress. In addition, the heat insulating material and the outer cylinder with a bottom prevent heat transfer to the cold trap to improve purification performance, and the outer cylinder with a bottom increases the temperature of the low-temperature purified sodium flowing into the high-temperature sodium. This feature is characterized by extending the life of the sodium purification unit by alleviating thermal shock and making it possible to replace the cold trap.

(Example) An example of the sodium purification unit of the present invention will be described in detail with reference to FIG. An inner cylindrical pipe 10 is provided concentrically inside the shell 1.
A narrow annular space 11 is formed between the two, and the space 11 is filled with a heat insulating material 12. The lower end of the space 11 is sealed by joining a bottom plate 13 to the lower end of the shell 1 and the lower end of the inner tube 10. 2 is a cold trap, the inside of which is filled with a metal mesh _2a , a vertical hole _2c in the center through which purified sodium flows, and a hat-shaped trap with a sodium outlet 5 in the center on the lower end surface. A support plate 14 is provided, and this hat-shaped support plate 14 is connected to the inner tube 1.
A flange _14a at the periphery of the hat-shaped support plate 14 is removably fixed to the bottom plate 13 at the lower end of the shell 1, and the cold trap 2 is housed inside the shell. A recess 16 is provided in the bottom plate 15 at the lower outer end of the shell 1 so as to be approximately at the same height as the cold trap 2.
An outer cylinder 17 with a bottom is arranged concentrically with the shell 1 with an appropriate gap 18 therebetween, and the bottom plate 15 of the outer cylinder 17 with a bottom is connected to the periphery of the hat-shaped support plate 14 via a spacer 19. Bottom plate 1 at the bottom end of shell 1 together
It is removably fixed to 3. Therefore, below the cold trap 2, a retention part 20 is formed by the hat-shaped support plate 14 and the recess 16 of the bottomed outer cylinder 17, in which purified sodium is temporarily retained. A cooler 4 is provided at the upper inlet of the cold trap 2, and the cooler 4 is supported in the inner tube 10 via a conical support structure _4a so as to seal the sodium inside. . A coolant outlet pipe 8 and an inlet pipe 9 for supplying and recovering coolant to the cooler 4 are partially formed into a spring shape and provided inside the inner cylindrical pipe 10, and are provided as a coolant supply source outside the system (not shown). It is connected to the. 6 is a sodium inlet of the purification unit, 7 is an electromagnetic flowmeter for measuring the flow rate of sodium, and 3 is an electromagnetic pump for circulating sodium, which is connected to the inner tube 10 via support fittings 7 _a and 3 _a , respectively.
The support is fixed. The piping 21 constituting the sodium circulation flow path is formed into a spring shape and is disposed between the sodium inlet 6, the electromagnetic flowmeter 7, the electromagnetic pump 3, and the cooler 4.

Next, the operation of the sodium purification unit constructed as described above will be explained. For example, the sodium purification unit is used in a sodium storage tank such as a nuclear reactor vessel.
Since it is inserted into sodium at a temperature of over 500℃, the temperature of Shell 1 is approximately 100℃ during plant operation.
The temperature has reached over 500℃. The sodium purification unit is operated by receiving electric power from an external power source (not shown) and operating the electromagnetic pump 3. Sodium at a temperature of 500°C or higher introduced from the sodium inlet 6 passes through an electromagnetic flowmeter 7, enters the electromagnetic pump 3, is pressurized, and is introduced into the cooler 4 through the sodium pipe 21. Since a portion of the sodium pipe 21 is formed into a spring shape, the difference in thermal expansion due to the temperature difference with the shell 1 is absorbed, and thermal stress is less generated.
Here, the sodium introduced into the cooler 4 exchanges heat with the coolant introduced from the coolant inlet pipe 9.
The sodium is cooled to about 140° C. and introduced into the upper sodium inlet of the cold trap 2 through the inside of the support structure 4 _a of the cooler 4 . On the other hand, after cooling the sodium in the cooler 4, the coolant itself is heated and returns to the outside of the system through the coolant outlet pipe 8, but the coolant inlet pipe 9 and outlet pipe 8 are similar to the sodium pipe 21. Since it has a portion shaped like a spring, similar to the sodium pipe 21, the generation of thermal stress is small. The sodium introduced into the inlet of the cold trap 2 goes around the outer periphery of the cold trap 2 and penetrates into the metal mesh _2a filled inside, and oxygen, hydrogen, etc. in the sodium are absorbed. Impurities in metal mesh 2
_Sodium is precipitated in the cold trap 2, purified, and exits through the vertical hole _2c at the center of the cold trap 2, and flows out into the retention section 20 from the sodium outlet 5 at the lower end. Purified sodium gradually flows from the retention section 20 to the gap 18 between the lower part of the shell 1 and the bottomed outer cylinder 17, and gradually rises through this gap 18, during which time the purified sodium is absorbed by the high temperature sodium in the sodium storage tank. Since the temperature rises due to heating, when the sodium is recovered from the upper end of the bottomed outer cylinder 17 into the high temperature sodium in the sodium storage tank, the temperature difference between the sodium is small, so thermal shock is alleviated.

The cold trap 2 includes a heat insulating material 1 filled in an annular space 11 between the shell 1 and the inner tube 10.
2 blocks heat conduction from the shell 1, and since a purified sodium retention section 20 is provided below the cold trap 2, the inside of the sodium storage tank, that is, the outer cylinder 17 with a bottom, The heat of the high temperature sodium on the outside is not directly transferred to the cold trap, and the purified sodium is transferred to the bottomed outer cylinder 17.
Since the heat raised by the high-temperature sodium on the outside of the cold trap is transmitted through the hat-shaped support plate 14, the temperature rise in the cold trap 2 is extremely small. High impurity removal efficiency and stable sodium purification.

However, when the impurities trapped in the cold trap 2 reach the trapping capacity and the function of capturing and removing them is lost, the hat-shaped support plate 14 is removed together with the bottomed outer cylinder 17 from the bottom plate 13 at the lower end of the shell 1, and the cold trap is removed. It is sufficient to remove the trap 2 from the inner tube 10, replace it with a new cold trap 2, and install it.

(Effects of the Invention) The sodium purification unit of the present invention described in detail above has an inner cylindrical pipe concentrically provided inside the shell forming the coolant boundary to form an annular space, and a heat insulating material is provided in the space. Since the internal components such as coolers and cold traps are filled with sodium, heat conduction from the shell is cut off, and a storage area for purified sodium is provided below the cold traps, so the cold The temperature rise in the trap is extremely small, so impurity removal efficiency is high and stable purification performance can be obtained. In addition, an outer cylinder with a bottom is provided concentrically on the outside of the lower part of the shell, and a recess is provided at the bottom of the outer cylinder to form a retention area for purified sodium. Thermal shock is alleviated because the sodium does not directly flow out into the high temperature sodium outside the shell, but is heated by the high temperature sodium outside the shell in the retention section and then gradually flows out from the upper end of the bottomed outer cylinder. Furthermore, since the cold trap is made removable and replaceable, the life of the sodium purification unit can be extended and costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is a sectional view schematically showing a conventional sodium purification unit, and FIG. 2 is a sectional view schematically showing an embodiment of the sodium purification unit of the present invention. 1...Ciel, 2...Cold Trap, 4...
... Cooler, 4 _a ... Support structure material, 10 ... Inner cylinder pipe,
11...Annular space, 12...Insulating material, 13...
... Bottom plate, 14 ... Hat-shaped support plate, 14 _a ... Flange, 15 ... Bottom plate, 16 ... Recess, 17 ...
Outer cylinder with bottom, 18... gap, 20... retention section.

Claims (1)

[Claims] 1. An inner cylindrical pipe is provided concentrically inside the shell to form a narrow annular space between it and the shell, the space is filled with a heat insulating material, and the lower end of the heat insulating material filled part is connected to the lower end of the shell and the inner pipe. A bottom plate is joined to the lower end of the tube to seal it, a cold trap is removably inserted and supported by a flange inside the lower part of the inner cylinder tube, and a cold trap is attached to the outside of the lower part of the shell at approximately the same height as the cold trap. A bottomed outer cylinder having a concave portion in the bottom plate is removably installed concentrically with the shell with an appropriate gap between the bottom plate and the cold trap to form a pool of purified sodium below the cold trap. 1. A sodium purification unit characterized in that a cooler is provided at an upper inlet of a cold trap, and the cooler is supported in an inner tube through a conical support structure so as to seal sodium therein.