JPS63156504A - Cold trap - Google Patents

Abstract

PURPOSE:To increase the efficiency in cooling Na, by arranging a partition plate made of a heat insulating material with both upper and lower ends opened on the side end part of the collector of the title cold trap to insulate the heat between the collector and the surrounding Na. CONSTITUTION:A mesh 1 is housed in a vessel 2, and the vessel 2 is also used as the passage of Na. A wick 22 is arranged on the outside of the vessel 2, and an annular space 25 surrounded with a heat insulating wall 24 is formed on the outside of the wick and forms a heat pipe. The upper part of the annular space 25 communicates with an upper space 26, a fin 19 is provided on the outside of the upper space 26, and the upper space is cooled by the cooling air by a fan 13. To facilitate the return of a liq. metal 23 condensed in the upper space to the wick 22, the partition plate 30 sloped toward the inside is provided to separate the insulating wall 24, the wick 22, and the upper space 26. The warming of the highly heat conductive Na can be prevented by the heat insulating partition plate 30.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for purifying liquid metal sodium used in fast breeder reactors and the like.

[Conventional technology]

Traditionally, in fast breeder reactors, the coolant sodium (
A cold trap is used to purify Na (hereinafter abbreviated as Na). For example, a cold trap used in a tank-type fast breeder reactor has a configuration as shown in FIG. A container 2 filled with a metal mesh 1 is assembled in a damp plug 3, and Na5 in the reactor vessel 4 is pumped into the container 2 by an electromagnetic pump 6.

Inside the mesh 1, there is a cooling pipe 7.
A liquid metal (for example, NaK alloy) 8 can be circulated inside. The cooling pipe 7 is connected to an external coolant circulation loop 9. The coolant circulation loop 9 includes an electromagnetic pump 10 for circulating NaK and an air cooler 11 for cooling NaK. Note that the air cooler 11 usually uses a combination of finned piping 12 and a fan 13.

The mesh 1 is cooled by the cooling pipe 7.

The temperature is lowered to about 110°C. The fins 14 attached to the outside of the cooling pipe 7 are for promoting cooling of the mesh 1. The Na5 pumped into the container 2 passes through the mesh 1 kept at a low temperature and flows downward.

At this time, impurities (particularly oxygen) dissolved in the Na are precipitated on the surface of the mesh 1 (in the case of oxygen, they are precipitated as oxides).

Since Na is captured, the impurity concentration in Na decreases.

The purified Na comes out from a pipe 15 provided at the bottom of the container 2 and returns to the Na pool in the furnace container 4 again. Note that the outlet pipe 15 has a double structure with the pumping pipe 16, and the return Na is pumped 1. It has a so-called eco-imizer function that recovers some of the heat from the raised Na.

[Problem that the invention seeks to solve]

The above-mentioned conventional cold trap has the following problems.

First, because the means for circulating Na and the coolant circulation loop necessary for mesh cooling have a complicated structure, it is difficult to assemble and remove the device, especially in cold traps. It is necessary to replace the mesh frequently, but it is difficult to remove and install the mesh.

The second problem is that an electromagnetic pump is required to circulate Na. The location where the electromagnetic pump is placed is under high radiation (~101'R) and high temperature (~101'R).
Therefore, around the electromagnetic pump,
Radiation shielding and cooling means are required to protect the electromagnetic pump (especially the coil), making the construction of the cold trap large-scale.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a cold trap that is simple in construction and easy to install and remove.

Other related prior art related to this type of device include Utility Model (Utility Model Patent Application 58-116002) patents (JP-A-60-194026 and JP-A-55-38906).

This utility model attempts to purify Na in the tank 17 by forcedly circulating Na5 through the tank 17, as shown in FIG. A mesh 1 cooled by a heat pipe 18 is disposed in the tank 17, and is intended to collect impurities in Na on the surface of the mesh 1. To cool the heat pipe 18, fins 19 and a fan are attached to the upper end of the heat pipe 18.

Further, in order to locally cool only the mesh 1, the heat pipe wall surface above the mesh is covered with a heat insulating wall 20.

However, even in this example, a loop 21 for circulating Na, an electromagnetic pump 6, and an Na tank 17 are required, and even if it is incorporated into a nuclear reactor, it has a complicated structure, so it is difficult to assemble and remove the device. is difficult. Further, there are problems such as radiation resistance of the electromagnetic pump and cooling of the coil.

Furthermore, with the structure of this utility model, the mesh 1 or Na cannot be sufficiently cooled by the heat pipe. The reason is that since Na is a good thermal conductor, heat conduction from the mainstream Na in the tank warms the mesh or the Na in the vicinity. In Na purification operation, it is necessary to cool the Na temperature to around 110°C. However, the temperature of Na in the reactor vessel is usually 55
There is also 0'C, and the temperature difference is 440°C. It is physically impossible to create such a large temperature difference in liquid Na. In other words, the configuration of this embodiment cannot function as a cold trap.

[Means for solving problems]

In order to achieve the above object, the present invention uses a heat pipe to cool Na. Also.

The mesh, which is an impurity trap, is inserted into the Na pool in the furnace vessel, and the natural circulation flow that occurs within the furnace vessel when the mesh is cooled is used to circulate Na.

In order to facilitate Na cooling, an insulating partition plate is placed at the side end of the mesh.

[Effect]

By using the above means, piping and pumps for circulating Na and NaK circulation loops for cooling the mesh become unnecessary, and the configuration of the cold trap is greatly simplified. This allows installation of cold traps,
Easy to remove.

In addition, since a heat insulating wall is attached to the mesh side end,
Heat exchange with surrounding Na is eliminated, and the cooling efficiency of the mesh is improved. This increases the natural convection flowing downward within the mesh, and traps impurities within the mesh efficiently.

〔Example〕

The present invention will be explained in detail below using examples.

FIG. 1 shows an embodiment of the present invention. A mesh 1 is housed in a container 2, and the container 2 also serves as a flow path for Na. A wick 22 is arranged on the outside of the container 2,
The wick 22 is constantly wetted with a liquid metal (for example, mercury) 23.

Outside the wick 22 there is an annular space 25 surrounded by a heat insulating wall 24, leading to a heat pipe structure. The annular space 25 communicates with the upper space 26, and the pressure in both spaces is low, close to the saturated vapor pressure of the liquid metal 23. Fins 19 are attached to the outside of the upper space 26,
The whole is surrounded by an air cooler casing 11. Fan 13 is used to send cooling air to casing 11.

When the fan 13 is activated, the upper space 26 is cooled and the pressure within the space is reduced. With this pressure drop, the vapor 27 of the liquid metal 13 evaporated from the wick 22 flows into the annular space rI.
! It flows into the upper space 26 through J25. Upper space 2
6, the liquid metal vapor 27 is condensed, becomes a liquid, and returns to the wick 22 again. in this way,
The liquid metal vapor 27 (1) evaporates from the wick (absorbs latent heat of vaporization), (2) moves in vapor state through the annular space to the upper space, (3) condenses in the upper space (releases latent heat of vaporization). (4) The so-called heat pipe cycle of turning into liquid and returning to the wick is repeated. Through this cycle, the Na5 and mesh 1 in the container 2 are cooled, and the N and A5 increase in density and flow down the container 2. . High-temperature Na in the furnace vessel 4 flows in from an inlet 28 provided near the liquid level, is cooled within the vessel 2, and returns to the furnace vessel 4 again. Note that the fins 4 attached to the inner wall of the container 2
2 is for promoting cooling of Na. In this way, a natural circulation flow occurs that goes around the furnace vessel → cold trap → furnace vessel, and Na in the furnace vessel can be supplied to the cold trap even without an electromagnetic pump.

Furthermore, since the heat from the container 2 is transported in the form of latent heat of vaporization, by selecting an appropriate working fluid (e.g. mercury) with a large latent heat of vaporization, the heat transport channel, that is, the annular space 25 in FIG. It can be made smaller.

,'・Furthermore, the strong 1,' control I-bu for cooling Na and the mesh becomes unnecessary, and the yaw 2. The configuration of the todrap can be greatly simplified and downsized. For this reason,
This has the effect of making it easier to install and remove the cold trap. For example, in the embodiment shown in FIG. 1, the cold trap can be easily replaced by removing flange 29.

FIG. 4 shows in detail an example of the configuration of the upper space in the embodiment shown in FIG.
However, in order to make it easier to return to the wick 22, the insulation wall 24
, the wick 22 and the upper space 26 are partitioned by an inwardly sloped plate 30, and the liquid metal vapor 2 is placed in the partition plate 30.
The nozzle 31 through which No. 7 flows is installed. Liquid metal vapor 27 from the annular space 25 enters the upper space 26 through the nozzle 31 and condenses on the inner wall 32 of the space. The condensed liquid metal 23 falls onto the partition plate 30, flows inward over the partition plate, and is sucked into the wick 22. As for the shape of the nozzle 31, a rectangular nozzle is shown in FIG. The circulation head will be explained.

In the cold trap shown in Figure 1, the required amount of heat removal Q (W) is Q=Cpp V (T)l-Tc)
-(1) where Cp: specific heat of Na (J/kg'C) ρ
: Density of Na (kg/V) V: Volumetric flow rate of Na (V/5) TH: Temperature of Na in the furnace vessel ('C) Tc: Na temperature required for purification operation (mesh average temperature (
℃)) Normally, in a fast breeder reactor, it is necessary to mainly remove oxygen from Na, and the cold trap has an oxygen concentration of ≦lp.
The required specification is "to purify down to pm". The saturated dissolution temperature of oxygen in Na corresponding to 1 ppwr of oxygen concentration is 110°C. Therefore, the temperature T in equation (1)
When calculating the required amount of heat removal by substituting 110 °C'- for a, the result is uniform as shown in Fig. 5. As shown in the results in Figure 5, the required amount of heat removal increases linearly with the degree of Na in the furnace vessel, and in the operating temperature range (250 to 550°C)
~630kw of heat removal is required.

On the other hand, in the present invention, this heat is transported by a heat pipe, and the dimensions of the heat pipe are determined as follows.

In FIG. 1, the maximum heat flux that steam can carry upward within the annular space 25 is determined by the sonic critical heat flux, qs.

qs= 0, 474 L (ρvPv) '/”
-(2) where, L: latent heat of vaporization of working fluid (liquid gold m) (J/kg), ρV: density of working fluid stream vapor (kg/rrr).

Pv: Vapor pressure of the working fluid (Pl) Therefore, the maximum amount of heat Q that steam can carry within the annular space 25
, Q h =qson・Ah・
= (3) Here, Ah is the cross-sectional area of the annular space 25, and the inner diameter of the ring is Di and the outer diameter is Do.

Ab= (Do"-Dt")
= (4) In equations (1) and (3), Q ” Q h
Then, rearranging using equations (2) and (4), the outer diameter Do of the annular space is.

In equation (5), the diameter of the conventional cold trap (
= 1m), and taking mercury as an example of a working fluid, and substituting its physical property values, the results of calculations for each sodium temperature TH are shown in Figure 5.According to the results shown in Figure 0, the annular space (therefore approximately equal to the outside diameter of the cold trap) is 1 in the operating temperature range (250-550°C)
．． It is 2 to 1.7 m, and the cold trap itself is not very large. (The size is such that it is easy to install and remove.) As Na cools down, the furnace vessel → cold trap vessel →
A natural circulation occurs that goes around the furnace vessel, but the natural circulation head ΔPsc (Pa) at this time is.

ΔPsc= (pc-gh)gh
-(6): Here, ρC: Density of -Na at the average Na temperature of the mesh part (kg/Po) ρh: Density of Na at the Na temperature of the furnace vessel (kg/Po)
rn') g: Gravitational acceleration (=9.8 m/s") h: Height from the inlet to the outlet of the container 2 (m) In equation (6), pc is the Na density at 110'c, h is the conventional cold trap length = 2 m
) is calculated by substituting 0 as shown in Figure 6.
According to the results in the figure, when the Na temperature in the furnace vessel increases,
The natural circulation head increases approximately linearly.

On the other hand, the loop pressure drop during natural circulation, especially the pressure drop at the mesh portion, can be evaluated using the pressure drop characteristics of a conventional cold trap. As a cold trap mesh, usually
Wire diameter'=0.1m+, porosity valve 95%, packed bed length'
=0.5m mesh is often used. Taking this mesh as an example, 1! When the ring Na flow rate is 5 v/h, the pressure loss at the mesh part at the initial stage of purification operation is 40
0 (Pa), purification operation - pressure loss after 3000 years
(pa) (based on conventional operating data), these two pressure losses are shown in FIG. Comparing with the natural circulation head already mentioned, the operating temperature range (250-550℃
), the pressure drop in the natural circulation head is greater than that in the mesh section. Therefore, even without a Na circulation pump, Na in the furnace vessel can be circulated through the mesh for one year by natural circulation.

Normally, nuclear reactors are shut down once a year for periodic inspections. If the cold trap is replaced with a new one during this shutdown period, it can be used for Na purification during the next reactor operation period.

In this embodiment, which shows another embodiment in FIG. 7, only the mesh 1 is replaced, resulting in eight configurations. A support rod 33 is attached to the mesh 1, and a flange 34 is provided at the upper end of the support rod 33. When replacing the mesh 1, the flange 34 is removed and the mesh 1 is pulled up using the support rod 33. In addition, in order to replace the mesh, the container 2 that stores the mesh 1 has an upper flange 3.
It has a configuration that extends to 4. Wick 22. The structure of the annular space 25 and the heat insulating wall 24 is the same as the embodiment shown in FIG.

Another embodiment is shown in FIG. 8, in which the heat pipe 35 is placed inside the mesh storage container 2. There is a wick 22 inside the heat pipe 35, and the liquid metal 23, which is a working fluid, constantly wets the wick 22. A fin 19 is attached to the upper end of the heat pipe 35, and the outside thereof is surrounded by the casing 11 of the air cooler. A heat insulating wall 24 is placed on the outside of the mesh storage container 2 to thermally isolate the Na inside the container and the mesh from the Na outside the container.

Fins 36 attached to the outside of the heat pipe 35 are provided to promote heat transfer from the surface of the heat pipe 35 to Na5. The mesh 1 can be replaced by removing the flange 29 and partially pulling out the heat pipe 35. In this embodiment, the heat pipe is circular and easy to manufacture. Additionally, the entire cold trap can be easily assembled.

FIG. 9 shows another embodiment. In this example, the mesh 1 is in close contact with the reactor vessel 4 of the nuclear reactor, and the heat pipe 35 is outside the reactor vessel 4. Cooling fins 19 are attached to the outer wall of the heat pipe 35.

The inner side wall of the mesh 1 is made of a heat insulating wall 24. The insulation wall 24 is a partition plate 37 between the upper plenum and the lower plenum.
It is welded onto the mesh 1, and there is a partial opening 38 in the part that contacts the bottom of the mesh 1. The Na5 and the mesh 1 are cooled by the external heat pipe 35, and as a result, natural circulation occurs in the Na5 in the furnace vessel 4 as shown by the broken line in the figure. How to replace mesh 1.

During nuclear reactor operation, which is carried out by pulling upward the support rod 33 attached to the mesh, a special shielding plug 40 is fitted into the first through hole 39 to prevent radiation from leaking to the outside. With such a configuration, maintenance of the heat pipe becomes easy.

〔Effect of the invention〕

According to the present invention, there is no need for piping or an electromagnetic pump for circulating Na, and no need for any coolant circulation loop for cooling the mesh and Na. Also,
Since the side wall of the mesh is insulated from the surrounding Na, the Na cooling efficiency increases. Therefore, the structure of the cold trap is greatly simplified and made smaller.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the present invention, FIGS.
The figure shows the configuration of a conventional cold trap.
The configuration diagrams of the upper space of the embodiment shown in the figure, FIGS. 5 and 6, show the results of calculating the dimensions of the cold trap and the natural circulation capacity, taking the embodiment shown in FIG. 1 as an example. Figure 7. FIGS. 8 and 9 are configuration diagrams of other embodiments. 1...Mesh, 2...Container, 3...Shiyahei plug, 4...Reactor vessel, 5...Sodium, 6
...Electromagnetic pump, 7. Cooling piping, 8. Liquid metal (working fluid).

Claims (1)

[Scope of Claims] 1. An apparatus for precipitating and collecting impurities in sodium on the surface of the trapping body, which comprises a trapping body such as a mesh and a means for cooling the trapping body, wherein the side end of the trapping body A cold trap characterized by a partition plate with openings at the top and bottom ends. 2. The cold trap according to claim 1, wherein the partition plate is made of a heat insulating material. 3. The cold trap according to claim 1, wherein a heat pipe is used as a cooling means for the trapping body.