JPH0481155B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a high-temperature gas furnace, and particularly to a sealing mechanism between a reflector made of a graphite structure having different coefficients of thermal expansion and a steel plenum of a steel structure. It is.

[Background of the invention]

Most current nuclear reactors use fuel rods coated with metal, so raising the temperature will destroy the metal coating on the fuel rods, so the temperature cannot be raised very high, and is used for nuclear power generation at around 650℃. It is being

On the other hand, the fuel structure of high-temperature gas reactors consists of black spherical grains with a diameter of less than 1 mm. These grains have a core of oxide or carbide such as uranium, and the outside is covered with a thin coating of special carbon or silicon. Encased in a triple or quadruple layer, this coating protects the uranium and prevents radioactive substances produced from the uranium during nuclear fission from escaping.

Carbon and silicon coatings are more resistant to heat than conventional metal coatings, so they do not break down even at temperatures of over 1,000 degrees Celsius, and are able to trap radioactive materials inside.

These coated fuel particles are baked together with graphite to make a fuel compact, and this fuel compact is molded into a short cylindrical shape and packed into a hexagonal graphite block to form a fuel element. The core of a high-temperature gas reactor is made up of many layers stacked on top of each other.

The core of this high-temperature gas reactor is made of graphite, which is resistant to heat and has good thermal conductivity, so it can withstand temperatures of over 1,000 degrees Celsius.

On the other hand, helium is used as a coolant in the core of high-temperature gas reactors.This helium cools the core and becomes a high-temperature coolant of around 1000℃, and the heat is converted into steam in a steam generator to generate nuclear power. used.

Figure 8 is a schematic configuration diagram of a high-temperature gas furnace, Figure 9 is a perspective view of the reflector in Figure 8, Figure 10 is a sectional view taken along line X-X in Figure 9, and Figure 11 is a reflector and steel structure. FIG. 12 is a perspective view illustrating the difference in expansion of the plenum, and FIG. 12 is a perspective view showing a seal structure between the reflector and the steel plenum.

In FIGS. 8 to 12, 1 is a pressure vessel;
2 and 3 are the graphite structure reflector and the steel plenum of the steel structure arranged in the pressure vessel 1, 4 is the reactor core where the fuel body is arranged, and 5 and 6 are connected to the pressure vessel 1. Inner pipe and outer pipe, 7 and 8 are pressure vessel 1
9 is a helium passage formed by the pressure vessel 1, the steel plenum 3, and the reflector 2; 10 is a mixing chamber within the steel plenum 3;

In such a structure, the low-temperature coolant of 400°C helium supplied between the inner tube 5 and the outer tube 6 is supplied to the upper chamber 7 as shown by the solid arrow, and descends through the helium passage 9 to the pressure vessel. At the same time, the reactor core 4 is cooled through the lower chamber 8, and becomes a high-temperature coolant at 950° C., which flows through the mixing chamber 10 and the inner pipe 5 to a steam generator (not shown).

The above describes the general flow state of low-temperature coolant and high-temperature coolant in a high-temperature gas reactor.
The flow of coolant inside the high-temperature gas reactor consists of a high-temperature coolant flow that cools the reactor core 4, as shown by the dashed arrow in FIG. 8, and a low-temperature coolant flow that cools the pressure vessel 1, as shown by the solid-line arrow. Divided into coolant streams. At this time, since the high-temperature coolant has a pressure loss in the core 4, a pressure difference is generated between the high-temperature coolant and the low-temperature coolant at the outlet of the core 4.

On the other hand, the reflector 2 has a block structure in which graphite blocks are stacked as shown in FIG. A step 11 of several mm is generated as shown.

In addition, since the reflector 2 and the steel plenum 3 are stacked on top of each other as shown in the perspective view of FIG.
Due to the difference in thermal expansion between the graphite in the steel plenum 3 and the metal in the steel plenum 3, it moves from the solid line at normal temperature in Fig. 11 to the two-dot chain line when the temperature rises, resulting in a radial displacement difference of 1.
2. Due to the axial displacement difference 13, a gap is created between the sealing surfaces 14 and 15 between the reflector 2 and the steel plenum 3, and from this gap or the step 11 of the reflector 2, the above-mentioned high temperature coolant and low temperature There is a drawback that the temperature of the high-temperature coolant at the core 4 outlet drops abnormally due to the differential pressure of the coolant causing the low-temperature coolant to flow into the high-temperature coolant or the high-temperature coolant to flow into the low-temperature coolant. .

Conventionally, a sealing mechanism shown in FIG. 12 has been used as a sealing mechanism between the reflector 2 and the steel plenum 3.

The seal mechanism shown in FIG. 12 has a seal plate 16 provided on the side surface of the reflector 2, and this seal plate 16
It is a structure that is pressed with 7.

However, in order to obtain a sealing effect with such a sealing mechanism, extremely high processing accuracy is required.
Further, in this case, the temperature of the sealing part is relatively low at about 400°C on the helium passage 9 side, but when used at a higher temperature, the leaf spring 17 causes stress relaxation and the pressing force of the sealing plate 16 increases. This has the disadvantage that the sealing effect cannot be expected.

Recently, high-temperature gas furnaces are planned to operate at even higher temperatures (950°C), so high machining accuracy is no longer required, and the development of a sealing mechanism inside the high-temperature gas furnace that is resistant to high temperatures is required. ing.

[Purpose of the invention]

The present invention attempts to eliminate the conventional drawbacks, and its purpose is to ensure a reliable seal even if there is a difference in elongation, step, or pressure due to thermal expansion on the sealing surface between the reflector and the steel plenum. The aim is to obtain a sealing mechanism that can

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention provides a groove on the sealing surface of the reflector and the steel plenum, and also provides a protrusion on the steel plenum side, and seals a ceramic fiber between the groove and the protrusion. This is with a material interposed.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing a sealing mechanism between a reflector and a steel plenum according to an embodiment of the present invention, and FIGS. 2a to 2f are enlarged sectional views of the sealing material.
c, e show the state of the sealing material before compression, b,
d and f indicate the state of the sealing material after compression. Fig. 3 is a characteristic curve diagram comparing the compressibility and leakage ratio of the sealing material, Fig. 4 is a sectional view showing another embodiment of Fig. 1, and Figs. 5 a to d are radial directions of the reflector. 6 and 7 are characteristic curve diagrams showing the relationship between the compressibility of the sealing material and the leakage ratio.

1 to 4, 2 is a reflector, 3 is a steel plenum, 11 is a step, and 14 and 15 are sealing surfaces between the reflector 2 and the steel plenum 3, which are the same as the conventional ones.

18 is a groove provided in the sealing surface 15 of the reflector 2;
9 is a projection provided on the sealing surface 14 of the steel plenum 3; 20a and 20b are sealing materials;
a is a ceramic fiber 2 as shown in Figure 2.
1. It is formed of ceramic cloth 22 and metal foil 23, and the sealing material 20b is formed only of ceramic fiber 21.

In such a structure, grooves 18, 18 are bored in the sealing surface 15 of the reflector 2, as shown in FIG.
Seal materials 20b, 20b are arranged in these grooves 18, 18.

On the other hand, protrusions 19 are provided on the sealing surface 14 of the steel plenum 3, and a sealing material 2 is provided between the sealing surface 15 of the reflector 2 and the sealing surface 15 of the steel plenum 3.
The seal surfaces 14 and 15 are sealed by interposing the seal 0a.

Here, the structure of the sealing material 20a will be described using FIG. 2.

In FIG. 2, a, c, and e show the states of the sealing material 20a before compression, and b, d, and f show the states of the sealing material 20a after being compressed.

As mentioned above, the reflector 2 has a block structure, and the sealing surface 15 of each block is machined.
Step 11 due to installation tolerance and variation in thermal expansion coefficient
occurs. Therefore, the sealing material 20a covers this step 1.
1, alumina-silica ceramic fiber 2 with high compressibility as shown in Fig. 2 is used.
Use 1. Since the ceramic fiber 21 has a high transmittance even when compressed, a metal foil 23 is installed within the sealing material 20a to prevent the flow from passing through the ceramic fiber 21.

Furthermore, since the reflector 2 and the steel plenum 3 have different coefficients of thermal expansion, a difference in elongation occurs between the steel plenum 3 and the sealing material 20a during the temperature rising process. At this time, if the frictional resistance between the steel plenum 3 and the sealing material 20a is large, excessive force will act on the reflector 2, so the sealing material 20a will be
A is coated as shown in FIG. This ceramic cloth 22 also serves to prevent the ceramic fibers 21 of the sealing material 20a from scattering.

Note that the sealing material 20b was only the ceramic fiber 21.

In this way, the sealing material 20a is placed between the reflector 2 and the sealing surfaces 14, 15 of the steel plenum 3, and the protrusions 19, 19 are placed on both sides of the sealing material 20a to seal the sealing surfaces 14, 15. do.

Further, the grooves 18, 18 are filled with sealing material 20b, 20b made of only the ceramic fiber 21, and the compression reaction force of the sealing material 20b, 20b causes the protrusion to
9 and 19 are always pushed up toward the steel plenum 3 side, thereby preventing the sealing effect and shearing deformation of the sealing material 20a due to surface contact between the sealing material 20a and the sealing surfaces 14 and 15.

Figure 3 shows experimental data on the effectiveness of the metal foil 23 in preventing permeation flow through the seal mechanism, and the solid line A indicates the data obtained when the metal foil 22 is provided on the sealing material 20a as shown in Figures 2 a to f. The leakage ratio is shown, and the leakage ratio is compared with the leakage amount when the metal foil 22 is provided at 50% compression as 1.0.

The broken line B is the leakage ratio when the metal foil 23 is not arranged.

By arranging the metal foil 23 in the sealing material 20a in this manner, the leakage ratio was reduced, and it was confirmed that arranging the metal foil 23 in the sealing material 20a was effective for the sealing mechanism.

Moreover, by arranging the metal foil 22, stable sealing performance can be obtained against changes in the amount of compression of the sealing material 20a.

FIG. 4 shows another embodiment of FIG. 1, with a groove 18 on the reflector 2 side and a protrusion 19 on the steel plenum 3 side.
A sealing material 20a shown in FIG. 2 is arranged between the groove 18 and the protrusion 19.

In the one shown in Fig. 4, the difference in thermal expansion between the reflector 2 and the steel plenum 3 is completely absorbed by the amount of compression of the sealing material 20a.Although there is a limit to the absorption of the difference in thermal expansion, the difference in thermal expansion between the reflector 2 and the steel plenum 3 is absorbed. The length can be made longer.

5 to 7 show a sealing mechanism in the radial direction when a step 11 occurs between the reflectors 2 and 2 as shown in FIG. 5a.

As shown in the perspective view of FIG. 5a, if the space between the reflector 2 and the steel plenum 3 is sealed only by the sealing material 20a, the sealing material 20a is highly compressible, but As shown in Figure 5a, there is a step 1.
1, a gap 24 shown in FIG. 5b is generated between the reflectors 2, and a leak amount ratio as shown in FIG. 6 is exhibited.

The leakage ratio in Fig. 6 is shown by curve C, assuming that the leakage ratio is 1.0 when the step 11 is 5 mm at 50% compression, and curve E when the step 11 is 5 mm.
indicates the leakage ratio when the step 11 is 10 mm.

In this way, as the step 11 becomes larger, the amount of leakage increases.

Therefore, as shown in FIG. 5 c and d, a groove 18 is bored as shown in FIG. The sealing material 20b is arranged as shown in FIG.

As a result, a gentle slope is formed in the step 11 by the sealing material 20b, and the generation of the gap 24 can be prevented.

Curve F in FIG. 7 is a curve when the leakage ratio is 1.0 when the sealing material 20b is compressed by 50% and the step 11 is 0. △ indicates the step 11 is 3 mm, and ▽ indicates the step 1.
1 indicates 5 mm, and □ indicates the case where the step 11 is 7 mm.

By providing the grooves 18 in the reflector 2 and filling the grooves 18 with the sealing material 20b as shown in FIGS. As a result, a sealing mechanism is obtained in which the amount of leakage in the radial direction of the reflector 2 is reduced.

As described above, since the temperature of the reflector 2 and steel plenum 3 is around 950°C in the sealing mechanism in a high-temperature gas furnace, conventional sealing means such as gaskets and O-rings cannot be used, but the seal of the present invention The mechanism is mainly ceramic fiber 2.
1, the reflector 2 and the steel plenum 3 are not required to have very strict processing accuracy.

〔Effect of the invention〕

In the present invention, a groove is provided on the sealing surface of the reflector and the steel plenum, and a protrusion is provided on the steel plenum side, and a ceramic fiber seal material is interposed between the groove and the protrusion. It is possible to reliably seal even if there is a difference in elongation, a step, or a pressure difference due to thermal expansion, and since this sealing mechanism can absorb processing and installation tolerances, the high-temperature gas furnace can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a sealing mechanism between a reflector and a steel plenum according to an embodiment of the present invention, and FIGS. 2a to 2f are enlarged sectional views of the sealing material.
c, e show the state of the sealing material before compression, b,
d and f show the state of the sealing material after compression. Figure 3 is a characteristic curve diagram comparing the compression rate and leakage ratio of the sealing material. Figure 4 is a cross section showing another example of Figure 1. Figures 5a to 5d are perspective views and sectional views showing the sealing mechanism in the radial direction of the reflector, Figures 6 and 7 are characteristic curve diagrams showing the relationship between the compressibility of the sealing material and the leakage ratio; Figure 8 is a schematic diagram of the high-temperature gas reactor, Figure 9 is a perspective view of the reflector in Figure 8, Figure 10 is a sectional view taken along the line X-X in Figure 9, and Figure 11 is the reflector and steel plenum. FIG. 12 is a perspective view showing a conventional seal structure between a reflector and a steel plenum. 1... Pressure vessel, 2... Reflector, 3... Steel plenum, 14, 15... Seal surface, 18... Groove,
19...Protrusion, 20a, 20b...Sealing material.

Claims (1)

[Claims] 1 A reflector made of graphite structure and a steel plenum made of steel structure are arranged in a pressure vessel, and low-temperature coolant is flowed on the outside of the reflector and steel plenum, and high-temperature gas is poured inside with high-temperature coolant. In the furnace, a groove is provided on the reflector side and a projection is provided on the steel plenum side in the sealing surface of the reflector and the steel plenum, and a ceramic fiber sealing material is interposed between the groove and the projection. High temperature gas furnace.