JPS606443B2 - Heat shielding device for descending section of heat exchanger tube of liquid metal heating steam generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sodium heated steam generator having a descending section of a heat exchanger tube, and particularly relates to a heat shielding structure for the descending section of the heat exchanger tube.

FIG. 1 shows a longitudinal cross-sectional view of a conventional sodium-heated steam generator for a fast breeder reactor.

In the figure, 1 is the body, 2 is the internal body, 3 is the hemical coil heat exchanger tube, 4 is the heat shield layer, 5 is the heat shield plate, 6 is the convection prevention plate, 7 is the descending part of the heat exchanger tube, 8 is the gas blowing pipe , 9 is a sodium overflow nozzle, 10 is a discharge system nozzle, 11
12 is the rising part of the heat transfer tube, 12 is the sodium liquid level, 13 is the water supply inlet tube plate, I4 is the water supply inlet nozzle, 15 is the steam outlet tube plate,
16 is a steam outlet nozzle, 17 is a sodium inlet nozzle,
18 is an upper flat tube plate, 19 is a cover gas nozzle, 20 is a sodium outlet nozzle, 21 is a cover gas area, and 22 is a sodium distribution pipe.

High-temperature liquid metal sodium, which is a heating medium, enters through the sodium inlet nozzle 17 and is distributed by a half-ring-shaped sodium distribution pipe 22 provided between the internal body 2 and the heat shield plate 5, and is composed of a helical coil heat transfer tube 3. The sodium flows down the eastern part of the tube, exchanges heat with the water-steam in the heat transfer tube, becomes low temperature, and flows out from the sodium outlet nozzle 20 attached to the lower fuselage end plate. On the other hand, the water supply flows in from the water supply inlet nozzle 14 attached to the upper part of the fuselage, is distributed to each heat exchanger tube by the tube plate 13, flows once through the annular area between the fuselage 1 and the heat shield plate 5, and then flows into the lower part of the fuselage. The heat exchanger tube 3 turns and rises inside the heat exchanger tube 3 which is wound in a helical coil shape at regular pitches in both the axial and radial directions in the annular region of the heat shield plate 5 and the inner body 2.

At this time, the feed water flowing in at a low temperature exchanges heat with the high-temperature sodium flowing down outside the tube, is preheated to boiling, is superheated, becomes high-pressure, high-temperature superheated steam, is collected in the steam outlet tube plate 15, and is then passed through the steam outlet nozzle 16. to a turbine (not shown). Since this steam generator uses metallic sodium as the heating medium, it is not allowed for water to leak out of the tubes due to damage to the heat exchanger tubes or the heat exchanger tube plate joints, etc., and for safety reasons, water inlet tube plate 13 and Steam outlet tube plate 15 covers gas area 2
Sodium liquid cocoon turtle 2 created by rapid transient changes.
Care has been taken to ensure that excessive thermal shock is not applied even in response to fluctuations in temperature.

Further, the water supply inlet nozzle 14 and the steam outlet nozzle 16 are attached to the upper flat plate 18, and the eastern part of the pipe is supported from the upper flat plate 18, so that it can be easily pulled out from the body 1 during maintenance and inspection. Furthermore, in the event that the heat transfer tube ruptures, the leaked water and the sodium outside the tube will react explosively, and the pressure inside the steam generator will increase due to the high heat and reaction products such as hydrogen gas. However, in order to prevent the fuselage from bursting due to this, when the pressure rises to a predetermined level, a rupture disk (not shown) provided at the outlet of the discharge system nozzle turtle 0 ruptures, and the rupture disk passes through the discharge system nozzle 10. It has a structure that releases reaction products.

In such a steam generator, since the water supply nozzle 14 and the steam outlet nozzle 16 are provided in the upper part of the steam generator, the heat exchanger tube descending section 7 is inevitably provided.

By the way, it is necessary to keep the amount of heat absorbed by the feed water low in the descending section 7 of the heat exchanger tube.The reason for this is that when the amount of heat absorbed by the supply water in the descending section 7 of the heat exchanger tube increases and boiling of the feed water occurs in the tube, the steam generator This is because there is a risk of causing unstable water-steam flow within the heat exchanger tube, which is extremely harmful to operation.For this reason, conventionally, a double-walled A cylindrical heat shield plate 5 is provided, and a gas is sealed in an annular region therebetween to form a heat shield layer 4, thereby reducing the amount of heat input from the helical coil heat transfer section 3.

FIG. 2 is a view taken along the 0--ro arrow in FIG. 1.

FIG. 3 shows details of the heat shielding structure in the descending section of the conventional heat exchanger tube. Gas is sent through the gas blowing pipe 8 to the annular area between the double cylindrical heat shield plates 5, and the sodium liquid level 23 is
is pushed down to the upper end of the gas relief hole 28, and excess gas escapes from the gas relief hole 28. In such a heat shielding structure for the descending part of the heat exchanger tube, "high temperature sodium flows from the lower end of the heat shield plate 5 ~ flows in the axial direction of the heat exchanger tube due to natural convection, significantly impairing the heat shielding effect ~ convection" Prevention plates 6 are provided at appropriate intervals.

A large heat shielding effect can be obtained by providing a large number of such convection prevention plates 6 so as to completely block the sodium flow path. However, on the other hand, measures against a sodium-water reaction accident in the descending section 7 of the heat exchanger tube must also be taken into consideration. In other words, if a sodium-water reaction accident occurs in the descending section 7 of the heat exchanger tube, the reaction product will quickly
It is necessary to minimize the flow resistance of the sodium flow path around the descending section 7 of the heat exchanger tube so that the sodium can flow out to the discharge system nozzle 10. Therefore, in the conventional heat shielding structure, it is not possible to provide a large number of convection prevention plates or to block the sodium flow path, and therefore, there is a drawback that a sufficient heat shielding effect cannot be obtained. The purpose of the present invention is to compensate for the above-mentioned drawbacks, and to provide a heat exchanger that has a small amount of heat absorbed by the feed water in the descending section of the heat exchanger tube. The object of the present invention is to provide a heat shielding structure for a descending portion of a heat exchanger tube from which heat can easily flow out into a discharge system.

The feature of the present invention is that instead of the conventional cylindrical heat shielding plate, a large number of inclined plates are provided along the direction of the descending portion of the heat exchanger tube, each having a shape that allows gas to be stored at the bottom to obtain a heat shielding effect. 1. Even if a sodium-water reaction accident occurs in the descending section of the heat transfer tube, the structure is designed to expel the reaction products from the gap between each inclined plate toward the edge of the calcoil heat transfer tube, allowing them to easily flow out to the release system. be.

FIG. 4 is a perspective view showing an embodiment of the heat shielding structure for the descending portion of the heat exchanger tube according to the present invention.

FIG. 5 shows a longitudinal section of FIG. 4. In FIGS. 4 and 5, ~ 1 is the body torso 4 is the heat shield layer, 7 is the descending part of the heat transfer tube, 8 is the gas blowing pipe, 23 is the sodium liquid level of the heat shield layer,
24 is a gas reservoir swash plate, and 26 is an external fuselage. The space around the descending portion 7 of the heat exchanger tube is partitioned along the tube axis direction by a large number of gas reservoir inclined plates 24 and an external gas reservoir inclined plate 26 . Sekiguchi 30 of the sloping board are arranged in order from the bottom one to the smallest one. Gas is sent through the gas blowing pipe 8, and when the gas is first stored in the lower part of the lowest gas reservoir inclined plate, the remaining gas becomes bubbles and rises. Since the oblique plate 24 of the gas reservoir protrudes longer in the horizontal direction toward the upper stage, gas bubbles rising from the lower stage are collected at the lower part of the slope of the upper stage. In this way, by continuing to feed the gas, a gas layer can be formed at the bottom of all the gas reservoir inclined plates 24. In addition, the descending part 7 of the heat exchanger tube and the gas reservoir inclined plate 24
and are connected via the gas reservoir inclined plate support 25 to prevent gas from the lower stage from leaking to the upper stage. Gas reservoir inclined plate 2
By appropriately determining the pitch, angle of inclination, length of the tip, etc. of heat exchanger tube 4, the periphery of descending portion 7 of the heat exchanger tube can be almost completely covered with a gas layer, and a better heat shielding effect can be obtained.

One side of the small chamber surrounded by the gas reservoir inclined plate 24 and the external body 26 is open to the calcoil heat exchanger tube section.

In the unlikely event that water leaks in the descending section 7 of the tube and a sodium-water reaction occurs, the reaction product will flow through the closed section and flow into the sodium flow path on the helical coil heat transfer tube side, increasing the flow resistance. It can be easily discharged into the release system. Since the present invention is configured and operates in this manner, it can achieve the following effects.

{1' Since the lower part of the heat exchanger tube can be almost completely surrounded by a gas layer, the heat shielding effect is great against heat input from the helical coil heat exchanger tube side.

[21] In response to the sodium-water reaction that occurs due to water leakage in the descending section of the heat transfer tube, the reaction product can flow out into the sodium flow path on the side of the calcoil heat transfer tube, so there is little flow resistance and there is no flow to the release system. Evacuation occurs quickly.

[Brief explanation of drawings]

Figure 1 shows a vertical cross-section of a sodium-heated steam generator for a secondary fast breeder reactor, Figure 2 shows a view from the 0-B arrow in Figure 1, and Figure 3 shows a conventional heat shielding structure for the descending part of heat transfer tubes. 4 is a perspective view showing an embodiment of the present invention, and FIG. 5 is a longitudinal sectional view of FIG. 4. 4...Heat shielding layer, 7...Heat transfer tube descending part, 8
...... Gas blowing pipe, 24... Gas reservoir swash plate, 26... External body, 30a, 30b... Opening of forehead swash plate. Figure 2 Figure 3 Figure 1 Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1. In a liquid metal heated steam generator having a descending section of a heat transfer tube, the descending section of the heat transfer tube is crossed in a depth direction of the liquid metal liquid,
In addition, a plurality of trapezoidal pyramid-shaped sloped plates that slope downward are provided, the opening diameter of the upper sloped plate is smaller than the opening diameter of the lower sloped plate, and a heat shielding layer containing gas is provided between these sloped plates. A heat shielding device for a descending section of a heat transfer tube of a liquid metal heated steam generator, characterized in that: 2. A heat shielding device for a descending portion of a heat exchanger tube of a liquid metal heated steam generator according to claim 1, wherein the opening of the heat shielding layer is closed by a liquid metal surface.