JPS5919893A - Thermal shielding device of fbr type reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a thermal shielding device for a fast breeder reactor that uses liquid metal such as liquid sodium as a coolant.

[Technical background of the invention]

Generally, fast breeder reactors use liquid metal such as liquid sodium as a cooling system. By the way, since such a liquid metal coolant has an extremely high heat transfer ability, the temperature of the wall of the reactor vessel that is in contact with the coolant follows the temperature change of the coolant very quickly. However, the portion of the reactor vessel above the coolant liquid level does not follow the temperature change of the coolant. For this reason, when the temperature of the coolant changes, such as when starting or stopping a nuclear reactor, a large temperature difference occurs between the part of the reactor vessel below the coolant liquid level and the part above the liquid level. . A large temperature gradient occurs on the reactor vessel wall near the liquid level in this cooling system, causing excessive thermal stress and impairing the integrity of the reactor vessel.

Therefore, the following method has been considered as a method for preventing the above-mentioned problems. In other words, a large number of hollow heat shields filled with gas are arranged along the inner surface of the reactor vessel, and these heat shields reduce the heat flux into the reactor vessel to reduce thermal stress. This is a configuration that ensures the integrity of the reactor vessel by alleviating the temperature gradient on the reactor vessel wall due to changes in coolant temperature when the reactor starts and stops operating. A large temperature difference occurs between the inside and outside of the body.7 This causes thermal stress to occur in the heat shield itself, and there is a fear that the integrity of the heat shield itself may be impaired.

[Purpose of the invention]

It is an object of the present invention to ensure the integrity of the reactor vessel by reducing the heat flux from the coolant to the reactor vessel and reducing the thermal stress in the reactor vessel that occurs when the temperature of the coolant changes. The object of the present invention is to provide a highly reliable heat shielding device for a fast breeder reactor by greatly reducing the thermal stress generated in the heat shield itself.

[Summary of the invention]

The heat shielding device for a fast breeder reactor according to the present invention includes a cylindrical partition wall provided at a predetermined distance from the inner surface of the reactor vessel, and a cylindrical partition wall arranged between the partition wall and the above-mentioned inner surface of the reactor vessel. This structure includes a plurality of heat shields whose thickness increases in stages along the inner surface of the furnace vessel.

That is, the thickness of the shield provided between the partition wall and the inner surface of the reactor vessel is gradually increased from the partition wall toward the inner surface of the reactor vessel.

Therefore, it is possible to reduce the temperature difference between the inside and outside of each shield, reducing the occurrence of thermal stress, and thereby eliminating the need to limit the temperature difference between rising and falling temperatures during plant startup and shutdown, which are thermal transient conditions. The operational controllability of the furnace can be simplified.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIGS. 1 to 8.

In the figure, 1 is a reactor vessel, and a reactor core barrel 2 is accommodated within this reactor vessel 1 . A reactor core 3 is housed within this reactor core barrel 2 .

Further, 4 is a coolant inflow pipe, and this coolant inflow pipe 4
A low-temperature coolant 5 is supplied to the lower part of the core tank 2 through the reactor. This low-temperature cooling moon 5 then flows upward through the reactor core 3 and is heated. The coolant 5 that has reached a high temperature flows out into the upper part of the reactor vessel 1 and further flows out of the reactor vessel 1 via the coolant outflow pipe 6. and,
The high temperature coolant flowing out from the coolant outflow pipe 6 is heat exchanged with the secondary coolant in an intermediate heat exchanger (not shown), and the coolant that has become low temperature is returned to the reactor core via the coolant inflow pipe 4. The upper end of the reactor vessel 1 is configured to flow into the lower part of the tank 2 and circulate through this path.
is blocked by. This shielding plug 7 is composed of a fixed plug Fa, a large rotation plug 7b, and a small rotation plug 7c, and a core upper mechanism 8 and a fuel exchanger 9 are attached to the small rotation Guagua c. A cover gas space 10 is formed above the liquid level of the coolant 5 in the reactor vessel 1, and a cover gas such as argon gas is sealed in the cover gas space 10. and,
A heat shielding device is provided inside the reactor vessel 1, and this heat shielding device will be explained below. The partition wall 11 has a cylindrical shape and is arranged concentrically with the inner surface of the reactor vessel 1 at a predetermined distance. The lower end of this partition wall 1 reaches the partition wall 12 that partitions between the reactor vessel 1 and the reactor core tank 2, and the space between the lower end of this partition wall 11 and the inner surface of the reactor vessel 1 is closed. There is. Further, the upper end of this partition wall 11 reaches the cover gas space 10K above the liquid level of the coolant 5. Note that a small diameter inflow hole (not shown) is formed in the lower part of this partition wall 1, and a coolant 5 is also formed in the gap between this partition wall 11 and the reactor vessel 1.
is flowing in. A large number of unit shielding bodies 13 are arranged between the partition wall 11 and the inner surface of the reactor vessel 1.

These unit shielding bodies 13 have a relatively small rectangular plate shape, and are curved in an arc shape along the inner surface of the reactor vessel 1. And these unit shielding bodies 13...
are supported by a plurality of delts lr... projecting from the partition wall 11, arranged on the same peripheral surface along the inner surface of the reactor vessel 1, and arranged in a plurality of layers, for example three layers, spaced apart from each other. ing. And thermal resistance element 13 in each layer
The arrangement of these unit shielding bodies 13 is shifted from each other in each layer so that the seams of the unit shielding bodies 13 do not overlap with each other. Furthermore, the unit shielding bodies 13 are configured such that their thickness increases from the partition wall 1 toward the inner surface of the reactor vessel 1. And these unit shielding bodies 13.
... is constructed as shown in FIGS. 4 and 5. That is, 13m is the main body, which is shaped like a hollow container,
It is completely airtight, and gas such as argon gas is sealed inside. Moreover, a plurality of radiation prevention plates 13b... are provided inside the main body 13a. The surfaces of these radiation prevention plates 13b are formed to have high reflectance, and are configured to prevent heat from passing through the main body 13a due to radiation. A portion of these radiation prevention plates 13b... are bent to form, for example, protrusions 13c with a chevron-shaped cross section that are continuous in the vertical direction,
The tops of these protrusions 13c are in contact with the inner surface of the main body 13a and the adjacent radiation prevention plates 13, and between the radiation prevention plates 13b and between the radiation prevention plates 13b and the inner surface of the main body 13a. It is configured to maintain a gap between the

In one embodiment of the present invention configured as described above, the high temperature coolant flowing out from the upper part of the reactor core 3 is blocked by the partition wall 11 and does not come into direct contact with the inner surface of the reactor vessel 1. Moreover, since the unit shielding bodies 13 are arranged between the partition wall 11 and the inner surface of the reactor vessel 1, the heat flux transmitted to the reactor vessel 1 by thermal conduction is extremely small. Therefore, even if the temperature of the coolant 5 suddenly changes when the reactor is started or stopped, the temperature change in the reactor vessel l is small, and therefore excessive thermal stress is generated in the portion of the reactor vessel l near the liquid level. is prevented. Incidentally, FIG. 6 shows the results of a test conducted on the results obtained by providing such unit shielding bodies 13. That is, curve A in FIG. 6 shows the temperature distribution near the liquid level of the reactor vessel 1 in this embodiment when the temperature of the coolant 5 changes. Note that curve B shows the temperature distribution when such unit shielding bodies 13 are not provided.

As is clear from this FIG. 6, the unit shielding body 13...
In the case where the temperature gradient is not provided, there is a rapid temperature change at the liquid level of the coolant, but in this example, the temperature gradient is gentle, and the thermal stress on the wall of the reactor vessel is reduced. is reduced.

Next, a case where the coolant temperature changes will be explained. 7th
Curve C in the figure shows the temperature gradient that occurs between the coolant and the reactor vessel 1 wall. If the thickness of each unit shielding body 13 is the same as in the past, there will be a large temperature difference (TI
Tz) (between DE and E in the figure). The thermal stress (σ) generated at this time is proportional to the above temperature difference and is Eα σ=2(1□)CTx−Tz)・・・・・・・・・(1
), resulting in large thermal stress. On the other hand, in the case of this embodiment, the thickness of the unit shielding bodies 13 is increased from the partition wall 11 toward the inner surface of the reactor vessel 1.
As shown in the figure, the temperature difference (TIT2) generated between the inner circumferential side and the outer circumferential side of each unit shielding body 13 is substantially uniform and takes a small value (between G and H in the figure). Therefore, the generated thermal stress is also greatly reduced.In other words, by providing the space between the partition wall 11 and the inner wall of the reactor vessel I so that its thickness increases from the partition wall 11 toward the inner surface of the reactor vessel 1. Therefore, the temperature difference between the inner circumferential side and the outer circumferential side of each of the heat shields 13 can be suppressed to a substantially uniform and small value, thereby reducing the occurrence of thermal stress. As a result, it is not necessary to limit the difference in elevation during plant startup and shutdown, which is a thermal transient condition, and the operational controllability of the reactor can be simplified.

〔Effect of the invention〕

A heat shielding device for a fast breeder reactor according to the present invention includes a cylindrical partition wall provided at a predetermined distance from the inner surface of a reactor vessel, and a cylindrical partition wall arranged between the partition wall and the inside surface of the reactor vessel. This structure includes a plurality of heat shields whose thickness gradually increases from the wall toward the inner surface of the reactor vessel.

That is, the thickness of the shield provided between the partition wall and the inner surface of the reactor vessel is gradually increased from the partition wall toward the inner surface of the reactor vessel.

Therefore, it is possible to reduce the temperature difference between the inside and outside of each shield, reducing the occurrence of thermal stress, and eliminating the need to limit the temperature difference between rising and falling temperatures during plant startup and shutdown, which is a thermal transient condition. Its effects, such as being able to simplify the driving control of the vehicle, are outstanding.

[Brief explanation of drawings]

Figures 1 to 8 are diagrams showing one embodiment of the present invention.
The figure is a vertical cross-sectional view of a loop fast breeder reactor, Figure 2 is a cross-sectional view taken along ■-■ in Figure 1, Figure 3 is a cross-sectional view taken along ■-■ in Figure 2, and Figure 4 is a cross-sectional view of a unit heat shield. 5 is a sectional view taken along the line v-■ in FIG. 4, FIG. 6 is a diagram showing the temperature distribution of the reactor vessel near the coolant liquid level, and FIGS. 7 and 8 are the reactor vessel. FIG. 3 is a diagram showing temperature distribution in the radial direction. DESCRIPTION OF SYMBOLS 1... Reactor vessel, 11... Partition wall, 13... Unit heat shielding body. Figure 1 Figure 2s Figure 3 Figure 7 Wall 1.500 ('C) (0C)

Claims (1)

[Claims] A cylindrical partition wall provided at a predetermined distance from the inner surface of the reactor vessel, and arranged between the partition wall and the inner surface of the reactor vessel, the thickness of which is gradually increased from the partition wall toward the inner surface of the reactor vessel. 1. A heat shielding device for a fast breeder reactor, comprising: a plurality of heat shielding bodies that increase the heat shielding temperature.