JPS61215993A - Thermal shielding device for fast breeder 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 invention] The present invention relates to a heat shielding device for a fast breeder reactor.

[Technical background of the invention and its problems]

Generally, a fast breeder reactor (hereinafter referred to as a nuclear reactor) is formed by using a liquid metal such as heptadium sodium as a coolant and filling a space with a cover gas made of an inert gas.

On the other hand, since the coolant made of liquid metal 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 extremely quickly. However, the temperature of the wall portion of the reactor vessel above the liquid level of the coolant 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, there is a large difference between the part of the reactor vessel below the coolant liquid level and the part above the liquid level. will occur. As a result, a large temperature gradient occurs on the reactor vessel wall located near the coolant liquid level, generating excessive thermal stress, which may impair the integrity of the reactor vessel.

Therefore, in the past, an insulating wall was attached to the inside of the reactor vessel, and a low-temperature coolant was inserted between this insulating wall and the inner surface of the reactor vessel.
The integrity of the reactor vessel is ensured by ensuring that the high temperature coolant flowing out from the top of the reactor core does not come into direct contact with the reactor vessel. That is, a coolant flow path is provided that allows a part of the low-temperature coolant sent toward the reactor core from a circulation pump provided in the reactor vessel to flow between the heat insulating wall and the inner surface of the reactor vessel. That's what I do.

However, this method often has problems such as not being able to provide insulation when the circulation pump trips.

In addition, an annular wall is installed near the liquid level on the inner wall of the reactor vessel to form an annular space (gas dam) with an upper opening that is surrounded by a gas space around the entire circumference. Direct contact with the inner surface of the reactor vessel is prevented to prevent temperature changes in the coolant near the loading surface from being directly transmitted to the reactor vessel.

However, with this method, if coolant condensed on the inner surface of the reactor vessel that is in contact with the cover gas flows down into the annular space, or if coolant flows into the annular space for some reason and accumulates, the insulation There were problems such as a significant decrease in the heat shielding effect and the need for equipment to restore performance.

D. Since the thermal conductivity of the coolant accumulated in the annular space (gas dam) is extremely high, the heat held by the coolant in the annular wall is transferred to the reactor vessel, resulting in insulation due to the annular space. There is a problem that the effectiveness is lost. Furthermore, a heat shield plate is installed in the annular space to suppress radiant heat from the annular wall surface to the reactor vessel, but coolant vapor evaporated from the liquid surface is cooled in the gas space and adheres to the heat shield plate. However, there was also the problem that the effect of suppressing radiant heat was also impaired. Although it has been proposed to use a pump to pump out the coolant accumulated in the annular space (gas dam), the inside of the reactor vessel is always treated with coolant at a temperature of 500°C or higher). Since the lifespan of pumps is long, several decades, it is difficult to manufacture pumps that can be manufactured reliably during this period.

As described above, conventional heat shielding devices do not have a sufficient heat shielding effect, resulting in problems that impair the integrity of the reactor vessel and complicate the structure of the reactor vessel.

[Purpose of the invention]

The present invention has been made in view of these points, and aims to reduce the intrusion of coolant and its vapor into the gas dam provided along the inner peripheral surface of the reactor vessel, thereby ensuring the integrity of the reactor vessel. It is an object of the present invention to provide a heat shielding device for a fast breeder reactor that has a simple structure and does not deteriorate in performance over a long period of time.

[Summary of the invention]

The inner surface is partitioned from the coolant between the portion from the upper free liquid level of the coolant to the lower free liquid level and the inner surface of the reactor vessel along the inner circumferential surface of the reactor vessel in which the coolant is stored. The gas dam is characterized in that an annular wall is provided to form an annular space (gas dam part), and the upper opening of the annular space is closed with a thin flexible cover.

Therefore, it is possible to prevent the coolant and its vapor from entering and accumulating in the gas dam, and as a result, the reactor vessel can be isolated from the coolant, so thermal stress and thermal deformation of the reactor vessel can be reliably reduced at all times. Moreover, it is possible to obtain a heat shielding device for a fast breeder reactor whose performance does not deteriorate over a long period of time.

[Embodiments of the invention]

The present invention is applicable to any reactor vessel in which coolant is freely filled, and is particularly applicable to reactor vessels that are often operated at coolant temperatures of 500°C or higher and high-speed tank-type reactors. Suitable for reactor vessels of breeder reactors.

An embodiment of the invention will be described with reference to FIGS. 1 and 2.

First, a tank type fast breeder reactor will be explained with reference to FIG.

A reactor vessel 1 having an upper opening (not shown) is filled with liquid metal sodium 3 as a coolant 9, and a reactor core 5 in which a large number of fuel assemblies (not shown) are arranged in an array. It is placed immersed in the sodium 3 so as to be located in the center of the furnace vessel 1. The inside of the reactor vessel 1 is vertically partitioned by a partition wall 6 connected to the outer periphery of the reactor core 5.
By driving the pump f7 (D) provided on the partition wall 6, the sodium 3 is circulated within the reactor vessel 1 so as to flow from the bottom to the top of the reactor core 5.

The upper opening of the reactor vessel 1 is closed by a roof slab 8, and the core 5 is located in the center of the roof slab 8.
A furnace upper mechanism 9 is vertically installed and faces directly above the furnace. In addition, the roof slab 8 has a secondary sl-IJ um supply 5A structure 1.
0 is attached and cut off.

In a fast breeder reactor with such a configuration, the reactor core 5 has approximately 500 to
Sodium 3 heated to 600°C is introduced from the high temperature sodium pool 12 above the partition wall 6 to the intermediate heat exchanger 11, where it is heat-converted to secondary sodium from the secondary sodium supply mechanism 10 and cooled. approx. 300-400℃
becomes. Thereafter, the IJ aluminum 3 flows down to the low-temperature sodium pool 13 below the partition wall 6, is pressurized by the pores, and is then recirculated to the core 5.

Next, the heat shielding device of the present invention will be explained with reference to FIGS. 1 and 2.

An annular wall 21 having an angular cross section that partitions the inner surface of the reactor vessel 1 from the sodium 3 is fixed inside the reactor vessel 1 and at a position between above and below the free liquid level of the sodium 3. ing.

Then, on the annular wall 2h side, there is a thin-walled flexible material that tightly closes the upper opening of the annular space 22 formed between the annular wall 21 and the furnace vessel 1, and makes the annular space 22 a closed space. Physical strength/(-, 23 is provided.The above-mentioned physical strength cover 23
is provided with a downward slope from the inner surface of the furnace vessel 1 to the top of the annular wall 21. In addition, referring to FIG. 1, the heat shielding effect according to this embodiment will be explained next.

The sodium 3 in the high-temperature sodium pool 12 is heated to about 500° C. while passing through the reactor core 5, and a portion of the sodium 3 evaporates from its free liquid level into the cover gas space 14. On the other hand, the upper surface of the roof slab 8 bends at a low temperature close to room temperature, so that the lower surface facing the cover gas space 14 also has a lower temperature than that of the sodium 3'. Therefore, the vapor of the sodium 3 evaporated into the cover gas space 14 is cooled. The temperature of the inner surface of the reactor vessel 1 in the cover gas space 14 is lower than the liquid temperature of the sodium 3, so that the vapor of the sodium 3 also condenses on the surface of the reactor vessel 1. This sodium 3 condensation occurs during reactor operation or during IJ
As long as the temperature of the reactor vessel 1 is maintained at a higher temperature than the inner wall of the reactor vessel 1, the process continues.

Therefore, if the wall temperature of the reactor vessel 1 is maintained above the solidification temperature of the coolant sodium 3 (approximately 98 degrees Celsius),
Since the soot-IJium condensed on the inner surface of the reactor vessel 1 is always kept in a liquid state, it flows down as droplets.

In the case of the conventional top-opening type, the droplets accumulate at the bottom of the annular space (gas dam) 22. Since the thermal conductivity of the sodium accumulated in the annular space 22 is extremely high, the annular wall 2
The heat held by the sodium in the reactor vessel 1 is transferred to the reactor vessel 1.

If a heat shield plate 24 is provided, the IJ vapor that evaporates from the liquid surface of sodium 3 will be cooled in the gas space and adhere to the heat shield plate 24, impairing the effect of suppressing radiant heat. .

However, in this embodiment, a thin flexible body cover 23 is provided to airtightly close the upper opening of the annular space 22, thereby forming a sealed annular space 22.

The flexible cover 23 is made of a material such as a bellows, which has properties that sufficiently satisfy the conditions of the installed atmosphere, heat resistance, sodium resistance (corrosion, etc.), and heat stress resistance. , and is provided with a downward slope from the furnace vessel 1 to the annular wall 21 .

Therefore, the sodium that evaporates from the liquid level of the sodium 3 and condenses downward from the vicinity of the upper inner surface of the reactor vessel 1 does not flow into the annular space 22 due to the existence of the flexible cover 23. It passes through the upper part of the body cover 23 and flows down to the liquid level. Furthermore, since the thin flexible cover 13 is used, it has sufficient strength and can withstand thermal stress generated in the annular wall 21 and the welded portion, buckling generated in the cover, and the like.

In this way, the annular space (gas dam) 22 is always maintained in a closed space. Therefore, the heat shielding effect is completely achieved, and no large thermal stress is generated in the reactor vessel 1. Further, since the lower part of the annular space (gas dam) 22, that is, the lower part of the annular wall 21, is a low-temperature sodium boule 13, the reactor vessel 1 is kept at a low temperature. Furthermore, with the above configuration, equipment such as a pump is not required, there are no moving parts, the structure is simple, and reliability can be improved.

〔Effect of the invention〕

As described above, according to the fast breeder reactor heat shielding device of the present invention,
In a heat shielding device that forms an annular space (gas dam) that is separated from the coolant all around the inner circumference of the reactor vessel wall, it is possible to reliably prevent the coolant from entering (flowing down, adhering to) the annular space (gas dam). As a result, the inner surface of the reactor vessel near the surface of the coolant and the high-temperature coolant can be reliably isolated from the gas space, reducing the amount of heat transferred from the coolant to the reactor vessel. The thermal stress of the reactor vessel is reduced, the integrity of the reactor vessel is ensured, and the structure is simple and heat shielding performance can be maintained over a long period of time. Therefore, it is possible to contribute to the realization of a highly reliable fast breeder reactor.

[Brief explanation of drawings]

The drawings show an embodiment of a heat shielding device for a fast breeder reactor according to the present invention, and FIG. 1 is a longitudinal cross-sectional side view of a fast breeder reactor equipped with an embodiment of the present invention, and FIG. 2 is a main part of another embodiment of the same. It is an enlarged sectional view. 1...Furnace vessel, 3...Liquid metal sodium, L...
-Liquid level, 8... Roof slab, 14... Cover gas, 21... Massive wall, 22... Annular space, 23...
Glazed body cover, 24...heat shielding plate. Applicant's agent Patent attorney Takeshi Suzue Diagram 1

Claims (1)

[Claims] (1) Along the inner circumferential surface of the reactor vessel in which the coolant is stored, the above-mentioned A heat shielding device for a fast breeder reactor, comprising: an annular wall forming an annular space separating the inner surface from the coolant; and a thin flexible cover sealing an upper opening of the annular space.