JPH0224480B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a reactor wall protection device for a fast breeder reactor.

[Technical background of the invention and its problems]

Generally, fast breeder reactors use liquid metal such as liquid sodium as a coolant, and the reactor vessel is filled with the coolant, and the upper space between the free liquid level and the roof slab is inert. It is formed by filling a cover gas made of 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 shutting down 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. It will happen. As a result, a large temperature gradient occurred on the reactor vessel wall near the coolant liquid level, generating excessive thermal stress and possibly impairing the integrity of the reactor vessel.

Therefore, in the past, an insulating wall was attached to the inside of the reactor vessel, and low-temperature coolant was passed between this insulating wall and the inner surface of the reactor vessel, and the high-temperature coolant flowing out from the top of the reactor core was The integrity of the reactor vessel is ensured by preventing direct contact with the vessel. In other words, cooling is performed by circulating a portion of the low-temperature coolant inside the reactor vessel, which is sent toward the reactor core from a circulation pump provided inside the reactor vessel, between the heat insulating wall and the inner surface of the reactor vessel. It is formed by providing a material flow path.

However, this system had problems such as a reduction in the insulation effect when the circulation pump tripped.

In addition, an inner wall liner is installed near the liquid level on the inner wall of the reactor vessel to form a gas dam, which is a gas space around the entire circumference, to prevent direct contact between the high-temperature coolant and the inner wall of the reactor vessel. Measures are being taken to prevent temperature changes in the coolant near the liquid surface from being transmitted directly to the reactor vessel.

However, in this structure, the coolant that evaporated from the free liquid surface and condensed on the inner wall of the reactor vessel in the upper gas space, which has a lower temperature than the free liquid level, and the lower surface of the roof slab, is transferred to the reactor vessel and the cylindrical inner wall liner. There was a problem that if the gas flowed into the gas dam and accumulated there, the insulation effect would be significantly reduced.

In other words, since the heat conductivity of the coolant accumulated in this gas dam is extremely high, there is a problem in that the heat held by this coolant is transferred to the reactor vessel, impairing the insulation effect achieved by providing the gas dam.

Therefore, it has been proposed in the past to use an electromagnetic pump to pump out the coolant accumulated in the gas dam. However, inside this reactor vessel there are always 500
It was difficult to create an electromagnetic pump that would operate reliably during this long period of time, as the reactor was covered with coolant at a temperature of over 30°F and had a long lifespan of several 10 years.

As described above, conventional reactor wall protection 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.

A conventional example of a tank-type fast breeder reactor will be described below with reference to FIG.

A tank-shaped reactor vessel 1 is protected on the outside by a safety vessel 2, and this safety vessel 2 is suspended and supported within a concrete containment vessel 3. This reactor vessel 1 has its upper end opening closed with a roof slab 4 to form a closed vessel, and the inside is filled with a coolant 5 made of liquid metal such as liquid sodium, and the free liquid of the coolant 5 is A cover gas space 6 between the surface 5a and the lower surface of the roof slab 4 is filled with a cover gas made of an inert gas such as argon gas or helium gas. Further, a reactor core 8 is provided at the center bottom of the reactor vessel 1 via a high-pressure plenum 7, and above the reactor core 8, a large-rotary plug 9 and a small-rotary plug 10 are connected to the roof slab 4 to provide an upper core mechanism. 11 are provided.

A circulation pump 12 for forcibly circulating the coolant 5 and an intermediate heat exchanger 13 for exchanging heat between the primary coolant and the secondary coolant are suspended and supported on the roof slab 4. Inside the reactor vessel 1 is a neutron shield 14
The upper high temperature area 14a and the lower low temperature area 14b are
It is isolated.

This tank type fast breeder reactor is operated as follows.

That is, the circulation pump 12 is operated to suck in low-temperature coolant in the low-temperature region 14b from the inlet 12a, and then feed the coolant into the high-pressure plenum 7 through the high-pressure piping 15. Coolant is in high pressure plenum 7
While rising in the core 8, the coolant is heated up and becomes a high-temperature coolant 5, which flows out into the high-temperature region 14a. The coolant 5 in this high temperature region 14a is transferred to the intermediate heat exchanger 13
into the intermediate heat exchanger 1 from the inlet 13a.
It is cooled by exchanging heat with the secondary coolant flowing inside 3,
It flows out from the outlet 13b into the low temperature region 14b and flows into the circulation pump 12 again.

During this operation, the cover gas in the cover gas space 6 absorbs and alleviates internal pressure changes in the reactor vessel 1 when the coolant expands and contracts in volume due to temperature changes. , prevent the occurrence of adverse effects on reactor components. Furthermore, it prevents thermal troubles in the upper reactor equipment attached to the roof slab 4 and rotating plugs 9 and 10, and also prevents thermal insulation from decreasing due to direct contact or adhesion of the coolant 5 itself. Preventing trouble from occurring.

A free liquid level 5 of the coolant 5 is located inside the reactor vessel 1.
A gas dam 17 that communicates with the cover gas space 6 is formed between the reactor vessel 1 and the inner wall liner 16 by fixing an inner wall liner 16 with an L-shaped cross section and extending all the way between the upper part of the reactor vessel 1 and the lower part thereof. has been done.

The coolant 5 in the high temperature region 14a is heated to approximately 500°C or more while passing through the core 8, and its free liquid level 5a
evaporates into the cover gas space 6. On the other hand, the top surface of the roof slab 4 is at a low temperature close to room temperature.
Therefore, the temperature of the lower surface facing the cover gas space 6 is also lower than the temperature of the coolant 5. There, the vapor of the coolant 5 evaporated into the cover gas space 6 condenses on the lower surface of the roof slab 4. Further, the wall surface of the reactor vessel 1 is also cooled by dissipating heat to the outside through the safety vessel 2. The temperature of the inner wall portion of the reactor vessel 1 in the cover gas space 6 is lower than the liquid temperature of the coolant 5, so that the vapor of the coolant 5 condenses. This condensation of the coolant 5 always proceeds during reactor operation or while the coolant 5 is maintained at a higher temperature than the inner wall temperature of the reactor vessel 1.

Therefore, the temperature of the inner wall of the reactor vessel 1 is lower than that of the coolant 5.
The solidification temperature of liquid metal sodium is (approximately 98℃)
If the temperature is maintained above, the sodium condensed on the inner wall surface of the reactor vessel 1 is always kept in a liquid state, so that it flows down as droplets and accumulates at the bottom of the gas dam 17. Since the thermal conductivity of the liquid metal sodium accumulated in the gas dam 17 is extremely high, the heat held by the coolant 5 in the inner wall liner 16 is transferred to the reactor vessel 1.

[Purpose of the invention]

The present invention has been made in view of these points, and is a reactor wall protection device having a cylindrical wall structure that partitions the reactor vessel inner wall near the liquid surface of the coolant and the high-temperature coolant with a gas space. Reliable technology that reduces the amount of heat transferred from the reactor material to the reactor vessel, reduces the thermal stress of the reactor vessel, suppresses the transfer of coolant into the gas dam, maintains the insulation effect of the gas dam, and ensures the integrity of the reactor vessel. An object of the present invention is to provide a reactor wall protection device for a fast breeder reactor with high durability.

[Summary of the invention]

In order to achieve the above object, the present invention provides a cylindrical liner that forms an annular space that is open at the top and closed at the bottom inside the reactor vessel, extending from above the liquid level of the coolant to below the liquid level, and An upper cylindrical liner is provided in close proximity to the inner wall of the reactor vessel in a gap formed between the outer edge of a roof slab that closes the upper opening of the reactor vessel and the inner wall of the reactor vessel, and the upper cylindrical liner The lower end of the cylindrical liner and the upper end of the cylindrical liner are connected via an upwardly widening conical cylinder.

[Embodiments of the invention]

The present invention is applicable to any type of reactor vessel filled with coolant with a free liquid level, and is particularly applicable to loop-type and tank-type reactor vessels that are often operated at coolant temperatures of 500°C or higher. Suitable for reactor vessels of fast breeder reactors.

FIG. 2 shows an embodiment in which the present invention is applied to a tank-type fast breeder reactor.

A part where the area above the cylindrical liner 16 provided inside the reactor vessel 1 is changed so that the area of the annular space formed by the reactor vessel 1 and the cylindrical liner 16 is gradually narrowed, that is, a conical base cylinder 18 is provided to minimize the annular space. The upper cylindrical liner 1 is provided from the narrowed area to the lower surface of the roof slab gap in parallel with the furnace vessel 1.
It is formed from 9. Note that the liner changing portion 20 where the annular space area begins to change is formed into a curved surface. The coolant 5 in the high temperature region 14a is heated to 500°C or more while passing through the core 8, and its free liquid level 5
evaporates from a into the cover gas space 6. On the other hand, the upper surface of the roof slab 4 is at a low temperature close to room temperature, and therefore the temperature of the lower surface facing the cover gas space 6 is also lower than the temperature of the coolant 5. There, the vapor of the coolant 5 evaporated into the cover gas space 6 is transferred to the roof slab 4.
It condenses on the bottom surface of. Furthermore, the wall surface of the reactor vessel 1 is also cooled by dissipating heat to the outside through the safety vessel. Since the temperature of the inner wall of the reactor vessel 1 in the cover gas space 6 is lower than the temperature of the coolant 5, in the structure shown in FIG.
condenses on the inner wall of the This condensation of the coolant 5 always proceeds while the reactor is operating or while the coolant 5 is maintained at a higher temperature than the inner wall temperature of the reactor vessel 1. Therefore, if the temperature of the inner wall of the reactor vessel 1 is kept above the solidification temperature (approximately 98°C) of liquid metal sodium, which is the coolant 5, the sodium condensed on the inner wall of the reactor vessel 1 will always remain in a liquid state. In order to be retained, the gas flows down as droplets and accumulates at the bottom of a conventional annular space (gas dam) 17 with an open top. This annular space 1
Since the thermal conductivity of the sodium accumulated at the bottom of the cylindrical liner 16 is extremely high, the thermal insulation effect of the cylindrical liner 16 is significantly reduced. Therefore, in this embodiment, as explained above,
Since the annular space area above the cylindrical liner 16 is narrowed and reaches all the way to the lower surface of the roof slab 4, the steam evaporated from the coolant 5a is less likely to condense and flow down onto the inner wall surface of the reactor vessel 1, thereby reducing the gas dam 17. Since the insulation space is maintained, the heat shielding effect is increased.

The conical base cylinder 18, whose annular space area changes gradually, not only narrows the annular space area, but also has a structure in which the coolant condensed on the wall surface on the side of the cover gas space 6 easily flows down as droplets. This is to absorb the elongation in the axial direction. Further, the curved surface portion of the liner changing portion 20 where the area of the annular space begins to change is intended to reduce thermal stress caused by elongation in the axial direction.

FIG. 3 shows another embodiment of the present invention, in which a heat shielding tube 21 is provided on the coolant side of the upper cylindrical liner 19 and hangs down from the lower surface of the roof slab 4.

〔Effect of the invention〕

As explained above, in the fast breeder reactor wall protection device according to the present invention, a cylindrical liner that forms an annular space that is open at the top and closed at the bottom inside the reactor vessel is heated from above the liquid level of the coolant. An upper cylindrical cylinder is provided near the inner wall of the reactor vessel in a gap formed between the outer edge of the roof slab that extends downward from the surface and closes the upper opening of the reactor vessel and the inner wall of the reactor vessel. A liner is provided, and the lower end of the upper cylindrical liner and the upper end of the cylindrical liner are connected via an upwardly expanding conical pedestal, thereby preventing sodium vapor within the reactor vessel from entering the inside of the cylindrical liner. This prevents sodium from accumulating at the bottom of the gas dam, allowing the gas dam to maintain its insulation performance.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a fast breeder reactor equipped with a conventional reactor wall protection device, FIG. 2 is an enlarged sectional view of a reactor wall protection device that is an embodiment of the present invention, and FIG. FIG. 2 is a partially enlarged sectional view of the furnace wall protection device in the embodiment. 1... Reactor vessel, 4... Roof slab, 5...
... Coolant, 5a ... Coolant liquid level, 6 ... Cover gas space, 16 ... Cylindrical liner, 17 ... Gas dam, 18 ... Conical base cylinder, 19 ... Upper cylindrical liner, 20 ... Liner change part , 21... Heat shield cylinder.

Claims (1)

[Claims] 1. A cylindrical liner is provided inside the reactor vessel from above the coolant liquid level to below the liquid level, forming an annular space that is open at the top and closed at the bottom.
An upper cylindrical liner is provided close to the inner wall of the reactor vessel in a gap formed between the outer edge of the roof slab that closes the upper opening of the reactor vessel and the inner wall of the reactor vessel, and 1. A reactor wall protection device for a fast breeder reactor, characterized in that a lower end of a cylindrical liner and an upper end of the cylindrical liner are connected via an upwardly expanding conical pedestal.