JPH0332037B2 - - Google Patents

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, fast breeder reactors use liquid metal such as liquid sodium as a coolant, and the reactor vessel is filled with the coolant, and the free liquid level and the space above the roof slab are filled with inert gas. It is formed by filling a cover 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, there is a large temperature difference 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, with this method, if the coolant condenses on the inner wall of the reactor vessel in the upper gas space, or if coolant flows into the gas dam between the reactor vessel and the inner wall liner for some reason and accumulates, heat transfer will occur. The effect of preventing this will be reduced.

[Purpose of the invention]

The present invention has been made in view of these points, and it is possible to pump out the coolant in the gas dam and reliably isolate the inner surface of the reactor vessel near the liquid surface of the coolant from the coolant by the gas space. It reduces the amount of heat transferred from the coolant to the reactor vessel, reduces the thermal stress of the reactor vessel, ensures the integrity of the reactor vessel, and has a simple structure and is movable for long-term operation. The purpose of the present invention is to provide a highly reliable heat shielding device for a fast breeder reactor.

[Summary of the invention]

The heat shielding device for a fast breeder reactor of the present invention is provided with an inner wall liner that extends over the entire inner circumference of the inner wall surface of the reactor vessel, and connects the portion above the free liquid surface of the internal coolant to the portion below the free liquid surface and the inner wall liner. A gas dam serving as a gas space is formed between the gas dam and the wall surface, and a bubble pump is installed to pump the coolant accumulated in the gas dam onto the free liquid surface using inert gas bubbles. It is characterized by preventing coolant from accumulating in the reactor vessel and isolating the reactor vessel from the coolant.

[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.

The embodiments shown in FIGS. 1 to 9 are applied to a tank-type fast breeder reactor.

1 and 2 show one embodiment of the invention.

First, a tank-type fast breeder reactor will be explained 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 the rotating plugs 9 and 10, and also prevents the thermal insulation from decreasing due to direct contact or adhesion of the coolant 5 itself. This prevents problems from occurring.

Next, the heat shielding device of the present invention shown in FIGS. 1 and 2 will be explained.

A free liquid level 5 of the coolant 5 is located inside the reactor vessel 1.
A gas dam 17 communicating 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 having an L-shaped cross section and covering the entire circumference between the upper part of the reactor vessel 1 and the lower part thereof. has been done. A bubble pump 18 is provided in the gas dam 17 for sucking out the coolant accumulated therein onto the free liquid surface 5a of the coolant 5 using inert gas bubbles.
This bubble pump 18 pumps inert gas into the gas dam 17
The lower end of the gas injection pipe 19 is fitted onto the upward blowing nozzle 19a of the gas injection pipe 19, and the upper end is directed toward the free liquid level 5a at a higher point than the upper end surface of the inner wall liner 16. It is formed by a suction pipe 20 which is bent. Further, the gas injection pipe 19 penetrates the roof slab 4 and is introduced from the outside of the reactor vessel 1, and the cover gas space 6 is injected by the gas circulation pump 21 through the gas discharge pipe 22 and the paper trap 23. The cover gas inside is supplied in circulation. An inert gas cylinder 24 is connected to the gas injection pipe 19 in order to adjust the cover gas pressure.

Next, the heat shielding effect according to the embodiment will be explained.

The coolant 5 in the high temperature region 14a is heated to about 500° C. while passing through the core 8, and evaporates from its free liquid level 5a 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. Therefore, the cover gas space 6
The vapor of the coolant 5 evaporated inward condenses on the underside 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 cooling 5, so that the vapor of the coolant 5 condenses. This coolant 5
Condensation 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, 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 be in a liquid state. Since the gas is maintained at a constant temperature, it flows down as droplets and accumulates at the bottom of the gas dam 17. Since the heat transfer coefficient of the liquid metal sodium accumulated in this gas dam 17 is extremely high, the inner wall liner 1
The heat held by the coolant 5 in the reactor vessel 1 is transferred to the reactor vessel 1.

Therefore, in this embodiment, the gas circulation pump 21 is operated to forcibly feed inert gas to the gas injection pipe 19. Then, the inert gas blown into the pumping pipe 20 from the blowing nozzle 19a of the gas injection pipe 19 becomes bubbles in the liquid metal sodium accumulated in the gas dam 17, and the liquid metal sodium is sandwiched between the bubbles. rise inside the pumping pipe 20,
The liquid metal sodium is discharged from the upper end opening 20a and returns onto the free liquid level 5a. By intermittent pumping out of the liquid metal sodium by the bubble pump 18, all of the liquid metal in the gas dam 17 can be pumped out onto the free liquid level 5a.

As a result, the inside of the gas dam 17 is always filled with inert gas, its heat shielding effect is completely achieved, and generation of large thermal stress in the reactor vessel 1 is prevented. Further, since the lower part of the gas dam 17, that is, the lower part of the inner wall liner 16 is a low temperature region 14b, the reactor vessel 1 is kept at a low temperature.
This bubble pump 18 has no mechanically moving parts inside the reactor vessel 1, is less likely to malfunction, and is highly reliable.

Furthermore, if the blow-off nozzle 19a of the gas injection tube 19 is inserted deeper into the pump-out tube 20, the air bubbles generated at the blow-off nozzle 19a will hardly leak to the outside of the pump-out nozzle 20, and a small amount of gas can be injected. Liquid metal sodium can be pumped out efficiently. In addition, even if the injection gas pressure is increased, bubbles will not leak from the pumping nozzle 20, so the flow rate of gas blowing out from the blowing nozzle 19a is increased, and the liquid metal sodium in the gas dam 17 can be pumped out at high speed and in a short time. can do.

In addition, the inert gas in the cover gas space 6 is circulated and supplied into the gas injection pipe 19.
There is no risk that radioactive gas will be released to the outside world, and there is no risk that the pressure of the cover gas in the reactor vessel 1 will increase abnormally, so safety is high. In addition, when the power supply to the gas circulation pump 21 is cut off in an emergency, an isolation valve (not shown) is opened and the inert gas in the inert gas cylinder 24 is fed to the gas injection pipe 19, so that the gas inside the gas dam 17 is The pumping of liquid metal sodium is intermittent, ensuring safety and reliability. At this time, the gas pressure within the cover gas space 6 is adjusted by an adjustment system (not shown).

FIG. 3 shows another embodiment of the invention.

In this embodiment, one or more bottomed liquid reservoirs 25 are provided at the bottom of the gas dam 17, and each liquid reservoir 2
5 into which the lower end of a bubble pump 18 consisting of a gas injection pipe 19 and a pumping pipe 20 is inserted.

In this embodiment, the liquid metal sodium accumulated in the liquid reservoir 25 is pumped out, and the liquid metal sodium accumulated in the gas dam 17 can be pumped out without leaving anything behind.

In addition, based on the principle of a bubble pump, the maximum liquid pumping height is 4 times the liquid height of the liquid to be pumped.
It is known that ~8 times more is required. On the other hand, in this type of tank-type fast breeder reactor, the diameter of the reactor vessel 1 is around 20 m, and the bottom area of the gas dam 17 provided all around the inner circumferential surface is wide. Since the height ranges from several meters to more than 10 meters, a very large amount of liquid metal sodium is required to reach the height that can be pumped up by the pumping pipe 20. However, in this example,
The liquid reservoir 25 can occupy most of the pumping height, and the volume of the liquid reservoir 25 is small, so even if a small amount of liquid metal sodium accumulates, it can be efficiently pumped out. Further, since the liquid reservoir 25 is not in contact with the reactor vessel 1, the reactor vessel 1 is not heated by the liquid metal sodium accumulated in the liquid reservoir 25.

4 and 5 show other embodiments of the present invention, in which bottomed level gauge guide pipes 26 and 26 are inserted from the top of the roof slab 4 to the bottom of the gas dam 17 and the bottom of the liquid reservoir 25, respectively. At the same time,
Level gauges 27, 27 for detecting the level of liquid metal sodium are installed at the bottom of each level gauge guide tube 26, 26.

With these liquid level gauges 27, 27, it is possible to constantly monitor how much liquid metal sodium is accumulated in the gas dam 17, and it is possible to judge when to operate the bubble pump 18, and also to determine when to operate the bubble pump 18.
It is possible to monitor whether or not the pumping operation according to No. 8 is being carried out smoothly and to determine when the pumping is to be completed. Further, by interlocking the detection signals of the liquid level gauges 27, 27 with the drive switch of the gas circulation pump 21, the liquid metal sodium accumulated in the gas dam 17 can be automatically pumped out.

FIGS. 6 to 8 show an embodiment in which the efficiency of pumping out liquid metal sodium by a bubble pump is improved.

On the other hand, FIG. 6 shows that a plurality of outlets are provided in the outlet nozzle 19a of the gas injection pipe 19,
The blowing nozzle 19a is made of porous sintered metal.

That is, the size and number of inert gas bubbles generated from the blow-off nozzle 19a are determined by the pumping pipe 20.
It is designed to pump up as much liquid metal sodium as possible in as short a time as possible with the smallest amount of injected gas possible, by adjusting it appropriately in relation to the inner diameter. is transmitted to the liquid metal sodium, mixes with each other, and rises as a two-phase flow, resulting in extremely efficient pumping.

7 and 8, a double pipe-shaped pumping pipe 20 is provided outside a straight gas injection pipe 19 in the center, and this gas injection pipe 19 and pumping pipe 2 are connected to each other.
Many (8 in this example) in the straight pipe section between 0 and 0.
The composite pipes 20b, 20b are interposed.

Generally, if the inner diameter of the pumping pipe 20 is made too large,
If the self-weight of the liquid metal sodium becomes larger than the lifting force of the liquid metal sodium in the pumping pipe 20 due to the rising force of the inert gas bubbles, or if the inner diameter is made too small, the viscosity and surface tension of the liquid metal sodium will act. The inert gas bubbles are pumped out through the pipe 20.
The bubbles may not be able to rise inside the bubbles, and the bubbles will no longer function as a bubble pump. Therefore, there is a limit to the inner diameter of the pumping pipe that can pump out efficiently.
There is also a limit to the amount of liquid metal sodium that can be pumped out by a single pumping tube.

In contrast, in this embodiment, a large amount of inert gas is injected from the central gas injection pipe 19, and a large amount of liquid metal sodium is divided into each composite pipe 20b, 20b, and can be pumped up well. A large amount of liquid metal sodium can be pumped out in a short period of time.

9a to 9c each show an arrangement in which the inert gas fed into the reactor vessel from the gas injection pipe is heated to a predetermined temperature.

That is, FIG. 9a shows a case in which a heater 28 is loaded into the gas injection pipe 19 and the inert gas is heated and heated by the heater 28, and FIGS. The gas injection pipe 19 is formed long by forming it into a spiral shape 19b or a meandering shape 19c, and the inert gas inside is heated and heated by the high-temperature cover gas inside the gas dam.

In this way, the inert gas injected from the outside of the roof slab 4 is sufficiently heated and heated in the heater 28, the spiral portion 19b, and the meandering portion 19c.
It is blown out from the blowing nozzle 19a at a low temperature,
This prevents impurities in the liquid metal sodium from precipitating around the nozzle and preventing the inert gas from generating bubbles.

In addition, in the bubble pump 18, the gas injection pipe 1
9 and the pumping pipe 20 may be simply formed into a double pipe shape, or the gas circulation pump 21 may be installed inside the reactor vessel 1.

In addition, for reactors that have a thermal resistor installed on the inner wall of the reactor vessel for heat shielding, and for the inner wall of the reactor by introducing cold coolant in the low temperature range in the lower part of the reactor vessel into the inner wall liner that forms the gas dam. If the heat shielding device of the present invention is applied to a wall-cooled nuclear reactor to be cooled, the heat shielding effect will be further enhanced.

In addition, if the roof slab penetrating part of the bubble pump is made to be able to be opened and closed with a flange structure or door valve structure, etc., and the constituent parts of the bubble pump are inserted into and removed from the gas dam from this opening/closing part, the liquid metal sodium in the gas dam can be pumped out. A bubble pump can be installed inside the reactor vessel only when
Maintenance, inspection, etc. are easy and reliability is high.

Moreover, since the constituent parts of the bubble pump 18, the inner wall liner 16, etc. are made of stainless steel material whose coexistence with sodium has been sufficiently confirmed, the durability is sufficient.

Furthermore, since the inert gas is supplied to the bubble pump 18 by circulating it in a closed loop, the operation of the gas circulation pump 21 can be intermittent.
When liquid metal sodium accumulates in the gas dam 17 to a height that can be pumped up, it can be pumped up automatically.
When the height is lower than that, operation can be performed in which only inert gas is circulated.

Since the device of the present invention is small in scale, the reactor vessel 1
There is no difficulty in designing, manufacturing, and assembling the roof slab 4, or there is no impact on the extension of the construction period, and the width of the gas dam 17 can be freely set, reducing the diameter of the reactor vessel 1 itself. It is also possible to suppress it.

〔Effect of the invention〕

In this way, the fast breeder reactor heat shielding device of the present invention can constantly pump out the liquid metal sodium accumulated in the gas dam, and can separate the high-temperature coolant on the inner surface of the reactor vessel near the liquid surface of the coolant into gas. It can be isolated reliably by space, reduces the amount of heat transferred from the coolant to the reactor vessel, reduces the thermal stress of the reactor vessel, ensures the integrity of the reactor vessel, and has a simple structure. It can operate over a long period of time and has high reliability.

[Brief explanation of the drawing]

The drawings show an embodiment of the heat shielding device for a fast breeder reactor according to the present invention, and FIG. 1 is a vertical side view of a fast breeder reactor equipped with an embodiment of the present invention, and FIG. 2 is a diagram showing a gas dam section of the same embodiment. 3 to 7 are sectional views similar to FIG. 2 showing other embodiments of the present invention, FIG. 8 is an enlarged sectional view taken along the - line of FIG. 7, and FIG. 9 is an enlarged sectional view. 2A to 2C are sectional views similar to FIG. 2, respectively, showing still other embodiments of the present invention. 1... Reactor vessel, 4... Roof slab, 5...
... Coolant, 5a ... Free liquid level, 6 ... Cover gas space, 16 ... Inner wall liner, 17 ... Gas dam,
18...Bubble pump, 19...Gas injection pipe, 19
a...Blowout nozzle, 20...Blowout pipe, 20a
...Compound pipe, 25...Liquid reservoir.

Claims (1)

[Claims] 1. An inner wall liner is provided over the entire inner circumference of the inner wall surface of the reactor vessel, and between the portion from the upper free liquid level of the internal coolant to the lower free liquid level and the inner wall surface. A fast breeder reactor, characterized in that a gas dam serving as a gas space is formed in the gas dam, and a bubble pump is provided for pumping the coolant accumulated in the gas dam onto the free liquid surface using inert gas bubbles. Heat shielding device. 2. The bubble pump includes a gas injection pipe that supplies inert gas from the outside of the roof slab to the lower part of the gas dam;
Claim 1, characterized in that the pumping tube is formed by a pumping tube whose lower end is loosely fitted over the blowout nozzle of the gas injection tube and whose upper end is open above the free liquid surface of the coolant. Thermal shielding equipment for fast breeder reactors. 3. The high speed according to claim 1 or 2, characterized in that one or more bottomed liquid reservoirs are provided at the bottom of the gas dam, and the lower end of the bubble pump is inserted into the liquid reservoirs. Heat shielding device for breeder reactor. 4. The fast breeder reactor according to claim 2, wherein the blow-off nozzle portion of the gas injection pipe is provided with a plurality of blow-off ports or made of porous metal so as to generate small-diameter air bubbles. Heat shielding device. 5. The gas injection pipe is straight, the outer side is made into a double pipe and covered with a pumping pipe, and a plurality of composite pipes are arranged in the straight pipe section between the pumping pipe and the gas injection pipe. A heat shielding device for a fast breeder reactor according to claim 2. 6. The heat shielding device for a fast breeder reactor according to claim 2, wherein the gas injection pipe is capable of heating the inert gas flowing therethrough.