JPS6147581A - Liquid-metal cooling type 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 the Invention] The present invention relates to a liquid metal cooled fast breeder reactor in which a reactor vessel and an upper core mechanism are provided with means for alleviating thermal stress generated near the coolant liquid level.

[Technical Background of the Invention] In general, liquid metal refrigeration F! In type I fast breeder reactors, liquid metals such as sodium are used as coolants.

As is well known, such a coolant has an extremely high thermal conductivity because it is a metal, and furthermore, because it is a liquid, it also transfers heat by convection, so its heat transfer ability is extremely large.

On the other hand, a cover gas such as argon gas is sealed above the liquid surface of the coolant, and this cover gas has an extremely small heat transfer ability compared to the coolant. Therefore, heat from the hot coolant is somehow transferred to the reactor vessel,
Heat transferred to the reactor vessel tends to be transmitted upward through the reactor vessel wall.

However, the reactor vessel is generally made of Stella 1 stainless steel, and since this stainless steel has low thermal conductivity, a relatively large temperature gradient occurs above the coolant liquid level.

Therefore, in the part of the reactor vessel that comes into contact with the coolant,
While the temperature is constant and the temperature gradient is zero, there is a relatively large temperature gradient above the coolant liquid level, and a discontinuity in the temperature gradient occurs near the coolant liquid level. As a result, excessive thermal stress is generated near the coolant liquid level, which may adversely affect the integrity of the reactor vessel. Particularly when the coolant temperature changes rapidly, such as when the reactor is started or shut down, the discontinuity of the temperature gradient becomes even greater, and the resulting thermal stress becomes extremely large.

The above description has been made regarding the reactor vessel, but the same applies to the upper core mechanism.

Incidentally, as means for reducing the thermal stress near the liquid level, for example, a packet method, a liquid level control method, and a furnace wall cooling method have been proposed. In the packet method, a bucket 1 containing cold 7Il material is installed on the furnace wall near the liquid level, and the coolant in the packet is maintained at a higher level than the liquid level in the furnace. This method uses the heat conduction effect to alleviate discontinuities in the temperature gradient near the liquid surface, and to reduce thermal stress that occurs due to discontinuities in the temperature gradient.

In the liquid level control method, the overflow nozzle that injects the coolant into the packet is looked into, and the liquid level in the packet is varied up and down by adjusting the amount of coolant injected into the packet by this overflow nozzle. It is. This creates a certain width at the point where the high-temperature coolant contacts the reactor vessel, and within this width, the temperature distribution near the liquid surface of the reactor vessel is averaged, thereby alleviating discontinuities in the temperature gradient. are doing.

In addition, the reactor wall cooling method extracts low-temperature, high-pressure coolant from the high-pressure blemish, routes this coolant to cool the reactor wall near the coolant liquid level by 2 J], and then transfers a portion of it to the high-temperature coolant. This reduces the temperature of the reactor vessel and weakens the heat transfer ability of the high-temperature coolant, thereby alleviating the discontinuity of the gradient.

[Problems with the background art] However, each of the above methods has the following 4 [
There are drawbacks. In other words, in the packet method, if the liquid level of the coolant in the packet decreases due to evaporation of the cold IJ material in the packet, or if control of the liquid level in the furnace fails and the liquid level in the furnace rises. If the liquid level in the packet becomes whiter than the liquid level in the furnace, there is a drawback that the effect of alleviating the thermal stress cannot be obtained.

The liquid level control method requires accessory equipment such as an overflow nozzle, so the structure becomes complex, and in order to constantly control the liquid level in the packet, the installation and operation conditions of the cooling system etc. It becomes complicated and the lotus transfer point is complicated.
The transformation becomes unavoidable. Furthermore, there is a drawback in that a countermeasure must be taken separately in case liquid level control within the packet fails.

In the case of the reactor wall cooling method, as mentioned above, in order to take out the low-temperature cold 7J] U from the high-pressure plenum, it is necessary to route the cold material through the reactor vessel, making the structure complicated and rough. In order to obtain a uniform cooling lJ1 effect around the liquid surface, it is necessary to fabricate and assemble the flow path with great precision, which has the disadvantage of increasing construction cost. Additionally, some of the low temperature coolant is released into the high temperature coolant, which reduces the thermal efficiency of the plant.

[Objective of the Invention] The object of the present invention is to reduce the thermal stress by reducing the axial temperature gradient that occurs near the liquid level of the reactor vessel and the upper core mechanism, especially during startup and shutdown of the reactor. We also provide a liquid metal fast-breeding reactor designed to prevent damage to the upper core mechanism.

[Summary of the Invention] The liquid metal blind fast breeder reactor according to the present invention has a cold uJ (3) provided with a 7-nuclear portion near the liquid level, the lower end of which is fully immersed in the coolant, and the upper end of which is immersed in the coolant. The material is placed above the liquid level, and a group of fine tubes are inserted into the annulus. However, by filling the annulus with metal porous or metal wool, capillary action can be used to cool the annulus (lower the A liquid level). It is characterized by the fact that it is made to rise.

[Embodiments of the Invention] Hereinafter, a case in which the present invention is implemented in a nuclear reactor vessel will be described in detail with reference to the drawings. In FIG. 1 showing the configuration of the liquid metal rapid breeder reactor of the present invention, a reactor vessel 1 has a core tank 2 housing a reactor core 3. A cold JJI material 4 of liquid metal is stored in the reactor vessel 1 up to the liquid level shown in the figure.
2 is supplied to the lower part of J3, core 1! ! The coolant 4 supplied to the lower part of I2 flows upward in the reactor core 3, is heated, and flows upward into the reactor vessel 1 at a high temperature. The high-temperature coolant 4 then flows out of the reactor vessel 1 through the cold 1.11 material outflow pipe 6, and is heat exchanged with the secondary coolant in an intermediate heat exchanger (not shown). and cooled down.

By the intermediate heat exchanger, the coolant 4 which has become low temperature is again supplied to the lower part of the core tank 2 through the coolant inlet pipe 5.
It circulates along the route mentioned above.

The upper end of the reactor vessel 1 is closed by a shielding plug,
The inside of the reactor vessel 1 is sealed. In addition, reactor vessel 1
A cover gas such as argon gas is sealed in a cover gas space 8 formed above the coolant liquid level in the shielding plug 7 (fixed plug 7a, large rotation plug 71), and From small rotation plug 7C (1°11
The small rotating plug 7C is provided with a horizontal 9 and a fuel exchanger 10 in the upper part of the reactor core, which incorporates a control salvage drive mechanism (not shown), a cooling 1.1'1/4 measurement system, and the like. Further, near the liquid level inside the reactor vessel 1, a reactor wall protection device 20 according to the present invention is provided.

As shown in FIG. 2, this reactor wall protection device 20 forms an annulus portion 20a with an inner partition plate 21 provided near the liquid surface 1z inside the reactor vessel 1, and cools the lower end of the partition plate 21 sufficiently. It is welded to the reactor vessel 1 at a position where it is immersed in the material, and its upper end is extended until it is sufficiently above the liquid level even if the liquid level in the reactor fluctuates, and a group of fine tubes 22 are inserted into the annulus interior 20a. It is.

Also, the partition plate 21 of the annulus section 20 is provided with a large number of holes 23 so that the coolant can freely move inside and outside the annulus section.

FIG. 3 shows a second embodiment of the furnace wall protection device 20 according to the present invention. As in the first embodiment described above, an annulus 120a is provided inside the reactor vessel 1 near the liquid level (the interior of the annulus 20a is filled with metal porous or metal wool 24. In the case of the embodiment, the partition 21 of the annulus part is installed to prevent metal porous or metal wool fragments 24 from falling into the reactor interior.
A metal rope 25 is attached to the hole 23.

Next, the operation of the embodiment of the present invention constructed as above will be explained. Furnace wall protection device “20” provided according to the present invention
At this time, the coolant is sucked up by the upper plate one-tube phenomenon, and rises from the liquid level H+ in the reactor vessel 1 to the liquid level T1 or -l2 in the annulus portion 20a. In general, the height that rises due to the upper plate one tube phenomenon is determined by the balance between the force due to surface tension and f3ffl of the raised part, so the height of the rise is
If the height of the coolant is 1-1, the surface tension is σ, the density of the cooling H is γ, the cross-sectional area of the tube is A, the wettability is S, and the contact angle between the coolant and the tube is θ, then 1'' -σCOSθS /Aγ. Now the surface tension of the cold NJ material is σ = 1.6
xlO'kgf/m, contact angle θ=O℃, specific gravity ffi
If we assume that 7 = 830 k (1/m') and use a circular tube with a diameter of 1 mm as the thin tube, H will be approximately 80 mm.

If metal porous or metal wool is used, the liquid level will further rise.

By the way, when the coolant liquid level in the annulus portion 20a rises, the reactor wall of the reactor vessel 1 is heated (at reactor startup) or cold IJ1 (at reactor shutdown) due to the heat conduction effect of the coolant.

Figure 4 shows the liquid level H+ of the reactor vessel 1 and the annulus section 20a.
This is a diagram showing the temperature distribution in the IIMl+ direction from the vicinity of the liquid level H2 to the top of the reactor wall, where (a> is at reactor startup, (b,)
is a typical temperature distribution during reactor shutdown.

Solid lines Ta and Tb in the figure indicate the furnace wall protection device 20 of the present invention.
The broken lines ta and tb show the temperature distribution when the protection device 20 is used. As is clear from FIG. 4, when the maintenance device (filter 20) of the present invention is installed,
Compared to a case without a protection device, the maximum value of the axial temperature gradient is reduced both when the reactor is started and when the reactor is stopped, and as a result, the thermal stress is reduced.

In the above embodiment, as the furnace wall protection device 20 of the furnace vessel (
Although the present invention has been used in the past, the L part of the reactor core is 1 ton!
Even if it is adopted as the protection RW device 20 of 2019, and the last part 20a is installed around it, the effect will be great.

Furthermore, in the present invention, if other methods are combined, such as cooling the portion of the furnace wall that is in contact with liquid sodium/lium from the outside with gas, the stress relaxation fl effect will be greater.

[Effect of the invention] As described above, according to the present invention, the reactor vessel J5,
J: An annulus communicating with the coolant is provided near the coolant liquid level in several sections above the core, and this annulus is affected by capillary action (
J: Packed with a substance that raises the liquid level of the coolant,
sr, equipment r), the reactor startup 1
Since it is possible to reduce the axial direction 'L: +A degree gradient that occurs near the liquid level of the reactor vessel at the time of 1i'i or shutdown, thermal stress can be reduced and damage to the reactor vessel can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing an embodiment of a liquid-cooled fast breeder reactor according to the present invention; FIG. 4(a) is a vertical sectional view showing different embodiments of J5 and (
b) is a characteristic diagram showing the temperature distribution in the axial direction of the reactor vessel at the time of startup J5 and at the time of shutdown of the reactor. 1... Reactor vessel 4... Coolant 7... Shielding plug 8... Cover gas 20... Reactor vessel protection device 20a... Annulus portion 21... Partition plate 22... Micro 11I tube group 23...hole 24...metal porous or metal wool (7317
)Representative Patent Attorney Noriyuki Chika (one idiot) Figure 1 Figure 2 Figure 3 ″

Claims (3)

[Claims] (1) An annulus is formed with a partition plate near the liquid level of the reactor vessel that houses the reactor core and the coolant circulating in the core, and the upper core mechanism that supports the control rod drive mechanism, etc., and the upper end of the partition plate is It is open above the liquid level, its lower end is welded to the furnace vessel at a position where it is sufficiently immersed in the coolant, and a hole is made in the part of the partition plate that forms the annulus that is in contact with the coolant. A liquid metal cooled fast breeder reactor characterized by a protection device with a group of fine tubes inserted. (2) A liquid metal cooled fast breeder reactor according to claim 1, characterized in that the annulus portion of the protection device is filled with metal porous material. (3) The liquid metal cooled fast breeder reactor according to claim 1, wherein the annulus portion of the protection device is filled with metal wool.