JPH0833462B2 - Reactor with pump for coolant circulation - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a nuclear reactor having a pump for circulating a coolant, and more particularly to a sodium-cooled fast breeder reactor using liquid metal as a coolant.

[Prior Art] A fast breeder reactor (hereinafter referred to as FBR) generally uses liquid sodium as a coolant, and is divided into a loop type and a tank type. Since the present invention can be applied to both types, a tank type FBR will be described as an example of the prior art. Fig. 2 shows the structure of the primary system of a general tank type FBR. As shown in the figure, a reactor core 2, a core 3, a plurality of intermediate exchangers 5, a plurality of pumps 4, a core upper mechanism 6, and the like are housed in a reactor vessel 2. A furnace vessel 2 is filled with sodium 1 and covered with a roof slab 9. The sodium 1 has a free liquid surface 11 and a cover gas space 12 of an inert gas above it. Also, sodium 1 is a partition structure.
It is divided by 10 into a high temperature plenum 7 in the upper part and a low temperature plenum 8 in the lower part.

The sodium 1 on the low temperature plenum 8 side driven by the pump 4 enters the core 3. The sodium 1 is heated by the nuclear reaction heat of the core 3, and flows out from the upper part of the core 3 to the high temperature plenum 7. Sodium 1 in the high temperature plenum 7 is the intermediate heat exchanger 5
To a secondary cooling system (not shown) piped in the intermediate heat exchanger 5 to be cooled and then return to the low temperature plenum 8 to form a loop. In the above circulation loop, the low temperature plenum 8 is operated at about 370 ° C and the high temperature plenum 7 is operated at about 530 ° C.

The overall structure of the pump 4 is shown in FIG. This type of pump 4 is a vertical mechanical pump, equipped with an electric motor 20 on top of the furnace vessel 2, a shaft 21 extending through the roof slab 9 to the region of the cold plenum 8 and connected to the impeller 22. . From the casing of the impeller 22, the reducer 23 of the pump inlet flow guide opens into the sodium 1 liquid in the low temperature plenum 8 area, and the reducer of the outlet flow guide.
24 is installed at the bottom of the core 3.

Since liquid sodium has a high chemical activity that burns violently when exposed to the atmosphere, and because primary sodium is a highly radioactive substance, the penetrating part of the pump rotating shaft should be completely sealed from the atmosphere. There is a need. FIG. 4 shows details of the shaft penetrating portion and the shaft sealing portion.
In addition to the shaft seal mechanism, a γ-ray shield 25 is provided at the penetrating portion of the roof slab 9.

The shaft sealing part 26 has a double structure of a mechanical seal 28 part and a labyrinth seal 29 part.

The mechanical seal 28 part is a general method for shaft sealing of rotating equipment.The driven ring attached to the rotating shaft and the seat ring surface attached to the casing seal through the lubricating oil to generate heat on the sliding surface. It has a structure that circulates oil to cool the. However, if oil should leak and come into contact with sodium, it may react violently,
A labyrinth seal 29 is also provided below the mechanical seal 28.

The labyrinth seal 29 has a narrow gap part and an expansion chamber part which are repeatedly provided between the rotating body and the stationary body in multiple stages in the axial direction.
It is a structure that seals by the pressure drop effect obtained by purging gas.

The portion of the γ-ray shield 25 is the pump shaft 21 and the γ-ray shield
An annular gap 27 is formed between the gap 25 and 25, and a gap wider than that of the seal is provided in consideration of thermal deformation or eccentricity during rotation so that rotation of the shaft 21 does not mechanically contact. There is. In the primary system pump used for 1000 MWe class FBR, the purge gas flowing through the labyrinth seal 29 is designed to obtain a flow rate of about several tens of mm / sec with a small flow rate of about several / min. However, the circular void of 25 parts of the γ-ray shield
In the case of 27, its cross-sectional area is wide, so it is about 1/10 of several mm / s
Decrease in flow rate of ec. Furthermore, since the diameter of the shaft 21 becomes thicker in the annular space 27, the peripheral speed is several tens of m / sec due to rotation.
It reaches the level. Therefore, the annular void portion 27 has almost no gas purging effect, and it is not possible to suppress the infiltration of sodium mist generated from the sodium free liquid surface 11.

[Problems to be Solved by the Invention] The above-mentioned prior art does not consider the point of preventing the infiltration of sodium mist into the annular cavity formed by the pump shaft and the γ-ray shield portion, and a fundamental measure is desired.

An object of the present invention is to provide a highly reliable mechanical pump for FBR by preventing sodium mist from penetrating into the shaft sealing portion of the mechanical pump and eliminating a factor that inhibits rotation of the pump shaft. .

[Means for Solving the Problem] The above-mentioned problems are solved by a reactor vessel that is filled with a coolant and stores a core, a prime mover that is disposed outside the upper part of the reactor vessel and that drives the coolant circulation pump, and a drive of the prime mover. In a shaft having a shaft sealing device and a penetrating portion of the upper shield of the furnace vessel,
The problem is solved by providing a vertical groove at the lower end of the penetrating portion of the upper shield surrounding the drive shaft to reach the lower end of the penetrating portion.

[Operation] According to the above configuration requirements, sodium mist existing in the drive shaft of the prime mover, that is, the pump shaft and the annular gap formed by the γ-ray shield portion is mixed as fine particles having a larger mass than gas. This mixed gas turns into a rotating flow having almost the same speed as the rotation speed of the pump shaft, and its peripheral speed reaches several tens of meters per second. Further, centrifugal force acts on the rotating flow of the mixed gas, and the sodium mist fine particles present in the gas have a function of segregating to the outside of the annular void.

Since a vertical groove is provided in the outer stationary portion of the annular gap, which is a component of the present invention, the rotating flow loses centrifugal force in the groove portion and the sodium mist segregated in the groove portion positively. Gather. Further, since the rotating flow in the groove flow path is in a cavitating flow state, the pressure is released in the groove portion, an overflow of the secondary flow occurs, and the pressure is reduced. As a result, sodium mist has an action of concentrating in the groove portion. Therefore, the synergistic effect of centrifugal force and cavitating flow completes the recovery of sodium mist.

The gathered sodium mist condenses into a liquid state, travels along the vertical groove, descends by gravity, and is returned to the sodium pool below. Further, the exhaust gas of the purge gas from the labyrinth seal descends in the annular gap portion, but since the pressure distribution in the groove portion is low, it acts so as to positively flow in this portion. Therefore, even a small amount of purge gas flow effectively flows through the groove portion where the sodium mist is most concentrated, so that the effect of further promoting the descending action of the sodium mist occurs.

Since it operates as described above, it is possible to prevent sodium mist from entering the pump shaft shaft seal portion.

[Embodiment] An embodiment of the present invention will be described below with reference to the accompanying drawings. Since the main structure of the mechanical pump for FBR of the present invention is the same as that of the conventional type, the overall configuration will be described with reference to FIGS. 3 and 4, and then one embodiment of the present invention will be described with reference to FIGS. 1 and 5. It demonstrates using. Furthermore, the sixth modification of the present invention
Referring to FIG. 9 to FIG.

As shown in Fig. 3, the mechanical pump used in the FBR is almost vertical. There is an electric motor 20 on the upper part, and a rotary shaft 21 extends vertically from the electric motor 20 to the lower part, penetrates the shaft sealing part 26 and the γ ray shield 25 part, and is connected to the impeller 22 in the sodium 1 liquid. Has been done. The impeller 22 casing has a pump inlet flow guide reducer 23
And the reducer 24 of the outflow flow guide is provided.

The mechanical pump 4 configured in this way operates as follows. The driving force of the electric motor 20 rotationally controlled by another device rotates the shaft 21 and the impeller 22 in the sodium 1 liquid. The sodium 1 flows in from the reducer 23, is pressurized in the casing by the impeller 22, and generates a pumping force flowing out of the reducer 24.

Since the vertical mechanical pump 4 is vertically installed so as to be suspended in the sodium 1 liquid from the opening of the roof slab 9 which is the upper lid of the furnace vessel 2, the upper electric motor 20 part is in the atmosphere and the roof slab is The portion below the penetration portion of 9 operates in a sodium atmosphere. High-temperature liquid sodium is a dangerous substance with a high degree of chemical activity that is rapidly ignited when exposed to the atmosphere.
Since it is radioactive in ²⁴ , the reactor vessel 2 needs to have a completely closed vessel structure. Therefore, the penetrating portion of the pump shaft 21, which is a rotating body, has a bearing bearing portion and a shaft sealing structure shown in FIG.

The penetrating portion is divided into a sealing structure 26 against a sodium atmosphere and a radiation shielding structure 25. The seal structure 26 has a double structure in which a labyrinth seal 29 part is provided below the mechanical seal 28 part. The mechanical seal 28 has a structure in which a driven ring attached to the rotary shaft and a seat ring surface attached to the casing slide through an oil film to seal the rotary shaft. The labyrinth seal 29 part has a structure in which a narrow gap part and an expansion chamber part are repeatedly provided in the axial direction between a rotating body and a stationary body, and sealing is performed by a pressure drop effect obtained by purging gas. The purge gas is injected from the purge gas injection port 30, descends around the shaft 21, and is discharged to the cover gas space 12. The radiation shield structure 25 is provided below the seal structure 26, and is mainly provided from the opening of the through portion.
It is provided for the purpose of blocking the leakage of wires, and has a structure filled with steel balls. Annular void in 25 part of γ-ray shield
The gap of 27 parts is approx.
It is about 10 times wider.

Therefore, in one embodiment of the present invention, a plurality of vertical grooves 31 according to the present invention are provided in the axial direction in the inner wall surface of the annular gap 27 in the portion of the gamma ray shield 25 having a wide gap, as shown in FIG. . Further, the circumferential cross-sectional shape of the vertical groove 31 is uneven as shown in FIG. Further, the lower end of the vertical groove 31 has a structure that extends to the region of the cover gas 12 shown in FIG. 4 and is opened.

Sodium 1 in the primary system flows at a high temperature of 500 ° C or higher,
An inert gas such as argon gas is used in the cover gas space 12 that covers the free liquid surface 11 in order to prevent the oxidation of sodium. Sodium generally produces a large amount of sodium mist from the free liquid surface 11 and is mixed in the argon gas. Further, the shaft seal portion of the pump shaft 21 is operated while being kept at 100 ° C. or lower. As described above, under the temperature conditions in which the upper portion is low temperature and the lower portion is high temperature, natural convection easily occurs in the mixed gas containing sodium mist. Natural convection spreads deep into the annular gap 27, and there is a possibility of sodium mist infiltration.

The shaft 21 diameter of the mechanical pump used for 1000 MWe class FBR is about 500 mmΦ, and the size of the annular gap 27 is designed to be about 1/100 of the diameter of the pump shaft 21 and the rating is about 1000 r.
It is driven at a rpm of pm. In FIG. 5, the annular gap 27
The mixed gas of becomes a rotating flow in conjunction with the rotation of the pump shaft 21, and reaches a speed of several tens of meters per second.

The centrifugal force (f) shown below acts on the rotating flow of the mixed gas.

f = mrω ² (1) where m: mass of rotating object r: radius of rotation ω: angular velocity Therefore, sodium mist with a large mass existing in the mixed gas segregates outside the annular void 27. But,
In the sodium mist trap 32 portion, since there is the uneven vertical groove 31 on the outer inner wall of the annular void 27, the centrifugal force is lost at the groove portion, and the sodium mist is positively collected. In addition, since the flow pattern in the concavo-convex flow path formed on the circumference is a hydrodynamically "interlocking cavity flow", the pressure of the gas flow is released at the concave portion and becomes a reduced pressure state, The sodium mist in the gas flow is further encouraged to collect in the recess. The collected sodium mist condenses while forming a vortex in the concave portion, is transmitted to the vertical groove by its own weight, descends, and is returned to the sodium pool.

As described above, according to the embodiment of the present invention, since the vertical groove portion provided in the penetrating portion of the pump shaft exerts the effect of effectively trapping sodium mist, it penetrates into the shaft sealing portion of the pump shaft. It is possible to prevent the accumulation of sodium mist that inhibits rotation, and it is possible to achieve a highly reliable mechanical pump for FBR.

As described above, in the embodiment of the present invention, the temperature of the annular gap 27 is not lower than the melting point temperature of sodium due to heat conduction from the pump shaft 21, so no special heating device is required, but if the temperature is low, Can be provided with a device for heating the annular space 27 from the γ-ray shield 25 side.

As another embodiment of the present invention, as shown in FIG. 6, the vertical groove 31 provided in the penetrating portion of the pump shaft is formed in a spiral shape so as to advance downward with respect to the rotation direction of the pump shaft. You can also Since the spiral groove becomes a swirling flow in the concave part, it has a function of promoting the descending action of the collected sodium mist, but if the spiral angle is made too large, the descending action decreases because the flow resistance of the concavo-convex channel increases. Tend to do.

Further, as another embodiment, as shown in FIG. 7, the concave portion is filled with a wick 33 such as a stainless steel mesh and condensed sodium is liquefied downward by a capillary phenomenon of the wick 33. It can also be shipped.

As another modification, the shape of the recess may be a trapezoid as shown in FIG. 8 or a circle such as an ellipse as shown in FIG. In these modifications, since the inlet of the recess is narrow, the rate of pressure drop in the recess due to the cavity flow is large, and the effect of the mist trap is further increased, but the structure becomes complicated, so And the assembly man-hour tends to increase.

As another application of the present invention, the invention can be applied to a shaft sealing part of a rotary device such as a pump or a stirrer for a chemical plant that handles organic solvents, poisons, deleterious substances, etc. in addition to dangerous substances such as sodium. Further, it can be applied as a highly efficient sodium paper trap utilizing the centrifugal separation function of the present invention, instead of the sodium vapor trap using a mesh filter or the like so far. Furthermore, when applied to various centrifugal separators such as those used in uranium concentrators, highly efficient centrifugal separators can be obtained.

[Effects of the Invention] As described above, according to the present invention, since the vertical groove portion provided in the penetrating portion of the pump shaft exerts an effect of effectively trapping sodium mist, it penetrates into the shaft sealing portion of the pump shaft. Therefore, it is possible to prevent the accumulation of sodium mist that inhibits rotation. Therefore, a sodium-cooled reactor equipped with a highly reliable mechanical pump can be obtained.

[Brief description of drawings]

FIG. 1 is a structural sectional view of a pump shaft penetrating portion according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a general tank type FBR, and FIG. 3 is a general mechanical pump structure for FBR. Partial cross-sectional view, FIG. 4 is a partial cross-sectional view showing a conventional shaft seal structure of a mechanical pump, FIG. 5 is a cross-sectional view of a pump shaft penetrating part according to an embodiment of the present invention, and FIG. Sectional drawing which shows the structure of the other modified example of the vertical groove structure of this invention, FIG. 7 is sectional drawing of the principal part which shows the structure of the other modified example of the groove part shape of this invention, FIG. 8, and FIG. FIG. 6 is a cross-sectional view of a main part showing a structure of another modification of the groove shape of the present invention. 1 ... Sodium, 2 ... Reactor vessel, 3 ... Reactor core, 4 ...
Mechanical pump, 5 ... Intermediate heat exchanger, 6 ... Core upper mechanism, 7 ... High temperature plenum, 8 ... Low temperature plenum, 9 ...
Roof slab, 10 ... Partition structure, 11 ... Sodium free liquid level, 12 ... Cover gas space, 20 ... Electric motor, 21
...... Pump shaft, 22 …… Impeller, 23 …… Inflow reducer, 24 …… Outflow reducer, 25 …… γ ray shield,
26 …… Shaft seal part, 27 …… annular gap, 28 …… mechanical seal, 29 …… labyrinth seal, 30 …… purge gas inlet, 31 …… groove, 32 …… sodium mist trap, 33…
… Wick.

Claims (6)

[Claims] Claims: 1. A reactor vessel for filling a coolant and containing a core, a prime mover arranged outside the upper portion of the furnace vessel for driving the coolant circulating pump, a shaft sealing device for a drive shaft of the prime mover, and a furnace vessel. In the one having a through portion of the upper shield, a vertical groove is provided in a stationary portion surrounding the drive shaft of the through portion of the upper shield, the lower end of which reaches the lower end of the through portion. Reactor with pump for circulating coolant. 2. A nuclear reactor having a pump for circulating a coolant according to claim 1, wherein a plurality of the vertical grooves are provided. 3. The nuclear reactor having a coolant circulating pump according to claim 1, wherein the longitudinal groove is formed in a spiral shape that is inclined in the rotation direction of the drive shaft. 4. The coolant circulation pump according to any one of claims 1 to 3, wherein a purge gas flowing from an upper portion to a lower portion of the drive shaft of the penetrating portion and a stationary portion is supplied. Reactor with. 5. A nuclear reactor having a coolant circulation pump according to any one of claims 1 to 4, wherein some or all of the longitudinal grooves are filled with a wick having a capillary action. 6. The coolant circulating pump according to claim 1, further comprising means for holding a portion of the penetrating portion between the drive shaft and the stationary portion at a melting point of liquid metal or higher. Reactor.