JPH0346592A - Nuclear reactor having coolant circulating pump - Google Patents

Abstract

PURPOSE:To prohibit the infiltration of sodium Na mists into a shaft sealing part by providing plural longitudinal grooves, the bottom ends of which arrive at the bottom ends of the through-part of an upper shielding body in the outer static part of an annular gap enclosing the driving shaft of a prime mover. CONSTITUTION:An Na mist trap 32 extended and formed with plural pieces of the longitudinal grooves 31 having a rugged shape on the circumferential surface up to the region of a cover gas 12 is constituted on th inside wall sur face of the annular gap 27 of the gamma ray shielding body 25 having a wide gap. The gaseous mixture in the gap 27 forms rotating flow cooperatively with the rotation of a pump shaft 21 and the Na mists of the large mass segregate to the outer side of the gap 27. Centrifugal force is, however, lost by the grooves 31 in the trap 32 part and the Na mists are gathered therein; in addition, a reduced pressure state is generated in the recessed parts by the cavity flow state and the gathering of the Na mists to the recesses is further promoted. Vortexes are thus formed in the recesses and the Na mists are concd. therein. The condensate flows through the grooves 31 and is returned to an Na pool.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a nuclear reactor having a coolant circulation pump, and particularly to a sodium-cooled fast breeder reactor using liquid metal as a coolant.

[Prior art] <Known example closest to the invention> Prototype Fast Reactor
Potier 5tation”P h enix”
(Catalog) Fast breeder reactors (hereinafter referred to as FBR) generally use liquid sodium as a coolant and are divided into loop type and tank type. Since the present invention is applicable to both types, a tank type FBR will be described as an example of the prior art. Second
The figure shows the structure of the primary system of a general tank-type FBR typified by the "Phenix" reactor. As shown in the figure, a reactor 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.

The furnace vessel 2 is filled with sodium l, and the roof slab 9
It is covered with. Sodium 1 has a free liquid level 11 and above it a cover gas space 12 of inert gas. Moreover, the sodium 1 is transported by the partition wall structure 10.
It is divided into two high temperature plenums 7 and a lower low temperature plenum 8.

Sodium 1 on the cold plenum 8 side driven by pump 4
enters core 3. Sodium 1 is heated by the heat of nuclear reaction in the reactor core 3 and flows out from the upper part of the reactor core 3 into the high-temperature plenum 7 . The sodium 1 in the high temperature plenum 7 flows into the intermediate heat exchanger 5, is cooled by heat exchange to a secondary cooling system (not shown) piped in the intermediate heat exchanger 5, and returns to the low temperature plenum 8 again. 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 kind of pump 4
is a vertical mechanical pump, which is equipped with an electric motor 20 in the upper part of the furnace vessel 2, with a shaft 21 extending through the roof slab 9 to the region of the cold plenum 8 and connected to an impeller 22. From the casing of the impeller 22, a pump inflow flow guide reducer 23 opens into the sodium 1 liquid in the low temperature plenum 8 region, and an outflow flow guide reducer 24 is piped to the bottom of the reactor core 3.

Because liquid sodium has such high chemical activity that it burns violently when exposed to the atmosphere, and secondary sodium is a highly radioactive substance, the penetrating part of the pump rotating shaft has a structure that completely seals it from the atmosphere. It is necessary to do so. FIG. 4 shows details of the shaft penetrating portion and the shaft sealing portion. In addition to the shaft seal mechanism, a gamma ray shield 25 is provided at the through-hole of the roof slab 9.

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

Mechanical seal 28 is a common method for shaft sealing of rotating equipment.The driven ring attached to the rotating shaft and the seat ring surface attached to the casing are sealed via lubricating oil, and heat generation on the sliding surface is achieved. The structure is such that oil is circulated to cool the system. However, in the unlikely event that oil leaks and comes into contact with sodium, there is a risk of a violent reaction.
At the bottom of the mechanical seal 28 is a labyrinth seal 29.
Also provided.

The labyrinth seal 29 is provided in multiple stages in the axial direction by repeating narrow gaps and enlarged chambers between the rotating body and the stationary body.
It has a sealing structure that uses the pressure drop effect obtained by purging gas.

The γ-ray shield 25 portion forms an annular gap 27 between the pump shaft 21 and the γ-ray shield 25, and the gap is caused by thermal deformation or eccentricity during rotation of the shaft 2.
A gap wider than the seal portion is provided to prevent mechanical contact between the two rotation parts. The primary system pump used in the 100,100 O class FBR is designed to provide a flow rate of several tens of mm/sec with a small flow rate of the purge gas flowing through the labyrinth seal 29 at a flow rate of approximately several fl/min.

However, since the annular cavity 27 of the γ-ray shield 25 has a large cross-sectional area, the number of processing steps lIl'n/s for about 10 minutes
The flow rate decreases to ec. Furthermore, since the diameter of the shirt 1-21 becomes thicker in the annular cavity 27, the circumferential speed reaches several tens of m/sec due to rotation. Therefore, in the annular cavity 27, there is almost no gas purge effect and it is not possible to suppress the infiltration of the sodium mist generated from the sodium free liquid level 11.

[Problems to be Solved by the Invention] The above-mentioned conventional technology does not take into account the prevention of sodium mist from entering the annular gap formed by the pump shaft and the γ-ray shielding portion, and a fundamental countermeasure is desired.

An object of the present invention is to provide a highly reliable mechanical pump for FBR by preventing sodium mist from entering the shaft seal of a mechanical pump and eliminating factors that inhibit rotation of the pump shaft. .

[Means for solving the problem] The above problem is caused by
A prime mover located outside the upper part of the reactor vessel that electrically drives the coolant circulation pump, a shaft sealing device for the driving shaft of the prime mover, and a penetrating portion of the upper shield of the reactor vessel, wherein This problem is solved by providing a vertical groove whose lower end reaches the lower end of the penetrating part in the stationary part surrounding the two rotational axes of the penetrating part.

[Operation] According to the above-mentioned configuration requirements, the sodium mist existing in the annular gap between the driving shaft of the prime mover, that is, the pump shaft, and the gamma ray shielding portion is mixed with the gas as fine particles with a relatively large mass. This mixed gas becomes a rotating flow at approximately the same speed as the rotation speed of the pump shaft, and its circumferential speed reaches several tens of meters per second. Furthermore, centrifugal force acts on the rotating flow of the mixed gas, causing the fine particles of sodium mist present in the gas to segregate to the outside of the annular gap.

Since vertical grooves are provided in the outer stationary part of the annular gap, which is a component of the present invention, the rotating flow loses centrifugal force in the groove area, and the sodium mist segregated in the groove area actively Gather. Further, since the rotational flow in the groove flow path becomes a cavity flow state, the pressure is released in the groove portion, a vortex of the secondary flow is generated, and the pressure is reduced. This causes the sodium mist to concentrate in the grooves.

Therefore, due to the synergistic effect of centrifugal force and cavity flow, the sodium mist can be completely recovered.

The collected sodium miss 1- condenses into a liquid state, descends by gravity along the vertical groove, and is returned to the sodium pool below. Furthermore, the exhaust gas from the labyrinth seal descends through the annular gap, but since the pressure distribution in the groove is low, it acts to actively flow through this part. Therefore, even a small amount of purge gas flow effectively flows through the portion of the groove where the largest amount of sodium mist has gathered, resulting in the effect of further promoting the downward movement of the sodium mist.

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

[Example] Hereinafter, an example of the present invention will be described based on 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 explained using FIGS. 3 and 4, and then one embodiment of the present invention will be explained using FIGS. 1 and 5. I will explain using Furthermore, modifications of the present invention will be described with reference to FIGS. 6 to 9.

As shown in FIG. 3, most mechanical pumps used in FBR are vertical. There is an electric motor 20 at the top, and two rotating shafts extend vertically from the electric motor 20 to the bottom, pass through the shaft seal 26 and the γ-ray shield 25, and reach the impeller 22 in the sodium solution. connected. The casing of the impeller 22 includes a reducer 23 of the pump inflow flow guide and a reducer 24 of the outflow flow guide.
is provided.

The mechanical pump 4 configured in this manner operates as follows. The driving force of the electric motor 20 whose rotation is controlled by another device rotates the shaft 21, which in turn rotates the impeller 22 in the sodium 1 solution.

Sodium 1 flows in from the reducer 23, is pressurized within the casing by the impeller 22, and generates a pumping force that flows out from the reducer 24.

Since the vertical mechanical pump 4 is installed vertically so as to be suspended in the glass 1 to lium 1 liquid at the opening of the roof slab 9, which is the upper lid of the furnace vessel 2, the electric motor 20 in the upper part
The section operates in an atmospheric atmosphere, and the section below the penetration of the roof slab 9 operates in a sodium atmosphere. High-temperature liquid sodium is a highly chemically active dangerous substance that can rapidly ignite when exposed to the atmosphere, and the primary sodium in the FBR is further radioactive to Na24, so the reactor vessel 2 is completely destroyed. It is necessary to have a closed container structure. Therefore, the penetrating portion of the pump shaft 21, which is a rotating body, is composed of a bearing portion and a shaft sealing structure, as shown in FIG.

The penetration part is divided into a sealing structure 26 from the sodium atmosphere and a radiation shielding structure 25. The seal structure 26 includes a labyrinth seal 29 below the mechanical seal 28.
It has a double structure with a section. Mechanical seal 2
Part 8 has a structure in which a driven ring attached to the rotating shaft ' and a seat ring surface attached to the casing slide through an oil film to seal the rotating shaft. The labyrinth seal 29 has a structure in which a narrow gap portion and an enlarged chamber portion are repeatedly provided in the axial direction between a rotating body and a stationary body, and sealing is achieved by a pressure drop effect obtained by purging gas. The purge gas is injected from the purge gas inlet 30, descends around the shaft 21, and is discharged into the cover gas space 12. The radiation shielding structure 25 is provided below the sealing structure 26, and is mainly provided for the purpose of blocking the leakage of γ-rays from the opening 10 of the penetration part, and has a structure filled with steel balls. There is. γ-ray shield 25
The gap in the annular gap 27 portion is about 10 times wider than the gap in the seal structure 26 portion.

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 on the inner wall surface of the annular gap 27 in the portion of the γ-ray shield 25 having a wide gap, as shown in FIG. . Further, the circumferential cross-sectional shape of the vertical groove 31 forms a sodium amide strap 32 having an uneven shape as shown in FIG. Furthermore, the lower end of the vertical groove 31 has a structure in which it extends to the region of the cover gas 12 shown in FIG. 4 and opens.

The primary system, sodium 1, flows at high temperatures of 500°C or higher,
In the cover gas space ↓2 covering the free liquid surface 11, an inert gas such as argon gas is used to prevent oxidation of sodium. Sodium generally generates a large amount of sodium mist from the free liquid level (1), which is mixed in the argon gas. Also, 1? The shaft seal portion of the pump shaft 21 is operated while being maintained at a temperature of 100° C. or lower. As described above, under the temperature conditions where the upper part is low temperature and the lower part is high temperature, natural convection is likely to occur in the mixed gas containing sodium mist. Natural convection spreads deep into the annular gap 27, and there is a possibility that sodium mist may infiltrate.

The diameter of the shaft 21 of the mechanical pump used in the 10QOMWa class FBR is approximately 500 m + Φ, the dimensions of the annular gap 27 are designed to be approximately 1/100 of the diameter of the pump shafts 1 to 21, and the pump is operated at a rated rotation speed of approximately 1100 Orp. Ru.

In FIG. 5, the mixed gas in the annular gap 27 becomes a rotating flow in conjunction with the rotation of the pump shafts 1 to 21, reaching 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=mrω2・・・・・・・・・・・・(1) Here, m: Mass of rotating object r: Radius of rotation ω: Angular velocity Therefore, the sodium mist with large mass present in the mixed gas has an annular shape. It segregates outside the void 27. but,
In the sodium mist trap 32 section, since there is an uneven longitudinal groove 31 on the outer inner wall of the annular cavity 27, the centrifugal force is lost in the groove part, and the sodium mist actively collects. In addition, since the flow form in the concave-convex channel formed on the circumference is a fluid-dynamically continuous 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 recesses.The collected sodium mist condenses in the recesses while forming a vortex, and due to its own weight it is transmitted down the vertical groove and returned to the sodium pool.

As explained above, according to the embodiment of the present invention, the vertical groove portion provided in the penetrating portion of the pump shaft effectively traps the monolithic mist, so that the mist enters the shaft sealing portion of the pump shaft. A highly reliable FBR that can prevent the accumulation of thorium mist that inhibits rotation.
mechanical pump can be achieved.

As described above, in the embodiment of the present invention, the temperature of the annular gap 27 is higher than the melting point of sodium due to heat conduction from the pump shaft 21, so a special heating device is not required. However, if the temperature is low, A device may be provided to heat the annular gap 27 from the γ-ray shield 25 side.

As another embodiment of the present invention, as shown in FIG. It can also be done. Since the spiral groove creates a swirling flow at the concave part, it works to promote the descending action of the collected thorium mist, but if the spiral angle is too large,
Since the flow resistance of the uneven channel increases, the downward action tends to decrease.

As another example, as shown in FIG. 7, a wick 33 such as a mesh made of stainless steel is filled in the recessed part, and the condensed and liquid sodium is drawn downward by the capillary action of the wick 33. You can also transport 5.

Further, as another modification, the shape of the recess may be a trapezoid as shown in FIG. 8, or a circular shape such as an ellipse as shown in FIG. 9. In these modified examples, since the entrance part of the recess is narrow, the pressure drop rate within the recess due to cavity flow increases, and the mist trap effect becomes even greater, but the structure becomes more complicated. Processing and assembly man-hours tend to increase.

Other applications of the present invention include shaft seals of rotating equipment such as pumps and agitators for chemical plants that handle hazardous substances such as sodium to lithium, as well as organic containers, poisonous substances, and deleterious substances. Applicable. Further, in place of conventional sodium paper traps using mesh filters, etc., the present invention can be applied as highly efficient sodium paper traps using the centrifugal separation function. Furthermore, when applied to various centrifugal separators such as those used in uranium concentrators, highly efficient centrifugal separation equipment can be obtained.

[Effects of the Invention] 6. As described above, according to the present invention, since the vertical groove portion provided in the penetrating portion of the pump shaft effectively traps sodium mist, It is possible to prevent the accumulation of sodium mist that penetrates and inhibits rotation.

Thus, a sodium-cooled reactor with a reliable mechanical pump is obtained.

[Brief explanation of drawings]

Fig. 1 is a structural sectional view of a pump shaft penetration part 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. 4 is a partial sectional view showing the shaft seal structure of a conventional mechanical pump; FIG. 5 is a cross-sectional view of a pump shaft penetrating portion according to an embodiment of the present invention; FIG. 7 is a sectional view showing the structure of another modification of the longitudinal groove structure of the present invention, and FIGS. 8 and 9 are sectional views of essential parts showing the structure of another modification of the groove shape of the invention. 2A and 2B are cross-sectional views of main parts showing structures of other modified examples of the groove shape of the present invention. 1... Su1~Rium, 2... Reactor vessel, 3... Reactor core, 4 Mechanical pump, 5... Intermediate heat exchanger, 6... Core two-part mechanism, 7... High temperature Plenum, 8... Low temperature plenum, 9... Roof slab 10... Partition structure, 11
...S1-lium free liquid level, 12...Cover gas space, 20...Electric motor, 21...Pump shirt 1~
．． 22... Impeller, 23... Inflow reducer-1
24・Outflow reducer-125...γ-ray shield, 26
- Shaft seal part, 27... Annular gap, 28... Mechanical seal, 29... Labyrinth seal, 30... Purge gas inlet, 31... Groove, 32... Sodium miss 1
~Trap, 33...Wick

Claims (1)

[Scope of Claims] 1. A reactor vessel filled with coolant and containing a reactor core, a prime mover disposed outside the upper part of the reactor vessel and driving the coolant circulation pump, a shaft sealing device for a drive shaft of the prime mover, and In the reactor vessel having a penetration part of the upper shield, a stationary part surrounding the drive shaft of the penetration part of the upper shield is provided with a vertical groove whose lower end reaches the lower end of the penetration part. A nuclear reactor having a coolant circulation pump characterized by: 2. A nuclear reactor having a coolant circulation pump according to claim 1, characterized in that a plurality of said vertical grooves are provided. 3. A nuclear reactor having a coolant circulation pump according to claim 1 or 2, wherein the vertical groove is spirally inclined in the rotational direction of the drive shaft. 4. An atom according to any one of claims 1 to 3, characterized in that the space between the drive shaft of the penetrating part and the stationary part is supplied with purge gas flowing from the upper part to the lower part thereof. Furnace. 5. A nuclear reactor having a coolant circulation pump according to any one of claims 1 to 4, characterized in that part or all of the longitudinal grooves are filled with a wick having capillary action. 6. A nuclear reactor having a coolant circulation pump according to any one of claims 1 to 5, further comprising means for maintaining the temperature between the drive shaft and the stationary part in the penetrating part at a temperature higher than the melting point of the liquid metal.