JPS6146796B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an ex-core fuel storage tank in which spent fuel taken out from the core of a nuclear reactor, which is a sodium fast breeder reactor, is cooled by immersing it in sodium coolant for a certain period of time. This invention relates to an improvement in the guide bearing structure of a rotating rack type fuel storage tank.

As is well known, in fast breeder reactors, the spent fuel removed from the reactor core has a high level of decay heat, making it difficult to take it outside and handle it immediately. The system uses an external fuel storage tank filled with sodium, which cools the reactor until the next fuel change. There are various types of such out-of-core fuel storage tanks depending on the structure of the rack, but the so-called rotating rack type is often used.

Next, an outline of this rotary rack type extra-core fuel storage tank will be explained with reference to FIG. In Figure 1, 1
2 is a storage container, and 2 is an outer container. Inside the storage container 1 filled with liquid metal sodium Na as a coolant, a rotating rack 4 in the form of a vertical shaft is housed with its shaft passing through an upper coolant plug 3. ing. Rotating rack 4
is configured to store a large number of fuels in line around its outer circumferential area, and is suspended and supported within the storage container 1 via an upper thrust bearing 5 and a lower guide bearing 6, and a rotary drive at the upper shaft end. Device 7 is connected. Fuel is taken in and out of the premises through a guide tube 8 provided through the shield plug 3 and a door valve 9 at the top, and a predetermined location of the rotary rack 4 is located directly below the fuel lifting passage in the guide tube 8. It is rotated around the axis via the drive device 7 as shown in FIG.

By the way, as shown in the figure, the guide bearing 6 of the rotating rack 4 is installed immersed in sodium, so lubricating oil cannot be used for the bearing as in a normal bearing. Moreover, liquid metal sodium has a low viscosity in the operating temperature range of the storage tank, so if a sliding bearing is used as the guide bearing, a good lubricant film will not be formed on the bearing surface, resulting in so-called "galling" during operation. ” easily occurs, resulting in unreliability such as inability to rotate. From this point of view, if a rolling bearing is adopted as a guide bearing, it can be smoothly guided and supported even in sodium without fear of "galling". However, since the rotating rack 4 is a very heavy object, the guide bearing 6 is
For example, the bearing load that a bearing receives is about 5 tons, but in the event of an earthquake, an excessive load of 700 tons, which far exceeds the normal bearing load, will be applied. The rolling bearing would have to be extremely large to support such an excessive load, making it unrealistically large to actually install in a fuel storage tank. In this regard, the above-mentioned sliding bearing has a large load capacity because the bearing surfaces are in surface contact, but there is a problem that the bearing performance cannot be fully demonstrated in the sodium of the fuel storage tank.

The present invention was proposed as a solution to the above-mentioned problems, and its purpose is to smoothly guide and support a rotating rack by using rolling bearings as guide bearings during normal operation, and also to provide support when large shock loads such as earthquakes are applied. Earthquake resistance that skillfully relieves the excessive load applied to the rolling shaft to prevent damage to the rolling bearing, absorbs the excessive load, suppresses the horizontal shaking of the rotating rack, and safely protects the reactor fuel stored in the rotating rack. The objective is to provide an excellent ex-core fuel storage tank.

According to the present invention, such an object is to provide a steady bearing structure having a sliding bearing structure in which a rotating member and a stationary member are arranged coaxially with a guide bearing of a rotating rack as a rolling bearing and face each other with a slight gap in the radial direction. In addition to installing the mechanism, the rigidity of at least one of the supporting members on the rotating rack side or the storage container side that supports the rolling bearing is made relatively small so that it will deflect when an excessive lateral load is applied during an earthquake. This is achieved by configuring it as a defined flexible structure.

The present invention will be described in detail below based on illustrated embodiments.

In FIGS. 1 and 2, the lower guide bearing 6 of the rotating rack 4 is a rolling bearing, the inner ring of which is fixed on a pedestal 10 fixed to the bottom of the storage container 1. In FIGS. It is firmly supported by a fixed shaft 11 via a support member serving as a support fitting 12 . On the other hand, the outer ring of the rolling bearing 6 is supported by the rotating rack 4 via a bearing housing ring 13 constructed as a flexible structure whose detailed structure will be described later. Further, a steadying mechanism 14 having a sliding bearing structure is installed coaxially with and below the rolling bearing 6. In this steady rest mechanism 14, a ring 15 as a fixed side member and a ring 16 as a rotating side member face each other with a slight gap g in the radial direction.
In addition, rings 15 and 16 are fixed to pedestal 10 and rotating rack 4, respectively. Particularly, the support tube 17, which is integrally constructed with the rotation side ring 16, has a large section modulus and therefore a large rigidity. On the other hand, the bearing housing ring 13, which is a rolling bearing support member of the flexible structure described above, is arranged between an upper ring 18, a lower ring 19, and between the upper and lower rings 18 and 19 in the vertical direction as shown in FIG. It consists of a plurality of connected flexible rods 20, and as shown in FIG. 2, the lower ring 19 supports the outer ring of the rolling bearing.
The upper ring 18 is connected to the rotating rack 4 via a support tube 21. Note that the reference numeral 22 in FIG. 2 is an eccentric ring for centering adjustment for correctly centering the fixed shaft 11 and the ring 15 of the steadying mechanism 14 to the center of the rotating shaft of the rotating rack 4. Furthermore, the flexible rod 20 of the housing ring 13 does not bend under the bearing load during normal operation;
The bending rigidity is selected to be appropriate so that when acceleration is applied to the rotating rack 4 due to an earthquake and an excessive lateral load is applied, the rack bends in the left-right direction as shown by the dotted line in FIG.

Next, the operation of the above configuration will be described. First, during normal operation, the bearing load applied to the rolling bearing 6 as a guide bearing is small, so the rotating rack 4 is smoothly supported by the bearing via the bearing housing ring 13 and the rolling bearing 6. On the other hand, when an excessive lateral load is applied, such as during an earthquake, the flexible rod 20 of the housing ring 13 bends as shown by the dotted line according to its bending rigidity, and the load is transmitted to the rolling bearing 6 due to the excessive bearing load. It breaks off in the middle of the route. At the same time, when the rotating rack 4 is slightly displaced left and right, the ring 16 of the steadying mechanism 14 is moved to the ring 15.
The excessive lateral load is received by the pedestal 10 and therefore the storage container 1 via the anti-sway mechanism 14, and the rotating rack 4 is supported with anti-sway. Moreover, since the steadying mechanism 14 has a sliding bearing structure, it can withstand large lateral loads. As a result, there is no possibility that the rolling bearing 6, which is a guide bearing, will be damaged.
Further, since an excessive load is not applied to the rolling bearing 6, the rated load can be selected according to the bearing load during normal operation, and a small bearing can be used.

The housing ring 13, which is a supporting member of the flexible structure described above, only needs to have appropriate bending rigidity, and is not particularly limited to the structure using the flexible rods 20 shown in the illustration. A vertical slit may also be formed. Furthermore, although the illustrated example shows an example in which the rotary rack 4 is supported from the outer periphery by a bearing on the fixed shaft 11, it is also possible to apply it to a system in which the rotary shaft of the rotary rack 4 is supported from the outer periphery via a bearing. Of course. In this case, the outer ring of the rolling bearing 6 becomes the fixed side, and the fixed side support member that supports this outer ring is configured as a flexible structure. Furthermore, the support member that supports the inner ring of the rolling bearing 6 in FIG. 2 may be configured as a flexible structure.

As described above, according to the configuration of the present invention, the rolling bearing smoothly guides and supports the rotating rack during normal operation, and also absorbs the excessive load applied to the rolling bearing when an excessive lateral load is applied, such as during an earthquake. The rotating rack can be safely supported and supported by a separately placed sliding bearing structure structure with a high load bearing capacity. Therefore, rolling bearings used as guide bearings eliminate the need to determine the rated load based on shock loads during earthquakes, etc., making it possible to use smaller rolling bearings, improving the reliability of bearings, and improving the reliability of external fuel storage tanks. Various excellent effects can be achieved, such as miniaturization, cost reduction, and improved seismic resistance.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing the overall configuration of an embodiment of the present invention, FIG. 2 is an enlarged sectional view of the main parts in FIG. 1, and FIG. 3 is an external perspective view of the bearing housing ring in FIG. 2. . 1... Storage container, 4... Rotating rack, 5... Thrust bearing, 6... Guide bearing as a rolling bearing,
13...Bearing housing ring which is a rolling bearing support member of the flexible structure, 14...Stabilizing mechanism,
Na...Sodium.

Claims (1)

[Claims] 1. A vertical shaft-shaped rotating rack that stores reactor fuel is housed in a storage container filled with sodium, and the rotating rack is suspended and supported via an upper thrust bearing and a lower guide bearing immersed in sodium. In the out-of-core fuel storage tank, a sliding bearing structure was used in which the fixed side member and the rotating side member were arranged coaxially with the guide bearing of the rotating rack as a rolling bearing, and the fixed side member and the rotating side member were set opposite to each other with a slight gap in the radial direction. In addition to installing a vibration prevention mechanism, at least one of the supporting members on the rotating rack side or the storage container side that supports the rolling bearing is made of a flexible structure with relatively low rigidity so as to be able to bend due to excessive lateral loads applied during an earthquake. An extra-core fuel storage tank for a nuclear reactor, characterized by the following: