JPS6351279B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structural improvement of a core upper rectifier which is a component of the upper core mechanism of a nuclear reactor.

In general, in sodium-cooled fast breeder reactors,
Core outlet instrumentation such as thermometers and flow meters is installed at each core fuel outlet for operation monitoring or abnormality diagnosis.
A structure is adopted in which this is supported by the upper core mechanism.

By the way, in the past, the upper core rectifier was installed in a region where high temperature sodium flowing out through the fuel section of the reactor core and low temperature sodium flowing out above the core through the control rod assembly section of the reactor core coexisted. The connecting part of the rectifying tube was worn out. Therefore, the members near the lattice plate of the rectifier suffer from creep fatigue damage due to steady thermal stress due to large temperature differences and thermal fatigue due to temperature fluctuations, which is not desirable in terms of strength.

The present invention has been made to address the above-mentioned drawbacks.
By installing the rectifier tube connection at a location sufficiently far away from the core fuel, that is, in an area where high-temperature sodium and low-temperature sodium are sufficiently mixed, creep fatigue damage to members is minimized and a reliable upper core rectifier is obtained. That is the purpose.

The present invention will be described in detail below with reference to the drawings of one embodiment.

In Figure 1, a reactor core 2 is placed in the center of a reactor vessel 1.
There is a core upper mechanism 3 directly above this, and this core upper mechanism 3 is installed on a shield plug 4 fixed to the reactor vessel 1. A control rod drive mechanism 5 and a large number of instrumentation wells 6 containing thermometers, flowmeters, etc. are housed in this upper core mechanism 3, and around the lower end of this instrumentation well, core outlet instrumentation is precisely installed. A core upper rectifier 7 is installed for this purpose. The rectifier 7 has a control rod drive mechanism (hereinafter referred to as CRD) guide tube 8 as shown in FIGS. 2 and 3.
and a lattice plate 12 arranged in a lattice shape around it.
The rectifying cylinder 9 is held directly above the fuel section 10 of the reactor core 2.
The lower end of the instrumentation well is inserted into the rectifier tube 9, and the flow is rectified by the rectifier tube 9 and isolated from the fuel section 10 or control rod assembly 11 of the adjacent core 2. It is now possible to measure The CRD guide tube 8 and the rectifier tube 9 are welded together by a grid plate 12. Incidentally, as a method of fixing the DRD guide tube 8 and the rectifying tube 9 to the lattice plate 12, screw connection may be used. Further, the grid plate 12 is provided with a large number of hexagonal flow holes 14.

According to the experimental results, there is a relationship as shown in FIG. 4 between the distance A from the top of the fuel section 10 to the grid plate 12 and the width of temperature fluctuation of the sodium that has flowed out above the reactor core 2. . In other words, the distance A is
It can be seen that the width of temperature fluctuation rapidly decreases when the distance exceeds 200 [mm], and becomes almost stable for distances over 200 [mm]. Therefore, as can be seen from FIG. 4, it is most desirable to install the lattice plate 12 at a distance A of 200 mm or more from the lattice plate 12, which is the connecting portion of the rectifier tube 9. The temperature fluctuation width explained above is the temperature between the high temperature sodium that has passed through the fuel section 10 and flowed upward, and the low temperature sodium temperature that has passed through the control rod assembly 11 and flowed upward. It's the difference.

As explained above, in the core upper rectifier of the present invention, by installing the rectifier cylinder connection part at a distance of 200 [mm] or more from the top of the core fuel, which is most important in terms of strength and where thermal stress is likely to occur. It is possible to significantly relax the ambient temperature conditions of the rectifier cylinder connecting portion having the shape, and it is possible to suppress creep fatigue damage to the member.

Furthermore, as the temperature conditions are relaxed, restrictions on plate thickness will be relaxed, making it possible to adopt a machined structure instead of a welded thin plate structure, which is expected to improve processing accuracy and structural reliability and reduce processing man-hours. can.

[Brief explanation of drawings]

Figure 1 is a sectional view of the entire reactor, Figure 2 is a longitudinal sectional view showing an embodiment of the upper core rectifier of the present invention, Figure 3 is a cross sectional view of Figure 2, and Figure 4 is a view from the top of the fuel. FIG. 3 is an explanatory diagram showing the relationship between the distance A to the grid plate and the temperature fluctuation width. 8... Control rod drive mechanism guide tube, 9... Rectifier tube, 12... Grid plate, 13... Rectifier tube support plate, 1
4...Flow hole.

Claims (1)

[Claims] 1. Core upper rectifier consisting of a lattice plate installed in the upper part of the core, rectifier tubes aligned and supported by the lattice plate, and guide tubes for control rod drive mechanisms arranged between the rectifier tubes. A reactor core upper rectifying device characterized in that the grate plate and the top of the reactor core fuel are installed with a distance of at least 200 mm.