JPS5914200B2 - Upper core mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an upper core mechanism in a fast breeder reactor, and in particular, to a mechanism for relieving thermal stress in members disposed at the lower end of the control rod drive mechanism guide tube. Regarding the mechanism.

Generally, a measuring device is installed above the core to detect the flow rate and temperature of the coolant at the outlet of the fuel assembly in order to detect abnormalities in each fuel assembly.

Conventionally, in order to accurately measure the outlet temperature and flow rate of each fuel assembly, it is generally known that a rectifier grid is disposed at the lower end of the upper core mechanism, and this rectifier grid is coupled to and supported by the control rod drive mechanism guide tube. There is.

However, this type of rectifying grid has a short length in the vertical direction, so the coolant is not mixed sufficiently.
There are disadvantages such as severe thermal stress at the joint between the rectifier grid and the control rod drive mechanism guide tube.

The present invention was devised to solve such conventional difficulties, and its purpose is to alleviate thermal stress at the joint between the lower end of the control rod drive mechanism guide tube and other members. This is to provide the upper core mechanism.

The present invention solves the problem of the conventional difficulty in using a rectifying grid.
Focusing on this issue, we replaced the rectifier grid with a sufficiently long rectifier tube, and installed a convex lower tube located at a position where the coolant around the rectifier tube was sufficiently mixed. The support plate is fixed to a conical support plate, and this support plate is welded and held to the control rod drive mechanism guide tube, thereby relieving the thermal stress of the rectifying tube and the support plate, and the conical support plate and heat shield. The appropriate angle E of the plate allows the core outlet coolant to flow in a uniform direction and promotes mixing within the upper plenum.

The present invention will be described below based on an illustrated embodiment.

FIG. 1 shows the reactor structure of a liquid metal cooled fast breeder reactor, and in the figure, 1 is a reactor vessel.

A reactor core 2 is built into the reactor vessel 1, and a core upper mechanism 3 that supports a control rod drive mechanism 4 is disposed above the reactor core 2.

This upper core mechanism 3 is supported by a shielding plug 5 that serves as a lid for the reactor vessel 1.

The upper core mechanism 3 is installed on the shielding plug 5 as described above, serves to guide and hold the control rod drive mechanism 4, etc., and also houses a thermocouple for measuring the temperature of the coolant at the outlet of the fuel assembly. .

As shown in FIG. 2, this core upper mechanism 3 is composed of an upper housing 6, an upper plate assembly 7, a shielding part 8, a joint shell 9, a straightening tube 10, various guide pipes, an instrumentation well 11, etc. The upper housing 6 of the device houses a control rod drive mechanism drive section and the like via an upper guide tube (not shown), and the upper plate assembly 7E supports the control rod drive mechanism 4 and instrumentation guide tube. There is.

Furthermore, like the shielding plug 5, the shielding part 8 has the function of shielding radiation from the reactor core and insulating it.

The lower part of the upper core mechanism 3 constructed in this way is immersed in sodium, and the lower end of the guide wall 12 for the control rod drive mechanism arranged inside the upper core mechanism 3 is provided with the structure shown in FIGS. As shown in Fig. 4, the rectifier tube 10 and the support plate 13
are respectively disposed therein, and the lower end opening of the joint body 9 is shielded by a heat shielding plate 14 having a conical plate shape and projecting downward.

As shown in FIG. 3, the rectifier tubes 10 are formed to have a sufficiently long length, and are arranged in large numbers in parallel with the guide tubes 12 for the control rod drive mechanism.

These straightening tubes 10 are fixed to a support plate 13 having a downwardly convex conical plate shape (shape), which is arranged at the upper end position, that is, at a position where the coolant around the straightening tubes 10 is sufficiently mixed. ing.

This support plate 13 is welded and held to the control rod drive mechanism guide tube 12, and an instrumentation well 11 is inserted into the rectifier tube 13 to accurately measure the outlet temperature and flow rate of each fuel assembly. It is configured to allow you to do this.

Incidentally, the inclination angles of the support plate 13 and the heat shield plate 14 are set appropriately so that the core outlet coolant flows in a uniform direction and mixing in the upper plenum can be promoted.

In the above configuration, the temperature and flow rate at the outlet of each fuel assembly are accurately measured by the instrumentation well 11 in the straightening tube 10, and the core outlet coolant is sufficiently mixed by the long straightening tube 10. Ru.

This coolant flows in a uniform direction due to the appropriate angle between the support plate 13 and the heat shield plate 14, promoting mixing within the upper plenum.

As explained above, the first embodiment provides the following effects.

(1) Since the coolant around the straightening tube is sufficiently mixed, thermal stress in the straightening tube can be alleviated.

(2) Since the straightening tube is long and the support plate is located away from the core, thermal stress on the support plate is also alleviated.

(3) By placing the support plate on a downwardly convex conical plate,
The angle with the heat shield plate matches, and the flow direction of the coolant can be made at a uniform angle.

As a result, mixing within the upper plenum can be promoted.

The present invention has been described above based on the preferred embodiments, but according to the present invention, thermal stress at the joint between the lower end of the control rod drive mechanism guide tube and other members can be alleviated.

[Brief explanation of the drawing]

Figure 1 is a longitudinal sectional view of a liquid metal cooled fast breeder reactor, Figure 2 is a partial sectional view of the upper core mechanism, Figure 3 is an enlarged sectional view of the main part of Figure 2, and Figure 4 is the same as that of Figure 3. FIG. 2...Core, 3...Core upper mechanism, 1
0... Rectifier cylinder, 12... Control rod drive mechanism guide tube, 13... Support plate, 14...
Heat shield.

Claims (1)

[Claims] 1. In the upper core mechanism, which is equipped with a control rod drive mechanism guide tube located above the core, a large number of straightening tubes for coolant mixing are arranged at the lower end of the control rod drive mechanism guide tube, and these An upper core mechanism characterized in that an upper end of a straightening cylinder is fixed to a support plate having a substantially conical plate shape convex downward, and the support plate is fixed to the control rod drive mechanism guide tube.