JPH0132478B2 - - 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.

Figure 1 shows the positional relationship of the entire reactor. There is a reactor core 2 in a reactor vessel 1, and a core upper mechanism 3 is placed directly above it and supported by a shield plug 4. A control rod drive mechanism 5 is located inside the core upper mechanism 3.
(hereinafter abbreviated as CRD), there are many instrumentation wells 6 that house thermometers, flowmeters, etc., and around the lower end of the instrumentation well there is a core upper rectifier 7 for accurate core exit instrumentation. is installed.

By the way, as shown in FIG. 2, the conventional core upper rectifier includes a rectifier tube 8 installed directly above each core fuel (not shown) and a rectifier tube mounting plate 9 that holds this.
It consists of a support pipe 10 for suspending the rectifying cylinder mounting plate, a CRD guide pipe 11 fitted into the support pipe for guiding the CRD, and a thermal liner 12 for relieving the thermal shock stress of the structure. The lower end of the instrumentation well 6 is inserted into the straightening tube 8, so that the temperature and flow velocity of the flow rectified by the straightening tube and isolated from the adjacent core fuel or control rod assembly can be measured. ing. In order to withstand the severe temperature fluctuation conditions directly above the core fuel, this straightening tube 8 is made of alloy material with excellent high-temperature strength.
718 is used, and in order to avoid dissimilar metal welding when joining the rectifier tube mounting plate 9, the rectifier tube 8 is inserted into the hole of the mounting plate 9.
A structure is adopted in which the mounting plate 9 is fitted over the mounting plate 9 by screw connection.

However, while the high-temperature sodium 20 flowing out from the core fuel flows into the straightening tube 8, the low-temperature sodium 21 flowing out from the control rod assembly flows into the CRD guide tube 11. There was a large temperature difference between the cylinder through hole and the CRD guide tube through hole, and there was a risk of creep fatigue failure due to high thermal stress.

The present invention has been made in view of the above points, and an object of the present invention is to reduce the thermal stress of the rectifying tube mounting plate by improving the structure of the rectifying device, and to obtain a rectifying device whose strength is sufficiently guaranteed. It is.

An embodiment of the present invention will be described below with reference to the drawings. 3 and 4 have almost the same configuration as the conventional plan shown in FIG.
The difference is that a heat insulating ring 13 of a separate structure is provided to surround the rectifying cylinder between the two. This insulation ring 13 is made of the same material and has the same thickness as the mounting plate 9,
In addition, since the hole in the mounting plate 9 is stepped so that the hole diameter becomes smaller on the lower side, the insulating ring 13
It is designed to support the weight of In other words, the heat insulating ring 13 is mechanically fitted to the rectifier tube mounting plate 9. Therefore, since a minute gap exists between the two, each can thermally expand independently.

Here the insulation ring is the same material as the mounting plate,
This name is used in this specification because although it does not have the function of blocking heat, it has the effect of cutting off the effects of thermal strain and stress by providing it in a separate structure from the mounting plate.

In the present application, as described above, a heat insulating ring is provided around the rectifying tube, and a rectifying tube mounting plate is provided around the heat insulating ring with a gap therebetween. Therefore, the heat insulating ring and the rectifier tube mounting plate can thermally expand freely to some extent and deform thermally, thereby reducing thermal stress.

Note that the nature of the heat insulating ring may be different from that of the mounting plate, and it is desirable to use a material with as low thermal conductivity as possible as long as there is no problem with the difference in thermal expansion. It is also possible to lower the thermal conductivity by making the heat insulating ring hollow and filling it with vacuum or inert gas. In the previous embodiment, a heat insulating ring was provided around the rectifying cylinder, but a heat insulating ring may be provided around the CRD guide tube, or may be provided on both sides. To reduce the thermal stress of the insulating ring itself, it may be divided into multilayer rings.

As explained above, the core upper rectifier of the present invention can reduce the temperature difference that occurs in the rectifier tube mounting plate by providing a separate heat insulating ring between the rectifier tube and the rectifier tube mounting plate. can.

In other words, in Figure 4, the conventional temperature difference is
T ₁ - T ₃ , whereas in the present invention the temperature difference is T ₂
- T becomes smaller than ₃ . Thermal stress is generally σ=
Calculated as αEΔT/2(1−ν) (where σ: thermal stress, α: coefficient of thermal expansion, E: modulus of longitudinal elasticity, ν: Boisson's ratio, ΔT: temperature difference), and σ, E, and ν are almost constant. Therefore, σ is proportional to ΔT, regardless of plate thickness, etc. Therefore, unless the temperature difference is small,
Thermal stress also decreases in proportion to this, making it possible to obtain a rectifying device with sufficient strength guaranteed.

[Brief explanation of drawings]

Fig. 1 is an elevational view of the entire reactor, Fig. 2 is an elevational view showing a conventional upper core rectifier, Fig. 3 is an elevational view showing an embodiment of the present invention, and Fig. 4 is an elevational view showing an embodiment of the present invention. FIG. 2 is a plan view showing an example. 7... Core upper rectifier, 8... Rectifier tube, 9...
... Rectifier cylinder mounting plate, 10 ... Support pipe, 11 ...
CRD guide pipe, 13...Insulation ring.

Claims (1)

[Claims] 1. In a core upper rectifier equipped with a rigid tube plate structure that holds a control rod drive mechanism guide tube and a rectifier tube arranged around it, the control rod drive mechanism guide tube or rectifier tube and tube plate are A reactor core upper rectifier characterized by having a separate structure heat insulating ring provided between the core.