JPH0219791A - Thermal shield plate - Google Patents

Abstract

PURPOSE:To absorb a differential thermal expansion and to secure sufficient rigidity by fixing a thermal shield plate so as to be slidable on a fitting ring by a stud bolt and a nut through a fitting hole which has been opened on said plate. CONSTITUTION:On a thermal shield plate 50, a fitting hole is opened, and said plate is fixed onto a fitting ring 54 by a stud bolt 51 and a nut 52. Also, in its fitting hole, as for its inside diameter, a gap is provided against the outside diameter of the nut 52 in order to avoid an interference caused by a differential thermal expansion from a temperature difference of the shield plate 50 and a heel drum 37. Moreover, this shield plate 50 is brought to regular division, and limits the differential thermal expansion to suitable magnitude. Also, a distance between the ring 54 and a collar of the nut 52 is made a little larger than plate thickness of the shield plate 50 so that the shield plate 50 is slidable within a range of the differential thermal expansion. In such a way, the differential thermal expansion is determined by a small temperature difference, the gap can be suppressed and the reliability is improved. Also, the shield plate 50 is supported by the ring 54 from the inside surface, and the rigidity is obtained enough by fitting a small number of bolts 51.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention provides a method for installing a joint shell on the surface of the joint shell in order to protect the joint shell from thermal stress caused by sudden temperature changes and temperature fluctuations. This invention relates to a thermal shield plate for the upper core mechanism of a fast breeder reactor.

(Conventional technique vg) The heat shield plate of the upper core mechanism of a fast breeder reactor is installed on the surface of the joint shell, and is protected against rapid temperature changes due to reactor startup and shutdown, scram, and even during normal steady operation. This prevents high-frequency temperature fluctuations from being directly transmitted to the joint shell and causing excessive thermal stress.

As illustrated in FIG. 1, the heat shield plate is installed at a certain distance from the joint shell 37 on the surface of the joint M37 that is in contact with the coolant 14.

This heat shield plate 50 also has the following functions from its required functions:
Since the temperature is different from that of the joint body 37, flexible mounting to absorb the difference in thermal expansion and division of the members are required to limit the difference in thermal expansion itself.

Furthermore, since it is exposed to the flow of coolant, it is also required to have rigidity to prevent fluid vibrations caused by this.

Several types of structures have been proposed and implemented to mount the heat shield plate 50 that meet these requirements, but a common example is the mounting of the heat shield plate 50 by welding or screwing stud bolts 51.
7 to ensure a gap with the connecting body 37 via a spacer, and then a stiffening plate 50 was fixed thereon with nuts 52. FIGS. 5 and 6 show examples of mounting structures.

(Problem to be solved by the invention) When the coolant temperature changes suddenly during a reactor trip,
Although the rapid temperature change is alleviated by the heat shield plate 50, the temperature change to the joint Jl 137 is not completely eliminated, and thermal stress is generated in the joint shell 37 due to the slow temperature change over several minutes to several hours.

Although this thermal stress is limited to an extent sufficient to maintain the structural integrity of the structure as a whole, the thermal shield plate 50
Due to the stress caused by the discontinuity in the local area of the stud bolt 51 etc. that attaches the bolt.

Stress levels were not necessarily low enough.

Therefore, when attaching the stud bolt 51 by welding, in order to minimize structural discontinuity, the bead is finished with a grinder or the like, and strict non-destructive testing is performed to ensure reliability. Furthermore, when the stud bolt 51 is attached by screws, the effective thickness of the structure is reduced at the screw hole portion, so the plate thickness is increased to compensate for the strength.

This invention was made in consideration of the above circumstances, and satisfies the functional requirements for installing a heat shield plate, that is, absorbs the difference in thermal expansion and ensures sufficient rigidity, and also prevents additional stress concentration on the joint body. The purpose is to provide a heat shield plate that can be installed without any heat shielding.

[Structure of the invention]

(Means for Solving the Problems) The present invention relates to a heat shield plate that is attached to the outer surface of a core upper mechanism having an outwardly convex joint shell such as a cylinder or an ellipse, and in which the mounting structure is on the outer surface of the joint shell. The mounting is fitted into a shallow groove with a ring.

The installation consists of a stud bolt set on the ring and a nut that is tightened into this bolt.The installation consists of a stud bolt and nut screwed into the hole in the heat shield plate, and the installation is slidably fixed onto the ring. It is something that

(Function) Therefore, when installing the heat shield plate of the fast breeder reactor/core upper structure according to the present invention, stud bolts are not directly installed on the surface of the structure, so no additional local stress is generated in the joint shell. .

Furthermore, since the ring supports the heat shield plate over its entire circumference, higher rigidity can be obtained compared to discrete point support using stud bolts and spacers.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a longitudinal cross-sectional view showing one embodiment of a heat shield plate of a core upper mechanism according to the present invention, and FIG. 2 is a plan view showing the mounting portion cut away.

FIG. 4 is a sectional view showing a fast breeder reactor to which the embodiment of FIG. 1 is applied.

As shown in FIG. 4, a fast breeder reactor 13 generally uses liquid metal such as liquid sodium as a coolant 14. This coolant 14 is filled into the reactor vessel 15 . The upper end of this reactor vessel 15 is closed by a shield plug 17, and a reactor core 19 is accommodated within the reactor vessel 15.

A coolant 14 such as liquid sodium is configured to flow into the reactor vessel 15 from a coolant port 21 in the lower part of the reactor vessel 15, flow upward in the reactor core 19, be heated, and flow out from a coolant outlet 23.

A core upper mechanism 25 is attached to the shield plug 17 .

This core upper mechanism 25 includes control rods, a control rod drive mechanism 27,
A shell 3 containing a control rod guide tube 29 and an instrumentation well 31
7 passes through the free liquid surface 40 of the coolant 14.

A rectifier 33 is attached to the lower part of the shell 37 to divert the coolant flowing out from the core and guide it to the upper plenum 41 of the reactor.

The outer periphery of the joint shell 37 is protected from thermal stress caused by sudden temperature changes and temperature fluctuations such as during a reactor trip.
A heat shield plate 50 is attached to protect the

The mounting structure of the heat shield plate 50 shown in FIGS. 2 and 3 is as follows.

A ring 54 is fitted and fixed in a shallow groove 53 provided in the circumferential direction on the outer surface of the joint body 37.

For installation, since the outside diameter of the joint body 37 is larger than the inside diameter of the ring 54, the ring 54 is assembled in parts and then integrated by welding or mechanical joints. This installation is for ring 5
4 has a plurality of female threads machined therein, and a stud bolt 5■ is inserted into each of them. A nut 52 is screwed into the threaded portion of the other end of the stud bolt 51, and a portion of the nut 52 is fitted by a counterbore provided in the threaded portion of the ring 54 and a spigot.

The heat shield [50] has holes for mounting and is fixed on the ring 54 with stud bolts 51 and nuts 52, but due to the difference in thermal expansion caused by the temperature difference between the heat shield @50 and the joint shell 37. In order to avoid interference, a gap is provided between the inner diameter of the mounting hole and the outer diameter of the nut 52.

Note that if the heat shield plate 50 is large, the required gap will be too large, so the heat shield plate 50 is usually divided to limit the difference in thermal expansion to an appropriate size. Further, the mounting structure is such that the distance between the ring 54 and the brim of the nut 52 is slightly larger than the thickness of the heat shield plate 50, so that the heat shield plate 50 can slide within the range of the difference in thermal expansion.

When attaching the stud bolt 51 to the conventional joint shell 37, this difference in thermal expansion occurs between the joint 1] 1437 and the heat shield plate 50.
However, according to the present invention, the installation is determined by the temperature difference between the ring 54 and the heat shield plate 50, so the temperature difference is small, which makes it possible to suppress the gap, which increases the reliability of the installation. will improve.

Further, each divided heat shield plate 50 has an arc shape and has high rigidity in the axial direction, but relatively low rigidity in the circumferential direction.
Therefore, sufficient rigidity is required to prevent fluid vibration, that is, a high natural frequency that can avoid resonance is required.

According to the present invention, the ring 54 continuously supports the heat shield plate 50 from the inner surface in the circumferential direction, and the heat shield plate 50
Since the vibration mode that deforms inward is limited, sufficient rigidity can be obtained by mounting with fewer stud bolts 51 than in the conventional mounting using only stud bolts 51.

Furthermore, for attachment, a shallow groove 53 is provided in the joint shell 37 for attaching the ring 54 to the joint shell 37, but this depth is sufficient to prevent the mounting ring 54 from coming off and falling downward. To give an example, it is about 2 to 3 m+m.

Therefore, the shape discontinuity on the surface of the joint shell 37 is hardly a problem, and when compared with the conventional method of attaching the stud bolt 51 directly to the joint shell 37 by welding or screwing, the difference in stress concentration is large.

〔Effect of the invention〕

As described above, according to the heat shield plate for the upper core mechanism according to the present invention, the heat shield plate can be attached without providing any shape discontinuity that would cause stress concentration on the surface of the joint shell.
Furthermore, the installation is supported by a ring, which provides high rigidity with fewer stud bolts.

Due to the small temperature difference resulting in differential thermal expansion, the mounting can eliminate hole gaps and provide a reliable mounting structure.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the upper core mechanism of a fast breeder reactor according to the present invention, FIG. 2 is a horizontal sectional view of the embodiment, and FIG. 3 is a sectional view showing the main parts of the embodiment. FIG. 4 is a sectional view showing a fast breeder reactor to which the embodiment is applied, and FIGS. 5 and 6 are sectional views showing essential parts of the upper core mechanism of a conventional fast breeder reactor. 13... Fast breeder reactor 25... Core upper mechanism 37... Joint shell 5o... Heat shield plate 51... Stud bolt 52... Nut 54.
...Installation is by Ring Agent Patent Attorney Nori Chika Ken Yudo Daishimaru Ken Diagram Diagram (Revised) (1!P) Diagram Diagram

Claims (1)

[Claims] In the upper core mechanism of a fast breeder reactor, which has a cylindrical or convex joint housing a control rod drive mechanism, etc., and a heat shield plate on its outer periphery, the attachment part of the heat shield plate is wrapped around the shell. A heat shielding plate for an upper core mechanism of a fast breeder reactor, comprising a mounting ring, a stud bolt screwed into the mounting ring, and a tightening member tightened and attached to the stud bolt.