JPS6159290A - Fast breeder reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to fast breeder reactors, and more particularly to improvements in the mounting structure of nuclear reactor vessels.

[Technical background of the invention]

In general, in liquid metal-cooled fast breeder reactors that use liquid metal such as liquid sodium as a coolant, the reactor vessel receives about two orders of magnitude more fast neutrons than in light water reactors, so the reactor vessel is made of austenitic stainless steel such as 5t JS304, which has less neutron damage. Steel is often used as a material. Inside this reactor vessel, a reactor core is housed and coolant is stored at a constant level, and the coolant liquid level is covered with inert gas to prevent contact between the coolant and air. ing. Therefore, the inside of the reactor vessel must have a sealed structure. Conventionally, the upper end of the reactor vessel was welded to the lower surface of the upper shield that shields the upper opening of the reactor vessel to maintain a sealed structure. has been done.

However, since the upper shield is subject to less thermal shock than the reactor vessel, carbon steel is usually used as a material.For this reason, the welding points between the reactor vessel and the upper shield are dissimilar metal welds, and this welded portion is subjected to thermal stress due to temperature changes in the reactor vessel. For this reason, in the past, welding defects such as cracks occurred in the weld between the reactor vessel and the upper shield, which could impair the integrity of the reactor, and the welding work had to be done in a confined space. Another problem was that work efficiency was poor and welding work took a long time. In order to solve this problem, the present inventors have previously proposed the following attachment structure for a nuclear reactor vessel.

Figures 2 and 3 are diagrams showing examples of the proposal, with Figure 2 showing the schematic configuration of a tank-type fast breeder reactor, and Figure 3 showing an enlarged view of the ■ part in Figure 2. . In the figure, reference numeral 1 denotes a reactor vessel made of stainless steel, and a radially projecting flange 2 is formed at the opening edge of the reactor vessel 1. As shown in FIG. The reactor vessel 1 is surrounded by an installation foundation 3, and a ring gutter 4 that supports the reactor vessel 1 is placed on top of the installation foundation 3. A groove 5 is formed in the upper part of the inner peripheral surface of the ring gutter 4, and the flange 2 is engaged with the groove 5 to support the reactor vessel 1. Further, a roof slab 6 as an upper shielding body in the form of a disc made of assembled steel plates is installed at the upper opening of the reactor vessel 1 to shield the reactor vessel 1 . This roof slab 6 is equipped with a plurality of intermediate heat exchangers 7, circulation pumps 8, etc., and is inserted into the reactor vessel 1.

A reactor core 9 consisting of a large number of fuel assemblies (not shown) is accommodated within the reactor vessel 1, and liquid sodium 10 as a coolant is stored so as to maintain a constant liquid level.

Further, the space between the coolant liquid level and the lower surface of the roof slab 6 is filled with argon gas 11 as a cover gas. A circular opening is formed in the center of the roof slab 6, and a rotary plug 12 is fitted into this opening. This rotary plug 12 is equipped with a core upper mechanism 13, a control rod drive mechanism 14, etc., and the control rod drive mechanism 1
Reference numeral 4 is configured to control the nuclear reaction in the reactor core 9 by inserting or withdrawing a control rod (not shown) from above into the reactor core 9 .

Further, a safety container 15 is provided around the reactor vessel 1 to prevent liquid sodium 10 from flowing out even if a leak occurs in the reactor vessel 1. and,
The temperature of the reactor vessel 1 changes from room temperature to about 500°C depending on the operating condition, and thermal deformation occurs repeatedly due to this temperature change. Therefore, the flange 2 is radially spaced between the ring gutter 4 and the ring gutter 4 as shown in FIG. are engaged with each other with a predetermined gap 16 formed therebetween. Further, a radial key 17 is provided between the flange 2 and the ring gutter 4 to prevent movement in the circumferential direction, and a pressing plate 18 is fixed to the upper surface of the flange 2 and the ring gutter 4 to prevent movement in the vertical direction. ing. Therefore, the reactor vessel 1 is supported by the ring gutter 4 and is movable only in the radial direction. Further, a skirt 19 is integrally provided on the outer periphery of the roof slab 6. This skirt 19 is attached to the outer periphery of the roof slab 6 to form an annular internal space 20 that is open at the bottom, and its lower end abuts against an annular thin-walled projection 21 projecting from the upper surface of the flange 2. The reactor vessel 1 and the roof slab 6 are welded together and configured to maintain airtightness between the reactor vessel 1 and the roof slab 6.

In this way, in the previously proposed example, the reactor vessel 1 and the roof slab 6 are welded together by the skirt 19 and the thin-walled protrusion 21. Since the stress can be absorbed by deformation, excessive thermal stress due to thermal deformation of the reactor vessel 1 is not applied to the weld between the skirt 19 and the thin protrusion 21, and the reliability of the weld can be improved. Further, since the welding work between the skirt 19 and the thin-walled protrusion 21 can be performed on the outer periphery of the roof slab 6, there is no need to perform welding in a narrow space, and the welding work can be performed easily and in a short time. There are advantages such as

[Problems with background technology]

In this way, the previous proposed example has various advantages, but
When actually using this method, there is room for improvement. That is, when welding the skirt 19 and the thin protrusion 21, groove alignment and centering.

It is necessary to perform work such as level adjustment easily and accurately. In addition, it must be possible to handle inner surface inspections of grooves after welding and inspections during the service period after the start of reactor operation.

[Purpose of the invention]

The present invention was made based on these circumstances, and
Its purpose is to be effective as a hermetic structure for nuclear reactor vessels, to enable easy and quick on-site welding, to inspect the inner surface of grooves after welding, and to improve the reliability and soundness of dissimilar metal weld joints. The objective is to provide a fast breeder reactor with improved performance.

(Summary of the Invention) In order to achieve the above-mentioned object, the present invention provides a protruding lug on the outer peripheral surface of the skirt, and a trolley for inspecting welded parts in the internal space between the skirt and the outer periphery of the upper shield. It is equipped with rails on which the trains run.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention, in which the same parts as in FIG. 3 are given the same reference numerals. In this embodiment, in addition to the above-mentioned proposed example, an annularly projecting lug 22 is provided on the upper part of the outer peripheral surface of the skirt 19. Also, skirt 19
An annular internal space 20 formed between the outer periphery of the skirt 19 and the roof protrusion 21 is provided with a rail 23 on which a trolley (not shown) for inspecting the welded portion between the skirt 19 and the thin protrusion 21 runs. , is fixed to the outer peripheral surface of the roof slab 6. Furthermore, a through hole 24 is provided at the upper edge of the roof slab 6.
is bored and communicates with the internal space 20. Note that this through hole 24 is normally closed with a plug 25.

Next, one skirt and thin protrusion 21 with such a configuration
The welding procedure will be described below, but here we will explain the case where the reactor vessel 1 is made of stainless steel and the roof slab 6 is made of carbon mu. First, after battering (overlay welding) stainless steel to the lower end of the skirt 19, the entire roof slab including the skirt 19 is lowered to near the top of the reactor vessel 1 using a crane (not shown). Next, in this state, install a hydraulic jack (not shown) between the flange 2 and the lug 22, and adjust the height of the hydraulic jack while lowering the crane to align the groove between one skirt and the thin protrusion 21. I do. After confirming that both grooves are set at the correct position, the skirt 19 and the thin protrusion 21 are welded together using stainless steel.

In this way, according to this embodiment, by providing the lugs 22 on the outer peripheral surface of the skirt 19, the skirt 19 and the thin protrusion 2
Groove alignment, centering, level adjustment, etc. of the welded part with 1 can be easily and accurately performed using a hydraulic jack or the like.

Furthermore, by providing the rail 23 in the internal space 20 around the outer periphery of the roof slab, various non-destructive inspection devices can be installed in the internal space 20.
Since the welded part can be approached from the side, it is possible to inspect the internal surface of the welded part, such as visual inspection, and it can also be used for inspections during the service period after the start of reactor operation. Furthermore, since the rail 23 narrows the lower part of the internal space 20, it can also contribute to reducing the amount of gases, including sodium vapor and fission products (FP), entering the space.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, a case has been described in which the reactor vessel 1 is made of stainless steel and the roof slab 6 is made of carbon steel, but the present invention can be applied regardless of the combination of materials. Further, in the above embodiment, an example was shown in which the present invention was applied to a tank type fast breeder reactor, but it is of course applicable to other types of fast breeder reactors such as a loop type, for example.

〔Effect of the invention〕

As explained above, according to the present invention, there is provided a reactor vessel which is open at the top and has a radially protruding flange on the edge of the mouth and houses a reactor core therein, and an upper opening of the reactor vessel. An upper shielding body for shielding, an installation foundation formed around the reactor vessel, a ring gutter placed on the upper part of the installation foundation and supporting the flange of the reactor vessel from below, and a ring gutter for supporting the flange of the reactor vessel from below; a skirt that is integrally provided on the outer periphery and forms an annular internal space that is open at the bottom between it and the outer periphery of the upper shield; and a skirt that protrudes from the upper surface of the flange of the reactor vessel and abuts against the lower end of the skirt and is welded to the outer periphery of the upper shield. A thin-walled protrusion, a lug protruding from and attached to the outer peripheral surface of the skirt, and a rail provided in the internal space on which a trolley runs to inspect the welded portion between the thin-walled protrusion and the skirt. It is effective as a sealed structure for the reactor vessel, allows easy and quick on-site welding, and enables inspection of the inner surface of the groove after welding, providing a fast breeder reactor with improved reliability and soundness of dissimilar metal weld joints. .

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of a part of the reactor vessel and roof slab of a tank-type fast breeder reactor showing one embodiment of the present invention, and FIGS. FIG. 2 is a longitudinal sectional view showing the schematic structure of a tank-type fast breeder reactor, and FIG. 3 is an enlarged sectional view of the top of FIG. 2. 1... Reactor vessel, 2... Flange, 3... Installation foundation, 4... Ring gutter, 6... Roof slab,
9... Core, 19... Skirt, 21... Thin protrusion, 22... Lug, 23... Rail.

Claims (3)

[Claims] (1) A reactor vessel that is open at the top, has a radially protruding flange on the edge of the opening, and houses a reactor core therein;
An upper shield that shields the upper opening of the reactor vessel, an installation foundation formed around the reactor vessel, and a ring that is placed on top of the installation foundation and supports the flange of the reactor vessel from below. a gutter, a skirt that is integrally provided on the outer periphery of the upper shield and forms an annular internal space with an opening at the bottom between the outer periphery of the upper shield; and a skirt that is provided protrudingly on the upper surface of the flange of the reactor vessel and that A thin-walled protrusion that abuts and is welded to the lower end, a lug that is protrudingly attached to the outer peripheral surface of the skirt, and a trolley that is provided in the interior space and that inspects the welded portion between the thin-walled protrusion and the skirt runs. A fast breeder reactor characterized by comprising a rail. (2) The fast breeder reactor according to claim 1, wherein the skirt is welded together after buttering the same material as the thin-walled protrusion. (3) The fast breeder reactor according to claim 1, wherein the reactor vessel and the thin protrusion are made of stainless steel.