JPH0142397B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure of a carbon dioxide gas seal part of an upper extension pipe of a pressure tube assembly of a pressure tube nuclear reactor, and in particular to a carbon dioxide gas seal bellows suitable for maintenance and repair of the pressure tube assembly. This article relates to a welded joint structure between a pressure pipe and an upper extension pipe.

Figure 1 shows a pressure tube reactor.

This reactor consists of a calandria tank 1 that holds heavy water as a moderator, an iron water shield 2 that shields radiation and heat, and the upper and lower parts of the calandria tank 1 that holds nuclear fuel and light water that is a coolant. It is composed of a calandria tube 9 connected to the pressure tubes 9 and a pressure tube assembly 3 that passes through the iron water shield body 2 and stands in a lattice shape. In addition, the pressure pipe assembly 3 is made of iron water shield body 2.
Supported (fixed) by a support bolt 5 at the tip of the flange type of the iron water sleeve 4 that protrudes further.
and the upper part can be freely slid.

Further, an inlet pipe 7 for supplying light water, which is a coolant, is connected to the lower extension pipe 6 extending below the support point (fixed point). here,
The pressure tube assembly 3 is composed of a pressure tube containing the fuel assembly in the reactor core, and stainless steel upper and lower pressure tube extension tubes 8 and 6 connected above and below the pressure tube, and is used to carry the primary coolant ( light water) as internal fluid,
It is a long tubular container that uses thermally insulating gas (carbon dioxide gas) as the external fluid. Note that carbon dioxide gas reduces the amount of heat transferred from the high-temperature pressure pipe assembly 3 to the heavy water moderator, and leakage from the pressure pipe assembly 3 and calandria tube 9 is detected by measuring the moisture in the carbon dioxide gas. Furthermore, in order to reduce corrosion of the pressure tube calandria tube 9, the annulus between the two is kept at low humidity.

FIGS. 2 and 3 are detailed views of section A in FIG. 1, which shows the conventional upper carbon dioxide gas seal structure. The lower support part of the pressure tube assembly 3 is fixed, but the upper part freely expands due to thermal expansion, so that it can absorb the thermal expansion of the pressure tube assembly 3 and suppress the leakage of carbon dioxide gas. A seal bellows (welded bellows) 11 that can be expanded and contracted is installed. Bellows 11 has sleeves 15 and 14
and the collar 13.

Further, the collar 13 is welded to the bellows protection tube 12 and the upper extension tube 8. As the upper extension tube 8 thermally expands, the protection tube 12 slides vertically via the collar 13. Furthermore, the pressure tube assembly 3
In order to improve the integrity of the connection between the pressure pipe and the upper and lower extension pipes 8 and 6 and protect the seal bellows 11,
The protection pipe 12 has a structure that prevents the torsional moment due to the piping reaction force from the primary cooling water inlet and outlet pipes from being transmitted.
A rotation stopper 10 is installed at one location (or two or more locations) in accordance with the notch provided in the sleeve 15 and the groove provided in the sleeve 15.

If a situation arises in which the pressure pipe assembly 3 must be replaced, the upper extension pipe 8
It is necessary to scrape off the welded portion 16 between the flange 13 and the flange 13 using a grinder or the like within the range shown in section B.
However, in order to completely remove the melted metal from the upper extension tube 8, it is difficult to remove only the area shown in part B, so it is thought that at least the area shown in part C must be scraped off. It is considered that after replacing the pressure tube assembly 3, there is a possibility that the collar 13 may not be able to be grooved and welded again.

In this case, it is expected that a situation will arise in which the welded portion 17 of the sleeve 15 and the sleeve 14 must be separated, the seal bellows mechanism removed, and a new seal bellows mechanism attached and rewelded.

The purpose of the present invention is to provide a pressure pipe assembly 3 in case of emergency.
To provide a seal part structure that simplifies the work of separating the joint part 16 between the upper extension pipe part seal part structure and the upper extension pipe during replacement work, and enables reuse without replacing the seal bellows part. It is in.

The present invention aims to improve the repairability of the seal structure and reuse the seal bellows by creating a two-step weldable structure for the joint portion of the upper extension tube seal structure with the upper extension tube.

An embodiment of the present invention will be described below with reference to FIGS. 4 and 5. The same reference numerals as in FIGS. 1 to 3 indicate the same parts.

The collar 13 has a reduced diameter and extends in the axial direction.
Grooves are provided in two locations to enable two-step welding. During construction, the joint 18 between the collar 13 and the extension pipe 8 is welded. Next, if it becomes necessary to replace the pressure tube assembly 3, replace the collar 13 with D-D.
After cutting the joint 18 with a grinder or the like, and replacing the pressure pipe, the joint 19 is welded as shown in FIG.

In the conventional structure, it would be necessary to replace the seal bellows structure at the same time when replacing the pressure pipe, but in this embodiment, there is no need for replacement and the seal bellows can be reused. Further, by reducing the diameter of the collar 13 and extending it in the axial direction, cutting work becomes easier, and the work of removing the welded portion 18 becomes easier.

In this embodiment, a two-stage welding method is adopted, but it is also possible to extend the welding process to three or more stages if necessary.

According to the present invention, the welded joint between the seal bellows part and the upper extension pipe can be easily removed and reattached, the seal bellows part can be reused, and the repairability of the carbon dioxide seal part structure of the upper extension pipe part can be improved. It has the effect of improving

[Brief explanation of drawings]

Figure 1 is an overall schematic sectional view of a pressure tube reactor;
Fig. 2 is a detailed view of part A in Fig. 1, Fig. 3 is a sectional view taken along line EE in Fig. 2, Fig. 4 is a sectional view of the same position as Fig. 3 according to the present invention, and Fig. 5 is a re-illustration. It is a sectional view showing a welding state. 3...Pressure tube assembly, 11...Seal bellows, 13...Brim, 18...Joint part, 19...Joint part.

Claims (1)

[Claims] 1. In a pressure tube nuclear reactor comprising a collar fixed to an upper extension pipe of a pressure tube assembly by welding, and a bellows connected to the collar as constituent members of a gas seal around the extension pipe, the collar is a portion that is thinner than other portions and extends in the axial direction, and a plurality of weld grooves for the upper extension tube that are spaced apart in the axial direction, and at least one of the plurality of weld grooves is The carbon dioxide gas seal structure of the upper extension pipe is characterized by being provided in the extended part.