NATURAL CIRCULATION BOILING WATER REACTOR AND HANDLING METHOD THEREOF

Abstract

A natural circulation boiling water reactor provides to a chimney with a plurality of tubes. That is to say, each of the plurality of tubes partitions the coolant flow path above a core. Thus, unlike the conventional natural circulation boiling water reactor providing the flow path partition wall grid in which the plate members are made integral by welding and coolant flow paths are partitioned, the chimney of the natural circulation boiling water reactor can reduce the number of welded portions because the edges of the four corners of each flow path do not need to be welded. The natural circulation boiling water reactor can avoid removal as a single unit, as in the case of the flow path partition wall grid in the conventional natural circulation boiling water reactor, by detaching each tube. The chimney can be easily detached from the reactor pressure vessel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural diagram showing a natural circulation boiling water reactor according to an embodiment of the present invention.

FIG. 2 a is a sectional view taken along a line X-X in FIG. 1.

FIG. 2 b is a disassembled perspective view of a chimney shown in FIG. 1.

FIG. 2 c is a sectional view taken along a line Y-Y in FIG. 2a.

FIG. 3 is an explanatory diagram showing the production steps for the square tube.

FIG. 4 is a process chart for exchanging the square tube.

FIG. 5 is an explanatory diagram showing the state where the square tubes are taken out from the reactor pressure vessel.

FIG. 6 is a process chart for performing maintenance and inspection.

FIG. 7 a is an explanatory diagrams showing switching of the square tubes in a handling method for the natural circulation boiling water reactor in FIG. 1.

FIG. 7 b is an explanatory diagrams showing switching of the square pipes in a handling method according to another embodiment.

FIG. 8 a is a perspective view showing the conventional chimney.

FIG. 8 b is a sectional view taken along a line Z-Z in FIG. 8a.

Claims

1. A natural circulation boiling water reactor having a chimney comprising: a cylindrical chimney shell disposed above the core in a reactor pressure vessel; anda plurality of tubes disposed so as to extend in the vertical direction in said chimney shell.

2. The natural circulation boiling water reactor according to claim 1, wherein said tubes are square tubes and edges of the adjacent square tubes are separated from each other by disposing said square tubes at an interval which exceeds the width of one square tube between them.

3. The natural circulation boiling water reactor according to claim 2, wherein the chimney further comprises a grid support plate disposed above the core, and the grid support plate has a plurality of grid holes and the lower ends of the square pipe are supported such that the grid holes communicate with the inside of the square pipes.

4. The natural circulation boiling water reactor according to claim 2, wherein said square tube is formed by bending a plate member and a seam of said plate members which extend in the longitudinal direction of said square tube is welded.

5. The natural circulation boiling water reactor according to claim 4, wherein a welding line for said seam is formed at the side surface of the square tube, and is set at a position that is ⅛-⅜ the width from said edge of said square tube to said side surface.

6. A handling method for a natural circulation boiling water reactor in including a chimney comprising a cylindrical chimney shell disposed above a core in a reactor pressure vessel, and a plurality of square tubes disposed so as to extend in the vertical direction in said chimney shell, and a grid support plate forming a plurality of grid holes and supporting lower end portion of the square tubes such that said grid holes communicate with the inside of said square tubes and said lower ends portion of said square tubes are supported such that adjacent square tubes are disposed at an interval which exceeds the width of one square tube between them, comprising steps of: a first step for shifting predetermined square tubes of said plurality of square tubes to between the square tubes; anda second step for performing maintenance and inspection of members around a core via said grid holes which appear at positions from which said predetermined square tubes are taken out due to shift said predetermined square tubes.