Method for maintaining a nuclear reactor

Patent metadata

Field	Value
Publication number	US-12567508-B2
Application number	US-202218284287-A
Country	US
Kind code	B2
Filing date	Mar 29, 2022
Priority date	Mar 31, 2021
Publication date	Mar 3, 2026
Grant date	Mar 3, 2026

Abstract

A maintenance method is applied to a nuclear reactor having a drive assembly for a control rod assembly. The drive assembly includes a casing for receiving a drive rod lifting mechanism and a sheath for receiving the drive rod. A first lip is at an upper end of the casing, and a second lip is at a lower end of the sheath. The lips are welded together forming a seal between the casing and said sheath. The method includes removing the lips via material removal; carrying out a maintenance operation on the control rod assembly; creating a welding surface by machining the upper end of the casing; and creating a leak-tight connection between the casing and the sheath by welding the created welding surface to a matching welding surface provided at the lower end of the sheath. A replacement sheath may be used instead of the original sheath.

First claim

What is claimed is:

1 . A maintenance method for a nuclear reactor,
the nuclear reactor comprising
at least one drive assembly of a control rod assembly,
each drive assembly comprising
an adapter rigidly attached to a closure head of a pressure vessel of the nuclear reactor,
a casing for receiving a mechanism for lifting a drive rod of the control rod assembly and
a sheath for receiving the drive rod,
 the casing having a casing lower end connected in a leak-tight way to the adapter,
 the casing having a first lip at a casing upper end,
 the sheath having a second lip at a sheath lower end,
 the first lip and the second lip being welded together and forming an omega seal,

the maintenance method comprising the following steps:
removing the first and second lips;
carrying out at least one maintenance operation on the control rod assembly;
creating a welding surface at the casing upper end by machining the casing upper end; and
creating a leak-tight welded connection between the casing and the sheath or a replacement sheath,
by welding the welding surface and a matching welding surface provided
at the sheath lower end of the sheath
or at a sheath lower end of the replacement sheath.

2 . The maintenance method according to claim 1 , wherein the matching welding surface is one piece with the sheath lower end, the welding surface being welded directly to the matching welding surface.

3 . The maintenance method according to claim 1 , wherein the casing upper end has a tubular shape about an axis of movement of the drive rod, the casing upper end having a substantially annular casing upper surface perpendicular to said axis of movement and oriented opposite the adapter, the casing upper end further having a casing radially inner surface and a casing radially outer surface, the sheath lower end having a substantially annular sheath upper surface perpendicular to said axis of movement and oriented opposite the adapter, the sheath lower end further having a sheath radially outer surface, the welding surface being produced by machining at least said casing upper surface.

4 . The maintenance method according to claim 3 , further comprising a step of creating the matching welding surface at the sheath lower end by machining at least the sheath upper surface.

5 . The maintenance method according to claim 3 , wherein the welding surface and the matching welding surface form a V-shaped groove provided in the sheath upper surface and in the casing upper surface.

6 . The maintenance method according to claim 3 , wherein the welding surface is an annular zone of the casing upper surface and the matching welding surface is a zone of the sheath radially outer surface, a fillet weld being made during the step of creating the leak-tight welded connection.

7 . The maintenance method according to claim 3 , wherein the welding surface is provided on a third lip machined into the casing upper end, the matching welding surface being provided on a fourth lip carried by a sheath upper end of the sheath, the third lip and the fourth lip together defining an omega-shaped seal.

8 . The maintenance method according to claim 3 , wherein a casing half-cavity is hollowed out in a surface of the casing, and a sheath half-cavity is hollowed out in a surface of the sheath, the casing half-cavity and the sheath half-cavity together defining a cavity arranged along the leak-tight welded connection, the welding surface and the matching welding surface forming a groove emerging into the cavity.

9 . The maintenance method according to claim 8 , wherein the cavity is arranged axially or radially below the leak-tight welded connection.

10 . The maintenance method according to claim 3 , wherein a casing stress-relief groove is provided in the casing upper surface, and/or a sheath stress-relief groove is provided in the sheath upper surface.

11 . The maintenance method according to claim 1 , wherein the casing upper end has a tubular shape about an axis of movement of the drive rod, the casing upper end having a substantially annular casing upper surface perpendicular to said axis of movement and oriented opposite the adapter, the casing upper end further having a casing radially inner surface and a casing radially outer surface, the sheath lower end having a substantially annular sheath upper surface perpendicular to said axis of movement and oriented opposite the adapter, the sheath lower end further having a radially outer surface, the welding surface being produced by machining at least said casing upper surface, and additionally by machining the casing radially inner surface and/or the casing radially outer surface.

12 . The maintenance method according to claim 3 , further comprising a step of creating the matching welding surface at the sheath lower end by machining at least the sheath upper surface and additionally the sheath radially outer surface.

Assignees

• Framatome Sa

Inventors

• Dupuis Alexandre
• Szczurek Eddy
• Lallier Mickael

Classifications

• Y02E30/30

  Nuclear fission reactors · CPC title

• G21C13/036

  the tube passing through the vessel wall, i.e. continuing on both sides of the wall · CPC title

• G21C13/032

  Joints between tubes and vessel walls, e.g. taking into account thermal stresses · CPC title

• G21C19/207 Primary

  Assembling, maintenance or repair of reactor components (G21C3/334 takes precedence) · CPC title