Method for providing a dry environment for underwater repair of the reactor bottom head using a segmented caisson
First Claim
1. In a nuclear reactor vessel having a core plate and a generally hemispherically shaped bottom head with a plurality of penetrations enabling control rod drives to pass through said plurality of penetrations to support a respective plurality of control rods, a method of repairing or mitigating crack formation at said hemispherically shaped bottom head of the vessel comprising the steps of:
- passing plural discrete segments of a first caisson through holes in the core plate to a location about a tube secured to said hemispherically shaped bottom head and surrounding a one of said plurality of penetrations;
assembling said plural discrete segments about said tube;
sealing said plural discrete segments to one another and to said generally hemispherically shaped bottom head;
passing a second caisson through one of said holes in the a core plate and causing a lower edge of said second caisson to engage an upper edge of said first caisson;
removing water from said first and second caissons to provide a water-free environment for welding; and
lowering a welding head through said second caisson and into the first caisson to apply a weld at a weld site about the tube or along said generally hemispherically shaped bottom head.
1 Assignment
0 Petitions
Accused Products
Abstract
Welding repairs are performed in an underwater environment adjacent the bottom head of the nuclear reactor vessel. To provide a dry welding environment, segments of a lower caisson are passed through the core plate holes and assembled along the interior surface of the bottom head. The assembled segments are held down by brackets and sealed to one another and to the bottom head by a water curable polymer. An upper caisson is passed through the core plate hole to sealingly engage the lower caisson. The caissons are pumped dry and welding equipment is passed through the caissons to effect weld repairs about the stub tube or along the bottom head cladding.
37 Citations
10 Claims
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1. In a nuclear reactor vessel having a core plate and a generally hemispherically shaped bottom head with a plurality of penetrations enabling control rod drives to pass through said plurality of penetrations to support a respective plurality of control rods, a method of repairing or mitigating crack formation at said hemispherically shaped bottom head of the vessel comprising the steps of:
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passing plural discrete segments of a first caisson through holes in the core plate to a location about a tube secured to said hemispherically shaped bottom head and surrounding a one of said plurality of penetrations; assembling said plural discrete segments about said tube; sealing said plural discrete segments to one another and to said generally hemispherically shaped bottom head; passing a second caisson through one of said holes in the a core plate and causing a lower edge of said second caisson to engage an upper edge of said first caisson; removing water from said first and second caissons to provide a water-free environment for welding; and lowering a welding head through said second caisson and into the first caisson to apply a weld at a weld site about the tube or along said generally hemispherically shaped bottom head. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. In a nuclear reactor vessel having a core plate and a generally hemispherically shaped bottom head, a method of repairing or mitigating crack formation at the bottom head of the vessel comprising the steps of:
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passing segments of a first caisson through holes in the core plate to a location adjacent the bottom head; assembling the segments to form an enclosure; sealing the segments to one another and to the bottom head; passing a second caisson through a core plate hole and sealing a lower end thereof to an upper end of the first caisson; removing water from the first and second caissons to provide a water-free environment for welding; and lowering a welding head through the second caisson and into the first caisson to apply a weld. - View Dependent Claims (10)
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Specification