Method of removing upper internals from a nuclear reactor pressurized vessel
View Patent ↗A lifting fixture for removing the upper internals from a nuclear reactor to provide access to the core during a refueling that does not require flooding of a refueling canal. A shield plate is integral to a lifting rig used to remove the upper internals. The shield plate is sized to be supported on the reactor vessel upper flange and to cover the reactor vessel opening with the closure head removed. The shield plate has openings that are in-line with the control rod assembly drive rod travel housings. Control rod assembly drive rods can be accessed through the openings. The lifting rig allows personnel to decouple the drive rods from the rod cluster control assemblies. The lifting fixture enables the decoupled drive rods to be lifted from the core with the upper internals, while shielding maintenance personnel without flooding the area above the reactor.
1. A method of removing an upper internals package from a nuclear reactor having a reactor vessel with an upper flange surrounding an opening in the reactor vessel that is sealed by a mating flange on a closure head, the reactor vessel enclosing the upper internals package that seats above a plurality of fuel assemblies within a core of the reactor, the upper internals package including a plurality of rod travel housings in which control rod assembly drive rods are housed and through which the drive rods travel along a vertical path, the method comprising the steps of:
removing the closure head from the reactor vessel;
lowering a shield plate over the opening in the reactor vessel after removing the closure head from the reactor vessel, the shield plate being sized to cover the opening when supported on the reactor vessel upper flange and being formed from a material that lessens the radiation exposure of workers working above the shield plate covering the reactor vessel opening, with openings through the shield plate in-line with the rod travel housings through which the control rod assembly drive rods can be accessed, the shield plate including an integral lifting rig extending above an upper surface thereof;
attaching the shield plate to the upper internals package;
accessing the control rod assembly drive rods through the openings; and
raising the shield plate to withdraw the upper internals package out of the reactor.
2. The method of claim 1 wherein the access openings include a drive rod latching tool that is reciprocally moveable along a substantially vertical travel path through the opening and into the rod travel housings to connect to the drive rods and decouple the drive rods from the corresponding control rod assemblies, including the steps of:
attaching the drive rod latching tool to at least one of the drive rods;
decoupling the drive rod from the corresponding control rod assembly; and
raising the drive rod latching tool to raise the drive rod within the rod travel housing.
3. The method of claim 2 including the step of latching the drive rod in a raised position within the rod travel housing after the raising step.
4. The method of claim 2 wherein before the step of raising the shield plate the method comprises the step of lowering a shield cylinder over the shield plate and around the upper internals package.
5. The method of claim 4 including the step of supporting the shield cylinder from the shield plate when the shield cylinder is fully lowered around the upper internals package.
6. The method of claim 4 including the step of maintaining a negative atmosphere within the shield cylinder.
7. The method of claim 6 wherein the step of maintaining a negative atmosphere within the shield cylinder comprises venting air within the shield cylinder and filtering the vented air before being exhausted outside the shield cylinder.