Induced nuclear reactions: processes – systems – and elements – Reactor protection or damage prevention – Corrosion or damage prevention
Reexamination Certificate
2001-09-14
2003-10-21
Carone, Michael J. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Reactor protection or damage prevention
Corrosion or damage prevention
C376S260000
Reexamination Certificate
active
06636579
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to repairing for a reactor pressure vessel and structures inside the reactor pressure vessel in service, particularly a method and a device for repairing an annulus of the pressure vessel while nuclear fuel and coolant are removed.
Though safety has a priority in any devices, the safety of a reactor pressure vessel has the highest priority in a nuclear power plant, and repairing the nuclear pressure vessel and structures inside the nuclear pressure vessel during service period is prescribed.
The repairing operation for the pressure vessel is usually conducted while a repairing device is installed inside the vessel. The prior art adopts an operation procedure, in which the repairing device is inserted into the pressure vessel from the top of the nuclear reactor, and the device is taken out after the repairing operation.
During the repairing operation, usually the pressure vessel is filled with water, and remote control devices with submersible capability are used in order to reduce the exposure to nuclear radiation of operators.
Usually a chain block is used for installing the repairing device, and a method of lifting the repairing device, and inserting it into and taking it out from the pressure vessel is adopted. When the repairing device is being lift down to a baffle plate of the annulus, it is difficult to check the position of lifting down from the top of the nuclear reactor since the structures inside the nuclear reactor stand together in the course.
Also, since this is a complicated operation requiring monitoring with a submersible television camera for an interference of the repairing device, the operation takes a long period.
Here, the annulus is a space in a toric shape formed in a part surrounded by an inner wall face of the pressure vessel outside a core shroud in the pressure vessel of a boiling water reactor.
Thus, in the prior art, the situation described above is a serious problem for reducing the exposure and shortening the process.
In addition, since the remote control devices with submersible capability require a waterproof seal structure or a waterproof pipe to be installed, designing such a device is demanding, and largely increases the cost.
In addition, welding and PT (liquid penetrant flaw detection) inspection require making the inside of the pressure vessel aerial. After the repairing device is installed, reactor water is drained the for operation. After the operation, the pressure vessel is filled with water to remove the repairing device. This repeated filling/draining operation extends the operation period, and increases the operation cost.
For instance, as described in Japanese Application Patent Laid-open Publication Nos. Hei 09-159788, Hei 09-211182, and 2000-258587, devices are disclosed for allowing individual operations of inspecting, repairing, and preventively maintaining structures in the nuclear reactor such as a jet pump and an outer surface of a shroud installed in the annulus while water is filled.
In this case, since the operation is conducted under water, it has a large effect on reducing the exposure of the repairing device itself and operators when installing the device. However as described before, the operation is conducted remotely, the operation is extremely difficult, and the increase of cost is not negligible. Further, the welding and the PT inspection in the repairing operation should be aerial, and they require filling/draining water in the reactor repeatedly, resulting in a problem of the extended operation period as described before.
On the other hand, Japanese Application Patent Laid-open Publication Nos. Hei 11-174192 and Hei 11-109082, for example, disclose devices, which have access to the annulus in the water and travel automatically on the baffle plate through remote operation for nondestructive inspection. Even in this case, as described before, since the remote operation under water is assumed, the operation is extremely difficult, and if a repairing is required, these devices cannot apply to the repairing and the repairing device since the repairing should be aerial.
The prior art described before does not consider repairing applied to an annulus of a pressure vessel, and has the problem of difficult operation and extended work period.
If the prior art is applied to repairing of a reactor pressure vessel in service, installing/removing the repairing device are conducted in water, and operations such as welding and PT inspection are conducted in air.
It takes a fairly long time to drain and to fill reactor water in the pressure vessel.
Installing/removing the repairing device requires monitoring with a submersible camera for an interference of the repairing device with the structures in the reactor. Further, when the repairing device is inserted into the annulus, since it is difficult to determine the position of the repairing device, the repairing operation becomes extremely difficult.
The previous art causes the problem of difficulty in the repairing operation and the extended work period.
Also, since the repairing device should be installed/removed under water, the repairing device should have waterproof capability, resulting in a large cost in design and production.
Further, the previous art does not provide a technique for repairing from the both sides when repairing is difficult for an operation from one side of the pressure vessel.
SUMMARY OF THE INVENTION
The purpose of the present invention is to provide a method and a device for repairing the inside of a pressure vessel of a nuclear reactor, which conduct the repairing operation in an annulus of the reactor pressure vessel easily in a short period.
The purpose described before is achieved such that coolant in a reactor pressure vessel of a boiling water reactor provided with a recirculating nozzle is drained, a recirculating piping connected to said recirculating nozzle is cut to produce an opening connected to said recirculating nozzle, the repairing device is brought into said annulus in said reactor pressure vessel from said opening, and said repairing device repairs the inside of said annulus.
The purpose described before is also achieved such that coolant in a reactor pressure vessel of a boiling water reactor provided with a recirculating nozzle is drained, a recirculating piping connected to said recirculating nozzle is removed from a recirculating pump to produce an opening connected to said recirculating nozzle, the repairing device is brought into said annulus in said reactor pressure vessel from said opening, and said repairing device repairs the inside of said annulus
Simultaneously, the purpose described before is also achieved such that either inspecting a repaired part with a camera, installing monitoring cameras during repairing, detecting flaws with ultrasonic or beveling for repairing with electrical discharge machining is conducted from the top of said pressure vessel before the coolant in said reactor pressure vessel is drained.
Simultaneously, the purpose described before is also achieved such that said repairing device is brought into said reactor pressure vessel through said opening, said repairing device is lifted up/down with a jig for lifting-up/down, said repairing device is separated from said jig for lifting-up/down after it reaches the height of a baffle plate, said repairing device is mounted on said jig for lifting-up/down again after repairing the inside of the reactor, and the repairing device is recovered from the inside of the reactor.
The purpose described before is also achieved such that said jig for lifting-up/down is brought in by a straight or curved guide held by a jig for bringing-in through said opening.
This allows installing the repairing device to the annulus to be repaired without interfering with constituting devices in a nuclear reactor. Since the distance between a recirculating water outlet nozzle and the annulus is short, and the repairing device can pass while avoiding a reactor core area with high nuclear radiation, the degradation of the re
Go Shinji
Hirano Katsuhiko
Kurosawa Kouichi
Mahara Youichi
Nagashima Toshiharu
Carone Michael J.
Crowell & Moring LLP
Hitachi , Ltd.
Matz Daniel
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