Induced nuclear reactions: processes – systems – and elements – Seal arrangements – For nozzle
Patent
1997-05-28
1999-02-02
Jordan, Charles T.
Induced nuclear reactions: processes, systems, and elements
Seal arrangements
For nozzle
376249, 376260, 138 93, G21C 17017
Patent
active
058675477
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention is generally directed to a pipe blocking apparatus that may be advantageously used to block up tubes, pipes, conduits and the like in a fluid-tight manner and, more particularly, to a device for temporarily blocking up a coolant inlet pipe to thereby prohibit the coolant in a nuclear reactor from entering into a steam generator during the period of, e.g., refueling and/or inspecting the reactor.
DESCRIPTION OF THE RELATED ART
Superannuation of a nuclear power plant makes it innevitable that inspection, repair and overhaul should be performed periodically, with the suspension of reactor operation, to avoid fatal accidents which might otherwise occur due to a failure of essential parts in the nuclear power plant. As is well-known in the art, the "overhaul" cannot be done without exposing the repairmen to a significant level of radiation. For the sake of safety, the radiation exposure dose tends to be strictly regulated by such organizations as NRC, OSHA and EPA under the fundamental rule that it should be maintained as low as reasonably achievable. Although the radiation exposure has been considered unavoidable to some extent, significant reduction in the exposure dose can be achieved by way of improving the manner in which the overhaul work is done.
From the view point of economy, it is essential to shorten the overhaul period, namely, the shutdown interval of the nuclear power plant, which is usually said to take approximately 60 days every year as in other kind of power plants. One way of shortening the overhaul period is to perform more than one repair works for different parts of the nuclear power plant concurrently with the replacement of fuel rods. This is often called an "in-service repair" in the sense that the repair work should be conducted within the service period of the nuclear power plant.
Typical examples of the in-service repair work include conducting an eddy current test of U-shaped heat transfer tubes, plugging up those tubes which are no longer usable because of certain defects and fitting a sleeve to defective portions of the tubes, all of which are to be carried out in the coolant chamber of a steam generator. Since the steam generator remains more highly contaminated with radioactive material than any other parts of the nuclear power plant, the repairmen are very reluctant to carry out their tasks inside the steam generator. This has motivated the researchers to develop a device, e.g., a remote-controlled robot, which may eliminate the need for the repairmen to personally enter into the steam generator. Until now, unfortunately, it appears that no practically applicable robotic device was developed to cater to the long-standing demand.
As schematically illustrated in FIG. 1, fuel rod changing or other similar works should be done when the reactor 10 is submerged in the coolant 12 with its head closure opened. At this time, the coolant will be gravitationally introduced into the steam generator 14, via a coolant inlet pipe 16, which, in turn, is connected to the reactor 10 by way of a coolant outlet pipe 18 and a coolant pump 20. By the way, in order to repair the steam generator in synchronism with the refueling of the reactor, it will be necessary to leave the coolant chamber of the steam generator empty. This can be effected by blocking up the coolant inlet pipe and draining the coolant out of the coolant chamber.
One conventional technique of choking up the coolant inlet pipe is shown in FIG. 2 wherein the steam generator 14 has a manway 22 through which the repairmen may gain access to the coolant chamber 24. A holddown nozzle ring 26 is fixedly attached to the downstream end of the coolant inlet pipe 16. It can be seen that a nozzle dam 28 is sealingly secured to the holddown nozzle ring 26 by a series of bolts 30 so as to prevent the coolant from entering into the coolant chamber 24.
As depicted in FIG. 3 on an enlarged scale, the nozzle dam 28 is of a generally circular configuration and comprises of three pieces, i.e., a center
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Jordan Charles T.
Lattig M. J.
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