Heat exchange – Non-communicating coaxial enclosures
Reexamination Certificate
1999-03-01
2001-05-22
Lazarus, Ira S. (Department: 3641)
Heat exchange
Non-communicating coaxial enclosures
C165S046000, C138S112000, C062S062000
Reexamination Certificate
active
06234244
ABSTRACT:
FIELD OF THE INVENTION
This invention was made under contract with the U.S. Department of Energy. The present invention relates to a non-intrusive heat exchange cooling system used primarily, but not limited to, removing residual (decay) heat from a nuclear power plant heat source during maintenance situations, by external cooling of adjunct piping.
BACKGROUND OF THE INVENTION
Power generating stations produce tremendous amounts of thermal energy. These stations generally use cooling systems to reduce or eliminate thermal heat, thereby keeping the plant at a suitable temperature during accidents and normal plant operation. However, these normal cooling methods are unavailable to remove residual (decay) heat during plant maintenance periods. Therefore, there is a need for a system to sufficiently cool the system to allow maintenance personnel to access and fix piping, wiring and instrumentation problems.
The current method for heat removal is to directly cut into and interface with the system loop piping so that a separate temporary system can be attached to circulate the internal fluid between the heat source and a heat exchanger. Referring to
FIG. 1A
, incisions G are made in the system piping C and temporary piping D is installed. A specially designed pump E and heat exchanger F are attached to the temporary piping. The pump E and heat exchanger F are specially designed (e.g., canned parts) to accommodate the flow of radioactive coolant. The normal flow path through the heat source (core) is used to cool the heat source. However, direct interface with system loop piping is particularly undesirable in Duclear power plant systems because 1) the work is time consuming resulting in excessive human exposure to higher radiation levels, and 2) the difficulty associated with containing radioactive fluid. Therefore, a non-intrusive method, which removes heat from nuclear power plant systems without cutting into the system piping, is desired. There is no way to directly cool the pressure vessel containing the nuclear fuel constituting the heat source. The system needs to utilize a heat exchanger located on the adjunct piping system which will cool the heat source. The system must rely on natural circulation of the internal fluid to transfer heat from the source to the heat exchanger.
Several types of non-intrusive heat exchangers currently exist which could be attached to the pipe, and these were considered for this application. One method uses commercially available clamp-on heat exchanger cooling jackets. The cooling jackets consist of two sheetmetal plates spaced to create an air gap between and to create an air gap around the system pipe curvature. The plates are edge-sealed and are spot welded together with a weld pattern that produces a dimpled or embossed surface on the outer plate. This raised embossment array provides for homogenous mixing of the coolant, as it passes through the cooling jacket. Couplant is applied to the pipe surface, prior to installing the cooling jackets, to transfer cold temperature from the cooling jacket to the pipe. However, this process is messy and the amount of heat extracted is inadequate.
Another method uses clamshell type covers. These covers are configured to provide a sufficient gap between the inside surface of the shell and the exterior surface of the pipe. The covers are then axially and circumferentially sealed when installed onto the pipe, but had a major disadvantage in requiring the shell to become flooded and necessitating pressure-tight seals between the pipe and exterior shells.
Therefore, there is a need to remove heat from nuclear power plant system piping in a non-intrusive manner while avoiding the disadvantages of the prior art. This invention would provide non-intrusive heat removal that is clean, provides adequate heat removal and uses commercially available parts.
OBJECT AND SUMMARY OF THE INVENTION
It is an object of the invention to provide an environmentally safe way to remove heat generated by radioactivity.
It is another object of the invention to provide maximum heat removal without actually cutting system piping.
It is still another object of the invention to provide maximum heat transfer in a clean, non-intrusive manner.
It is yet another object of the invention to provide a cooling jacket adaptable with standard available equipment.
It is an object of the invention to provide heat transfer with lower operating costs and minimal involvement from plant personnel.
It is another object of the invention to provide a system adaptable for cooling.
It is still another object of the invention to provide increased heat transfer capacity over other non-intrusive heat exchangers.
It is yet another object of the invention to provide a heat removal system that eliminates disadvantages of prior art.
It is a further object of the invention to provide a non-intrusive heat transfer system that is lightweight, and quickly assembled to minimize radiation exposure during installation.
In summary, the present invention is directed toward a system which can remove residual heat from a nuclear power plant by utilizing a readily replaceable heat exchanger jacket at a remote piping location. The cooling jacket is located to promote natural circulation of the fluid inside the pipe so that heat is transferred from the heat source to the cooling jacket. The cooling jacket comprises at least two members, separable into upper and lower portions, such that a chamber is formed between the conduit pipe and cooling jacket once the members are positioned about the pipe. The upper portion includes a fluid spray means positioned above the pipe, while the bottom portion includes a fluid removal means.
The heat exchange cooling jacket is adaptable with standard equipment to provide a system for removing heat from a pipe. This heat removing system includes the aforementioned cooling jacket, a drain tank for receiving the fluid from the cooling jacket, a heat exchanger for cooling the fluid or coolant and a pump for suctioning the fluid from the drain tank.
A method is also provided enclosing a portion of the pipe with a jacket to form a chamber between an outside surface of the pipe and the cooling jacket; spraying cooling fluid at low pressure from an upper portion of the cooling jacket, allowing the fluid to flow downwardly by gravity along the surface of the pipe toward a bottom portion of the chamber; and removing the fluid at the bottom portion of the chamber.
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Bergman John W.
Morrison Edward F.
Caress Virginia B.
Gottlieb Paul A.
Lazarus Ira S.
McKinnon Terrell
The United States of America as represented by the United States
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