Fluid handling – Back flow prevention by vacuum breaking – Air vent in liquid flow line
Reexamination Certificate
1999-12-17
2001-08-07
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Back flow prevention by vacuum breaking
Air vent in liquid flow line
C137S582000
Reexamination Certificate
active
06269833
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention provides a system for transferring liquid from one location to another while preventing the siphoning of the liquid through the system opposite the intended direction of flow. More particularly, the present invention provides a system for transferring water from a transfer canal to a spent fuel pool in a nuclear reactor facility, the system preventing the siphoning of water from the spent fuel pool, which may contain radioactive contaminants, back into the transfer canal.
2. Description of the Prior Art
The transfer of liquid between locations that are at different levels or heights creates the potential problem of liquid being siphoned between the two locations. In many applications, siphoning is unacceptable and adequate measures must be taken to prevent its occurrence. This need is particularly important where radioactive materials are involved and the possibility of contamination is present, such as in a nuclear reactor facility where water must be transferred into the spent fuel pool. The spent fuel pool is a large tank with racks to hold spent nuclear reactor material. The pool is filled to a specified level with water. Trace chemical elements present in the water may become radioactive in the presence of the reactor material over time. It is important that the water level in the spent fuel pool be kept within specific limits. Water must be added at times to maintain the proper water level within these limits for cooling and safety reasons. The source for additional water is typically a transfer canal. The water and any dissolved trace elements in the transfer canal to be added are not radioactive. It is desirable for safety and contamination prevention not to have water from the spent fuel pool siphoned back into the transfer canal. Otherwise, there is the potential for radioactive contamination of water in the transfer canal, as well as causing of an undesirable decrease of the water level in the spent fuel pool.
One technique for prevention of siphoning is shown in U.S. Pat. No. 5,046,529 (Corella), which describes a potable water system having a container with an internally disposed standpipe. The standpipe has an anti-siphon port near the top to prevent the backflow of water from within the container out through the inlet flow line. A significant disadvantage of this system is that the water level inside the container may rise to a level above the port in the standpipe, and water in the container could then flow out through the inlet flow line. Clearly, this type of system would be unsatisfactory for use in a nuclear facility, as backflow, in any amount, presents a contamination hazard and is therefore unacceptable.
Another system is shown in U.S. Pat. No. 5,268,942 (Newton), which is directed to a temporary cooling system for use in nuclear power plants. The system includes an anti-siphon mechanism in the form of one or more anti-siphon holes in the primary pump suction line. However, the location of the anti-siphon holes is below the maximum water level, thereby allowing at least some amount of water to back flow through the system.
The use of one-way valves and check valves have also been used in attempted prevention of siphoning. For instance, U.S. Pat. No. 3,951,164 (Crist) describes a relatively complex antisiphon and backflow prevention valve. The valve comprises a check valve and an air valve inside a valve body. The use of a complex valve with a large number of parts increases the cost and reduces the reliability of such a system. In a nuclear facility, reliability is of paramount importance. Many systems in a reactor facility are not used until an emergency condition arises. However, they must be in proper working order, even after sitting dormant for relatively long periods of time.
An air gap anti-siphon system for drainage of waste water from a water treatment system to a drain line is shown in U.S. Pat. No. 5,592,964 (Traylor), with an air gap anti-siphon system capable of blocking a sudden sewage backflow. This is accomplished through the use of a disk and tube apparatus fitted into the system. So far as is known, this sewage treatment system with complex and additional apparatus has not been suitable for use in a radioactive material system where a high degree of reliability is necessary.
SUMMARY OF THE INVENTION
The present invention provides a system for transferring a liquid coolant, such as water from a non-contaminated source to a contaminated source while preventing the siphoning of contaminated liquid back into the uncontaminated source. Nuclear contamination is one of the biggest concerns of reactor operators. Great care and expense is taken to minimize the risk of contaminated material being released into an uncontaminated area. With regards to the present invention, the transfer canal is an uncontaminated water source that can be used to provide water for the spent fuel pool, when necessary. The spent fuel pool is a relatively large, sealed compartment that is used to store spent fuel from a nuclear reactor. The pool is filled with water, the level of which must be kept within very specific limits. The water in the pool is in direct contact with the spent fuel and serves to regulate the temperature of thereof. Therefore, the water in the spent fuel pool becomes contaminated with nuclear material over time, due to its exposure to the spent fuel. The water in the spent fuel pool cannot be allowed to enter an uncontaminated source, such as the transfer canal. Likewise, the water in the pool should not be allowed to contaminate the air, equipment or personnel in the vicinity of the spent fuel pool, such as by splashing during a water transfer. When the water level of the spent fuel pool must be raised, water is typically pumped from the transfer canal, through a pipe or hose, and added to the surface of the pool. The difference in height between the canal and the surface of the water in the pool can be substantial, this creates the possibility of a siphon occurring when the pump, which is located near the transfer canal and substantially below the water surface in the pool, stops pumping. Therefore, the anti-siphon system of the present invention is capable of greatly decreasing the risk of contamination associated with maintain the water level in the spent fuel pool.
Preferably, the present invention is an anti-siphon system for transferring uncontaminated water from a transfer canal into the spent fuel pool in a nuclear reactor facility. The system comprises a fluid conduit capable of carrying coolant from the transfer canal to the spent fuel pool. The conduit is typically made from a rigid, non-corrosive material, such as stainless steel, and is substantially L-shaped. A coupling may be attached to the inlet end of the system to facilitate connection of the system with a supply line. At the outlet end of the conduit, a tube is attached. The tube has a larger diameter than the conduit. The tube is attached such that one end is located below the minimum water level of the pool and the opposite end is located above the maximum water level of the pool. The outlet end of the conduit is likewise located above the maximum water level of the pool. The tube may contain a baffle, which is preferably located above the outlet end of the conduit. The baffle serves to prevent splash during a transfer operation, thereby decreasing the likelihood of airborne contamination.
The system may also have a mounting apparatus so that it can be mounted to the seal gates of the spent fuel pool. This allows the system to be properly positioned each time a transfer occurs. It also eliminates the need for personnel to support the system, which can be quite heavy. The mounting apparatus is formed from a bracket which has at least one channel to receive a tab which is attached to a seal gate. Preferably, the apparatus have a plurality of channels for receiving a plurality of tabs. The apparatus also has locking pins to further secure the system when in use.
The system of the present invention does no
Gonzalez Rene R.
Hein Herman W.
Bracewell & Patterson L.L.P.
Michalsky Gerald A.
STP Nuclear Operating Company
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