1. Field of the Invention
Example embodiments relate generally to nuclear reactors, and more particularly to a method and system for measuring a spent fuel pool (SFP) temperature and liquid level that may be accomplished without the use of external electrical power. The system may be particularly beneficial in the event a plant emergency that causes plant electrical power to be disrupted, or normal cooling of the spent fuel pools to otherwise become impaired.
2. Related Art
A flow of cooling water, provided by conventional fuel pool cooling and cleanup system (not shown), provides shielding from radiation and maintains the SFP 10 at cool temperatures that ensure the cooling water does not boil (thereby exposing the spent fuel to open air). Specifically, the conventional fuel pool cooling pumps transfer the water from the spent fuel pool to the fuel pool cooling and cleanup system. The conventional fuel pool cooling and cleanup system cools and cleans the water, using a heat exchanger and demineralizers (removing some radioisotopes, and other impurities). The spent fuel pool cooling pumps then send the cool, clean water back to the SFP 10.
During a serious plant accident, normal plant electrical power may be disrupted. In particular, the plant may be without normal electrical power to run the conventional spent fuel pool cooling pumps, operate the spent fuel pool cooling and cleanup system, and power fuel pool instrumentation. If electrical power is disrupted for a lengthy period of time, disruption in the use of the fuel pool cooling and cleanup system may cause water in the spent fuel pool to warm and eventually boil. When enough boiling occurs, water levels in the pool may drop to levels that no longer provide enough cooling water to effectively shield radiation that may be caused by the spent fuel. In very serious emergencies, water in the SFP 10 may boil and evaporate to the point that the spent fuel 7 may become exposed to open air. Furthermore, other events such as earthquakes, fires or explosions, may cause water to be lost from the spent fuel pool even in the absence of boiling. Such an emergency may pose grave dangers for plant personnel and the environment.
Conventionally, the level of the SFP 10 is monitored indirectly via level measurement instruments (requiring external electrical power) at a skimmer surge tank (attached to the SFP 10). Also, the temperature of the SFP 10 is indirectly measured at the spent fuel pool cooling system via temperature instruments (also requiring external electrical power). Therefore, during a serious plant accident when plant power may be disrupted, the conventional temperature and level measurement instruments may not be used. This may cause plant operators to be unaware of the true temperature and/or liquid level of the water in the SFP 10. By not knowing this information, preventative measures to cool and/or restore a volume of water to the SFP 10 may not be taken to prevent a serious accident from occurring.
Example embodiments provide a method and/or system for measuring a spent fuel pool (SFP) temperature and liquid level without the use of electrical power. The method and system may include a cable, with string of thermocouples attached to the cable, that may be mounted along a side wall of the SFP. Each thermocouple may supply their own power (when heated from the water exposed to the thermocouple), such that external electrical power is not needed to operate the thermocouple. The thermocouples may measure the temperature in the SFP. By measuring the temperature, the string of thermocouples may also measure the liquid level within the SFP. Specifically, the liquid water level of the SFP may be inferred by comparing a difference in temperature measurements of the thermocouples, as thermocouples exposed to ambient air will experience a noticeably different temperature from the thermocouples covered by water. Therefore, the string of thermocouples may provide both temperature and liquid level information, without the need for external power. The cable (with the thermocouples on one end) may terminate in a remote location to provide temperature and level information to plant personnel who may be a distance away from the SFP during a potential plant accident.
The above and other features and advantages of example embodiments will become more apparent by describing in detail, example embodiments with reference to the attached drawings. The accompanying drawings are intended to depict example embodiments and should not be interpreted to limit the intended scope of the claims. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted.
Detailed example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.
Accordingly, while example embodiments are capable of various modifications and alternative forms embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.).
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
The thermocouples (TC1-TCn) may be used to take temperature measurements within the SFP 10. In doing so, the liquid level 10c of the SFP 10 may be inferred by comparing the temperature readings of the thermocouples to each other. Specifically, thermocouples exposed to ambient air (such as TC10-TC12) will provide a noticeable different temperature reading than the thermocouples (TC1-TC9) below the water level 10c. For instance, when the water in SFP 10 and the ambient air above SFP 10 is about room temperature, the thermocouples (TC1-TC9) below the water level 10c will normally provide a temperature reading that is noticeably below the temperature reading of the thermocouples (TC10-TC12) above the water level 10c. Therefore, the water level 10c may be inferred as being located between thermocouple TC9 and TC10. By knowing the height (relative to the floor 10b of SFP 10) of thermocouples TC9 and TC10, the liquid water level 10c can therefore be determined. Furthermore, when a plant accident occurs and water in the SFP 10 heats up significantly (to temperatures that may reach boiling, at about 212° F.), the level of liquid in the SFP 10 may drop (due to boiling/evaporation of the heated water) to a lower level 10e. Because the water would be hot during an accident, thermocouples below the water level 10e (specifically, thermocouples TC1-TC6) will provide a temperature reading that is higher than thermocouples exposed to air (specifically, thermocouples TC10-TC12, as well as thermocouples TC7-TC9 that were exposed to air due to water level boiling/evaporation). Therefore, the water level 10e may be inferred as being located between thermocouple TC6 and TC7. By knowing the height (relative to the floor 10b of SFP 10) of thermocouples TC6 and TC7, the liquid water level 10e can therefore be determined.
The thermocouples TC may be spaced apart about equidistantly from each other along the cable 20. Increasing the number of thermocouples (and, thereby, reducing the spacing between the thermocouples) may increase the accuracy of water level measurements of system 30. Furthermore, prior to taking water level measurements, an accurate measure of the distance between the floor 10b of the SFP 10 and each thermocouple TC must be obtained for the system 30 to provide accurate liquid level measurements.
Because ambient heat (from the water in the SFP 10, and air above the SFP 10) may power the thermocouples (TC1-TCn), no external power source is required to operate system 30. Wiring 22 may be attached to the top of the cable 20. A terminal portion 21 of the wiring may extend to a remote location positioned a distance away from the SFP 10. The remote location may include a simple multi-meter 24 or multiple voltage indicators 24 attached to the thermocouples TC via the wiring 21. This may provide plant personnel with temperature and level measurement information at a location that is a safe distance from the potentially hazardous environment of the SFP 10 during a plant accident.
A processor 25 may optionally be included in the system 30. The processor 25 may be in communication with the simple multi-meter 24 or multiple voltage indicators 24. The processor 25 may be used to compare temperatures output from the thermocouples TC in order to infer a liquid level in the SFP 10. Alternative to using a processor 25, the comparison of the temperatures output from the thermocouples TC may be done manually (by a person) in order to infer a liquid level in the SFP 10.
Example embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the intended spirit and scope of example embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.