Patent Application
20140072085
1. Field of the Invention
Example embodiments relate generally to nuclear reactors, and more particularly to a method and system for a spent fuel pool (SFP) level measurement that may be accomplished without the use of 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.
Furthermore, during a serious plant accident when power may be disrupted, conventional level measurement instruments (requiring power) may not be used. This may cause plant operators to be unaware of the true level of the water in the SFP 10, which could prevent them from taking actions to restore the water level of the SFP 10 in the event the water level decreases to dangerous level.
Example embodiments provide a method and system for a spent fuel pool (SFP) measurement that may be accomplished without the use of electrical power. The method and system may include a pressurized gas source that injects a gas through tubing that terminates near the bottom of the SFP. The tubing may include a flow meter and pressure gauge that may be located between the gas source and the SFP. Calibration data for the system may be obtained by measuring a required gas pressure (measured by the pressure gauge) to obtain a specified flow rate (measured by the flow meter) for different known SFP water levels. The pressure of the gas source may be adjusted via an optional throttle valve (located between the gas source and the pressure gauge), or it may be adjusted directly at the gas source itself. Once the calibration data is obtained, a water level measurements of the SFP may then be determined by measuring how much gas pressure is required to obtain the specified flow rate for otherwise unknown SFP water levels. Operation and controls of the system may be located in a remote location to ensure the safety of plant personnel 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 tubing 12 may include a flow meter 16 (for measuring the flow rate of gas passing through tubing 12) and a pressure gauge 20 (for measuring the pressure of the inside of the tubing 12) located relatively near the gas source 14. Optionally, the gas pressure of the gas source 14 may be controlled by a throttle valve 18 or other suitable type of valve located upstream of the pressure gauge 20. Alternatively, gas pressure of the gas source 14 may instead be controlled by the gas source 14, itself (for instance, if the source 14 includes a valve on the source 14). The pressurized gas source 14, the flow meter 16, and the pressure gauge 20 (and, optionally the throttle valve 18) may be located at a safe, remote location that is a distance from the SFP 10, allowing plant personnel to operate the system 30 from a safe distance from the potentially hazardous environment of the SFP 10 (in the event of a serious plant accident). For convenience (in installation and maintenance), the pressurized gas source 14, the flow meter 16, and the pressure gauge 20 (and, optionally the throttle valve 18) may also be located on a pre-fabricated skid 32.
Steps S46-S56 relate to calibrating system 30. Step S46 includes measuring a water level of SFP 10 (using structure other than system 30) to determine a known water level 10c of the SFP 10. Step S48 includes controlling a flow of gas (via throttle valve 18, or via structure on the source 14, such as a shut-off valve) from the gas source 14 to meet a specified flow rate of gas traveling through tubing 12 (the flow rate being measured via flow meter 16). For tubing with an inner diameter of about ½ inch, the flow rate may be about 2 standard cubic feet per hour. Step S50 includes measuring a gas pressure of the gas in tubing 12 (via pressure gauge 20), once the specified flow rate is obtained and held steady. This pressure reading constitutes the amount of gas pressure that is required to discharge gas into the SFP 10 (see gas bubbles 14a of
The final curve 40 inherently discounts pressure drop losses of gas flowing through the tubing 12 during system 30 calibration, because each pressure measurement P may be taken at a same, specified flow rate, such that this pressure drop is approximately the same for each pressure measurement P. For this reason, if changes to the tubing 12 layout are made during the course of plant operation and maintenance, the system 30 should be recalibrated (using steps S46-S56) to account for potential pressure loss changes that may occur due to the changed tubing 12 layout.
Once the calibration curve 40 has been obtained, future liquid level 10c measurements of the SFP 10 may be measured only through the use of system 30, and without the need for external power (such as power that would normally be required for electronic liquid level measurement equipment). These future liquid level 10c measurements may be measured by determining the pressure P that is required to obtain the same specified flow rate that was used during the system calibration steps (S46-S56), and then using the calibration curve 40 to determine the liquid level L based on the pressure measurement P.
It should be noted that temperature changes in the SFP 10 may vary greatly, from the calibration of system 30 (with water temperatures that may be about 72 F, or approximately room temperature) to an actual plant accident (with water temperatures near boiling, at about 212 F). However, the density changes of the liquid in the SFP 10 are small enough that the density changes have a negligible impact on the measurement of liquid level of the SFP 30 using the above-described system 30 and method.
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.
