JP2015522816A - Device for detecting the level of liquid contained in a container - Google Patents

Abstract

The present invention relates to an apparatus for detecting the liquid level of a liquid (1) contained in a container (2). This device is a temperature sensor (4) having means (3) for detecting the liquid level of the liquid and an optical fiber (41), and the optical fiber (41) is distributed in the length direction. Having a Bragg grating (411), the temperature sensor having means for determining the temperature of the liquid measured by the optical fiber (41) in a plurality of regions (412), each region (412) having its own The liquid level of the liquid stored in the container is determined from the temperature sensor (4) disposed in the vicinity of the Bragg diffraction grating (411) and the temperature measured in the plurality of regions (412) by the optical fiber. Analyzing means. [Selection] Figure 1

Description

  The present invention relates to an apparatus for detecting the level of a liquid contained in a container. In particular, the present invention relates to detecting the level of liquid contained in a spent fuel pool of a nuclear reactor. This is because it is essential to detect fluctuations in the liquid level of the liquid contained in such a container.

  In the context of the present invention, a bubble-type liquid level sensor relates to any sensor capable of measuring the liquid level by ventilation. The liquid level measurement is performed by delivering a constant flow of gas, preferably air, into a tube open at one end under the surface of the water.

  Reactor vessel level measurement is a particularly critical step because reliability must be optimized for the liquid characteristics involved. Variations in the liquid level contained in the reactor vessel must be detected as quickly and as accurately as possible in order to make the most appropriate measurement required for the variation in the liquid level. I must. In the case of a spent fuel pool, the spent fuel must always be immersed in water.

  Various devices are known to those skilled in the art in the technical field of liquid level detection in vessels, especially reactor vessels.

  U.S. Pat. No. 7,926,345 discloses an apparatus for measuring the liquid level in a reactor pressure vessel using a thermocouple for liquid level measurement. Apart from its high cost and measurement complexity due to the need for a large number of tubes, such a liquid level measuring device has major drawbacks in terms of measurement reliability. The thermocouple is arranged along the container perpendicular to the bottom surface of the container for each check liquid level. Measurements in this device are detected using a pair of thermocouples, one being a heated thermocouple and one being an unheated thermocouple. There is a pair of thermocouples for each check level. A temperature difference between two thermocouples for the same check liquid level indicates that the liquid level is below this check liquid level. Detection of leaks against the check liquid level may be delayed due to a failure of at least one thermocouple. This can cause a serious delay to manage the leak. In addition, in this device, all unheated thermocouples are installed in the same tube. If there is a failure in a tube containing all unheated thermocouples, all devices will not work and liquid level measurement and thus leak detection will no longer work.

  Japanese Patent Application Laid-Open No. 2010-085367 discloses a bubble type liquid level measuring device in a reactor storage vessel. Such a device is composed of a bubble rod that is vertically inserted into a container, and a predetermined flow rate of air is blown into the upper end of the rod. The air flow blown into the rod is adjusted so that bubbles are continuously obtained at the outlet at the lower end of the rod. The air pressure applied to create bubbles at the outlet from the rod is equal to the pressure of the liquid at the end of the rod and is therefore proportional to the depth of the liquid in the container. Such a bubble-type liquid level measuring device has the major drawback that it does not provide optimum measurement reliability. The end of the bubble rod can be plugged in the event of an accident or after accumulation of particles contained in the container. This causes even incorrect liquid level measurements or even no liquid level measurements on all liquids in the container. If there is a malfunction in the apparatus due to blockage at the end of the bubble rod, it is impossible to detect the change in the liquid level until the obstacle is removed from the end of the bubble rod. If it is used as a reactor vessel, it takes a lot of time to perform the operation required to remove this blockage, taking into account the special nature of the operating environment and the nature of the liquid contained in the vessel. In particular, it will no longer be possible to continue detecting changes in the liquid level in the container.

  The present invention specifically discloses a reliable measurement of the liquid level of a vessel, in particular a reliable measurement of the level of a reactor vessel, such as a spent fuel pool, and thus the liquid level of this type of vessel. The aim is to remedy some or all of the drawbacks of the background art set forth above by detecting changes in the system as quickly and effectively and continuously as possible.

In order to achieve this, one aspect of the present invention relates to an apparatus for detecting a liquid level of a liquid contained in a container having the following.
-A liquid level detection means;
A temperature sensor comprising an optical fiber configured to receive an optical signal having a wide frequency spectrum, the optical fiber comprising a plurality of Bragg gratings distributed along the length of the optical fiber; Each Bragg grating is designed to backscatter a signal having a specific wavelength, the optical fiber is arranged substantially along the liquid level detection means, and the sensor is connected to each Bragg grating. Means for determining the temperature of the liquid measured by the optical fiber in a plurality of regions using the wavelength of the signal backscattered by the diffraction grating, each region being arranged in proximity to each of said Bragg diffraction gratings A temperature sensor,
-Analyzing means for determining the liquid level of the liquid contained in the container using the temperature measured by the optical fiber in a plurality of regions.

  Such an apparatus has the advantage of providing various means of liquid level measurement and providing a reliable measurement of liquid level. The liquid level contained in the container may be determined by several methods. For example, it may be determined using only the liquid level detection means, using only the analysis means, or using a combination of the liquid level detection means and the analysis means. Therefore, even if one of the means fails, the liquid level detection can be switched to a means that has not failed. This switching can be performed, for example, when repairing a failed means. If the liquid level is determined by the combination of the liquid level detection means and the analysis means, for example, the two liquid level values obtained are compared, and if the difference between the two values is very large, one of the means will fail. You can decide that you are. The failure may occur in the liquid level detection means, the temperature sensor or the analysis means that determines the liquid level from the temperature recorded by the sensor. This is the temperature of the liquid measured by the optical fiber in multiple areas even when the fiber is no longer immersed in the liquid, whether the area is not immersed in the liquid or is still immersed in the liquid Will.

  In addition, the presence of a temperature sensor also indicates that the temperature of the liquid or air contained in the vessel is fixed by the vessel's inherent operating conditions, especially when the vessel is used in a reactor vessel. The temperature can be measured to make sure that the threshold is not exceeded. For example, in a spent fuel pool, the liquid contained in the pool must remain at a constant temperature. Since temperature changes can cause undesired resumption of spent fuel nuclear reactions, it (temperature change) must be detected.

  In addition, an advantage of such a detection device is that it can be mounted in a container that already has liquid level detection means in order to ensure liquid level measurement. Attachment is performed by inserting a fairly small device, an optical fiber temperature sensor, along the liquid level detection means in place.

In some specific embodiments that can be used alone or in combination,
● Analysis means includes the following.
-Means for determining a temperature gradient at a plurality of points distributed along the optical fiber;
-Means for checking that said slope value belongs to a required range of slope values (thresholds);
-Means for determining the liquid level when the value of the gradient is outside said range.
The analysis means is triggered periodically so that an alarm is triggered when the difference between two subsequently calculated liquid level values exceeds a predetermined threshold.
This apparatus has a failure detection means in the liquid level detection means, and the failure detection means triggers the operation of the analysis means in the case of a failure of the liquid level detection means.
The liquid level detection means and the analysis means simultaneously determine the liquid level stored in the container.
The liquid level detecting means is a bubble type liquid level sensor having a tube.
● The optical fiber is fixed along the tube.

  The invention also relates to a container comprising a device according to the invention in which the liquid level detection means is arranged along its length along an axis perpendicular to the bottom surface of the container. The vessel may consist of a spent fuel pool of the reactor.

Other features and advantages of the present invention will become apparent upon reading the following description with reference to the accompanying drawings, which are presented as information and not limiting.
It is a diagram of a container and a liquid level detection device in one embodiment of the present invention. It is a figure which shows that a series of temperature measurement points (namely, collection points) { _Pn } along a fiber are prepared. It is a figure which shows the observation window which has a collection point in the center. It is a figure which shows the example of a series of points { _Pn }. It is a figure which shows one example (example located in the threshold value range shown in FIG. 3) of the obtained gradient. It is a figure which shows one example of the obtained gradient (example in which the window is close to the maximum gradient, but the gradient is in a position where the gradient remains in the threshold tolerance range). An example of the resulting gradient (gradient [P _l P _r] is greater than the reference, longer examples not within the threshold range) is a diagram showing a.

  For clarity of description, identical or similar elements are denoted by the same reference numerals in all figures.

  FIG. 1 schematically shows an embodiment of a liquid level detection device for a liquid 1 contained in a container 2.

  In this container is a liquid level detecting means 3. This detection means is above the bottom surface 21 of the container and along its length perpendicular to the bottom surface 21 of the container in order to measure the liquid level 1 at a depth 1 of the liquid contained in the container 2. Are arranged. The liquid level detecting means 3 may be a thermocouple type liquid level detecting means, a bubble type liquid level detecting means, a liquid level detecting means using magnetic or non-magnetic floating, or any other liquid level detecting means.

  The apparatus also comprises a temperature sensor 4 of the Bragg grating optical fiber type. Such a temperature sensor includes an optical fiber 41 in which a plurality of Bragg diffraction gratings 411 are written. The plurality of Bragg diffraction gratings 411 are distributed along the length direction of the optical fiber. The optical fiber is configured to receive an optical signal having a wide frequency spectrum. The optical signal may be transmitted by a source connected to one end 42 of the optical fiber 41. Each Bragg grating 411 is designed to backscatter a signal having a particular wavelength under predetermined temperature and mechanical stress conditions in the region 412 in which the grating 411 is made. If these conditions are changed, the Bragg grating 411 reflects a signal having a wavelength changed from the original wavelength. The ratio of the initial wavelength to the reflected wavelength is temperature dependent, which can be used to determine the temperature change. Accordingly, the temperature of the region 412 surrounding the Bragg diffraction grating 411 corresponds to the observed wavelength. With respect to the specific wavelength of each Bragg grating 411 written along the optical fiber, its temperature can be determined in multiple regions 412. The temperature is determined using the sensor 4 and these means take the wavelength of the signal reflected by each of the Bragg gratings and analyze them to determine the temperature of the liquid 1 in the plurality of regions 412. To do.

  The optical fiber 4 is arranged in the vertical direction along the liquid level detection means 3, and the optical fiber 4 can be fixed along the liquid level detection means 3. Since this means (liquid level detection means) is arranged perpendicularly to the bottom surface 21 of the container as shown in FIG. 1, the optical fiber 41 is used in the same manner. The Bragg grating 411 is distributed along the length of the optical fiber 41, and as a result, the temperature is determined by a plurality of regions 412 distributed along an axis perpendicular to the bottom surface 21 of the container. The temperature of the liquid 1 can be checked in this way.

  The liquid level detection means includes analysis means for determining the liquid level of the liquid 1 contained in the container 2 starting from the temperature of the liquid 1 measured by the optical fiber 41 in the plurality of regions 412. The analysis means takes out the temperature determined in each region 412 by the means of the sensor 4. The temperature sensor 4 is disposed in a container 2 containing a liquid 1 and a medium 5 other than the liquid. If the region 412 is no longer immersed in the liquid 1, the temperature gradient around this region 412 will change. This change in the gradient reflecting the change in the medium (liquid 1 -medium 5 other than liquid) is detected by analysis means used to estimate the liquid level of the liquid 1 contained in the container 2. For example, the liquid level detection response time is 0.1 second for an optical fiber in which 20 Bragg gratings are written. In order to monitor the change over time of the liquid level of the liquid 2 contained in the container 1, a calculation means may be connected to the analysis means.

The analyzing means operates to calculate a slope between each subsequent temperature value. The calculation means makes temperature measurements along the optical fiber in or out of the liquid. In this case (outside of the liquid), the area is no longer immersed in the liquid. A series of temperature measurement points (ie collection points) {P _n } along the fiber is thus prepared (see FIG. 2). An observation window is defined in which the collection point is centered. Such a window is shown in FIG. This window has a fixed size and defines a desired slope and tolerance characterized by a second order deadband. This deadband and desired slope thus define a threshold slope range.
The detection method first consists of centering the collection point P _k in the sequence {P _n } in the detection window as shown in FIG. 3 (for a series of points {P _n }). An example is shown in FIG. Note that the series {P _n } may not have a fixed collection time. The detection method then includes the intersection P ₁ between the segment [P _k-1 P _k ] and the observation window, and the segment [P _k P _{k + 1} ] (the segment following [P _k-1 P _k ]) It is configured to find the intersection P _r between the observation window. The gradient is obtained by the segment [P _l P _r ]. As shown in FIG. 5, the slope in this case is located within the threshold range shown in FIG. 3, and therefore coincides with the required value within the dead band tolerance.
The observation window then propagates to the next point (FIG. 6) while maintaining centering from point to point. The window in this case is close to the maximum gradient, but at a position where the gradient remains in the threshold tolerance range.
At the next point (FIG. 7), the slope [P _l P _r ] exceeds the reference and is no longer within the threshold range. The change point of the slope is therefore considered as point P _k-1 . Depending on the “shape” of the signal, it may be necessary to maintain P _l instead of P _k−1 as the slope change point. The calibration curve then uses the liquid level obtained in response to the detected gradient change.
A liquid level is found for each collection based on a periodic collection of points. If the difference between two successive liquid level values exceeds a predetermined threshold value, it can be considered that the liquid level is changing. An alarm can be triggered when a liquid level change is detected.

  Such a liquid level detection device has the advantage that it provides two liquid level measurements of liquid 1 and thus provides reliable liquid level management. There may be an analysis means for comparing two provided liquid level values. If there is a discrepancy between these two liquid level values, this analyzing means detects that there is a failure in the detecting means 3, the temperature sensor 4, or the analyzing means for determining the liquid level using the temperature recorded by the temperature sensor 4. To do.

  Preferably, such a liquid level detection device may be installed in order to ensure the liquid level measurement of a container that already has the liquid level detection means 3. The optical fiber temperature sensor 4 is a compact device. The liquid level detecting device 3 may be used so as to ensure the existing liquid level measurement by the liquid level detecting means 3 in which the temperature sensor 4 including an optical fiber having a Bragg diffraction grating is arranged along the means 3.

  The liquid level determination by the analyzing means can be activated only when the liquid level detecting means 3 has a failure. The liquid level detection means may include means for detecting a failure of the liquid level detection means 3. If the fault detection means indicate that the liquid level measurement is no longer provided or is no longer reliable, the analysis means begins to estimate the liquid 1 level from the temperature in each of the regions 412. The analysis means may be started by using a switch. Therefore, the liquid level measurement of the container is ensured by enabling diversification of the liquid level measurement.

  The liquid level detection means 3 shown in FIG. 1 is a bubble-type liquid level sensor 3 having a tube 31, and the tube 31 is disposed along its length along an axis perpendicular to the bottom surface 21 of the container. Yes.

This liquid level detection device may be attached to the spent fuel pool of the nuclear reactor. In this container type, spent fuel must be permanently immersed in a predetermined amount of water. A reliable liquid level detection device as disclosed above is essential for monitoring the water level of the spent fuel pool.

Claims (9)

An apparatus for detecting the liquid level of the liquid (1) contained in the container (2),
Liquid level detection means (3);
A temperature sensor (4) comprising an optical fiber (41) configured to receive an optical signal having a wide frequency spectrum, wherein the optical fiber (41) is distributed along a length direction of the optical fiber (41). A plurality of Bragg diffraction gratings (411), each Bragg diffraction grating (411) being designed to backscatter a signal having a specific wavelength, and the optical fiber (41) is substantially at the liquid level. Arranged in the length direction along the detection means (3),
Means for determining the temperature of the liquid measured by said optical fiber (41) in a plurality of regions (412) using the wavelength of the signal backscattered by each said Bragg grating (411); (412) is a temperature sensor (4) disposed proximate to each said Bragg diffraction grating (411);
An analysis means for determining the liquid level of the liquid stored in the container using the temperature measured by the optical fiber in a plurality of regions (412), and the liquid of the liquid stored in the container A device that detects the position. The analysis means includes
Means for determining temperature gradients at a plurality of points distributed along the optical fiber;
Means for checking that the gradient value belongs to a required range of gradient values;
The apparatus according to claim 1, further comprising means for determining a liquid level when the value of the gradient is outside the range.   The analysis means is triggered periodically such that an alarm is triggered when the difference between two subsequently calculated liquid level values exceeds a predetermined threshold. The device described in 1.   The liquid level detection means (3) has a failure detection means, and the failure detection means triggers the operation of the analysis means in the case of a failure of the liquid level detection means. The device according to any one of the above.   The apparatus according to any one of claims 1 to 3, wherein the liquid level detection means (3) and the analysis means simultaneously determine the liquid level stored in the container (2).   6. The device according to claim 1, wherein the liquid level detection means is a bubble type liquid level sensor (3) having a tube (31).   7. The device according to claim 6, wherein the optical fiber (41) is fixed along the tube (31).   A container (2) comprising the device according to any one of claims 1 to 7, wherein the liquid level detection means (3) has a length along an axis perpendicular to the bottom surface (21) of the container. A container characterized by being arranged along a direction. 9. A vessel according to claim 8, comprising a spent fuel pool of a nuclear reactor.

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