Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21C—NUCLEAR REACTORS
  • G21C17/00—Monitoring; Testing ; Maintaining
  • G21C17/06—Devices or arrangements for monitoring or testing fuel or fuel elements outside the reactor core, e.g. for burn-up, for contamination
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E30/00—Energy generation of nuclear origin
  • Y02E30/30—Nuclear fission reactors

Definitions

• the invention relates to the method of contactless measurement of the geometry of a nuclear fuel assembly consisting of a head, a socket, a supporting structure (including spacing grids), and a bundle of fuel rods, by means of ultrasound.
• Deformation measurement of irradiated nuclear fuel always takes place deep below the coolant level, to remove residual heat, and simultaneously to shield radioactive radiation. Measurements are conducted using remote-controlled devices that are equipped with contact or non-contact sensors or optical systems.
• contact sensors e.g. LVDT
• contact sensors e.g. LVDT
• This disadvantage is the safety risk in the event of a fault condition of the sensor when stuck in the area of the fuel rods, where an undesired interaction of the sensor with the fuel rods may occur. Another dangerous condition can occur even if the sensor does not come into contact with any part of the fuel system, and its position relative to the fuel system is unknown.
• the fuel rods can be damaged by the sensor when removing the fault condition, so that a risk to nuclear and radioactive safety can occur.
• the advantage of measurement by contact sensors is the high accuracy of the measured values and the low degree of influence on the refrigerant flowing around the fuel system.
• optical systems are based on the uniformity and simplicity of the geometry measurement system and the simultaneous use of this visual inspection system.
• the progress of visual systems compared to measurements by contact sensors is in the use of contactless measurement, and thus the elimination of the risk condition of a sensor failure (mostly a camera) or its control.
• the disadvantage of these visual systems is the high dependence of measurement accuracy on the optical conditions occurring in the environment between the camera and the fuel system (waves in the refrigerant due to temperature fluctuation, bending of the light, cooling of the refrigerant), and the need for special radiation-resistant optical systems (ordinary camera lenses in the radiation environment lose transparency, and used semiconductors degrade under the influence of radiation). Because of the difficulty of evaluating image output, the use of optical systems is significantly influenced by the human factor.
• the use of an automated image processing system is also relatively slow, due to the high computational complexity, and the complexity of decision algorithms.
• Another innovative step is to use a contactless ultrasonic sensor array, positioned in fixed positions so that an ultrasonic beam contacts the fuel system via the side plate of the spacing grids.
• This method of measurement like the use of contact sensors, requires a precise stationary state of the fuel system, which can be considered a disadvantage.
• An important element that occurs in the measurement of the deformation of fuel systems is a certain degree of automation of the measurement and evaluation process, especially the processing of signals and images, thereby limiting the inappropriate influence of the human factor on the measurement and evaluation.
• the basic principle of the present invention is the simultaneous measurement of two variables, while detection of the second value is used to derive the correct value of one quantity needed to calculate the deformation.
• Changes in the values of the first magnitude are in the order of tenths of a millimetre, and it is difficult to tell which value is the reflection of ultrasound waves from the spacing grid or the fuel rods, respectively.
• the second measured quantity (energy reflected from the surface of the spacing grid or fuel rods), which is significantly more sensitive to changes in the shape and gradient of the reflecting surface, is used to detect the distance grids.
• the second measured quantity energy reflected from the surface of the spacing grid or fuel rods
• the second measured quantity is used to detect the distance grids.
• most of the probe transmitted energy is reflected off the ultrasonic probe.
• the ratio of reflected energy returning to the probe to energy transmitted by the probe (this value is considered as the base - 100%) reaches low values.
• most of the energy emitted by the surface incident probe is reflected back into the ultrasound probe.
• the ratio of the reflected energy returning to the probe to the energy transmitted by the probe is high.
• the difference in the reflected energy between the high and low values is tens of percent, and therefore, when moving the ultrasonic probe in the direction of the longitudinal axis of the fuel system, it clearly identifies the parts with significantly higher values corresponding to the spacing grids, and the lower values corresponding to the fuel rods.
• the correct value of the distance of the distance grid from the ultrasonic probe is determined by subtracting the value of the measured distance at the defined point of the section, denoted by the reflected energy as the spacing grid.
• This innovative measurement and evaluation method makes it possible to measure the geometry of the entire fuel system (meaning deflection and torsion) in a single motion, during the extraction or lowering of the fuel system to or from the reactor or storage grid, storage container, or other location.
• By taking the measurements in the course of movements that would have been carried out without this measurement it significantly saves time in performing the measurements, and obtains information about all of the fuel systems with which it is being handled. It is not necessary to set the spacing grids in the appropriate position relative to the ultrasonic measuring probes; their detection is performed automatically from a measured distance and energy signals. This can also be considered to be one of the advantages of this measurement method.
• Another advantage is the ability to measure fuel systems with different numbers of spacing grids, without changing the location of the ultrasonic probes.
• An important advantage is also the simple automation of the process, and thus the limitation of the influence of the human factor on the measurement and evaluation of the results.
• the method detects an ambiguous evaluation of the position of the distance grid when the lateral surface of the grid is significantly deformed, or when the perimeter of the ultrasound beam is not secured to the side surface. The method allows measurement even in cases where the angle of the beam is not kept on the lateral surface of the distance grid, but the reflected beam energy is high enough to detect the resolution of the reflection from the distance grid and from the fuel rods.
• Figure 1 shows a basic measurement scheme and the principle of the measured signals. At the bottom right, the appearance of the signals of the measured quantities and their mutual relation to each other is schematically shown.
• Fig. 2. shows the difference between the reflection of the ultrasound waves from the level plane of the distance grid (upper part) and from the fuel rods (the lower part).
• This device consists of a tank filled with water, in which a fuel system imitator is located, and a system allowing movement of the ultrasonic probe 3, pointing to the side of the imitator.
• the ultrasonic probe 3 is positioned at a predetermined distance, verified by another method (ruler, calibration), and the perpendicularity of the beam 3 of the probe to the imitator surface, where the focusing on the spacer is assumed, is verified on the reflected energy curve, and should reach high values of the defined distances.
• the ultrasound probe 3 is moved in a direction other than in the direction of the longitudinal axis of the fuel system imitator, the reflected energy value should decrease.
• the imitator surface is curved or non-perpendicular to the beam of the ultrasonic probe 3, and is therefore assigned to the range of fuel rods bundle 2.
• Sections that contain high energy from the energy-reflected proportions of the energy transmitted by the probe are assigned to distance grid L
• the longitudinal coordinates of each section are determined in the axis signal by the longitudinal co-ordinates 7 from the beginning, which is referred to as the distance grid J_, where the positioning centre of the grid 1 is determined by the reflected energy. All of these longitudinal co-ordinates are then assigned the distance values of the distance grid I from the ultrasonic probe 3 from the signal in the measured distance graph 10.
• the deflecting curve of the imitator of the fuel system is interpreted in the direction of the beam of the ultrasonic probe 3.
• multiple probes are required, each of which uses the above-mentioned method, along with another mathematical procedure.
• a special case for determining the distance of elements of the fuel system from the plane of ultrasonic probe 3 is the case of replacing one ultrasonic probe 3 in the transmitter- receiver mode with two probes, each of which having a separate function (one being a transmitter, the other being a receiver). These two probes must be placed in a pair, so that the distance between the probes is known, and the plane passing through these probes is almost parallel to the side plane of the fuel system imitator. In this case, the measured distance is determined from the ultrasound wave flight time along the transmitter-reflecting surface- receiver track. Subsequent signal processing is the same as using one ultrasonic probe 3.
• the method of measurement of ultrasound geometry and the measurement of the measured signal can be applied in devices handling fuel systems, devices for inspection, and measurement of fuel systems or their storage.
• This method can also be used to measure the geometry of other objects in which there is a significant difference in the shape of the reflecting surface (flatness-curvature).

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Monitoring And Testing Of Nuclear Reactors (AREA)

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Citations (5)

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• 2017
  • 2017-10-05 CZ CZ2017-617A patent/CZ2017617A3/cs not_active IP Right Cessation
  • 2017-10-31 WO PCT/IB2017/056754 patent/WO2019069122A1/en not_active Ceased

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