Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M3/00—Investigating fluid-tightness of structures
  • G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
  • G01M3/04—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point
  • G01M3/24—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using infrasonic, sonic, or ultrasonic vibrations
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M3/00—Investigating fluid-tightness of structures
  • G01M3/02—Investigating fluid-tightness of structures by using fluid or vacuum
  • G01M3/04—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point
  • G01M3/20—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material
  • G01M3/22—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators
  • G01M3/226—Investigating fluid-tightness of structures by using fluid or vacuum by detecting the presence of fluid at the leakage point using special tracer materials, e.g. dye, fluorescent material, radioactive material for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators for containers, e.g. radiators
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/04—Wave modes and trajectories
  • G01N2291/044—Internal reflections (echoes), e.g. on walls or defects
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/04—Wave modes and trajectories
  • G01N2291/048—Transmission, i.e. analysed material between transmitter and receiver

Definitions

• This invention relates to apparatus and methods for monitoring, non-intrusively, the contents of a container containing fluid.
• the invention relates particularly, but not exclusively, to a method of non-mtrusively monitoring the gaseous contents of a container in order, for example, to confirm the composition or purity of the gas within the container.
• the invention therefore has particular application in, for example, the nuclear industry where the storage of radioactive substances requires continual or periodic monitoring of storage conditions to confirm continuous safe storage.
• the invention may also be useful in monitoring the contents of containers in the vicinity of potentially hazardous processes such as in the operation of high voltage switch gear where gas within containers provides electrical insulation for the switchgear .
• Spent nuclear fuel is highly radioactive and it is necessary to appropriately deal with the fuel to ensure that the radioactive spent fuel does not contaminate the environment.
• Interim storage There is a requirement to be able to safely store spent nuclear fuel for an intermediate period known as "interim storage” which period may be prolonged if required, pending a decision as to whether reprocessing or disposal of the fuel is to be undertaken.
• Spent fuel is typically stored within a sealed container during such storage.
• a container suitable for interim storage of spent fuel comprises a canister made of pressure vessel grade steel within which the spent fuel is held.
• the canister incorporates radioactive shielding in its lid. Once the canister has been filled with spent fuel, it is fitted with a lid and welded. The final welding of the lid seals the fuel.
• the lid of the canister will typically have a double seal. Prior to final sealing of the lid, the canister is filled with helium so that the spent fuel is held in a sealed container in a helium atmosphere .
• the canister is placed in a concrete storage cask which is also fitted with a lid.
• the canister may be positioned within a concrete cask such that there is a space between the canister and the cask.
• the cask has inlet ports at the bottom and outlet ports at the top so that air may flow within the concrete cask in order to cool the canister .
• the concrete outer cask provides shielding for both gamma and neutron radiation and protection against external hazards. It is desirable to be able to, from time to time, monitor the contents of the canister m order to ensure that no untoward reactions are occurring within the canister. Such checks would also indicate the continued integrity of the fuel cladding m the canister .
• a known method of monitoring spent fuel within a sealed canister or dual purpose metal cask involves opening the sealed canister to examine the fuel and the atmosphere surrounding the fuel known as the cover gas within the canister.
• a disadvantage with this known method is that there 15 a risk of contamination to the surroundings and the facilities required are extensive and expensive. In addition, it is neither easy nor practical to be able to continuously monitor the canister and contents thereof using such a method.
• a second known method of monitoring spent fuel within a canister is through use of an installed penetration by which it is possible to attach instrumentation to measure the pressure or quality of the cover gas over the spent fuel or the seal interspace gas. Measurement of such gases will provide information relating to the chemical composition of the cover gas m the canister.
• a disadvantage of this known method is that the presence of the penetration prejudices or degrades the integrity of the containment barrier of the canister thus providing a potential leak which could lead to radioactive contamination.
• a method for non-mtrusively monitoring the contents of a sealed container comprising steps of: transmitting an ultrasonic signal through a wall of the container into the contents of the container, receiving a signal from within the container, and analysing the received signal thereby deducing the composition of the contents of the container. This can thus be achieved without having to ⁇ nseal the container.
• apparatus for non-mtrusively monitoring the contents of a sealed container comprising: transmitter means for transmitting an ultra-sonic signal through a wall of the container into the contents of the container; receiving means for receiving a signal from within the container; analysing means for analysing the received signal thereby deducing the composition of the contents of the container.
• the canister may be a substantially gas tight canister.
• the canister may be a metal canister, for instance of carbon steel or stainless steel.
• the canister may be formed of a body and one or more lid elements.
• the one or more lid elements may be sealed to the body in use.
• a first lid is provided , together with a second outer lid.
• the first lid is received within the opening to the canister.
• the first and/or second lid may rest on one or more internal lips provided by the canister.
• the one or more lid elements may be welded to the body. The welds may provide a gas tight seal between a first lid and the canister and a second lid and the canister.
• the canister has the general form of a right cylinder.
• the lids are provide ⁇ on the top end of the canister, most preferably within the profile of the side wall of the canister, such that an end wall of the side wall is exposed.
• the canister contains spent nuclear fuel rods or other irradiated nuclear material.
• the canister may be provided with an internal gas pressure of greater than ambient, a positive pressure.
• the positive pressure may be at least 1.1 atmospheres, more preferably at least 1.2 atmospheres.
• the gas in the canister _ ⁇ substantially helium.
• the canister is provided within a furtr.er container m use.
• the outer container may be a cask, fcr instance a concrete cask.
• the internal configuration of the outer container generally matches the outer configuration of the canister.
• the outer container may be provided with a lid to seal the body of the container following insertion of the canister.
• the outer container is provided with a supply of cooling gas to its interior.
• the cooling gas directly cools the outside of the canister.
• the cooling gas is preferably air.
• An inlet to the inside of the outer container and an outlet therefrom may be provided.
• the inlet and outlets are dog-legged.
• the invention may be used to measure the fluid contents of a container and may therefore be used to monitor a gaseous or liquid content of a container.
• the invention may be used to measure the presence of one or more components of a gas. For instance, the presence of air in an helium atmosphere or the presence of xenon and/or krypton in an helium atmosphere may be measured.
• the invention may be used to measure the level of one or more components of a gas. For instance, the level of air in an helium atmosphere may be measured or the level of xenon and/or krypton m an helium atmosphere may be measured.
• the method comprises the steps of measuring the sound velocity and/or attenuation of the transmitted signal and / or the reflected signal.
• the sound velocity ana/ or attenuation may ⁇ e considered at more than one frequency of transmitted signal.
• the metnod may measure the velocity and/or attenuation using transmission measurements.
• the method may measure the velocity and/or attenuation using reflected measurements.
• the method comprises the step of measuring velocity and attenuation of both a transmitted signal, such as a "line of sight" received signal, and a reflected signal .
• the transmitted ultrasound signal may be provided by a transducer .
• the ultrasound source and/or receiver therefore is removed from the canister between at least some of the tests.
• the transmitter and/or receiver may be removed whenever the time period between tests exceeds 1 hour, or more preferably 1 day.
• a calibration and/or checking station is provided for the transmitter and/or receiver and/or accompanying electronics between at least some of the tests.
• such checks are made when tests are separated by more than 1 hour and more preferably by more than 1 day.
• the source of the transmitted signal is positioned outside the container, and a receiver is positioned outside the container.
• the source of the signal and/or receiver are preferably mounted on the lid of the container.
• the source of the signal and/or receiver may be mounted on a side wall of the container, preferably on the top of the side wall.
• the source of the signal and/or receiver are preferably provided in a housing.
• the housing may be mounted on the lid of the canister, for instance the outer lid or the inner lid.
• the housing may be mounted en the outer surface of the outer lid, with a passage connecting the monitoring location in the housing to the body of gas within the canister, the passage being provided in a passage defining element which passes through the lid or lids, the cross-sectional profile of the passage defining element as it passes through at least a part of a lid being less than the cross-secticnal profile of the housing, parallel to the lid.
• the cross-sectional profile is less throughout the elements passage through the outer lid, ana if present the inner lid.
• the housing may be mounted on the outer surface of the inner lid, witn a passage connecting the monitoring location xr the housing to the body of gas within the canister, the passage being provided in a passage defining element which passes through the inner lid, the cross-sectional profile of the passage defining element as it passes through at least a part of the inner lid being less than the cross-sectional profile of the housing, parallel to the lid.
• the cross-sectional profile is less throughout the elements passage through the inner lid.
• the cross-sectional profile of the housing as it passes through the outer lid is substantially the same as the housings cross-sectional profile outside the outer lid.
• the housing may be mounted on the end wall of the side wall of the canister, most preferably wholly within the outline of the extension of that side wal'l .
• the housing may be welded to the canister.
• the housing may be formed of one or more different materials .
• the received signal is preferably subjected to signal processing to extract the desired information.
• the signal processing may involve Fast Fourier Transform and / or chromatic base ⁇ processing.
• the signal processing may involve the application of one or more Gaussian processors to the signal.
• the processors are preferably nonorthogonal .
• the processors cover the range of transmitted and / or received signal frequencies. Three processors maybe applied.
• the processor outputs are further processed algorithmically .
• the algorithm results corresponding to the nominal energy content of the signal and / or the dominant frequency and / or the effective bandwidth, most preferably all three.
• the signal may be represented as a point on a three dimensional plot defined by the nominal energy content of the signal, the dominant frequency and tne effective bandwidth.
• the condition within the container may be represented as ⁇ point on a three dimensional plot.
• the change in conditions may be represented as a deviation in one or more dimensions relative to that point. The extent of the deviation may represent the magnitude of the change in conditions. The direction of the deviation may represent the type of change in conditions.
• the transmitter may be positioned within the container and may be activated by, for example, a signal transmitted from outside the container.
• a transmitter suitable for positioning within the container may comprise, for example, a tuning fork or resonant cavity.
• the canister will normally be filled with helium at a pressure of about m atmospheres at the time of sealing the canister.
• the internal gas at a monitoring location may be investigated.
• the monitoring location may be within the body of the canister.
• the monitoring location is preferably provided outside the body of the canister, but still sealed relative to the surrounding environment.
• the monitoring location is provided with a housing, most preferably the housing for the transmitter and/or receiver for the ultrasound.
• the monitoring location is provided m proximity to the outside of the canister lid.
• the monitoring location is preferably connected to the internal body of gas m the canister via a bore or other passageway.
• the bore may be of circular cross-section.
• the bore includes one or more dog-legs.
• the bore passes from within the canister oody to outside.
• the bore most preferably passes through the lid or lids of the canister.
• the bore may alternatively pass through the side wall of the canister.
• the bore may pass up through the side wall of the canister, towards the lid end of the canister.
• the bore may pass through the side wall of the canister, for instance to connect to an element externally provided on the canister and leading to the monitoring location.
• the monitoring location is preferably m proximity to the transmitter and/or receiver. Ideally the monitoring location is provided between the transmitter and the receiver.
• the transmitter and receiver may be separated by a gap of between 0.5 and 20cm or more preferably 3 and 8cm.
• the transmitter and/or receiver are preferably separated from the monitoring location by a thickness of material.
• the material thickness is preferably at least 5mm and more preferably at least 10mm or even 20mm.
• a volume of gas is provided in the housin ⁇ on the distal side of the monitoring location relative to the body of the canister.
• the body of gas has a greater extent, perpendicular to the bore supplying it and/or parallel to the axis of the transmitter/receiver alignment, than the monitoring location itself.
• a d sc shaped gas volume ma_ be provided. In this way reduction of noise is facilitated. It has previously been thought impossible to use sound or ultrasonic waves to determine the contents of a canister due to the fact that the temperature of the gas within the canister will affect the characteristics of reflected sound waves .
• the signal sound wave has to travel through a thick container wall without unacceptable signal loss. It had previously been thought that the attenuation of signals due to the thickness and nature of the canister material would be an insurmountable problem in using ultra-sonic signals to determine the contents of the container.
• the present invention therefore provides a method where ultra-sound is transmitted through a container wall which may be metallic and may have considerable thickness, or alternatively may be a non-metallic material.
• the ultra-sound may traverse through the gas or fluid within the container and then be received and detected through the container wall at a different point to that of which the ultrasound was transmitted into the canister wall initially. Alternatively, it may be received and detected at the same point at which it was transmitted through the canister wall following reflection of the signal.
• the passage of the signal through the gas at ospnere or fluid will have modified the signal signature so by comparing the transmitted and received signals the composition of the gas or fluid may be inferred.
• the speed of sound, ICS attenuation and its frequency may be modified by differences m gas or flui ⁇ composition .
• the resonance frequencies of the container and internal structures will be altered by the contained gas or fluid composition and this change may be used to infer the composition.
• the signal may be produced by means positioned outside the canister for example a transmitter.
• the signal may be produced from transmission means contained within the canister.
• Such transmission means may be m the form of, for example, a tuning fork or resonant cavity which may be activated from outside the container.
• Figure 1 is a schematic representation of canister containing spent fuel monitored by means of an embodiment of the present invention
• Figure 2 is a partial cross-sectional view of the top portion of a spent fuel canister illustrating a further embodiment of the invention
• Figure 3 is a detailed cross-sectional view of the sensor component of Figure 2;
• Figure 4 is a partial cross-sectional view of the top portion of a spent fueJ canistei illustrating a still further embodiment of the invention
• Figure 5 is a partial cross-sectional view of the top portion of a spent fuel canistei illustrating a yet further embodiment of the invention
• Figure 6 illustrates a variation on the top portion of the canister of Figure 2
• Figure 7 illustrates a further variation on the top portion of the canister of Figure 2;
• Figure 8 illustrates in plan view a variation on the embodiment of 4.
• Figure 9 displays experimental results for time difference between transmission and reception for ultrasound signals with varying gas composition
• Figure 10 illustrates a typical input signal and a typical detected signal
• Figure 11a to lie illustrate the application of a signal processing technique suitable for use in the present invention.
• a container suitable for storing spent fuel is designated generally by the reference numeral 10.
• the container comprises a canister 12 which is loaded with spent fuel rods 13 and is then is sealed with a welded lid. Once the spent fuel 13 is sealed within the canister 12 the canister 12 is vacuum dried then back filled with an inert gas, such as helium, which surrounds the spent fuel rods 13. Thermal conduction from the fuel rods 13 within the canister 12 is enhanced through the use of the helium atmosphere at a pressure slightly above atmospheric .
• the canister 12 is positioned within a concrete cask 14 such that the outer surface 15 of the canister 12 and the inner surface 16 of the cask 14 are spaced apart from one another. This allows air flow from an air inlet 17 to an air outlet 18 formed in the outer wall 9 of the cask 14. It is necessary to have air flow passing over the canister 12 to maintain fuel temperature below regulatory limits.
• the spent fuel rods 13 may be stored within container 10 for many decades. This means that it may be prudent to be able to provide for monitoring the contents or tne canister regularly and reliably over these time scales to assist m demonstrating and confirming safe confined storage conditions to government regulatory officials.
• the present invention it is possible to detect the leakage of oxygen from the surrounding air into the helium atmosphere with a sealed canister m a non-mtrusive manner.
• the atmosphere of the canister is probed with ultrasonic signals.
• An ultrasonic signal transmitted into the canister will emerge from the canister, and by measuring changes m the ultrasound signature of the received signal produced by any oxygen influx, presence of oxygen may be detected.
• changes m sound velocity, attenuation, resonant frequencies and structures may indicate oxygen leakage into the canister.
• variations in pressure within the canister may be monitored by detecting similar variations with pressure.
• xenon and krypton gases may also be released during storage of spent fuel within the sealed canister m the event of failure of fuel rod cladding it, it is desirable to be able to monitor relatively small variations in the levels of such gases within the helium atmosphere. These Eaffects can also be monitored by suitable consideration of their effect on the ultrasound investigation.
• ⁇ ratio of specific heats
• r gas constant
• T temperature
• o molecular weight
• Equation (1) also indicates that the velocity scales with T as it does with p so that a temperature change from 30 to 300 " Z would approximately lead to a velocity increase of x(3 - 4) .
• t is of the upmost importance m many applications to provide for an accurate compensation for any temperature variation between measurements. This can be achieved by direct measurement of temperature conditions, with appropriate compensation for changes.
• investigation at a number of frequencies can also determine temperature and thus account for it.
• the sonic velocity will vary with both frequency and gas pressure.
• the variation is due to visco thermal, and in the case of diatomic gases, vibrational and rotational relaxation effects.
• variations m the attentuation of the sound wave can be expected.
• the attenuation, ⁇ , ⁇ f a soundwave in a gas is usually quoted in terms of the parameter :-
• the embodiment illustrated in Figure 2 shows the top portion of a canister of the general type designated 12 in Figure 1.
• the canister 200 comprises a cylindrical side wall 202 and lid structure 204.
• the lid structure 204 is formed of an inner shield lid 206, which rests on lip 208, and an outer structural lid 210, which rests on lip 212. Both the shield l d 206 and structural lid 210 are welded in position with gas tight wields.
• the spent fuel rods are contained in the volume 214 below the shield lid 206.
• the monitor housing 216 Mounted on the structural lid 210 is the monitor housing 216.
• the housing 216 provides a structural wall thickness 218 around the monitoring location 220.
• the structural wall thicknesses required to met regulatory standards vary for materials (for instance 25mm thickness for carbon steel, 19mm thickness for stainless steel).
• the monitoring location 220 consists of a cylindrical bore 222 leading from the cavity volume 214 to the monitoring location 220 and beyond to a "top hat" configuration 224.
• the bore 222 is fully enclosed by the housing 216 to manitam the isolation of the cavity volume 214 and its helium atmosphere from the surrounding cooling air volume 226.
• the bore 222 is dog leg for shielding purposes.
• the housing 216 On either side of the monitoring location are two bores 228 m the housing 216, the bores receiving the transmission transducer 230 and receiver 232. Ultrasound is passed through the monitoring location 220 and the appropriate characteristics of its passage are measured to g ve the desired information.
• measurements at the monitoring location 220 are accurate representations of the cavity volume due to the extreme mobility of helium. Additionally the time period between measurements is likely to be days or more with very gradual or no change expected between tests, as a consequence this gas volume is fully representative .
• the bore 222 consists of a main bore 234 and subsidiary bore 236 connected by a cross-bore 238.
• the housing 216 is mounted on the structural lid 210 by plate 240 which is wielded thereto by wields 242 and 244.
• gel is provided on the end faces of the bores 228.
• concave or convex faces can be used to focus the ultasound.
• the top hat shape to the upper section 246 of the bore 222 is so shaped for the purposes of damping noise signals spreading from the source to reciever transducer.
• the transducers 230, 232 face each other across a gap of 5 to 6cm m the case of a 40kHz ultrasound system.
• the transducers may be provided with plates connected to the end surfaces of the transducers by spigots .
• Figure 2 and 3 imply the use of a unitary element to form the housing 216 acoustic filtering advantages can be obtamed by forming the housing of different materials.
• the different materials may filter the noise signal an ⁇ /or give enhancing directional effects.
• Acoustic filtering of the signals arising m the system is important m ensuring that the quicker signal transmission of the ultrasound through the housing does not give a noise signal which swamps th slower transmission of the ultrasound through the gas oemg monitored.
• the frequency of the ultrasound, the gap between the teansducers, the relative thicknesses of the intervening walls, side walls and surrounding walls all, individually and together, effect the system and can be used to effect its operation accordingly.
• the transducers 230, 232 are only introduced once the fuel has been loaded, as part of the loading procedure will involve the complete emersion of the canister 200 including the housing 216 in the cooling pond where the fuel is stored.
• the transducers 230, 232 and accompanying electronics to which they are attached are removed from the housing 216 between tests to reduce the potential for radiation damage of the transducers and their surrounding electronics and also to reduce the number of measuring equipment sets that are needed. As tests on the gas content may be days, months or even years apart, it is wasteful to leave that part of the equipment m-situ during that time.
• the measurement system is checked against a known standard or other claibration technique, before and/or after being used, to ensure correct operation. True verification of the systems correct operation can therefore be provided, away from the canister if desired.
• the temperature monitoring can be effected by a thermal couple attached to the housing at a consistent position between tests.
• a pair of thermocouple, one at substantially the same location as the transmitting transducer, one at substantiall th « same position as the receiver are preferred m this regar ⁇ .
• the output from the thermocouples are fed to the processing electronics to provide a correction signal. This signal can be used to correct the gas monitoring result to ensure that variations m temperature, for instance cooling of the cannister over the years, does not give a false reading of gas change.
• Measurement of pressure within the cavity may also be desirable to remove the effect of any pressure variation from the signal analysis m a similar manner to that discussed above for temperature .
• FIG 4 an alternative positioning of the housing 216 is provided on the top wall 400 of the cylindrical wall 402 of the canister 200. This provides the necessary clearance for the introduction of the shield lid 204 and structural lid 210 following introduction of the spent fuel.
• the conection between the monitoring location 404 and the cavity volume 406, m this case, is provided by a bore 408 in the cylindrical side wall 402. The monitoring operates in a similar manner to that outlined above .
• the housing 216 is provided on the end of a bore carrying element 500 fixed to the side wall 502 of the canister.
• the bore 504 in this element 500 conects the measuring location 506 to the cavity volume 508.
• the housing base 600 penetrates the structural lid 210 and rests on the shield lid 204. In this way only the, relatively narrow, bore carrying element 602 needs to penetrate the shield lid 204, thereby reducing the variation between the existing canister and a canister 200 embodying the present invention.
• the housing 216 rests on the top surface 700 of the structural li ⁇ 210. In this way the structural lid 210 and the shield lid 204 are both only penetrated by the relatively narrow, bore carrying element 702.
• the housing must have quite deep bores for the transducers to give sufficient signal introduction and sufficent signal collection capability for the best results to be achieved. Transducers of 6 to 8 inches in length and 3 inches m diameter are suitable for many applications. In general the longer the transducer the better the filtering that is achieved.
• the Figure 4 and Figure 5 type embodiment positioning of the housing can be a problem m this regard.
• Figure 8 illustrates an embodiment of the invention which provides the necessary clearance for the lids 800, but provides the necessary bore length 802 by extending the housing 804 around and within the profile of the cylindrical wall 806.
• This form of housing 804 also avoids intrusion of the housing 806 outside the cylindrical profile, an important consideration given the very limited clearances which exist between the outside 810 of the cylindrical wall 806 and other parts of the apparatus during transfer of the canister from the cooling pond, where it recieves the spent fuel, and the concrete cask.
• the Figure 8 and other embodiments of the invention illustrate a transmission system for determining the ultrasonic effects.
• This and the other embodiments of the invention can, however, use reflective measurements.
• a substantially coincident transmission and reception location may be provided or the transmission ana reception locations may be provided close to one another, but separated by a small angle.
• the opposing side of the core containing the gas may be shaped to promote ultrasound rerlection.
• Figure 9 displays the time difference between signal emission and reception against different gas compositions for air to helium mixtures.
• FIG 10 a typical input signal (solid line 1000 i and a typical detected signal (solid line 1002) are illustrated.
• the detected form includes both that part of the signal which crosses the gas gap to the detector and also a significant noise signal which travels around through the housing itself to reach the detector .
• Preferred embodiments of the invention use Fast Fourier Transform method or the new technique of chromatic filtering to extract the desired information from the detected signal.
• Chromatic filtering of a signal involves the use of n nonorthogonal Gaussian processors (figure 11(b)) which cover the range of frequencies covered by the signal.
• n 3 the outputs of the Gaussian processors are manipulated algorithmically to provide at each instant m time a signal detection m terms of three parameters namely the nominal energy content of the signal, the dominant frequency and the effective bandwidth.
• the signal is effectively represented by a single point in a three dimensional chromatic space defined m terms of these parameters (figure 11(c)).
• the conditions within the fluid containing canister are defined by the position of the signal defining point n cnromatic space.
• Deviation of this point from its nominal equilibrium position is indicative of chang e d conditions m the canister.
• m ⁇ icate tnat
• Fault types and their characteristics are determined empirically from a prior calibration.
• Sound velocity and attenuation co-efflcients may be evaluated m detail for the gaseous components He, 0 , N , Xe and Kr separately m various combinations for a range of acoustical frequencies .
• Differences m acoustical velocities will indicate the presence of different species. Differences m attenuation coefficient will indicate temperature effects, whilst the frequency dependence of the velocity and attenuation coefficient may enable different contaminants to oe distinguished. Calculations used to determine the composition of a gas content within a canister will take into account tne structural considerations of the canister. Some of the resonances will depend on the mass density of the gaseous atmosphere.
• the acoustic transducer could be either electromagnetic, a capacitance, or any other type of transducer.
• optical fibres it may be advantageous to use optical fibres in order to detect the received signal.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
• Monitoring And Testing Of Nuclear Reactors (AREA)

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• 1997
  • 1997-09-19 GB GBGB9719940.0A patent/GB9719940D0/en not_active Ceased
• 1998
  • 1998-09-21 JP JP2000513121A patent/JP2001517785A/ja active Pending
  • 1998-09-21 WO PCT/GB1998/002794 patent/WO1999015870A1/en not_active Application Discontinuation
  • 1998-09-21 AU AU91717/98A patent/AU9171798A/en not_active Abandoned
  • 1998-09-21 EP EP98944039A patent/EP1015863A1/de not_active Withdrawn
  • 1998-09-21 ZA ZA9808605A patent/ZA988605B/xx unknown

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