US 2989965 A
Abstract available in
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Description (OCR text may contain errors)
June 27, 1961 R. ROD 2,989,965
FOOTWEAR DECONTAMINATING APPARATUS Filed March 13, 1958 2 Sheets-Sheet 1 INV EN TOR.
TE 2 205E27- L. 200
Mme/ways I June 27, 1961 R. L. ROD
FOOTWEAR DECONTAMINATING APPARATUS Filed March 13, 1958 2 Sheets-Sheet 2 205527 L. BOD BY 1 a Z W M ATTOQ/VEY United States Patent Filed Mar. 13, 1958, Ser. No. 721,287 4 Claims. (Cl. 134-46) This invention relates to protection against the carrying of radioactive matter out of a plant conducting nuclear operations, and it relates more particularly to apparatus for decontaminating footwear.
The primary object of the present invention is to facilitate the decontamination of personnel engaged in nuclear operations. The present practice is to wear disposable, protective clothing over the head and body, and to wear rubbers on the feet. On leaving the plant, the radioactive count of the subject is taken and, if too high, he must go into scrubbing showers. This is done even though the contamination may be only at the feet.
The latter represent a problem frequently encountered in operations involving radioactive materials, because material settles on the floors, and then adheres to the soles of protective shoes or rubbers. It is not a good idea simply to remove the protective footwear, because of the risk of contaminating ones hands while doing so.
'Accordingly, one object of the present invention is to provide apparatus readily and rapidly to decontaminate footwear. Most of the contaminating particles are removed as the employee leaves the area, and prior to removal of his protective garments, and without contacting the hands. For this purpose, I provide an open-topped tank having a support positioned somewhat below the top of the tank,'on which support a person may step to partially immerse his footwear, say several inches. One or more electroacoustic transducers are provided for vibratirig the liquid in the tank, and if desired, appropriate detergent or solvent solutions may be mixed with the water in the tank.
A further object is to prevent excessive accumulation of contaminant in the tank, and for this purpose fresh liquid may be supplied through an inlet while contaminated liquid is carried off through an outlet or discharge pipe. The latter may be connected to the radioactive waste line usually provided in such plants, or the liquid may be recirculated through an appropriate filter in order to remove contaminant. In any case some possible contamination of the liquid is not really serious when using acoustic vibration as here taught, because of the greatly reduced dragout as a foot is removed from the tank. This .dragout is less than of what it would be if the liquid were not undergoing acoustic vibration.
;A further object is automatically to control the operation of the high-frequency generator which excites the transducer. The apparatus may be run continuously, if desired, particularly in a busy plant. However, if it is to be operated intermittently, the control of the operation maybe made automatic, and in accordance with one object and feature of my invention the operation is made responsive to the loading of the support in the tank, and in accordance with another object and feature of the invention the operation is made responsive to the contamination of the liquid or the feet of the subject. Thus, the generator having been started by an appropriate manual switch, or even by a treadle switch as described above, may be stopped when the contamination has been sufiiciently reduced. There is preferably a signal, and a delay before stopping the generator, permitting the subject to leave While the generator is still working.
. Still another object of the invention is to so design the support on which the subject stands as not to obstruct the acoustic vibration and the resulting cavitation and improved wetting action caused by acoustic vibration. For this purpose the support may be an open-mesh =gn'l1e having openings larger than the wave length of the acoustic vibration.
To accomplish the foregoing general objects, and other more specific objects which will hereinafter appear, the invention resides in the apparatus elements and their relation one to another as are hereinafter more particularly described in the following specification. The specification is accompanied by drawings in which:
FIG. 1 is a schematic elevational view explanatory of the invention;
FIG. 2 is a similar view showing the use of liquid cir-i culating means and nuclear detection means;
FIG. 3 is a similar view showing the use of nuclear detection means on a 'waste line;
FIG. 4 is a plan view of one form of apparatus em bodying the invention;
FIG. 5 is a vertical section through the same; FIG. 6 is a schematic elevation showing nuclear detection means aimed at the footwear immersed in the tank;
FIG. 7 shows nuclear detection apparatus disposed adjacent and above the tank.
Referring to the drawing, and more particularly to the liquid 18 in the tank. The liquid level may be so set relative to the height of the support as to immerse several inches of the footwear in the liquid. One or more. electroacoustic transducers 20 are secured in the tank for vibrating the liquid at a high frequency which is in the sonic or ultrasonic range, preferably the latter. Typical frequencies employed may be 25 kc. and 40 kc. A suitable high-frequency generator 22 is provided to excite the transducer, through electrical connections schematically represented at 24.
If desired, a circulating system may be provided to filter the liquid in the tank, and such an arrangement is schematically shown in FIG. 2. Here again there is a tank 12 having a support 14, and containing liquid '18 vibrated by transducer 20 excited by a generator 22. In this case liquid is supplied through an inlet pipe 24, and leaves through a discharge pipe 26. An overflow pipe 28 may also be provided to establish the desired liquid level in the tank. The discharged liquid is led by pipe 30 to a filter 32 and after filtration is returned to pipe 24. A'
pump 34 is provided to insure circulation of the liquid. Thus contaminant is removed from the liquid, until finally the filter itself becomes heavily loaded, whereupon the filter element may be changed and the operation resumed.
However, it is not essential to provide circulating apparatus, and in FIG. 3 I show a simpler arrangement in which fresh liquid is supplied to an inlet pipe '36. At the same time liquid is removed through overflow pipe 38, and flows to a radioactive waste line such as is commonly provided in nuclear plants. The valves control the rate of change. If desired, the apparatus may be provided with means to determine whether the footwear has been sufficiently decontaminated. This measurement may be made in a variety of ways, and referring to FIG. 3, a nuclear energy detector 40 may be exposed to the liquid in the waste line 38. This detector may be a Geiger tube or a scintillator combined with a counter or other means to indicate the rapidity of the count. The detector may be designed for response to alpha, beta and gamma rays. A slow or a rapid count may appropriately operate a relay 42 which in as-shown in FIG. 1.
turn controls a signal 44, and this may indicate, as by means of a green light, when the footwear has been sufficiently decontaminated.
wsir'nilar means may be provided in the circulating systern shown in FIG. 2, in which it will be seen that detector'40 controls a relay 42 which in turn controls a signal 44.
Another method of checking decontamination of the footwear is'shown in FIG. 6; in which a nuclear energy detector 46 is exposed through tube 48 to the inside of the tank at a point immediately above the support or grille 14, so that the detector is aimed at the footwear resting on the support. Here again a relay 50 may appropriately respond to the slowness or rapidity of the count of the detector, and may itself control a signal 52.
For all practical purposes it may be assumed that both feet are approximately similarly contaminated or decontaminated, and a detector aimed at one foot is sutficient. However, if desired, another detector may be provided as indicated at 56, with a window 58 aimed at the other foot. Here again a relay 60 and an alarm 62 may be provided, or the circuitry may be such that a single alarm will not show clear until both detectors 46 and 56 are satisfied.
'Still another detection arrangement is shown in FIG. 7. In this case the nuclear detector 64 has a window or focussing tube 66 disposed immediately adjacent the tank 12 but somewhat above the tank. The location is such that a person standing on the support 14 may conveniently raise one foot out of the tank to the tube 66 and thus secure a signal at 68 through an appropriate relay 70. Here again the check of one foot is applicable to both but, if desired, a second detector may be provided on the other side, as indicated at 72, and here again a relay 74 and a signal 76 may be provided.
As so far described the operation of the generator 22 (FIG. 1) and transducer 20 may be continuous. The power consumption is not large, and such continuous operation is entirely feasible. However, if desired, appropriate means may be provided to operate the apparatus only when needed. In FIG. 1 the'operation of generator 22' depends on the loading of the support 14, and for that purpose the support is made slightly movable vertically, as by providing a pivot or fulcrum at 80, and a pressure-responsive switch at 82; This is connected through appropriate circuitry, schematically represented by conductor 84, to the generator 22. It will be understood that when the support 14 is loaded the generator is stopped. If the generator employs tubes, the filaments may be heated continuously, and the treadle may control the plate voltage. This will avoid delay for warm-up.
The subject may stand in the tank for a reasonable time, and then leave, relying on a subsequent overall check such as is performed now. However, the arrangement may also be combined with any of the detector and signalarrangements shown in FIGS. 2, 3, 6, and 7, with the subject remaining in the tank until given a clear or equivalent signal.
If desired, the operation of the generator may be controlled by the nuclear energy detector itself. Thus in FIG. 2 a conductor 86 may lead from relay 42 or/and' signal 44 to the generator 22. The arrangement could be such that when the detector count is sufliciently low the generator 22 is stopped at the same time that signal 44 indicates clear. However, this would lose the benefit of the greatly reduced dragout mentioned above. To retain that benefit a delay relay, 88-may'be provided, so that the generator is stoppedaftersuitable delay, say one minute, following the clear signal. Thusthe subject steps out of the tank while the'transducer is still operating.
In FIG. 3 a similar circuit 86 and delayrelay 88 are provided, and the same remark applies to FIGS: 6 and 7. In all of these cases the generator may be started by a n'eadle switch responsive to loading'ofthe-support14; However, that is not essential, and
4 a manual switch or start button may be provided at a convenient height above the tank, so that the subject may press the button as he steps into the tank. The operation will then proceed until the clear signal is given.
The support 14 is best shown in FIGS. 4 and 5, and as there constructed is made up of strips "of stainless steel disposed edgewise, and arranged in crossed relation, somewhat like the egg separator of an egg crate. Theresirlting grille is sturdy, and has a maximum area of openings. These openings are preferably larger in size than a single wave length of the acoustic vibration used.
In another form the support 14 may be a solid sheet of metal with a thickness appreciably less than the wave length of the applied acoustic energy. Without these precautions the support may block a considerable portion of the energy transmitted from the transducer.
The transducers and the mounting of the same may vary considerably. In the particular case shown the transducers are blocks of barium titanate ceramic cemented to the top wall of waterproof housings. These have a threaded pipe through which electrical conductors may pass to the electrodes on the barium titanate. Appropriate gaskets and nuts may be disposed on pipe 90 to prevent leakage. This is a known transducer construction.
The use of a detergent increases the wetting action and is helpful along with the increased wetting action caused by the vibration. In the arrangement of FIG. 2, a desired quantity of detergent may be added, and onpccasion the system may be drained and supplied with new liquid and detergent.
The waste-line system shown in FIG. 3 may be used without detergent, but if it be desired to provide detergent, the flow into and out of the tank may be made quite slow by adjustment of the valves, and added detergent may be fed to the supply pipe or the tank drop by drop at a suitable rate relative to the rate of flow of water. i
In a typical case the transducers each employ six blocks of barium titanate, each 1" x 2" x 2" in dimension. The generator operates at 40 kc., and has watt capacity. The wave length is about one inch, and the openings in the grille are preferably made larger, and in this case are two inches square.
To summarize, the invention involves the use of high frequency acoustic power applied to a bath in which the soles of the contaminated rubbers or other shoe covering are immersed. The bath containing plain water or an appropriate detergent or solvent solution in which the particular radioactive soils are soluble, is fitted with electroacoustic transducers of the magnetostrictive, electrostrictive or electrodynamic types, or with any other common type of sonic or ultrasonic vibration generator. When driven by an appropriate power source, suchtransducers generate cavitation in the region of the vibrating surfaces. This is of great assistance in'degassing the bath, and weakening the surface tension holding soils to objects immersed in the bath. The action of the cavitation, and the increased wetting action of the solution, combine to provide a far more rapid removal of soils then is found possible by the use of conventional cleaning baths, sprays and mechanical or pneumatic agitators. In the case of typical radioactive soils, reduction of contaminants from a level which is hazardous to personnel, to a safe level, is accomplished in a small fraction of the time hitherto found necessary.
It is believed that the construction and operation of my apparatus for decontaminating footwear, as well as the many advantages thereof, will be apparent from the foregoing detailed description. It will also be apparent that while I have shown and described the invention in several preferred forms, changes may be made in the structures shown, without departing from the scope of the invention as sought to be defined in the following claims. The reference to a support is not intended to exclude the bottom of a shallow tank.
1. A footwear decontaminating apparatus comprising an open-topped tank having a support positioned somewhat below the top of the tank, on which support a person may step to only partially immerse his footwear, an electroacoustic transducer for vibrating a liquid in the tank, a high frequency generator to energize the transducer, said support being so mounted as to be somewhat movable vertically, an electrical switch responsive to depression of the support by the load of a person standing thereon, and circuitry connecting said switch to said generator and so arranged that the generator operates when the support is loaded and stops when the support is unloaded.
2. A footwear decontaminating apparatus comprising an open-topped tank having a support positioned somewhat below the top of the tank on which a person may step to only partially immerse his footwear, an electroacoustic transducer for vibrating a liquid in the tank, a high frequency generator to energize the transducer, said support being so mounted as to be somewhat movable vertically, an electrical switch responsive to depression of the support by the load of a person standing thereon, and circuitry connecting said switch to said generator and so arranged that the generator operates when the support is loaded and stops when the support is unloaded, an inlet pipe connected to said tank for supplying liquid to the tank, a discharge pipe for removing liquid from the tank, a nuclear energy detector exposed to the liquid in the discharge line for measuring the contamination of the liquid leaving the tank, and circuitry responsive to the count of the nuclear energy detector for stopping the generator when the contamination has been reduced to a safe value while said support is loaded.
3. A footwear decontaminating apparatus comprising an open-topped tank having a support positioned somewhat below the top of the tank on which a person may step to only partially immerse his footwear, two elongated electroacoustic transducers secured to the bottom of the tank in collateral spaced relation to underlie the soles of a pair of feet standing on the support, and a high frequency generator to energize the transducers, said support being so mounted as to be somewhat movable vertically, an electrical switch responsive to depression of the support by the load of a person standing thereon, and circuitry connecting said switch to said generator and so arranged that the generator operates when the support is loaded and stops when the support is unloaded.
4. A footwear decontarninating apparatus comprising an open-topped tank having a supporting grille positioned somewhat below the top of the tank, on which grille a person may step to only partially immerse his footwear, an electroacoustic transducer secured to said tank for vibrating liquid in the tank, a high frequency electricity generator to energize the transducer, said grille being so mounted as to be somewhat movable vertically, an electrical switch responsive to depression of the grille by the load of a person standing thereon, and circuitry connecting said switch to said generator and so arranged so that the generator operates when the grille is loaded and stops when the grille is unloaded.
References Cited in the file of this patent UNITED STATES PATENTS 657,872 Horner Sept. 11, 1900 2,407,462 Whiteley Sept. 10, 1946 2,520,788 Wales Aug. 29, 1950 2,586,910 Rolle Feb. 26, 1952 2,702,260 Massa Feb. 15, 1955 2,776,558 Vang Ian. 8, 1957 2,845,077 Branson July 29, 1958 FOREIGN PATENTS 969,803 France May 31, 1950