Patent Description:
The invention relates to a method for sampling an intact cross-section of a multi-layered structure, and more particularly, a method for taking micro-samples of the structure.

Many structures used in commercial and scientific processes are made of a structural base material, coated by multiple layers of materials such as interlayers and one or more coating layers. During use, many of these structures may accumulate oxidation layers, or may collect debris and other extraneous matter incident to their function or environment. In addition, some structures may have a finite useful life for carrying out a process. It often is necessary to assess the integrity of these materials or to investigate the nature and/or amount of accumulated extraneous matter to evaluate the continuing efficacy and safety of the structure for carrying out a given process.

For example, in a commercial nuclear reactor, there are numerous fuel rods having a cladding material that contains fuel pellets. Cladding materials are generally comprised of a metal, metal alloy, or a ceramic base layer, or a combination of such layers, covered with one or more coating layers, which may also be a metal, metal alloy, or a ceramic. Most commonly in reactors, water is used as a coolant, so the cladding rods are surrounded in use by water. The integrity of the fuel cladding is of vital importance to the safe operation of the fuel rod assembly. Characterization of irradiated cladding is a necessary but very costly process, because it sometimes requires removal of the entire fuel rod, shipment to and processing in a specialized hot cell facility licensed for irradiated fuel handling. In most cases in the United States, for example, the entire fuel rod has to be removed from the fuel assembly and shipped overseas to a facility licensed to handle irradiated material. The cost can easily meet or exceed one million U. Once at the facility, however, only a very small portion of the harvested cladding is actually characterized.

In other industries, pipes, steam generator or other heat exchanger tubes, pipe-walls, the interiors of reactors and generators, and similar components critical to the operation of a process should be evaluated, but are not because to do so would require removal from service and shutting down operations, which in many facilities is not an option to be taken except in exigent circumstances. In these and similar cases, usually kilograms of samples are removed, shipped and processed, only for several micrograms to nanograms of samples to be actually analyzed.

<CIT> discloses a specimen collecting method, including collecting a specimen from a surface of a blade, feeding an ultrasonic cutter with a cylindrical cutting blade from the surface of the blade to a surface of a base material thereby forming a cylindrical incision, expanding the incision by cutting outwardly, and cutting inwardly from the cylindrical incision with a rotating cutter having a disc-shaped to cut away a part situated inside the incision is cut away, the part becoming the specimen.

disclose an overview of the techniques that have been developed to prepare TEM specimens. <CIT> discloses a method for excising a biological sample on a solid support with a minimum risk of carry over contamination, and analytical kits and systems and an excising device for excising a biological sample on a solid support.

<CIT> discloses a method to perform an analysis of two types of CRUD on a nuclear fuel rod, including providing a nuclear fuel rod with a first and second layer of CRUD on an exterior of the fuel rod, brushing the first layer of CRUD from the fuel rod with a CRUD tool (with a brushing device) on a selected area, applying a force to the brushing device on the fuel rod to remove the first layer of CRUD, collecting the first layer of CRUD from the brushing device, scraping the second layer of CRUD from the fuel rod in the selected area with the tool, the tool having a scraping device, collecting the second layer of CRUD from the scraping device, and analyzing the first layer and second layer of CRUD separately with a scanning electron microscope.

<CIT> discloses a crustal core sampler comprising a drilling mechanism, a barrel, the barrel equipped with a flow-able coating material-ejecting mechanism, and a columnar crustal core portion coated with a flow-able coating material. <CIT> discloses a coolant liquid feeding method comprising feeding a coolant liquid, with air bubbles caused to form continuously therein, for cutting or grinding operation to a region under machining, expediting the splashing of air bubbles in all directions when the air bubbles impinge on the region under machining and burst, and expediting the entry of accelerated splashed liquid particles into a cutter/workpiece pressure contact plane, thereby improving the cooling and lubrication of the region under machining, whereby the air bubbles in the coolant liquid which has failed to reach the region under machining or which, though reaching there, has left there for the recovery channel are allowed to adhere to suspended foreign matters in the liquid, thereby expediting the surfacing of the foreign matters.

The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, and abstract as a whole.

This invention describes a method of minimally invasive micro-sampling, designed to remove and retain a very small amount (for example, a sample that is ≤ <NUM> diameter and < <NUM> deep) of material from the surface of a component, with the express purpose of maintaining the integrity of any surface deposits or coating and the deposit/substrate interface. Samples removed in this manner can then be shipped from their point of origin to a facility for thorough microstructural characterization using various forms of electron microscopy. Effectively, it is a method of removing a "micro-sample" where the surface of the sample is preserved.

In various aspects, the invention provides a method of sampling a multi-layered material having a top surface and a metallic or ceramic base, as defined in claim <NUM>.

The method may also include penetrating the top surface by making a first cut at a first angle relative to the plane of the top surface and making a second cut at a second angle relative to the plane of the top surface. The angles may each be right angles or may be supplemental angles relative to the top surface. The angles may be angled such that the first and second cuts approach each other. In various aspects, the depth of penetration is adjustable by tooling design. For fuel cladding, it is best to be no greater than half the thickness of the cladding, or about <NUM> microns.

The step of the step of removing the micro-sample may include drawing the plug into a container, for example by suction, and sealing the container.

In various aspects, the end mill may be an coring end mill. The end mill preferably includes a plurality of cutters positioned at the bottom end of the minor shank.

In certain aspects, a protective layer may be applied to the top surface of the material prior to penetration with the end mill. In certain aspects where the material includes an iron-containing material, the filter may have magnetic properties to secure the sample on the filter.

The end mill may include a plurality of cutters, with each cutter having an internal blade section that extends laterally into the bore and an external blade section that extends outwardly from the minor shank, wherein the length of the internal blade sections is greater than the length of the external blades and the length of the internal blade sections is less than the radius of the central bore, thereby defining a central area within the bore that determines the width of the micro-sample.

Also described herein is a micro-sampler as defined in claim <NUM>. The depth may be based on the length of the cutting portion of the micro-cutting tool. In various aspects, the cutting depth may be no greater than <NUM>, and in certain aspects, about <NUM>, and in certain aspects, equal to or less than <NUM> microns. In various aspects, the container may include a chamber, the filter which separates the chamber into first and second sections, an inlet channel having one end opening into the first section of the chamber and a second open end for operative connection to a site of interest to be removed by the cutting tool, and a suction port fluidly connected on one end to the second section of the chamber and another end fluidly connected to a suction source.

The characteristics and advantages of the present disclosure may be better understood by reference to the accompanying figures.

As used herein, the singular form of "a", "an", and "the" include the plural references unless the context clearly dictates otherwise. Thus, the articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, lower, upper, upward, down, downward, front, back, and variations thereof, shall relate to the orientation of the elements shown in the accompanying drawing and are not limiting upon the claims unless otherwise expressly stated.

In the present application, including the claims, other than where otherwise indicated, all numbers expressing quantities, values or characteristics are to be understood as being modified in all instances by the term "about. " Thus, numbers may be read as if preceded by the word "about" even though the term "about" may not expressly appear with the number. Accordingly, unless indicated to the contrary, any numerical parameters set forth in the following description may vary depending on the desired properties one seeks to obtain in the compositions and methods according to the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter described in the present description should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Further, any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "<NUM> to <NUM>" is intended to include any and all sub-ranges between (and including) the recited minimum value of <NUM> and the recited maximum value of <NUM>, that is, having a minimum value equal to or greater than <NUM> and a maximum value of equal to or less than <NUM>.

The purpose of the sampling method and cutters described herein is to remove a very small sample from the surface of a component or area of interest. The sample can be any shape, such as boat-shaped, rectangular, cylindrical, cone-shaped, and the like, but is extracted such that all layers of the component, including a portion of the base layer, any intermediate layers, coating layers, and deposits of extraneous matter on the surface of the area of interest remain fully intact and undisturbed. Samples removed in this fashion can then be shipped to an analytical facility where they are characterized using microanalysis techniques such as scanning and transmission electron microscopy. The invention has numerous applications, but it is particularly salient in two cases: <NUM>) highly radioactive specimens such as post-service nuclear fuel cladding, where the cost of extraction, shipment, defueling and sample preparation has heretofore been so costly that it is done for vital programs and exigent circumstances only; and <NUM>) large and/or critical components where removal from service is not an option, such as steam generator tubes, pipe walls, reactor internals, and components of similar systems which would cause noticeable disruptions in critical operations if shut down.

Rather than incur the high cost of mobilization, extraction, shipment, preparation and disposal for analysis of only a minute amount of material, it is better to extract a very small samples which will drastically reduce the overall cost. Doing so will also allow more samples to be withdrawn, and greatly increase the quality of the data obtained by improving sampling statistics.

An exemplary application for the method is to remove small samples from the surface of fuel cladding tubes after service, in order to examine the surface morphology of extraneous matter on the surface of the fuel rod, accident-tolerant coatings, and the extraneous matter, coating, and cladding interfaces. The method described herein will require significantly less mobilization, deployment and shipping costs than heretofore possible because only a very small portion of the sample of interest has to be removed. With the method described herein, only a portion of the outer surface of the base cladding material is removed, reducing the amount of radioactive material in the sample, and thereby eliminating the need to ship the sample to a facility licensed to handle radioactive material. The micro-samples can be tested at a routing testing facility at a significantly reduced cost compared to shipment to a facility licensed to handle radioactive materials.

For convenience, the method will be described for use in removing micro-samples of fuel cladding, but it is not limited to sampling fuel cladding. The invention can be used to obtain samples from virtually any surface, such as pipe walls, steam generator surfaces including tubing in the portion supported by the tube sheet, and internal surfaces of reactors and generators.

A process is described herein where a metallic or ceramic based specimen is sampled on the surface of a component or area of interest in such a way to allow for simultaneous removal of extraneous matter from the surface, such as surface oxides and deposits, together with coating layers, any intermediate layers and some, but not all of the base metal, alloy, or ceramic layer, with all of the layers and extraneous matter, if any, intact. The surface sample should then be extracted, stored and transported in such a way that the deposits and coatings remain attached to the specimen and undisturbed to allow for subsequent observation and characterization.

The various embodiments of sampling depend on the shape and location of the component that needs to be sampled. For example, convex surfaces such as the outer surfaces of fuel rods and pipes, may be sampled using either a micro-diamond wire saw, with a preferred wire diameter ≤<NUM>, or a combination of plunge and wire electrical discharge machining (EDM). The micro-diamond wire saw operation can be performed in air, with water providing cooling, or with parts immersed in water. When wire EDM sampling is used, the process is performed under water.

For samples removed from flat surfaces, such as steam generator manway inserts, large pipe walls, and reactor vessel walls, the cutting tool may be by a combination of plunge and wire EDM, micro-focus lasers to oblate material around the region of interest and perform the final cutting to free the sample, or micro-core drills end mills to machine a post which is then removed either by retaining the sample in a cavity of the core drill or drawing it away with a suction device. Preferably, micro-focus lasers are operated in air. End mills and core drills may be operational in air or water.

For samples removed from concave surfaces, such as steam generator tubes and the inner diameters of pipe walls, the sampling options include a combination of plunge and wire EDM, micro-focus lasers, and micro core drills and/or end mills.

Referring to <FIG>, a component of interest <NUM> having a convex outer surface is shown as a pipe or cladding tube. A micro-sample <NUM> is shown as having been removed from the surface <NUM> of the component <NUM>, leaving a notched area <NUM> in the component <NUM>. The notch <NUM> does not extend through to the interior <NUM> of the component <NUM>. The sample <NUM>, in various aspects, may have sloped or beveled edges, as shown, but may be any shape, such as boat-shaped, rectangular, cylindrical, cone-shaped, and the like.

<FIG> illustrates a sample <NUM> taken from a flat surface <NUM> of a component of interest <NUM>. It should be kept in mind, that because such a small sample is being removed, the surface area to be cut may be substantially flat even though the component as a whole is curved, either convexly or concavely. The area within the dashed circle is blown up to show the layers of the component <NUM> and sample <NUM> in detail. The enlarged portion of <FIG> illustrates the wire <NUM> of a cutting tool <NUM>, such as a wire EDM tool or a diamond wire cutter, cutting a sample <NUM> from component <NUM>. The component <NUM> includes a base layer <NUM>, which may be a metal, metal alloy, or a ceramic material. The component <NUM> as shown also includes an intermediate layer <NUM>, a coating layer <NUM>, and surface extraneous matter <NUM> that has accumulated on the outer surface <NUM> of component <NUM>. The composition of the layers may be any solid material. The sample <NUM> is removed so that all of the layers <NUM>, <NUM>, and <NUM>, and some of the base layer <NUM> are maintained intact, arranged in the same manner as the layers had been before removal. In components such as nuclear cladding tubes, it is important that only a portion of the base layer <NUM> is removed, so that the depth of the sample <NUM> is less than the depth, D, of component <NUM>. In this way, the radioactive contamination on the interior <NUM> of the cladding tube where the fuel pellets are housed will remain sealed per design and will not enter into the surrounding area like the spent fuel pool.

Referring to <FIG>, an embodiment of a cutting tool <NUM> in the form of a modified diamond wire saw is shown. The wire <NUM>, which is constantly fed from one of the spools <NUM>, is held between rollers <NUM> of computer numerical controlled (CNC) guides to move in the x-y plane. One of the guides may optionally also move independently in three axes, giving rise to the ability to cut tapered and transitioning shapes, such as a boat-shaped, v-shaped, cylindrical or rectangular cut. Other shapes, may be programmed into the computer. The rollers <NUM> may be directly or operatively connected to the computer controlled guides for directing the moving wire from one wire roller <NUM> to another, with the depth of the cut set by the distance between and the diameter of the guides. The rollers <NUM> and guides can control axis movements in multiple directions, allowing the diamond wire saw to be programmed to cut predetermined very small intact pieces of an area of interest in component <NUM>. In the embodiment shown, the wire <NUM> is wound between two spools <NUM>. The spools <NUM> rotate to advance the wire <NUM> over a pair of roller guides <NUM> which are mounted on spacer posts <NUM> that extend from a cassette or housing <NUM>. Alignment guides <NUM> positioned on each side of component <NUM> hold the component in place while the diamond wire removes material from the surface <NUM>.

Application of wire EDM in general shares many similarities with diamond wire saw in the delivery mechanism. The wire <NUM>, which may be a thin single-stranded metal wire, made for example of brass, is fed through the area of interest in component <NUM>, submerged in a tank of dielectric fluid, typically deionized water. EDM uses electrical discharges to cut a desired shape from a surface. Material is removed from the work piece by a series of rapidly recurring current discharges between two members that function as electrodes, separated by a dielectric liquid, usually water, and subject to an electric voltage. In various aspects, one of the electrodes is the wire <NUM> and the other is the component <NUM>. When the voltage between the two electrodes is increased, the intensity of the electric field in the volume between the electrodes becomes greater in certain areas than the strength of the dielectric, thereby allowing current to flow between the two electrodes. As a result, material is removed from the surface <NUM> of component <NUM>. Once the current stops, new liquid dielectric is usually conveyed into the inter-electrode volume, flushing the debris away and restoring the insulating properties of the dielectric, so that a new liquid dielectric breakdown can occur. Wire EDMs optically follow lines on a master drawing produced by computer numerical controlled (CNC) plotters to provide finely controlled surface cuts. CNC plotters are well known in the art and need not be described in detail. The size, angle and direction of the cuts will be determined in advance and programmed into the computer by suitable known coding techniques to provide predetermined depth, angle, and other relevant measurements for the sample and directions for the guides. Wire EDM does not require high cutting forces for removal of material so is advantageous for controlled removal of micro-sized samples <NUM>.

In various aspects, the cutting tool may be a novel coring end mill <NUM> that allows small surface samples <NUM> to be removed from a surface <NUM> of a component <NUM> without risk of exceeding a predetermined sample depth and without surface damage. Referring to <FIG>, an embodiment of a micro-sampling end mill <NUM> includes a major shank <NUM> and a minor shank <NUM> which together define an open central bore <NUM>. Cutters <NUM> are mounted on the bottom end of minor shank <NUM>. Cutters <NUM> have sharpened cutting edges on all surfaces not attached to the minor shank <NUM>. The cutters <NUM>, in various aspects, are composed of a hard, tough, material such as tungsten carbide that can remove material from the sample <NUM> without significant wear. The cutters <NUM> are attached to minor shank <NUM> such that the cutting surfaces extend beyond the inner and outer diameters of shank <NUM>. In various aspects, the cutters <NUM> have an outwardly facing blade section <NUM> and an inwardly facing blade section <NUM>. The number of cutters <NUM> can vary. The embodiment shown has two cutters, but the number can vary from one to as many as can be fit around the diameter of the minor shank <NUM>.

Inwardly facing blades <NUM> extend only part way into the bore <NUM> so that a section having a diameter W at the center of the central bore <NUM> will not be swept by the cutters <NUM> as the end mill <NUM> rotates, as shown by rotational motion indicator R in <FIG>. The diameter W must be smaller than the distance Y that outwardly extending section <NUM> of cutter <NUM> extends from the outer diameter of the minor shank <NUM>. The diameter W is very small, for example less than <NUM>, in keeping with the need to collect only a very small sample <NUM>.

The length of the minor shank <NUM> is set such that the distance L between the bottom end of the cutters <NUM> and the bottom flange <NUM> of major shank <NUM> determines the maximum depth of sampling. The depth of sampling is small compared to the total thickness D of the component <NUM> being sampled. The bottom flange <NUM> of the major shank <NUM> is not sharpened and cannot perform a cutting function. It must extend radially beyond the end of the cutters <NUM> so that it represents a barrier to penetration of the tool <NUM> into the material of component <NUM>. In the case of pressurized water nuclear fuel cladding, the distance L between the end of the cutters <NUM> and the bottom flange <NUM> is ideally <NUM> millimeters or less. This allows sufficient remaining cladding wall thickness to retain the integrity of the cladding and prevent egress of the nuclear fuel into the coolant.

The bore <NUM> is of sufficient size to allow coolant flow to the cutters <NUM> and to allow for removal of the micro-sample <NUM> to a sample collector <NUM>, such as that shown in <FIG>.

The precise diameter of the major shank <NUM> can be adjusted and shaped to give more precise depth control on concave, convex, or complex surfaces of interest. Like the wire EDM, the micro end mill cutting tool is preferably computer controlled so that the depth of the penetration of the cutters <NUM> and shanks <NUM> and <NUM> into the material of component <NUM> and the distance of the perpendicular under-cut to free the sample <NUM> are precisely controlled and conform to predetermined desired sample dimensions.

<FIG> illustrate the end mill micro-sampler <NUM> in use in a cutting operation. In certain aspects, (see <FIG>, a thin polymer coating <NUM> may be applied to the surface <NUM> to protect it from machine turnings and chips. The polymer is selected to be insoluble in water but easily removed with another solvent that does not harm the sample such as acetone. The end mill <NUM> is rotated in rotational direction R with coolant flowing downwardly into the bore <NUM>. The coolant direction is initially from the major shank <NUM> to the cutters <NUM>. The end mill <NUM> is advanced into the material <NUM> to be sampled, as shown in <FIG>, producing a sample <NUM> in the form of a pillar in the central bore <NUM> of the end mill <NUM>. Once the desired depth is reached, a depth which will be less than the distance L between the bottom end of the cutters <NUM> and the bottom flange <NUM> of major shank <NUM>, the direction of coolant flow is reversed with coolant flowing upwardly from the cutter <NUM> towards the top of major shank <NUM>. The end mill <NUM> is moved in a direction perpendicular to the surface normal such that blade section <NUM> cuts into component <NUM> and blade section <NUM> cuts into and separates the pillar <NUM> from base <NUM> of component <NUM>, as shown in <FIG>. The sample <NUM> flows upwardly with the coolant flow through the central bore <NUM> of end mill <NUM> into a sample collector. The collector, in various aspects, includes a filter or fine mesh screen to capture the sample <NUM> while allowing the coolant to flow out of the collector. In various aspects, the filter may be made of a magnetic material to better secure samples made from low alloy steel or other magnetic materials on the filter. Following capture of the sample <NUM>, the sample may be washed with a solvent to remove the protective material in those instances where a protective layer had been applied. The collector may then be closed to become a storage and transport container, or may be used to transfer the sample <NUM> to another container for storage and transport. An exemplary collector is shown in <FIG>.

Alternative cutting tools <NUM> may include laser beam machining or laser ablation, which are subtractive processes in which a laser is directed towards the structure of interest. Thermal energy is used to remove material from surfaces. The high frequency of monochromatic light will fall on the surface then heating, melting and vaporizing of the material take place due to impinge of photons. There are many different types of lasers including gas, solid states lasers, and excimers. Ablation is removal of material from the surface of an object by vaporization, chipping, or other erosive processes. The material removed from the surface <NUM> of component <NUM> would be around the area that is intended to be sample <NUM>, so that the layers of sample <NUM> would remain intact as material around it is ablated. When the surrounding material is removed, the remaining plug of material can be undercut, freeing it from attachment to component <NUM>. As with the other examples, only a very small section of component <NUM> is removed and all layers are removed intact. Any of the cutting tools described herein are preferably computer controlled so that the depth of the penetration into the material of component <NUM> and the distance of the under-cut to free the sample <NUM> are precisely controlled and conform to predetermined desired sample dimensions.

The choice of sample <NUM> cutters will vary depending on the nature of the component being sampled. However, the method, regardless of the embodiment of cutter used cuts the surface deposits, oxides, coatings, intermediate layers, if any, and a portion of the base material together, without disturbing the surface deposits and layers. In various aspects, the sample target dimension are less than <NUM> deep and less than or equal to <NUM> in length and width. Those skilled in the art will recognize that the exact size of the sample <NUM> can be varied depending on the specific need, planned testing, and the size of component being sampled.

In various aspects, the method includes extraction, retention and storage of multiple samples <NUM> without damage, using, for example, a sample keeper that is incorporated with or may be attached to the cutting tool in a single unit. A method of capturing and storing the micro-samples <NUM> removed from the components or areas of interest <NUM> so that the layers of removed samples <NUM> are not damaged may optionally be added to the method of sampling.

<FIG> illustrates an exemplary extraction, retention and storage chamber <NUM>. Chamber <NUM> includes an upper section <NUM> separated from a lower section <NUM> by a fritted glass, fine mesh screen, or other suitable filter membrane <NUM>. An inlet <NUM> would, in use, be connected to the cutting tool of choice. A suction port <NUM> is releasably connected to any suitable suction source (not shown). Continuous suction can be, for example, by a remote pump through a tube attached to port <NUM>. In the embodiment shown in <FIG>, a wall <NUM> separates inlet <NUM> from upper section <NUM>. The inlet <NUM> may include an intake nozzle (preferably no more than ¼" in its inner diameter) which would be positioned in very close proximity to the sampling site.

In use, inlet <NUM> or an intake nozzle connected to inlet <NUM> may be fluidly connected to top of bore <NUM> (for example, either directly or indirectly connected through conduits or other means such that fluid flows between the inlet <NUM> and bore <NUM>) of end mill <NUM> shown in <FIG>, or proximate the area adjacent to wire <NUM> between guides <NUM> in the wire EDM shown in <FIG>. When a sample <NUM> is cut from a component <NUM>, a vacuum is pulled through suction port <NUM> sufficient to draw the sample <NUM> and any coolant in which the sample <NUM> is carried from the cutting tool through inlet <NUM>, over wall <NUM> and into upper section <NUM> of chamber <NUM>, but gently enough to avoid damage to the layers and any extraneous matter on sample <NUM>. Filter <NUM> captures sample <NUM>, preventing it from being drawn into lower section <NUM> or through port <NUM>. The coolant, if any, passes through filter <NUM>. Upon capture, the vacuum is stopped, port <NUM> released from the vacuum source and closed, and inlet <NUM> is removed from the cutting tool and closed. The sample <NUM> would be retained, intact in chamber <NUM> and delivered to the appropriate testing facility. As stated above, in instances where the sample surface was coated with a protective layer, the protective material would be removed, for example, with a solvent, allowing the solvent to flow through the filter, and retaining the sample <NUM> on filter <NUM>. Removal of the protective layer may take place before transport or upon arrival at the testing facility.

In various aspects, the cutting tool may be a novel flexible flute core drill <NUM> that allows small surface samples <NUM> to be removed from a surface <NUM> of a component <NUM> without risk of exceeding a predetermined sample depth and without surface damage. Referring to <FIG>, and <FIG>, an embodiment of a flexible flute core drill <NUM> includes a flute collet <NUM> and a shank <NUM> which together define an open central bore <NUM>. Cutters <NUM> are mounted on the bottom end of collet <NUM>. Cutters <NUM> have sharpened cutting edges on all surfaces not attached to the flute collet <NUM>. The cutting edges may take the form of abrasive particles. The cutters <NUM>, in various aspects, are composed of a hard, tough, material such as diamond imbedded in cobalt that can remove material from the sample <NUM> without significant wear. The cutters <NUM> are attached to flute collet <NUM> such that the cutting surfaces extend beyond the inner diameter of flute collet <NUM>. The cutters <NUM> must also extend to or beyond the outer diameter of the flute collet <NUM>. The number of cutters <NUM> can vary. The embodiment shown has four cutters, but the number can vary from two to as many as can be fit around the diameter of the flute collet <NUM>.

The inwardly facing portion of the cutters <NUM> extend only part way into the bore <NUM> so that a section having a diameter W' at the center of the central bore <NUM> will not be swept by the cutters <NUM> as the drill <NUM> rotates, as shown by rotational motion indicator R in <FIG>. The diameter W' divided by two must be smaller than the distance S between the outer portion of cutter <NUM> and the outer diameter of the flute collet <NUM>. The diameter W' is very small, for example less than <NUM>, in keeping with the need to collect only a very small sample <NUM>.

The angle of the of the sloping face <NUM> of the collet <NUM> is set such that the cutters <NUM> meet at the center of core drill rotation after a distance L' between the bottom end of the cutters <NUM> and the flute collet <NUM> is traversed. This distance is the maximum depth of sampling. The depth of sampling is small compared to the total thickness D of the component <NUM> being sampled. The outer surface of the flute collet <NUM> is not sharpened and cannot perform a cutting function. It must extend radially outward beyond the end of the cutters <NUM> so that it represents a barrier to penetration of the tool <NUM> into the material of component <NUM> once the cutters <NUM> have met at the center of rotation. In the case of pressurized water nuclear fuel cladding, the distance L' between the end of the cutters <NUM> and the flute collet <NUM> when the cutters <NUM> have met at the center of rotation is ideally <NUM> millimeters or less. This allows sufficient remaining cladding wall thickness to retain the integrity of the cladding and prevent egress of the nuclear fuel into the coolant.

Both the flute collet <NUM> and shank <NUM> are slotted to add flexibility. The slots <NUM> are to be wide and long enough to allow movement of the cutters to the center of tool rotation. A retaining ring <NUM>, as shown in <FIG>, may be added to the shank <NUM> above the collet flute to prevent the distance between the cutters <NUM> from increasing as the tool <NUM> is used.

The thickness of the cutters <NUM> and the angle of the flute collet <NUM> can be adjusted and shaped to give more precise depth control on concave, convex, or complex surfaces of interest. Like the diamond saw, wire EDM, and the micro end mill cutting tools, the flexible flute core drill <NUM> may be computer controlled so that the speed of the penetration of the cutters <NUM> and collet <NUM> and shank <NUM> into the material of component <NUM> is precisely controlled, optimizing the cutting time. However, since both the diameter of the microsampler and the depth of the drill penetration are set by the dimensions of the drill, the flexible flute core drill <NUM> may be applied with a simple known drive system that does not require a computer.

<FIG> illustrate the flexible flute core drill <NUM> in use in a cutting operation. In certain aspects, (see <FIG>, a thin polymer coating <NUM> may be applied to the surface <NUM> to protect it from machine turnings and chips. The polymer is selected to be insoluble in water but easily removed with another solvent that does not harm the sample such as acetone. The core drill <NUM> is rotated in rotational direction R with coolant flowing upwardly into the bore <NUM>. The coolant direction is initially from the cutters <NUM> to the shank <NUM>. The flexible flute core drill <NUM> is advanced into the material <NUM> to be sampled, as shown in <FIG>, producing a sample <NUM> in the form of a pillar in the central bore <NUM> of the core drill <NUM>. Once the desired depth is reached, a depth which will be equal to the distance L' between the bottom end of the cutters <NUM> and the flute collet <NUM>, the cutters <NUM> meet at the center of rotation and the micro sample <NUM> is separated from the component <NUM> as shown in <FIG>. The sample <NUM> flows upwardly with the coolant flow through the central bore <NUM> of core drill <NUM> into a sample collector. The collector, in various aspects, includes a filter or fine mesh screen to capture the sample <NUM> while allowing the coolant to flow out of the collector. In various aspects, the filter may be made of a magnetic material to better secure samples made from low alloy steel or other magnetic materials on the filter. Following capture of the sample <NUM>, the sample may be washed with a solvent to remove the protective material <NUM> in those instances where a protective layer had been applied. The collector may then be closed to become a storage and transport container, or may be used to transfer the sample <NUM> to another container for storage and transport. An exemplary collector is shown in <FIG>.

The choice of sample <NUM> cutters will vary depending on the nature of the component being sampled. However, the method, regardless of the embodiment of cutter used cuts the surface deposits, oxides, coatings, intermediate layers, if any, and a portion of the base material together, without disturbing the surface deposits and layers. In various aspects, the cutting depth may be no greater than <NUM>, and in certain aspects, about <NUM>, and in certain aspects, equal to or less than <NUM> microns. In various aspects, the sample target dimension are less than <NUM> deep and less than or equal to <NUM> in length and width or diameter, depending on the cutting tool used and the thickness of the component <NUM>. Those skilled in the art will recognize that the exact size of the sample <NUM> can be varied depending on the specific need, planned testing, and the size of component being sampled.

The method described herein significantly reduces the cost of cladding analyses, including the characterization of lead test assembly, dissolved hydrogen measurements, and measurement of cladding oxide thickness in conventional cladding. The method can be used to supplant what is referred to as fuel crud scraping products. Currently, the cost of mobilization, extraction and shipping are prohibitive. This method of micro-sampling can significantly reduce those costs, making crud scrapes a more attractive proposition for nuclear power plant operations. Easier and lower costs associated with sampling would allow cladding analysis to assess the safety of moving spent fuel from spent fuel pools to dry storage facilities, and allow corrosion analysis on various alloys for utilities.

The method and cutting tools described herein remove minute quantities from the surface of interest of a component with the purpose of keeping the surface layers and interfaces intact and undisturbed. The method also may include steps and devices to capture and store the micro-samples, all without disturbing any surface deposits and oxides.

The present invention has been described in accordance with several examples, which are intended to be illustrative in all aspects rather than restrictive. Thus, the present invention is capable of many variations in detailed implementation, which may be derived from the description contained herein by a person of ordinary skill in the art.

Claim 1:
A method of sampling a multi-layered material having a top surface (<NUM>) and a metallic or ceramic base (<NUM>), the method comprising:
penetrating a top surface (<NUM>) of the material (<NUM>) with a micro-cutting tool to a predetermined depth sufficient to include each layer of the multi-layered material (<NUM>) and a portion of the base (<NUM>), without cutting through the full depth of the base (<NUM>);
under-cutting from the depth of penetration through the base (<NUM>) to define a micro-sample (<NUM>) of the multi-layered material (<NUM>); and
removing the micro-sample (<NUM>) with each layer of the multi-layered material (<NUM>) intact,
characterized in that
the micro-cutting tool comprises an end mill (<NUM>) comprising:
a major shank (<NUM>) having a top end and a bottom end;
a minor shank (<NUM>) having a top end and a bottom end, the top end of the minor shank (<NUM>) extending from the bottom end of the major shank (<NUM>), the major shank having a diameter larger than the diameter of the minor shank;
the major and minor shanks (<NUM>, <NUM>) together defining a central bore (<NUM>); and
at least one cutter (<NUM>) positioned at the bottom end of the minor shank (<NUM>); and
the step of penetrating the material (<NUM>) comprises:
rotating the end mill (<NUM>) while penetrating the material (<NUM>) to cut into the material (<NUM>) to the predetermined depth;
flowing a coolant downwardly through the central bore (<NUM>) toward the material (<NUM>);
undercutting through the material (<NUM>) by moving the at least one cutter (<NUM>) in a perpendicular direction relative to the bore (<NUM>) sufficient to free the micro-sample (<NUM>) from the material, and simultaneously changing the direction of flow of the coolant upwardly through the bore (<NUM>) towards the top of the major shank (<NUM>); and
drawing the micro-sample (<NUM>) with the coolant flow through the bore (<NUM>) upwardly through a filter (<NUM>) for capturing the micro-sample (<NUM>).