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062326139 | abstract | An angular pumped and emitting capillary(APEC) discharge light source having a blocking electrode installed on the axis of the capillary just beyond the end of the capillary bore. Thus, the emitting region occurs in an angular fashion between the end of the capillary and the blocking electrode. The blocking electrode prevents debris generated within the capillary from being expelled onto collecting optics for the discharge source. A second version shapes the blocking electrode into a trap so that emitted debris will be collected within the trap. Alternatively, the trap can be a collector separate and apart from the electrodes of the light source. The capillary bore and electrode configuration allow for emissions to be enhanced by placing the electrode in front of the outlet to the capillary bore. A still another version has a discharge source without a capillary bore where gas flows through a first electrode to a space in front of a second electrode to generate a discharge therebetween so that debris is blocked and collected by the second electrode. |
059600497 | abstract | The operator of a nuclear steam supply system manually selects a lineup of either one, two, or three main feedwater pumps for normal reactor operation to generate power. This selection sets or resets a status latch for each pump, representative of intended pump operation. A system (RPCS) for implementing a step reduction in the power output of the reactor, includes an associated logic circuit which combines signals indicative of tripping of one or more pumps, with the pump status latches, to achieve the following outcomes: (a) with one pump selected, a trip of this one pump does not produce an RPCS trip demand signal (because the reactor will be tripped); (b) with two pumps selected, (i) a trip of one pump will produce an RPCS trip demand signal, whereas (ii) a trip of these two pumps will not produce an RPCS trip demand signal; (c) with three pumps selected, (i) a trip of one pump will not produce an RPCS trip demand signal (because the transient can be handled by the basic control system), (ii) a trip of two pumps will produce an RPCS trip demand signal, and (iii) a trip of three pumps will not produce an RPCS trip demand signal. |
summary | ||
summary | ||
053393465 | description | DEFINITIONS Plasma Source--A thermally-produced plasma for yielding x-ray radiation--generally pumped by a high power pulsed laser. PA0 Illumination Radiation--The delineating radiation as incident on and producing an PA0 Illumination Field on the mask, characterized by intensity, direction, divergence and spectral width. PA0 Divergence--As used by itself, the term refers to mask divergence, i.e., the largest angle about the axis of the cone of radiation as incident on the mask. In projection, the axis is generally a few degrees off normal incidence as required for reflection masking. The magnitude of divergence required in projection is that needed to reduce ringing at feature edges to the extent necessary for desired resolution and contrast. In full-field exposure, divergence should be similar at every illumination point. In scanning, some non-uniformity in the scanning direction may be averaged out. PA0 Condenser--Optical system for collecting radiation from the plasma source, for processing the radiation to produce a ringfield illumination field, and for illuminating the mask. PA0 Collecting Optics (or Collector)--The Optics within the condenser responsible for collecting the plasma-derived radiation. The collector has a focus. PA0 Processing Optics--Optics, in addition to the collecting optics, within the condenser for processing collected radiation for delivery to the mask. PA0 Imaging Optics--Optics following the condenser responsible for delivering mask-modulated radiation to the wafer, i.e. the camera optics. PA0 Camera Pupil--Real or virtual aperture which defines the position through which illumination radiation must enter the camera, of angular size defining the diffraction limit of the camera. Its physical size is that of an image of the real limiting aperture of the camera. PA0 Lens--The term is used in this description to define any optical element which causes x-ray radiation to converge or diverge. "Lenses", in x-ray systems, are generally reflecting--are sometimes referred to as "mirrors". contemplated lenses may be multi-faceted or may be non-faceted, i.e. continuous--e.g., of ellipsoidal or other curvature. The convergence or divergence is a result of action analogous to that of a transmission optical lens. PA0 Facet--Individual segment of a lens--either a separate element, or part of a monolithic structure, which, generally in concert with other facets, is responsible for convergence or divergence of the radiation. Individual facets may be planar or curved. PA0 Scatter Plate--Optical element for increasing divergence. Divergence may be in one or two dimensions. PA0 General--There is a continuing effort directed to development of x-ray plasma sources for pattern delineation at feature sizes .ltoreq.0.25 .mu.m. See, W. T. Silfvast, M. C. Richardson, H. Binder, A. Hanzo, V. Yanovsky, F. Jin, and J. Thorpe, "Laser-Produced Plasmas for Soft-X-ray Projection Lithography" J. Vac. Sci. Tech. B 106, Nov./Dec. 1992, pp. 3126-3133. By its nature, emission from a plasma source is omnidirectional. Device fabrication of this invention depends upon a condenser designed to capture this omnidirectional emission and to shape it to produce a high-aspect ratio illumination field for ringfield projection lithography. PA0 The Drawing--Detailed design and processing information is discussed in conjunction with the figures. DETAILED DESCRIPTION In addition to shaping, directing, and tailoring divergence, the condenser must filter the natural plasma spectrum of perhaps .lambda.=50 .ANG.-400 .ANG. to yield the favored ringfield wavelength range within a spectrum of .lambda.=100 .ANG.-200 .ANG. (at this time the preferred spectral range is .lambda.=125 .ANG.-140 .ANG.). Use of this "soft x-ray projection lithography" (SXPL) takes advantage of ability to make high reflectivity normal incidence mirrors. It also expedites use of glancing mirror optics, in permitting larger angles of incidence than those required for the "hard x-ray" used in proximity printing. Filtration, to yield the desired x-ray spectrum, will likely use multi-layer reflectors (MLR) operating on the Distributed Bragg Reflector (DBR) principle. In FIG. 1a YAG or excimer laser 11 emits a beam 12 which is focused by lens 13 to heat a spot 14 on target material 15, thereby yielding plasma ball 16 which emits x-rays 17. Radiation is emitted over an entire 180.degree. half sphere. FIG. 2 is a perspective view of a state-of-the-art system for using a plasma source for powering a projection camera. Plasma source 21 emits a half sphere of x-ray radiation shown as rays 22. An MLR 23 focuses radiation at focus 24 on mask 25. The illumination field is an image of the source. As depicted, the illumination field is a spot 24 incident on mask 25, where the radiation is either transmitted or reflected to be introduced into camera 26 by partially filling entrance pupil 27. For the proper pupil fill shown only a relatively small cone of radiation is collected, and radiation outside this cone is wasted. If the size of the condenser is increased in order to collect the relatively large angle radiation represented rays 28, the camera pupil is greatly overfilled as shown by field 29, produced by the condenser-emitted rays shown as broken lines. Energy is wasted and the image is degraded. Neither arrangement produces a ringfield illumination field. FIGS. 3 and 4 show an illustrative system for effectively producing the high-aspect ratio illumination field for ringfield projection. FIG. 3, an "elevational" view illustrates processing to deliver the short dimension of the high-aspect-ratio field. Plasma 31, produced by laser beam 30 emits x-rays 32 over a wide angle, near-half sphere, which is captured by lens facets 33. While not seen in this view, most or all of facets 33 are members of paired complementary facets, common to all collectors used in the inventive processing. An aperture can be placed in the beam path, either at position 91 or 92 in FIG. 3, (.about.93 or 94 in FIG. 4). The aperture can block part of the beam to produce greater uniformity in intensity on the mask, if needed. If ellipsoidal, the first focus may conveniently correspond with the source, and the second focus may correspond with the image. The curved facet surface may be of "Lopez" form. The Lopez mirror is explicity designed to produce a single focus for many-angled emission. Its use for the individual facets of the multi-faceted collector lens may be justified. Each of the facets may be viewed as having an effective height comparable to that of mirror 23 in FIG. 2 to produce a field dimension in the scanning direction which is the same as that of a spot 24. Each of the facets focuses an image of source 31 as image 34 on lens 35. Lens 35 is a many-faceted mirror which directs reflected radiation and overlaps individual beams at processing optic 36. Mirror 37, likely a single, continuous surface, concave lens, is a redirecting optic. The several images are brought to a common focus at or near mask 38 and are directed to enter camera pupil 39. Companion FIG. 4 shows illumination of the transverse (or long dimension) of the high-aspect-ratio ringfield. Laser plasma radiation from source 40 is collected by the array of ellipsoidal mirrors, here shown as paired facets 41a-41b. The collector focuses an image of the source to a series of spots on processing lens (mirror array) 42, with individual spots made incident on individual facets of lens 42. The facets of lens 42 are oriented such that the center ray of the reflected beam strikes the center of the processing lens 43 which is again a multi-faceted array in this example, but may be a continuous curved surface such as a cylindrical mirror or an ellipsoidal or toroidal mirror. The distance between the processing lens 42 and processing lens 43 is such that the processed radiation emitted by lens 42 covers the length of lens 43. Lens 43 in conjunction with lens 37 of FIG. 3, together, shape the beam to produce the proper arc shape illumination field 44 as incident on mask 45. The same optics introduce the convergence shown upon reflection from mask 45 to produce the desired fill of entrance pupil 46. The multi-faceted lens 50 shown in FIG. 5 is illustrative of optics serving the function of lens 42 of FIG. 4. Lens 50 is constituted of 8 facets 51 oriented such that incoming cones of radiation 52 are reflected as cones 54 toward the processing optics. The aspect-ratio of facets 51 may approximate that of the desired illumination field--image dimension 53 corresponding with the long dimension of facet 51. In FIG. 6a, collector facets 60 are arranged to have a quadrupole distribution, to focus into two series of spots on multi-faceted lens 61 (e.g. corresponding with lens 42 of FIG. 4). In FIG. 6b, it is seen that facets 61 are split along their length so that each consists of two facets 62, oriented at different angles to result in radiation being reflected in two slightly different directions 63 in the vertical or scanning direction. Viewed from FIG. 6c, radiation upon reaching the pupil is split into four separate multi-image fields 64, 65, 66 and 67. FIGS. 7a-7d show various collector lens designs, always including paired complementary facets. Discrete compensating facets separate lens functions and facilitate design. Members of pairs, always producing equal and opposite intensity gradients, to, together, produce a composite image which is evenly illuminated in the compensating direction, are independently directed to suit the camera optics. Illumination in the compensating direction is at least .+-.15%. Careful facet placement results in .+-.5% or even .+-.1% or better. In FIG. 7a, the lens array 70 is constituted primarily of paired facets 71a-71b. Facets 71c, positioned at the extremities of the emission sphere, are not paired. Pairing, here to, is preferred in principle, but any intensity gradients may be small enough to be ignored. In general, single-faceted mirrors over the final 65.degree.-75.degree. of emission in this direction are tolerable. (Consistent with usual practice, angles are measured relative to the optic axis.) As in all arrangements, members of paired facets are symmetrically placed about source 75. In FIG. 7b, collector lens 72 is constituted of five pairs of facets 72a-72b. This arrangement may result in a somewhat smaller aspect-ratio slit than the 7-tier arrangement of FIG. 7a. The variations of FIGS. 7c and 7d are trivial. For the four-tier arrangement of facets 73a-73b, the horizontal center line of spot source 75 is naturally located at the intercept of two pairs. It is of little importance that source-to-facet spacing is different in the two dimensions--it is desirable only that each dimension spacing by symmetrical. Collector lens 74 is a three-tier array of paired facets 74a-74b. Illustrative facet aspect-ratio may be suited to a similarly shaped illumination field. FIG. 7e is an elevational (or side) view of the arrangement of FIG. 7b, showing stacked facets 72a. The facet arrangements shown are based on minimal facet count. The inventive requirements may be met by higher count arrangements. As an example, lateral faceting may involve four rather than two facets, providing that inner and outer pairs produce the required evenly-illuminated composite field image. Should there be reason to do it, it is required only that the entire lateral set produce such a field image (so that neither the inner nor the outer pair is completely self-compensating). FIGS. 8a and 8b are plan and vertical views, respectively, showing a three-lens condenser system used as the basis for Example 1. Collector includes five paired facets of the arrangement shown in FIG. 7b. The facets are MLRs, consisting e.g. of 40 paired Mo-Si layers. The radiation passes through a window 88 that keeps dirt produced by the plasma from damaging the mirrors of the camera 86. The first processing lens 81, a grazing incidence multi-faceted mirror, directs the radiation to processing lens 82 which combines the functions of vertical processing lens 37 of FIG. 3, and horizontal processing lens 43 of FIG. 4. Processed radiation as leaving lens 82 produces arc-shaped illumination field 83 on mask 84, which in turn, creates an image of the arc on wafer 87 via reflection into camera pupil 85 of camera 86. Device Fabrication--Basic device fabrication is not otherwise altered. Reference may be made to a number of texts, e.g. Simon Sze, VLSI Technology, McGraw Hill, 1983. The following examples 1 and 2 are directed to the critical window level in MOS VLSI device fabrication. Example 1--Fabrication of a 256 mbit, 0.1 .mu.m design rule MOS device is illustrated by fabrication at the window level as follows: The apparatus of FIGS. 8a and 8b is provided with a plasma source of 500 watt emission consisting of a 500 watt YAG laser-pumped tin source. The collector lens of the arrangement of lens 80 consists of eight 35 mm.times.90 mm multi-layered facets, each containing 40 pairs of successive Mo-Si layers, to result in focused beams of .lambda.=135.+-.3 .ANG. of total power 2.5 watts. As received by wafer 87, the ringfield scanning line is of dimensions. 1 mm in the scanning direction and 25 mm as measured along the chord of the arcuate line. Example 2--The x-rays projection camera is of the family designed by Jewell. (See U.S. patent application Ser. No. 07/732,559, filed Jul. 16, 1991.) It has a numerical aperture of 0.1 and is capable of printing 0.1 micron lines. In the first applications it will be used only for the critical levels, e.g. the gate and the contact windows. Other printers, e.g., deep UV, will print other levels. In later models, when the numerical aperture has been increased to 0.2, it will print critical levels with 0.05 micron features and also many other levels--the other levels will have 0.1-0.15 micron features that are too small to be printed even by Deep UV. Suppose 1 watt strikes the mask of the gate level. Due to losses in the mirrors of the camera, a thin silicon window (0.3 .mu.m thick) between the wafer and the camera, only 75 .mu.m (or less, depending on how much of the mask is reflective) arrive on the wafer. The wafer has patterning from previous levels. Immediately before the lithography, the wafer was coated with a very thin oxide layer, a polysilicon conductor and on top, a thick oxide layer. An x-ray resist covers the whole wafer. The wafer is placed under the x-ray projector, aligned, and exposed. If the resist has a sensitivity of 15 mj/cm.sup.2, 5 cm.sup.2 will be exposed each second. The resist is developed, and, where there is no resist, the top oxide and polysilicon layers are removed by dry etching, leaving the very thin oxide layer on the bottom intact. Later an ion beam implants dopants through the thin oxide into the silicon, forming conductive layers that act as source and drain regions. The region of silicon under the polysilicon gate remains resistive, and will conduct only when a voltage is applied to the gate. |
abstract | A modular nuclear reactor comprises a plurality of sections arranged in a pattern and a side reflector material surrounding the plurality of sections. Each section includes a tank comprising a front plate, a back plate, side plates, a top plate, and a bottom plate. A plurality of grid plates are located within the tank. Each grid plate comprises a plurality of apertures and is vertically separated from an adjacent grid plate. The tank further includes a plurality of fuel elements extending through each grid plate. A plurality of heat pipes extend through each grid plate, the top plate, and an upper reflector. Methods of forming the modular nuclear reactor are also disclosed. |
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claims | 1. An optical axis adjusting mechanism for an X-ray lens to be implemented in an X-ray analytical instrument, comprising:an exit side adjusting mechanism for adjusting an exit side focal point of the X-ray lens to focus on an X-ray detector; andan entrance side adjusting mechanism for adjusting an entrance side focal point of the X-ray lens to focus on an analytical point of a sample,wherein the entrance side adjusting mechanism is disposed at a greater distance from the X-ray lens than a distance between the exit side adjusting mechanism and the X-ray lens. 2. The optical axis adjusting mechanism for an X-ray lens according to claim 1, whereinthe exit side adjusting mechanism includes a mechanism capable of translating the X-ray lens in parallel with two directions perpendicular to the optical axis of the X-ray lens. 3. The optical axis adjusting mechanism for an X-ray lens according to claim 2, whereinthe exit side adjusting mechanism includes a detachable section configured to allow at least a portion operated by an operator to be detached. 4. The optical axis adjusting mechanism for an X-ray lens according to claim 1, whereinthe exit side adjusting mechanism includes a mechanism capable of rotationally moving the X-ray lens around two axes passing through the entrance side focal point of the X-ray lens and perpendicular to the optical axis of the X-ray lens. 5. The optical axis adjusting mechanism for an X-ray lens according to claim 3, whereinthe exit side adjusting mechanism includes a detachable section configured to allow at least a portion operated by an operator to be detached. 6. The optical axis adjusting mechanism for an X-ray lens according to claim 1, whereinthe X-ray lens includes a holding mechanism for keeping the X-ray lens in a position adjusted by the exit side adjusting mechanism. 7. The optical axis adjusting mechanism for an X-ray lens according to claim 1, whereinthe X-ray detector is a superconducting X-ray detector mounted on a refrigerator,the entrance side adjusting mechanism is disposed adjacent to the refrigerator, andthe exit side adjusting mechanism is movable integrally with the refrigerator. 8. The optical axis adjusting mechanism for an X-ray lens according to claim 7, whereinthe entrance side adjusting mechanism includes a mechanism capable of translating the refrigerator in parallel with two directions traversing the optical axis of the X-ray lens. 9. The optical axis adjusting mechanism for an X-ray lens according to claim 8, whereinthe two directions are substantially perpendicular to the optical axis of the X-ray lens. 10. The optical axis adjusting mechanism for an X-ray lens according to claim 7, whereinthe entrance side adjusting mechanism includes a mechanism capable of translating the refrigerator in parallel with a horizontal direction perpendicular to the optical axis of the X-ray lens. 11. The optical axis adjusting mechanism for an X-ray lens according to claim 7, whereinthe entrance side adjusting mechanism includes a mechanism capable of rotationally moving the refrigerator around each of two axes positioned differently from the optical axis of the X-ray lens and passing through one of the refrigerator and an area adjacent to the refrigerator. 12. The optical axis adjusting mechanism for an X-ray lens according to claim 7, whereinthe entrance side adjusting mechanism includes:a mechanism capable of rotationally moving the refrigerator around a rotational axis positioned differently from the optical axis of the X-ray lens and passing through one of the refrigerator and an area adjacent to the refrigerator; andthe rotational axis of the mechanism rotationally moving the refrigerator is substantially perpendicular to the ground. 13. The optical axis adjusting mechanism for an X-ray lens according to claim 12, whereinthe entrance side adjusting mechanism moves the entrance side focal point of the X-ray lens approximately parallel to a direction substantially perpendicular to the optical axis of the X-ray lens by the rotational movement around the rotational axis. 14. The optical axis adjusting mechanism for an X-ray lens according to claim 12, whereinthe entrance side adjusting mechanism includes a mechanism capable of moving the entrance side focal point of the X-ray lens integrally with the refrigerator in a horizontal direction. 15. The optical axis adjusting mechanism for an X-ray lens according to claim 7, whereinthe entrance side adjusting mechanism includes:a mechanism capable of translating the entrance side focal point of the X-ray lens integrally with the refrigerator in parallel with a direction traversing the optical axis of the X-ray lens; anda mechanism capable of rotationally moving the entrance side focal point of the X-ray lens integrally with the refrigerator around an axis positioned differently from the optical axis of the X-ray lens. 16. The optical axis adjusting mechanism for an X-ray lens according to claim 7, whereinthe entrance side adjusting mechanism is capable of adjusting the entrance side focal point of the X-ray lens, while firmly connecting a stage mounting the entrance side adjusting mechanism thereon with an analytical vessel containing the sample, an excitation source and a detector, and then inserting the X-ray lens in the analytical vessel. 17. The optical axis adjusting mechanism for an X-ray lens according to claim 7, whereinthe entrance side adjusting mechanism is capable of adjusting the entrance side focal point of the X-ray lens, while connecting the refrigerator with a scanning electron microscope via a bellows, and firmly connecting a stage mounting the entrance side adjusting mechanism thereon to the scanning electron microscope, and then inserting the X-ray lens in a vacuum vessel of the scanning electron microscope. 18. An X-ray analytical instrument comprising the optical axis adjusting mechanism according to claim 1. 19. A method of adjusting an optical axis of an X-ray lens to be implemented in an X-ray analytical instrument, comprising:disposing an entrance side adjusting mechanism for adjusting an entrance side focal point of the X-ray lens to focus on an analytical point of a sample at a greater distance from the X-ray lens than a distance between an exit side adjusting mechanism for adjusting an exit side focal point of the X-ray lens to focus on an X-ray detector and the X-ray lens;adjusting the exit side focal point of the X-ray lens to focus on the X-ray detector by the exit side adjusting mechanism; andadjusting the entrance side focal point of the X-ray lens to focus on the analytical point of the sample by the entrance side adjusting mechanism. |
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summary | ||
042499950 | abstract | In a fast reactor constituted by an open-topped main vessel containing liquid metal coolant and an inner vessel mounted within the main vessel, a transverse skew wall forming an inner vessel extension is associated with a baffle which extends above the skew wall. A space formed between the baffle and the skew wall and containing a practically static volume constitutes a thermal shield between the hot liquid metal located within the inner vessel above the baffle and the cold liquid metal located between the inner vessel and the main vessel beneath the skew wall. |
summary | ||
description | Calibration devices for optical scanners and methods for their use are provided. The subject devices are characterized by having a polymeric coating with at least one fluorescent agent, where the devices have minimal local and global nonuniformities. The subject device may also include one or more photobleached regions. In using the subject devices, a surface is illuminated with at least one light source, fluorescence data is obtained from the surface and the optical system is calibrated based upon the obtained fluorescence data. The subject invention finds use in a variety of optical scanners, including biopolymeric array optical scanners. Also provided are kits for use in verifying and calibrating optical scanners. Before the present invention is described, it is to be understood that this invention is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims. Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either both of those included limits are also included in the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. It must be noted that as used herein and in the appended claims, the singular forms xe2x80x9caxe2x80x9d, xe2x80x9candxe2x80x9d, and xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to xe2x80x9ca laserxe2x80x9d includes a plurality of such lasers and reference to xe2x80x9cthe arrayxe2x80x9d includes reference to one or more arrays and equivalents thereof known to those skilled in the art, and so forth. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed. As summarized above, calibration devices are provided for use in calibrating optical scanners, particularly biopolymeric array optical scanners (herein referred to as xe2x80x9coptical scannersxe2x80x9d) and more particularly biopolymeric array optical detectors, lenses, stages and mirrors. In further describing the subject invention, a review of optical scanners suitable for use with the subject invention will be presented first to provide a proper foundation for the invention, followed by a description of the subject calibration devices and methods of using the subject calibration devices to calibrate an optical scanner and scan an array. Optical Scanners A variety of optical scanners are known in the art, and particularly optical scanners for scanning arrays are known in the art. By array is meant a collection of separate probes or binding agents each arranged in a spatially defined and a physically addressable manner. In other words, a substrate having a plurality of probes or binding agents stably attached to, i.e., immobilized on, its surface, where the probes or binding agents may be spatially located across the surface of the substrate in any of a number of different patterns. xe2x80x9cProbesxe2x80x9d or xe2x80x9cbinding agentxe2x80x9d as used herein refers to any agent or biopolymer that is a member of a specific binding pair, where such agents include: polypeptides, e.g. proteins or fragments thereof; nucleic acids, e.g. oligonucleotides, polynucleotides, and the like, as well as other biomolecules, e.g., polysaccharides, etc. Typically, such array optical scanners include a light source for irradiating light upon the array surface and a light detector for subsequently measuring detectable light from the array surface, e.g., fluorescence emission, etc. Representative biopolymeric array optical scanners include, but are not limited to, those disclosed in U.S. Pat. Nos. 5,585,639 and 6,258,593, the disclosures of which are herein incorporated by reference and commercially available optical scanners such as the Microarray Scanner, model number G2565AA, manufactured by Agilent Technologies, Inc., Palo Alto, Calif., for example. As described above, the optical scanners suitable for use with the present invention generally include at least one light source for generating at least one coherent light beam at a particular wavelength, a scanning means for scanning the beam over a substrate surface such as an array surface and a light detector for detecting a light produced from the sample regions on the substrate surface, e.g., fluorescence. The at least one light source is typically a source of light that is capable of irradiating or illuminating the substrate surface, e.g., array surface, with a light that is in the portion of the electromagnetic spectrum to which a photomultiplier tube of the optical scanner is sensitive. Usually, the light is in the ultraviolet, visible or infrared regions, but may include other wavelengths as well if appropriate. Oftentimes, the substrate surface is illuminated by light over a range of wavelengths, where the wavelengths correspond to the fluorescence excitation wavelengths of one or more fluorescent agents, as will be described below, which are bound to the probes or binding agents associated with the surface of the substrate. Where visible light is used, typically a wavelength from about 400 to 700 nm, usually from about 500 to 640 nm and more usually from about 550 to 590 nm is used to illuminate the array surface. Oftentimes, at least two sources of light or two wavelengths are used to illuminate the surface of the substrate. For example, a dual laser scanner may be used, where such a dual laser scanner may include a first laser capable of emitting light in the wavelength from about 570 to 490 nm and a second laser capable of emitting light in the wavelength from about 780 to 620 nm. Any convenient light source may be employed, where suitable light sources include, light emitting diodes, laser diodes, filtered lamps, and the like, where laser light sources are of particular interest and include dye lasers, titanium sapphire lasers, Nd:YAG lasers, argon lasers and any other suitable lasers. More particularly, SHG-YAG lasers and HeNe lasers are typically used as light sources in array optical scanners. The light source(s) oftentimes also includes a scan lens system for focusing the illuminating light to a desired size illumination area on the array, such as described in Smith, W. J., Modern Lens Design, McGraw Hill, p. 413. The light source usually generates a light beam with a width that ranges from about 1 to 200 microns at the focus, usually about 2 to 20 microns and more usually about 5 to 8 microns at the focus. Usually a scanning means is associated with the light source to scan or raster the light beam in one or more directions over a substrate surface. A suitable scanning means includes, but is not limited to, a mirror, e.g., a scanner mirror as is known in the art, under the control of a motor, such as a galvo-scanner motor also commonly known in the art. The scanning means is usually capable of moving the light beam over a surface having a length from about 4 to 200 mm, usually from about 2 to 150 mm and more usually from about 4 to 125 mm and a width from about 4 to 200 mm, usually from about 4 to 120 mm and more usually from about 4 to 80 mm, for example a 25 mm by 75 mm array or a 22 mm by 22 mm array, as are known in the art. The scan time for a two color, simultaneous scan of a 25 mm by 75 mm array surface usually ranges from about 4 minutes to about 18 minutes, usually from about 6 minutes to about 12 minutes and more usually from about 6 minutes to about 8 minutes. The optics of the scanner also includes a suitable detector that is capable of detecting light, e.g., fluorescently emitted light, from the substrate, usually in the visible wavelength range, as described above. Any convenient detector may be used, where suitable detectors include, but are not limited to, photodiodes, photomultipliers, photodetectors, phototransistors and the like. An imaging lens system may be associated with the detector, where such a system is designed to image light emitted from the substrate surface, in response to the light source, in an imaging plane alignable with the detector. The imaging system may also include a filter for selectively blocking illumination beam light reflected from the substrate surface. A microprocessor, operatively connected at least to the scanner motor, controls the movement and position of the mirror and the detector to receive digitized or analog detector signals related to light emission levels measured by the detector. In a typical scanning operation, the one or more illumination beams are scanned across the array surface, oftentimes simultaneously, exciting fluorescent light emission in each region of each scanned linear array where fluorescently labeled analyte is bound. The emitted light is imaged onto the detector and the intensity of such light emission is measured. The measured intensity associated with each region of the array is recorded and stored with the associated region. After an array has been completely scanned, an output map may be generated, typically automatically by the scanner, which shows the light intensity associated with each region in the array. The output may also include the identity of the molecular species at which fluorescence signal was observed or analyte sequencing information. Calibration Devices As noted above, the invention provides devices used for calibrating an optical scanner, such as a biopolymeric array scanner as described above. More particularly, the invention provides devices used to calibrate the optical system""s scale factor (i.e., the sensitivity of the system""s optical detector), focus position (i.e., the distance between the system""s stage and lens(es), dynamic focus (i.e., the rate of speed the stage travels), the scanner mirror and to verify the system""s jitter. In general, the subject calibration devices include a substrate and a polymeric layer thereon, usually a single polymeric layer, but in certain embodiments is a plurality of layers, where the polymeric layer includes one or more fluorescent agents. The subject calibration devices may also include at least one region in the polymeric layer that is absent the fluorescent agent and in certain embodiments, the at least one region absent fluorescent agent is photobleached, as will be described in greater detail below. A variety of substrates, upon which the polymer layer is deposited, may be used with the invention, and the size and shape of the substrate and substrate surfaces, and the substrate material, will necessarily vary according to the particular optical scanner with which it is to be used. Substrates may be flexible or rigid. By flexible is meant that the support is capable of being bent, folded or similarly manipulated without breakage. Examples of solid materials which are flexible solid supports with respect to the present invention include membranes, flexible plastic films, and the like. By rigid is meant that the support does not readily bend, i.e. the support is inflexible. Both flexible and rigid substrates must provide physical support and structure for biopolymeric array fabrication thereon. The substrates may take a variety of configurations ranging from simple to complex. Thus, the substrate may have an overall slide or plate configuration, such as a rectangular, square or disc configuration. In many embodiments of the subject invention, the substrate will have a rectangular cross-sectional shape, having a length of from about 4 mm to 200 mm, usually from about 4 to 150 mm and more usually from about 4 to 125 mm and a width of from about 4 mm to 200 mm, usually from about 4 mm to 120 mm and more usually from about 4 mm to 80 mm, and a thickness of from about 0.01 mm to 5.0 mm, usually from about 0.1 mm to 2 mm and more usually from about 0.2 to 1 mm. The above dimensions are, of course, exemplary only and may vary as required. The substrates may be fabricated from a variety of materials. In many situations, a suitable substrate material will be transparent to visible and/or UV and/or infrared light. For flexible substrates, materials of interest include, for example, nylon, nitrocellulose, polypropylene, polyester films, such as polyethylene terephthalate, polymethyl methacrylate or other acrylics, polyvinyl chloride or other vinyl resin, and the like. Various plasticizers and modifiers may be used with polymeric substrate materials to achieve selected flexibility characteristics. For rigid substrates, specific materials of interest include: silicon; glass; rigid plastics, e.g. polytetrafluoroethylene, polypropylene, polystyrene, polycarbonate, and blends thereof, and the like; metals, e.g. gold, platinum, and the like; etc. As described above, at least one polymeric layer, usually a single polymeric layer such as a thin monolayer (or in certain embodiments a plurality of such layers), having at least one fluorescent agent or moiety (i.e., in those embodiments having more than one layer each layer has at least one fluorescent agent) is layered or coated on a surface of the substrate, typically deposited over substantially the entire area of a surface of the substrate. (The terms xe2x80x9cfilmxe2x80x9d and xe2x80x9ccoatingxe2x80x9d herein mean a layer of polymeric material positioned in association with a surface. The term xe2x80x9clayerxe2x80x9d thus encompasses both xe2x80x9ccoatingxe2x80x9d and xe2x80x9cfilmxe2x80x9d.) A variety of polymers may be used, where such a polymer will typically be rigid, thermally stable, photo non-reactive, non-fluorescent, chemically resistant and substantially transparent across the wavelength region of interest. Representative materials suitable for use include, but are not limited to, acrylates such as polyacrylates, polymethyl-methacrylate, polyacrylamide, polyacrylic acid, epoxides such as polyglycidoxyether polyethylene oxide, polyprolyleneoxide, urethanes such as various polyurethanes, and may also include polycarbonates, polyolefins, polyetherketones, polyesters, polystyrenes, polyethylstyrene, polysiloxanes, and the like, and copolymers thereof. The polymer coating has a substantially uniform thickness, i.e., the thickness of the polymer layer does not vary significantly across its area, but rather is substantially constant. By significantly is meant that the deviation in the thickness across the area of the polymer layer is usually less than about 0.05% to about 20% and more usually less than about 0.1% to about 10%. More particularly, the thickness of the polymer layer usually ranges from about 0.25 microns to about 10 microns, usually from about 0.40 microns to about 7 microns and more usually from about 0.40 microns to about 1 micron with a deviation of less than about 0.05% to about 20% and more usually with a deviation of less than about 0.1% to about 10%. It will be apparent that using a confocal optical system enables use of such minimal polymer layer thicknesses. The polymer coating may be formed by any convenient method, including, but not limited to, draw coating, roller coating, electrocoating, dip coating, spin coating, spray coating, or any other suitable coating technique wherein a solution or suspension of the polymer is deposited on the substrate surface, where spin coating is of particular interest. Oftentimes, deposition of the polymer layer will be followed by drying via vacuum, forced air oven, convection oven, or other drying technique. As mentioned above, a feature of the polymer layer (i.e., each polymer layer if more than one layer used) is the presence of at least one fluorescent agent or moiety, where in many embodiments at least two fluorescent agents or more are used, for example three, four or more fluorescent agents may be employed. By fluorescent agent is meant any dye, pigment or the like capable of emitting radiation or fluorescence in response to radiation excitation thereof. Typically, the radiation or light absorbed and emitted from the fluorescent agent, i.e., the response radiation, (the wavelength of the response radiation) is chosen to be in the portion of the electromagnetic spectrum to which a photomultiplier tube of the optical scanner is sensitive. Usually, the light absorbed and emitted from the fluorescent agent is in the ultraviolet, visible or infrared regions, but may include other wavelengths as well if appropriate. The particular fluorescent agent(s) used may vary depending on a variety of factors, where such factors include the particular optical scanner used, the probe or binding agent bound to the scanned substrate surface such as a biopolymer array, the excitation and/or response wavelength, and the like. The fluorophoric moieties or fluorophores of the fluorescent agents, may be cyclic, or polycyclic, particularly polycyclic, aromatic compounds having at least two rings, usually at least three rings and not more than six rings, more usually not more than five rings, where at least two of the rings are fused and in certain embodiments at least three of the rings are fused, where usually not more than four of the rings are fused. The aromatic compounds may be carbocyclic or heterocyclic, particularly having from one to three, more usually one to two nitrogen atoms as heteroannular atoms. Other heteroannular atoms may include oxygen and sulfur (chalcogen). The rings may be substituted by a wide variety of substituents, which substituents may include alkyl groups of from one to six carbon atoms, usually from one to two carbon atoms, oxy, which includes hydroxy, alkoxy and carboxy ester, generally of from one to four carbon atoms, amino, including mono- and disubstituted amino, particularly mono- and dialkyl amino, of from 0 to 8, usually 0 to 6 carbon atoms, thio, particularly alkylthio from 1 to 4, usually 1 to 2 carbon atoms, sulfonate, including alkylsulfonate and sulfonic acid, cyano, non-oxo-carbonyl, such as carboxy and derivatives thereof, particularly carboxamide or carboxyalkyl, of from 1 to 8 or 1 to 6 carbon atoms, usually 2 to 6 carbon atoms and more usually 2 to 4 carbon atoms, oxo-carbonyl or acyl, generally from 1 to 4 carbon atoms, halo, particularly of atomic number 9 to 35, etc. Specific fluorescent agents of interest include at least one of, but are not limited to: xanthene dyes, e.g. fluorescein and rhodamine dyes, such as fluorescein isothiocyanate (FITC), 2-[ethylamino)-3-(ethylimino)-2-7-dimethyl-3H-xanthen-9-yl] benzoic acid ethyl ester monohydrochloride (R6G)(emits a response radiation in the wavelength that ranges from about 500 to 560 nm), 1, 1, 3, 3, 3xe2x80x2, 3xe2x80x2-Hexamethylindodicarbocyanine iodide (HIDC) (emits a response radiation in the wavelength that ranged from about 600 to 660 nm), 6-carboxyfluorescein (commonly known by the abbreviations FAM and F),6-carboxy-2=,4=,7=,4,7-hexachlorofluorescein (HEX), 6-carboxy-4xe2x80x2, 5xe2x80x2-dichloro-2xe2x80x2, 7xe2x80x2-dimethoxyfluorescein (JOE or J), N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-6-carboxyrhodamine (TAMRA or T), 6-carboxy-X-rhodamine (ROX or R), 5-carboxyrhodamine-6G (R6G5 or G5), 6-carboxyrhodamine-6G (R6G6 or G6), and rhodamine 110; cyanine dyes, e.g. Cy3, Cy5 and Cy7 dyes; coumarins, e.g umbelliferone; benzimide dyes, e.g. Hoechst 33258; phenanthridine dyes, e.g. Texas Red; ethidium dyes; acridine dyes; carbazole dyes; phenoxazine dyes; porphyrin dyes; polymethine dyes, e.g. cyanine dyes such as Cy3 (emits a response radiation in the wavelength that ranges from about 540 to 580 nm), Cy5 (emits a response radiation in the wavelength that ranges from about 640 to 680 nm), etc; BODIPY dyes and quinoline dyes. Specific fluorophores of interest include: Pyrene, Coumarin, Diethylaminocoumarin, FAM, Fluorescein Chlorotriazinyl, Fluorescein, R110, Eosin, JOE, R6G, HIDC, Tetramethylrhodamine, TAMRA, Lissamine, ROX, Napthofluorescein, Texas Red, Napthofluorescein, Cy3, and Cy5, etc. Where at least two or more are agents are used, any combination of suitable agents may be used, where particular combinations of interest include R6G, i.e., 2-[ethylamino)-3-(ethylimino)-2-7-dimethyl-3H-xanthen-9-yl] benzoic acid ethyl ester monohydrochloride and HIDC, i.e., 1, 1, 3, 3, 3xe2x80x2, 3xe2x80x2-Hexamethylindodicarbocyanine iodide; Cy3 (Indocarbocyanine) and Cy5 (Indodicarbocyanine); and other suitable combinations, where combinations of green and red dyes are of particular interest. A feature of the at least one fluorescent agent is that it is distributed substantially uniformly throughout the polymer. In other words, the at least one fluorescent agent is homogenously dispersed throughout the polymer such that the concentration of the fluorescent agent(s) is substantially constant throughout the polymer layer. For example, the at least one fluorescent agent is distributed throughout the polymer such that the ratio of % fluorescent agent to % polymer for any given area is substantially the same for all areas of the polymer layer. It will be apparent that if more than one fluorescent layer is used, all fluorescent agents employed will be distributed substantially uniformly throughout the polymer. Specifically, any variation in fluorescent agent distribution that is present typically does not exceed from about 1 ppm to 5000 ppm, usually does not exceed from about 100 ppm to 800 ppm and more usually does not exceed from about 150 ppm to 180 ppm, where such variation is determined by determining dye concentration prior to coating using fluorescent or absorption measurements employing typical laboratory instruments (e.g., Fluorimeter or UV/N spectrometer). The concentration of the fluorescent agent (i.e., the concentration of each fluorescent agent if there is more than one) may vary depending on the particular scanning detector to be calibrated, the type and/or number of fluorescent agents used, etc. However, typically, the final concentration of fluorescent agent will range from about 1 ppm to 5000 ppm, usually from about 100 to 500 ppm and more usually from about 150 to 200 ppm. It will be apparent that the fluorescent agent""s concentration is variable, depending on the final thickness of the polymeric coating, where such concentration is determined to provide approximately the same number of fluorescent molecule per unit area regardless of the coating thickness, e.g., a 50 micron film will have a 100 fold more fluorescent molecules than a film having a thickness of 0.5 microns. However, each fluorescent molecule""s concentration will be dependent on its efficiency, i.e., a dye with high quantum efficiency may have a lower concentration than a fluorescent molecule with a lower efficiency. In other words, the subject calibration devices have a consistent intensity in all wavelength ranges, rather than a consistent number of fluorophores. Another feature of the subject calibration devices is that the local and global fluorescence variations are minimal, i.e., the local and global nonuniformities are minimal. By local variations or nonuniformities is meant that the light emitted from each pixel in a certain area or region, (pixel size ranges from about 2 to 15 microns) i.e., the number of photons detected in each pixel of the calibration device is substantially the same or constant, where it will be obvious that the exact local and global variation or nonuniformity requirement of the intensities of light emitted may vary depending on a variety of factors such as the specific device to be calibrated and the like. In general, the local and global nonuniformities are minimized to a degree sufficient to enable calibration, as described below, of the particular optical scanner employing the subject device. In regards to local nonuniformities, in certain embodiments of the subject device the difference or deviation between the response radiation or light emitted from each pixel in a certain area of the subject device is typically less than about 5%, usually less than about 2.5% and more usually less than about 1%. Usually, the local nonuniformity is based upon a local area having about 5 to 10 pixels, usually about 7 to 9 pixels, where each pixel ranges in size from about 2 to 15 microns, usually from about 4 to 12 microns and usually from about 5 to 10 microns. As such, the response radiation or number of photons emitted from a first pixel is substantially the same as the number of photons emitted from each of five to ten substantially adjacent pixels. In other words, the quantity of light emitted from between about five to ten substantially adjacent pixels will have minimal variation or nonuniformty, i.e., the variation is typically be less than about 5%, usually less than about 2.5% and more usually less about 1%. The global variation or nonuniformity is similarly minimal. By global variation or nonuniformity is meant a statistically relevant value (mean, median, etc.) corresponding to all or substantially all of the individual local variations of the entire calibration device. As noted above, the exact global nonuniformity requirement may vary depending on a variety of factors. In certain embodiments, the global nonuniformity is typically less than about 5%, usually less than about 3.5% and more usually less than about 2.5%. In other words, the quantity of light emitted from each local area will be substantially the same as or similar to the quantity of light emitted from each other local area, i.e., the variation or nonuniformity is typically less than about 5%, usually less than about 3.5% and more usually less than about 2.5%. As described above, the calibration devices of the subject invention may also include at least at least one region in the polymeric layer that is absent fluorescent agent. By absent is meant that there is less than about 5% of the molar amount of fluorescent agent in active form (i.e., the molar amount of fluorescent agent that fluoresces), usually less than about 2% the molar amount of fluorescent agent in active form. The at least one region absent fluorescent agent may thus include photobleached regions and/or background regions, as will be described below. As mentioned, the subject devices may include one or more photobleached region or feature. In other words, a photobleached region is typically a region made of a material that includes a bleached fluorescent agent(s), where such bleaching reduces or attenuates the fluorescence of the fluorescent agent(s) by at least about 40% to 60%. For example, the at least one photobleached region or feature will usually be made of the same polymer material and fluorescent agent(s) used to produce the polymeric calibration layer, i.e., the fluorescently dispersed polymer layer described above. Generally, the calibration device will include a plurality of such photobleached regions or features positioned in predetermined locations on the surface of the device. For example, on a calibration device having a width of about 25 mm and a length of about 75 mm, about 1 to 5000 photobleached regions may be positioned in various locations, more typically about 200 to 750 photobleached regions may be positioned in various locations. Usually, a photobleached region has a size substantially equal to the size of about 1 to 3 pixels in at least one dimension on the device. More specifically, where the photobleached regions or features are rectangular, typically the length ranges from about 175 to 225 microns, usually from about 190 to 210 microns and the width typically ranges from about 5 to 15 microns, usually about 7 to 9 microns and, for an example having about 1000 features on a 25 mm by 75 mm calibration device, about 250 to 270 of these features are positioned horizontally and about 670 to 690 of these features are positioned vertically. The subject devices may also include one or more background areas or features, as mentioned above. The one or more background area is an area or region that is outside of the calibration area, i.e., an area that does not include fluorescent agents (whether photobleached or not), i.e., that is absent fluorescent agent. Usually, a background region will be a region of the calibration device off of the surface of the device, i.e., not on the surface of the device, e.g., one or more edges of the substrate of the calibration device, negative space such as air space, and the like. As summarized above, the subject invention also provides methods for calibrating an optical scanner. More specifically, methods are provided for calibrating an optical system associated with an optical scanner and in particular a biopolymeric array optical scanner. In general, a surface is illuminated with at least one light source, e.g., the surface of the calibration device described above. In other words, the polymeric layer having at least one fluorescent agent or moiety dispersed therethrough and having minimal local and global nonuniformities is illuminated with at least one light source and fluorescent data from the surface is obtained. Oftentimes, the calibration device is positioned on the support stage or the like such that the substrate side of the device (as distinguished from the polymeric coated side) is faced up. In other words, light is directed first through the substrate side of a subject calibration device. An optical system is then confirmed (in other words no adjustments are made) or the system is adjusted or calibrated based upon this obtained fluorescence data. By adjusted or calibrated is meant that one or more of the following is confirmed and/or adjusted: (1) scale factor (i.e., the sensitivity of the optical detector is adjusted), (2) the focus position (i.e., the distance between the stage and one or more lenses of the system is adjusted), (3) the dynamic focus (i.e., the rate of speed the stage travels is adjusted), (4) the scanner mirror (i.e., the synchronicity of the light beams is adjusted), and (5) the jitter, where each of these will be discussed in greater detail below. Thus, the first step in all of the subject methods for calibrating or adjusting certain optical components of an optical scanning system is to illuminate a surface with at least one light source, and more particularly irradiate a surface with a source of excitation radiation, where the surface includes at least one fluorescent agent dispersed therethrough and which has minimal local and global nonuniformities. In other words, a surface, such as the fluorescently-infused polymer layer of the calibration device having minimal local and global nonuniformities, as described above, is irradiated with one or more light beams having specific wavelengths, where the one or more light beams are used to excite the one or more fluorescent agents associated with the surface being illuminated. It will be understood that unless otherwise noted, the surface scanned according to the methods described below is a non-photobleached area. That is, for the detector, lens, stage and mirror calibration methods, the area scanned does not include photobleached regions, i.e., either the calibration device does not include photobleached regions or such photobleached areas are not scanned or the data therefrom is not used in the subject methods to calibrate the optical detector, lens, stage and mirror. However, as will be described below, for the subject methods relating to jitter verification, the area(s) scanned are photobleached areas. As mentioned above, in many embodiments, the light is directed through the substrate side of the calibration device first, i.e., light is directed through the substrate and then to the polymeric layer. More specifically, a calibration device is provided having a polymer coating having at least one fluorescent agent therein and minimal local and global fluorescence variations, i.e., the local and global nonuniformities are minimal, such as a calibration device described above. As noted above, by local variations or nonuniformities is meant that the light emitted from each pixel in a certain area or region, (pixel size ranges from about 2 to 15 microns) i.e., the number of photons detected in each pixel of the calibration device is substantially the same or constant. More specifically, the difference or deviation between the response radiation or light emitted of pixels of the subject device is typically less than about 5%, usually less than about 2.5% and more usually less than about 1%. Usually, the local variation is based upon a local area having about 5 to 10 pixels, usually about 7 to 9 pixels, where each pixel ranges in size from about 2 to 15 microns, usually from about 4 to 12 microns and usually from about 5 to 10 microns. As such, the response radiation or number of photons emitted from a first pixel is substantially the same as the number of photons emitted from each of five to ten substantially adjacent pixels. In other words, the quantity of light emitted from between about five to ten substantially adjacent pixels will have minimal variation, i.e., the variation is typically be less than about 5%, usually less than about 2.5% and more usually less about 1%. The global variation or nonuniformity is similarly minimal. As described above, by global variation or nonuniformity is meant a statistically relevant value (mean, median, etc.) corresponding to all or substantially all of the individual local variations of the entire calibration device. Typically, the global variation is less than about 5%, usually less than about 3.5% and more usually less than about 2.5%. In other words, the quantity of light emitted from each local area will be substantially the same as or similar to the quantity of light emitted from each other local area, i.e., the variation is typically less than about 5%, usually less than about 3.5% and more usually less than about 2.5%. Each light source will typically produces a coherent light beam, e.g., the light source will typically be a laser light source, and the like. More typically, the light sources will include two laser light sources or produce two different beams of light (i.e., beams of light of two different wavelengths, e.g., a red laser light source and a green laser light source. Typically, each light beam having an excitation wavelength that is within the ultraviolet, visible or infrared spectrum illuminates the surface of the calibration device described above. In general, the at least one light beam illuminates the surface with light of a selected wavelength, where the selected wavelength is usually at or near the absorption maximum of the particular fluorescent agent being illuminated or excited. Illuminating or exciting a fluorescent agent at such a wavelength produces the maximum number of photons emitted at the emission wavelength. In certain embodiments of the subject methods, light beams from at least two light sources are used, where the light beams from the various light sources are of different wavelengths, each source usually corresponding to fluorescent excitations of the different fluorescent agents being illuminated and excited. In other words, the wavelengths of the light beams are at or near the absorption maximum of the fluorescent agents illuminated. For example, light from a first light source illuminates the surface with light in a wavelength ranging from about 500 to 560 nm corresponding to the fluorescence excitation of about 500 to 560 nm of a first fluorescent agent, e.g., of 2-[ethylamino)-3-(ethylimino)-2-7-dimethyl-3H-xanthen-9-yl] benzoic acid ethyl ester monohydrochloride, and light from a second light source illuminates the surface with light in a wavelength ranging from about 600 to 660 nm corresponding to the fluorescence excitation of about 600 to 660 nm of a second fluorescent agent, e.g., 1, 1, 3, 3, 3xe2x80x2, 3xe2x80x2-Hexamethylindodicarbocyanine iodide. Where more than one light source is used, the light sources may illuminate the surface at the same or different time, but usually the light sources will illuminate the surface simultaneously. A feature of the subject methods is that substantially the entire surface (excluding the photobleached regions, if present, as mentioned above) is illuminated by the at least one light source. By substantially entire surface is meant that almost the total surface area is illuminated, where such an illumination area may be as great as about 70% of the entire surface area, usually as great as about 75% of the entire area and more usually as great as about 80% of the entire area is illuminated. In other words, usually one or more light beams are swept or rastered across a substrate surface, as opposed to simply illuminating one discrete region. For example, in those embodiments using a calibration device as described above, e.g., a 25 mm by 75 mm calibration device, one or more light beams will usually scan or raster over an area having a width ranging from about 10 to 30 mm, usually about 15 to 25 mm and a length ranging from about 50 to 70 mm, usually from about 55 to 65 mm. In those embodiments where the calibration device has dimensions of about 22 mm by 22 mm, one or more light beams will usually scan or sweep over an area having a width ranging from about 10 to 20 mm, usually about 15 to 20 mm and a length ranging from about 10 to 20 mm, usually from about 15 to 20 mm, where such illumination usually occurs in a predefined pattern, oftentimes in a linear pattern. The surface may be illuminated by more than one light source at the same or different times. In other words, a surface or a region of the surface may first be illuminated by a first light source and then subsequently illuminated by a second light source. Usually, a two color, simultaneous illumination or scan of a 25 mm by 75 mm surface usually is performed in about 5 to 10 minutes and more usually in about 7 to 9 minutes. Once substantially the entire surface has been excited by one or more light sources, the next step is to detect fluorescence from the surface. More specifically, data are acquired from the surface, where such data corresponds to the light emitted, i.e., the intensity of light emitted, from the at least one fluorescent agent associated with the surface. Thus, one or more fluorescent agents are excited by the illumination from the one or more light beams, where each fluorescent agent emits light of a certain wavelength, at a certain intensity. The intensity of light emitted from each pixel is detected and measured by an optical detector such as a photomultiplier tube (PMT) or the like, where the PMT generates a current proportional to the number of photons that reach it. The PMT typically generates a current ranging from about 500 nanoamps to 50 microamps within its range of operation, more usually from about 1 microamp to 10 microamps. Output from the detector is used to calibrate the detector, or make certain other optical system adjustments, as will be described below, where the adjustments may be made manually or automatically, for example by an operatively associated microprocessor. As mentioned above, each of the methods described below can be utilized separately or in any combination during the scanner optimization process, however they may be interrelated, as will be apparent to one of skill in the art. 1. Scale Factor Calibration As described above, data from the above described scanning method may be used to calibrate the scale factor of the optical system, i.e., used to verify the sensitivity of the optical detector of the system and, if necessary, calibrate or adjust the sensitivity of the detector. As such, following the above described scan of the calibration device, an empirical calibration value is calculated based upon the intensity of the signal, where such a calibration value is defined as the number of photons in a pixel to fluorophores per square micron. Thus, current corresponding to the intensity of light emitted per pixel is converted to digital counts and such counts are used to determine a calibration value for the respective optical detector. This empirically derived calibration value and corresponding digital signal are then compared to a reference calibration value/signal function. In other words, the empirically derived calibration value/signal is compared to a predetermined or reference value that is a function dependent upon the particular fluorescent agent used, the type of optical detector employed, the area of the pixel, and the like. The optical system""s gain is then adjusted in response to this comparison. In other words, the gain is adjusted to more closely approximate the reference calibration value. The values obtained from a single calibration device may be used to calibrate a plurality of optical systems or scanners in parallel. More specifically, a detector such as a photomultiplier tube is used to detect the intensity of the light emitted from the one or more fluorescent agents, where such intensity is in the form of a voltage measurement. Such intensity is relayed to a microprocessor, i.e., a microprocessor operatively associated with the optical scanner containing the detector, where such a microprocessor is under the control of a software program and carries out all of the steps necessary to determine if the detector is within specification or if it needs adjustment. The microprocessor may also performs the steps necessary to adjust the detector. The detector is calibrated or adjusted by altering the voltage of the detector, where the voltage determines the sensitivity of the detector. In other words, an empirical calibration value is determined according to the method described above, i.e., the signal from the PMT operated at a known voltage is obtained, and this empirical value is compared to a reference or standard value. If the voltage relating to the empirical calibration value is different, i.e., substantially or significantly differs, from the reference or predetermined voltage, the sensitivity or voltage of the detector is altered to change the response of the detector. For example, a typical photomultiplier response is shown in FIG. 1. FIG. 1 shows an x-y graph having photomultiplier sensitivity values or response (defined as photons per fluorophores, where the photons counted are typically normalized to fluorescent molecules as opposed to area) on the y-axis and voltage on the x-axis. A typical plot is represented by a line having an increasingly positive or ascending slope. Thus, a mathematical function described by this calibration curve value and corresponding voltage can be derived and which allows extrapolation of the proper response for the calibrated detector. The photomultiplier voltage, i.e., sensitivity, is adjusted if the signal from the photomultiplier is different from the optimum signal. The calibration is complete for the detector when the relationship between the extrapolated value and the real values are within a certain range, for example less than a certain predetermined percentage, such as 1%, etc. 2. Focus Position Calibration In addition to, or independent of, the above described methods for calibrating the scale factor of the system, methods for calibrating or adjusting the one or more scanning stages (i.e., the distance between the scanning stage and an optical lens) of an optical scanner are also provided so as to adjust the focus position of the laser(s) relative to the surface of a scanned object, i.e., adjust the stage position to optimize the intensity of the light detected, where such intensity may not correspond to the maximum of the fluorescence signal collected. FIG. 3 illustrates the subject method, whereby a laser beam is illuminated or directed through a lens to a focus position. Thus, in certain embodiments of the subject methods, the focus position of the optical system is evaluated and adjusted, if necessary. In other words, the depth of the focus of the illuminated light is verified and/or adjusted to an optimal focus position such that at such an optimal position or distance, the intensity of light from one or more channels, as measured by the detector, will be optimized and have the qualities necessary for an optimum scan, e.g., minimal noise in an optimum two color scan. It will be apparent that the device, i.e., the calibration device, used to check and/or adjust the focal position must have minimal local and global nonuniformities so that the intensities detected and measured are a function of the focal position, and not the variation in the scanned device, i.e., the area scanned must be able to provide a consistent signal. Thus, after the provision of a calibration device having a polymer coating with at least one fluorescent agent associated therewith and local nonuniformities of less than about 5%, usually less than about 2.5% and more usually less about 1% and global nonuniformities of less than about 5%, usually less than about 3.5% and more usually less than about 2.5%, the calibration device is scanned with at least one light source, as described above, at various depths. That is, the light beam will scan the surface of the calibration device, where a number of different focal positions are used to scan the surface. As will be apparent, the scanned area must be of sufficient proportion to enable acquisition of consistent signal. More specifically, scanning a small, localized area over a significant period of time, i.e., an amount of time necessary to scan at various focus depths, may result in the fluorescence fading in a particular scanned area, thus yielding unreliable signals. As such, an area of the calibration device of about 5 mm to about 20 mm, usually about 10 mm to about 100 mm and more usually about 20 mm to about 60 mm is scanned by at least one light source, usually two light sources such as a red laser and a green laser, as described above, where such a scan typically takes from about 4 minutes to about 18 minutes, usually from about 6 minutes to about 12 minutes and more usually from about 6 minutes to about 8 minutes. After the area has been scanned at various depths, i.e., various focal positions, the focal position providing the optimum signal is selected, and the distance between the optical or focusing lens and the scanning stage is calibrated or adjusted to provide the optimum focal depth, where such a focal distance is then stored in the optical system""s memory, i.e., stored in a microprocessor operatively associated with the optical system, such that the optical system will scan subsequent devices at this focal distance. In other words, an optimal focus depth is determined based upon the above described scan and the position of the fluorescent coated surface relative to the scanning lenses of the optical system, i.e., the distance between the stage and lens(es), is then adjusted by adjusting the position of the scanning stage to correspond to this optimal configuration to provide the optimum scanning depth for subsequent scans, e.g., subsequent biopolymeric array scans. 3. Dynamic Focus Calibration Methods are also provided for verifying and/or calibrating or tuning the dynamic focus of the scanning light beams, i.e., adjusting the rate at which the optical stage travels, of an optical scanning device, where such a stage is configured to provide a platform or area onto which a scanned object such a biopolymeric array may be placed during a scanning procedure. The stage aligns the scanned object in a certain position to correspond with the scanning light beam(s). That is, in use, the stage is moved to align an optical system or scanning plane to correspond to an area of the scanned object to be scanned such as a certain linear array area on a substrate. Thus, it will be apparent that the focus of the system is dependant upon certain stage parameters associated with the optical stage such as the rate of movement of the stage, etc. For example, if the stage is moved too quickly or is out of alignment, the scan will be out of focus. As mentioned above, the first step in the subject methods for verifying and/or adjusting the rate of speed of a stage of an optical system is to provide a device having minimal local and global nonuniformities, as described above. After the provision of the above described calibration device, a series of horizontal scan lines or planes are scanned by at least one light source, typically two, as noted above. Next, the oscillation of the detected intensity image of these scanned horizontal planes is measured. More specifically, the oscillation over about 75 to 100 pixels, usually over about 90 to 110 pixels and more usually over about 95 to 105 pixels is measured. If the oscillation is less than about 0.15%, usually if it is less than about 0.1%, no adjustments to the rate of speed of the stage is made. If the oscillation is greater than about 0.15%, usually if it is greater than about 0.1%, the rate of speed of the stage is adjusted, i.e., the rate is increased or decreased so as to optimize the focus of the system, where such a rate of speed is then stored in the optical system""s memory, i.e., stored in a microprocessor operatively associated with the optical system, such that the optimum rate of movement of the stage will be fixed at this adjusted rate for subsequent scans. 4. Scanner Mirror Calibration Methods are also provided for verifying and calibrating one or more optical or scanner mirrors associated with the optical system, as described above, where such scanning mirrors are used to direct one or more light sources to a focus lens of the optical system, as described above, typically by pivoting the mirrors to position the light beam(s) to optimize the associated response. As mentioned above, in a two color scan, i.e., a scan using more than one light source or beam, e.g., a red laser and a green laser, typically the two lasers scan or raster a scan area simultaneously, or alternatively the surface is moved in a controlled manner with a motorized stage. Thus, the scanner mirrors, which dictate the alignment and positioning of the laser beams, must be synchronized to enable such a simultaneous scan, i.e., the scanning mirrors must direct the two lasers to substantially the same location at the substantially same time. FIG. 2 show exemplary response curves related to the alignment of laser light, by adjusting the alignment of the two beams, the focus depth for the two channels is optimized at a value that gives the lowest noise such as depicted in FIG. 2 as the region of overlap of the two channels. Synchronicity or calibration of the scanner mirrors according to the subject invention is thus accomplished by scanning a device having minimal local and global nonuniformities and evaluating the relationship between the intensity profiles or scan images of the different lasers and comparing the relationship of the scans to a predetermined relationship. In other words, where a green laser and a red laser are used for a simultaneous scan, an optimum scan, as it relates to the scanner mirrors, can be characterized by evaluating the relationship between the location of the green channel fluorescent peak and the red channel fluorescent peak. For example, the response at specific focus positions for a first laser and a second laser, such as a red and green laser, is evaluated and compared to a predetermined relationship. As FIG. 2 shows, the overlap between a first channel and a second channel, such as a red channel and a green channel, is optimized at a certain point or focus depth, so as to produce a scan with minimal noise. Thus, the beams or peak positions are adjusted by rotating or translating the mirror(s) in the laser beam path, where this alignment is a function of the focus position/response generated by the above described method, which is compared to a predetermined relationship and adjusted based upon any deviation from such a predetermined relationship. More specifically, if the lasers are not synchronized, i.e., out of alignment, the relationship of the channels differs from a predetermined relationship and are adjusted to approximate the predetermined relationship. Accordingly, a device having minimal local and global nonuniformities, i.e. a calibration device as described above, is provided and scanned with at least two light sources, typically having different wavelengths, e.g., two laser light sources such as a red laser and a green laser, where such methods for scanning such a device with two light sources is described above and will not be repeated here. After the calibration device is scanned by the two light sources, e.g., a red laser light source and a green laser light source, the intensity profiles for each color scan is evaluated. That is, the relationship between the two color scans is determined and compared to a predetermined relationship, where such a predetermined relationship is based upon a variety of factors such as the wavelengths of the two laser light sources (red and green as used herein), the time of the scan, the size of the area scanned, and the like. Specifically, the location of a first channel peak or maximum intensity, such as a green channel peak, is determined and the location of a second channel peak or maximum intensity, such as a red channel peak, is determined, where the relationship between the locations of the two peaks is evaluated and compared to a predetermined channel peak relationship. The change or deviation from the predetermined relationship is a manifestation of the lateral movement of the laser beam across the rigidly fixed focusing lens. If the relationship is substantially similar to the predetermined relationship, no adjustments to the scanning mirrors are made. If, however, the relationship substantially differs from the predetermined relationship, adjustments to one or more mirrors are made, i.e., the direction or pivotal motion of one or more mirrors is adjusted. If adjusted, the adjusted configuration of the one or more mirrors is fixed, at the adjusted configuration for subsequent scans. 5. Jitter Verification Also provided are methods for verifying the jitter of an optical scanner. More specifically, methods are provided for verifying the jitter of an optical system associated with an optical scanner and in particular a biopolymeric array optical scanner. By jitter is meant the time interval between each successive pulse in a pulse train. In other words, a pulse train of the above described light sources, i.e., laser light sources, should have minimal jitter between the pulses so that in a scan using more than one light source, i.e., more than one light beam for example a red laser and a green laser, the beams reach the scan surface simultaneously (i.e., the red and green channels are synchronized). In such a method, the jitter is typically verified or confirmed to be in a particular acceptable range, where such a range will not substantially interfere with the performance or imaging of the optical scanner. In other words, the jitter is usually not adjusted, but rather confirmed or verified to be suitable. The calibrations, alignments and focusing methods outlined above determine the associated jitter in the scanning instrument. In other words, jitter is a function at least of the alignment or calibration of the optical system""s other optical components (described above) and thus if jitter is found to be out of specification, one or more of the above described methods for calibrating the optical system is employed to make the appropriate adjustment(s) to the system. Following such adjustments, the jitter is again verified or confirmed. In this particular method for verifying the jitter of an optical system or rather the deviation in jitter between two channels, a device having a pattern of photobleached regions is provided, such as the calibration device described above having one or more photobleached regions. In other words, a calibration device having a polymer coating with one or more fluorescent agents bleached in a pattern, for example bleached from a first calibration device edge to a second calibration device edge, or the like, to produce one or more photobleached regions or features is employed to verify the jitter of an optical system. The calibration device is scanned by two light sources, e.g., a red laser and a green laser. More particularly, a pattern of photobleached areas is scanned simultaneously by a red laser and a green laser. As mentioned above, the mechanical stage directs or moves the calibration device into the appropriate focusing position to align the area to be scanned with the scanner light beams. Thus, once positioned, the photobleached area(s) are scanned and an intensity profile for each channel is produced. In other words, an intensity profile including the channel peaks or maximum wavelength intensity is produced for both the red and green channels. The relationship between the red channel peak and the green channel peak is analyzed, where such a relationship generated by the simultaneous scanning of photobleached areas is a function of the jitter of the optical system, i.e., is dependent on the amount of jitter in each pulse train. The relationship is compared to a predetermined value or standard to determine the amount of deviation of jitter in the optical system relative to the standard. In other words, the amount of jitter of the optical system is determined by scanning the photobleached patterns of the subject devices. The optical system is determined to be suitable for use, i.e., the scanning lasers are capable of scanning a device such as a biopolymeric array substantially simultaneously, if the jitter is less than a certain predetermined jitter value or standard. That is, the time between pulses in each pulse train are substantially synchronized such that a simultaneous scan using the above tested lasers, i.e., red and green lasers, is verified. As mentioned, if the jitter substantially deviates from the predetermined value, the system is calibrated using one or more of the above described methods for calibrating certain optical components of the scanner""s optical system, e.g., dynamic focus calibration, and the jitter is then again verified. Background Signal Subtraction The subject invention also includes background subtraction methods for subtracting a value from the emitted fluorescence values, where such subtracted value corresponds to background signal. By background signal is meant the amount of signal generated from one or more non-fluorescent areas. Background signal may be a function of the xe2x80x9cnoisexe2x80x9d of the optical scanner, the polymeric material, the substrate material, particular solutions, electronic noise, reflections or scattering from surface or particles, and the like. Thus, the background signal is determined, where the background signal is defined as signal generated from outside of the calibration area, i.e., does not include fluorescent agents (whether photobleached or not). Usually, a background region will be a region of the calibration device off of the surface, i.e., not on the surface, of a calibration device being scanned, e.g., one or more edges of the substrate of the calibration device, negative space such as air space, and the like. Accordingly, the signal from a background area is detected by an optical detector and is calculated, usually as a statistically relevant value. In certain embodiments, the background signal will be predetermined and stored in the memory of an optical system. Regardless of whether the background signal is determined or predetermined, the background signal is then subtracted from the value corresponding to the intensity of light emitted from the fluorescent calibration regions (photobleached and/or non-photobleached areas) on the calibration device. The final value represents a background corrected signal corresponding to the intensity of light per pixel due to the fluorescent agent. Also provided by the subject invention are methods for calibrating an optical scanner and subsequently using the calibrated scanner to scan an array, more specifically a biopolymeric array, e.g., a nucleic acid array. More specifically, in the subject methods, an optical scanner is calibrated, i.e., a detector, a lens, a stage and/or a mirror of an optical scanner is adjusted, an array is provided and a hybridization assay is performed with the array and one or more samples or agents of interest. The hybridized array is then optically scanned by the calibrated scanner, where such steps may be performed serially or simultaneously. Accordingly, an optical scanner, e.g., a biopolymeric array optical scanner, is calibrated. More specifically, one or more of the following is confirmed and/or adjusted: (1) scale factor (i.e., the sensitivity of the optical detector is adjusted), (2) the focus position (i.e., the distance between the stage and one or more lenses are adjusted), (3) the dynamic focus (i.e., the rate of speed the stage travels is adjusted), (4) the scanner mirror (i.e., the synchronicity of the light beams is adjusted), and (5) the jitter, as described above. In other words, generally, a calibration device is illuminated with at least one light source, e.g., the calibration described above, in other words the polymeric layer having at least one fluorescent agent or moiety dispersed therethrough and having minimal local and global nonuniformities, is illuminated with at least one light source, and fluorescent data from the calibration device is obtained, where such data may include subtracting background values therefrom, as mentioned above. In one embodiment, the scale factor of the optical system is calibrated, i.e., an optical detector is confirmed (in other words no adjustments are made) or the detector is adjusted or calibrated based upon this obtained fluorescence data. By adjusted or calibrated is meant that the sensitivity and/or resolution of the detector is altered depending on the obtained fluorescent data. In addition to, or in place of the above described detector sensitivity calibration, one or more other optical components of the system are confirmed and/or calibrated or adjusted. For example, the focus position, dynamic focus and scanner mirror may be confirmed and/or adjusted, where such methods are described above. In certain embodiments of the subject methods, the jitter of the optical scanner is verified or confirmed by scanning a pattern of photobleached regions or features, e.g., by scanning the photobleached regions of the above described calibration devices, where such methods are described above. As mentioned above, an array is provided and a hybridization assay is performed to bind certain analytes or agents of interest, i.e., labeled analytes or agents (fluorescently labeled), to the array, or more specifically to certain polymeric binding agents or probes which make up an array. The subject arrays include at least two distinct polymers that differ by monomeric sequence covalently attached to different and known locations on the substrate surface. Each distinct polymeric sequence of the array is typically present as a composition of multiple copies of the polymer on a substrate surface, e.g. as a spot on the surface of the substrate. The number of distinct polymeric sequences, and hence spots or similar structures, present on the array may vary, but is generally at least 2, usually at least 5 and more usually at least 10, where the number of different spots on the array may be as a high as 50, 100, 500, 1000, 10,000 or higher, depending on the intended use of the array. The spots of distinct polymers present on the array surface are generally present as a pattern, where the pattern may be in the form of organized rows and columns of spots, e.g. a grid of spots, across the substrate surface, a series of curvilinear rows across the substrate surface, e.g. a series of concentric circles or semi-circles of spots, and the like. The density of spots present on the array surface may vary, but will generally be at least about 10 and usually at least about 100 spots/cm2, where the density may be as high as 106 or higher, but will generally not exceed about 105 spots/cm2. In the broadest sense, the arrays of the subject invention are arrays of polymeric binding agents, where the polymeric binding agents may be any of: peptides, proteins, nucleic acids, polysaccharides, synthetic mimetics of such biopolymeric binding agents, etc. In many embodiments of interest, the arrays are arrays of nucleic acids, including oligonucleotides, polynucleotides, cDNAs, mRNAs, synthetic mimetics thereof, and the like. The biopolymeric arrays of the subject invention may be produced by a number of different methods, where such methods are known to those of skill in the art. The arrays scanned according to subject methods find use in a variety applications, where such applications are generally analyte detection applications, as mentioned above, in which the presence of a particular analyte in a given sample is detected at least qualitatively, if not quantitatively. Protocols or hybridization techniques for carrying out such assays are well known to those of skill in the art and need not be described in great detail here. Generally, the sample suspected of comprising the analyte of interest is contacted with an array produced according to the subject methods under conditions sufficient for the analyte to bind to its respective binding pair member that is present on the array. Thus, if the analyte of interest is present in the sample, it binds to the array at the site of its complementary binding member and a complex is formed on the array surface. The presence of this binding complex on the array surface is then detected, e.g. through use of a signal production system, e.g. fluorescent label present on the analyte, etc. The presence of the analyte in the sample is then deduced from the detection of binding complexes on the substrate surface. Specifically, in hybridization assays, a sample of target nucleic acids or the like is first prepared, where preparation may include labeling of the target nucleic acids with a label, e.g., a member of signal producing system. Following sample preparation, the sample is contacted with the array under hybridization conditions, whereby complexes are formed between target nucleic acids that are complementary to probe sequences attached to the array surface. The presence of hybridized complexes is then detected. Specific hybridization assays of interest which may be practiced using the subject arrays include: gene discovery assays, differential gene expression analysis assays; nucleic acid sequencing assays, and the like. Patents and patent applications describing methods of using arrays in various applications include: WO95/21265; WO96/31622; WO97/10365; WO 97/27317; EP 373 203; and EP 785 280; and U.S. Pat. Nos. 5,143,854; 5,288,644; 5,324,633; 5,432,049; 5,470,710; 5,492,806; 5,503,980; 5,510,270; 5,525,464; 5,547,839; 5,580,732; 5,661,028; 5,800,992; the disclosures of which are herein incorporated by reference. In gene expression analysis with microarrays, an array of xe2x80x9cprobexe2x80x9d nucleic acids is contacted with a nucleic acid sample of interest. Contact is carried out under hybridization conditions and unbound nucleic acid is then removed. The resultant pattern of hybridized nucleic acid provides information regarding the genetic profile of the sample tested. Gene expression analysis finds use in a variety of applications, including: the identification of novel expression of genes, the correlation of gene expression to a particular phenotype, screening for disease predisposition, identifying the effect of a particular agent on cellular gene expression, such as in toxicity testing; among other applications. Once the hybridization assay has been performed, the array is then interrogated, i.e., scanned, rastered or read by an optical means calibrated according to the subject invention, to detect, i.e., qualitate and/or quantify, labeled analyte or agent bound to the array. As such, the calibrated optical means (in other words at least one light source and a calibrated scanner) then scans or xe2x80x9creadsxe2x80x9d the hybridized array. Thus, a biopolymeric array is exposed to a sample (for example, a fluorescently labeled polynucleotide or protein containing sample) and the array is then read using an apparatus calibrated according to the subject invention. Reading of the array may be accomplished by illuminating the array and reading the location and intensity of resulting fluorescence at each feature of the array. For example, a scanner, and more particularly a scanner calibrated according to the subject invention, may be used for this purpose which is similar to the GENEARRAY scanner available from Agilent Technologies, Palo Alto, Calif. Other suitable apparatus and methods are described in U.S. patent applications: Ser. No. 09/846125 xe2x80x9cReading Multi-Featured Arraysxe2x80x9d by Dorsel et al.; and Ser. No. 09/430214 xe2x80x9cInterrogating Multi-Featured Arraysxe2x80x9d by Dorsel et al. These references are incorporated herein by reference. More specifically, the hybridization array is placed in or on a calibrated optical scanner, i.e., is positioned in operative association with the calibrated optical means described above. Typically, a plurality of such hybridized arrays may be positioned in operative association with the calibrated optical means, for example a plurality may be indexed in an indexing means such as a carousel or the like, whereby each array is moved into a scanning position or is scanned by the optical means, followed by the scanning or reading of another array, i.e., an array positioned in an adjacent position in the indexing means to the previous scanned array. Regardless of the number of scanned arrays, an array is illuminated with at least one light source and the light emitted by each of the fluorescent labels thereon is detected by the calibrated detector. Specifically, a signal or voltage related to the presence and/or quantity of light emitted by the fluorescent labels is detected. Patents describing methods of optically detecting fluorescently labeled arrays include, but are not limited to: U.S. Pat. Nos. 5,631,734 and 5,981,956, the disclosures of which are herein incorporated by reference. Thus, it will be apparent that using the calibrated optical system to scan an array will result in more accurate and precise array scans. Results from the reading may be raw results (such as fluorescence intensity readings for each feature in one or more color channels) or may be processed results such as obtained by rejecting a reading for a feature which is below a predetermined threshold and/or forming conclusions based on the pattern read from the array (such as whether or not a particular target sequence may have been present in the sample). The results of the reading (processed or not) may be forwarded (such as by communication) to a remote location if desired, and received there for further use (such as further processing). In certain embodiments, as mentioned above, the subject methods include a step of transmitting data from at least one of the detecting and deriving steps, as described above, to a remote location. By xe2x80x9cremote locationxe2x80x9d is meant a location other than the location at which the array is present and hybridization occur. For example, a remote location could be another location (e.g. office, lab, etc.) in the same city, another location in a different city, another location in a different state, another location in a different country, etc. The data may be transmitted to the remote location for further evaluation and/or use. Any convenient telecommunications means may be employed for transmitting the data, e.g., facsimile, modem, Internet, etc. When one item is indicated as being xe2x80x9cremotexe2x80x9d from another, this is referenced that the two items are at least in different buildings, and may be at least one mile, ten miles, or at least one hundred miles apart. xe2x80x9cCommunicatingxe2x80x9d information references transmitting the data representing that information as electrical signals over a suitable communication channel (for example, a private or public network). xe2x80x9cForwardingxe2x80x9d an item refers to any means of getting that item from one location to the next, whether by physically transporting that item or otherwise (where that is possible) and includes, at least in the case of data, physically transporting a medium carrying the data or communicating the data. Finally, kits for use in calibrating optical scanners are provided. The subject kits at least include one or more calibration devices of the subject invention. Typically, a plurality of subject calibration devices is included. The kits may further include an optical scanner. The subject kits may also include one or more arrays. The kits may further include one or more additional components necessary for carrying out an analyte detection assay, such as sample preparation reagents, buffers, labels, and the like. As such, the kits may include one or more containers such as vials or bottles, with each container containing a separate component for the assay, such as an array, and reagents for carrying out nucleic acid hybridization assays according to the invention. Thus, the kit will comprise in packaged combination, an array, wherein the array comprises hybridization probes that selectively hybridize to the detectably labeled target nucleotide sequence, where such arrays may include background probes that do not selectively hybridize to the target nucleotide sequence. The kit may also include a denaturation reagent for denaturing the analyte, hybridization buffers, wash solutions, enzyme substrates, negative and positive controls and written instructions for carrying out the assay. Finally, the kits may further include instructions for using the subject devices for calibrating an optical scanner. The instructions may be printed on a substrate, such as paper or plastic, etc. As such, the instructions may be present in the kits as a package insert, in the labeling of the container of the kit or components thereof (i.e., associated with the packaging or sub-packaging) etc. In other embodiments, the instructions are present as an electronic storage data file present on a suitable computer readable storage medium, e.g., CD-ROM, diskette, etc. The following example is put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the present invention, and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to ensure accuracy with respect to numbers used (e.g. amounts, temperature, etc.) but some experimental errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, molecular weight is weight average molecular weight, temperature is in degrees Centigrade, and pressure is at or near atmospheric. The following method describes an exemplary method of manufacturing the subject calibration devices. I. Preparation of Stock Dye Solutions Weigh out approximately 10(xc2x12) mg of Green dye (for example Rhodamine 6G.HCl) and place in a clean, dry vial. Dissolve R6G in 10 ml ethanol and agitate on a shaker, stir plate or ultrasonic bath until solution is clear and all dye dissolved. Repeat the process using Red dye (for example HIDCI). Dilute the stock solutions in ethanol to a known absorbance, i.e., about 300 xcexcL of prep solutions in 4.7 mL ethanol. Check the absorbances for these solutions to ensure they are about 0.161@530 nm for R6G and about 0.278@639 nm for HIDCI. II. Preparation of Polymer Solution Weigh out sufficient PMMA powder to produce a solution of about 1-20 wt % (depending on thickness of coating desired.) and place in a 100-150 ml glass bottle. Dissolve PMMA in 75 g of chlorobenzene by rotating jar overnight at 0.5 Hz (Cole-Parner Roto-Torque cat. #E-07637-00). (If the solution is not clear and particle free, heat to 50xc2x0 C. until it appears homogenous, and rotate for about 3 additional hours and allow to cool to room temperature.) (Solution viscosity determines the final thickness of the spin coated test chip. Any changes in molecular weight or concentration affects the solution viscosity and necessitates revalidating the spin coating procedure.) III. Preparation of Final PMMA/Dye Calibration Devices Add 10 xcexcL of prepared dye solution(s) to 100 ml of PMMA solution from above and stir on an orbital mixer for about 12-18 hours, allow any air bubbles to escape by letting the solution stand for 1 hour after removing from the stirrer (sonication or using reduced pressure can aid in degassing the solution if bubbles remain). Clean substrates for coating and store in PTFE or similar wafer container. (Proceed with spin coating using outlined procedure to produce polymeric coatings of the desired thickness.) IV. Spin Coating Verify the vacuum and inert gas supply to the spin coating instrument. Spin material onto glass wafers according to the following exemplary protocol: 1) one (1) second ramp-up to 500 rpm, 2) hold at 500 rpm for 10 seconds, 3) while holding at 500 rpm, pour PMMA/Dye solution for approximately 5-8 seconds, 4) three (3) second ramp to 1500 rpm, 5) hold at 1500 rpm for 60 seconds. After spin program is finished, bake the calibration devices at about 60xc2x0 C. for 60 seconds using contact mode on hot plate (or other suitable drying methods, as outlined above). Dice the devices or cut to a final size. V. Results The results of the above described process for spin coating calibration devices produce calibration devices have a polymer coating with two florescent agents therein and minimal local and global nonuniformities. It is evident from the above results and discussions that the above described invention provides a simple and efficient way of aligning and calibrating an optical scanner and more particularly a biopolymeric array optical scanner. The above described invention provides for a number of advantages, including producing a stable output at the frequency or wavelength of interest, minimal local and global nonuniformities, ease of manufacture and ease of use. As such, the subject invention represents a significant contribution to the art. All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims. |
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051606950 | abstract | An apparatus and method of enhancing nuclear fusion reactions utilizes a plasma, made up of ions and electrons, contained within a region, and enhances the density of the plasma using a collision-diffusion compressional enhancement process. Ion acoustic waves generated within a central region of the system permit increased reflection and scattering of ions and thereby reduces their mean free path within the core region to permit greatly increased ions density sufficient to enhance nuclear fusion reactions within the core. |
claims | 1. A control rod drive mechanism (CRDM) comprising:a hollow lead screw;a lifting rod having an upper end disposed in the hollow lead screw;latches secured to the lead screw and configured to latch the upper end of the lifting rod to the lead screw;a latch engagement mechanism configured to close the latches onto the upper end of the lifting rod; anda latch holding mechanism configured to hold the latches closed; anda four-bar linkage including cam bars, the four-bar linkage configured to drive the cam bars inward to cam the latches closed responsive to operation of the latch engagement mechanism, the latch holding mechanism configured to hold the cam bars in the inward position to keep the latches closed;wherein the latch holding mechanism is separate from the latch engagement mechanism and the four-bar linkage is configured to bias the latches closed under force of gravity. 2. The CRDM of claim 1 wherein the latch engagement mechanism operates responsive to lowering the latches over the upper end of the lifting rod and is not effective to keep the latches closed when the latches are raised again after the latch engagement mechanism operates. 3. The CRDM of claim 2 wherein the latch holding mechanism is located at a top of the CRDM and is configured to engage the upper ends of the cam bars to hold the cam bars in the inward position. 4. The CRDM of claim 3 wherein the latch holding mechanism comprises a magnetic coupling including an electromagnet that when energized magnetically holds the cam bars in the inward position. 5. The CRDM of claim 3 wherein the latch holding mechanism comprises elements configured to move in a horizontal plane responsive to a holding force applied by an actuator to hold the cam bars in the inward position. 6. A nuclear reactor comprising:a pressurized water reactor (PWR) including:a pressure vessel;a reactor core disposed in the pressure vessel; anda CRDM as set forth in claim 1 disposed in the pressure vessel. 7. The nuclear reactor of claim 6 wherein the latch holding mechanism is magnetically operated. 8. The nuclear reactor of claim 6 comprising multiple CRDMs, wherein each CRDM has an independent latch holding mechanism. 9. The nuclear reactor of claim 8 wherein the latch holding mechanisms are magnetically operated. 10. The nuclear reactor of claim 9 wherein the latch holding mechanisms operate independent of one another. 11. A control rod drive mechanism (CRDM) including:a CRDM motor;a hollow lead screw translated under control of the CRDM motor;a lifting rod supporting at least one control rod;a latch configured to engage a portion of the lifting rod that is disposed in the hollow lead screw so that the lead screw and the lifting rod are non-rotatably secured to each other;a latch engagement mechanism configured to close the latch onto the lifting rod;a latch holding mechanism, separate from the latch engagement mechanism, configured to hold the latch in its closed position; anda four-bar linkage including cam bars, the four-bar linkage being configured to cam the latches closed responsive to operation of the latch engagement mechanism,wherein the four-bar linkage is configured to cam the latches closed responsive to operation of the latch engagement mechanism. 12. The CRDM of claim 11 wherein the latch holding mechanism is magnetically actuated. 13. A control rod drive mechanism (CRDM) comprising:a lead screw having an upper end;a lifting rod having an upper end;latches secured to the upper end of the lead screw and configured to latch the upper end of the lifting rod to the lead screw;a latch engagement mechanism configured to close the latches onto the upper end of the lifting rod;a latch holding mechanism configured to hold the latches closed; anda four-bar linkage including cam bars, the four-bar linkage configured to drive the earn bars inward to cam the latches closed responsive to operation of the latch engagement mechanism, the latch holding mechanism configured to hold the cam bars in the inward position to keep the latches closed,wherein the latch holding mechanism is separate from the latch engagement mechanism and the four-bar linkage is configured to bias the latches closed under force of gravity. 14. The CRDM of claim 13, wherein the lead screw is hollow and the upper end of the lifting rod is disposed in the lead screw. 15. The CRDM of claim 13 wherein the latch engagement mechanism operates responsive to lowering the latches over the upper end of the lifting rod and is not effective to keep the latches closed when the latches are raised again after the latch engagement mechanism operates. |
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048851221 | description | DETAILED DESCRIPTION Referring now to FIGS. 3 and 4, one embodiment of the clamping apparatus of the present invention is shown in plan and cross sectional views respectively. The clamping apparatus, generally designated as 30, comprises two end body members 31. Each of the end body members has an unflanged end 31U and a flanged end 31F. In the closed or assembled position, the flanged ends 31F are held together by cap screw 35. In a preferred embodiment, one of the flanged ends 31F contains an unthreaded cap screw aperture therein while the other flanged end 31F contains a threaded cap screw aperture therein. The unflanged ends 31U of the end body members 31F are connected in such a manner so as to allow the radial spacing between the flanged ends 31F to be adjustable. In this way, the present invention provides a unitary clamp having an adjustable end which is adapted to be opened in a jaw like fashion. During the assembly procedure, this feature allows the clamp, which is assembled except for the insertion of the cap screw, to be moved to an open position in which the clamp is easily placed into position over flanges 10 and 11. In one embodiment of the present invention, the means for linking the end body members so as to permit the spacing between the flanged ends of the clamp to be adjustable comprises intermediate body members 32. Means, such as link plates 33, are provided for pivotally joining the intermediate body members 32 to one another and to the unflanged ends 31U of the end body members 31. Bosses 34 extend substantially axially from each end of the intermediate body members 32 and from the unflanged ends 31U of the end body members 31. Each boss extends into an aperture in link plate 33 in known fashion. In a preferred embodiment, each boss 34 has a holding means, such as a cotter pin for example, for holding the link plates on the bosses. It is preferred that the body members be joined by a pair of link plates 33 as shown in FIG. 4. It will be appreciated by those skilled in the art that means other than those described in detail above are available for linking the unflanged ends of said end body members. For example, it may be preferable in some applications to provide more than two intermediate body members. In other applications, it may be desirable to extend the arcuate span of the end body members and link the unflanged ends 31U directly together by a link plate. The operation of an apparatus according to one embodiment of the present invention may be usefully illustrated by describing the use of the clamping apparatus shown in FIGS. 3 and 4 in connection with the instrumentation port interface shown in FIG. 1. Due in part to the articulated nature of the clamping apparatus of the present invention, the clamp may be assembled around the instrument port interface shown in FIG. 1 with a minimum of effort. With cap screw 35 removed from the clamping apparatus 30, the flanged ends 31F of the clamp are easily separated in jaw like fashion. In particular, due to the provision of at least two pivotally joined body members 31, the flanged ends 31F are easily separated a sufficient distance to allow passage of the clamp 30 around flanges 10 and 11. The flanged ends 31F are then easily rejoined by cap screw 35. As revealed by FIGS. 3 and 4, the clamp 30 according to one embodiment of the present invention is generally ring-shape when in assembled form, the inner portion of said ring-shape clamp being adapted to engage the outer portions of flanges 10 and 11. As mentioned above, it is desirable for the clamping apparatus of the present invention to exert the proper axial seating pressure on the flange interface. As best revealed in FIGS. 1 and 4, this is achieved by providing the inwardly facing portions of clamp 30 with generally flat surfaces 36 and 37 which are non-perpendicular with respect to the axis 38 of the flanges 10 and 11. In assembled form, the surfaces 36 and 37 of clamp 30 are generally parallel with respect to surfaces 39 and 40 of flanges 10 and 11 respectively. When clamp 30 is assembled around flanges 10 and 11, the internal diameter of clamp 30 tends to decrease until cap screw 35 draws flanged ends 31F together. This reduction in the internal diameter of clamp 30 in turn tends to cause opposed axially pressure on flanges 10 and 11 as a result of the engagement of surface 36 with surface 39 and surface 37 with surface 40. In order to provide the most precise application of axial pressure, the inwardly facing portions of the clamp are preferably machined, cast, and/or forged to precisely engage the surfaces 39 and 40 of flanges 11 and 10. More particularly, the spacial relationship between the surfaces 36 and 37 of clamp 30 and surfaces 39 and 40 is controlled so that the proper axial pressure is exerted when the flanged ends 31F are in contact. As mentioned above, it is critical for instrument port interface clamps of the types disclosed herein to achieve and maintain the proper uniform contact and pressure on the interface. Such uniform contact and pressure will insure a properly seated gasket 12 and will prevent gasket over overcompression. In addition this uniform contact and pressure will aid in the maintenance of a proper seal during emergency conditions. These objectives are achieved, in part, by providing a datum surface on the flanged ends 31F of the end body members. According to the present invention, the clamp 30, for example, is machined, cast, and/or forged according to methods well known in the art to exert the proper contact and pressure upon the interface between flanges 10 and 11 when datum surfaces 31D are in contact. By "preloading" the clamp of the present invention in this way, the time required to position and assemble the clamp on the instrument port interface is minimized and the need for a space limiter is eliminated. That is, once the clamp is placed around the flanges in the manner described above, the proper clamp geometry will be achieved when the cap screw is torqued sufficiently to cause intimate contact between the datum surfaces of the flanged ends. This will properly seat and compress the gasket. Further torquing of the cap screw will not overcompress the gasket and is preferred as a means for preloading the clamp flanges so that the gasket will remain seated when the pressure within the flanges increases. In particular, the clamp of the present invention will achieve these objectives upon the application of only about 60 ft/lbs. torque to the cap screw. In a preferred embodiment of the present invention, the datum surfaces are simply the flat surfaces 31D of the flanged ends 31F. It will be appreciated by those skilled in the art, however, that the use of any particular configuration or shape of datum surface is within the scope of the present invention. For example, it may be desirable to provide datum surfaces with mating portions which provide axial alignment of the flanged ends 31F. Gasket 12 is properly seated by clamping apparatus of the present invention without the need for the heretofore used axial loading device. This advantage is achieved, in part, by providing body members 31 and 32 with an arcuate span which is substantially less than the arcuate span of the body members 13A, 13B, and 13C according to heretofore used clamping apparatus. It is preferred that the body members according to the present invention span an arc no greater than about 90.degree.. Applicant has found that such a reduction in arcuate span and a decrease in the clamp inner radius increases the contact area between the clamp 30 and the flanges 10 and 11. This increased contact aids in the seating of gasket 12 as the clamp 30 is assembled. In addition, the provision of an increased number of body members having reduced arcuate span aids in the seating of the gasket 12 as the clamp 30 is assembled. Providing a clamp according to the present invention eliminates the requirement of an axial loading device and hence simplifies the assembly procedure thereof and reduces the exposure of workers to potentially hazardous conditions. Referring now to FIG. 5, another embodiment of the clamping apparatus of the present invention is shown in cross sectional view with respect to another typical instrument port interface. In this configuration, tubular members or flanges 41 and 42 cooperate in a telescoping manner to seal the interface therebetween. In the context of a nuclear reactor vessel, flange 41 comprises the upper portion of flange 10 (FIG. 1) and member 42 is the cylindrical conduit seal and carries thermocouples which pass into the interior of member 41. As with the prior interface, a gasket 12 is provided to insure a proper seal between the flanges 41 and 42. In contrast to the interface shown in FIG. 1, proper seating of gasket 12 in FIG. 5 requires application of axial pressure to each flange which is directed away from the interfacing end thereof. That is, it is necessary for the clamping apparatus to exert an upward axially pressure on cylindrical conduit 42 with respect to flange 41. Clamping apparatus heretofore used to achieve this objective are described in copending application Ser. No. 925,861. According to one embodiment of the present invention, this objective is achieved by the cooperation of positioner clamp 50 and wedge clamp 60. Although clamps 50 and 60 may have any appropriate plan view construction, it is preferred to use an articulated construction as shown in FIG. 3. As shown in FIG. 5, however, the cross sectional configuration of clamps 50 and 60, and flanges 41 and 42 is substantially different from the cross sectional configuration of clamp 30 and flanges 10 and 11 as shown in FIGS. 1 and 4. In particular, flange 42 contains an annular groove 43 on its outer surface for receiving positioner clamp 50. Positioner clamp 50 contains an inwardly extending flange 51, at least a portion of which engages groove 43. Positioner clamp 50 also contains a lower surface 52 which is nonperpendicular with respect to the central axis 44 of flanges 41 and 42. In this way, the axial distance between any portion of surface 52 and the end of flanges 41 and 42 is functionally related to the radial distance of that portion from axis 44. In particular, the distance between surface 52 and the end of flange 42 decreases with decreasing surface radius. The upper end of flange 41 contains a generally flat surface 45 which is also generally nonperpendicular with respect to axis 44. The distance between surface 45 and the interfacing end of flange 41 also decreases with decreasing surface radius. As the term is used herein, the end of a flange refers to the furthest axial extent of the flange, For example, the end of flange 41 refers to the innermost radius of surface 45. Surface 45 and surface 52 cooperate to create a wedge like opening 70 for clamp 60. The inner surface of clamp 60 provides an engaging means adapted to cooperatively engage the wedge like opening 70. In particular, clamp 60 contains an upper surface 61 and a lower surface 62, each of which are also disposed at a nonperpendicular angle with respect to axis 44. It is preferred that surface 62 be in engagement with and generally parallel to surface 45 and that surface 61 be parallel to and in engagement with surface 52, as shown in FIG. 5. Both surfaces 61 and 62 slope towards the axial center of opening 70 as the radial distance from axis 44 decreases. Due in part to the articulated nature of clamp 60 (see FIG. 3), the internal diameter of clamp 60 is reduced as the flanged ends 31F are drawn together. Due to the relationship between the axial and radial distances of the surfaces described above, this reduction in the internal diameter of the clamp 60 in turn tends to exert an upward axially pressure on flange 42 with respect to flange 41. It will be appreciated by those skilled in the art that various modifications of the clamping system shown in FIG. 5 are possible and may be desirable. In one alternative embodiment, a two-piece split ring may be substituted for positioner 50. It may be desirable in other applications to eliminate positioner 50 entirely and simply form flange 42 with the appropriate outer configuration. It should also be noted, however, that in many situations, nuclear power systems in particular, it is not practical to replace or redesign flange 42 and hence in those applications the provision of a clamp such as 50 may be desirable. Alternatively, positioner 50 and 60 may be combined into a single clamp having an inner surface similar to the combination of the clamp/positioner arrangement. It will also be appreciated by those skilled in the art that while the clamping system shown in FIG. 5 provides sloping surfaces 45, 52, 61 and 62, the provision of only one of these surfaces is sufficient to achieve the objects of the clamping apparatus disclosed therein. For example, it is possible to provide surfaces 45, 52, and 61 in a perpendicular arrangement with respect to axis 44 while maintaining surface 62 in a sloped configuration. Due to the provision of this one sloped surface, assembly of clamp 60 between surfaces 42 and 45 will tend to exert upward axial pressure on flange 42. As indicated by the foregoing description, the clamping apparatus and systems of the present invention will quickly and efficiently seal instrument port interfaces, thus reducing the exposure of nuclear power plant workers to hazardous conditions while maintaining a high degree of protection against leakage. In particular, the present invention provides a clamping apparatus which, even for relatively large instrument ports, can be easily operated by one worker. In addition, the clamps can be quickly applied to the instrument port interface since only one cap screw is required to assembly the clamp on the interface. It will be appreciated by those skilled in the art that the form of the invention shown and described above is presented by way of illustration only. For example, the clamping apparatus has been described with respect to use on the generally tubular conduits associated with instrument port interfaces. The present clamping apparatus, however, is adaptable to other conduit configurations, such as square, rectangular or triangular, for example. In addition, the present clamping apparatus may be used in other applications, such as shipping and/or storage casks, for example. Various other changes may be made in the shape, size, etc. without departing from the spirit and scope of the invention as set forth below in the claims. |
summary | ||
051630788 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the embodiments shown in the drawings, the present invention will be described in detail below. FIRST EMBODIMENT In this embodiment, where the multilayer film reflecting mirrors each comprised of Ni and Sc (the number of layers: 201, an X-ray wavelength: 39.8 .ANG.) are fabricated within the tolerance defined by Equation (8), the deteriorative state of the reflectance against the optimum design value of the film thickness is simulated by changing in turn the film thickness of each layer of Ni and Sc, the incident angle .phi. of X rays, and a deviation SD from the optimum design value of the film thickness. The simulation is performed by the following procedure. That is, it is assumed that, with respect to 100 multilayer film reflecting mirrors, the tolerance of the film thickness is generated at random within the deviation SD in the probability according to the normal distribution given by Equation (7), and the reflectances of individual reflecting mirrors and their generation frequency (which is hereinafter called merely the frequency) are thus obtained. By Equation (1), the reflectance is calculated for each layer in regard to the film thickness deviated from the optimum design value. Also, the complex indices of refraction of Ni and Sc in the case of the X-ray wavelength of 39.8 .ANG. are derived from the tables of atomic scattering factors by B. Henke [B. Henke, Atomic Data & Nuclear Data Tables 27, pp. 1-144 (1982)] and the literature [Sadao Aoki, Phys. Appl., Vol. 56, No. 3, pp. 16-18 (1981)], resulting in the following numerical data: EQU n(Ni)=0.9882-0.0041183i EQU n(Sc)=0.9975-0.0005738i EMBODIMENT 1-1 In this embodiment, the multilayer film reflecting mirrors are designed on the condition of normal incidence, namely, .phi.=0.degree.. The film thickness of each Ni layer is 8.2 .ANG., that of each Sc layer 11.8 .ANG., and the deviation SD 0.8 .ANG.. FIG. 8 shows the relationship between the reflectance and the frequency in Embodiment 1-1. The design value of the reflectance is 24%, and according to FIG. 8, the mirrors exhibiting the reflectances of a half (12%) of the design value or more are 36 ones, which indicates that Equation (8) is effective. EMBODIMENT 1-2 In this embodiment, the multilayer film reflecting mirrors are designed on the condition of .phi.=30.degree.. The film thickness of each Ni layer is 8.8 .ANG., that of each Sc layer 14.4 .ANG., and the deviation SD 1.2 .ANG.. FIG. 9 shows the relationship between the reflectance and the frequency in Embodiment 1-2. The design value of the reflectance is 28%, and according to FIG. 9, the mirrors exhibiting the reflectances of a half (14%) of the design value or more are 30 ones. EMBODIMENT 1-3 In this embodiment, the multilayer film reflecting mirrors are designed on the condition of .phi.=60.degree.. The film thickness of each Ni layer is 13.4 .ANG., that of each Sc layer 27.1 .ANG., and the deviation SD 3.0 .ANG.. FIG. 10 shows the relationship between the reflectance and the frequency in Embodiment 1-3. The design value of the reflectance is 36%, and according to FIG. 10, the mirrors exhibiting the reflectances of a half (18%) of the design value or more are 42 ones. EMBODIMENT 1-4 In this embodiment, the multilayer film reflecting mirrors are designed on the condition of .phi.=75.degree.. The film thickness of each Ni layer is 26.3 .ANG., that of each Sc layer 55.8 .ANG., and the deviation SD 9.0 .ANG.. FIG. 11 shows the relationship between the reflectance and the frequency in Embodiment 1-4. The design value of the reflectance is 39%, and according to FIG. 11, the mirrors exhibiting the reflectance of a half (20%) of the design value or more are 52 ones. As mentioned above, according to the first embodiment, each deviation SD satisfies Equation (8) and hence the multilayer film reflecting mirror having a desired quality of reflection can be fabricated in the probability of 30% or more. SECOND EMBODIMENT In this embodiment, the states of the reflectances of the multilayer film reflecting mirrors each comprised of Ni and Sc (the number of layers: 101, the X-ray wavelength: 39.8 .ANG.) are simulated like the first embodiment. Also, the optical constants are the same as in the first embodiment. EMBODIMENT 2-1 In this embodiment, the multilayer film reflecting mirrors are designed on the condition of .phi.=0.degree.. The film thickness of each Ni layer is 8.6 .ANG., that of each Sc layer 11.4 .ANG., and the deviation SD 1.2 .ANG.. FIG. 12 shows the relationship between the reflectance and the frequency in Embodiment 2-1. The design value of the reflectance is 11%, and according to FIG. 12, the mirrors exhibiting the reflectances of a half (6%) of the design value or more are 30 ones, which indicates that Equation (8) is effective. EMBODIMENT 2-2 In this embodiment, the multilayer film reflecting mirrors are designed on the condition of .phi.=30.degree.. The film thickness of each Ni layer is 9.7 .ANG., that of each Sc layer 13.4 .ANG., and the deviation SD 1.5 .ANG.. FIG. 13 shows the relationship between the reflectance and the frequency in Embodiment 2-2. The design value of the reflectance is 14%, and according to FIG. 13, the mirrors exhibiting the reflectances of a half (7%) of the design value or more are 41 ones. EMBODIMENT 2-3 In this embodiment, the multilayer film reflecting mirrors are designed on the condition of .phi.=60.degree.. The film thickness of each Ni layer is 14.8 .ANG., that of each Sc layer 26.3 .ANG., and the deviation SD 3.0 .ANG.. FIG. 14 shows the relationship between the reflectance and the frequency in Embodiment 2-3. The design value of the reflectance is 34%, and according to FIG. 14, the mirrors exhibiting the reflectances of a half (17%) of the design value or more are 57 ones. EMBODIMENT 2-4 In this embodiment, the multilayer film reflecting mirrors are designed on the condition of .phi.=75.degree.. The film thickness of each Ni layer is 26.3 .ANG., that of each Sc layer 55.8 .ANG., and the deviation SD 7.5 .ANG.. FIG. 15 shows the relationship between the reflectance and the frequency in Embodiment 2-4. The design value of the reflectance is 39%, and according to FIG. 15, the mirrors exhibiting the reflectances of a half (20%) of the design value or more are 64 ones. THIRD EMBODIMENT In this embodiment, the states of the reflectances of the multilayer film reflecting mirrors each comprised of Re (rhenium) and Al (aluminum) (the number of layers: 41, the X-ray wavelength: 210 .ANG.) are simulated by the same procedure as in the above embodiments. The incident angle is set at .phi.=15.degree., the film thickness of each Re layer is 28.3 .ANG., and that of each Al layer is 80 .ANG.. Also, the optical constants of Re and Al are cited from the literature [Takeshi Namioka et al., "Developments of Light Sources and Optical systems for Soft X-ray Lithography", Report of Research by Scientific Research-Aid Fund for the 1985 Fiscal Year (Test Research (2)), pp. 1-36, 1986], resulting in the following numerical data: EQU n(Re)=0.65-0.12i EQU n(Al)=0.99-0.00458i FIG. 16 shows the relationship between the reflectance and the frequency in the third embodiment in which the deviation SD is 6.0 .ANG.. The design value of the reflectance is 64%, and according to FIG. 16, the mirrors exhibiting the reflectances of a half (32%) of the design value or more are 87 ones, which indicates that Equation (8) is effective. |
description | The present invention relates to a method for determining the value of a parameter representative of the operability of a nuclear reactor. The invention is used, for example, in pressurised water reactors. In conventional manner, the core of such a reactor is charged with nuclear fuel assemblies. Each assembly comprises a bundle of nuclear fuel rods, the rods comprising a cladding which contains nuclear fuel pellets. It may be advantageous, particularly in countries such as France where 80% of electricity is produced by nuclear reactors, for the overall power supplied by the reactors to vary in order to adapt to the requirements of the electrical power network which they supply. In particular, it is desirable to be able to operate reactors with reduced overall power for a long period of time when the demand on the network is low, before returning if necessary to nominal overall power. Nonetheless, operating each reactor in this manner, which allows the capacities thereof to be better exploited, must not involve safety problems. One of the phenomena limiting the operability of nuclear rectors is in particular the phenomenon of Pellet/Cladding Interaction (PCI). When the reactor operates at the nominal overall power PN thereof, the nuclear fuel rods are, according to the term used in the art, processed. For a specific rod, the processing is characterised substantially by the radial clearance being closed between the pellets and the cladding, owing to the creep of the cladding and the swelling of the pellets. Although there is no risk of fracture of the cladding during permanent operation owing to the thermomechanical equilibrium in the cladding at relatively low stress levels, a risk does arise as soon as the power provided by the rod in question varies significantly. An increase of local power brings about an increase of the temperature in the rod. Given the difference of the mechanical characteristics (thermal expansion coefficient, Young's modulus) and the temperature difference between the pellet based on uranium oxide and the cladding which is conventionally of zirconium alloy, the pellet will expand more than the cladding and impose its deformation on the cladding. Furthermore, the presence in the space between the cladding and the pellet of corrosive fission products, such as iodine, creates corrosion conditions under stress. In this manner, the deformation imposed by the pellet on the cladding during a transient occurrence of overall power may bring about a fracture of the cladding. Such a fracture of the cladding is not admissible for safety reasons since it could result in fission products being released into the coolant system of the nuclear reactor. The patent application EP-1 556 870 describes a method which, using the phenomenon of PCI, allows the limit values of the operating parameters of a nuclear reactor to be determined. More precisely, the limit values determined are such that, in the event of an accidental transient occurrence of overall power which will become evident with an increase in the local power in the entire core, the phenomenon of PCI will not result in a fracture of the nuclear fuel rod cladding. This method thus allows the fields of use to be defined in which the nuclear reactor can operate in a safe manner, even in the event of an accidental transient occurrence of overall power. Alarms can also be introduced to verify that the limit values determined are not exceeded during the operation of the nuclear reactor. The PCI phenomenon is particularly disadvantageous with respect to a specific operating method of nuclear reactors. This is Extended Reduced Power Operation (ERPO). In France, extended reduced power operation is more precisely defined as being the permanent operation of the reactor, at an overall power PI less than or equal to, for example, approximately 92% of the nominal power PN thereof, for example, over a cumulative period of time of more than 8 hours in a given 24 hour period. Such a method of operation has the effect of de-processing the rods. During a reduction of the overall power, the power decreases locally. There is consequently a temperature reduction in the pellets and in the cladding of each rod, which brings about a reduction of the thermal expansions of these elements. Since each pellet has a greater thermal expansion coefficient than that of the associated cladding, it therefore retrocedes a greater absolute expansion. This is further amplified by the fact that, for a specific local power reduction, the temperature variation in each pellet is greater than that in the cladding. In this manner, during operation in ERPO mode, for the rods in which the contact between the cladding and the pellets is not established, the radial clearance increases. With regard to the rods in which the clearance was closed, the clearance re-opens. In the event of reopening of the clearance, there is creeping in terms of compression towards the inner side of the cladding owing to the effect of pressure. The stresses which appear in the cladding in the event of an accidental transient occurrence of power during operation in ERPO mode thus reach greater values than if the transient occurrence takes place when the reactor is operating at nominal overall power. The risks of a fracture owing to the PCI phenomenon are therefore increased when the reactor operates in ERPO mode. In order to allow nuclear reactor operators to evaluate the extent to which they are able to use ERPO mode, without compromising the integrity of the claddings of the rods, a parameter has been developed, the credit K. This parameter which is representative of the operability of the nuclear reactor is defined by the formula: K = K 0 - ∑ i A i T i + ∑ j B j T j where K0 is the initial value of the credit K; Ai is a deprocessing coefficient calculated from the laws of deprocessing; Ti is the duration of a phase i of use of the ERPO mode; Bj is a reprocessing coefficient calculated from the reprocessing laws; and Ti is the duration of a phase j of nominal overall power operation after a period of operation in ERPO mode. The operator is capable using this formula of calculating the development during a cycle of the value of the credit K in accordance with the successive phases of operation in ERPO mode and at nominal overall power. The lower the value of the credit K is, the less possibility there is for the operator to use ERPO mode. When the value of the credit K is 0, the operator can no longer function in ERPO mode and must only operate the reactor at nominal power or shut it down. In order to increase the value of the credit K, the operator may choose to operate the reactor at nominal overall power for a specific length of time. The establishment of this formula, and in particular that of the coefficients Ai and Bj which takes almost two years, requires very significant calculations which are carried out over a period of several months on processors operating in parallel. Taking into account the complexity involved in calculating the coefficients Ai and Bj, the determination of the value of the credit K is carried out in a generic manner for a specific reactor, fuel assembly and control which requires the introduction of a number of careful considerations. Although the use of the credit K allows safe operation to be ensured for the nuclear reactor, unfortunately it therefore leads to limited operability. An object of the invention is to solve this problem by providing a method which is for determining the value of a parameter representative of the operability of a nuclear reactor core and which allows the operability of the reactor to be increased whilst ensuring safe operation. To this end, the invention provides a method of determining the value of a parameter representative of the operability of a nuclear reactor, the core comprising nuclear fuel assemblies, each assembly comprising nuclear fuel rods in which nuclear fuel is enclosed in a cladding, the method involving the periodic implementation, during the same operating cycle of the reactor, of the following steps of: a) calculating, from measurements provided by sensors present in the reactor, the three-dimensional distribution of the local power in the core, b) simulating at least one accidental transient occurrence of power applied to the calculated three-dimensional distribution of local power, c) identifying, using thermomechanical calculations, at least one rod which is the most likely to be subject to a fracture of the cladding thereof during the simulated transient occurrence of power, and d) determining, using thermomechanical calculations on the rod identified, the value of the parameter which is representative of the operability of the reactor. According to specific embodiments, the method may comprise one or more of the following features, taken in isolation or according to any technically possible combination: step c) comprises a sub-step c1) of calculating the maximum value of a parameter which is representative of the stress state in the cladding (33) of each rod (24) during the simulated transient occurrence of power; in the sub-step c1), the contact pressure between the pellets and the cladding of the rod in question is calculated by means of correlation or interpolation from values previously calculated; steps a) to d) are carried out periodically with a time step of less than one month; steps a) to d) are carried out with a time step of less than one week; steps a) to d) are carried out with a time step of less than one day; the nuclear reactor is a pressurised water nuclear reactor; and it comprises a step e) of using the determined value in order to command and/or control the operation of the nuclear reactor. The invention further relates to a system for determining the value of a parameter representative of the operability, characterised in that it comprises means for implementing the steps of a method as defined above. According to one variant, the system comprises at least one processor and storage means in which there is stored at least one program for carrying out steps of the determination method implemented by the system. The invention further relates to a computer program which comprises instructions for implementing the steps of a method as defined above. The invention further relates to a medium which can be used in a processor and on which a program as defined above is recorded. FIG. 1 schematically illustrates a pressurised water nuclear reactor 1 which conventionally comprises: a core 2, a steam generator 3, a turbine 4 which is coupled to an electrical energy generator 5, and a condensor 6. The reactor 1 comprises a cooling system 8 which is provided with a pump 9 and in which the pressurised water flows along the path indicated by the arrows in FIG. 1. This water rises in particular through the core 2 in order to be reheated there, providing the cooling of the core 2. The cooling system 8 further comprises a pressuriser 10 which allows the water flowing in the cooling system 8 to be pressurised. The water of the cooling system 8 also supplies the steam generator 3 where it is cooled providing the evaporation of the water flowing in a secondary system 12. The steam produced by the generator 3 is channelled by the secondary system 12 towards the turbine 4 then towards the condenser 6 where this steam is condensed by means of indirect heat exchange with cooling water flowing in the condenser 6. The secondary system 12 comprises downstream of the condenser 6 a pump 13 and a reheating device 14. Also in conventional manner, the core 2 comprises nuclear fuel assemblies 16 which are charged in a vessel 18. A single assembly 16 is illustrated in FIG. 1 but the core 2 comprises, for example, 157 assemblies 16. The reactor 1 comprises control rod clusters 20 which are arranged in the vessel 18 above some of the assemblies 16. A single cluster 20 is illustrated in FIG. 1, but the core 2 may comprise, for example, approximately 60 clusters 20. The clusters 20 may be moved by mechanisms 22 for being inserted into the fuel assemblies 16 over which they are arranged. Conventionally, each control rod cluster 20 comprises rods which comprise one or more neutron-absorbing materials. In this manner, the vertical movement of each cluster 20 allows the reactivity of the reactor 1 to be regulated and allows variations in the overall power P provided by the core 2 from zero power up to nominal power PN, in accordance with the introduction of the clusters 20 in the assemblies 16. Some of these clusters 20 are intended to control the operation of the core 2, for example, in terms of power or temperature, and are referred to as control rod clusters. Others are intended only to shut down the reactor 1 and are referred to as shutdown clusters. The clusters 20 are assembled in groups in accordance with their type and destination. For example, for reactors of the type 900 MWe, these groups are referred to as groups G1, G2, N1, N2, R, SA, SB, SC, SD . . . . The reactor 1 also comprises a given number of sensors for measuring the effective values of operating parameters of the reactor, in particular a thermoelectric couple 21A for measuring the mean temperature of the water of the cooling system at the outlet of the vessel 18 and a thermoelectric couple 21B for measuring the mean temperature of the water of the cooling system at the inlet of the vessel 18. Also in conventional manner, the nuclear reactor 1 comprises external chambers 21C for measuring the neutron flux, which chambers 21C are arranged around the vessel 18 of the core 2. The number and the positions of the chambers 21C, generally referred to as “ex-core chambers”, vary in accordance with the model of the reactor 1. Also in conventional manner, the reactor 1 comprises thermoelectric couples 21D which are arranged in the core 2 above assemblies 16 in order to measure the temperature of the water of the cooling system at the outlet of the assemblies 16. A single chamber 21C and a single sensor 21D have been illustrated in FIG. 1. The ex-core chambers 21C and the thermoelectric couples 21D provide information relating to both the axial distribution, that is to say, vertically, and radial distribution of the local power in the core. In order to calibrate the various sensors, and in particular the chambers 21C and the thermoelectric couples 21D, the reactor also comprises an item of equipment which is referred to as “in-core” (not illustrated) and which comprises movable probes which are fixed to the end of flexible cables in order to allow them to be inserted inside measurement tracks of some of the assemblies 16. These probes are introduced regularly into the core 2 in order to recalibrate the values measured by the various sensors relative to the measurements carried out by these probes, and thus to calibrate the various sensors of the reactor 1. As illustrated in FIG. 2, each assembly 16 conventionally comprises a grid of fuel rods 24 and a support skeleton 26 for the rods 24. The skeleton 26 conventionally comprises a bottom nozzle 28, a top nozzle 30, guide tubes 31 which connect the two nozzles 30 and 28 and which are intended to receive rods of the control rod clusters 20 and spacer grids 32. As illustrated in FIG. 3, each fuel rod 24 conventionally comprises a cladding 33 in the form of a tube which is closed at the lower end thereof with a bottom end plug 34 and, at the upper end thereof, with an upper end plug 35. The rod 24 comprises a series of pellets 36 which are stacked in the cladding 33 and which are in abutment against the lower end plug 34. A retention spring 40 is arranged in the upper portion of the cladding 33 so as to be supported on the upper end plug 35 and on the upper pellet 36. Conventionally, the pellets 36 are based on uranium oxide and the cladding 33 is of zirconium alloy. In FIG. 3, which corresponds to a fuel rod 24 from production and before irradiation, there is a radial clearance J between the pellets 36 and the cladding 33. That is illustrated more specifically by the enlarged circled portion of FIG. 3. This clearance J is what closes during processing and reprocessing of the fuel rod and opens when the fuel rod is deprocessed. As illustrated in FIG. 1, the reactor 1 also comprises a data-processing system 40 for determining a parameter representative of the operability of the nuclear reactor 1. The system 40 is, for example, the one used more generally to command and control the operation of the nuclear reactor 1. This system 40 comprises, for example, a data-processing unit 42 comprising one or more processor(s), data storage means 44, input/output means 46 and optionally display means 48. The storage means 44 which comprise, for example, one or more memories, store one or more computer program(s) in order to carry out the steps described below. The system 40 is connected to the different sensors for measuring the operating parameters of the nuclear reactor 1, including sensors 21A to 21D. In the example given below, the parameter for measuring the operability of the reactor 1 calculated by the system 40 is the parameter Δ defined by:Δ=(σθ−σr)lim−(σθ−σr)sup where σθis the circumferential and normal stress in a cladding 33; σr is the radial and normal stress in the same cladding 33; (σθ−σr)sup is i the greatest value reached by (σθ−σr) from the rods 24 of the core 2; and (σθ−σr)lim is the limit value of (σθ−σr) beyond which a cladding 33 breaks. This limit value has, for example, been determined as described in the document EP-1 556 870. The method used by the system 40 to determine the value of Δ will now be described with reference to the flow chart of FIG. 4. This method involves the regular execution of the loop comprising steps 50, 52, 54 and 56 during an operating cycle of the nuclear reactor 1. The time step for carrying out this loop may be less than one month, one week, or even one day. In a first step 50, the system 40 calculates the three-dimensional distribution of local power in the core 2 at the time step in question. More precisely, a first rough calculation of the three-dimensional distribution of the local power in the core 2 is carried out by an item of neutron calculation software. The neutron calculation software used may be a conventional item of software, for example, the software SMART from the company AREVA NP (Registered Trade Mark). This rough calculation is, for example, provided based on: the charging characteristics of the core 2, that is to say, the arrangement and the characteristics of the assemblies 16 present in the core 2, characteristics stored, for example, in the storage means 44, the mean thermal power of the core 2 established in conventional manner by the system 40, for example, using the measurements provided by the thermoelectric couples 21A and 21B, and the mean temperature of the water at the inlet of the vessel 18 measured by the thermoelectric couple 21B, the reference positions of the control rod clusters 20 stored in the storage means 44, and the distribution of local power determined during the previous implementation of the loop of steps 50, 52, 54 and 56. The results of this first rough calculation are then refined by adjusting the values calculated in this manner owing to the effective values measured by the chambers 21C and the thermoelectric couples 21D. The use of such a rough calculation which is subsequently refined allows a good representation to be obtained of the three-dimensional distribution of the local power in the core 2, in a time which is compatible with the frequency of implementation of the method for determining the value of Δ. Then, in step 52, the system 40 simulates transient occurrences of overall power, for example, using the above-mentioned neutron calculation software. Preferably, the simulated transient occurrences are the accidental transient occurrences referred to as being of category 2 which bring about the most significant and rapid variations of power in the core 2. These transient occurrences may be, for example: the excessive increase in charge, the uncontrolled retraction of groups of control rod clusters 20 when the reactor 1 is in a powered state, the fall of cluster(s) 20. The excessive increase of charge corresponds to a rapid increase of the flow rate of steam in the steam generator 3. Such an increase brings about an imbalance between the thermal power of the core 2 and the charge of the steam generator 3. This imbalance leads to a cooling of the cooling system 8. Owing to the moderating and/or the regulating effect of the mean temperature in the core 2 by the control rod clusters 20, the reactivity, and therefore the nuclear flux, increase in the core 2. In this manner, the overall power P provided by the core 2 increases rapidly. In order to simulate this transient occurrence, it is considered that the flow rate of steam in the generator 3 increases from the initial value thereof up to the maximum value allowed by the characteristics of the secondary system 12. This increase is further sufficiently slow for the levels of power examined in order to prevent the automatic shutdown of the reactor owing to low pressure of the pressuriser 10. The uncontrolled removal of groups of control rod clusters 20 when the reactor operates brings about an uncontrolled increase in the reactivity. There is consequently a rapid increase in the overall nuclear power P and the flux of heat in the core 2. Until a relief valve or a safety valve of the secondary system 12 is opened, the dissipation of heat in the steam generator 3 increases less quickly than the power released in the cooling system 8. There is consequently an increase of the temperature and pressure of water in the cooling system 8. In order to simulate this transient occurrence, a removal is assumed of the power groups at the maximum speed of 72 steps/min until complete removal. If one or more of the control rod clusters 20 falls into the core, there is an immediate reduction of the reactivity and the overall power P in the core 2. Without protective action, the imbalance brought about in this manner between the cooling system 8 and the secondary system 12 brings about a reduction in the temperature of water entering the core 2, and an increase in the neutron power owing to the counter-reactions and the temperature control, until a new equilibrium is achieved between the cooling system 8 and the secondary system 12. The presence of the control rod cluster(s) 20 which have fallen brings about a deformation of the radial distribution of power, whilst the removal of the control group leads to an axial modification of the power. Then, during step 54, the system 40 will determine the rods 24 which are subject to the most stress during the transient occurrences of power simulated during step 52. This determination is carried out using an item of sorting software. More precisely, during this step 54, the value will be calculated for a parameter which is representative of the state of stress in the cladding 33 of each rod 24, for example, the value of (σθ−σr). In the example described, the parameter which is representative of the state of stress and the parameter which is representative of the operability of the reactor are based on the same difference of physical parameter (σθ−σr). However, this is not necessarily the case and the two parameters can be based on physical variables or functions of physical variables which are different but mutually coherent. The calculation is carried out, for example, for each rod 24 by repeating, for the entire duration of the processing and/or deprocessing thereof and each simulated transient occurrence of power, the following loop comprising the sub-steps involving: calculating the new dimensions of the cladding 33 and the pellets 36 of the rod 24 in accordance with the values of (σθ−σr) determined during the previous implementation of the loop, calculating the number of moles of fission gas released during the new time step, calculating the resultant increase of the pressure inside the cladding 33 during the new time step, calculating the contact pressure between the pellets 36 and the cladding 33 resulting from the new dimensions and in particular the development of the linear power density and the combustion rate of the nuclear fuel in the rod 24 during the new time step, and calculating the new value of (σθ−σr) in accordance with the new contact pressure value calculated, the new internal pressure value calculated and the new dimensions calculated. The calculations relating to the number of moles of fission gas released, the internal pressure and the contact pressure are carried out not by means of explicit resolution of the corresponding equations, but instead by means of correlations. More precisely, correlations are used to allow the values of the variables in question to be determined in accordance with the values of the same known variables for known conditions (linear power density, burnup . . . ). These known values originate, for example, from a database constructed from an item of thermomechanical calculation software. This may be a conventional item of software, such as the software COPERNIC from the company AREVA NP (Registered Trade Mark). The sorting software used for step 54 will preferably be a simplified version of the same item of thermomechanical calculation software. The use of items of software based on the same models in order to implement steps 52 and 54 allows robustness and reliability to be ensured for the method for determining the value of the parameter representative of the operability of the nuclear reactor. The use of correlations, rather than explicit calculations, allows the necessary calculations to be carried out in shorter periods of time which are compatible with the time step for implementing the method for determining the value of Δ. In other variants, it is possible to use interpolations rather than correlations. After carrying out the loop of step 54, there is known, for each transient occurrence of simulated power, a rough estimation of the maximum value (σθ−σr)max of (σθ−σr) reached in each rod 24. Based on these maximum values, the system 40 is able to identify the rods 24 which are subject to the most stress during transient occurrences of power. Then, in step 56, the system 40 carries out complete thermomechanical calculations on the rods 24 which are subject to the most stress identified during step 54. These calculations are carried out using an item of thermomechanical calculation software of conventional type, for example, the software COPERNIC from the company AREVA NP. These complete thermomechanical calculations allow the value of (σθ−σr)sup to be determined and thus allow the effective value of Δ to be determined. This effective value can be supplied in particular to an operator in charge of the reactor 1, for example, using the display means 48. The operator is then in a position to know the extent to which he can operate the reactor in ERPO mode, or whether he must instead make it operate with nominal overall power PN. In the same manner, the effective value of Δ calculated using the method described above may be used by the system 40 in order to initiate the automatic implementation of some operations within the reactor 1, for example, the sounding of an alarm, the shutdown of the reactor 1, the increase of the overall power. The determined value of Δ is therefore used to command and/or control the operation of the reactor 1. As indicated above, the steps 50, 52, 54 and 56 are repeated regularly during an operating cycle of the core, which allows the value of Δ to be updated. This calculation of Δ which is almost in real time allows the careful considerations used up to the present time to be dispensed with for calculating the credit K and therefore allows gains to be made in terms of operability, whilst ensuring safe operation of the nuclear reactor. Generally, the method described above can be used to calculate values of other parameters representative of the operability, other than Δ. Such a parameter can be based on the circumferential and normal stress σθ only or on a density of deformation energy. It may also be the credit K. The above principles can be used for types of reactor other than pressurised water reactors, for example, for boiling water reactors. In some variants, step 50 may use calculations other than those described above. Also in some variants, a single transient occurrence of power is simulated during step 52. In the same manner, the transient occurrence(s) simulated may be transient occurrences of local or overall power. Also in some variants, step 52 may involve loops which are different from those described. In the same manner, a correlation or interpolation may be used only to determine the contact pressure between the pellets 36 and the cladding 33 of a rod 24. In still other variants, it is possible to identify during step 54 a single rod which is subject to the most stress, step 54 being implemented on this single rod. |
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040299686 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Illustrated in FIGS. 1 and 2 is a rack 10 for storing spent nuclear fuel elements in a boiling water reactor nuclear power plant. The rack 10 has been generally disclosed in an application filed by Herbert J. Rubinstein, Philip M. Clark and James D. Gilcrest on July 11, 1975, Ser. No. 595,444, entitled Rack For Storing Spent Nuclear Fuel Elements. The assignee of the present application is the same as the assignee for the aforementioned application. The present invention is equally applicable for racks for storing spent nuclear fuel elements in a pressurized water nuclear power plant. Such racks have been described in detail in the just-mentioned pending application. The rack 10 for storing spent nuclear elements is conventionally disposed in a spent fuel pool P for a nuclear power plant. The spent fuel pool P is well-known. However, for the purposes of the present invention, the spent fuel pool P may be deeper than conventional spent fuel pools, although this is not essential. The pool P, of course, contains water and all the racks for storing spent nuclear fuel elements disposed therein are submerged in the water. The rack 10 comprises a suitable base 11. In the exemplary embodiment, the base 11 includes a horizontal base plate 12 of a rectangular configuration, which is made of a case or fabricated metal, such as aluminum or steel. Depending from the base plate 12 are four longitudinally extending, transversely spaced support member 13 and four transversely extending, longitudinally spaced support members 14. The members 13 and 14 are vertically disposed and are made of cast or fabricated metal, such as aluminum or steel. The members 13 and 14 are suitably fixed to the base plate 12, such as by welding. Openings 15 are formed in the members 13 as passageways for water. Likewise, openings 17 are formed in the members 14 as passageways for water. A feature of the present invention is the provision of guide pins 20 (FIG. 3), which are fixed to the bottom of the pool P in the upright position. Depending from the base 11 are four feet 21. Formed in the feet 21 are suitable receptacles 22 (FIG. 3) which receive respectively the guide pins 20 for aligning the rack 10 in the pool P. Fixed to the base plate 12 by suitable means, such as welding, is a plurality of upstanding nuclear fuel element enclosures 25. In the preferred embodiment, each of the enclosures 25 is formed with a generally square cross-sectional area to dispose therein a spent nuclear fuel element of the type employed in nuclear power plants. The enclosures 25 are preferably made of aluminum or stainless steel. Openings 38 and 39 are formed in the enclosures 25 as passageways for water. In the exemplary embodiment, each enclosure 25 has an inside cross-sectional dimension of six inches. The outside cross-sectional dimension can suitably be six and one-half inches. Additionally, each enclosure 25, in the exemplary embodiment, is approximately thirteen feet or fourteen feet long. In rack 10, the enclosures 25 form, in the exemplary embodiment, three columns which are spaced apart. The spaces between columns of enclosures 25 form pockets 50. The bottoms of the pockets 50 are formed by the base plate 12, the sides of the pockets 50 are formed by confronting walls of the spaced apart enclosures 25 and the ends of the pockets 50 are formed by extensions 32. Disposed within the pockets 50 are suitable neutron absorbers, such as sheets 51 of Boral. Other high absorption neutron absorbers, such as cadmium, borated stainless steel, or poisoned plastic sheets, may also be employed. Extensions 32, preferably, extend along the entire length of the enclosures 25 associated therewith and are of projected dimension from the associated enclosure equal to the distance between confronting walls of spaced apart enclosures 25. In the exemplary embodiment, the thickness of each of the sheets 51 of Boral is one-eighth inch. The sheets 51 of Boral extend along the length of the enclosures 25 in an area corresponding to the active length of the nuclear fuel elements. Boral is sold by Brooks & Perkins Corporation and comprises boron carbide particles disposed in an aluminum metal. The Boral sheets serve as a neutron absorber. Selected rows of enclosures 25 are spaced apart to form pockets 55. The bottom of the pockets 55 is the base plate 12, the sides of the pockets 55 are the confronting walls of spaced apart enclosures 25, and the ends of the pockets 55 are the extensions 32. Disposed within the pockets 55 are suitable neutron absorbers, such as sheets 56 of Boral. Other neutron absorbers may be employed as above-mentioned. In the exemplary embodiment, the thickness of each sheet 56 of Boral is one-eighth inch. The sheets 56 of Boral extend along the length of the enclosures 25 in an area corresponding to the active length of the nuclear fuel elements. In a typical embodiment, there are ten or twelve rows of enclosures 25 and three columns of enclosures 25. Contiguous enclosures are preferably welded together along the lengths thereof for rigidifying the rack 10. The rack 10, in the exemplary embodiment, provides storage areas for thirty-six or thirty nuclear fuel elements. Surrounding the sides and ends of the rack 10 are vertically disposed panels, such as panels 30 of Boral sheets. Other high absorption neutron absorbers, such as cadmium sheets, borated stainless steel sheets, and the like, may also be employed. The sheets 30 of Boral serve as a neutron absorber. The sheets 30 of Boral are employed to maintain the effective multiplication factor (K.sub.eff) for the full array below the required limit or the point of criticality. The panels 30 of Boral are supported by a weld across the top of the edge thereof. Clips 31 inhibit horizontal movement of the panels 30 and allow vertical displacement. The load on the rack is not applied to the panels 30 of Boral. Thus, thermal expansion and rack flexure are accommodated without any load applied to the panels 30. In the exemplary embodiment, the thickness of each of the panels 30 of Boral is one-fourth inch. It is the pockets 50 that provide the enclosures for the sheets 51 of Boral for maintaining the correct positions thereof with respect to the spent reactor fuel elements for effective neutron absorption. The sheets 51 of Boral are welded to the enclosures 25 to prevent inadvertent removal from the pockets 50. Similarly, it is the pockets 55 that provide the enclosures for the sheets 56 of Boral for maintaining the correct positions thereof with respect to the spent reactor fuel elements for effective neutron absorption. Some of the sheets 56 of Boral are removable from the pockets 55 while under water for in-service inspection, while other sheets 56 of Boral are welded to the enclosures 25 to prevent inadvertent removal from the pockets 55. Sheets of Boral, cadmium or borated stainless steel are preferred in the pockets 50 and 55 over water as a neutron absorber because Boral, cadmium and borated stainless steel have a greater shielding capacity. This allows a closer geometric spacing of spent fuel elements without exceeding the K.sub.eff limit. Thus, the spent nuclear fuel elements can be located closer to one another without exceeding the critical limit for the effective greater shielding capacity. This allows a closer geometric spacing of spent fuel elements can be located closer to one another without exceeding the critical limit for the effective multiplication factor (K.sub.eff) for the fuel array. More specifically, the spent nuclear fuel elements can be spaced closer together and the effective multiplication factor (K.sub.eff) for the fuel array will remain below the required limit. In this manner, more spent nuclear fuel elements can occupy a given space in the storage pool of a nuclear power plant. Welded to the outside walls of the exterior columns of enclosures 25 are suitable lift plates 40 and 41. Conventional grapples or hoisting devices grip the lift plates 40 and 41 for raising and lowering the rack 10. According to the present invention, racks for storing spent nuclear fuel elements are placed one above the other (FIG. 3). In this manner, the floor space of a nuclear storage pool for a nuclear reactor plant can accommodate a greater number of spent nuclear reactor fuel elements. In FIG. 3, a rack 10a for storing spent nuclear fuel elements is disposed above the rack 10 for storing nuclear fuel elements. The rack 10a is similar to rack 10 and, hence, parts of the rack 10a similar in construction and operation to parts of the rack 10 have been designated with the same reference numeral accompanied by the suffix "a". For disposing the rack 10a for storing spent nuclear fuel elements above the rack 10 for storing spent nuclear fuel elements, a rack cover 60 (FIG. 3) is placed over the rack 10. The rack cover 60 comprises a top plate 61 with depending longitudinal walls 60'. Formed in the walls 60'are suitable openings 60" for the passage of water. Welded to the top plate 61 are upstanding guide pins 62. Depending from the base plate 12a of the rack 10a are feet 63. Formed in the feet 63 are suitable receptacles 64 for receiving the pins 62, respectively. There are preferably four pins 62 and four feet 63 formed with receptacles 64. The pins 62 are located in the vicinity of the four corners of the top plate 61. The pins 62 and receptacles 64 serve to align the rack 10a relative to the rack 10. For supporting an assembly of racks 10 and 10a, a frame-like support 70 (FIGS. 3 and 4) is provided. The frame-like support 70 comprises a plurality of parallel, longitudinally extending support members, such as I-beams 71a-71e, which are preferably made of structural steel or aluminum. Each rack, such as racks 10 and 10a, has along each end thereof a longitudinally extending support member. For example, along the ends of the rack 10 are I-beams 71a and 71b, and along the ends of the rack 10a are I-beams 71c and 71d. The longitudinal support members 71a-71b extend in a tightfit relation from the wall at one side of the pool P to the confronting wall on the opposite side of the pool P. Additionally, parallel, transversely extending support members, such as I-beams, cross over the support member 71a-71e at right angles. For example, transversely extending support member 72 extends in a direction parallel to the sides of the racks from the wall at one end of the pool in tight-fitting relation. As shown in FIG. 4, the frame-like support 70 can accommodate a group of racks, such as racks 10 and 10a. Suitable interengaging members (FIG. 3) of metal, such as steel or aluminum, are welded to upright members at the four corners of the racks and engage an adjacent inboard wall of the contiguous longitudinal support member of the frame-like support 70 to retain the rack in position relative to the frame-like support 70. For example, fixed to the rack 10 are upright members 80 and 81 of suitable metal material, such as steel or aluminum. The upright members 80 and 81 are disposed at opposite ends of the rack 10. Interengaging member 83 is welded to the upright members 80 at one end of the rack, and interengaging member 84 is welded to the upright members 81 at the other end of the rack 10. Similarly, fixed to the rack 10a are upright members 85 and 86 of suitable metal material, such as aluminum or steel. The upright members 85 are positioned at opposite ends of the rack 10a. Interengaging member 87 is welded to the upright members 85 at one end of the rack 10a, and interengaging member 88 is welded to the upright members 86 at the other end of the rack 10a. Illustrated in FIG. 5 is the I-beam 71d and the interengaging member 88 for the other end of the rack 10a. While the interaction between the I-beam 71d and the interengaging member 88 will be described in detail, it is understood that the interaction and construction of the other I-beams and interengaging members will be similar. The interengaging member 88 has a T-shape configuration with the stem of the T-shaped member fixed to the rack 10a and received by a suitable opening 89 (FIG. 5) formed in the I-beam 71d. The cross-piece of the interengaging member engages an adjacent inboard wall of the I-beam 71d and is of greater dimension than the opening 89 so as to engage the inboard walls of the I-beam 71d adjacent thereto. Through this arrangement, the rack 10a can be raised by grapples or a hoist gripping the lifting members 40a and 41a to remove the rack 10a from the pool P. On the other end, the rack 10a is retained, through this arrangement, securely in the pool P by the frame-like support 70. To avoid the weakening of the I-beams 71a-71e because of the openings formed therein to accommodate the stems of the T-shaped support members, suitable blocks are fixed thereto in the vicinity of the openings, such as metal blocks 90a-90d. Illustrated in FIGS. 6-9 is a modification of the interengaging arrangement between the rack and the I-beam of the frame-like support 70. In the modification shown in FIGS. 6-9, there are no openings formed in the I-beam, such as the opening 89, to accommodate the stem of a T-shaped member. Thus, the blocks 90a-90d are not employed. Welded to the upper surface of the I-beam, such as I-beam 71b, is a flat metal plate 100. Fixed to the angle membes 80 and 81 of the rack 10, such as by welding, is an angle bar 101. Formed in the base of the angle bar 101 is a suitable slot 103. A bolt 102 is swivelly attached to the plate 100 and is received by the slot 103 in the angle bar 101 to enable the rack 10 to be removably secured to the frame-like support 70. A nut 104 retains the bolt 102 in a fixed position against the angle bar 101. |
044477333 | claims | 1. A radiation-shielding transport and storage container for radioactive material, said container comprising: a radiation shielding vessel composed of cast iron or cast steel and defining a storage chamber for said radioactive material and a mouth opening into said chamber and formed with a plurality of seats; a plug-type radiation-shielding cover received in one of said seats and sealed with respect to said vessel by an inner seal; a safety cover speced outwardly from said shielding cover, received in another of said seats and sealed with respect to said vessel by an outer seal whereby said covers define a control space between said inner and outer seal containing gas at a pressure significantly higher than that in said chamber and than atmospheric pressure; and pressure-monitoring means communicating with said space and responsive to a drop in the pressure therein below a predetermined threshold value for signaling a failure of one of said seals. (a) introducing radioactive material into the chamber of the cast iron or cast steel vessel having a wall thickness sufficient to prevent escape of radiation through the walls of said vessel; (b) sealing a radiation-absorbing cover in said vessel; (c) sealing a safety cover to said vessel above said radiation-absorbing cover establishing a control space between said covers which is sealed by said covers from the interior of said vessel and the atmosphere respectively; (d) pressurizing said space with gas at a pressure established above the pressure in the interior of said vessel and above atmospheric pressure; and (e) monitoring the pressure in said space and signaling the failure of a seal of one of said covers upon the monitor pressure dropping below a predetermined threshold value. inserting a plug into said vessel of a thickness sufficient to prevent radiation from escaping through said plug while sealing said chamber with at least one inner seal formed between said plug and said vessel; disposing on said vessel above said plug a safety cover and sealing said safety cover to said vessel with at least one outer seal; establishing a pressure within said chamber of substantially 0.8 to 1.5 bar; establishing with the compartment defined between said cover and said plug and between said inner and outer seals a pressure of substantially 6 bar; and monitoring the pressure in said compartment to detect a change in pressure representing a breach of one of said seals, thereby enabling corrective action. 2. The container defined in claim 1 wherein the pressure in said space is about 6 bar and the pressure in said chamber is between 0.8 and 1.5 bar. 3. The container defined in claim 1 or claim 2 wherein a further cover is mounted on said vessel and sealed relative thereto above said safety cover. 4. The container defined in claim 3 wherein said shielding cover has a frustoconical inner portion and cylindrical outer portion overhanging said inner portion, said outer portion forming a shoulder, said inner seal including sealing rings between each of said portions and said vessel. 5. The container defined in claim 4 wherein said shielding cover and said vessel are composed of spherolytic cast iron. 6. A method of packaging radioactive material which comprises the steps of: 7. A method of operating a transport and storage vessel for radioactive waste which comprises introducing radioactive material into a chamber of a cast iron or steel vessel having a wall thickness sufficient to prevent escape of radiation therefrom; |
043702961 | claims | 1. A compact toroidal fusion reactor for producing energy from fusion reactions having a plasma containing toroidal fusion region and having a main axis, comprising: (a) a toroidal field generating means for producing a toroidal magnetic field in said fusion region upon the passage of current therethrough, said toroidal field generating means having an inner circumferential contour and an outer edge, said inner circumferential contour having a recessed portion extending for an arcuate section along the side nearest said main axis and being positioned substantially immediately proximate said toroidal fusion region; and (b) ohmic heating coils for ohmically heating said plasma, said ohmic heating coils positioned adjacent to said toroidal fusion region and between said toroidal fusion region and said toroidal field generating means in a region provided on the inner circumferential contour of said toroidal field generating means along the side nearest the main axis of said toroidal fusion region. 2. A fusion reactor as recited in claim 1 wherein said toroidal field generating means comprises a plurality of toroidal field coils each having an inner circumferential contour and an outer edge. 3. A fusion reactor as recited in claim 1 wherein said fusion reactor further comprises means for producing fission reactions and wherein said fission producing means comprises a region of fissile-fertile material positioned within the region of said toroidal field generating means. 4. A fusion reactor as recited in claim 3 wherein said toroidal field generating means comprises a plurality of toroidal field coils forming a toroid about a main axis and having an inner circumferential contour positioned substantially adjacent said toroidal fusion region except in the region of said ohmic heating coils and wherein said fissile-fertile material is positioned primarily on the side away from the main axis of said toroidal coils. 5. A fusion reactor as recited in claim 4 wherein said fissile-fertile material forms discrete regions within the region of said plurality of toroidal field coils and extends generally from the inner circumferential contour of said toroidal coils to an outer circumferential contour of said toroidal coils on the side away from the main axis of the toroidal coil. 6. A fusion reactor as recited in claim 5 or 1 wherein the main axis of said toroidal field generating means coincides with the main axis of said toroidal fusion region. 7. A method of increasing efficiency of a fusion reactor of a toroidal configuration having a main axis and having toroidal field generating means with an inner contour positioned substantially immediately adjacent a toroidal fusion region and ohmic heating coils for ohmically heating plasma within said toroidal fusion region comprising the steps of forming a recessed portion in said inner contour of said toroidal field generating means extending for an arcuate section along a side nearest the main axis and positioning said ohmic heating coil between the toroidal fusion region and the toroidal field generating means in said recessed portion region whereby space is made available near the axis of the toroidal fusion region. 8. A method as recited in claim 7 further comprising the steps of utilizing the space made available near the main axis of the fusion region by increasing the radial dimension of the toroidal field generating toward a side nearest the main axis of said toroidal fusion region, to increase the cross-sectional area of the toroidal field generating means in the region nearest the main axis of the toroidal fusion region. |
summary | ||
abstract | A method and system for the thermoelectric conversion of nuclear reactor generated heat including upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy and supplying the electrical energy to a mechanical pump of the nuclear reactor system. |
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047605898 | description | DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a grid cabinet 1 with an X-ray film cassette tray 2, also known as a cassette holder, which slides in and out of the cabinet 1. The tray 2 does not separate completely from the cabinet 1, but slides out only to the position shown in FIG. 1 to allow for easy inserting or removing of film cassettes. The tray 2 locks automatically at both farthermost inner and outer positions. The lock holding the tray 2 in either of the end positions can be released by squeezing the trigger 11 in the handle 7. The tray 2 has two pairs of jaws 3, 4 and 5, 6 for centering a cassette inserted in the tray. The jaws of each pair are coupled together and move isocentrically in respect to the center of the tray 2. Each pair of the jaws move independently of the other. When the tray 2 is pulled out of the cabinet to the end position by the handle 7, the jaws 3, 4 open automatically to full size. The jaws 5, 6 can be opened by (a) pulling out the handle 8 or (b) in a one-hand operation by pushing the jaw 5 into the cabinet with a film cassette being inserted, then the jaw 6 linked to the jaw 5 will open automatically and the cassette can be inserted under a lip 9. The lip 9 on the jaw 5 and the lip 10 on the jaw 6 prevent the cassette from falling out when the cabinet 1 is used in the vertical or upside down positions. In another embodiment of this disclosure the pair of the jaws 5, 6 is connected to the cabinet 1 in such a way that both pairs of the jaws open automatically together when the tray is pulled out. A choice between these two embodiments depend on a user's preference and specific applications. For example, when the cabinet 1 is used in the vertical or upside down position an automatic opening of the jaws 5, 6 together with the jaws 3, 4 will result in the cassette falling out. A grid 12 can be placed in a frame 14 either (a) from the top by unlocking flippers 17 or (b) from the front by opening a grid frame lock 15 together with a spring 13, then sliding the frame 14 up to the front to the position in which the flippers 17 can be unlocked and the grid can be inserted or removed. The grid frame lock 15 holds the progressive spring 13 in tension all the time except when the grid is being replaced from the front. The grid 12 inserted into the frame 14 moves on the ball rolling slides from the front to the back of the cabinet 1 whenever actuated by the motor drive system 16 described in FIG. 3. The motor drive system 16 is disposed in the back of the cabinet 1. This location and the compactness of said assembly allows reduction of the width of the cabinet 1 by at least the width of said system and, therefore, for a longer travel of the cabinet in the X-ray table and, thus, for an additional coverage of a patient. Stationary grids are also used in some applications; a grid cabinet for stationary grids, according to this disclosure, is identical to the aforementioned grid cabinet, except for the absence of the motor drive system 16. FIG. 2 illustrates the tray 2 with the cassette centering jaws 3, 4, 5, 6 and means for sensing both the width and the length of the cassette, continuously variable throughout the range of sizes. The tray 2 is shown in the position slid all the way into the cabinet 1. The jaws 3, 4 are connected by respective arms 18 and 19 to the arm 20 which pivots about the shoulder rivet 21 placed in the center of the tray 2. The jaws 5, 6 are connected by the respective arms 22 and 23 to the arm 24 which pivots about the pivot point 25 placed toward the back of the tray 2. The jaws 3, 4, 5, 6 move on ball rolling slides in respective channels 26, 27, 28, 29. The channels 26, 27, 28, 29 are offset in respect to the point 21 and are longer than one half of the tray dimensions to provide a longer travel path of the jaws than the largest difference in the cassette sizes in order to have enough structural distance between the balls of said slides and better rigidity. Movement of one of the jaws of the pair 3, 4 causes the other jaw of said pair through the linking arms 18, 19, 20 to move simultaneously and center the cassette between said jaws. Similarly, the jaws 5, 6 are coupled together by the linking arms 22, 23, 24 and movement of one of the jaws of the pair 5, 6 causes the other jaw of said pair to move simultaneously and center the cassette between said jaws. The jaws 3, 4 are retracted by the spring 30 and the jaws 5, 6 are retracted by the spring 31. The tension of the springs 30, 31 holds the cassette in the center of the tray 2. When the tray 2 is being pulled out of the cabinet 1 by the handle 7, firstly, the bearing 32 attached to the jaw 4 rolls in the channel 33 to the end of said channel, then an arm 34 connected to the channel 33 starts pivoting about the pivot point 35 affixed to the cabinet 1 and not to the tray 2 and causes the jaws 3, 4 to open to the full gap. When the tray 2 is inside the cabinet 1, one dimension of the cassette is determined by the position of the jaw 4 and the bearing 32 in the channel 33. The position of bearing 32 determines, in turn, the position of the arm 34 and a sensing arm 36 extending from the latter to a rack 37. The rack 37 rotates gear 38 on potentiometer 39 disposed in the cabinet 1. The other dimension of the cassette is determined by the position of the jaw 5 and the arm 40 actuated by the bearing 41 attached to the jaw 5. A sensing arm 43 extends from the arm 40 to a rack 44 and moves as the arm 40 pivots about the pivot point 42 affixed to the cabinet 1. The rack 44 rotates the gear 45 on the potentiometer 46 disposed in the cabinet 1. The potentiometers 39, 46 send signals to an X-ray collimator which adjust the collimator 69 in a relationship consistent with the X-ray film cassette held by the tray. In another embodiment of this invention the sensing arms 36 and 43 are connected by a mechanical linkage 71 directly to the collimator's shutters 70 and automatically adjust the shutters to match the fields of an X-ray beam with the film size as shown in FIG. 2A. This system does not require potentiometers nor servomechanisms and is less expensive and simpler. Still in another embodiment of this invention in place of the potentiometers 39, 36 incremental encoders can be used. For an automatic opening of the jaws 5, 6 together with the jaws 3, 4 the arm 24 is connected to hinge arms 47 and 48. The hinge arm 47 is affixed to the cabinet 1 at the pivot point 49. When the handle 7 is being pulled out, firstly, the hinge arms 47 and 48 extend completely and hold the arm 24, then said arm starts moving and opening the jaws 5, 6. For a manual opening of the jaws 5, 6 the arms 47, 48 are disconnected from the arm 24. FIG. 3 illustrates means for actuating the grid frame comprising the motor drive system 16. A variable speed motor 50 when operating rotates a cam 51 which in turn actuates a cam follower 52 with an offset bushing 53. The cam follower 52 is attached to an arm 54 which pivots about the pivot point 55. On the opposite end of the arm 54 a roller 56 pushes the grid frame 14 counter to the tension of the progressive spring 13 which holds the frame 14 in contact with the roller 56. An actuator 57 affixed to the arm 54 actuates microswitches 58, 59. In another embodiment a light breaking device can be used in place of said microswitches. The microswitch 58 brings the motor 50 to the starting position also known as the homing position when the exposure switch is disconnected. The cam 51 is shown in the homing position. The microswitch 59 initiates an exposure whenever the cam follower 53 is at the point of the steepest curvature of the cam 51, that is when the grid 12 in the frame 14 is moving at the highest speed. The shape of the cam 51 is designed to insure: firstly, rapid but controlled release of the spring 13; secondly, gradual decrease in the grid speed; thirdly, reversing the direction of the grid travel in a very short time; and fourthly, progressive slowing of the spring loading when the spring tension increases. The function of the arm 54 is to increase the length of the grid travel as compared to the conventional designs and to keep the motor drive system 16 compact enough to place it in the back of the cabinet 1. The bushing 53 on the cam follower 52 has an offset outside diameter compared to the hole in the bushing and the ratio of the circumference of the bushing 53 to the circumference of the cam 51 is equal to an odd number. This design insures that the reversing of the grid travel direction takes place at random points within the distance between grid lines and, therefore, prevents the grid lines from being photographed. FIG. 4 illustrates graphically the characteristics of the grid movement; one cycle of the grid travel is shown. A displacement of the grid from its starting position is shown on the vertical axis and the time is presented on the horizontal axis. The initial point (0,0) on the graph represents the grid at the homing position when the progressive spring 13 is fully loaded. At the time zero the motor is turned on, said spring is released and the grid moves to point A when acceleration reaches maximum. The cam 51 is designed to maintain the contact with the cam follower 52 with a minimum reduction in the acceleration. An X-ray exposure starts at the point A when the grid travels at the maximum speed and for this reason allows for very short exposures to be taken without grid lines being photographed. Past the point B the speed of the grid is being progressively reduced as controlled by the shape of the cam 51 and the speed of the motor 50. The grid movement at high speeds in the initial phase of the cycle, from A to B, allows for short exposures and, therefore, for reduced radiation doses to a patient when high speed films and rare earth screens are used. Gradual decrease in the grid speed results in a longer cycle suitable for medium exposures to be taken before the travel direction of the grid is reversed at the point C. In addition, lower cycling frequency causes less vibrations and, thus, improved picture quality. From the point C to the point D the grid speed is gradually further reduced for easier loading of the spring. At the longer exposure times, as used in tomography, the speed of the grid is not critical because there is enough time for several grid lines to pass the same point and, thus, not to be photographed. The motor drive system 16 as described in FIG. 3 insures that the time for reversing the grid travel direction is short and that the reversing takes place at random points. The variable speed motor 50 used in this invention allows for adjusting the frequency of the grid lines travel: (a) to accommodate different exposure times, (b) to avoid the said frequency to synchronize with the X-ray generator's frequency and (c) to reduce resonance vibration of the suspension. FIG. 5 illustrates the ball rolling slides also known as rails for the jaws 3, 4, 5, 6. The tray 2 has lips 60 bent 45 degrees up. Two identical rails 61 are spot welded to the bottom of the tray 2, each has a lip 62 symmetrical to the lips 60. The top part 63 and the bottom part 64 of said slides are formed as shown in FIG. 5 to provide a symmetrical four point loading on the ball 65, said parts 63, 64 constitute also an integral structure of respective jaw. This design allows for very small structural thickness and for preloading of the balls. Preloaded balls provide smooth motion, durability and no rattling. FIG. 6 is the cross section of one side of the ball rolling slides for the grid frame 14 movement. The grid cabinet 1 has a spot welded channel 66. The grid frame 14 with the grid 12 rolls between two rows of balls 67, 68 in the channel 66. The frame 14 formed as shown in FIG. 6 constitute an integral structure of said slides. Ball rolling slides for the tray movement, wherein part of the structure of the cabinet and the tray constitute also an integral structure of said slides, are very similar to the ball rolling slides for the grid frame movement. Utilization of all linear moving components of the device, comprising the grid cabinet, the cassette tray, cassette centering jaws and the grid frame, as an integral structure of the ball rolling slides significantly reduces dimensions of the device, improve its rigidity and at the same time lowers the cost. Although, one detailed embodiment of the invention is illustrated in the drawings and previously described in details, this invention contemplates any configuration and design of the components which will accomplish the equivalent results. |
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