A laser surveillance system installed at spent fuel storage pools (SFSP's) will provide the safeguard inspector with specific knowledge of spent fuel movement that cannot be obtained with current surveillance systems. The laser system will allow for the division of the pool's spent fuel inventory into two populations - those assemblies which have been moved and those which haven't - which is essential for maximizing the efficiency and effectiveness of the inspection effort. We have designed, constructed, and tested a full size laser system operating in air and have used an array of 6 zircaloy BWR tubes to simulate an assembly. The reflective signal from the zircaloy rods is a strong function of position of the assembly, but in all cases is easily discernable from the reference scan of the background with no assembly. A design for a SFSP laser surveillance system incorporating laser ranging is discussed. 10 figures

Bieber, A.M. Jr.

Fiarman, S.

Zucker, M.S.

A laser surveillance system installed at spent fuel storage pools will provide the safeguard inspector with specific knowledge of spent fuel movement that cannot be obtained with current surveillance systems. The laser system will allow for the division of the pool&#x27;s spent fuel inventory into two populations - those assemblies which have been moved and those which haven&#x27;t - which is essential for maximizing the efficiency and effectiveness of the inspection effort. We have designed, constructed, and tested a laser system and have used it with a simulated BWR assembly. The reflected signal from the zircaloy rods depends on the position of the assembly, but in all cases is easily discernable from the reference scan of background with no assembly

Fiarman, S

Zucker, M S

Bieber, A. M., Jr.

UNT Digital Library

Laser surveillance system for spent fuel

Zucker, M. S.

A LASER SURVEILLANCE SYSTEM FOR SPENT FUEL *S. Fiarman, M.S. Zucker, A.M. Bieber, Jr.AbstractBNL-27660I S - -A laser surveillance system installed at spent fuel storage pools (SFSP's)will provide the safeguard inspector with specific knowledge of spent fuel move-ment that cannot be obtained with current surveillance systems. The laser sys-tem will allow for the division of the pool's spent fuel inventory into two popu-lations — those assemblies which have been moved and those which haven't —which is essential for maximizing the efficiency and effectiveness of the inspec-tion effort. We have designed, constructed, and tested a full size laser systemoperating in air and have used an array of 6 zircaloy BWR tubes to simulate anassembly. The reflective signal from the zircaloy rods is a strong function ofposition of the assembly, but in all cases is easily discernable from the refer-ence scan of the background with no assembly. A design for a SFSP laser surveil-lance system incorporating laser ranging will be discussed.1. IntroductionBy the year 2000 it is estimated that there will be 1 million spent fuelassemblies in storage at-reactor (AR? or affay-froili-reclCtOr (AFR) Spent fuel Stor-age pools (srsp). safeguarding these assemblies will impose an increasingburden, on the IAEA inspectorate. Presently, the IAEA safeguards spent fuelassemblies by a combination of item counting and containment and surveillance(C/S) systems such as seals and TV or movie cameras. For the future, new C/Ssystems will undoubtedly be introduced to improve the efficiency and effective-aess of Che periodic inspections at reactors. The actual routine inspection ef-fort (ARIE) for power reactors is only 9-15 man-days per year1 with a maximum*Research carried out under the auspices ofthe United States Department ofEnergy under Contract No. DE-AC02-76CH00016.-DISCLAIMER •TKl Bool « » preo»W » • » account ol v«.V »on«,rM by «i ajenCV O< « • Unit* Sm GMn.nv.rl.Npuher ine united Stales Government nor any m w thereof, nor any ol Irwr ~nolovpes. makesanvS L i . or MM. or animei m, W* Maiw or nwmftalw tor « . aconcy.^ISLesTe? u«d««o ol any inlornunon. ananlut 0-M^B. or oocra discloW. ore ^ n n i a l »'0<l»cl oroces.. or service by trada i m ir»»m..l. manutaclurer, or othenMe. doaanot rrass.rlly w w or Imply M endor«™.t. recommencalion. or larerio, bythe Unil«aStale. Go^meni or m «eney Ihaml. Th. viam aM opWor. ol ~,hor, . « » here.n do notnecessarily slate or ref s.1 those ol the United Slates Government or .ny agency tuereor.DISTW3UTI0N OF THIS DQCUMEST IS L!KLfi«fT9rroutine inspection effort (MRIE) of 1/6 of a man-year.2Some of the new systems being developed include Cerenkov glow detectors,NDA scanning of spent fuel, radiation and notion detection in the pool,3 *nd alaser surveillance system. The laser system, described in this paper, recordsthe specific information of storage rack location and times of spent fuel move-ment during the inspector's absence. The inspector can use this information todivide the assemblies in the pool into two populations — those that have beenmoved and those that haven't — and direct the appropriate safeguard system athis disposal toward each population. The assumption being made is that any cred-ible diversion scenario involves movement of the spent fuel.NDA scanning of spent fuel will probably be too slow to scan the hundredsof assemblies in the pool necessary to achieve high detection probability. ForPWR's, where two spent fuel assemblies contains a goal quantity of plutonium,95% detection probability is achieved by assaying 77% of the assemblies. Onlywhere sampling plans are based on solely those assemblies which have been movedcan high detection probabilities be achieved.The inspector spends many hours watching TV or movie frames of poolside ac-tivity. If he had a knowledge of the times and locations of fuel movement, hecan focus his attention on the important frames and not waste time with framesshowing irrelevant poolside activity such as the maintenance and testing of fuelhandling equipment or the training of bridge operators. The time spentreviewing irrelevant occurrences in the pool area decreases safeguards effective-ness by numbing alertness to genuine suspicious activity.2. The Laser ConceptThe laser system extracts the fuel movement information by creating a sheetof light s 25' below the surface of the pool and directly over the assemblies inthe storage racks. The light is generated by two separate laser beams sweepingin a horizontal plane (see Figure 1) just below the bottom of the fuel transfermechanism. Movement of the fuel transfer mechanism alone without an assemblydoes not intercept the laser beams. Laser light reflected from the stainlesssteel sides of the pool (the reference scan) is detected by two phoComultiplier(PM) tubes. The laser scanning signals from the PM tubes are amplified andprocessed by a small computer. The laser, PM Cubes, electronics and mini-computer are housed in a tamper-indicating container at poolside whil : thescanning and receiving mirrors and stepping motor are located below water.A raised assembly will slowly break through the covering sheet of lightcausing a change in the reflective signal when the laser beams are at specificangles. The response anomaly in both PM tubes is interpreted by the computer asassembly movement and the location of the assembly is determined by triangula-tion and perhaps by laser ranging as well.3. A Laser System PrototypeA prototype laser system has been designed and constructed to operate inair with approximately the same geometry as exists in a SFSP. Only one laserbeam and PM tube were assembled to demonstrata the engineering principles of thesystem. Tests were run using a mock assembly of six BWR zircaloy fuel rods.The details of the system are shown in Figures 2 through 6 and are describedbelow.Figure 1. A PWR SFSP Showing the Placement ofTwo Laser Systems, the Beam Scan-ning Housings and the Laser Beams.uaexs•> ' . • •22 I' 'LASSS BS4M3,'»•>Figure 2. Detailed Diagram of the Later.System Constructed at BHL.MOTORCONTROL\DISCLAERHeNeMOTORX1OBEAMEXPANDERMIRRORSSTEPPINGMOTORCURRENT TOVOLTAGE CONVERTEROPAQUE>-TUBEINTERFACEl AiHP-9830ACOMPUTERFigure 3. Photograph of ths BXL Laaar System.Figure 4. Photograph of the Electronics, and HPCompuCer Used for Controlling theLaser System.rFigure 3. Photograph of th« Housing for theMirror System Showing Lasar BeamBeing Bent 90°.Figure 6. Photograph of the Simulated BWR As-sembly Using 6 Zircaloy Rods. TheBright Spot is the Laser Beam.Laser and Associated EquipmentA small 0.5 milliwatt HeN* red laser (632,onm) emitting a lmm dia. laserbeam waa used. A b«aa enlarger was mounted on the laser to increase the beamsize, provide focussing, and to reduce beam divergence. Between the laser andbeam enlarger, discs with small holes or slits were located to mechanically chopthe beam. An a.c. synchronous motor allowed a chopping frequency of 60xN whereN is the number of holes or slits on the disc. We used discs of N»30 and N-100.The purpose of the chopped beam was to -generate an a.c. light signal, therebyallowing Che filtering of the d.c. background lighting component.Mirror GeometryThe laser beam was directed down 18 feet to a 1 inch dia. 45° mirror andthen horizontally 75' to a wall. The reflected light was received by a 3 inchmirror on an adjustable 45° mount. The two mirrors are mounted close to one an-other and linked by gears to a single stepping motor that allows for synchronousscanning and receiving. Scanning rates of up Co 50 steps/sec were used which at0.125° per step resulted in a 90° sweep in ̂  15 seconds. Careful partitioningof the sending and receiving signals prevented the background scattered laserlight from entering the PM tube.PM DetectorThe PM detector was an RCA C7164R, lh" diameter, 10 stage head-on type tubeemploying a multialkali pbotocathode having exended red response. Two red fil-ters having bandwidths of <r lOnm centered at «f 632.8nm were mounted on the tube.The tube was encased in an anti-magnetic shield to reduce pick-up from the syn-chronous motor. The light from the receiving mirror was directed to the PM tube10rvia an opaque 18' tube to block background lighting and scattered laser light.The PM tube was operated at 900-1200 volts.Electronics System.All control, data storage, and data analysis are carried out using aHewlett-Packard 9830A desktop computer system, with suitable signal conditioningand interfacing.Figure 7 is a block diagram of the overall system. Two major functions areperformed: control of the stepping motor which drives cha mirrors sweeping thelaser beam and PM tube field of view; and input and storage of voltage readingsfrom the PM tube. A single interface, designed, and built at BNL, handles commu-nications between the computer and the peripheral devices. A commercial 7k.digit 200 millivolt digital voltmeter (DVM) with BCD outputs is used for analogto digital conversion of the PM tube output. The pulsed output of the PM tubeis pi.-oces*i!d through current-to-voltage conversion and precision rectificationprior to being fed to the DVM. Each of the major pieces of the system isdescribed in detail below.Current-to-Voltage Converter and Precision Rectifier (CVCPR). Since achopped laser beam is used, the signal from the PM tube is current pulses, thepeak height of which is a function of the intensity of the reflected beam. TheCVCPR simply converts these current pulses to voltage pulses and rectifies them,providing a slowly varying DC signal to the DVM. Conventional integrated opera-tional amplifier circuitry is used.11PhotomultiplierTubeCurrent-To-VoItageConverter and PrecisionRectifier3% Digit 200mVDigital Voltmeterwith BCD OutputSteppingMotorInterface4tHewlett-Packard9830A DesktopComputerFigure 7. Electronics System Block Diagram12Digital Voltneter (DVM). A 3% digit 200 millivolt digital voltmeter isused for analog-to-digital (A-to-D) conversion of the processed DC signal fromthe PM tube. The output of this DVM is standard 8-4-2-1 BCD data.Stepping Motor. A 12V DC stepping motor is used to drive the mirrors ofthe system. This motor requires properly phased control pulses to each of fourwindings to advance. The pulses are provided by a special purpose integratedcircuit stepping motor controller which is part of the system interface.Interface. The interface performs three major functions: (1) selection ofthe proper peripheral (DVM or stepping motor) to be addressed by the computer;(2) synthesis of proper control signals for the computer and the peripherals;and (3) provision of 12V DC power for the stepping motor. The interface alsohas limited capability to control the system without the computer. Allinterface electronics (except the stepping motor controller) are conventionalTTL logic.Hewlett-Packard 9830A Computer. The laser system is controlled by aHewlett-Packard model 9830A desktop computer. This computer is programmable inBASIC, and has 16K words of memory, cassette tape storage for data and programs,and an X-Y plotter. All system functions are under computer control, includingmirror positioning, data acquisition and storage, and data analysis. All soft-ware is modular, and data storage is handled separately from data analysis toprovide maximum flexibility.Simulated Fuel Assembly.Six %" zircaloy rods were aligned roughly into a section of a BWR assembly(see Figure 6) to obtain a realistic reflective response to the incident laserbeam.4. ResultsUnder manual control, a 1%" dia. laser beam was scanned across thesimulated BWR assembly located at. various distances from the mirrors. Severalof Che scans shown in Figure 8 demonstrate Che variety of responses possible.Besides solid angle geometric effects on the response, there is a tremendousvariation in reflective intensity depending on just where on the rods the laserspot fell. Some of this sensitivity may be reduced if the beam size isincreased to the largest which will still allow resolution sufficient to locateprecisely an assembly.The present method of separating the two axes of the sending and receivingmirrors produces an assembly shadow effect when the light from the laser beamhitting the wall and returning to the receiving airror is blocked by the assem-bly. This effect is indicated in Figure 3.The scan step was 1/8° which translates to 2" at R«75' compared with an 8x8BWF assembly dimension of 5". Hence, even at the furthest distances, there willbe at least three anomalous points to a BUR assembly and even more for a FWR as-sembly. Reproducibility of a scan in all tests was very good.At no time was there any ambiguity that an anomaly was being detected sincethe reference scan (either from a highly dispersive wall or from a sheet ofstainless steel) with i.o assembly had a fairly smooth variation with angle(dotted line in Figure 8). The determination of the location of the assembly14Figures. Laser System Response as Beam ScansAcross BWR Rods Located at VariousDistances From the Scanning Mirror.RECEIVER MIRROR SENDING MIRROR15from a triangulation calculation baaed on Che two angles of the laser beams andthe known distance between the lasers will be performed by the computer.The uncertainties in the determination of angle can only be found from morerealistic tusts at a SFSP, but must be compatible with the goal of locating theassembly to within the size of one storage rack location.Ultimately, the computer, upon request by the inspector, will generate atable (see Table I)- which will list the X-Y coordinates and times of anomalies.These coordinates can be correlated with assembly location with either anoverlay map such as shown in Figure 9 or directly if the storage rack geometryis stored in the computer.Table IAtlantis Nuclear Power StationSpent Fuel Pool Surveillance AnomaliesDate Time Scan # _X_ _Y_14317767206584857478491/2/2/3/3/4/4/5/5/6/2/4/6/8/10/12/14/16/18/20/818181SI8181818181810: 23: 430: 25: 3712: 37: 521: 17: 359: 12: 5014: 26: 2322: 20: 515: 53: 1920: 25: 3918: 57: 83.737.581.692.158.568.970.835.296.625.502.742.072.056.903.055.849.961.445.936.7816Figure 9. Overlay Map of a SFSP ShowingComputer Generated Storage Rack andLaser. System Coordinates and aListing of Simulated SFSP Anomalies.RTLRNTI5 NUCLERR POWER 5TRTIDN0HB7BSH321c2>EF5H1JKLMN0N 7 H f t t 1 1 1111 11115TDRRBE RR<!< CDDRDINRTE5X/Y CDDRD1NRTEBX MRRK5 LR5ER LDCRTJDN51111 1111 r t T T 1111 LLLL LL112 3 H S B 7 B 3 12 11 12 13 1M IS2 3 H 5 B 7 B 3 I 0175. The Design Features for a Prototype SFSP Laser SystemWith the encouraging results from the first prototype laser system, we aredesigning a second system to be tested at a SFSP. Several changes will be madeto account for the change in beam path from air to water. Foremost is thechange from a red laser to either a c.w. blue laser or to a pulsed u.v. nitrogenlaser.The attenuation length vs. wavelength for underwater transmission of lightis a maximum for blue light (see Figure 10). At a total path length of 150' theintensity loss for blue light is only about 80S whereas for red light it isseven orders of magnitude.If it is thought necessary to strengthen the laser system by incorporatinglaser ranging, a pulsed nitrogen laser will probably be used. This type oflaser is known to be reliable and inexpensive and capable of producing the shortpulses necessary for tanging to within a few inches in a path length of lessthan 75'.* Although u.v. light is highly attenuated in water, the narrow pulsesallow for compensating high peak power.Besides the intensity attenuation of the water, the water temperature gradi-ents may introduce beam bending problems that will require a larger field ofview for the receiving mirror. The tests j.er formed in air used a field of viewabout 20 times the laser beam spot size.An overall improvement of the luirror design should reduce the size and com-plexity of the unit that is lowered in the pool. Perhaps the long tube can beeliminated if the sending and receiving beams can be transmitted to the pool'ssurface in water.18Figure 10. Attenuation Length vs. Wavelengthfor Underwater Transmission ofLight in (A) Distilled Water,(B) Oceanic Coastal Water, and(C) Typical. Lake Water.5300 1)00 500 600IN NANOMETERS19The electronic package will require a redeaign if laser ranging isintroduced. Even if a blue laser is used, the electronics may be changed to in-corporate a lock-in amplifier and precision chopping of the beam. Also, the com-puter software will have to be revised to calculate the assembly location byboth triangulation and ranging. With laser ranging, two laser beams are stillnecessary to detect the raising of one assembly in the shadow of another.6. ConclusionsThe laser surveillance system described above will introduce an electroniccover — a sheet of laser light — over the spent fuel assemblies. When an as-sembly is raised and intercepts the two sweeping laaer beams, the altered reflec-tive signals are processed by a small computer and the exact position of theraised assembly is calculated by triangulation, or by ranging, or both. If atthe start of an inspection of a SFSP, the inspector ess; Id know which assemblieshad been moved between inspections, then he could apportion his time so that themoved assemblies would receive the greater safeguard effort. The system we haveconstructed and tested demonstrates the engineering principles involved and hasprovided enough information to design a system to be used at a SFSP. The lasersystem is basically a simple system consisting of a laser, some mirrors, astepping motor, and a FM tube interfaced to a small computer. The small com-puter can be time-shared with other C/S devices under development. The final de-sign should be rugged and long-lived and also relatively inexpensive.207. Acknowledgement 3We wish to thank Mike Degen for valuable assistance in testing the lasersystem and Tony Fabiano for his help in designing and constructing the hardware.We are indebted to Jon Sanborn for helpful discussions.218. Reference!1. D. Tolchenkov, A. Bilyk and M. Honami, "Study on Estimation of Nuclear Hate-rial Facilities Under Safeguards and Inspection Manpower Requirements for1978-1984," IAEA/STR-74, October 1978.2. "The Structure and Content of Agreements Between the Agency and StatesRequired in Connection with the Treaty on the Non-Proliferation of NuclearWeapons," INFCIRC/153, IAEA, Vienna (June 1972).3. Proceedings of the 1st Annual Symposium on Safeguards and Nuclear MaterialsManagement, ESARDA, April 25-27, 1979, Brussels, Belgium.4. Tom Oavies, Mel Nelson, EG&G, Goleta, California, private communication.5. CRC Handbook of Lasers, Robert J. Pressley, Ph.D., Editor, The Chemical Rub-ber Company, CRC Press, Cleveland, Ohio.22

Laser surveillance system for spent fuel

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