A unique radioisotopic label as a new concept for safeguarding and tagging of long-term stored items and waste
AA unique radioisotopic label as a new concept forsafeguarding and tagging of long-term stored items andwaste
Dina Chernikova ∗ ,a , K˚are Axell a,b a Chalmers University of Technology, Department of Applied Physics, Nuclear Engineering,Fysikg˚arden 4, SE-412 96 G¨oteborg, Sweden b Swedish Radiation Safety Authority, SE-171 16 Stockholm, Sweden
Abstract
The present paper discuss a novel method of tagging and labeling of wastecasks, copper canisters, spent fuel containers, mercury containers, waste pack-ages and other items. In particular, it is related to the development of newlong-term security identification tags/labels that can be applied to articles forcarrying information about the content, inventory tracking, prevention of falsifi-cation and theft etc. It is suggested to use a unique combination of radioisotopeswith different predictable length of life, as a label of the items. The possibil-ity to realize a multidimensional bar code symbology is proposed as an optionfor a new labeling method. The results of the first tests and evaluations ofthis are shown and discussed in the paper. The invention is suitable for use initems assigned to long-term (hundreds of years) storing or for final repositories.Alternative field of use includes fresh nuclear fuel handling and shipment ofgoods.
Key words: identification tags, radioisotopes, multidimensional bar codesymbology, long-term storage, mercury waste, nuclear waste, environmentalsafety
1. Introduction ”...The desire to uniquely identify valuables is not new to human thought.Written history shows that the ancient Egyptians used seals to identify govern-ment documents, while the Babylonians used tags and seals for their trade withthe Indian and Chinese civilizations” , - Christos Makris (DOE Office of Researchand Development) [1]. Thousands of years has passed since then, technologyprogresses, and even despite this tags and seals did not loose their actuality andimportance. Nowadays security and identification labeling are extensively usedin everyday life and industry to track containers and products, in automatic ∗ Corresponding author, email: [email protected]
Preprint is not submitted October 30, 2018 a r X i v : . [ phy s i c s . i n s - d e t ] J a n nd manual ways. There are several reasons for using identification tags, suchas to provide the verification of the items in question, to identify the theft orthe misuse of an item and to provide the information about the item withoutbreaking its integrity. Therefore, while choosing a particular type of tag it isnecessary to consider a number of important parameters. There were a few attempts to systematize criteria for the selection of a spe-cific tag, for example, based on: purpose of tag, type of the container, robust-ness, reliability, easy of application, effectiveness, interface with other safeguardsand security elements, cost etc. [1]. Although, in connection with a long-term(hundreds of years) stored item, such as nuclear waste, spent fuel or mercurycontainers, one can consolidate these requirements in five main points (”intuitiverequirements”), i.e. the ideal tag must provide:1. Environmental safety (avoid corrosion effects of e.g. copper canisters).
The labeling system should avoid corrosion effects of canisters which canbe induced in the long-term run, thus for instance avoiding leakage of spentfuel waste components later on.
2. Non-contact reader system (preferably).3. Long operation time.
The labeling system should have an operating timeat least from ten to a few hundred years.
4. Large and unique tag memory.
The labeling system should enable fullyunique identification of the canister content in a manner consistent withpermanent records of the storage or repository.
5. Security technique against falsification of data, errors/multiple verifica-tion.
The labeling system should have high level of security, i.e. low riskof falsification or error.
Thus, an ideal identification tag meet all the challenges of the internationalinitiative on a holistic Safety, Security and Safeguards (’3S’) concept. Therefore,hereafter we will consider the suitability of the currently existing technologiesand new approach to these ”intuitive requirements”.
The conventional tagging techniques include etching characters, affixing iden-tification plates, welding, etc. However, when considering an application forlong-term storage of waste canisters they have a number of gaps in the factorsof environmental safety, security and long operation time. Other disadvantagesof the traditional labeling technology are described in [2]. Modern labeling tech-niques may partly solve these problems and be useful for meeting the goals ofa unique labeling system compatible with the record keeping of the storage orrepository. Among the modern labeling techniques are radio frequency taggingsystems, electronic tags, ultrasonic systems [3] and reflective particle tags [4] etc.The main disadvantages of some of the techniques are well analyzed in [5, 6],2ereafter we only give a short overview of them in the light of the previouslydefined ”intuitive requirements”.Radio frequency systems (RF) consist of a memory chip, an antenna, and atransmitter/receiver system and therefore overcome problems related to printingor etching characters on the side of the container. RF devices can be active orpassive. Active tags contain a small internal power source to communicate, storeand process large amounts of information in the chip. A power source is usuallya lithium battery lasting less than 5 years. This makes them unsuitable for use inlong-term storages. Passive tags have no battery. In order to provide power anddata to the chip, they use the current in the loop antenna which is induced by theinterrogating RF signal. Thus, they receive power from the reader’s antenna.However, their main drawback is that only a limited amount of information(roughly a few bits) can be stored. The main problems encountered with bothactive and passive RF devices is related to interference of the metallization layerwith the RF signal, locating methods and low transmission range.Electronic tag technology contains transponder units that hold a uniqueidentification number retrievable by touching it to an inductively-coupled reader.However, they are able to store up to a few tens of kilobytes of information andwork for up to 10 years. When considered for application to long-term storeditems (i.e. stored for more than 10 years), e.g. nuclear waste containers or spentfuel copper canisters, present labeling methods listed above fail either in termsof operation time or security, namely risk of falsification or error.Ultrasonic tagging [3] is based on the assumption of the uniqueness of thewelding area of the cask. Thus, it assumes that in the process of ultrasonicscanning one can obtain a unique fingerprint for each stored container. However,this method is rather young and therefore it is difficult to explicitly evaluate itsperformance in terms of environmental safety, long operating time and security.The definite drawback of this method is inability to provide a large and uniquetag memory.Reflective particle tags have been proposed by Sandia National Laboratories(SNL) in 1992 [7]. The tag represents the transparent adhesive matrix withencapsulated reflective particles. Although this system would be good enough toprovide the identification for non-nuclear long-stored waste it will be difficult toapply it to casks containing radioactive material due to the difficulties connectedto the reader system (a number of lights which induce the reflection in the tag)and presence of gamma background outside the cask walls. The characteristicsof the reflective particle tag regarding long operating times, a large and uniquetag memory and security can not be evaluated explicitly due to the presentresearch stage of the technology.Accordingly there is a recognized need for a labeling system which last atleast from ten to a few hundred years (time factor), at the same time enablingfully unique identification of the canister contents in a manner consistent withpermanent records of the storage or repository (information factor), have a highlevel of security, i.e. low risk of falsification or error (security factor), and givethe possibility to avoid a corrosion effect of canisters induced by the traditionaltagging methods (environmental factor). A potential and drawbacks of a new3ungsten-based method was considered in following publications [8, 9]
2. The main concept
The main idea of the proposed method consists of using a unique combinationof radioisotopes with different predictable length of life and a long operatingtime, wherein the unique combination of radioisotopes comprises the mixture oftwo or more radioisotopes [10].
Radioisotopes are atoms with nuclei that decay to a more stable nuclearconfiguration by emitting radiation. Different radioisotopes emit different typesof ionizing radiation, such as gamma ( γ ), neutron (n), alpha ( α ) and beta( β ) radiation. The gamma, neutron, alpha and beta radiation have differentpenetration properties.For example, alpha particles have very little penetrating power and can bestopped by a sheet of paper; a beta particle is lighter than an alpha particleand can be stopped by a thin sheet of metal. At the same time gamma raysand neutrons can be extremely energetic and highly penetrating, so that severalmeters of concrete might not be enough to stop them.Thus, the type of emitting radiation can be selected based on the penetrationproperties of the radiation and the material of item assigned to the long-termstoring or for final repositories and the long-term storage. As an example, forspent fuel waste copper canisters the preference in choice of radioisotopes willbe given to radioisotopes emitting gamma rays, which are used frequently inmedical applications and in industry to check for cracks or flaws in valves.Thus, the use of a unique combination of radioisotopes as a tag enable thepossibility to have a non intrusive reader system. Another inherent property of radioisotopes is a predictable length of life.The radioisotopes decay over time. The time it takes one-half of the atoms ofthe radioisotope to decay by emitting radiation is the half-life of the radioiso-tope. After ten half-lives only one thousandth of the atoms of the radioisotoperemains. The half-life of the radioisotopes can range from a few seconds (short-lived radioisotopes, e.g. 54.5 seconds for
Rn) to hundreds of years (long-livedradioisotopes, e.g. 432.2 years for
Am).In connection with the half-life of the radioisotope a number of parametersmay be determined, such as the number of decays per unit time (total activity),the number of decays per unit time per mass or volume of the radioisotope at atime set to zero (specific activity) and the total number of atoms present. Theseand other parameters without limitation can be used in order to evaluate theage of radioisotopes in a unique combination of radioisotopes.Thus, the long operating time, up to a few hundreds years, can be accom-plished by the present approach because the method for radioisotope labeling of4aste and items assigned to long-term storing or for final repositories includes,but is not limited to, using various radioisotopes with different half-lifes. In re-gards to the spent fuel copper canister assigned to long-term storing or for finalrepositories the preference in choice of radioisotopes will be given to long-livedradioisotopes.
One operative feature of the present method is that it provides an approachto avoid corrosion effects of canisters induced by traditional tagging methods.Compared to traditional tagging methods, the penetrating properties of radia-tion emitted by a unique combination of radioisotopes do not require a violationof the integrity of the container material. Thus, it provides a possibility to re-alize a non-destructive labeling approach to avoid corrosion effects of canistersinduced by traditional tagging methods.As an example, the embossing of bar codes on the copper layer of the spentfuel copper canister can lead to corrosion of copper in the long-term run andleakage of spent fuel components later on. However, when using the presentmethod, as best seen in Figure 1, the tag can be placed inside the item, inthis specific case, inside the spent fuel copper canister. Thus, a non-destructivelabeling approach can be accomplished. The radiation emitted by the unique
Figure 1: An example of how to practically introduce a method of radioisotope labeling. combination of radioisotopes, in this specific case, gamma radiation, will pene-trate the material of the item, here copper, and can therefore be detected. Thetype of detector can be chosen based on the type of radiation emitted by theunique combination of radioisotopes. In this specific case, a gamma radiationdetector will be chosen. Data obtained by the detector will be provided to theanalyzing device to make operational decisions based upon the results. The tag5an be arranged in various configurations based on the needs of the identifica-tion process. It can be encapsulated in various places inside or outside the item,to optimize use of space and radiation emitted by the unique combination ofradioisotopes.
Selection of types and quantities of radioisotopes includes determining activ-ity, the age of the radioisotopes, ratios between the lines in the spectra emittedby the radioisotopes in connection with the amount of information to be car-ried. Among other parameters, the ratios between the lines in the spectrumemitted by radioisotopes can be emphasized. The lines in the spectra emittedby radioisotopes will be one among other unique characteristics of radioisotopeswhich is used by the method for radioisotope labeling of waste. Each radioiso-tope has a unique structure of the spectrum emitted (e.g. gamma spectrum).Thus, the lines in the spectra emitted by radioisotopes might be used to iden-tify the presence of a particular radioisotope in the tag. Accordingly, the ratiosbetween the lines of the same or different radioisotopes present in the uniquecombination of radioisotopes might be used as a unique identifier capable ofcarring the information about the item assigned to long-term storing or for finalrepositories.As a simplified example on how to use the method in order to separatebetween different types of waste and to determine when the waste was encapsu-lated or placed in the storage, different radioisotopes may be used in a uniquecombination of radioisotopes as an identifier of the specific type of waste. Forexample, the unique combination of radioisotopes of
Am (a) +
Cs (b) + Co (c) + etc. can be used in a following form but not excluding alternativecombinations:1.
Am (a) +
Cs (b=0) + Co (c=0) + etc. as identifier of liquid waste;2.
Am (a) +
Cs (b) + Co (c) + etc. as identifier of medical waste;3.
Am (a=0) +
Cs(b=0) + Co (c) + etc. as identifier of solid waste.Parameters a, b, c, etc. refer to the activity or quantity of radioisotopes. In thisparticular example, every item which has the radioisotope
Cs in the uniquecombination of radioisotopes in the tag will be referred to as medical waste.Thus, in order to identify a canister with medical waste among other items,the combination with radioisotope
Cs, i.e.
Am (a) +
Cs (b) + Co(c) + etc. will be used. Time characteristics of this cask, such as time whenthe item was encapsulated, placed in the storage, moved etc., will be evaluatedbased on the combination of the parameters of the radioisotopes in the uniquetag. Among these parameters, relative strength of lines in the spectra emittedby the tag, the half-life of the radioisotopes, activity of the radioisotopes andother characteristics can be used.The number of radioisotopes in the tag can be limited to a number of uniquecombinations available in order to label all items to be stored uniquely. Thus, thenumber of radioisotopes to be used in the unique combination of radioisotopes6ill be related to the capacity of the storage or repository. In the generalcase, the affiliation of waste to storage or repository might be also included andidentified in the way similar to described above or in any alternative way.Alternatively, a large and unique tag memory might be obtained by selectingcoding technology for the spraying of radioisotopes. Then, the unique combina-tion of radioisotopes might be imprinted or plated or sprayed or distributed inthe form of an one-dimensional or two-dimensional matrix symbology or image.A visualization of the one-dimensional or two-dimensional matrix symbologycan be provided via detection of radiation emitted by the unique combinationof radioisotopes. The information contained in the obtained image or symbologymight be extracted or decoded in a way similar to that which reading systemsuse for decoding of 1D/2D bar codes.Conventional one-dimensional (1D) bar coding technology is composed ofparallel strips holding tens of characters per inch. High speed scanning systemsallow this code to be read even from large distances. However, the amount ofdata encoded in a 1D bar code is limited. Therefore, recently a bi-directionaltwo-dimensional (2D) matrix bar code symbology was developed, where infor-mation is encoded through orthogonal lines containing individual bits of infor-mation. Thus, 2D bar codes allows carrying hundred times more information inthe same space as the 1D bar code. Examples of 2D symbology can be foundin [11].Bar codes are generally printed or etched onto the side of each canister oritem. Therefore, in the present state of art they can be falsified, can eventuallylead to the corrosion of container material and leakage of nuclear material.However, the proposed approach of using a unique combination of radioisotopesas a tag allows to avoid the described drawbacks and use the advantages of barcode methodologies.The amount of unique tag memory of the method for radioisotope labelingof waste might be increased if the strength, the ratios of the lines in the spec-tra emitted by radioisotopes are utilized in the coding and further analysis ofvisualization of the one-dimensional and/or two-dimensional matrix symbology.Thus, the three-dimensional (3D) bar code symbology or multidimensional barcode symbology might be realized.The simple illustration of an example how the three-dimensional (3D) barcode symbology might be achieved with a number of lines in the spectra emittedby radioisotopes is best seen in Figure 2.The tag 1 in Figure 2 includes the combination of two radioisotopes, im-printed in a form of a two-dimensional matrix symbology. In this particularexample, gamma emitting radioisotopes, namely
Cs and Co are used. Asidentifiers gamma radiation 2 is used. The
Cs radioisotope can be character-ized by the γ -line with energy 662 keV as best seen in the spectrum 3, whereas Co can be characterized by two γ -lines with energy 1173 keV and 1332 keV, asbest seen in spectrum 4. Thus, at least two two-dimensional matrix symbologycan be realized, 5 provided by the γ -line with energy 662 keV and 6 providedby the γ -line with energy 1173 keV. Each of them can have different or similarinformation encoded. In a similar way, by using larger amount of radioisotopes7 igure 2: An illustration of an example how the three-dimensional (3D) bar code symbologymight be achieved with a number of lines in the spectra emitted by isotopes used in a methodof radioisotope labeling of waste. and the lines in the spectra emitted by radioisotopes, a multidimensional barcode symbology might be accomplished. As alternative, the unique combinationof radioisotopes might be imprinted, plated, sprayed or distributed in the formof image or text. Security against falsification of data or errors can be accomplished by us-ing a unique digital code and a list of independently evaluated parameters asshown in Figure 3. The unique digital code includes, but is not limited to,
Figure 3: A simplified illustration of the security concept against falsification of the databaseor the tag. determination of a limited sequence of symbols which lend itself to an auto-mated inventory/database system. The upper limit for the sequence of symbolscan be chosen based on the capacity of the storage or repository. Further, theunique digital code can be linked to the inventory/database system. Thus, the8tem in question can be identified. The information which is contained in theinventory/database system may include, but is not limited to the informationabout the content of the item and information about the item itself. Thus, thisinformation obtained from the inventory/database system may be compared tothe list of independently evaluated parameters.The list of independently evaluated parameters includes determination ofparameters describing the item itself and the content of the item. As a simpleexample, analysis of visualization of, at least, the one-dimensional or multi-dimensional matrix symbology can be used to obtain independently, i.e. notfrom the inventory/database system, parameters in question. Thus, the timelydetection of errors, falsification of the data in the inventory/database systemmay be provided by comparison of two data sets obtained from independentevaluation (the list of independently evaluated parameters) and from databaserecord through the unique digital code.
It is interesting to notice that the idea to use radioisotopes as tracers hasbeen shown to be a robust method in labeling nucleic acids, where radioisotopesare incorporated into the DNA through enzyme action [12]. Some studies fromthe early 60-s also give the example of tagging small animals, e.g. voles, moles,mice and bats etc. with radioisotopes, such as Ca,
Ta,
Sb, I, Au, Co for tracing purposes [13]. Later on, radioisotope tracers based on m Agwere applied to the problem of identification of stolen electrical copper cable[14]. The technique was demonstrated, but did not get a wide application dueto the radiation safety requirements.
3. Realization of a multidimensional bar code symbology by a uniqueradioisotope tag
As was mentioned above, one option for a new labeling method can berealized through implementation of a multidimensional bar code symbology witha unique combination of radioisotopes or just one single isotope with specificcharacteristics. Despite the attractiveness of this concept, there are a numberof difficulties associated to it. They are related to the handling of the isotopesand providing security against falsification of the tag. In particular, if a uniquecombination of radioisotopes should be imprinted, plated, sprayed or distributedin the form of a one-dimensional or two-dimensional matrix symbology or image,as shown in Figure 4, the company/lab/facility must have a permission fromthe radiation safety authorities and have specific equipment in order to handleradioisotopes. This could lead to time and cost implications.
However, if the information about the item is known in advance, a series ofradioisotope tags can be produced at a facility licensed for this type of work andafterwards used by the encapsulation company. The operation principle of such9 igure 4: A simplified illustration of the implementation of bar code symbology [15] by aunique radioisotope tag - type I. a bar code is similar to the original version of the unique radioisotope tag, i.e.radiation emitted by the isotope is detected by using a radiation detector. Afterthat the required parameters (types of isotopes, activity etc.) are estimated. Inaddition to this, the distribution of radioisotopes in the unique radioisotope tagis measured by using a position sensitive detector or collimator. As a final step,the bar code image is reconstructed and presented.
In a situation where the information about the item is not known in advanceand should be encoded in the unique radioisotope tag directly at the encapsu-lation plant, we propose to use another version of the tag, as shown in Figure5. This realization of the tag includes two components: a radioisotope plate
Figure 5: A simplified illustration of the concept for providing the multidimensional bar codesymbology [15] by a unique radioisotope tag - type II. prepared by authorities at a facility licensed for this work and a foil which isprinted at the encapsulation plant. This concept is appealing in that whileprinting the tag a specific color could be used. As an example, the base of thetag can be made of an
Am or Po α -emitting isotope which are widely usedin smoke detectors. Then the foil which contains the bar code could be printedwith colors based on Be, Na, F, , B, P, , Li etc. materials. After10hat, the printed foil must be placed in close contact with the α -emitting baseof the tag. These materials have a high cross-section for α -induced reactions,such as ( α ,n), ( α ,p) etc. Thus, the bar code might be read detecting α -inducedgamma rays. The energy of the gamma rays depends on the material which ischosen for printing the tag. As an example, Table 1 shows the energy of thegamma rays which are released in α -induced reactions on various materials asillustrated in Figure 5. Table 1: Main γ -lines originating from α -induced reactions in Be, Na, F, , B, Li Materials Energy of γ -rays, keV Reactions References Li Li( α , α (cid:48) γ ) [16], [17], [19] Be Be( α ,n γ ) [16], [18], [19] F F( α ,p γ ) [16], [17] F F( α , α (cid:48) γ ) [17] F F( α ,n γ ) [17] F F( α ,p γ ) [17] Na Na( α ,p γ ) [16] B B( α ,n γ ) [17], [19] B B( α ,p γ ) [17], [19]
4. General example of application of a method for steel containersand copper casks
Here we present first test studies of the new concept. In particular, we con-sider two general cases, when the tag is applied to steel and copper containers.
The steel container chosen corresponds to the one which is commonly usedfor long-term storing of mercury in Europe and USA [20], while the design ofcopper canister is the one which is proposed for storing spent fuel in a nuclearrepository [26], both types are in Figure 6.Since normally the tag should be placed inside the container, in the ex-perimental studies we consider two different setups, i.e. a steel block with athickness of 19 mm and a copper cylinder with a thickness of 10 cm which istwice that of a real cask.
The first test of concept was performed with the use of two types of sources,
Cs and Co, as an example to cover the low and high energy regions. In realconditions the choice of isotopes must be done taking into account all details ofthe industrial application. In the present experiment these sources just playedthe role as one of the variations of the simple implementation of the radioisotope11 igure 6: Images and dimensions of steel and copper canisters: picture from r.h.s. is takenfrom [26] - copper canister with 50 mm wall thickness; picture from l.h.s. is taken from [20] -steel canister with 19 mm wall thickness. tag. The gamma signatures were measured by a high purity germanium (HPGe)detector of coaxial type with high voltage bias set to -3000 V.The sources were placed approximately 10 cm and 1.9 cm from the detectorfor the copper and steel container, respectively. The copper cylinder (10 cmin thickness) and steel block (1.9 cm in thickness) were positioned between thedetector and sources, as shown in Figure 7.
Figure 7: Photo and schematic drawing of the configuration of the experimental set-up.
The data was collected during 3646 seconds with a dead time of 1.26 % forthe steel container and during 3617 seconds with a dead time of 0.47 % for thecopper cask. Experimental errors were estimated as in [21]. Thus, the live timeof measurement was always equal to 3600 seconds. The energy calibration wasdone by using
Am (26.3 keV and 59.5 keV γ -lines), Cs (662 keV γ -line), Co (1173.2 keV and 1332.5 keV γ -lines) calibration standards and background12ines, namely 609 keV ( Bi), 1460.8 keV ( K), 1764 keV (
Bi), 2614 keV(
Tl). As shown in Figure 8 the linear fit works well at both low and highenergies. The measured spectra with background substraction for both cases
Figure 8: The energy calibration of the HPGe detector and linear function fit. (copper and steel) are shown in Figure 9. The observed γ -lines corresponds tothe Cs (662 keV γ -line), Co (1173.2 keV and 1332.5 keV γ -lines) isotopeswhich made up the tag. The results are rather straightforward and indicate thatthe concept of the radioisotope tag can be implemented even with low activitysources. However, it should be mentioned that in the case of application of theradioisotope tag to spent fuel safeguarding, one must be aware of the presenceof Cs and Co isotopes in the spent fuel. It should be mention that thereare a lot of effort spent in order to evaluate content of the spent fuel prior toencapsulation [22, 23, 24, 25].
The majority of the background gamma rays in spent fuel originates fromactivation and fission products, e.g.
Cs (662 keV (0.9) γ -line), Cs (569keV (0.15), 605 keV (0.98), 796 keV (0.85), 802 keV (0.09), 1039 keV (0.01),1168 keV (0.02) and 1365 keV (0.03) γ -lines), Pr (697 keV (0.0148), 1489 keV(0.003) and 2185 keV (0.008) γ -lines), Eu (723 keV (0.19), 873 keV (0.12), Here and further branching factor shown in the brackets following the energy. igure 9: Energy distribution of pulses created in the HPGe detector, obtained in the config-uration of the experimental set-up.
996 keV (0.1), 1005 keV (0.17), 1275 keV (0.36) and 1595 keV (0.03) γ -lines)and Ru (512 keV (0.21), 622 keV (0.1), 1051 keV (0.02), 1128 keV (0.004) and1357 keV (0.006) γ -lines). Thus, for a fuel cooled for a short period of time ( ∼ less than four years), the high energy gamma lines, e.g. a 2185 keV gamma linefrom Pr, will be possible to measure. However, when the fuel will be sent toan encapsulation plant after a number of years of cooling, m Ba, the daughternuclide of
Cs, will be the main gamma emitter. Thus, if the radioisotopetag will have high energy signatures, there will be no problem with radiationbackground coming from the fuel. Moreover, lead filters can be placed betweenthe detector and the cask in order to suppress low energetic gammas comingfrom spent fuel placed in the cask. Thus, even the HPGe or CDZT detectorscan be used as a reader of the tag.Thus, the simplest version of the conventional radioisotope tag may just in-clude the specific radioisotopes which emits γ -rays with energies higher than 1MeV. Although, access to these isotopes can be restricted or their cost mightbe rather high. Therefore, we suggest to use the following version of the ra-dioisotope tag based on the α -emitting isotopes Am or
Po, for example,in a mixture with one of the materials described in Section 3 ”Realization ofthe multidimensional bar code symbology by the unique radioisotope tag” . Theconcept is shown in Figure 10. This version of the tag will serve the needs oflong-term tagging of nuclear waste, as well as it can solve the existing problemof disposing of smoke detectors or other devices (surge voltage protection de-vices, electronic valves etc. [27]) which nowadays contain radioisotopes such as14 igure 10: The simplest version of the conventional radioisotope tag for safeguarding of nuclearwaste.
Am. It should be mentioned that according to the Report of the EU com-mission [27], as of the balance sheet date of year 2001, Ireland manufactured 2million ionization chamber smoke detectors per year (activity of each detector is33.3 - 37 kBq), while for example Sweden imported 700 000 of them. Thus, theprice of the radioisotope tag based on this type of waste will be partly coveredby the costs of the waste disposing. At the same time this method will openthe possibility of recycling nuclear waste of this type.
5. First test of the multidimensional bar code symbology
As we noticed above, one of the attractive options for realization of the ra-dioisotope tag is implementation of the multidimensional bar code symbology,for example in a way as shown in Figure 11. In order to explore this alterna-
Figure 11: A simplified illustration of the radioisotope barcode tag. tive the first conceptual studies were done numerically and experimentally, asdescribed below.Test experiments and simulations were aimed at identifying the possibilityto reconstruct the radioisotope bar code. There are two ways how one can do15his. The simplest one, which has been used in the present work, is related tothe use of a collimator together with a detector. Another method is relatedto the use of mathematical methods for reconstruction of the image obtainedby the detector or position sensitive detector. This requires additional studiesand development. However, these two options can be implemented only if thereis any observable difference between the results of measurements of the twopositions, with source and without it.
Therefore, two extreme cases were considered in both simulations and ex-periments, i.e. when the measurements position represents the empty spacebut is surrounded with positions where the source is distributed, and when theposition contains the source but is surrounded by empty positions, as shown inFigure 12.
Figure 12: A schematic drawing of the configuration of the simulation set-up.
In order to simulate the realistic situation, information was encrypted in areal barcode [15, 28]. Afterwards the precise MCNPX [29] model of the barcodewas created, as shown in Figure 12. The blue positions are positions witha distributed source, the white positions are empty positions. One positionrepresents a square with width of 0.1 cm. The total size of the code is 4.9 cmx 4.9 cm. Two point detectors of gamma radiation were placed at a distanceof about 5 cm from the top of the tag. Between the tag and the detector,a lead collimator was installed, as shown in Figure 12. Detector 1 detectedthe collimated signal from the position which contained the source but wassurrounded by the empty positions, detector 2 recorded the signal coming fromthe empty position.The experimental study was organized in a different way, i.e. for a case witha combination of
Cs and Co source in the area of the collimation window16nd for a case where the sources were surrounding the collimation window. Thecollimator was represented by a lead block with a 3 mm hole in the center, asshown in Figure 13.
Figure 13: A photo of lead collimator with 3 mm hole in the center used in the experiments.
In the experiments the HPGe detector was used in the same way and withthe same settings as described in the Section 4 ”General example of applicationof a method for steel containers and copper casks” . The configuration set-up isshown in Figure 14.
Figure 14: A photo of the experimental set-up.
The data was collected during 12615 seconds with a dead time of 0.12 % forthe case when the sources were in the area of the collimation window and during12605 seconds with a dead time of 0.04 % for for the case when the sources weresurrounding the collimation window, thus, the live time of the measurementwas always equal to 12600 seconds. The energy calibration was done by usinga
Am (26.3 keV and 59.5 keV γ -lines), Cs (662 keV γ -line), Co (1173.2keV and 1332.5 keV γ -lines) calibration standards and background lines, namely609 keV ( Bi), 1460.8 keV ( K), 1764 keV (
Bi), 2614 keV (
Tl).
The simulated gamma spectra for the source (detector 1) and empty (de-tector 2) positions are shown in Figure 15. The line of
Cs, which has been17 igure 15: Energy distribution of gamma detections obtained in the configuration of thesimulation set-up. used as a source material, is detected in both cases. However, the intensity ofthe photopeak for the case of measuring the empty space surrounded with thesources is lower than for the case of the source position surrounded by emptypositions. This difference is also observed in the structure of the spectra be-tween two measurements in the middle and low energy regions. For example inthe low energy region the 34 keV gamma-line is observed only for a case whenthe collimator is facing the source position.Experimental spectra, shown in Figure 16, are following the same trend asthe simulations. However, they have a better resolution in terms of intensity ofthe spectra and the photopeaks. This can be due to the width of the collimator.The diameter of the collimation hole was 3 times larger in diameter (3 mm)compared to what was used in the simulations (1 mm). Therefore, furtheroptimization studies are planned to be done in the future work in order tooptimize the parameters of the barcode. It is interesting to notice that the34 keV gamma-line is observed only for a case when the collimator is facingthe source position of the experiment in exactly the same way as it was inthe simulations. Thus, we can conclude that there are differences observed inmeasuring the two extreme cases in both simulations and experiments. Thisindicates that these differences or specific signatures might be further used inorder to reconstruct the barcode. 18 igure 16: Energy distribution of pulses created in a HPGe detector, obtained in the config-uration of the experimental set-up.
6. Conclusions
In this paper we have described a new concept of long-term security identifi-cation tags/labels that can be applied to articles for carrying information aboutthe content, inventory tracking, prevention of falsification and theft etc. Thesuggested concept is based on the use of unique combinations of radioisotopeswith different predictable half life, and the like as a label of the items.The idea of a new tag was tested with two general designs of storage canisters,namely a steel container which corresponds to the one which is commonly usedfor long-term storing of mercury in Europe and USA and a copper canisterwhich is the one which is in applications for nuclear repositories. The results ofthe first test experiments indicate that the concept of the radioisotope tag canbe implemented even with low activity sources.However, in the case of application of the radioisotope tag to spent fuelsafeguarding it is suggested to use a mixture of α -emitting isotopes, such as Am or
Po, with materials that easily undergo α -induced reactions withemission of specific γ -lines, e.g. Be, Na, F, , B, P, , Li etc. Thus, ifthe radioisotope tag will have a high energy signature, there will be no problemwith radiation background coming from the fuel. Moreover, this version of theradioisotope tag allows to solve the existing problem of the disposing of smokedetectors or other devices [27] which contain radioisotopes, such as
Am, thus,indirectly providing a recycling of nuclear waste. As an economical advantage,19t should be mentioned that the price of the radioisotope tag based on this typeof waste will be partly covered by the costs of the waste disposing.As an attractive option for a new labeling method we proposed the possi-bility to realize a multidimensional bar code symbology. Two different waysof realization are suggested. The first option is when the unique combinationof radioisotopes is imprinted, plated, sprayed or distributed in the form of aone-dimensional or two-dimensional matrix symbology or image. Another real-ization of the tag includes two components: a radioisotope plate prepared byauthorities at a facility licensed for this work and a foil which is printed at theencapsulation plant with specific colors based on Be, Na, F, , B, P, , Li etc. materials. The results of the experiments showed the presence ofspecific signatures in the spectra which give the possibility to realize a multidi-mensional radioisotope bar code symbology.Thus, the new radioisotope label offers several advantages, as compared tothe currently used tagging methods. It provides1. Environmental safety.2. Non-contact reader system.3. Long operating time.4. Large and unique tag memory.5. Security technique against falsification of data, errors/multiple verifica-tion.6. Recycling option for ionization chamber smoke detectors and other devices[27].A further experimental, simulation and mathematical study is planed to bedone to optimize and evaluate the different options of the radioisotope label.
Acknowledgement
The authors want to thank ASTOR (the Application of Safeguards TO ge-ological Repositories) experts group for useful discussions.
References [1] Arms Control and Nonproliferation technologies,
Tags and seals for con-trolling nuclear materials.
Department of Energy/Office of Intelligence andNational Security, DOE/AN/ACNT-93A, Second Quarter, 1993.[2] Culbreth, W. G., and Chagari, A. K.,
A Labeling of the Spent Fuel WastePackage.
Proceedings of the 3-rd International High Level RadioactiveWaste Management Conference, 1992.[3] Demyanuk, D., Kroening, M., Lider, A., Chumak, D., Sednev, D.,
Intrinsicfingerprints inspection for identification of dry fuel storage casks.
Unpub-lished results, to appear in ESARDA Bulletin 50, 2013.204] Bennett, J. C., Day, D. M., Mitchell, S. A.,
Summary of the CSRI Workshopon Combinatorial Algebraic Topology (CAT): Software, Applications andAlgorithms , SANDIA REPORT, SAND2009-7777, November, 2009.[5] Culbreth, W. G., Bhagi, B. G., Kanjerla, A.,
Review of Advanced Tech-niques for Waste Canister Labeling.
Progress report on the DOE wastepackage project at University of Nevada, Las Vegas, 89154-4014, 1993.[6] D Chernikova, K Axell,
A new concept for safeguarding and labeling of long-term stored waste and its place in the scope of existing tagging techniques. ,IAEA.[7] Tolk, K. M.,
Reflective Particle Technology for Identification of CriticalComponents.
Proceedings of the 33-rd Annual Meeting of the Institute ofNuclear Materials Management, July, 1992.[8] D Chernikova, K Axell, A Nordlund, H Wirdelius,
Novel passive and activetungsten-based identifiers for maintaining the continuity of knowledge ofspent nuclear fuel copper canisters. , Annals of Nuclear Energy 75, 219-2272015.[9] D Chernikova, K Axell,
Passive and Active ways of Unique tagging/labelingof long-term stored nuclear waste copper canisters. , INMM 55th AnnualMeeting, Atlanta, 2014.[10] Chernikova, D., Axell, K.,
A method of radioisotope labeling of waste.
Patent pending, 1330036-3, April, 2013.[11] Naddor, D. J., Creek, J.,
HD barcode. , Patent US 2011/0240749, 2011.[12] Stephenson, F.,
Calculations for Molecular Biology and Biotechnology: AGuide to Mathematics in the Laboratory.
Academic Press, second edition,2010.[13] Gerrard, M.,
Tagging of small animals with radioisotopes for tracking pur-poses: Literature review.
International Journal of Applied Radiation andIsotopes, Volume 20, pp. 671-676, 1969.[14] Bate, L. G., and Dyer, F.F.,
Invistigation of radioisotope tagging of CopperWire.
Analytical Useof Alpha-Source Induced Gamma-Ray Emission.
Analytical Chemistry,321:739-747, 1985.[17] Croft, S., and Venkataraman, R.,
Gamma ray to neutron production ratesfor Alpha-particle induced reactions on Li, Be, B, C and F.
Proceedings ofWM’04 Conference, Tucson, AZ, March, 2004.2118] Croft, S.,
The use of neutron intensity calibrated Be-9(alpha,n) sources as4438 keV gamma-ray reference standarts.
Nuclear Instruments and Meth-ods in Physics Research A 281, 103-116, 2089.[19] Ravazzani, A., Jaime, R., Looman, M. R., Pedersen, B., Peerani, P., Schille-beeckx, P., Thornton, M. I., Foglio-Para, A., Maiorov, V. P.,
Characteri-sation of neutron sources by NDA.
Proceedings of the Symposium on safe-guards and nuclear material management, pp. 181-191, 2001.[20] Carroll, A. J.,
Design of Mercury Storage Containers.
Presentation of Re-mote Systems Group/Nuclear Science and Technology Division, Oak RidgeNational Laboratory, October 13, 2009.[21] D. Chernikova, K. Axell, I. P´azsit, A. Nordlund, R. Sarwar, A directmethod for evaluating the concentration of boric acid in a fuel pool us-ing scintillation detectors for joint-multiplicity measurements, Nuclear In-struments and Methods in Physics Research Section A: Accelerators, Spec-trometers, Detectors and Associated Equipment, (11/2013) 9097.[22] Yury N Barmakov, Evgeny P Bogolyubov, Oleg V Bochkarev, Yury GPolkanov, Vadim L Romodanov, Dina N Chernikova. System of combinedactive and passive control of fissile materials and their nuclide compositionin nuclear wastes, International Journal of Nuclear Energy Science andTechnology 6 (2), 127-135, 2011.[23] D Chernikova, VL Romodanov, V Sakharov, A Isakova. Analysis of 235U,239Pu and 241Pu content in a spent fuel assembly using Lead SlowingDown Spectrometer and time intervals matrix, Journal of Nuclear MaterialsManagement 40 (2), 2012.[24] D Chernikova, V Romodanov, V Sakharov. Time intervals matrix analysisof 235U and 239Pu content in a spent fuel assembly using lead slowingdown spectrometer, Spec. Session on Determination of Pu Mass in SpentFuel with NDA of the 52nd INMM, 2011.[25] VL Romodanov, VK Sakharov, DN Chernikova, SV Ktitrov, AV Isakova.Evaluation of 235 U and 239 Pu content in fuel assembly by using neutronslowing-down time in lead, Proceedings of the Third International Confer-ence, Current Problems in Nuclear Physics and/ltomie Energy. nuclides,2010[26] Andersson, C-G.,
Development of fabrication technology for copper canis-ters with cast inserts.
Technical Report TR-02-07, Status report in August2001, Swedish Nuclear Fuel and Waste Management Co, April, 2002.[27] The EUROPEAN COMMISSION,
A Review of Consumer ProductsContaining Radioactive Substances in the European Union.
Final Re-port of the Study Contract for the European Commission, B4-3040/2001/327150/MAR/C4, Unit H.4, Radiation Protection, 2007.2228] Carroll, L.,
Alice’s Adventures in Wonderland.
Macmillan, United King-dom, November, 1865.[29] Pelowitz, D. B.,