Paper

MANAGEMENT OF SPENT SEALED RADIATION SOURCES

Roberto Vicente, Gian-Maria Sordi, and Goro Hiromoto*

Abstract—Spent or disused sealed radiation sources—nolonger needed sources—may represent a risk of radiologicalaccident or may be a target for criminal acts in countrieswhere final disposal options are unavailable and where anincreasing number of sources are being kept in extendedstorage. In developing countries, thousands of radium needles,teletherapy sources, oil well logging neutron sources, andmiscellaneous industrial radioactive gauges are annually col-lected as waste and stored in research institutes. The objectivesof the study described in this paper are to inventory suchsources in Brazil, including those presently in use and thosealready collected as waste, and to design a dedicated repositorywhere spent sources could be disposed of properly. Theinventory of sources in Brazil and the concept of the repositoryare presented and its feasibility is discussed.Health Phys. 86(5):497–504; 2004

Key words: waste management; waste disposal; radiationprotection; waste storage

INTRODUCTION

SPENT OR disused radioactive sealed sources are theundesirable, but inevitable remnants of many applica-tions of radiation in industry, medicine, and other fields.They are present in almost all countries and represent awaste management problem in all but a few countrieswhere an operational final disposal facility is alreadyavailable. The terms “spent” and “disused” refer tosources that are no longer utilized for the intendedpurpose or for which no further use is foreseen. Thedistinction between spent and disused sources becomeirrelevant after sources are declared as radioactive waste,therefore both terms apply to sources entering the wastemanagement system.

Common sealed sources are radioactive materialsencapsulated in small, usually cylindrical, metallic con-tainers. Sizes are in the range of a few centimeters.Activities range from tens of kBq (millionth of a curie) to

tens of TBq (thousands of curies). This makes spentsources the radioactive waste with the highest activityconcentration in the category of non-fuel cycle wastes.The recommended useful life of most sealed sources istypically 5 to 15 y, but the half-lives of the encapsulatedradionuclides can span hundreds or even thousands ofyears. Therefore, sources will still represent a potentialradiation hazard long after the devices containing themare decommissioned.

Worldwide, devices with sealed sources have beencommissioned without definition of their destinationafter useful life is completed. In countries with opera-tional sites for low- and intermediate-level wastes, anumber of sources can be disposed of safely, althoughbecause of long half-life, high activity, and the presenceof alpha-emitting radionuclides, some sources are unac-ceptable in these sites. On the other hand, in thosecountries without operational disposal sites, all disusedsources must be held in safe storage until a final disposaloption is found. Uncertainties about safety and securityraise questions on how long it is acceptable to keep thosesources in long term storage.

Concerns on the management of spent or disusedsealed sources arose in the late 1980’s, as the number ofsources requiring special management were escalatingand after improperly controlled and insecurely storedsources caused accidents around the world. Some ofthese accidents resulted in human deaths and contamina-tion of large areas. Examples of such events are theradiation accident in Ciudad Juarez, Mexico (CNSNS1984), in Goiania, Brazil (IAEA 1988), in Tammiku,Estonia (IAEA 1998), in Lilo, Georgia (IAEA 2000a), inIstanbul, Turkey (IAEA 2000b), and in Samut Prakarnm,Thailand (IAEA 2002a). The threat of criminal acts andterrorism using radioactive material that emerged re-cently put even more pressure on the issue. After theterrorist attack on 11 September 2001, safety and securityof sealed sources became of great concern, e.g., Lubenauand Strom (2002), and Ferguson (2003).

A number of sources went astray, some sourceswere diverted purposely and some accidentally. TheInternational Atomic Energy Agency (IAEA) countedabout 100 accidents up until 1989, which resulted in 39

* Instituto de Pesquisas Energeticas e Nucleares, Av. Prof. LineuPrestes, 2242—Cidade Universitaria, CEP 05508-000, Sao Paulo,Brazil.

For correspondence or reprints contact: R. Vicente at the aboveaddress, or email at rvicente@ipen.br.

(Manuscript received 9 June 2003; revised manuscript received10 October 2003, accepted 19 December 2003)

0017-9078/04/0Copyright © 2004 Health Physics Society

497

fatalities and significant exposure of 266 other persons(IAEA 1991). Bellian and Johnstone (1995) reported 299events involving sealed sources found in scrap metalbetween 1983 and 1993 in the U.S. Lubenau and Yusko(1995) reported 35 events of contamination of metalproducts and 300 events in which sources were detectedbefore scrap was fed to metal recycling plants. In anupdate of the previous report, Lubenau and Yusko (1998)reported 14 additional worldwide accidental smeltings upuntil 1997. IAEA reports (IAEA 2002b), citing UnitedStates Nuclear Regulatory Commission and EuropeanUnion reports, that U.S. companies have lost track ofnearly 1,500 radioactive sources since 1996, and thatabout 70 sources are lost yearly from regulatory controlin the EU. In the Republic of Georgia, about 280 sealedsources were found adrift in the field in the last decade,some of them after severely exposing members of thepublic (IAEA 2002c). “Orphaned” radioactive sourc-es—a term used to denote radioactive sources that areoutside official regulatory control—are a widespreadphenomenon in the former USSR countries (IAEA2002b). In developing countries, although source inven-tories are smaller, the risk that sources become orphanedis greater because of weak national regulatory infrastruc-tures. For instance, many nuclear-powered pacemakers,containing a sealed source with about 1011 Becquerel of239Pu, which are lost sometimes in developed countries,[e.g., the notice by the Office of Nuclear Material Safetyand Safeguards (ONMSS 1998)], may be never put underregulatory control in developing countries. These sourcesdo not represent a risk of exposure to members of thepublic, but they do represent a high priority sourcebecause of their potential to be used in a dirty bomb. It isnecessary to keep in mind that psychosocial and eco-nomic effects are the major effects of a radiologicaldispersion device (Lubenau 2003).

To help ensure that sources are secured at all timesin developing countries, the IAEA launched a program toassist states in creating and strengthening national regu-latory infrastructure. One aim within the program was tospot, inventory and package unwanted sources and safelystore them until final disposal was available (IAEA1991). The Agency suggested that a geological reposi-tory in developed countries, when available, receive thespent sources from developing countries.

These initiatives reduce the immediate risk ofsources being left unattended, avoiding misuse andaccidents. However, deep repositories may only be avail-able far in the future, and the proposal of transferringthousands of disused sources from developing countriesto repositories in developed countries may face insur-mountable difficulties. The “not in my back yard” syn-drome, hard to overcome when wastes are transported

from different states or cities in the same country, willprobably hinder the import of spent source waste fromabroad. Proposals of international disposal sites, in Aus-tralia and elsewhere, are accordingly receiving strongopposition too.

Therefore, countries with existing large source in-ventories, like Brazil, must search for an alternativecourse of action as soon as possible.

Management of spent or disused sources in BrazilWhen the National Commission on Nuclear Energy

(CNEN), the Brazilian regulatory authority, was createdby the Federal Law 4118 of 1962, and entrusted with thecontrol over radiation sources, an unknown number ofsealed sources was already in use, mainly radium needlesin hospitals. In the ensuing two and a half decades, thenumber of users increased faster than the licensing andinspection capabilities. However, the Goiania accident in1987 led CNEN to start a comprehensive program tostrengthen further the control over radiation sources,sealed and unsealed. CNEN identified source owners,recorded data of each source in a centralized data bank,and established a chain-of-custody transfer system. Aseries of inspections allowed CNEN staff to identify andrecover disused and/or unwanted sealed sources and totransport them to safe storage. Presently, there are aboutforty thousand sources stored at three nuclear researchinstitutes in Brazil: Nuclear Energy Research Institute inSao Paulo; Center for Development of the NuclearTechnology in Belo Horizonte; and Nuclear EngineeringInstitute in Rio de Janeiro. This number increases byabout 3,000 per year as decayed sources in nucleonicindustrial gauges are replaced and sources in discontin-ued applications are discarded.

As the number of sources under storage grows, itbecomes more urgent to define where to dispose of them.

In Brazil, disposal of radioactive wastes is theresponsibility of CNEN and, as part of the study tosupport decisions, the concept of a dedicated and exclu-sive repository was developed, where spent sealedsources could be disposed of, apart from other radioac-tive waste streams. One reason to treat sources as aseparate stream from other low- and intermediate-levelwastes is that a fraction of the inventory is not acceptablefor disposal in a shallow ground repository. Examplesfrom sites elsewhere have shown that shallow grounddisposal is improper for at least some of the sources withlong-lived radionuclides. Another reason is that sourceshave the unique property of a high activity concentratedin a very small volume.

The study on disposal options for the sources fo-cused on four aspects of the problem:

498 Health Physics May 2004, Volume 86, Number 5

● assessment of the number and characteristics of thesources that would require final disposal as radioactivewaste;

● assessment of the fraction of this inventory that couldnot be disposed of in a shallow ground repository;

● development of the concept of a dedicated and exclu-sive geological repository;

● evaluation of the feasibility of the repository.

Inventory of sourcesTwo main sources of data were used to estimate the

number of sealed sources in Brazil:

● the national database of licensed users of radioactivematerial, which provided information on sealedsources held by licensees; and

● the records of wastes received at storage centers thatsupplied data on sources stored as radioactive waste.

Additional material was used to complete inventorywork, including a report by CNEN (Heilbron and Xavier1992) and the IAEA radioactive waste database (IAEA2000c).

It was estimated that about 270,000 sealed sourceswill be requiring disposal as radioactive waste in the nearfuture. Table 1 shows the number of sources in eachclass, according to origin. Table 2 shows details of theinventory, in terms of number, activity, and volume ofsources classified by radionuclide.

Some remarks about these figures are necessary:

1. Only sources with half-lives greater than a few yearswere included;

2. The inventory is dynamic and figures reflect the timeof the compilation of the data. As different sources ofdata have different time baselines, results have un-avoidable inaccuracies;

3. Using a broader definition of sealed source, 241Amsources attached to lightning rods and smoke detec-tors were counted as sealed sources. A report on

radioactive lightning rods in Brazil indicates thatmanufacturers sold and installed 75,000 lightningrods between 1970 and 1986 (Heilbron and Xavier1992);

4. Smoke detectors are an exempted consumer product.However, manufacturers and retailers are sendingreplaced detectors as radioactive waste to the threecollection centers. The number of installed smokedetectors with 241Am sources is unknown, thus onlysources existing at the time of the inventory atmanufacturers premises and those already collected aswaste were included in the inventory;

5. Lightning rods with radium sources imported before1970 are a few percent of the total number of rods buttheir number is even more uncertain and only thosealready collected as waste were included in theinventory;

6. Hundreds of thousands of 60Co sources in largeirradiators were not included in the inventory ofsources requiring disposal as waste because usersusually return these sources to suppliers for recycling;and

7. There are about 2,000 sources collected as wastewithout entries of radionuclides and/or activity. Basedon average characteristics of sources, we adoptedconservatively an average activity of 0.1 GBq persource, and a gross volume of each individual sourceas 0.0074 dm3. (See note “a” in Table 2.)

These sources had to be classified in two groups,one that meets acceptance criteria to a surface repositoryand another that exceeds those limits. The aim of theclassification was to estimate the fraction of the inven-tory that would be unacceptable for shallow grounddisposal.

Table 2. Estimated number, activity and gross volume of sources.

RadionuclidesNumber of

sourcesTotal activity

(TBq)Gross volume

(dm3)a

60Co 2,611 2.60 � 1016 3.085Kr 440 4.93 � 1012 42.90Sr 846 1.82 � 1012 4.0137Cs 6,153 3.27 � 1014 13.226Ra 4,535 1.29 � 1012 0.92241Am 255,548 1.35 � 1013 130.241Am-Be 319 4.16 � 1013 35.Other SLb 419 1.03 � 1013 10.Other LLc 311 2.45 � 1012 3.5Unknownd 2,331 2.33 � 1010 17.

Total 273,513 2.64 � 1016 257.

a Volume of sources randomly packed, without shielding.b Short-lived (T1/2 � 30 y), mainly 55Fe, 147Pm, 244Cm, 252Cf.c Long-lived, mainly 63Ni, 226Ra-Be, 238Pu, 238Pu-Be.d Individual source activity; 0, 1 GBq. Volume: 0.0074 dm3.

Table 1. Estimated inventory of sealed sources in Brazil.

Class of the source Amount

226Ra needles collected as waste 2,535Industrial gauge sources collected as waste 5,808241Am sources in lightning rods collected as

radioactive waste39,478

241Am sources in smoke detectors collected asradioactive waste

13,548

226Ra sources in lightning rods collected asradioactive waste

440

Miscellaneous sources held by licensees 9,182241Am sources in lighting rods awaiting

replacement116,522

241Am sources at the premises of smokedetector manufacturers

86,000

499Spent sealed radiation sources ● R. VICENTE ET AL.

However, Brazil lacks acceptance criteria for arepository appropriate for sealed sources. So, the expe-riences of other countries were examined.

Generally, disposition of sealed sources in surfacerepositories is restricted. Examples from operational sitesaround the world show that acceptance criteria imposelimits on activity of sources and restrict disposal of sourceswith alpha-emitting nuclides. Requirements on homogene-ity of waste forms—in this case, drums containing thesources encapsulated in mortar or concrete—further limitacceptance of this waste. However, differences in wastemanagement policies hinder import of that know-how toBrazil because it reflects the specific resources and demandsof each country. As a result, the trial of deriving values ofactivity from foreign repositories to apply in the classifica-tion of the Brazilian source inventory was unfruitful.

Therefore, a method of classification was proposedbased on the assessment of the radiological impact of asource disposed in a surface repository under intrusion,and using dose limits as criteria of classification. Radio-logical impact means here the dose incurred by themembers of the public being exposed to the radiationfield from sources.

Two scenarios of intrusion were used, all startingwith exhumation of the source during extensive publicworks like road construction. Scenario 1 is the exposureof a worker to the radiation of an exhumed source for 1 h,at a distance equal or less than 1 m. An individualhandling one source and keeping it in the pocket of thegarment for 8 h characterizes Scenario 2; in this case,dose rates at 5 cm from the sources were used incalculations.

Activities of sources were allowed to decay 100,200, or 300 y before intrusion occurred. These timeintervals represent three possible periods of post-closurecontrol of the disposal site. The resulting doses werecompared with the dose limits to members of the publicrecommended by ICRP as applied to accident conditions(ICRP 1993). A conservative limit of 1 mSv was used incalculations.

Threshold activity of selected radionuclides and thefraction of the number of sources in the inventoryrequiring a deep repository are presented in Table 3 andTable 4. Threshold activity is the activity of a source thatwould deliver a dose equal to the dose limit applied to amember of the public under the conditions of eachscenario. The fraction of the number of sources requiringa deep repository, represented in Table 3 and Table 4 asp percent, is the ratio of the number of sources withactivity higher than the threshold activity to the totalnumber of sources of each radionuclide in the inventory.

Results show that a significant fraction of thenumber of sources requires geological disposal, both onnumber of sources and on gross volume basis. As part ofthe conclusions of this work, all sealed sources of theinventory are proposed to be disposed of in a deeprepository as presented here.

Accordingly, the facility was designed with capacityto receive all currently existing sources. The disposal ofall sources at the same place, instead of only therestricted fraction, has the advantage of simplifying themanagement of this waste and has little impact onrepository construction technology and costs.

Table 3. Threshold activity (At), for relevant radionuclides and decay times, and percent number (p) of sources of theclass in the inventory, in Scenario 1: external exposure at one meter from the source (see text for details).

Decay time

100 y 200 y 300 y

At (Bq) p (%) At (Bq) p (%) At (Bq) p (%)

90Sr 4.3 � 1012 0 4.9 � 1013 0 5.6 � 1014 0137Cs 9.2 � 108 53 9.2 � 109 14 9.1 � 1010 2.5226Ra 7.9 � 107 61 8.2 � 107 58 8.6 � 107 58241Am 3.9 � 108 0.40 4.5 � 108 0.40 5.3 � 108 0.40241Am-Be 1.0 � 1010 0 1.2 � 1012 0 1.4 � 1012 0

Table 4. Threshold activity (At), for relevant radionuclides and decay times, and percent number (p) of sources of theclass in the inventory, in Scenario 2: external exposure on handling the sources (see text for details).

Decay time

100 y 200 y 300 y

At (Bq) p (%) At (Bq) p (%) At (Bq) p (%)

90Sr 4.4 � 108 50 5.0 � 109 3.2 5.7 � 1010 0.24137Cs 2.9 � 105 98 2.9 � 106 95 2.8 � 107 93226Ra 2.5 � 104 100 2.6 � 104 100 2.7 � 104 100241Am 1.2 � 105 58 1.4 � 105 58 1.7 � 105 58241AmBe 3.2 � 108 98 3.7 � 108 98 4.4 � 108 97

500 Health Physics May 2004, Volume 86, Number 5

Concept of the repositoryDespite Brazil’s continental dimensions, most users

of radioisotopes and the three above-mentioned wastestorage facilities are situated in the southeast region;therefore, one disposal facility is proposed for the wholeinventory. The proposed repository is a single deepborehole penetrating a stable geological formation. Thedepth of the well is dependent on the geological charac-teristics of each site but must be deep enough toaccommodate completely the wastes inside a granitebatholith, yet provide enough isolation space above thewastes and below the weathered strata of the geologicalsetting. Fig. 1 shows an example of the proposed con-figuration of the repository. The height of the zone of thewell where the wastes are stored is the “emplacementzone;” the rest of the well toward the surface is the“isolation zone.” The actual profile of the geologicalsetting will be known after completion of the siteselection process, an endeavor that is yet to be under-taken and that is outside the scope of the present work. Ingeneral, the site characteristics must include reasonabledistance from populated areas, access to transportation,distance from areas subject to flooding, erosion, orsubsidence, subsurface emplacement zone with longhistory of tectonic stability, limited open fractures orvoid spaces, little free water, lack of evident recoverablemineral resources, and adequate thickness to accommo-date the repository.

Technology for drilling is found in many geotech-nical drilling companies and deep gas and oil exploration

industry in Brazil. Rotary drilling is a viable method ofborehole construction.

The well is clad with a flush joint steel pipe, and theannulus between the pipe and the geological formation isfilled with cement paste (Fig. 2). Sources are disposed ofinside lead containers stacked in a single column. Fig. 3shows details of the container. The capacity of eachcontainer is about 1 L, and gross volume of the sourcesis estimated as 0.3 cubic meters. Therefore, about 300such containers can hold all inventoried sources, fillingthe well to about 100 m from the bottom.

In order to keep costs low, using available technol-ogy, the choice of materials is first dictated by availabil-ity to conventional well construction technology andusual package/shielding material, rather than by perfor-mance of structures as a waste isolation barrier. The longterm safety of the facility will be governed by ground-water intrusion in the repository and isolation againstwater intrusion is achieved by the multi barrier conceptof the repository. The first barrier is the geologicalmedium which must be a continuous, dry granite batho-lith, with no open fractures. The second is the cementedannulus that will restrict water flow between the differentstrata crossed by the well. The third is the borehole steelcladding that also functions as a smooth casement wall.The fourth is the lead container and the fifth is the steelcapsules of the sources themselves. The barriers as awhole will postpone the contact of groundwater with thewastes and retard the transport and migration of theradioactive materials back to the surface, allowing radio-nuclides to decay before dispersion into the biosphere.

Using a hot cell to protect workers, sources areremoved from their original shielding and put into the

Fig. 1. Schematic view of borehole disposal concept. Fig. 2. Cross section of the borehole.

501Spent sealed radiation sources ● R. VICENTE ET AL.

disposal container. If necessary, a recoverable shieldedoverpack is used during transfer of the containers fromthe hot cell to the disposal borehole. Fig. 4 shows theproposed method of emplacement. Each container islowered to the bottom of the borehole and can be broughtback to the surface by a hoist cable. Depending on whichwaste management policy authorities adopt, arrange-ments can easily be made to raise the containers back tothe surface during the operational phase of the repository,making it a retrievable storage.

After the decision to close and to decommission thesite, the space above the containers will be filled withconcrete up to the top and the well definitely sealed.

At the same site, other wells can be bored to receivethe sources of applications that will be entering the wastemanagement system in the future.

DISCUSSION

The following aspects were considered in assessingthe suitability of the proposed concept to meet the needsof Brazil to dispose its inventory of spent sealed sourcessafely and properly.

First, construction technology is available and doesnot demand development work. The expertise necessaryto construct the disposal structure is the same used ingroundwater exploitation. The technology is available tomany deep well engineering companies in the country.As regards to surface facilities, the main structure is thehot cell in which sources are transferred to disposalcontainers. There exists in Brazil experience in designing

and constructing hot cells for the production of sealedsources; it is the same technology necessary for the wastemanagement project.

Second, investment and operational costs are withinbudgetary limits and will not become unduly expensiveto the ongoing practices that use sealed sources. The costof drilling and cladding a borehole is in the range ofUS$100,000–US$200,000. The cost estimate for the hotcell is about US$100,000. Land, buildings, ancillaryequipment, engineering services, licensing, and otherimportant components of cost are much lower than, orcan be shared with, the project of construction of adisposal site for other low- and intermediate-levelwastes.

Third, the proposed concept allows for an easymanagement strategy and compares favorably against thealternatives of extended storage, disposal of a fraction inshallow ground, or transfer of high activity long-livedsources to repositories in developed countries. A central-ized collection facility helps in strengthening regulatorycontrol over the sources, making it simpler to account foreach individual source and to keep track of all sources.

Fig. 4. Method of emplacement in the repository.

Fig. 3. Cut view of disposal container.

502 Health Physics May 2004, Volume 86, Number 5

The disposal of the spent sources in an exclusive struc-ture separated from other low- and intermediate-levelwaste streams takes advantage of the low volume ofsources and high concentration of activity. The spent ordisused sources can be put immediately in a structure thatsecures them against theft or uncertain future adminis-trative control in face of potential future social andpolitical instabilities.

Fourth, the concept is safe to workers and to presentand future populations. Compliance with the relevantrecommendations of IAEA’s Safety Guides (IAEA 1981,1983a, 1983b, 1983c, 1989, 1994, 1999a, 1999b) andICRP’s waste disposal related publication (ICRP 2000)were used as a preliminary assessment of safety. Thoserecommendations served as a checklist to demonstratethe safety of the concept. The following aspects wereanalyzed in detail: 1) the concept of the disposal system;2) the characteristics of the geological setting; 3) thecharacteristics of the disposal structure; 4) the character-istics of the waste form; and 5) general aspects related toquality assurance, industrial safety, and administrativecontrol.

The discussion of the forty-five items of perfor-mance under the five headings above that were consid-ered in this work is too long to be presented here, but waspublished elsewhere (Vicente 2002), and led to theconclusion that the proposed repository meets all therelevant safety recommendations of IAEA and ICRP.

CONCLUSION

Spent or disused sealed sources pose a significantradiological risk to people in developing countries wherehundreds of thousands of such sources must be recoveredand disposed. Many sources with dangerous levels ofradiation are annually lost or stolen, some of themcausing serious injuries to members of the public. Onecause of risk that may become important in the nearfuture is the lack of a disposal option for those sources.In a longer range, sources containing alpha-emitting andtransuranic isotopes in quantities greater than thoseallowed for current disposal pathways may become aproblem in developed countries too.

In Brazil, irradiation facilities, industrial and medi-cal applications, and consumer products account forhundreds of thousands of sealed sources with totalactivity of over 26 PBq, which will require disposal asradioactive waste. The number of sources already storedas waste is over 60,000 and is rising, and there iscurrently no option to dispose of them.

The concept of repository presented in this paper isa proposed solution to this problem. It would requireconstruction technologies already available, its costs

would be lower than costs of other concepts, and thesafety would be reasonably assured.

The proposed repository has the advantage of facil-itating the management and limiting the radiologicalrisks for present and future generations represented bythe spent or disused sealed sources.

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