IEEE Transactions on Nuclear Science, Vol. NS-26, No. 3, June 1979

REUTILIZATION POTENTIAL OF ACCELERATOR COMPONENTS: A DECOMMISSIONING PERSPECTIVE*

James H. Opelka, Gary J. tlarmer, Robert L. Mundis, John M. Peterson, and Barry Siskind**

Abstract

There are perhaps as many as 1,200 particleaccelerators in the United States, ranging in sizefrom the very small Cockroft-Walton and electron linearaccelerators to the multi-GeV research synchrotrons.At least 50 accelerators produce significant inducedactivation, and several hundred more are capable ofproducing fluxes of neutrons that could result inactivation of various components of the acceleratorfacility. At decommissioning, some accelerators leavea legacy of low-level induced radioactivity in massivecomponents. Although guidelines for acceptable surfacecontamination levels for release of materials andequipment to the general public do exist, there arepresently no standards for release of materials andequipment with radioactivity distributed throughouttheir volumes. The decommissionings of five AEC-fundedaccelerators were examined: synchrocyclotrons operatedby the University of Rochester and by Carnegie-MellonUniversity, the Cambridge Electron Accelerator, theYale Heavy-Ion Linear Accelerator, and the BrookhavenCosmotron. One common feature of these decommission-ings was that major components usually were assignedand shipped for use or storage at other acceleratorlaboratories. In addition to reviewing selected pastdecommissionings, the authors also examined variousaspects of decommissioning accelerators presentlyoperating. The average mass with residual induced ac-

tivity ranges from 1.5 x 102 kg for electrostatic de-

vices and small cyclotrons up to 9.5 x 107 kg for alarge proton synchrotron such as the Zero GradientSynchrotron at Argonne National Laboratory. The esti-mated cost ($ 1978) of decommissioning ranges from

$8.8 x 104 for an electron linac to $7.0 x 106 for theZGS. Consideration of decommissioning during thedesign phase can decrease dismantling costs, minimizeunavoidable activation areas, and maximize potentialfor reuse.

Introduction

Over the past several years, there has been in-creasing concern over the accumulation of radioactivematerials at various scientific, industrial, and educa-tional and medical facilities in the United States, andincreasing pressure to ensure that any potentiallyserious problems are not being overlooked. The subjectof nuclear facility decommissioning has recently beenaddressed by the U. S. Comptroller General in aJune 16, 1977, report to the Congress entitled "Clean-ing Up the Remains of Nuclear Facilities - a Multi-

billion Dollar Problem.'(1) The primary thrust of thereport is toward the nuclear power industry; however,other aspects of the problem, which include isotopeusage and accelerator facilities, are recognized aspotential problems.

The Department of Energy has initiated a compre-hensive study of the quantities and types of radio-active materials in existence both at its existingfacilities and at the facilities formerly utilized aspart of the Manhattan Engineer District/Atomic EnergyCommission (MED/AEC) program. The Division of Environ-mental Impact Studies at Argonne National Laboratory

*Work performed under the auspices of the U. S.Department of Energy.

**Argonne National Laboratory, 9700 South Cass Avenue,Argonne, Illinois, 60439.

was requested to perform a comprehensive study ofproblems associated with the dismantling and disposalof all types of particle accelerators (excludingneutron generators) in the United States.

The potential for induced radioactivity is very

slight at energies below 10-MeV.(2) Until recently,medical and industrial accelerators (almost exclusivelyelectron accelerators) have been of energies less than10-MeV; however, the use of medical linacs in theenergy region above 10-MeV is now increasing at therate of 200 to 240 units per year. A total of 2000such units are expected to be in use in the United

States eventually.(3) Heavy ion and neutron therapyboth are receiving increased attention from medicalresearchers and may eventually add significantly to theneutron-producing accelerator population. The number ofcompact neutron generators used as analytical tools nowexceeds 200 in the United States. Although the problemsof decommissioning medical and industrial acceleratorsare much smaller than those associated with high-energyresearch machines, the medical and industrial accelera-tors comprise over 80% of those presently operating. Asthe energy of medical and industrial accelerators in-creases, the radiological burden on society of accelera-tor technology will increase and will necessitate use ofproper management similar to that currently required atthe larger facilities described in this paper.

History of Past Accelerator Decommissionings

Over 70 accelerators of all types have already beendecommissioned. Some of the earliest cyclotrons andbetatrons were simply disassembled and the componentsreused for other purposes or sold as scrap metal. Thebeam energy and intensity of the early machines weregenerally very low, so any induced radioactivity wouldhave been essentially undetectable except by very sensi-tive survey techniques. There are virtually no recordsof the very early decommissionings, although acceleratorcomponents of some early machines have been placed in exhi-bits at university museums and at the Smithsonian Insti-

tute exhibit entitled "Atom Smashers: Fifty Years." (4)

Using information obtained from contract files andpersonal communications, the authors examined thedecommissionings of five AEC-funded accelerators: thesynchrocyclotrons operated by the University of Roches-ter and by Carnegie-Mellon University, the CambridgeElectron Accelerator at Harvard, the Yale Heavy-IonLinear Accelerator, and the Brookhaven Cosmotron. Onefeature in common to all five decommissioning operationswas found: components ranging from electronics toshielding to magnets were usually assigned and shippedto other laboratories for reuse or storage. In parti-cular, magnet frames and coils, even those exhibitinginduced radioactivity, were generally used again else-where rather than being disposed of; this was becauseof the high cost of new steel and copper. Other radio-active wastes generated either during the operation orthe dismantling of the accelerators were shipped fordisposal to a commercial burial ground. For example,the radioactive wastes from the dismantling at Rochesterwere shipped to the Nuclear Fuel Services burial site atWest Valley, New York, for custodial care, i.e., the AECand its successors retained title to and responsibilityfor the wastes. Again requiring the services of a com-mercial radioactive waste burial ground, the AEC turnedto the Nuclear Engineering Company's burial facility atMaxey Flats, KY, for disposal of the radioactive wastes

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from the decommissioning of the Carnegie-Mellon machine.

In two of the cases considered, the Yale HILAC andthe Harvard CEA, the dismantlement activities beganshortly after the cessation of operation, but in theother cases examined, there was a period of at leastone year between shutdown and dismantlement. In thecase of the Carnegie-Mellon cyclotron, this hiatusallowed the CMU administrators to seek, without suc-cess, alternate funding from the National Cancer Insti-tute for medical use of the accelerator. No record wasfound of any similar attempt by the University ofRochester or by Brookhaven. (Attempts by PrincetonUniversity to obtain alternate funding for medical usesof the 3-GeV proton synchrotron had limited success,and the facility continued to operate at a much lowerlevel. That machine is presently mothballed.) Sum-maries of the five decommissionings follow.

Operation of the 130-inch, 250 MeV synchrocyclo-tron at the University of Rochester was terminated latein 1968, and the accelerator was dismantled during thefirst five months of 1971. The steel main frame of themagnet was cut into blocks and shipped to the FermiNational Accelerator Laboratory for use as shielding.The radioactive wastes were buried at West Valley, NewYork. The highest exposure level encountered was 140mR/hr at the magnet pole tips. The building was leftintact for further use by the university. The cost ofdecommissioning, approximately $104,500, was borne bythe AEC.

The Cambridge Electron Accelerator, a 6-GeV elec-tron synchrotron at Harvard, was shut down at the endof May 1973. Major components were shipped to otherlaboratories, but the title to some components wastransferred to Harvard for the salvage value. Dis-assembly and demolition activities continued throughJuly 1975. The contract termination resulted in thedisplacement of 83 people. The highest induced radio-activity found at the facility was 100 mR/hr at thelinac converter assembly, and activities of up to 1mR/hr were found on the tunnel walls a year after shut-down. Total recorded dose-equivalent for the decom-missioning was less than 0.67 man-rem. The cost of thedecommissioning to the U. S. Energy Research andDevelopment Administration (successor to the AEC) was$735,200, including $96,500 paid to Harvard to assumeresponsibility for the final demolition activities.

The Nuclear Research Center owned by Carnegie-Mellon University was closed in 1969. The 130-inch,440-MeV synchrocyclotron was dismantled in 1974 and1975. All radioactive components were disposed ofeither by transfer within ERDA or burial as radioactivewastes. Other radioactive wastes that had been buriedat the site were retrieved for reburial at Maxey Flats,KY. Exposure levels of up to 175 mR/hr were encoun-tered in the cyclotron chamber in January, 1973. Inpreparation for sale, the site was decontaminated byremoval of all radioactive components, wastes, andconcrete. The cost to ERDA was approximately $504,000.

The Heavy-Ion Accelerator at Yale University wasdismantled during the six-month period beginningJanuary 1975, immediately after cessation of opera-tions. Most of the major components were shipped toother laboratories during the disassembly. Tentechnicians and three of the scientific staff weredisplaced by the contract termination, although somewere kept on during the dismantling. Induced radio-activity was present, but did not result in significantexposure to personnel. Following the disassembly, thebuilding was found to be radiologically clean. The$105,000 cost of decommissioning was the responsibilityof the ERDA.

The Brookhaven Cosmotron, a 3-GeV proton synchro-tron, was shut down on December 31, 1966. The machinewas kept in standby condition for one year after shut-down. During that time the experimental area wasdismantled and much of the equipment was transferredto the Alternating Gradient Synchrotron (AGS) facilityat Brookhaven National Laboratory. At the end of theyear, the AEC, which owned the Cosmotron, authorizedits dismantlement. The reusable equipment and compo-nents were removed on a spare-time bases by Brookhavenpersonnel. The actual disassembly of the synchrotronring mangets was done by contract technician laborover a three- to four-month period. The one-year wait-ing period resulted in a significant reduction of theinduced activity levels. The magnet segments, copperwindings, vacuum chambers, and vacuum pumps were placedin the radioactive material storage area, where mostof them remain today. The presence of induced radio-activity in these items precluded their release toscrap dealers. A number of magnet blocks have beenused as shielding at the AGS and more recently by theFermi National Accelerator Laboratory. Because of thedifficulty in removing the epoxy resin and fiber glassinsulation bonded to the copper magnet windings, veryfew of these have been reused.

As an alternative to dismantling, accelerators,especially smaller machines such as particle injectors,have been transferred relatively intact to otheraccelerator facilities. For example, the AGS 50-MeVproton linac injector was moved to the Bevatron atLawrence Berkeley Laboratory; the 2.2-GeV CornellElectron Synchrotron was sent to Argonne NationalLaboratory for use as a proton booster; and the Univ-ersity of Chicago synchrocyclotron was shipped toFermi National Accelerator Laboratory.

Long Range Radiological Considerationsof Accelerator Design

In the usual case of accelerator design, the onlyradiological considerations that are carefully treatedare the shielding and perhaps the target-handlingmachanism. There are four other areas of concern inwhich careful decisions can result in reduced radiationexposure to personnel during the operating life of anaccelerator and lessen the magnitude of radiationproblems upon decommissioning. They are (a) choice ofmaterials, (b) physical layout of accelerator compo-nents, (c) method of assembly, and (d) care in opera-tion.

Where choices are available, materials should bechosen to result in minimum induced activity fromtheir use in the particular accelerator environment.For example, the use of aluminum in place of copper formagnet coils will eliminate the possibility for produc-tion of 60Co in the windings. Where the option exists,components and equipment should not be placed nearlocations where a large fraction of the acceleratedbeam interacts. The intense neutron fluence at suchlocations will result in high levels of induced activ-ity in nearby components and may shorten the operatinglife of electronic or electrical equipment. Themethods of assembly and operation of such componentsas target positioners and septum magnets will affectradiation exposure to operating and maintenancepersonnel. The use of refinements such as quick dis-connects and remotely operable fasteners will speed uprepair and maintenance work, thereby reducing personnelexposure. Beam tuning will have an obvious effect uponthe amount of spurious induced activity produced by agiven accelerator. Constant striving for higherefficiency in extraction of the beam from the accelera-tor and transport to the target is desirable to mini-mize the unwanted activations.

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Table 1

ESTIMATED COSTS (1978 $) FOR DISMANTLING FOUR ACCELERATORSAT ARGONNE NATIONAL LABORATORY

Dismantl ingAccelerator Period ctivity

Zero Gradient Synchrotronb 2.8 x 106 2.2 x 106

60-inch Cyclotronc 2.1 x 10 8.5 x 105

20-MeV Tandem Van de Graaff 9.3 x 104 5.1 X 104

TruckPackaging Transportationa Disposal Total

4.1 x 10' 1.7 x 106 2.9 x 105 7.0 x 106

3.6 x 104 3.3 x 105 6.2 x 104 1.5 x 106

5.0 x 102 3.9 x 10' 7.3 x 102 1.5 x 105

17-MeV Electron Linac 3.6 x 10' 4.7 x 10' 5.0 x 102 3.9 x 10o 7.3 x 102 8.8 x 104

aTransportation cost based upon distance from Chicago, Illinois, to Richland, Washington area.bActivity cost includes scarfing and replacement of concrete shielding in the main ring tunnel.cActivity cost includes removal of concrete vault shielding.

High-energy accelerators (above l-GeV) generallywill require remote handling techniques or a moth-balled period prior to disassembly of highly activatedcomponents. Most medium energy accelerators can bedismantled using contact methods with some localizedshielding. Low-energy accelerators (below 1O-MeV),such as Van de Graaffs and linear electron accelera-tors used in medical and industrial applications, willgenerally not produce radiation levels which wouldaffect the decommissioning procedure.

Decommissioning Planning Considerations

For smaller accelerators where little or nointerest has been expressed in component reutiliza-tion, it may be best to request competitive bidding ona single contract for dismantlement and removal forradioactive burial or scrap resale. The sequence fora large accelerator will include dismantlement andremoval of the accelerator, demolition of concretestructures, and possibly land reclamation. The entiredecommissioning process will require about 18 to 24months, not including a possible mothballing periodfollowing shutdown. Actual dismantlement work could

aa

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o

a

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Im-

L S

c

C,

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Figure 1INDUCED ACTIVITY IN SELECTED ACCELERATORS

A AGS

ALAMPF

TOTAL ANNUAL NON-FUEL CYCLERADIOACTIVE WASTES A ZGS

A BEVATRON FNAL A

x

RESEARCH X PPA

CYCLOTRONS

X SLACXvX ACES

* BATES

-A 1 2 3 f1 2 3

la to toACCELERATOR ENERGY (MeY)

4 6 6to to is

require six months. Part of the cost could be offsetthrough salvage value of the nonradioactive material.

In Figure 1, the radioactive mass at decommis-sioning for selected accelerators is presented andcompared with the total non-fuel cycle wastes present-ly generated (based on 1 x 106 ft3 per year(5) assum-ing that the density of these wastes is equal to thatof water.) The estimated costs associated with thedismantling of four representative accelerators atArgonne National Laboratory are presented in Table 1.Although hundreds of components of major acceleratorsare extremely massive, they present generally manage-able activation levels. However, the costs exhibitedin Table 1 and the masses in Figure 1 assume no re-cycle or reutilization at other accelerator facili-ties.

The massive waste, substantial cost and potentialfuture recycle of valuable copper and iron from adecommissioned accelerator should not be ignored inthe design of new accelerators. The disposal ofcomponents, such as sections of magnets, in low-levelwaste burial grounds merely because they contain smallquantities of induced activity may represent a wasteof natural resources. However, since regulations onthe amount of permissible induced activity for releasefor unrestricted use do not exist, present practice isto send these components to other accelerator loca-tions for reuse, to radioactive waste burial sites fordisposal, or to storage areas which exist at severalnational laboratories. Release of this material tothe general public may not be advisable at this timedue to the lack of regulations which would limit thequantity of radionuclides added to the environmentthrough this route.

References

1. Comptroller General's Report to the Congress,"Cleaning Up the Remains of Nuclear Facilities -

A Multibillion Dollar Problem" EMD-77-46, June 16,1977.

2. National Bureau of Standards Handbook 107, "Radio-logical Safety in the Design and Operation of aParticle Accelerator," June 1970, Table 1.

3. Dr. David Romer, Siemens Corporation, privatecommunication.

4. P. Forman, "'Atom Smashers: Fifty Years' Previewof an Exhibit on the History of High EnergyAccelerators," IEEE Transactions on NuclearScience, Volume NS-24, Number 3, pp. 1896-1899,June 1977.

5. "Report of Task Force for Review of Nuclear WasteManagement (Draft)," United States Department ofEnergy, DOE/ER-0004/D, Appendix K, February 1978.

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