Regulatory Guide 5.47

Control and Accountability of Plutonium in Waste Material

ML13064A078
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Issue date:	02/28/1975
From:	Office of Nuclear Regulatory Research
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RG-5.047
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U.S. NUCLEAR REGULATORY COMMISSIONREGULATOR GUIDEFebruary 1975REGULATORY GUIDE 5.47CONTROL AND ACCOUNTABILITY OF PLUTONIUM IN WASTE MATERIAL

A. INTRODUCTION

Section 73.60, "Additional Requirements for thePhysical Protection of Special Nuclear Material at FixedSites," of 10 CFR Part 73, "Physical Protection ofPlants and Materials," requires that certain licenseessearch each package leaving a material access area* forconcealed special nuclear material to prevent plutoniumfrom being removed from the licensee's control. Physicalsearch procedures or equipment capable of detectingconcealed plutonium may be used. Nondestructivesearch techniques such as gamma ray spectrometry andneutron assay are recommended when used with atamper-safing system to ensure that no concealedplutonium is removed from 'a material access area inwaste containers.Section 70.51, "Material Balance, Inventory, andRecords Requirements," of 10 CFR Part 70, "SpecialNuclear Material," requires certain licensees to conductphysical inventories at bimonthly intervals. On the basisof each bimonthly inventory, those licensees are re-quired to calculate a material balance, including thematerial unaccounted for (MUF) and its associated limitof error (LEMUF). Discards of contaminated waste mustbe included in the material balance. Section 70.51further states that the LEMUF must not exceed speci-fied limits. With proper controls, nondestructive assay(NDA) techniques may be applied to the assay ofplu-tonium-contaminated waste material.This guide describes procedures which are accept-able to the NRC staff for the control and accountabilityof plutonium-contaminated waste. Specifically, thisguide describes procedures for complying with paragraph73.60(b) for searching plutonium-contaminated wastepackages for concealed plutonium. In addition, this`" 'Material access area'," as defined in 10 CFR Part 73,§73.2, "means any location which contains special nuclearmaterial, within a vault or a building, the roof, walls, and floorof which each constitute a physical barrier."guide describes procedures for complying with assayrequirements related to plutonium-contaminated wastegiven in paragraph 70.5 l(e)(4)(i).

B. DISCUSSION

A variety of materials become contaminated duringthe processing of plutonium. To be economically re-coverable, the contaminated material must containenough plutonium to offset the scrap recovery costs.Materials containing very small quantities of plutonium,or process materials from which the plutonium cannotbe economically separated, are often considered asprocess waste. Provisions relating to the disposition ofsuch materials are contained in 10 CFR Part 20.As noted in the introduction, the materials protec-tion interest in such materials is twofold. First, toprevent significant quantities of plutonium from beingconcealed in containers, which would permit plutoniumto be removed from the licensee's control. Second, toinclude in the measured material balance, all plutoniumcontained in waste. The same measurement systems andoperations are able to search packages for substantialquantities of concealed plutonium and to assay contam-inated waste for plutonium content. Thus, both of theseconsiderations are addressed in this guide.1. Container SelectionPlutonium-contaminated waste is typically packagedin 55-gallon drums for storage or shipment. It is oftenpackaged in small primary containers (typically 4-6 literscapacity) first and then combined in large containers toreduce the waste-handling problem.It is desirable to search and assay the waste in smallcontainers rather than in large containers for thefollowing reasons:1. High concentrations of plutonium in waste materialcan be identified more easily when small containers areassayed. The plutonium can then be recovered ratherUSNRC REGULATORY GUIDES Copies of published guides may be obtained by request indicating the divisionsdesired to the U S Nuclear Regulatory Commission, Washington. D.C. 20555Regulatory Guides are issued to describe and make available to the public Attention: Director of Standards Development Comments and suggestions formethods acceptable to the NRC staff of implementing specific parts of the improvements in these guides are erncouraged and should be sent to theCommissions regulatio.s, to delineate techniques used by the staff in Secretary of the Commission, U S, Nuclear Regulatory Commission.evaluating specific problems or postulated accidents, or to provide guidance to VWashington. DC. 20555. Attention: Docketing and Service Section.upplicants. Regulatory Guides are not substitutes for regulations and compliance-ith them is not required. Methods and solutions different from those set out in The guides are issued itn the following ten broad divisionsie guides will be acceptable if rhey provide a basis for the findings requisite tothe issuance or continuance of a pernit or license by the Commission. I Power Reactors 6 Products2. Research and Test Reactors 7 Transooration3 Fuels and Materials Facilities 8 Occupational HealthPublished guides will be revised periodically, as appropriate, to accommodate 4 Environmental and Siting 9 Antitrust Reiewcomments and to reflect new information or experience, 5 Materials and Plant Proxectio,, 10 General than discarded, thus reducing the waste disposalproblem.2. The use of small containers would improve the assayaccuracy and thus lower the contribution of waste to theMUF and LEMUF.3. Assaying small containers of waste, each from alocalized area, simplifies the calculation of individualarea material balances (see Regulatory Guide 5.26,"Selection of Material Balance Areas and Item ControlAreas").4. Use of small containers facilitates the comparativeassay procedures which are recommended to generatecurrent estimates of the systematic assay error. Fabri-cating calibration standards and testing the performanceof the instruments is made easy by assaying smallcontainers.5. It is more difficult to conceal material in smallcontainers than in large containers. Therefore, assay ofthe small containers, combined with an effectivetamper-safing program, would enhance the ability toensure that waste packages are not used to concealplutonium to remove it from the site.Since the same volume of waste can be packaged inlong, narrow-diameter cylindrical containers as in short,wide-diameter containers, narrow-diameter containersshould be preferred because they can be assayed moreaccurately than wide-diameter ones (as discussed inRegulatory Guide 5.11, "Nondestructive Assay ofSpecial Nuclear Material Contained in Scrap andWaste").The size of the small containers and the materialfrom which they are constructed are important factors.From the materials protection viewpoint, the mostimportant factor in selecting and packaging the primarycontainers is the requirement that enough of theradiations emitted throughout each container must bedetected to ensure that there are no blind spots. Suchblind spots may conceal plutonium and would introducelarge biases into the assay.2. Segregation of Waste MaterialsPlutonium spontaneously emits gamma rays andneutrons. Gamma rays are highly attenuated by heavyelements or densely compacted light elements. Neutrons,on the other hand, penetrate quite well through mostheavy elements but are strongly attenuated by lightclements.Waste materials often consist of contaminatedhydrogenous materials like paper wipes and plastics.Water is often present, the amount varying.Different types of waste are often separatelypackaged for subsequent disposal. To achieve the desiredsearch and accountability performance, waste which canbe assayed using gamma ray methods should be pack-aged separately from waste which should be assayedusing neutron methods.3. Packaging and SealingFor effective control and accurate accounting ofplutonium-contamiinated waste. waste should he pack-aged and sealed at the point where it is collected.Typically, contaminated waste is generated in cleanup ormaintenance operations. It is collected and then trans-ferred to a point where it can be removed ("bagged-out") from a glovebox line. Waste is often packaged incardboard cylindrical containers ("ice cream con-tainers") which are then individually heat-sealed intransparent polyethylene bags which prevent contami-nation after their transfer outside the glovebox en-closures. It is recommended that pressure-sensitive seals*be applied on the next to the outermost heat-sealedplastic bag across each opening. Following assay andsearch, the package can be handled under item-controlprocedures.** Comparable procedures are necessary forwaste materials that cannot be packaged in this manner.4. Assay and Search MeasurementsThe penetrability of gamma rays through a wastecontainer can be determined by measuring the responseto an external source of gamma rays. That response ismeasured under two conditions-first with the wastecontainer not located in the vicinity of the instrumentand then with the container positioned between thegamma ray source and the detector. The percenttransmission (100 x container present/container absent)provides an indication of whether gamma ray assay isappropriate or whether neutron assay must be used. Thepercent transmission is also used to correct the gammaray assay for internal attenuation, thereby improving theassay accuracy.4.1 Gamma Ray AssayThe application of gamma ray spectrometry toplutonium assay is described in a report published by theLos Alamos Scientific Laboratory (ref. I). A bibliog-raphy of other relevant references is also provided in thatreport, together with a description of the necessarytheory, instrumentation, and data analysis procedures.The report also describes procedures to determine agamma ray attenuation correction, container rotationand vertical scanning, and guidance on material categori-zation and packaging. Guidelines on the calibration ofgamma ray waste assay are included in the LASL report,in ANSI Standard N15.20, "Guide to Calibrating Non-*See Regulatory Guide 5.10, "Selection and Use of Pressure-Sensitive Seals on Containers for Onsitc Storage of SpecialNuclear Material."**See 10 CFR Part 70, §70.51..47-2 destructive Assay Systems,"* and in a regulatory guidein preparation, "Calibration and Error EstimationMethods for Nondestructive Assay."4.2 Neutron AssayNeutrons are spontaneously emitted in the decay ofplutonium when the even-even isotopes (plutonium-238,240, and 242) decay by spontaneous fission. Neutronsmay also be emitted when alpha particles, emitted eitherin the decay of the plutonium isotopes or their daughterproducts, strike certain light nuclei. Neutron yieldinformation is given in Regulatory Guide 5.23, "In SituAssay of Plutonium Residual Holdup." Large errors ingross neutron assay can arise (1) when the isotopiccomposition changes, (2) when the concentration ofhigh-yield (a, n) target materials changes, and (3) whenlarge differences occur in the amount or distribution ofneutron-moderating materials. In assay applicationsrequiring higher accuracy, spontaneous fission events aredetected by the coincident detection of two or more ofthe radiations emitted in that type of reaction.**In the present application, high-density materials(i.e., materials having a gamma ray transmission of 1% orless at 414 keV) are examined by neutron assay.It is necessary to establish a threshold sensitivity fordetecting plutonium present for all types of wastematerials. Items for which the assay indicates less than astatistically significant quantity (i.e., the detectionthreshold) are assumed (for material balance accounting)to contain no plutonium. Those items are not factored' into the LEMUF calculation.When the waste consists of machine parts, pipes,tools, etc. that have surface contamination, it may benecessary to disassemble or cut the item into smallpieces. Such items are cleaned by appropriate methods(e.g., brushing, chipping, and acid leaching) to remove asmuch plutonium as possible prior to disposal.5. Homogeneous Waste MaterialsWaste materials consisting of relatively homoge-neous process residues can be searched using theprocedures described above. However, more accurateassays may be made of homogeneous waste materials bytraditional sampling and chemical analysis, coupled witha determination of the bulk quantity present.6. Abundance of Plutonium IsotopesThe assay for plutonium by gamma ray spectro-metry is based on observation of one or, at most, a few*Presently in development. Copies may be obtained from theInstitute of Nuclear Materials Management, 505 King Avenue,Columbus, Ohio, 43201. Attention: M. H. L. Toy.**See Regulatory Guide 5.34, "Nondestructive Assay for Pluto-nium in Scrap Material by Spontaneous Fission Detection."of the gamma rays emitted during the radioactive decayof plutonium-239. Therefore, it is also necessary toverify or measure the abundance of the isotope Pu-239relative to the total plutonium to account for the quantityof materials by element, as required in 10 CFR Part 70.Gamma ray spectrometry can be used to measurethe relative abundances of the plutonium isotopes ifthey are unknown (ref. 1). When waste material isseparated into single plutonium isotopic blends, gammaray spectrometry can be used to verify a prior measure-ment of the isotopic abundances of the batch. Isotopicabundances can be verified by measuring the ratio of theintensity of gamma rays from two or more plutoniumisotopes during-waste assay (ref. I).7. Instrument ShieldingThe amount of plutonium contained in typicalpackages of waste will he small, often less than tengrams. It is necessary to provide enough shielding aroundthe detectors to ensure that the detected radiationscome from the waste package, and not the process line.To avoid this problem, a measurement area should bemarked off to prevent inadvertent radiation backgroundproblems caused by moving plutonium too close to theinstruments.8. Post-Assay HandlingSmall packages of waste may be combined in largecontainers for offsite disposal. Each assayed sealed wastepackage is weighed and set aside until a sufficientnumber of packages are accumulated to fill a shippingcontainer. A shipping container is then brought in, exam-ined, and filled. After filling, it is immediately closedand sealed and transferred from the material access areato an approved storage area to await further disposition.Accountability records are prepared by combining theassay values of all the sealed packages loaded into eachshipping container.

C. REGULATORY POSITION

This guide describes procedures for the control andaccountability of plutonium-contaminated waste. Theprocedures are acceptable to the NRC staff for materialsprotection purposes.1. Handling ProceduresPlutonium-contaminated waste should be separatedinto distinct categories, each of which should bepackaged separately. Criteria for separation shouldinclude density and neutron-moderating considerations,in addition to health and safety criteria.5.47-3 2. Containers and Packaging ProceduresWaste should be packaged for in-plant handling insmall-diameter containers wherever possible. The diam-eter of the package should be less than 15 cm.* Thesame type and size of container should be used for allwaste categories except special types of waste (e.g.,solutions or large metal pieces). Large items should bedisassembled or cut up to facilitate handling, assay, andsearch procedures. Packages should be heat-sealed inmultiple transparent polyethylene bags to avoid contam-ination when they are removed from approved en-closures. Contaminated tools, machine parts, or sectionsof vessels or interconnecting plumbing should bethoroughly cleaned to remove as much plutonium aspossible before they are packaged as waste.3. Sealing ProceduresPressure-sensitive seals** should be applied acrosseach heat-sealed closure in the next to the outermosttransparent plastic bag. On each package having more' than one heat-sealed closure, the identification numberof each seal should be written on all other seals on thatpackage. Each completed package should be weighedindividually and the weight recorded.4. Assay and Search ProceduresGamma ray assay procedures should be used when-ever the transmission through the entire package from anexternal source of 414-keV gamma rays is greater than1%. Packages failing to meet this criterion should beassayed by neutron detection methods. Homogeneousmaterials containing low concentrations of plutoniummay be assayed either by sampling and chemical analysisor by the nondestructive assay procedures describedbelow.An acceptable upper limit on the plutonium contentin each package should be established for each type ofwaste. Packages indicating higher amounts should beopened and examined for conspicuous attempts toconceal plutonium. The appropriate NRC RegionalOffice should be notified immediately if a conspicuousattempt to conceal plutonium is detected.4.1 Isotopic AnalysisThe isotopic composition of each container of wasteshould be traceable to a measured value. A previouslymeasured value can be used when verified by measuringthe ratio of the intensity of gamma rays from at least*See Regulatory Guide 5.11. "Nondestructive Assay of SpecialNuclear Material Contained in Scrap and Waste," for furtherguidance on this matter.**See Regulatory Guide 5.10, "Selection and Use of Pressure-.Sensitive Seals on Containers for Onsite Storage of SpecialNuclear Material."two plutonium isotopes. When the isotopic compositioncannot be verified, the package should be either sampledfor mass/alpha spectrometric assay (ref. 2) or measuredby gamma ray spectral analysis.4.2 Gamma Ray Assay ProceduresGamma ray assay for plutonium in waste should beaccomplished by applying gamma ray spectrometry toeach package of plutonium waste by proceduresdescribed in reference 1. Of the options discussed inreference 1, those described below are generally accept-able to the NRC staff.4.2.1 Detection SystemA high-resolution Ge(Li) gamma ray detectionsystem should be used. The system should have, as aminimum, the performance specifications of a type Isystem as described in Regulatory Guide 5.9, "Specifi-cations for Ge(Li) Spectroscopy Systems for MaterialProtection Measurements."4.2.2 Collimation and Scanning ProceduresEach package should be rotated and scanned ver-tically during assay. The detector should be collimatedto view a vertical segment of the container measuring nomore than 2-3 cm high. The collimator should bedesigned to view the entire diameter or width dimensionof the package during assay. The intensity of theappropriate gamma rays should be measured indepen-dently for each vertical segment. The total packagecontents should be determined by summing the con-tributions from all of the contiguous vertical segments..4.2.3 Attenuation CorrectionsTo measure attenuation corrections, an externalsource of gamma rays (see ref. 1) should be positioneddirectly in front of the detector collimator opening, suchthat the gamma rays emitted by the source will travelthrough the waste package before striking the detector.The assay results for each segment of each packageshould be corrected for internal attenuation, based onthe measured transmission of the external source gammarays through that segment. When the transmission at 414keV through any segment is less than 1%, that packagemust be searched using the neutron assay proceduresdescribed below.4.3 Neutron Assay ProceduresEach waste package that fails to meet the criteriafor gamma ray assay should be examined using neutronassay procedures. Regulatory Guide 5.34, "Nondestruc-tive Assay for Plutonium in Scrap Material by Sponta-neous Fission Detection," describes procedures that arealso applicable to high-density waste. Simple neutron5.47-4 detection probes may also be applicable.4.4 Calibration and Error Estimation ProceduresAssay systems should be calibrated and errorsdetermined as described in the publications mentionedbelow. Guidance related to calibration is described in theLASL report (ref. I!. Frror estimation procedures forthe separate calculation of random and systematic errorsassociated with the assay are described in a regulatoryguide being prepared, "Calibration and Error EstimationProcedures for Nondestructive Assay." Additional dis-cussion of these topics as they specifically relate toplutonium waste assay is given in the LASL report [ref.1,Section II, items (a) through (e)].5. Post-Assay Handling5.1 Interim StorageWaste packages should be stored until a sufficientquantity is accumulated to fill a shipping container.5.2 Shipping Container ManifestA make-up sheet for each shipping container shouldbe prepared. The sheet should list information for eachwaste package container, including the identifying codeof the pressure-sensitive seals, the gross package weight,and the assayed plutonium content. The sheet shouldidentify the types of waste. It should also note if the-..< assay values for concealed plutonium were obtained bysampling and analysis (homogeneous waste only) com-bined with a neutron search, or by gamma ray assay orneutron assay. The sheet should identify the shippingcontainer and its empty weight, including the weights ofall items to be used for closing and sealing.5.3 Shipping Container Loading and Tamper-SafingProceduresImmediately prior to the loading of a shippingcontainer, the shipping container should be emptied ofall contents and visually examined for integrity andunusual characteristics. A minimum of two operatorsshould perform the loading and sign the make-up sheet.Each container should be continuously observed fromthe time loading is started until the container is closedand sealed. Each package should be checked for seal andclosure integrity as it is loaded into the shippingcontainer. Care should be exercised to ensure that thecontainers are not ruptured during loading.When the shipping container is filled, it should beclosed and sealed immediately with tamper-indicatingseal(s), each of which bears an identification code (seeRegulatory Guide 5.15, "Security Seals for the Pro-tection and Control of Special Nuclear Material"). Theidentification code(s) of the seal(s) used on eachshipping container should be recorded on the containermake-up sheet. The sealed shipping container should bepromptly transferred from the material access area to anapproved onsite storage facility, awaiting offsiteshipment.5.4 Preshipment Verification of ContentsA copy of each shipping container make-up sheetshould be maintained in the nuclear material controlfiles. Immediately prior to shipment, each shippingcontainer should be weighed and the weight recorded onthe make-up sheet. The integrity and identification of allseals used to seal the shipping container should bechecked. The gross weight of each shipping containershould be compared with the combined weights of theempty shipping container and the waste packages thathave been loaded into that container. When the weightsdo not match or when the seals are not intact or are notproperly identified, the shipping container should bequarantined, opened, and its contents examined.

D. IMPLEMENTATION

The purpose of this section is to provide infor-mation to applicants and licensees regarding the NRCstaff's plans for utilizing this regulatory guide.Except in those cases in which the applicantproposes an alternative method for complying withspecified portions of the Commission's regulations, themethod described herein will be used in the evaluationof submittals in connection with a special nuclearmaterial license, operating license, or constructionpermit for applications docketed after October 1, 1975.If an applicant whose application for a specialnuclear material license, an operating license, or aconstruction permit is docketed on or before October 1,1975, wishes to use this regulatory guide in developingsubmittals for applications, the pertinent portions of theapplication will be evaluated on the basis of this guide.REFERENCES1. T.D. Reilly and J.L. Parker, "A Guide to GammaRay Assay for Nuclear Material Accountability,"Los Alamos Scientific Laboratory Report LA-5794-MS (1974).2. See, for example, R. G. Gutmacher, F. Stephens, K.Ernst, J.E. Harrar, J. Magistad, T.E. Shea, and S.P.Turel, "Methods for the Accountability of Pluto-nium Nitrate Solutions," WASH- 1282 (1974).5.47-5 UNITED STATESNUCLEAR REGULATORY COMMISSIONWASHINGTON, D. C. 20555OFFICIAL BUSINESSPENALTY FOR PRIVATE USE, $300POSTAGE AND FEES PAIDUNITED STATES NUCLEARREGULATORY COMMISSION