Regulatory Guide 5.47

Control and Accountability of Plutonium in Waste Material

ML13064A078
Person / Time
Issue date:	02/28/1975
From:	Office of Nuclear Regulatory Research
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RG-5.047
Download: ML13064A078 (6)

February 1975 U.S. NUCLEAR REGULATORY COMMISSION

REGULATOR GUIDE

REGULATORY GUIDE 5.47 CONTROL AND ACCOUNTABILITY OF PLUTONIUM IN WASTE MATERIAL

A. INTRODUCTION

guide describes procedures for complying with assay requirements related to plutonium-contaminated waste Section 73.60, "Additional Requirements for the given in paragraph 70.5 l(e)(4)(i).

Physical Protection of Special Nuclear Material at Fixed Sites," of 10 CFR Part 73, "Physical Protection of

B. DISCUSSION

Plants and Materials," requires that certain licensees A variety of materials become contaminated during search each package leaving a material access area* for the processing of plutonium. To be economically re- concealed special nuclear material to prevent plutonium coverable, the contaminated material must contain from being removed from the licensee's control. Physical enough plutonium to offset the scrap recovery costs.

search procedures or equipment capable of detecting Materials containing very small quantities of plutonium, concealed plutonium may be used. Nondestructive or process materials from which the plutonium cannot search techniques such as gamma ray spectrometry and be economically separated, are often considered as neutron assay are recommended when used with a process waste. Provisions relating to the disposition of tamper-safing system to ensure that no concealed such materials are contained in 10 CFR Part 20.

plutonium is removed from 'a material access area in As noted in the introduction, the materials protec- waste containers.

tion interest in such materials is twofold. First, to Section 70.51, "Material Balance, Inventory, and prevent significant quantities of plutonium from being Records Requirements," of 10 CFR Part 70, "Special concealed in containers, which would permit plutonium Nuclear Material," requires certain licensees to conduct to be removed from the licensee's control. Second, to physical inventories at bimonthly intervals. On the basis include in the measured material balance, all plutonium

"*'* of each bimonthly inventory, those licensees are re- contained in waste. The same measurement systems and quired to calculate a material balance, including the operations are able to search packages for substantial material unaccounted for (MUF) and its associated limit quantities of concealed plutonium and to assay contam- of error (LEMUF). Discards of contaminated waste must inated waste for plutonium content. Thus, both of these be included in the material balance. Section 70.51 considerations are addressed in this guide.

further states that the LEMUF must not exceed speci- fied limits. With proper controls, nondestructive assay

1. Container Selection (NDA) techniques may be applied to the assay of plu-tonium-contaminated waste material.

Plutonium-contaminated waste is typically packaged This guide describes procedures which are accept- in 55-gallon drums for storage or shipment. It is often able to the NRC staff for the control and accountability packaged in small primary containers (typically 4-6 liters of plutonium-contaminated waste. Specifically, this capacity) first and then combined in large containers to guide describes procedures for complying with paragraph reduce the waste-handling problem.

73.60(b) for searching plutonium-contaminated waste It is desirable to search and assay the waste in small packages for concealed plutonium. In addition, this containers rather than in large containers for the following reasons:

`" 'Material access area'," as defined in 10 CFR Part 73,

§73.2, "means any location which contains special nuclear 1. High concentrations of plutonium in waste material material, within a vault or a building, the roof, walls, and floor can be identified more easily when small containers are of which each constitute a physical barrier." assayed. The plutonium can then be recovered rather USNRC REGULATORY GUIDES Copies of published guides may be obtained by request indicating the divisions desired to the U S Nuclear Regulatory Commission, Washington. D.C. 20555 Regulatory Guides are issued to describe and make available to the public Attention: Director of Standards Development Comments and suggestions for methods acceptable to the NRC staff of implementing specific parts of the improvements in these guides are erncouraged and should be sent to the Commissions 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 divisions ie guides will be acceptable if rhey provide a basis for the findings requisite to the issuance or continuance of a pernit or license by the Commission. I Power Reactors 6 Products

2. Research and Test Reactors 7 Transooration

3 Fuels and Materials Facilities 8 Occupational Health Published guides will be revised periodically, as appropriate, to accommodate 4 Environmental and Siting 9 Antitrust Reiew comments and to reflect new information or experience, 5 Materials and Plant Proxectio,, 10 General

than discarded, thus reducing the waste disposal 3. Packaging and Sealing problem.

2. The use of small containers would improve the assay For effective control and accurate accounting of accuracy and thus lower the contribution of waste to the plutonium-contamiinated waste. waste should he pack- MUF and LEMUF.

aged and sealed at the point where it is collected.

3. Assaying small containers of waste, each from a Typically, contaminated waste is generated in cleanup or localized area, simplifies the calculation of individual maintenance operations. It is collected and then trans- area material balances (see Regulatory Guide 5.26, ferred to a point where it can be removed ("bagged-

"Selection of Material Balance Areas and Item Control out") from a glovebox line. Waste is often packaged in Areas"). cardboard cylindrical containers ("ice cream con-

4. Use of small containers facilitates the comparative tainers") which are then individually heat-sealed in assay procedures which are recommended to generate transparent polyethylene bags which prevent contami- current estimates of the systematic assay error. Fabri- nation after their transfer outside the glovebox en- cating calibration standards and testing the performance closures. It is recommended that pressure-sensitive seals*

of the instruments is made easy by assaying small be applied on the next to the outermost heat-sealed containers. plastic bag across each openin

g. Following assay and

5. It is more difficult to conceal material in small search, the package can be handled under item-control containers than in large containers. Therefore, assay of procedures.** Comparable procedures are necessary for the small containers, combined with an effective waste materials that cannot be packaged in this manner.

tamper-safing program, would enhance the ability to ensure that waste packages are not used to conceal plutonium to remove it from the site.

4. Assay and Search Measurements Since the same volume of waste can be packaged in long, narrow-diameter cylindrical containers as in short, The penetrability of gamma rays through a waste wide-diameter containers, narrow-diameter containers container can be determined by measuring the response should be preferred because they can be assayed more to an external source of gamma rays. That response is accurately than wide-diameter ones (as discussed in measured under two conditions-first with the waste Regulatory Guide 5.11, "Nondestructive Assay of container not located in the vicinity of the instrument Special Nuclear Material Contained in Scrap and and then with the container positioned between the Waste"). gamma ray source and the detector. The percent The size of the small containers and the material transmission (100 x container present/container absent)

from which they are constructed are important factors. provides an indication of whether gamma ray assay is From the materials protection viewpoint, the most appropriate or whether neutron assay must be used. The important factor in selecting and packaging the primary percent transmission is also used to correct the gamma containers is the requirement that enough of the ray assay for internal attenuation, thereby improving the radiations emitted throughout each container must be assay accuracy.

detected to ensure that there are no blind spots. Such blind spots may conceal plutonium and would introduce large biases into the assay.

4.1 Gamma Ray Assay

2. Segregation of Waste Materials The application of gamma ray spectrometry to plutonium assay is described in a report published by the Los Alamos Scientific Laboratory (ref. I). A bibliog- Plutonium spontaneously emits gamma rays and raphy of other relevant references is also provided in that neutrons. Gamma rays are highly attenuated by heavy report, together with a description of the necessary elements or densely compacted light elements. Neutrons, theory, instrumentation, and data analysis procedures.

on the other hand, penetrate quite well through most The report also describes procedures to determine a heavy elements but are strongly attenuated by light gamma ray attenuation correction, container rotation clements. and vertical scanning, and guidance on material categori- Waste materials often consist of contaminated zation and packaging. Guidelines on the calibration of hydrogenous materials like paper wipes and plastics. gamma ray waste assay are included in the LASL report, Water is often present, the amount varying. in ANSI Standard N15.20, "Guide to Calibrating Non- Different types of waste are often separately packaged for subsequent disposal. To achieve the desired search and accountability performance, waste which can be assayed using gamma ray methods should be pack- *See Regulatory Guide 5.10, "Selection and Use of Pressure- Sensitive Seals on Containers for Onsitc Storage of Special aged separately from waste which should be assayed Nuclear Material."

using neutron methods. **See 10 CFR Part 70, §70.51.

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destructive Assay Systems,"* and in a regulatory guide of the gamma rays emitted during the radioactive decay in preparation, "Calibration and Error Estimation of plutonium-239. Therefore, it is also necessary to Methods for Nondestructive Assay." verify or measure the abundance of the isotope Pu-239 relative to the total plutonium to account for the quantity

4.2 Neutron Assay of materials by element, as required in 10 CFR Part 70.

Gamma ray spectrometry can be used to measure Neutrons are spontaneously emitted in the decay of the relative abundances of the plutonium isotopes if plutonium when the even-even isotopes (plutonium-238, they are unknown (ref. 1). When waste material is

240, and 242) decay by spontaneous fission. Neutrons separated into single plutonium isotopic blends, gamma may also be emitted when alpha particles, emitted either ray spectrometry can be used to verify a prior measure- in the decay of the plutonium isotopes or their daughter ment of the isotopic abundances of the batch. Isotopic products, strike certain light nuclei. Neutron yield abundances can be verified by measuring the ratio of the information is given in Regulatory Guide 5.23, "In Situ intensity of gamma rays from two or more plutonium Assay of Plutonium Residual Holdup." Large errors in isotopes during-waste assay (ref. I).

gross neutron assay can arise (1) when the isotopic composition changes, (2) when the concentration of high-yield (a, n) target materials changes, and (3) when 7. Instrument Shielding large differences occur in the amount or distribution of neutron-moderating materials. In assay applications The amount of plutonium contained in typical requiring higher accuracy, spontaneous fission events are packages of waste will he small, often less than ten detected by the coincident detection of two or more of grams. It is necessary to provide enough shielding around the radiations emitted in that type of reaction.** the detectors to ensure that the detected radiations In the present application, high-density materials come from the waste package, and not the process line.

(i.e., materials having a gamma ray transmission of 1%or To avoid this problem, a measurement area should be less at 414 keV) are examined by neutron assay. marked off to prevent inadvertent radiation background It is necessary to establish a threshold sensitivity for problems caused by moving plutonium too close to the detecting plutonium present for all types of waste instruments.

materials. Items for which the assay indicates less than a statistically significant quantity (i.e., the detection threshold) are assumed (for material balance accounting) 8. Post-Assay Handling to contain no plutonium. Those items are not factored

' into the LEMUF calculation. Small packages of waste may be combined in large When the waste consists of machine parts, pipes, containers for offsite disposal. Each assayed sealed waste tools, etc. that have surface contamination, it may be package is weighed and set aside until a sufficient necessary to disassemble or cut the item into small number of packages are accumulated to fill a shipping pieces. Such items are cleaned by appropriate methods container. A shipping container is then brought in, exam- (e.g., brushing, chipping, and acid leaching) to remove as ined, and filled. After filling, it is immediately closed much plutonium as possible prior to disposal. and sealed and transferred from the material access area to an approved storage area to await further disposition.

Accountability records are prepared by combining the

5. Homogeneous Waste Materials assay values of all the sealed packages loaded into each shipping container.

Waste materials consisting of relatively homoge- neous process residues can be searched using the procedures described above. However, more accurate

C. REGULATORY POSITION

assays may be made of homogeneous waste materials by traditional sampling and chemical analysis, coupled with This guide describes procedures for the control and a determination of the bulk quantity present.

accountability of plutonium-contaminated waste. The procedures are acceptable to the NRC staff for materials

6. Abundance of Plutonium Isotopes protection purposes.

The assay for plutonium by gamma ray spectro- metry is based on observation of one or, at most, a few

1. Handling Procedures Plutonium-contaminated waste should be separated

• Presently in development. Copies may be obtained from the into distinct categories, each of which should be Institute of Nuclear Materials Management, 505 King Avenue, packaged separately. Criteria for separation should Columbus, Ohio, 43201. Attention: M. H. L. Toy.

• • See Regulatory Guide 5.34, "Nondestructive Assay for Pluto- include density and neutron-moderating considerations, nium in Scrap Material by Spontaneous Fission Detection." in addition to health and safety criteria.

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2. Containers and Packaging Procedures two plutonium isotopes. When the isotopic composition Waste should be packaged for in-plant handling in cannot be verified, the package should be either sampled small-diameter containers wherever possible. The diam- for mass/alpha spectrometric assay (ref. 2) or measured eter of the package should be less than 15 cm.* The by gamma ray spectral analysis.

same type and size of container should be used for all waste categories except special types of waste (e.g., 4.2 Gamma Ray Assay Procedures solutions or large metal pieces). Large items should be disassembled or cut up to facilitate handling, assay, and Gamma ray assay for plutonium in waste should be search procedures. Packages should be heat-sealed in accomplished by applying gamma ray spectrometry to multiple transparent polyethylene bags to avoid contam- each package of plutonium waste by procedures ination when they are removed from approved en- described in reference 1. Of the options discussed in closures. Contaminated tools, machine parts, or sections reference 1, those described below are generally accept- of vessels or interconnecting plumbing should be able to the NRC staff.

thoroughly cleaned to remove as much plutonium as possible before they are packaged as waste. 4.2.1 Detection System

3. Sealing Procedures A high-resolution Ge(Li) gamma ray detection system should be used. The system should have, as a Pressure-sensitive seals** should be applied across minimum, the performance specifications of a type I

each heat-sealed closure in the next to the outermost system as described in Regulatory Guide 5.9, "Specifi- transparent plastic bag. On each package having more cations for Ge(Li) Spectroscopy Systems for Material

'than one heat-sealed closure, the identification number Protection Measurements."

of each seal should be written on all other seals on that package. Each completed package should be weighed 4.2.2 Collimation and Scanning Procedures individually and the weight recorded.

Each package should be rotated and scanned ver-

4. Assay and Search Procedures tically during assay. The detector should be collimated to view a vertical segment of the container measuring no Gamma ray assay procedures should be used when- more than 2-3 cm high. The collimator should be ever the transmission through the entire package from an designed to view the entire diameter or width dimension external source of 414-keV gamma rays is greater than of the package during assa

y. The intensity of the

1%. Packages failing to meet this criterion should be appropriate gamma rays should be measured indepen- assayed by neutron detection methods. Homogeneous dently for each vertical segment. The total package materials containing low concentrations of plutonium contents should be determined by summing the con- may be assayed either by sampling and chemical analysis tributions from all of the contiguous vertical segments.

or by the nondestructive assay procedures described below. .4.2.3 Attenuation Corrections An acceptable upper limit on the plutonium content in each package should be established for each type of To measure attenuation corrections, an external waste. Packages indicating higher amounts should be source of gamma rays (see ref. 1) should be positioned opened and examined for conspicuous attempts to directly in front of the detector collimator opening, such conceal plutonium. The appropriate NRC Regional that the gamma rays emitted by the source will travel Office should be notified immediately if a conspicuous through the waste package before striking the detector.

attempt to conceal plutonium is detected. The assay results for each segment of each package should be corrected for internal attenuation, based on

4.1 Isotopic Analysis the measured transmission of the external source gamma rays through that segment. When the transmission at 414 The isotopic composition of each container of waste keV through any segment is less than 1%, that package should be traceable to a measured value. A previously must be searched using the neutron assay procedures measured value can be used when verified by measuring described below.

the ratio of the intensity of gamma rays from at least

4.3 Neutron Assay Procedures Each waste package that fails to meet the criteria

• See Regulatory Guide 5.11. "Nondestructive Assay of Special for gamma ray assay should be examined using neutron Nuclear Material Contained in Scrap and Waste," for further guidance on this matter.

assay procedures. Regulatory Guide 5.34, "Nondestruc-

• • See Regulatory Guide 5.10, "Selection and Use of Pressure-. tive Assay for Plutonium in Scrap Material by Sponta- Sensitive Seals on Containers for Onsite Storage of Special neous Fission Detection," describes procedures that are Nuclear Material." also applicable to high-density wast

e. Simple neutron

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detection probes may also be applicable. container. Care should be exercised to ensure that the containers are not ruptured during loading.

4.4 Calibration and Error Estimation Procedures Assay systems should be calibrated and errors When the shipping container is filled, it should be determined as described in the publications mentioned closed and sealed immediately with tamper-indicating below. Guidance related to calibration is described in the seal(s), each of which bears an identification code (see LASL report (ref. I!. Frror estimation procedures for Regulatory Guide 5.15, "Security Seals for the Pro- the separate calculation of random and systematic errors tection and Control of Special Nuclear Material"). The associated with the assay are described in a regulatory identification code(s) of the seal(s) used on each guide being prepared, "Calibration and Error Estimation shipping container should be recorded on the container Procedures for Nondestructive Assay." Additional dis- make-up sheet. The sealed shipping container should be cussion of these topics as they specifically relate to promptly transferred from the material access area to an plutonium waste assay is given in the LASL report [ref. approved onsite storage facility, awaiting offsite

1,Section II, items (a) through (e)]. shipment.

5. Post-Assay Handling 5.4 Preshipment Verification of Contents

5.1 Interim Storage A copy of each shipping container make-up sheet should be maintained in the nuclear material control Waste packages should be stored until a sufficient files. Immediately prior to shipment, each shipping quantity is accumulated to fill a shipping container. container should be weighed and the weight recorded on the make-up sheet. The integrity and identification of all

5.2 Shipping Container Manifest seals used to seal the shipping container should be checked. The gross weight of each shipping container A make-up sheet for each shipping container should should be compared with the combined weights of the be prepared. The sheet should list information for each empty shipping container and the waste packages that waste package container, including the identifying code have been loaded into that container. When the weights of the pressure-sensitive seals, the gross package weight, do not match or when the seals are not intact or are not and the assayed plutonium content. The sheet should properly identified, the shipping container should be identify the types of waste. It should also note if the quarantined, opened, and its contents examined.

-.. < assay values for concealed plutonium were obtained by sampling and analysis (homogeneous waste only) com-

D. IMPLEMENTATION

bined with a neutron search, or by gamma ray assay or neutron assay. The sheet should identify the shipping The purpose of this section is to provide infor- container and its empty weight, including the weights of mation to applicants and licensees regarding the NRC

all items to be used for closing and sealing. staff's plans for utilizing this regulatory guide.

Except in those cases in which the applicant

5.3 Shipping Container Loading and Tamper-Safing proposes an alternative method for complying with Procedures specified portions of the Commission's regulations, the method described herein will be used in the evaluation Immediately prior to the loading of a shipping of submittals in connection with a special nuclear container, the shipping container should be emptied of material license, operating license, or construction all contents and visually examined for integrity and permit for applications docketed after October 1, 1975.

unusual characteristics. A minimum of two operators If an applicant whose application for a special should perform the loading and sign the make-up sheet. nuclear material license, an operating license, or a Each container should be continuously observed from construction permit is docketed on or before October 1, the time loading is started until the container is closed 1975, wishes to use this regulatory guide in developing and sealed. Each package should be checked for seal and submittals for applications, the pertinent portions of the closure integrity as it is loaded into the shipping application will be evaluated on the basis of this guide.

REFERENCES

1. T.D. Reilly and J.L. Parker, "A Guide to Gamma 2. See, for example, R. G. Gutmacher, F. Stephens, K.

Ray Assay for Nuclear Material Accountability," Ernst, J.E. Harrar, J. Magistad, T.E. Shea, and S.P.

Los Alamos Scientific Laboratory Report LA-5794- Turel, "Methods for the Accountability of Pluto- MS (1974). nium Nitrate Solutions," WASH- 1282 (1974).

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