Regulatory Guide 5.58

Considerations for Establishing Traceability of Special Nuclear Material Accounting Measurements

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Issue date:	02/29/1980
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Revision 1 C; p o U.S. NUCLEAR REGULATORY COMMISSION February 1980

"R EGULATORY GUIDE

liO; OFFICE OF STANDARDS DEVELOPMENT

REGULATORY GUIDE 5.58 CONSIDERATIONS FOR ESTABLISHING TRACEABILITY OF

SPECIAL

NUCLEAR MATERIAL ACCOUNTING MEASUREMENTS

A. INTRODUCTION

individual measurement results to the national standards of measurement through an unbroken chain of comparisons.

Part 70, "Domestic Licensing of Special Nuclear Material,"

Reference standard means a material, device, or instrument of Title 10 of the Code of Federal Regulations requires that whose assigned value 5 is known relative to the national for approval to possess and use more than one effective kilo standards of measurement.

gram of special nuclear material (SNM)l the licensee must provide an adequate material control and accounting sys This guide presents conditions and procedural approaches tem. Section 70.51, "Material Balance, Inventory, and Re acceptable to the NRC staff for establishing and maintaining cords Requirements," requires licensees to calculate material traceability of SNM control and accounting measurements.

unaccounted for2 (MUF) and the limit of error of the MUF 3 No specific methods will be presented herein since the value (LEMUF) following each physical inventory and to com methodology to be used for any given measurement must pare the LEMUF with prescribed standards. Section 70.58, be tailored to the needs and peculiarities of the relevant

"Fundamental Nuclear Material Controls," requires licensees process material, reference standards, instrumentation, and to maintain a program for the continuing determination of circumstances. Rationales and pertinent analytical factors systematic and random measurement errors and for main will be presented for consideration as to their applicability taining control of such errors within prescribed limits. Sec to the measurement at hand.

tion 70.57, "Measurement Control Program for Special Nu clear Materials Control and Accounting," provides criteria for establishing and maintaining an acceptable measurement

B. DISCUSSION

and control system. 4 Reference 1 describes the technical and

1. BACKGROUND

administrative elements that are considered to be important in a measurement control program.

SNM measurements for control and accounting are performed on a great variety of material types and concen Implicit in the criteria stated in §70.57 is the require trations, with a diversity of measurement procedures, by a ment of traceability of all SNM control and accounting large number of licensees at all the various systems to the national standards of measurement as industrial, research and development, and academic facilities involved.

maintained by the National Bureau of Standards (NBS) by Accurate, reliable measurements are necessary to achieve means of reference standards.

valid overall accountability. To this end, all measurement systems must be compatible with the national standards of Reference standard is defined in §70.57(a)(3). Trace ability is defined in §70.57(a)(4). These definitions are measurement through the national measurement system (NMS). To obtain this necessary compatibility for any SNM

clarified as follows: Traceability means the ability to relate measurement task, reference materials appropriate for each SNM type and measurement system may be required.

Table I defines the various types of reference materials.

1 Lines indicate substantive changes from previous issue.

For definitions, see paragraphs 70.4(m) and (t) of 10 CER Part 70.

2 Currently called inventory Traceability is a property of the overall measurement,

3 difference (ID).

Currently called the limit of error of including all Certified Reference Materials (CRMs), instru the inventory difference (LEID). ments, procedures, measurement conditions,

4 The listed regulations do not apply to techniques, special nuclear involved in the operation of a nuclear reactor or in waste materials operations or used in sealed sources. See paragraphs disposal 5

70.51(e), The term "value" includes instrument

70.57(b), and 70.58(a) of 10 CFR Part 70. response and other pertinent factors.

USNRC REGULATORY GUIDES Comments should be sent to the Secretary Regulatory Guides are issued to describe and make U.S. Nuclear Regulatory Commission, Washington, of the Commission, available to the Attention: Docketing and Service Branch. D.C. 20555, public methods acceptable to the NRC staff specific parts of the Commission's regulations, to of implementing niques used by the staff in evaluating specific problems delineate tech The guides are issued in the following ten broad divisions:

lated accidents, or to provide guidance to applicants. or postu Guides are not substitutes for regulations, and compliance Regulatory 1. Power Reactors with 6. Products them is not required. Methods and solutions different 2. Research and Test Reactors 7. Transportation out in the guides will be acceptable if they provide from those set 3. Fuels and Materials Facilities 8. Occupational Health findings requisite to the issuance or continuance a basis for the 4. Environmental and Siting 9. Antitrust and Financial Review of a permit or 5. Materials and Plant Protection 10. General.

license by the Commission.

Comments and suggestions for improvements in Copies of issued guides may be purchased at thecurrent Government encouraged at all times, and guides will be revised,these guides are Printing Office price. A subscription service for future to accommodate comments and to reflect new as appropriate, cific divisions is available through the Government guides in spe information or Information on the subscription service and current GPOPrinting Office.

experience. This guide was revised as a result of substantive prices may ments received from the public and additional staff review. com be obtained by writing the U.S. Nuclear Regulatory Washington, D.C. 20555, Attention: Publications Sales Commission, Manager.

Table I

TYPES OF REFERENCE MATERIALS

Definition Example Type Any or all of the materials listed Reference Material (RM) A material or substance one or more properties of below.

which are sufficiently well established to be used for the calibration of an apparatus or for the verifi cation of a measurement method.*

A' generic class of characterized homogeneous mate rials produced in quantity and having one or more physical or chemical properties experimentally deter mined within stated measurement uncertainties. This term is recommended for use instead of "standard"

or "standard material."

Any primary or secondary Certified Reference Material RM accompanied by, or traceable to, a certificate certified reference material (see (CRM) stating the property value(s) concerned, [and its below).

associated uncertainty,1 issued by an organization, public or private, which is generally accepted as technically competent.*

Standard Reference Materials Primary Certified Reference A certified reference material of high purity possess- of the National Bureau of Material (PCRM) ing chemical stability or reproducible stoichiometry Standards (NBS SRMs), mate and generally used for the developmentlevaluation rials of the International Atomic of reference methods and for the calibration of RMs.

Primary certified reference materials are certified Energy Agency (IAEA) bearing the IAEA classification "S", and using the most accurate and reliable measurement certified reference materials methodologies available consistent with end-use from the Department of Energy requirements for the RM. New Brunswick Laboratory.

Some Reference Materials avail Secondary Certified Reference An RM characterized relative to a primary certified I

able from the Department of Material (SCRM) reference material generally used for development/

Energy New Brunswick Labora evaluation of field measurement methods, for day- tory. IAEA Reference Materials to-day intralaboratory quality assurance, or for classification "R".

interlaboratory comparison programs. SCRMs may be less pure or less stable than PCRMs, depending on their intended end use. Accuracy required of the certifying measurements also depends on intended end use.

Process stream materials and any Working Reference Material An RM characterized relative to a primary or second- RM prepared according to Refer (WRM) ary certified reference material usually for use within ences 8, 9, 10, and 11 and related a single laboratory or organization. WRMs are gener- reports; IAEA's intercomparison ally used to assess the level of performance of mea- exchange samples.

surements on a frequent (e.g., daily) basis. WRMs are usually prepared from material typical of a given process. (Previously known as Working Calibration and Test Materials (WCTMs).)

S* This definition is that used by ISO Guide 6-1977(E) of the International Standards Organization.

5.58-2

and calculations employed. Each component of a measure ment contributes to the uncertainty of may not be at all valid. The variances may, in the measurement fact, be due result relative to national standards of me-s , to a combination of systematic errors that appear

+ U......, to be the NMS. The NMS N.is composed .... 1 randomly distributed over the long run but of

a. number

.ssu~ -411l . LtlrugII

of components, that are not at including the NBS (which has the responsibility all random in their occurrence for a given analyst for main employing taining the national standards of measurement), a given combination of standards, tools, and instruments.

CRMs, Thus, it is necessary to derive the uncertainty national laboratories, calibration facilities, value of a standards-writing groups, national standards, and the person measurement from methods that also involve making the a summation ultimate measurement. of the nonrandom (systematic) uncertainties, not from the mathematics of random events alone. The valid determina If the NBS, as the legal caretaker of the national tion of the uncertaintyof a measurement standards relative to the NBS,

of measurement for the United States, and thus of the degree of traceability, is not a is viewed as an rigorousproce entity capable of making measurements dure but is the result of sound judgment based without error, on thorough traceability can be defined as the ability knowledge and understanding of all factors to relate any involved.

measurement made by a local station (e.g.,

licensee) to the

"correct" value as measured by the NBS. Obviously, the effects of systematic error can for the NBS to make measurements on If it were possible if Reference Materials (RMs) are included be reduced I

the same item at least once in or material as the local station, this relationship, every series of related measurements by a and hence given analyst and traceability, could be directly obtained. combination of tools, instruments, and Since such direct conditions. The comparisons are not ordinarily possible, an calibration and correlation factors so obtained alternative means cannot be for achieving traceability must be employed. applied uncritically to successive measurements.

This necessary It also linkage of measurement results and their uncertainties follows that the applicability of any given to the RM to a series of NBS through the NMS may be achieved by: measurements of process material should be examined critically both periodically and with every change or hint of a. Periodic measurements by the licensee change in the measurement characteristics of CRMs or of the process Standard Reference Materials (SRMs). The material.

measurement, per se, of an SRM or CRM without rigorous internal control of measurements does not provide the It is doubtful that RMs can ever be exact representations necessary linkage.

Adequate and suitable reference materials, of the material under measurement along with in any given instance, reliable measurement methods and good even for highly controlled process materials internal measure such as formed ment assurance programs, are necessary to fuel pieces or uniform powdered oxide ensure accuracy shown to be sub stantially uniform in both composition (Ref. 1). and measurement affecting physical characteristics (e.g., density or shape for b. Periodic measurements of well-characterized nondestructive assay (NDA) measurements).

process However, in materials or synthesized artifacts that have most cases RMs that yield measurement been shown to uncertainties be substantially stable and either being within the selected limits for the material homogeneous or in question can having small variability of known limits. be achieved. Obviously, the errors resulting The uncertainties from mismatch associated with the values assigned to such of the RM with the measured material process materials will be largest in or artifacts are obtained by direct or indirect heterogeneous matter such as waste materials, comparisons but in these with Primary Certified Reference Materials cases the SNM concentrations normally (PCRMs). will be low and the allowable limits of uncertainty correspondingly less stringent.

c. Periodic submission of samples for comparative The important truth being stressed here measurement by a facility having established is that every traceability in measurement must be considered, in all aspects, the measurement involved, employing one as an indi or both of the vidual determinationsubject to errorfrom above procedures, and involving only samples a variety ofsources, not subject to none of which may be safely ignored.

change in their measured values during storage The all-too-natural or transit. tendency to treat successive measurements

("Round-robin" sample exchanges between as routine must facilities can be useful in confirming or denying compatibility be rigorously avoided. Test object and of results, device RMs, in but such exchanges do not of themselves particular, tend to be mistakenly accepted constitute the as true and establishment or maintenance of traceability.) unvarying, but they may well be subject to changes in effective value (measured response) as well as unrepre Valid assignment of an uncertainty value sentative of the samples unless wisely selected to any measure and carefully ment result demands a thorough knowledge handled.

of all the observed or assigned uncertainties in the measurement system, including an understanding of The characteristics required of CRMs include:

the nature of the sources of these uncertainties, not just a statistical measure of their existence. It is not sufficient, for example, a. Sufficiently small and known uncertainties to derive in the a root-mean-square value for a succession assigned values. (Normally, the uncertainties of observed or of the CRMs assigned uncertainties (CRM, instrumental, will contribute only a small fraction of the total and procedural) uncertainty for which standard deviation values have been of the measurement.)

calculated by statistical methods for random events. To do so involves assumptions as to the randomness of these b. Predictability in the response produced in the variances that meas urement process. (Ideally, the measurement process will

5.58-3

and therefore should be employed only if it has a substantial respond to the RMs in the same way as to the item or mate economic or time advantage, if the interferences or biasing rial to be measured. If there is a difference in measurement effects are small and limited in range, if the corrected response to the measured parameter arising from other method is reliable, and if the correction itself is verifiable measurement-affecting factors, these effects must be known and is regularly verified.

and quantifiable.)

Systematic measurement calibration errors frequently c. Adequate stability with respect to all measurement arise and can be ascribed to improper use, handling, or affecting characteristics of the standard. (This is necessary treatment of reference materials. These errors are independent to avoid systematic errors due to changes in such properties of the effect of impurities, concentration differences, etc.,

as density, concentration, shape, and distribution.) and are almost impossible to detect via an internal mea surement control program. Interlaboratory measurement d. Availability in quantities adequate for the intended comparison programs where carefully characterized materials applications.

are used are means by which these systematic errors may be identified and corrective action initiated.

It cannot be assumed that RMs will always remain wholly stable as seen by the measurement system employed, 3.1 National Standards - Uses and Limitations that working RMs will forever remain represesentative of the measured material for which they were prepared or PCRMs generally are not recommended for use directly selected, or that the measured material itself will remain as WRMs, not only because of cost and required quantities unchanged in its measurement characteristics. Therefore, it but also because of differences in composition (or isotopic is essential that these RMs, as well as the measurement ratios) compared to the process materials to be measured.

instrumentation and procedures, be subject to a program of PCRMs are more often used to prepare RMs of composition continuing confirmation of traceability. Many of the factors and form matching the process material or to evaluate (and in Reference 2.6 involved in such a program are discussed give traceability to) non-NBS but substantially identical material from which matching WRMs are then prepared.

2. MASS AND VOLUME MEASUREMENTS This is necessary because of both the wide diversity of process materials encountered and the very small number The national systems of mass and volume measurements and variety of SNM PCRMs available. These RMs may be are so well established that RMs meeting the above criteria used directly as WRMs, if appropriate, or may be reserved are readily available. Where necessary, the licensee can use for less frequent use in the calibration of suitable synthetic the RMs to calibrate Working Reference Materials (WRMs) or process-material WRMs of like characteristics, as well as that more closely match the characteristics of the measured for verifying instrument response factors and other aspects material in terms of mass, shape, and density in the case of of the 'measurement system. However, each level of subsidiary mass measurements or are more easily adapted to the cali RMs adds another level of uncertainty to the overall uncer bration of volume-measurement equipment. tainty of the SNM measuremen

t. I

Specific procedures for the use of mass and volume RMs PCRMs can be used to "spike" process samples or WRMs for the calibration of measurement processes and equipment to determine or verify the measurability of incremental are given in the corresponding national standards (Refs. 3 changes at the working SNM level. However, because of and 4). Factors likely to affect uncertainty levels in inventory possible "threshold" or "zero error" effects and nonlinearity measurements of mass and volume are discussed in regulatory or irregularity of measurement response with concentration, guides (Refs. 5, 6, and 7). this process does not of itself establish traceability.

3. CHEMICAL ASSAY AND ISOTOPIC MEASUREMENTS 3.2 Working Reference Materials Methods for chemical analysis and isotopic measurement WRMs that closely match the effective composition of often are subject to systematic errors caused by the presence process material, or a series of such WRMs that encompass of interfering impurities, gross differences in the concentra the full range of variation therein, serve as the traceability tions of the measured component(s) or of measurement link in most chemical analyses and isotopic measurements.

affecting matrix materials, and other compositional factors. The WRMs derive traceability through calibration relative Traceability in these measurements can be obtained only if to either PCRMs, Secondary Certified Reference Materials such effects are recognized and either are eliminated by (SCRMs), or, more often, synthesized RMs containing adjustment of the RM (or sample) composition or, in some either PCRMs or other material evaluated relative to the cases, are compensated for by secondary measurements PCRM (see Section B.3.1 of this guide).

of the measurement-affecting variable component(s) and corresponding correction of the measured SNM value. The The characteristics required of a WRM are that it be latter procedure involves additional sources of uncertainty chemically similar to the material to be measured (including

6 interfering substances), that it be sufficiently stable to have Regulatory guides under development on measurement control a useful lifetime, and that it have sufficiently low uncertainty programs for SNM accounting and on considerations for determining in its assigned value to meet the requirements of the mea the systematic error and the random error of SNM accountingofmeas con urements will also discuss the factors involved in a program surement methods and of the accountability limits of error.

tinuing confirmation of traceability.

5.58-4

WRMs can be prepared (a) from process matorials char b. Interfacility interchange and measurement of well acteristic of the material to be measured or (b) by synthesis characterized and representative materials with values using known quantities of pure SNM. The former method assigned by a facility having demonstrated traceability in offers the advantage that the WRM will include all the pro the measurement.

perties that can affect the measurement such as impurities, SNM concentration level, and chemical and physical form;

Round-robin programs in which representative samples it suffers from the disadvantage that the assigned value is are analyzed by a number of laboratories do not establish determined by analyses subject to uncertainties that must be traceability but can only indicate interlaboratory agreement ascertained. The latter method involves preparations using or differences, unless traceability of one or more of the PCRMs (not usually economical unless small amounts are samples in a set has been established as above.

used) or SCRMs with the appropriate combination of other materials to simulate the material to be measured. The ad vantages of the latter method include more accurate knowl The Safeguards Analytical Laboratory Evaluation (SALE) program as administered by the Department of edge of the SNM content and better control of other variables Energy New Brunswick Laboratory (NBL) is an example of such as the amount of impurities and the matrix composi an acceptable comparative-measurement program.

tion. The chief disadvantage is that the synthesized WRM

may not possess all the subtle measurement-affecting char

4. NONDESTRUCTIVE ASSAY

acteristics of the process material. Moreover, the prepara tion of synthesized WRMs may be substantially more costly than the analysis of WRMs prepared from process material. Nondestructive assay (NDA) measurement methods are those that leave the measured material unchanged Detailed procedures for preparing plutonium and uranium (e.g.,

gamma emission methods) or with no significant change WRMs are described in References 8, 9, 10, and 11.

(e.g., neutron activation) relative to its corresponding unmeasured state (Ref. 2). NDA offers the advantages that The primary concern in the use of a WRM to establish the same RM or the same sample can be measured repeatedly traceability in SNM measurements is the validity of the and yields valuable data on system uncertainties not other assigned value and its uncertainty. Considerable care is nec essary to ensure that the WRMs are prepared with a minimal wise obtained, that the measurement made does not consume process material, and that measurements can be made more increase in the uncertainty of the assigned value above that frequently or in greater number, usually at a lesser unit cost of the PCRM upon which the WRM value is based. If the than with destructive chemical methods. These advantages assigned value of a WRM is to be determined by analysis, the often yield better process and inventory control and use of more than one method of analysis is necessary to enhanced statistical significance in the measurement data.

enhance confidence in the validity of the assigned value.

However, like chemical measurement methods, NDA

The methods should respond differently to impurities and methods have many sources of interferences that may to other compositional variations. If the WRM has been affect their accuracy and reliability. The interferences and synthesized from a PCRM or other reference materials, the their sources must be identified before valid traceability can composition and SNM content can be verified by subsequent be assured.

analyses.

In nearly all NDA methods, the integrity and traceability The composition of a WRM can change with time, e.g.,

of the measurements depend on the validity changes in oxidation state, crystalline form, hydration, of the RMs by or which the NDA system is calibrated. Calibrations generally adsorption. These changes and their effects on measurement are based on WRMs that are or are intended to be are minimized by appropriate packaging and proper storage well characterized and representative of the process material or conditions. Additional assurance is attained by distributing items to be measured. While the matching of RMs to premeasured amounts of the material into individual packets process items, and consequent valid traceability, is not at the time of preparation, and these packets can be appro difficult to achieve for homogeneous materials of substan priately sized so that the entire packet is used for a single tially constant composition (e.g., alloys) having fixed size calibration or test. Even among such subsamples, there may and shape (e.g., machined pieces), such ideal conditions are be variability in SNM content, and this variability must be not obtained for most SNM measurements. Many of the taken into account in determining the uncertainty of the materials and items encountered are nonhomogenebus, assigned value.

nonconforming in distribution, size, or shape, and highly variable in type of material and compositio

n. In order to

3.3 Standard Laboratories and Sample Interchange ensure traceability of the measurement results through the NMS, variations in the physical characteristics and composi Traceability of chemical assay and isotopic analysis values tion of process items and in their effects upon the response also may be obtainable through comparative analyses of of the NDA measurement system must be evaluated and identical samples under parallel conditions. A comparative carefully considered in the selection or design of WRMs and measurement program may take either or both of two forms:

measurement procedures (Refs. 12 and 13).

a. Periodic submission of process samples for analysis by WRMs usually (a) are prepared from process materials that a facility having demonstrated traceability in the desired have been characterized by measurement methods whose measurement.

uncertainties have been ascertained through the NMS (i.e.,

5.58-5

4.2 Characterization by a Second Method are traceable) or (b) are artifacts synthesized from well

7 characterized materials to replicate the process material.

If the process items or materials being measured are However, calibration of the NDA method by means of such subject to non-SNM variations that affect the SNM measure RMs does not automatically establish continuing traceabil ment, it may be possible to employ one or more additional ity of all process item measurement results obtained by that methods of analysis to measure these variations and thus to method. The effects of small variations in the materials characterize process materials in terms of such analysis being assayed may lead to biased results even when the results. If the secondary analyses also are of an NDA

WRM and the material under assay were obtained from method, they may often be performed routinely with the nominally the same process material. It therefore may be SNM measurements. In many cases, the results of secondary necessary either (a) to establish traceability of process item analyses may be used to derive simple corrections to the measurement results by comparing the NDA measurement SNM measurement results. Correction also may be obtained results with those obtained by means of a reliable alter and traceability preserved by the judicious modification of native measurement system of known traceability, e.g., by RMs so as to incorporate the same variable factors, i.e., so total dissolution and chemical analysis (see Section B.4.1)

that they can produce the same relative effects in the SNM

or (b) to establish adequate sample characterization to and non-SNM measurements as do the process variable(s).

permit the selection of a similarly characterized WRM for method calibration (see Section B.4.2).

Alternatively, it may be advantageous to prepare WRMs that span the normal range of variability of the measurement

4.1 Traceability Assay by a Second Method affecting non-SNM parameter(s) (and also the SNM-concept range, if appropriate). These WRMs can then be characterized Any NDA method would be of little practical use if on the basis of their non-SNM measurement results or of every measurement also required a confirmatory analysis.

some function(s) of SNM and non-SNM measurement However, in cases in which there are a number of items or results and can be assigned a correspondingly "characteristic material samples of established similar characteristics, it figure." If this procedure can be carried out with adequate is practical to establish traceability for a series of measure sensitivity and specificity relative to the interfering factors ments by means of second-method evaluations of an and within acceptable limits of uncertainty, the process appropriate proportion of randomly selected samples. If the material can be routinely characterized in like manner and correlation between the two methods is then found to be the appropriate WRM selected on the basis of such charac consistent, traceability is established for all NDA measure terization.

ments on that lot of SNM and on other highly similar material.

5. CONTINUING TRACEABILITY ASSURANCE

For nominally uniform process or production material Initial or occasional demonstration that a laboratory has of which multiple subsamples can be obtained from a gross made measurements compatible with the NMS is not sample, the uniformity can be deduced from the distribution sufficient to support a claim of traceability. Measurement of the NDA measurement data. For thus characterized processes are by their nature dynamic. They are vulnerable material, traceability can be established for all subsamples

8 to small changes in the skill and care with which they are that approximate the mean from the separate traceable performed. Deterioration in the reliability of their measure second-method analysis of a few of the subsamples. Other ment results can be caused by (a) changes in personnel like subsamples can then be selected as traceable WRMs performance, (b) deterioration in or the development of whose assigned values are related to the separately analyzed defects in RMs, instrumentation, or other devices, or (c)

subsamples through their respective NDA measurement variation in the environmental conditions under which the results.

measurements are performed. The techniques discussed in preceding sections ensure traceability only if they are For subsample populations exhibiting a range of NDA

used within a continuing program of measurement control values, especially where a destructive second-method (Ref. 1).

analysis is used, the "twinning" method of sample selection may be employed. In this method, pairs of subsamples are

C. REGULATORY POSITION

matched by their NDA measurement values, and the matches are confirmed by NDA reruns. One member of The measurement control program (Ref. 1) used by the each pair is evaluated by the traceable second-method licensee should include provisions to ensure that individual analysis; the other member of that pair is then assigned the measurement results are traceable to the national standards value determined for its twin and may serve thereafter as a of measurement through the national measurement system traceable WRM for the measurement of that process material (NMS). RMs used to establish traceability of measurement by that NDA method.

results through the NMS should have assigned values whose uncertainties are known relative to the national standards

7 The advantages stated for similarly derived WRMs (see Section of measurement. To meet this condition, the licensee

1.3.2) also apply here. should maintain a continuing program for calibrating each

8 Subsamples whose measured values markedly deviate from the measurement process, using RMs that meet the criteria in mean (i.e., "flyers") are not used for second-method analysis or for the following paragraphs.

WRMs.

5.58-6

1. REFERENCE MATERIALS

If WRMs are prepared from NBS SRMs or other PCRMs,

1.1 The National Bureau of Standards they should be analyzed to verify that the makeup value is correct, i.e., that no mistakes have been made in their pre Devices and instruments calibrated by, paration. For this verification, at least five samples and CRMs should certified by, NBS along with reference material be analyzed using the most reliable method available.

data supplied Should

9 are acceptable RMs for calibrating either methods the analytical results differ significantly from or WRMs. the makeup However, it is very important that the licensee value, the WRM should not be used. Typical be able to statistical and demonstrate that the RMs are stable under analytical procedures acceptable to the NRC staff the conditions for pre for which they are used, that their validity has paring WRMs are found in References 8, 9, not been com 10, and 11.

promised, and that they meet the accuracy requirements of the intended applications. Storage and packaging of WRMs should follow procedures designed to minimize any changes likely to affect the validity

1.2 Secondary Certified Reference and Working of the assigned values. Whenever practical, the Reference WRM should be divided into small measured quantities Materials at the time of preparation, and the quantities should be of appropriate size SCRMs or WRMs that have been produced so that each entire unit is used for a single by the licensee calibration or or by a commercial supplier are acceptable calibration test (Refs. 8, 9, 10, and 1I).

provided their uncertainties relative to PCRMs are known.

1.2.2 Nondestructive Assay A statement of uncertainty should be assigned to each RM RMs for NDA should be prepared from well-characterized based on an evaluation of the uncertainties of the calibration process. The statement should contain both materials whose SNM contents have been measured the standard by meth deviation and the estimated bounds of the ods that have been calibrated with CRMs or systematic errors from synthetic associated with the assigned value similar materials of known SNM conten

t. The NDA

to the statistical RMs should information contained within the most recent closely resemble in all key characteristics the NBS PCRM process items to be measured by the system. Since destructive certificates. measure ments ordinarily cannot be made on NDA RMs in order to

1.2.1 RMs for Chemical and Isotopic Analyses verify makeup, as required for WRMs for chemical assay and isotopic analyses, RMs should be prepared in sets of at least WRMs used for calibrating chemical assay three using procedures that guard against errors and isotopic common to measurements may be prepared from standard all members of the set. If all three RMs respond reference mate consistently rials (SRMs) supplied by NBS or from other well-characterized to the NDA system, one RM could be used as the intended materials available to the industry. Such NDA RM, the second could be kept in reserve, WRMs should be and the third prepared under conditions that ensure high characterized using destructive chemical measurement reliability and tech should be packaged and stored in a way that niques whenever possible. If destructive eliminates any analysis is not potential for degradation of the WRM. possible, the consistency of the NDA system response to all the RMs in the set would provide a basis for judging the The assigned values of WRMs prepared from validity of the set of RMs. If one or more of process mate the RMs in the rials should be determined by analysis, using set differs significantly from the expected response, two different no RMs methods whenever possible. A sufficient number from that set should be used. Statistical tests of analyses for this com should be done by both methods to allow a parison can be found in References 8, 9, 10,

reliable estimate and I1.

of the components of random variation that affect the meas The design and fabrication of the RMs should urement. If two methods are not available, take into as may be the account the measurement process parameters case for isotopic analysis, it is recommended affecting the that a verifica response of the system (Ref. 2), including:

tion analysis be obtained from another laboratory.

The components of variance (random variation) a. SNM content, of measure b.

ments used to assign a value to an RM should Isotopic content, be known in advance. The statistical design of an RM characterization c. Matrix material, plan d. Density, requires that measurement precision, etc.,

be known in order to calculate the number of measurements e. Container material and dimensions, to be performed and the number of samples to be analyzed f. Self-absorption effects, and so that the g.

desired uncertainty in the mean value assigned Absorption and moderation effects.

to the RM

can be achieved. The maximum uncertainty permitted by the proposed end use of the RM must be Studies should be carried out in sufficient an assumption detail to that is factored into the characterization plan. identify the process item characteristics and the variations of the characteristics that can cause systematic error. The results of the studies should be used to establish reasonable bounds for the systematic errors.

9

1nternational RMs and reference material such as IAEA RMs NDA systems whose uncertainties relative to the are included, if accepted by NBS. national standards of measurement cannot be satisfactorily established

5.58-7

Table 2 directly through the calibration process should be tested by comparative analysis. This test should be done by periodically RECERTIFICATION OR REPLACEMENT

analyzing randomly selected process items with the NDA INTERVALS FOR CRMs system in question and by another method with known uncertainty. The verification analysis can be done on samples Maximum Test Objects and Devices (Years)Period obtained after reduction of the entire item to a homogeneous form. In some cases, verification analysis by small-sample the NDA or by other NDA methods may be acceptable if Mass 51 uncertainties of the verification method are known relative Length

2 to the national standards of measuremen

t. Volumetric Provers

2 Thermometers and Thermocouples

2. MEASUREMENT ASSURANCE

2 Calorimetric Standards The traceability of each measurement process through Certified Reference Materials of the NMS should be maintained by a continuing program measurement assurance (Ref. 1). This program should include Because of the complex chemical/physical proper planned periodic verifications of the assigned values of all ties of chemical CRMs such as Pu metal, U 3 08, U

RMs used for calibrations. metal, UO 2 , radioactive materials, etc., and the varied end uses to which they are put, a formal

2.1 Verification of Calibrations program of comparison or replacement frequency should be established. The required frequencies are A formal program fixing the frequency at which calibrations strongly dependent on the system stability and and calibration checks are performed should be established. should be determined for each CRM by historical The required frequencies are strongly dependent on system performance experience.

stability and should be determined for each case by using of historical performance experience. Current performance based on measurement control pro the measurement system should be carefully and traceably certified so that any devia gram data may signal the need for more frequent verifications. tion that may occur can be readily identified and quantified.

Also, the effects of changes in process parameters such as composition of material or material flows should be evaluated The data obtained through this participation and other when they occur to determine the need for new calibrations. comparative measurement data (such as shipper-receiver dif ferences and inventory verification analyses) should be used to WRMs that are subject to deterioration should be substantiate the uncertainty statements of his measurements.

The recertified or replaced on a predetermined schedule.

replacement should be based frequency of recertification or When statistically significant deviations indicating lack of on performance history. If the integity of an RM is in consistency in measurements occur in the results of the com doubt, it must be discarded or recalibrated. parative measurements, the licensee should conduct an in vestigation. The investigation should identify the cause of

2.2 Recertification or Replacement of CRMs the inconsistency and, if the cause is within his organization, the licensee should initiate corrective actions to remove the Objects, instruments, or materials calibrated by NBS or inconsistency. The investigation may involve a reevaluation the other authoritative laboratories and used as CRMs by of the measurement process and the CRMs to locate sources of licensee should be monitored by intercomparisons with bias or systematic error or a reevaluation of the measurement other CRMs to establish their continued validity. In any errors to determine if the stated uncertainties are correct.

case, the values should be periodically recertified by the the certifying agency or compared with other CRMs by

3. RECORDS

licensee in accordance with Table 2.

The licensee should retain all records relevant to the

2.3 Interlaboratory Exchange Programs uncertainty of each measurement process for 5 years

[§70.51(e)(4)(iv) and (v); §70.57(b)(12)]. The records The licensee should participate in interlaboratory ex should include documents or certificates of CRMs, the change programs when such programs are relevant to the measurement and statistical data used for assigning values types of measurements performed and the materials analyzed to WRMs, and the calibration procedures used in preparing in his laboratory. The values assigned to the materials that the WRMs.

are to be analyzed in the interlaboratory exchange programs

5.58-8

REFERENCES

1. R. J. Brouns, F. P. Roberts, J. A. Merrill, and W. B. Brown, 8. G. C. Swanson, S. F. Marsh, J. E. Rein, G. L. Tietjen,

"A Measurement Control Program for Nuclear Materials R. K. Zeigler, and G. R. Waterbury, "Preparation of Accounting," NRC report NUREGJCR-0829 (1979). Working Calibration and Test Materials-Plutonium Nitrate Solution," NRC report NUREG-0118 (1977).

2. Regulatory Guide 5.11, "Nondestructive Assay of Special Nuclear Material Contained in Scrap and Waste" (1973). 9. S. S. Yamamura, F. W. Spraktes, J. M. Baldwin, R. L.

Hand, R. P. Lash, and J. P. Clark, "Preparation of

3. ANSI Standard N 15.18, "Mass Calibration Techniques Working Calibration and Test Materials: Uranyl Nitrate for Nuclear Material Control," American National Stand Solution," NRC report NUREG-0253 (1977).

ards Institute, 1430 Broadway, New York, New York

(1975). 10. J. E. Rein, G. L. Tietjen, R. K. Zeigler, G. R. Waterbury, G. C. Swanson, "Preparation of Working Calibration

4. ANSI Standard N15.19, "Volume Calibration Tech and Test Materials: Plutonium Oxide," NRC report niques for Nuclear Material Control," American NUREG/CR-0061 (1978).

National Standards Institute, 1430 Broadway, New York, New York (1975). 11. J. E. Rein, G. L. Tietjen, R. K. Zeigler, G. R. Waterbury,

"Preparation of Working Calibration and Test Materials:

5. Regulatory Guide 5.25, "Design Considerations for Mixed Oxide," NRC report NUREG/CR-0139 (1978).

Minimizing Residual Holdup of Special Nuclear Material in Equipment for Wet Process Operations" (1974). 12. ANSI Standard N15.20, "Guide to Calibrating Non destructive Assay Systems," American National Stand

6. Regulatory Guide 5.42, "Design Considerations for ards Institute, 1430 Broadway, New York, New York Minimizing Residual Holdup of Special Nuclear Material (1975).

in Equipment for Dry Process Operations" (1975).

13. Regulatory Guide 5.53, "Qualification, Calibration, and

7. Regulatory Guide 5.48, "Design Considerations-Systems Error Estimation Methods for Nondestructive Assay"

for Measuring the Mass of Liquids" (1975). (1975).

5.58-9

UNITED STATES

NUCLEAR REGULATORY COMMISSION

WASHINGTON, D. C. 20555 POSTAGE AND FEES PAID

U.S. NUCLEAR REGULATORY

OFFICIAL BUSINESS

COMMISSION

PENALTY FOR PRIVATE USE, $300