Regulatory Guide 5.34: Difference between revisions

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{{#Wiki_filter:Revision 1" May 1984 U.S. NUCLEAR REGULATORY  
{{#Wiki_filter:Revision 1"
COMMISSION
                          U.S. NUCLEAR REGULATORY COMMISSION                                                                       May 1984
0 SREGULATORY  
                    0
GUIDE OFFICE OF NUCLEAR REGULATORY  
                    SREGULATORY
RESEARCH REGULATORY  
                        OFFICE OF NUCLEAR REGULATORY RESEARCH
GUIDE 5.34 (Task SG 046-4) NONDESTRUCTIVE  
                                                                                                          GUIDE
ASSAY FOR PLUTONIUM  
                                                        REGULATORY GUIDE 5.34 (Task SG 046-4)
IN SCRAP MATERIAL BY SPONTANEOUS  
                    NONDESTRUCTIVE ASSAY FOR PLUTONIUM IN SCRAP MATERIAL
FISSION DETECTION  
                                          BY SPONTANEOUS FISSION DETECTION


==A. INTRODUCTION==
==A. INTRODUCTION==
Section 70.51, "Material Balance, Inventory, and Records Requirements," of 10 CFR Part 70, "Domestic Licensing of Special Nuclear Material," requires certain licensees authorized to possess at any one time more than one effective kilogram of special nuclear material to establish and maintain a system of control and accountability so that the standard error (estimator)
standard error. Unlike the major quantity of material flowing through the process, scrap is typically Section 70.51, "Material Balance, Inventory, and                   inhomogeneous and difficult to sample. Therefore, a Records Requirements," of 10 CFR Part 70, "Domestic                     separate assay of the entire content of each container of Licensing of Special Nuclear Material," requires certain               scrap material is a more reliable method of scrap account licensees authorized to possess at any one time more                   ability. NDA is a method for assaying the entire content than one effective kilogram of special nuclear material                 of every container of scrap.
associated with the inventory difference (SEID), obtained as a result of a measured material balance, meets minimum standards.


This guide is intended for those licensees who possess plutonium scrap materials and who are also subjected to the requirements of § 70.51 of 10 CFR Part 70. Included in a typical material balance are containers of inhomogeneous scrap material that are not amenable to assay by the traditional method of sampling and chemical analysis.
to establish and maintain a system of control and accountability so that the standard error (estimator)                      The term "scrap" refers to material that is generated associated with the inventory difference (SEID),                        from the main process stream because of the ineffi obtained as a result of a measured material balance,                    ciency of the process. Scrap material is generally meets minimum standards. This guide is intended for                     economically recoverable. Scrap, therefore, consists of those licensees who possess plutonium scrap materials                   rejected or contaminated process material such as pellet and who are also subjected to the requirements of                       grinder sludge, sweepings from gloveboxes, dried filter
 
  § 70.51 of 10 CFR Part 70.                                             sludge, and rejected powder and pellets. Scrap is generally distinguished from "waste" by the density or concentra Included in a typical material balance are containers               tion of heavy elements in the two materials, but it is of inhomogeneous scrap material that are not amenable                   the recovery cost (per mass unit of special nuclear to assay by the traditional method of sampling and                       material) that determines whether a material is "scrap"
With proper controls, the non destructive assay (NDA) technique of spontaneous fission detection is one acceptable method for the assay of plutonium in containers of bulk scrap material.
chemical analysis. With proper controls, the non                         or "waste."      The concentration of uranium and pluto destructive assay (NDA) technique of spontaneous                         nium in scrap is approximately the same as it is in fission detection is one acceptable method for the assay                 process material, i.e., 85-90 percent (uranium + pluto of plutonium in containers of bulk scrap material. The                   nium) by weight. However, on occasion the fraction in use of spontaneous fission detection thus facilitates the               both process and scrap material can be less than 25 preparation of a complete plant material balance whose                   percent. Plutonium in fast reactor scrap material is SEID meets established requirements.                                     15-20 percent by weight and in thermal reactor recycle material, 2-9 percent by weight. The main difference This guide describes procedures acceptable to the                   between scrap and process material is that scrap is NRC staff for applying the NDA technique of                             contaminated and inhomogeneous. Waste, on the other spontaneous fission detection to plutonium in scrap.                     hand, contains a low concentration of uranium and plutonium, ie., a few percent or less (uranium + pluto Any guidance in this document related to informa                     nium) by weight. However, the recovery of combustible tion collection activities has been cleared under OMB                   waste by incineration may produce ash that is high in Clearance No. 3150-0009.                                                 uranium and plutonium concentrations. Such incinerator ash is also considered "scrap" in this guide. However, it
 
The use of spontaneous fission detection thus facilitates the preparation of a complete plant material balance whose SEID meets established requirements.
 
This guide describes procedures acceptable to the NRC staff for applying the NDA technique of spontaneous fission detection to plutonium in scrap. Any guidance in this document related to informa tion collection activities has been cleared under OMB Clearance No. 3150-0009.


==B. DISCUSSION==
==B. DISCUSSION==
Plutonium in scrap material can contribute signif icantly to the inventory difference and its associated standard error. Unlike the major quantity of material flowing through the process, scrap is typically inhomogeneous and difficult to sample. Therefore, a separate assay of the entire content of each container of scrap material is a more reliable method of scrap account ability. NDA is a method for assaying the entire content of every container of scrap.  The term "scrap" refers to material that is generated from the main process stream because of the ineffi ciency of the process. Scrap material is generally economically recoverable.
should be noted that ash may be more homogeneous in Plutonium in scrap material can contribute signif                      
* The substantial number of changes in this revision has made icantly to the inventory difference and its associated                 it impractical to indicate the changes with lines in the margin.


Scrap, therefore, consists of rejected or contaminated process material such as pellet grinder sludge, sweepings from gloveboxes, dried filter sludge, and rejected powder and pellets. Scrap is generally distinguished from "waste" by the density or concentra tion of heavy elements in the two materials, but it is the recovery cost (per mass unit of special nuclear material)
USNRC REGULATORY GUIDES                                Comments should be sent to the Secretary of the Commission, U.S. Nuclear Regulatory Commission, Washington, D.C. 20555, Regulatory Guides are issued to describe and make available to the      Attention: Docketing and Service Branch.
that determines whether a material is "scrap" or "waste." The concentration of uranium and pluto nium in scrap is approximately the same as it is in process material, i.e., 85-90 percent (uranium + pluto nium) by weight. However, on occasion the fraction in both process and scrap material can be less than 25 percent. Plutonium in fast reactor scrap material is 15-20 percent by weight and in thermal reactor recycle material, 2-9 percent by weight. The main difference between scrap and process material is that scrap is contaminated and inhomogeneous.


Waste, on the other hand, contains a low concentration of uranium and plutonium, ie., a few percent or less (uranium + pluto nium) by weight. However, the recovery of combustible waste by incineration may produce ash that is high in uranium and plutonium concentrations.
public methods acceptable to the NRC staff of implementing specific parts of the Commission's regulations, to delineate tech-      The guides are issued in the following ten broad divisions:
niques used by the staff in evaluating specific problems or postu lated accidents or to provide guidance to applicants. Regulatory        1. Power Reactors                  6.  Products Guides are no? substitutes for regulations, and compliance with          2.  Research and Test Reactors      7. Transportation them is not required. Methods and solutions different from those set    3. Fuels and Materials Facilities  8. Occupational Health out in the guides will be acceptable if they provide a basis for the    4. Environmental and Siting        9. Antitrust and Financial Review findings requisite to the issuance or continuance of a permit or         5. Materials and Plant Protection 10.  General license by the Commission.


Such incinerator ash is also considered "scrap" in this guide. However, it should be noted that ash may be more homogeneous in
Copies of issued guides may be purchased at the current Government This guide was issued after consideration of comments received from      Printing Office price. A subscription service for future guides in spe the public. Comments and suggestions for improvements in these          cific divisions is available through the Government Printing Office.
* The substantial number of changes in this revision has made it impractical to indicate the changes with lines in the margi


====n. USNRC REGULATORY ====
guides are encouraged at all times, and guides will be revised, as      Information on the subscription service and current GPO prices may appropriate, to accommodate comments and to reflect new Informa-        be obtained by writing the U.S. Nuclear Regulatory Commission, tion or experience.                                                    Washington, D.C. 20555, Attention: Publications Sales Manager.
GUIDES Comments should be sent to the Secretary of the Commission, U.S. Nuclear Regulatory Commission, Washington, D.C. 20555, Regulatory Guides are issued to describe and make available to the Attention:  
Docketing and Service Branch.  public methods acceptable to the NRC staff of implementing specific parts of the Commission's regulations, to delineate tech- The guides are issued in the following ten broad divisions:
niques used by the staff in evaluating specific problems or postu lated accidents or to provide guidance to applicants.


Regulatory
its characteristics compared to most scrap and may,                    This guide gives recommendations useful for the assay therefore, be accountable using sampling and chemical            by spontaneous fission detection of containers, each analysis methods.                                                containing a few liters of scrap and having contents ranging from a few grams to 10 kilograms of plutonium or up to approximately 2 kilograms of effective
1. Power Reactors 6. Products Guides are no? substitutes for regulations, and compliance with 2. Research and Test Reactors 7. Transportation them is not required.
                                                                                                                                240
                                                                                                                                    Pu 2 NDA of plutonium can be accomplished primarily by the passive methods of gamma ray spectrometry,                    (see Ref. 7). Containers with a significant plutonium calorimetry, and spontaneous fission detection. Active            content (i.e., 50 grams or more) give a spontaneous neutron methods using total count rates or delayed                fission response that must be corrected for the effects neutron detection can also be used in scrap assay                of neutron multiplication (Refs. 8, 9). Scrap materials measurements. Regulatory Guide 5.11, "Nondestructive              that have large loadings of plutonium in addition to Assay of Special Nuclear Material Contained in Scrap              fluorine, oxygen, or other alpha/neutron-producing and Waste," provides        a framework for the use of these    elements are difficult to measure and correct for multi
                  1 NDA methods.                                                     plication effects because of the large random neutron flux from the (ct,n) reactions in the matrix materials.


Methods and solutions different from those set 3. Fuels and Materials Facilities
The NDA of dense scrap materials using gamma ray              These samples should be segregated into smaller quanti spectroscopy can be unreliable because of severe gamma            ties for measurements. In general, a large quantity of ray attenuation. However, the isotopic composition of              plutonium can be assayed by spontaneous fission detec plutonium in scrap materials, with the exception of                tion by subdividing the scrap into smaller amounts, or
8. Occupational Health out in the guides will be acceptable if they provide a basis for the 4. Environmental and Siting 9. Antitrust and Financial Review findings requisite to the issuance or continuance of a permit or 5. Materials and Plant Protection
242pu, can be obtained quite reliably using high-resolution        the items may be more amenable to assay by calorim gamma ray spectrometry measurements (Ref. 1).                     etry.
10. General license by the Commission.


Copies of issued guides may be purchased at the current Government This guide was issued after consideration of comments received from Printing Office price. A subscription service for future guides in spe the public. Comments and suggestions for improvements in these cific divisions is available through the Government Printing Office. guides are encouraged at all times, and guides will be revised, as Information on the subscription service and current GPO prices may appropriate, to accommodate comments and to reflect new Informa- be obtained by writing the U.S. Nuclear Regulatory Commission, tion or experience.
==C. REGULATORY POSITION==
Calorimetry is an accurate method of plutonium assay when there is an accurate knowledge of the                     The spontaneous fission detection method for the relative  abundance of each plutonium isotope and               NDA of plutonium in bulk inhomogeneous scrap material
24 tAm. Scrap may contain a mixture of materials of              should include (1) discrimination of spontaneous fission different radionuclide compositions, especially different        radiations from random background by coincidence
241Am concentrations, thereby necessitating the measure          techniques and (2) measurement of the relative pluto ment of the average radionuclide composition. The                nium isotopic composition of the scrap. An acceptable average radionuclide abundances can be accurately meas            spontaneous fission detection method of plutonium ured only when the scrap is reasonably homogeneous.               assay is described below.


Washington, D.C. 20555, Attention:
When the radionuclide abundances can be accurately measured or controlled, calorimetry can be applied to            1. SPONTANEOUS FISSION DETECTION SYSTEM
Publications Sales Manager.
scrap assay (Ref. 2). However, calorimetry is time con suming for materials of high heat capacity and may                1.1    Detectors not be a practical method for the routine assay of large numbers of containers.                                                Instruments based on moderated thermal neutron detectors, i.e., neutron well coincidence counters, are Spontaneous fission detection is a practical NDA              recommended for applications in which the gross technique for the assay of plutonium in scrap material.          neutron detection rate does not exceed 2 x 105 The assay method involves the passive counting of                neutrons/sec. The dead time inherent in these slow spontaneous fission neutrons emitted primarily from the          coincidence systems can be reduced by employing a fission of 240 Pu. Neutron coincidence counters are used          shift-register coincidence circuit. If the gross neutron to detect these time-correlated neutrons. The theory and          detection rate is Lprimarily due to random background practice of neutron coincidence counting for plutonium            and exceeds 2 x 10 neutrons/sec, a fast-neutron-detection, assay are discussed thoroughly in References 3 through 6.        single-coincidence system can be used, provided adequate Spontaneous fission neutrons are sufficiently penetrating        corrections can be made for matrix effects. Matrix to provide a representative signal from all the plutonium        effects are more severe in fast-neutron-detection systems, within a container. Since the neutron coincidence signal          as shown in Table 1.


its characteristics compared to most scrap and may, therefore, be accountable using sampling and chemical analysis methods.
is dependent on both the quantity and relative abundance
        8      240
of 2 3 Pu,          pu, and 242pu, the plutonium isotopic
                                                                        2 composition must be known for assay of total plutonium                  The effective 24 0 Pu mass is a weighted average of the mass by spontaneous fission detection. The quantity of scrap            of each of the plutonium isotopes. The weighting is equal to the spontaneous
                                                                          0
                                                                                  fission neutron yield of each isotope relative to that material on inventory when a material balance is com              of 2 4Pu. Since only the even-numbered isotopes have significant puted can be reduced through good management, and                 spontaneous fission rates, the effective 240 Pu mass is given approxi mately by:
  the scrap remaining on inventory can be assayed by M(240)eff = M(240) + (1.64    + 0.07)M(242)
  spontaneous fission detection to meet the overall plant inventory difference (ID) and SEID constraints required                              + (2.66 +/- 0.19)M(238)
  by paragraph 70.5 1(e)(5) of 10 CFR Part 70.                      where M is the mass of the isotope indicated in parentheses. The uncertainties in the coefficients and in the effective 240 Pu abun dances in the table are from the reported standard deviations in the most reliable data available (Ref. 7). The mathematical procedure for converting from M(240)eff to M(total Pu) is presented in the
        1Revision I to this guide was issued in April 1984.        appendix to this guide together with a sample calculation.


NDA of plutonium can be accomplished primarily by the passive methods of gamma ray spectrometry, calorimetry, and spontaneous fission detection.
5.34-2


Active neutron methods using total count rates or delayed neutron detection can also be used in scrap assay measurements.
TABLE 1 MATRIX MATERIAL EFFECTS ON NEUTRON ASSAY
                                                                                                                Correcteda (Ref. 10)
                                Neutron Detection Efficiency (Ref. 11)                          Coincidence  Coincidence Efficiency,    Efficiency,
                                    3                4                                        3 Matrix Material            Mass      He Detector,      He Detector,        ZnS Detector,        He Detector, 3He Detector, (in %4-liter can)          (kg)      Thermal              Fast                  Fast            Thermal        Thermal Empty Can                -              1.00              1.00                  1.00                1.00          1.00
Carbon Pellets          1.89          1.03              -                    -                    1.05          0.97 Metal                    3.60          1.04              0.83                0.75                1.09          1.02 Slag-Crucible            1.80          1.03              0.94                0.91                1.08          1.01 Concrete                3.24          1.05              0.84                0.79                1.10          1.02 String Filters          0.60          1.07              0.95                0.86                1.17          1.05 CH 2 (p=0. 6 5 g/cc)    0.27          1.06              0.96                  0.92                1.11          1.00
CH 2 (p=0.1  2 g/cc)    0.43          1.09              0.92                  0.90                1.19          0.98 CH 2 (p=0. 2 7 g/cc)    0.97          1.19              0.71                  0.67                1.36          0.04 H120 (p=l.00 g/cc)      3.62          0.98              0.36                  0.35                0.98          0.96 aCorrected using the source addition technique (see Ref. 7).
1.2 Detection Chamber                                            uniformity of spatial response, and insensitivity        to matrix effects. Therefore, information should            be The chamber should permit reproducible positioning            obtained regarding:
of standard-sized containers in the location of maximum spatial response uniformity.                                          1. The precision of the coincidence response as a function of the real-coincidence counting rate and the
1.3  Fission Source                                              accidental-to-real-coincidence ratio. Extremes in the back ground or accidental-coincidence rate can be simulated A spontaneous fission source with a neutron intensity        by using a source of random neutrons (nonfission).
comparable to the intensity of the largest plutonium mass to be assayed should be used for making matrix                  2. The uniformity of spatial response. Graphs should corrections using the source addition technique (Ref. 10).        be obtained on the relative coincidence response to a A nanogram of 252Ca is approximately equivalent to a              small fission neutron source as a function of position in gram of effective 2 40 Pu.                                        the counting chamber.


Regulatory Guide 5.11, "Nondestructive Assay of Special Nuclear Material Contained in Scrap and Waste," provides a framework for the use of these NDA methods.1 The NDA of dense scrap materials using gamma ray spectroscopy can be unreliable because of severe gamma ray attenuation.
1.4  Readout                                                        3. The sensitivity of matrix interference. A table of the relative coincidence response to a small fission Readout should allow computation of the accidental            neutron source as a function of the composition of the to-real-coincidence ratio in addition to the net real              matrix material surrounding the point source should be coincidence rate. Live-time readout or a means of                 obtained. Included in the matrix should be materials computing the dead time should also be provided.                  considered representative of common scrap materials.


However, the isotopic composition of plutonium in scrap materials, with the exception of 242pu, can be obtained quite reliably using high-resolution gamma ray spectrometry measurements (Ref. 1).  Calorimetry is an accurate method of plutonium assay when there is an accurate knowledge of the relative abundance of each plutonium isotope and 2 4 tAm. Scrap may contain a mixture of materials of different radionuclide compositions, especially different
Table 1 is an example of such a tabulation of the
241Am concentrations, thereby necessitating the measure ment of the average radionuclide composition.
1.5  Perfonnance Specifications                                  relative response for a wide range of materials.


The average radionuclide abundances can be accurately meas ured only when the scrap is reasonably homogeneous.
The performance of a spontaneous fission detection                This information should be used for evaluating the instrument should be evaluated according to its stability,        expected instrument performance and for estimating
                                                            5.34-3


When the radionuclide abundances can be accurately measured or controlled, calorimetry can be applied to scrap assay (Ref. 2). However, calorimetry is time con suming for materials of high heat capacity and may not be a practical method for the routine assay of large numbers of containers.
errors. The above performance information can be                     6. Density (both average density and local density requested from the instrument suppliers during instru            extremes should be considered), and
                                                                                                                                  3/4'
ment selection and should be verified during preopera tional instrument testing.                                          7. Matrix composition.


Spontaneous fission detection is a practical NDA technique for the assay of plutonium in scrap material.
2. ANALYST                                                     


The assay method involves the passive counting of spontaneous fission neutrons emitted primarily from the fission of 240 Pu. Neutron coincidence counters are used to detect these time-correlated neutrons.
===5. CALIBRATION===
 
    A trained individual should oversee spontaneous                 Guidelines for calibration and measurement control fission detection assay of plutonium and should have            for NDA are available in Regulatory Guide 5.53, "Qualifi primary responsibility for instrument specification,            cation, Calibration, and Error Estimation Methods for preoperational instrument testing, standards and calibra        Nondestructive Assay," which endorses ANSI N15.20
The theory and practice of neutron coincidence counting for plutonium assay are discussed thoroughly in References
tion, an operation manual, measurement control, and              1975, "Guide to Calibrating Nondestructive Assay error analysis. Experience or training equivalent to a           Systems." 3 The guide and standard include details on bachelor's degree in science or engineering from an              calibration standards, calibration procedures, curve fitting, accredited college or university and a laboratory course        and error analysis. Guidelines relevant to spontaneous in radiation measurement should be the minimum                  fission detection are given below.
3 through 6. Spontaneous fission neutrons are sufficiently penetrating to provide a representative signal from all the plutonium within a container.
 
Since the neutron coincidence signal is dependent on both the quantity and relative abundance of 2 3 8 Pu, 2 4 0 pu, and 242pu, the plutonium isotopic composition must be known for assay of total plutonium by spontaneous fission detection.


The quantity of scrap material on inventory when a material balance is com puted can be reduced through good management, and the scrap remaining on inventory can be assayed by spontaneous fission detection to meet the overall plant inventory difference (ID) and SEID constraints required by paragraph
qualifications of the analyst. The spontaneous fission detection analyst should frequently review the sponta                Calibration can be used for either a single isotopic neous fission detection operation and should authorize          composition or variable isotopic mixtures. In the former any changes in the operation.                                   case, the resulting calibration curve will be used to convert "net real-coincidence count" to "grams pluto
70.5 1(e)(5) of 10 CFR Part 70. 1 Revision I to this guide was issued in April 1984.This guide gives recommendations useful for the assay by spontaneous fission detection of containers, each containing a few liters of scrap and having contents ranging from a few grams to 10 kilograms of plutonium or up to approximately
3. CONTAINERS AND PACKAGING                                      nium." In the latter case, the conversion is from "net real-coincidence count" to "effective grams 24°pu."
2 kilograms of effective  
    A single type of container should be used for              The mathematical procedure for converting from packaging all scrap in each category. A uniform con              effective grams 2 4 0 pu, M( 24 0 )eff, to total grams pluto tainer that would facilitate accurate measurement and            nium, M(total Pu), is presented in the appendix to this would standardize this segment of instrument design,             guide together with a sample calculation.
2 4 0 Pu 2 (see Ref. 7). Containers with a significant plutonium content (i.e., 50 grams or more) give a spontaneous fission response that must be corrected for the effects of neutron multiplication (Refs. 8, 9). Scrap materials that have large loadings of plutonium in addition to fluorine, oxygen, or other alpha/neutron-producing elements are difficult to measure and correct for multi plication effects because of the large random neutron flux from the (ct,n) reactions in the matrix materials.


These samples should be segregated into smaller quanti ties for measurements.
e.g., a thin-walled metal (steel) can with an inside diameter between 10 and 35 cm, is recommended. For                    A minimum of four calibration standards with further guidance on container standardization in NDA            isotopic compositions similar to those of the unknowns measurements, see Reference 12.                                  should be used for calibration. If practicable, a calibra tion curve should be generated for each isotopic blend
4.    REDUCING ERROR DUE TO MATERIAL                            of plutonium. When plutonium of different isotopic VARIABILITY                                                composition is assayed using a single calibration, the effect of isotopic composition on the spontaneous The variation in spontaneous fission detection              fission detection response should be determined over the response due to material variability in scrap should be           operating ranges by measuring standards of different reduced by (1) segregating scrap into categories that are        plutonium isotopic compositions. This is necessary independently      calibrated,  (2) correcting for matrix        because the use of the effective 2 40 pu concept can lead effects using the source addition technique (Ref. 10), or        to error owing to the uncertainty in the spontaneous
(3) applying both the categorization and the source              fission half-lives and the variation in response with addition technique. Categorization should be used if the        isotopic composition. Table 2 illustrates the uncertainty spontaneous fission detection method is more sensitive          in effective 2 40 Pu abundance with different isotopic to the material variability from scrap type to scrap type        compositions (Ref. 13).
than to the material variability within a scrap type.


In general, a large quantity of plutonium can be assayed by spontaneous fission detec tion by subdividing the scrap into smaller amounts, or the items may be more amenable to assay by calorim etry.  C. REGULATORY
Application of the source addition technique reduces the             Calibration standards should be fabricated from sensitivity to material variability and may allow the           material having a plutonium content determined by a majority of scrap types to be assayed under a single            technique traceable to or calibrated with the standard calibration. Material characteristics that should be            reference material of the National Bureau of Standards.
POSITION The spontaneous fission detection method for the NDA of plutonium in bulk inhomogeneous scrap material should include (1) discrimination of spontaneous fission radiations from random background by coincidence techniques and (2) measurement of the relative pluto nium isotopic composition of the scrap. An acceptable spontaneous fission detection method of plutonium assay is described below.


===1. SPONTANEOUS ===
considered in selecting categories include:                      Well-characterized homogeneous material similar to the process material from which the scrap is generated can
FISSION DETECTION
      1. Plutonium isotopic composition and content,             be used to obtain calibration standards.
SYSTEM 1.1 Detectors Instruments based on moderated thermal neutron detectors, i.e., neutron well coincidence counters, are recommended for applications in which the gross neutron detection rate does not exceed 2 x 105 neutrons/sec.


The dead time inherent in these slow coincidence systems can be reduced by employing a shift-register coincidence circuit. If the gross neutron detection rate is Lprimarily due to random background and exceeds 2 x 10 neutrons/sec, a fast-neutron-detection, single-coincidence system can be used, provided adequate corrections can be made for matrix effects. Matrix effects are more severe in fast-neutron-detection systems, as shown in Table 1.  2 The effective
2. Uranium/plutonium ratio,                                     Fabrication of calibration standards that are truly representative of the unknowns is impossible for scrap
24 0 Pu mass is a weighted average of the mass of each of the plutonium isotopes.
      3. Types of container and packaging,                       assay. To measure the reliability of the calibration based on the fabricated standards discussed above and to
 
      4. Abundance of high-yield alpha/neutron    material,       improve this calibration, unknowns that have been i.e., low-atomic-number impurities,                                  3 Copies of this standard may be obtained from the American National Standards Institute, Inc., 1430 Broadway, New York,
The weighting is equal to the spontaneous fission neutron yield of each isotope relative to that of 2 0 4Pu. Since only the even-numbered isotopes have significant spontaneous fission rates, the effective
      5. Size  and distribution  of materials in packages,       New York 10018.
240 Pu mass is given approxi mately by: M(240)eff
= M(240) + (1.64 + 0.07)M(242)
+ (2.66 +/- 0.19)M(238)
where M is the mass of the isotope indicated in parentheses.
 
The uncertainties in the coefficients and in the effective
240 Pu abun dances in the table are from the reported standard deviations in the most reliable data available (Ref. 7). The mathematical procedure for converting from M(240)eff to M(total Pu) is presented in the appendix to this guide together with a sample calculation.
 
5.34-2 TABLE 1 MATRIX MATERIAL EFFECTS ON NEUTRON ASSAY Correcteda (Ref. 10) Neutron Detection Efficiency (Ref. 11) Coincidence Coincidence Efficiency, Efficiency, Matrix Material Mass 3 He Detector, 4 He Detector, ZnS Detector, 3 He Detector, 3He Detector, (in %4-liter can) (kg) Thermal Fast Fast Thermal Thermal Empty Can -1.00 1.00 1.00 1.00 1.00 Carbon Pellets 1.89 1.03 --1.05 0.97 Metal 3.60 1.04 0.83 0.75 1.09 1.02 Slag-Crucible
1.80 1.03 0.94 0.91 1.08 1.01 Concrete 3.24 1.05 0.84 0.79 1.10 1.02 String Filters 0.60 1.07 0.95 0.86 1.17 1.05 CH 2 (p=0.6 5 g/cc) 0.27 1.06 0.96 0.92 1.11 1.00 CH 2 (p=0.1 2 g/cc) 0.43 1.09 0.92 0.90 1.19 0.98 CH 2 (p=0.2 7 g/cc) 0.97 1.19 0.71 0.67 1.36 0.04 H120 (p=l.00 g/cc) 3.62 0.98 0.36 0.35 0.98 0.96 aCorrected using the source addition technique (see Ref. 7).1.2 Detection Chamber The chamber should permit reproducible positioning of standard-sized containers in the location of maximum spatial response uniformity.
 
1.3 Fission Source A spontaneous fission source with a neutron intensity comparable to the intensity of the largest plutonium mass to be assayed should be used for making matrix corrections using the source addition technique (Ref. 10).  A nanogram of 252Ca is approximately equivalent to a gram of effective
2 4 0 Pu. 1.4 Readout Readout should allow computation of the accidental to-real-coincidence ratio in addition to the net real coincidence rate. Live-time readout or a means of computing the dead time should also be provided.
 
1.5 Perfonnance Specifications The performance of a spontaneous fission detection instrument should be evaluated according to its stability, uniformity of spatial response, and insensitivity matrix effects. Therefore, information should obtained regarding:
to be 1. The precision of the coincidence response as a function of the real-coincidence counting rate and the accidental-to-real-coincidence ratio. Extremes in the back ground or accidental-coincidence rate can be simulated by using a source of random neutrons (nonfission). 
2. The uniformity of spatial response.
 
Graphs should be obtained on the relative coincidence response to a small fission neutron source as a function of position in the counting chamber.
 
3. The sensitivity of matrix interference.
 
A table of the relative coincidence response to a small fission neutron source as a function of the composition of the matrix material surrounding the point source should be obtained.
 
Included in the matrix should be materials considered representative of common scrap materials.
 
Table 1 is an example of such a tabulation of the relative response for a wide range of materials.
 
This information should be used for evaluating the expected instrument performance and for estimating
5.34-3 errors. The above performance information can be requested from the instrument suppliers during instru ment selection and should be verified during preopera tional instrument testing.2. ANALYST 6. Density (both average density and local density extremes should be considered), and 7. Matrix composition.
 
===5. CALIBRATION===
A trained individual should oversee spontaneous fission detection assay of plutonium and should have primary responsibility for instrument specification, preoperational instrument testing, standards and calibra tion, an operation manual, measurement control, and error analysis.


Experience or training equivalent to a bachelor's degree in science or engineering from an accredited college or university and a laboratory course in radiation measurement should be the minimum qualifications of the analyst. The spontaneous fission detection analyst should frequently review the sponta neous fission detection operation and should authorize any changes in the operation.
5.34-4


===3. CONTAINERS ===
TABLE 2
AND PACKAGING
                                          24 EFFECTIVE      °pu ABUNDANCE AND UNCERTAINTYa'b CORRESPONDING TO DIFFERENT ISOTOPIC COMPOSITION
A single type of container should be used for packaging all scrap in each category.
                                                    Approximate Abundance (%)
BURNUP
(MWd/t)                                239
                        23pu                pu          240pu            241pu          242 pu          24°PUeff
8,000
10,000                    0.10          87            10                2.5            0.3       10.75 +/- 0.03(0.3%)
16,000
18,000                    0.25          75            18                4.5            1.0      20.30 +/- 0.08(0.4%)
25,000
27,000                    1.0            58            25                9.0            7.0      39.14 +/- 0.50(1.3%)
38,000
40,000                    2.0            45            27                15.0            12.0      52.00 +/- 0.87(1.7%)
    aComputed using the equation given in footnote 2.


A uniform con tainer that would facilitate accurate measurement and would standardize this segment of instrument design, e.g., a thin-walled metal (steel) can with an inside diameter between 10 and 35 cm, is recommended.
bplutonium isotopic compositions were selected based on light-water-reactor fuel exposures.


For further guidance on container standardization in NDA measurements, see Reference
assayed by spontaneous fission detection should                response for each assay. If not used routinely, the source addition technique should be applied to a periodically be selected for assay by an independent technique. Calorimetry (Ref. 2) can be used to assay a          random selection of items with a frequency comparable random selection of scrap in containers and to provide          to the assay schedule. The results of random applica reliable data that should be fed back into the calibra          tions of the source addition technique can be used in two ways:
12.  4. REDUCING ERROR DUE TO MATERIAL VARIABILITY
tion fitting procedure to improve spontaneous fission detection calibration. The original calibration standards should be retained as working standards.                            1. As an average correction factor to be applied to a group of items, and
The variation in spontaneous fission detection response due to material variability in scrap should be reduced by (1) segregating scrap into categories that are independently calibrated, (2) correcting for matrix effects using the source addition technique (Ref. 10), or (3) applying both the categorization and the source addition technique.
6. MEASUREMENT CONTROL                                              2. As a check on the item being assayed to verify that it is similar to the standards used in calibration and For proper measurement control, on each day that            that no additional matrix effects are present, ie., purely as a qualitative assurance that the calibration is valid.


Categorization should be used if the spontaneous fission detection method is more sensitive to the material variability from scrap type to scrap type than to the material variability within a scrap type. Application of the source addition technique reduces the sensitivity to material variability and may allow the majority of scrap types to be assayed under a single calibration.
scrap is assayed, a secondary standard should be assayed as a background measurement. Also, on each day that scrap is assayed, control (or working) standards should       


Material characteristics that should be considered in selecting categories include: 1. Plutonium isotopic composition and content, 2. Uranium/plutonium ratio, 3. Types of container and packaging, 4. Abundance of high-yield alpha/neutron material, i.e., low-atomic-number impurities, 5. Size and distribution of materials in packages, Guidelines for calibration and measurement control for NDA are available in Regulatory Guide 5.53, "Qualifi cation, Calibration, and Error Estimation Methods for Nondestructive Assay," which endorses ANSI N15.20 1975, "Guide to Calibrating Nondestructive Assay Systems." 3 The guide and standard include details on calibration standards, calibration procedures, curve fitting, and error analysis.
===7. ERROR ANALYSIS===
be assayed for normalization and for ensuring reliable operation.                                                         The sources of error in spontaneous fission detection are discussed in Regulatory Guide 5.11. Analysis of the The source addition technique (Ref. 10) is recom            error in the calibration is discussed in ANSIN15.20-1975 and in References 4 and 13.


Guidelines relevant to spontaneous fission detection are given below.  Calibration can be used for either a single isotopic composition or variable isotopic mixtures.
mended for correcting the spontaneous fission detection
                                                          5.34-5


In the former case, the resulting calibration curve will be used to convert "net real-coincidence count" to "grams pluto nium." In the latter case, the conversion is from "net real-coincidence count" to "effective grams 24°pu." The mathematical procedure for converting from effective grams 2 4 0 pu, M(2 4 0)eff, to total grams pluto nium, M(total Pu), is presented in the appendix to this guide together with a sample calculation.
REFERENCES
1. J. F. Lemming and D. A. Rakel, "Guide to Pluto              8. N. Ensslin, J. Stewart, and J. Sapir, "Self nium Isotopic Measurements Using Gamma-Ray                    Multiplication  Correction Factors for Neutron Spectroscopy," MLM-2981, August 1982.                        Coincidence Counting," Nuclear Materials Manage ment, Vol. VIII, No. 2, p. 60, 1979.


A minimum of four calibration standards with isotopic compositions similar to those of the unknowns should be used for calibration.
2. U.S. Nuclear Regulatory Commission, "Calorimetric Assay for Plutonium," NUREG-0228, 1977.


If practicable, a calibra tion curve should be generated for each isotopic blend of plutonium.
9. M. S. Krick, "Neutron Multiplication Corrections
3. N. Ensslin et al., "Neutron Coincidence Counters                for Passive Thermal Neutron Well Counters," Los for Plutonium Measurements," Nuclear Materials                Alamos Scientific Laboratory, LA-8460-MS, 1980.


When plutonium of different isotopic composition is assayed using a single calibration, the effect of isotopic composition on the spontaneous fission detection response should be determined over the operating ranges by measuring standards of different plutonium isotopic compositions.
Management, Vol. VII, No. 2, p. 43, 1978.


This is necessary because the use of the effective
10. H. 0. Menlove and R. B. Walton, "41r Coincidence
2 4 0 pu concept can lead to error owing to the uncertainty in the spontaneous fission half-lives and the variation in response with isotopic composition.
4. R. Sher, "Operating Characteristics of Neutron                  Unit for One-Gallon Cans and Smaller Samples,"
    Well Coincidence Counters," Brookhaven National                Los Alamos Scientific Laboratory, LA-4457-MS,
    Laboratory, BNL-50332, 1972.                                  1970.


Table 2 illustrates the uncertainty in effective
5. K. Boehnel, "Determination of Plutonium in Nuclear Fuels Using the Neutron Coincidence Method,"              11. H. 0. Menlove, "Matrix Material Effects on Fission AWRE-Trans-70(54/4252) (English translation of                Neutron Counting Using Thermal- and Fast-Neutron KfK 2203), 1978.                                               Detectors,"    Los Alamos Scientific Laboratory, LA-4994-PR, p. 4, 1972.
2 4 0 Pu abundance with different isotopic compositions (Ref. 13). Calibration standards should be fabricated from material having a plutonium content determined by a technique traceable to or calibrated with the standard reference material of the National Bureau of Standards.


Well-characterized homogeneous material similar to the process material from which the scrap is generated can be used to obtain calibration standards.
6. M. S. Zucker, "Neutron Correlation Counting for the Nondestructive Analysis of Nuclear Materials,"        12. K. R. Alvar, H. R. Lukens, and N. A. Lurie, in Analytical Methods for Safeguards and Account              "Standard Containers for SNM Storage, Transfer, ability Measurements of Special Nuclear Materials,            and    Measurement,"    U.S.  Nuclear  Regulatory NBS    Special  Publication    528,  pp. 261-283,            Commission, NUREG/CR-1847, 1980.


Fabrication of calibration standards that are truly representative of the unknowns is impossible for scrap assay. To measure the reliability of the calibration based on the fabricated standards discussed above and to improve this calibration, unknowns that have been 3 Copies of this standard may be obtained from the American National Standards Institute, Inc., 1430 Broadway, New York, New York 10018.5.34-4 TABLE 2 EFFECTIVE
November 1978.
2 4°pu ABUNDANCE
AND UNCERTAINTYa'b CORRESPONDING
TO DIFFERENT
ISOTOPIC COMPOSITION
Approximate Abundance
(%) BURNUP (MWd/t) 23pu 2 3 9 pu 240pu 241pu 2 4 2 pu 24°PUeff 8,000 10,000 0.10 87 10 2.5 0.3 10.75 +/- 0.03(0.3%)
16,000 18,000 0.25 75 18 4.5 1.0 20.30 +/- 0.08(0.4%)
25,000 27,000 1.0 58 25 9.0 7.0 39.14 +/- 0.50(1.3%)
38,000 40,000 2.0 45 27 15.0 12.0 52.00 +/- 0.87(1.7%)
aComputed using the equation given in footnote 2.  bplutonium isotopic compositions were selected based on light-water-reactor fuel exposures.


assayed by spontaneous fission detection should periodically be selected for assay by an independent technique.
7. J. D. Hastings and W. W. Strohm, "Spontaneous              13. J. Jaech, "Statistical Methods in Nuclear Material Fission Half-Life of 2 3 8 Pu,' Journal of Inorganic          Control," Atomic Energy Commission, TID-26298, and Nuclear Chemistry, Vol. 34, p. 25, 1972.                  Section 3.3.8, 1974.


Calorimetry (Ref. 2) can be used to assay a random selection of scrap in containers and to provide reliable data that should be fed back into the calibra tion fitting procedure to improve spontaneous fission detection calibration.
BIBLIOGRAPHY
    American National Standards Institute, "Standard              Brouns, R. J., F. P. Roberts, and U. L. Upson, Test Methods for Nondestructive Assay of Special              "Considerations for Sampling Nuclear Materials for Nuclear Materials Contained in Scrap and Waste,"              SNM Accounting Measurements,"          U.S. Nuclear ANSI/ASTM C 853-79, 1979.                                      Regulatory Commission, NUREG/CR-0087, 1978.


The original calibration standards should be retained as working standards.
5.34-6


===6. MEASUREMENT ===
APPENDIX
CONTROL For proper measurement control, on each day that scrap is assayed, a secondary standard should be assayed as a background measurement.
                                            Procedure for Converting M( 2 4 0)eff to M(total Pu)
                                                          and Sample Calculation When the measurement situation dictates the expres f242 = (2.0 +/- 0.2)% = 0.020 +/- 0.002 sion
  24 0 of the primary assay result as "effective grams of pu," it is necessary to convert this result to total                Using these results in Equation 3, we have:
  grams of plutonium using the relationship between these two quantities and the known isotopic composi                          M(total Pu) = 10.0/[0.20 + 1.64 x 0.02 tion of the plutonium sample. Let f 2 38,' f2 3 9 ' f 2 40 '
  f241' f242 represent the weight fractions of the pluto                                      + 2.66 x 0.01]
  nium isotopes in the unknown sampl


Also, on each day that scrap is assayed, control (or working) standards should be assayed for normalization and for ensuring reliable operation.
====e. The effective====
  24°pu mass from coincidence counting, M( 2 4 0)eff, and                                  = 10.0/0.259 the individual masses of the spontaneously fissioning plutonium isotopes are related by:                                                        = 38.6 grams M( 2 4 0)eff = M(240) + 1.64M(242)                                      To obtain the value of the variance of the M(total Pu) result, we must propagate the variances of the
                      + 2.66M(238)                              (1)        M( 2 4 0)eff and the isotopic weight fractions. Let the variance in M( 24 0)eff = cieff, and let the variances The masses of the 2 4 2 Pu and 2 3 8 pU isotopes can be                  in the relevant plutonium weight fractions be G238'
  "expressed in terms of M(240), using the isotopic weight                  2
                                                                          0240'2j  and G:42.


The source addition technique (Ref. 10) is recom mended for correcting the spontaneous fission detection response for each assay. If not used routinely, the source addition technique should be applied to a random selection of items with a frequency comparable to the assay schedule.
4    The variance of the total plutonium fractions, so that:                                                      mass, apu, is given by:
      M( 2 4 0)eff = M(240)[f  2 40    + 1.64f 2 4 2                            2  = [M(total Pu)] 2  {[ Oeff/M( 2 4 0)eff] 2
                      + 2.66f 2 3 8 1/f 240                    (2)                    + [ 242 + (1.6 4    24  )2 + (2.660238)]/
S Since M(240)/f 2 4 0 = M(total Pu), we have the final                                [f240 + 1.64f 2 4 2 + 2.66f 2 38 ] 2}      (5)
  results:
                                                                                                            0
                                                                          In our example calculation,        eff = 0.5 gram, 02ý8 =
                          24                                              0.005, 0240 = 0.004, and 0242 = 0.002. The variance M(total Pu) = M(      0)eff/[f 2 4 o  +  1.64f 24 2 in the total plutonium          mass is therefore given by:
                        + 2.66f 2 3 8 ]                        (3)              2  = IM(total Pu)]2 [(0.5/10.0)2 The quantity in the denominator of Equation 3 is called the " 2 40 Pu effective weight fraction, f 2 4 0 (effect                      + 0.000204/(0.259)2 ]
  ive)." Thus the total plutonium mass can be expressed as the 2 4 0 Pu effective mass divided by the 2 4 0 pu                        0
                                                                                Pu = M(total Pu) [(0.5/10.0)2 effective weight fraction:
                                                                                      + 0.000204/(0.259)2] 1/2 M(total Pu) = M(240)eff/f 2 4 o(effective)                (4)
                                                                                    = 38.6 x 0.074 As an example, suppose that the net coincidence count from an unknown sample indicates 10.0 +/- 0.5                                = 2.9 grams effective grams of 2 4 0 Pu. Furthermore, suppose that the plutonium isotopic composition of the unknown                      Thus the final assay result from this coincidence count sample was previously established to be:                                is quoted as:
      f238 = (1.0 +/- 0.5)% = 0.010 +/- 0.005                                      M(total Pu) = 38.6 +/- 2.9 grams.


The results of random applica tions of the source addition technique can be used in two ways: 1. As an average correction factor to be applied to a group of items, and 2. As a check on the item being assayed to verify that it is similar to the standards used in calibration and that no additional matrix effects are present, ie., purely as a qualitative assurance that the calibration is valid.  7. ERROR ANALYSIS The sources of error in spontaneous fission detection are discussed in Regulatory Guide 5.11. Analysis of the error in the calibration is discussed in ANSIN15.20-1975 and in References
f239 = (73.0 +/- 0.5)%                                                    For most plutonium samples, the dominant measure ment uncertainties will be in the 2 4 °pu effective mass f240 = (20.0 +/- 0.4)% = 0.200 +/- 0.004                                and the 2 4 0 pU isotopic weight fraction, f24 0 . Thus good precision in M(total Pu) is achieved primarily through f241 = (4.0 +/- 0.2)%                                                minimizing the uncertainties in these quantities.
4 and 13.5.34-5 REFERENCES
1. J. F. Lemming and D. A. Rakel, "Guide to Pluto nium Isotopic Measurements Using Gamma-Ray Spectroscopy," MLM-2981, August 1982.  2. U.S. Nuclear Regulatory Commission, "Calorimetric Assay for Plutonium," NUREG-0228, 1977.  3. N. Ensslin et al., "Neutron Coincidence Counters for Plutonium Measurements," Nuclear Materials Management, Vol. VII, No. 2, p. 43, 1978.  4. R. Sher, "Operating Characteristics of Neutron Well Coincidence Counters," Brookhaven National Laboratory, BNL-50332, 1972.  5. K. Boehnel, "Determination of Plutonium in Nuclear Fuels Using the Neutron Coincidence Method," AWRE-Trans-70(54/4252) (English translation of KfK 2203), 1978.  6. M. S. Zucker, "Neutron Correlation Counting for the Nondestructive Analysis of Nuclear Materials," in Analytical Methods for Safeguards and Account ability Measurements of Special Nuclear Materials, NBS Special Publication
528, pp. 261-283, November 1978.  7. J. D. Hastings and W. W. Strohm, "Spontaneous Fission Half-Life of 2 3 8 Pu,' Journal of Inorganic and Nuclear Chemistry, Vol. 34, p. 25, 1972.8. N. Ensslin, J. Stewart, and J. Sapir, "Self Multiplication Correction Factors for Neutron Coincidence Counting," Nuclear Materials Manage ment, Vol. VIII, No. 2, p. 60, 1979.  9. M. S. Krick, "Neutron Multiplication Corrections for Passive Thermal Neutron Well Counters," Los Alamos Scientific Laboratory, LA-8460-MS, 1980.  10. H. 0. Menlove and R. B. Walton, "41r Coincidence Unit for One-Gallon Cans and Smaller Samples," Los Alamos Scientific Laboratory, LA-4457-MS, 1970.  11. H. 0. Menlove, "Matrix Material Effects on Fission Neutron Counting Using Thermal- and Fast-Neutron Detectors," Los Alamos Scientific Laboratory, LA-4994-PR, p. 4, 1972.  12. K. R. Alvar, H. R. Lukens, and N. A. Lurie, "Standard Containers for SNM Storage, Transfer, and Measurement," U.S. Nuclear Regulatory Commission, NUREG/CR-1847, 1980.  13. J. Jaech, "Statistical Methods in Nuclear Material Control," Atomic Energy Commission, TID-26298, Section 3.3.8, 197


===4. BIBLIOGRAPHY===
5.34-7
American National Standards Institute, "Standard Test Methods for Nondestructive Assay of Special Nuclear Materials Contained in Scrap and Waste," ANSI/ASTM
C 853-79, 1979.Brouns, R. J., F. P. Roberts, and U. L. Upson, "Considerations for Sampling Nuclear Materials for SNM Accounting Measurements," U.S. Nuclear Regulatory Commission, NUREG/CR-0087, 1978.5.34-6 APPENDIX Procedure for Converting M(2 4 0)eff to M(total Pu) and Sample Calculation When the measurement situation dictates the expres sion of the primary assay result as "effective grams of 2 4 0 pu," it is necessary to convert this result to total grams of plutonium using the relationship between these two quantities and the known isotopic composi tion of the plutonium sample. Let f 2 3 8 ,' f 2 3 9' f 2 4 0' f241' f242 represent the weight fractions of the pluto nium isotopes in the unknown sampl


====e. The effective ====
VALUE/IMPACT STATEMENT                                                        -V
24°pu mass from coincidence counting, M(2 4 0)eff, and the individual masses of the spontaneously fissioning plutonium isotopes are related by: M(2 4 0)eff = M(240) + 1.64M(242)
1. PROPOSED ACTION                                                1.3.3 Industry
+ 2.66M(238)
1.1    Description                                                Since industry is already applying the techniques discussed in the guide, updating these techniques should Licensees authorized to possess at any one time            have no adverse impact.
(1) The masses of the 2 4 2 Pu and 2 3 8 pU isotopes can be "expressed in terms of M(240), using the isotopic weight fractions, so that: M(2 4 0)eff = M(240)[f 2 4 0+ 1.64f 2 4 2+ 2.66f 2 3 8 1/f 2 4 0 (2)f242 = (2.0 +/- 0.2)% = 0.020 +/- 0.002 Using these results in Equation 3, we have: M(total Pu) = 10.0/[0.20
+ 1.64 x 0.02 + 2.66 x 0.01] = 10.0/0.259
= 38.6 grams To obtain the value of the variance of the M(total Pu) result, we must propagate the variances of the M(2 4 0)eff and the isotopic weight fractions.


Let the variance in M(2 4 0)eff = cieff, and let the variances in the relevant plutonium weight fractions be G238' 2 and G:42. The variance of the total plutonium
more than one effective kilogram of plutonium are required in § 70.51 of 10 CFR Part 70, "Domestic                    1.3.4 Public Licensing of Special Nuclear Material," to establish and maintain a system of control and accountability so                No impact on the public can be foreseen.
0240'2j 4 mass, apu, is given by: 2 = [M(total Pu)] 2 {[ Oeff/M(2 4 0)eff] 2 + [ 242 + (1.6 4 2 4)2 + (2.660238)]/
= M(total Pu), we have the final M(total Pu) = M(2 4 0)eff/[f 2 4 o + 1.64f 2 4 2 + 2.66f 2 3 8]The quantity in the denominator of Equation 3 is called the " 2 4 0 Pu effective weight fraction, f 2 4 0 (effect ive)." Thus the total plutonium mass can be expressed as the 2 4 0 Pu effective mass divided by the 2 4 0 pu effective weight fraction: M(total Pu) = M(240)eff/f
2 4 o(effective)
(4)As an example, suppose that the net coincidence count from an unknown sample indicates
10.0 +/- 0.5 effective grams of 2 4 0 Pu. Furthermore, suppose that the plutonium isotopic composition of the unknown sample was previously established to be: f238 = (1.0 +/- 0.5)% = 0.010 +/- 0.005 f239 = (73.0 +/- 0.5)% f240 = (20.0 +/- 0.4)% = 0.200 +/- 0.004 f241 = (4.0 +/- 0.2)%[f240 + 1.64f 2 4 2+ 2.66f 2 3 8] 2}(5)In our example calculation, 0 eff = 0.5 gram, 02ý8 = 0.005, 0240 = 0.004, and 0242 = 0.002. The variance in the total plutonium mass is therefore given by: 2 = IM(total Pu)]2 [(0.5/10.0)2
+ 0.000204/(0.259)2
] 0 Pu = M(total Pu) [(0.5/10.0)2
+ 0.000204/(0.259)2]
1/2 = 38.6 x 0.074 = 2.9 grams Thus the final assay result from this coincidence count is quoted as: M(total Pu) = 38.6 +/- 2.9 grams.  For most plutonium samples, the dominant measure ment uncertainties will be in the 2 4°pu effective mass and the 2 4 0 pU isotopic weight fraction, f24 0.Thus good precision in M(total Pu) is achieved primarily through minimizing the uncertainties in these quantities.


5.34-7 S Since M(240)/f 2 4 0 results: (3)
that the standard error (estimator) associated with the inventory difference (SEID) ascertained as a result of a       1.4    Decision on Proposed Action measured material balance meets minimum standards.
VALUE/IMPACT
STATEMENT 1. PROPOSED ACTION 1.1 Description Licensees authorized to possess at any one time more than one effective kilogram of plutonium are required in § 70.51 of 10 CFR Part 70, "Domestic Licensing of Special Nuclear Material," to establish and maintain a system of control and accountability so that the standard error (estimator)  
associated with the inventory difference (SEID) ascertained as a result of a measured material balance meets minimum standards.


Included in a typical material balance are containers of inhomogeneous scrap material that are not amenable to assay by the traditional method of sampling and chemical analysis.
The guide should be revised to reflect improvements Included in a typical material balance are containers     in the technique and to bring the language of the of inhomogeneous scrap material that are not amenable         guide into conformity with current usage.


With proper controls, the nondestruc tive assay (NDA) technique of spontaneous fission detection is one acceptable method for the assay of plutonium in containers of bulk scrap material.
to assay by the traditional method of sampling and chemical analysis. With proper controls, the nondestruc        


The use of spontaneous fission detection thus facilitates the preparation of a complete plant material balance whose SEID meets established requirements.
===2. TECHNICAL APPROACH===
tive assay (NDA) technique of spontaneous fission detection is one acceptable method for the assay of                 Not applicable.


Regulatory Guide 5.34 was issued in June 1974 to describe procedures acceptable to the NRC staff for applying the NDA technique of spontaneous fission detection to plutonium in scrap.  1.2 Need for Proposed Action Improvements in technology have occurred since Regulatory Guide 5.34 was issued, and the proposed action is needed to bring it up to date.  1.3 Value/Impact of Proposed Action 1.3.1 NRC Operations The improvements in technology that have occurred since the guide was issued will be made available for the regulatory procedure.
plutonium in containers of bulk scrap material. The use of spontaneous fission detection thus facilitates the          


Using these updated tech niques should have no adverse impact. 1.3.2 Other Government Agencies Not applicable.
===3. PROCEDURAL APPROACH===
preparation of a complete plant material balance whose SEID meets established requirements.                               Of the procedural alternatives considered, revision of the existing regulatory guide was selected as the most advantageous and cost effective.


1.3.3 Industry Since industry is already applying the techniques discussed in the guide, updating these techniques should have no adverse impact.  1.3.4 Public No impact on the public can be foreseen.
Regulatory Guide 5.34 was issued in June 1974 to describe procedures acceptable to the NRC staff for            4. STATUTORY CONSIDERATIONS
applying the NDA technique of spontaneous fission detection to plutonium in scrap.                              4.1    NRC Authority Authority for this guide is derived from the safety
1.2    Need for Proposed Action                                requirements of the Atomic Energy Act through the Commission's regulations, in particular, § 70.51 of Improvements in technology have occurred since            10 CFR Part 70.


1.4 Decision on Proposed Action The guide should be revised to reflect improvements in the technique and to bring the language of the guide into conformity with current usage.
Regulatory Guide 5.34 was issued, and the proposed action is needed to bring it up to date.                      4.2    Need for NEPA Assessment The proposed action is not a major action that may
1.3    Value/Impact of Proposed Action                         significantly affect the quality of the human environ ment and does not require an environmental impact
    1.3.1 NRC Operations                                      statement.


===2. TECHNICAL ===
The improvements in technology that have occurred          5.   RELATIONSHIP TO OTHER EXISTING OR
APPROACH Not applicable.
since the guide was issued will be made available for                PROPOSED REGULATIONS OR POLICIES
the regulatory procedure. Using these updated tech                The proposed action is one of a series of revisions niques should have no adverse impact.


===3. PROCEDURAL ===
of existing regulatory guides on NDA techniques.
APPROACH Of the procedural alternatives considered, revision of the existing regulatory guide was selected as the most advantageous and cost effective.


===4. STATUTORY ===
1.3.2  Other Government Agencies                          6. SUMMARY AND CONCLUSIONS
CONSIDERATIONS
    Not applicable.                                                 Regulatory Guide 5.34 should be updated.
4.1 NRC Authority Authority for this guide is derived from the safety requirements of the Atomic Energy Act through the Commission's regulations, in particular, § 70.51 of 10 CFR Part 70. 4.2 Need for NEPA Assessment The proposed action is not a major action that may significantly affect the quality of the human environ ment and does not require an environmental impact statement.


===5. RELATIONSHIP ===
5.34-8
TO OTHER EXISTING OR PROPOSED REGULATIONS
OR POLICIES The proposed action is one of a series of revisions of existing regulatory guides on NDA techniques.


6. SUMMARY AND CONCLUSIONS
UNITED STATES
Regulatory Guide 5.34 should be updated.5.34-8-V
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Latest revision as of 11:27, 28 March 2020

(Task SG 046-4), Nondestructive Assay for Plutonium in Scrap Material by Spontaneous Fission Detection
ML003739949
Person / Time
Issue date: 05/31/1984
From:
Office of Nuclear Regulatory Research
To:
References
RG-5.34, Rev 1
Download: ML003739949 (9)
v • d • e


Revision 1"

U.S. NUCLEAR REGULATORY COMMISSION May 1984

0

SREGULATORY

OFFICE OF NUCLEAR REGULATORY RESEARCH

GUIDE

REGULATORY GUIDE 5.34 (Task SG 046-4)

NONDESTRUCTIVE ASSAY FOR PLUTONIUM IN SCRAP MATERIAL

BY SPONTANEOUS FISSION DETECTION

A. INTRODUCTION

standard error. Unlike the major quantity of material flowing through the process, scrap is typically Section 70.51, "Material Balance, Inventory, and inhomogeneous and difficult to sample. Therefore, a Records Requirements," of 10 CFR Part 70, "Domestic separate assay of the entire content of each container of Licensing of Special Nuclear Material," requires certain scrap material is a more reliable method of scrap account licensees authorized to possess at any one time more ability. NDA is a method for assaying the entire content than one effective kilogram of special nuclear material of every container of scrap.

to establish and maintain a system of control and accountability so that the standard error (estimator) The term "scrap" refers to material that is generated associated with the inventory difference (SEID), from the main process stream because of the ineffi obtained as a result of a measured material balance, ciency of the process. Scrap material is generally meets minimum standards. This guide is intended for economically recoverable. Scrap, therefore, consists of those licensees who possess plutonium scrap materials rejected or contaminated process material such as pellet and who are also subjected to the requirements of grinder sludge, sweepings from gloveboxes, dried filter

§ 70.51 of 10 CFR Part 70. sludge, and rejected powder and pellets. Scrap is generally distinguished from "waste" by the density or concentra Included in a typical material balance are containers tion of heavy elements in the two materials, but it is of inhomogeneous scrap material that are not amenable the recovery cost (per mass unit of special nuclear to assay by the traditional method of sampling and material) that determines whether a material is "scrap"

chemical analysis. With proper controls, the non or "waste." The concentration of uranium and pluto destructive assay (NDA) technique of spontaneous nium in scrap is approximately the same as it is in fission detection is one acceptable method for the assay process material, i.e., 85-90 percent (uranium + pluto of plutonium in containers of bulk scrap material. The nium) by weight. However, on occasion the fraction in use of spontaneous fission detection thus facilitates the both process and scrap material can be less than 25 preparation of a complete plant material balance whose percent. Plutonium in fast reactor scrap material is SEID meets established requirements. 15-20 percent by weight and in thermal reactor recycle material, 2-9 percent by weight. The main difference This guide describes procedures acceptable to the between scrap and process material is that scrap is NRC staff for applying the NDA technique of contaminated and inhomogeneous. Waste, on the other spontaneous fission detection to plutonium in scrap. hand, contains a low concentration of uranium and plutonium, ie., a few percent or less (uranium + pluto Any guidance in this document related to informa nium) by weight. However, the recovery of combustible tion collection activities has been cleared under OMB waste by incineration may produce ash that is high in Clearance No. 3150-0009. uranium and plutonium concentrations. Such incinerator ash is also considered "scrap" in this guide. However, it

B. DISCUSSION

should be noted that ash may be more homogeneous in Plutonium in scrap material can contribute signif

  • The substantial number of changes in this revision has made icantly to the inventory difference and its associated it impractical to indicate the changes with lines in the margin.

USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission, U.S. Nuclear Regulatory Commission, Washington, D.C. 20555, Regulatory Guides are issued to describe and make available to the Attention: Docketing and Service Branch.

public methods acceptable to the NRC staff of implementing specific parts of the Commission's regulations, to delineate tech- The guides are issued in the following ten broad divisions:

niques used by the staff in evaluating specific problems or postu lated accidents or to provide guidance to applicants. Regulatory 1. Power Reactors 6. Products Guides are no? substitutes for regulations, and compliance with 2. Research and Test Reactors 7. Transportation them is not required. Methods and solutions different from those set 3. Fuels and Materials Facilities 8. Occupational Health out in the guides will be acceptable if they provide a basis for the 4. Environmental and Siting 9. Antitrust and Financial Review findings requisite to the issuance or continuance of a permit or 5. Materials and Plant Protection 10. General license by the Commission.

Copies of issued guides may be purchased at the current Government This guide was issued after consideration of comments received from Printing Office price. A subscription service for future guides in spe the public. Comments and suggestions for improvements in these cific divisions is available through the Government Printing Office.

guides are encouraged at all times, and guides will be revised, as Information on the subscription service and current GPO prices may appropriate, to accommodate comments and to reflect new Informa- be obtained by writing the U.S. Nuclear Regulatory Commission, tion or experience. Washington, D.C. 20555, Attention: Publications Sales Manager.

its characteristics compared to most scrap and may, This guide gives recommendations useful for the assay therefore, be accountable using sampling and chemical by spontaneous fission detection of containers, each analysis methods. containing a few liters of scrap and having contents ranging from a few grams to 10 kilograms of plutonium or up to approximately 2 kilograms of effective

240

Pu 2 NDA of plutonium can be accomplished primarily by the passive methods of gamma ray spectrometry, (see Ref. 7). Containers with a significant plutonium calorimetry, and spontaneous fission detection. Active content (i.e., 50 grams or more) give a spontaneous neutron methods using total count rates or delayed fission response that must be corrected for the effects neutron detection can also be used in scrap assay of neutron multiplication (Refs. 8, 9). Scrap materials measurements. Regulatory Guide 5.11, "Nondestructive that have large loadings of plutonium in addition to Assay of Special Nuclear Material Contained in Scrap fluorine, oxygen, or other alpha/neutron-producing and Waste," provides a framework for the use of these elements are difficult to measure and correct for multi

1 NDA methods. plication effects because of the large random neutron flux from the (ct,n) reactions in the matrix materials.

The NDA of dense scrap materials using gamma ray These samples should be segregated into smaller quanti spectroscopy can be unreliable because of severe gamma ties for measurements. In general, a large quantity of ray attenuation. However, the isotopic composition of plutonium can be assayed by spontaneous fission detec plutonium in scrap materials, with the exception of tion by subdividing the scrap into smaller amounts, or

242pu, can be obtained quite reliably using high-resolution the items may be more amenable to assay by calorim gamma ray spectrometry measurements (Ref. 1). etry.

C. REGULATORY POSITION

Calorimetry is an accurate method of plutonium assay when there is an accurate knowledge of the The spontaneous fission detection method for the relative abundance of each plutonium isotope and NDA of plutonium in bulk inhomogeneous scrap material

24 tAm. Scrap may contain a mixture of materials of should include (1) discrimination of spontaneous fission different radionuclide compositions, especially different radiations from random background by coincidence

241Am concentrations, thereby necessitating the measure techniques and (2) measurement of the relative pluto ment of the average radionuclide composition. The nium isotopic composition of the scrap. An acceptable average radionuclide abundances can be accurately meas spontaneous fission detection method of plutonium ured only when the scrap is reasonably homogeneous. assay is described below.

When the radionuclide abundances can be accurately measured or controlled, calorimetry can be applied to 1. SPONTANEOUS FISSION DETECTION SYSTEM

scrap assay (Ref. 2). However, calorimetry is time con suming for materials of high heat capacity and may 1.1 Detectors not be a practical method for the routine assay of large numbers of containers. Instruments based on moderated thermal neutron detectors, i.e., neutron well coincidence counters, are Spontaneous fission detection is a practical NDA recommended for applications in which the gross technique for the assay of plutonium in scrap material. neutron detection rate does not exceed 2 x 105 The assay method involves the passive counting of neutrons/sec. The dead time inherent in these slow spontaneous fission neutrons emitted primarily from the coincidence systems can be reduced by employing a fission of 240 Pu. Neutron coincidence counters are used shift-register coincidence circuit. If the gross neutron to detect these time-correlated neutrons. The theory and detection rate is Lprimarily due to random background practice of neutron coincidence counting for plutonium and exceeds 2 x 10 neutrons/sec, a fast-neutron-detection, assay are discussed thoroughly in References 3 through 6. single-coincidence system can be used, provided adequate Spontaneous fission neutrons are sufficiently penetrating corrections can be made for matrix effects. Matrix to provide a representative signal from all the plutonium effects are more severe in fast-neutron-detection systems, within a container. Since the neutron coincidence signal as shown in Table 1.

is dependent on both the quantity and relative abundance

8 240

of 2 3 Pu, pu, and 242pu, the plutonium isotopic

2 composition must be known for assay of total plutonium The effective 24 0 Pu mass is a weighted average of the mass by spontaneous fission detection. The quantity of scrap of each of the plutonium isotopes. The weighting is equal to the spontaneous

0

fission neutron yield of each isotope relative to that material on inventory when a material balance is com of 2 4Pu. Since only the even-numbered isotopes have significant puted can be reduced through good management, and spontaneous fission rates, the effective 240 Pu mass is given approxi mately by:

the scrap remaining on inventory can be assayed by M(240)eff = M(240) + (1.64 + 0.07)M(242)

spontaneous fission detection to meet the overall plant inventory difference (ID) and SEID constraints required + (2.66 +/- 0.19)M(238)

by paragraph 70.5 1(e)(5) of 10 CFR Part 70. where M is the mass of the isotope indicated in parentheses. The uncertainties in the coefficients and in the effective 240 Pu abun dances in the table are from the reported standard deviations in the most reliable data available (Ref. 7). The mathematical procedure for converting from M(240)eff to M(total Pu) is presented in the

1Revision I to this guide was issued in April 1984. appendix to this guide together with a sample calculation.

5.34-2

TABLE 1 MATRIX MATERIAL EFFECTS ON NEUTRON ASSAY

Correcteda (Ref. 10)

Neutron Detection Efficiency (Ref. 11) Coincidence Coincidence Efficiency, Efficiency,

3 4 3 Matrix Material Mass He Detector, He Detector, ZnS Detector, He Detector, 3He Detector, (in %4-liter can) (kg) Thermal Fast Fast Thermal Thermal Empty Can - 1.00 1.00 1.00 1.00 1.00

Carbon Pellets 1.89 1.03 - - 1.05 0.97 Metal 3.60 1.04 0.83 0.75 1.09 1.02 Slag-Crucible 1.80 1.03 0.94 0.91 1.08 1.01 Concrete 3.24 1.05 0.84 0.79 1.10 1.02 String Filters 0.60 1.07 0.95 0.86 1.17 1.05 CH 2 (p=0. 6 5 g/cc) 0.27 1.06 0.96 0.92 1.11 1.00

CH 2 (p=0.1 2 g/cc) 0.43 1.09 0.92 0.90 1.19 0.98 CH 2 (p=0. 2 7 g/cc) 0.97 1.19 0.71 0.67 1.36 0.04 H120 (p=l.00 g/cc) 3.62 0.98 0.36 0.35 0.98 0.96 aCorrected using the source addition technique (see Ref. 7).

1.2 Detection Chamber uniformity of spatial response, and insensitivity to matrix effects. Therefore, information should be The chamber should permit reproducible positioning obtained regarding:

of standard-sized containers in the location of maximum spatial response uniformity. 1. The precision of the coincidence response as a function of the real-coincidence counting rate and the

1.3 Fission Source accidental-to-real-coincidence ratio. Extremes in the back ground or accidental-coincidence rate can be simulated A spontaneous fission source with a neutron intensity by using a source of random neutrons (nonfission).

comparable to the intensity of the largest plutonium mass to be assayed should be used for making matrix 2. The uniformity of spatial response. Graphs should corrections using the source addition technique (Ref. 10). be obtained on the relative coincidence response to a A nanogram of 252Ca is approximately equivalent to a small fission neutron source as a function of position in gram of effective 2 40 Pu. the counting chamber.

1.4 Readout 3. The sensitivity of matrix interference. A table of the relative coincidence response to a small fission Readout should allow computation of the accidental neutron source as a function of the composition of the to-real-coincidence ratio in addition to the net real matrix material surrounding the point source should be coincidence rate. Live-time readout or a means of obtained. Included in the matrix should be materials computing the dead time should also be provided. considered representative of common scrap materials.

Table 1 is an example of such a tabulation of the

1.5 Perfonnance Specifications relative response for a wide range of materials.

The performance of a spontaneous fission detection This information should be used for evaluating the instrument should be evaluated according to its stability, expected instrument performance and for estimating

5.34-3

errors. The above performance information can be 6. Density (both average density and local density requested from the instrument suppliers during instru extremes should be considered), and

3/4'

ment selection and should be verified during preopera tional instrument testing. 7. Matrix composition.

2. ANALYST

5. CALIBRATION

A trained individual should oversee spontaneous Guidelines for calibration and measurement control fission detection assay of plutonium and should have for NDA are available in Regulatory Guide 5.53, "Qualifi primary responsibility for instrument specification, cation, Calibration, and Error Estimation Methods for preoperational instrument testing, standards and calibra Nondestructive Assay," which endorses ANSI N15.20

tion, an operation manual, measurement control, and 1975, "Guide to Calibrating Nondestructive Assay error analysis. Experience or training equivalent to a Systems." 3 The guide and standard include details on bachelor's degree in science or engineering from an calibration standards, calibration procedures, curve fitting, accredited college or university and a laboratory course and error analysis. Guidelines relevant to spontaneous in radiation measurement should be the minimum fission detection are given below.

qualifications of the analyst. The spontaneous fission detection analyst should frequently review the sponta Calibration can be used for either a single isotopic neous fission detection operation and should authorize composition or variable isotopic mixtures. In the former any changes in the operation. case, the resulting calibration curve will be used to convert "net real-coincidence count" to "grams pluto

3. CONTAINERS AND PACKAGING nium." In the latter case, the conversion is from "net real-coincidence count" to "effective grams 24°pu."

A single type of container should be used for The mathematical procedure for converting from packaging all scrap in each category. A uniform con effective grams 2 4 0 pu, M( 24 0 )eff, to total grams pluto tainer that would facilitate accurate measurement and nium, M(total Pu), is presented in the appendix to this would standardize this segment of instrument design, guide together with a sample calculation.

e.g., a thin-walled metal (steel) can with an inside diameter between 10 and 35 cm, is recommended. For A minimum of four calibration standards with further guidance on container standardization in NDA isotopic compositions similar to those of the unknowns measurements, see Reference 12. should be used for calibration. If practicable, a calibra tion curve should be generated for each isotopic blend

4. REDUCING ERROR DUE TO MATERIAL of plutonium. When plutonium of different isotopic VARIABILITY composition is assayed using a single calibration, the effect of isotopic composition on the spontaneous The variation in spontaneous fission detection fission detection response should be determined over the response due to material variability in scrap should be operating ranges by measuring standards of different reduced by (1) segregating scrap into categories that are plutonium isotopic compositions. This is necessary independently calibrated, (2) correcting for matrix because the use of the effective 2 40 pu concept can lead effects using the source addition technique (Ref. 10), or to error owing to the uncertainty in the spontaneous

(3) applying both the categorization and the source fission half-lives and the variation in response with addition technique. Categorization should be used if the isotopic composition. Table 2 illustrates the uncertainty spontaneous fission detection method is more sensitive in effective 2 40 Pu abundance with different isotopic to the material variability from scrap type to scrap type compositions (Ref. 13).

than to the material variability within a scrap type.

Application of the source addition technique reduces the Calibration standards should be fabricated from sensitivity to material variability and may allow the material having a plutonium content determined by a majority of scrap types to be assayed under a single technique traceable to or calibrated with the standard calibration. Material characteristics that should be reference material of the National Bureau of Standards.

considered in selecting categories include: Well-characterized homogeneous material similar to the process material from which the scrap is generated can

1. Plutonium isotopic composition and content, be used to obtain calibration standards.

2. Uranium/plutonium ratio, Fabrication of calibration standards that are truly representative of the unknowns is impossible for scrap

3. Types of container and packaging, assay. To measure the reliability of the calibration based on the fabricated standards discussed above and to

4. Abundance of high-yield alpha/neutron material, improve this calibration, unknowns that have been i.e., low-atomic-number impurities, 3 Copies of this standard may be obtained from the American National Standards Institute, Inc., 1430 Broadway, New York,

5. Size and distribution of materials in packages, New York 10018.

5.34-4

TABLE 2

24 EFFECTIVE °pu ABUNDANCE AND UNCERTAINTYa'b CORRESPONDING TO DIFFERENT ISOTOPIC COMPOSITION

Approximate Abundance (%)

BURNUP

(MWd/t) 239

23pu pu 240pu 241pu 242 pu 24°PUeff

8,000

10,000 0.10 87 10 2.5 0.3 10.75 +/- 0.03(0.3%)

16,000

18,000 0.25 75 18 4.5 1.0 20.30 +/- 0.08(0.4%)

25,000

27,000 1.0 58 25 9.0 7.0 39.14 +/- 0.50(1.3%)

38,000

40,000 2.0 45 27 15.0 12.0 52.00 +/- 0.87(1.7%)

aComputed using the equation given in footnote 2.

bplutonium isotopic compositions were selected based on light-water-reactor fuel exposures.

assayed by spontaneous fission detection should response for each assay. If not used routinely, the source addition technique should be applied to a periodically be selected for assay by an independent technique. Calorimetry (Ref. 2) can be used to assay a random selection of items with a frequency comparable random selection of scrap in containers and to provide to the assay schedule. The results of random applica reliable data that should be fed back into the calibra tions of the source addition technique can be used in two ways:

tion fitting procedure to improve spontaneous fission detection calibration. The original calibration standards should be retained as working standards. 1. As an average correction factor to be applied to a group of items, and

6. MEASUREMENT CONTROL 2. As a check on the item being assayed to verify that it is similar to the standards used in calibration and For proper measurement control, on each day that that no additional matrix effects are present, ie., purely as a qualitative assurance that the calibration is valid.

scrap is assayed, a secondary standard should be assayed as a background measurement. Also, on each day that scrap is assayed, control (or working) standards should

7. ERROR ANALYSIS

be assayed for normalization and for ensuring reliable operation. The sources of error in spontaneous fission detection are discussed in Regulatory Guide 5.11. Analysis of the The source addition technique (Ref. 10) is recom error in the calibration is discussed in ANSIN15.20-1975 and in References 4 and 13.

mended for correcting the spontaneous fission detection

5.34-5

REFERENCES

1. J. F. Lemming and D. A. Rakel, "Guide to Pluto 8. N. Ensslin, J. Stewart, and J. Sapir, "Self nium Isotopic Measurements Using Gamma-Ray Multiplication Correction Factors for Neutron Spectroscopy," MLM-2981, August 1982. Coincidence Counting," Nuclear Materials Manage ment, Vol. VIII, No. 2, p. 60, 1979.

2. U.S. Nuclear Regulatory Commission, "Calorimetric Assay for Plutonium," NUREG-0228, 1977.

9. M. S. Krick, "Neutron Multiplication Corrections

3. N. Ensslin et al., "Neutron Coincidence Counters for Passive Thermal Neutron Well Counters," Los for Plutonium Measurements," Nuclear Materials Alamos Scientific Laboratory, LA-8460-MS, 1980.

Management, Vol. VII, No. 2, p. 43, 1978.

10. H. 0. Menlove and R. B. Walton, "41r Coincidence

4. R. Sher, "Operating Characteristics of Neutron Unit for One-Gallon Cans and Smaller Samples,"

Well Coincidence Counters," Brookhaven National Los Alamos Scientific Laboratory, LA-4457-MS,

Laboratory, BNL-50332, 1972. 1970.

5. K. Boehnel, "Determination of Plutonium in Nuclear Fuels Using the Neutron Coincidence Method," 11. H. 0. Menlove, "Matrix Material Effects on Fission AWRE-Trans-70(54/4252) (English translation of Neutron Counting Using Thermal- and Fast-Neutron KfK 2203), 1978. Detectors," Los Alamos Scientific Laboratory, LA-4994-PR, p. 4, 1972.

6. M. S. Zucker, "Neutron Correlation Counting for the Nondestructive Analysis of Nuclear Materials," 12. K. R. Alvar, H. R. Lukens, and N. A. Lurie, in Analytical Methods for Safeguards and Account "Standard Containers for SNM Storage, Transfer, ability Measurements of Special Nuclear Materials, and Measurement," U.S. Nuclear Regulatory NBS Special Publication 528, pp. 261-283, Commission, NUREG/CR-1847, 1980.

November 1978.

7. J. D. Hastings and W. W. Strohm, "Spontaneous 13. J. Jaech, "Statistical Methods in Nuclear Material Fission Half-Life of 2 3 8 Pu,' Journal of Inorganic Control," Atomic Energy Commission, TID-26298, and Nuclear Chemistry, Vol. 34, p. 25, 1972. Section 3.3.8, 1974.

BIBLIOGRAPHY

American National Standards Institute, "Standard Brouns, R. J., F. P. Roberts, and U. L. Upson, Test Methods for Nondestructive Assay of Special "Considerations for Sampling Nuclear Materials for Nuclear Materials Contained in Scrap and Waste," SNM Accounting Measurements," U.S. Nuclear ANSI/ASTM C 853-79, 1979. Regulatory Commission, NUREG/CR-0087, 1978.

5.34-6

APPENDIX

Procedure for Converting M( 2 4 0)eff to M(total Pu)

and Sample Calculation When the measurement situation dictates the expres f242 = (2.0 +/- 0.2)% = 0.020 +/- 0.002 sion

24 0 of the primary assay result as "effective grams of pu," it is necessary to convert this result to total Using these results in Equation 3, we have:

grams of plutonium using the relationship between these two quantities and the known isotopic composi M(total Pu) = 10.0/[0.20 + 1.64 x 0.02 tion of the plutonium sample. Let f 2 38,' f2 3 9 ' f 2 40 '

f241' f242 represent the weight fractions of the pluto + 2.66 x 0.01]

nium isotopes in the unknown sampl

e. The effective

24°pu mass from coincidence counting, M( 2 4 0)eff, and = 10.0/0.259 the individual masses of the spontaneously fissioning plutonium isotopes are related by: = 38.6 grams M( 2 4 0)eff = M(240) + 1.64M(242) To obtain the value of the variance of the M(total Pu) result, we must propagate the variances of the

+ 2.66M(238) (1) M( 2 4 0)eff and the isotopic weight fractions. Let the variance in M( 24 0)eff = cieff, and let the variances The masses of the 2 4 2 Pu and 2 3 8 pU isotopes can be in the relevant plutonium weight fractions be G238'

"expressed in terms of M(240), using the isotopic weight 2

0240'2j and G:42.

4 The variance of the total plutonium fractions, so that: mass, apu, is given by:

M( 2 4 0)eff = M(240)[f 2 40 + 1.64f 2 4 2 2 = [M(total Pu)] 2 {[ Oeff/M( 2 4 0)eff] 2

+ 2.66f 2 3 8 1/f 240 (2) + [ 242 + (1.6 4 24 )2 + (2.660238)]/

S Since M(240)/f 2 4 0 = M(total Pu), we have the final [f240 + 1.64f 2 4 2 + 2.66f 2 38 ] 2} (5)

results:

0

In our example calculation, eff = 0.5 gram, 02ý8 =

24 0.005, 0240 = 0.004, and 0242 = 0.002. The variance M(total Pu) = M( 0)eff/[f 2 4 o + 1.64f 24 2 in the total plutonium mass is therefore given by:

+ 2.66f 2 3 8 ] (3) 2 = IM(total Pu)]2 [(0.5/10.0)2 The quantity in the denominator of Equation 3 is called the " 2 40 Pu effective weight fraction, f 2 4 0 (effect + 0.000204/(0.259)2 ]

ive)." Thus the total plutonium mass can be expressed as the 2 4 0 Pu effective mass divided by the 2 4 0 pu 0

Pu = M(total Pu) [(0.5/10.0)2 effective weight fraction:

+ 0.000204/(0.259)2] 1/2 M(total Pu) = M(240)eff/f 2 4 o(effective) (4)

= 38.6 x 0.074 As an example, suppose that the net coincidence count from an unknown sample indicates 10.0 +/- 0.5 = 2.9 grams effective grams of 2 4 0 Pu. Furthermore, suppose that the plutonium isotopic composition of the unknown Thus the final assay result from this coincidence count sample was previously established to be: is quoted as:

f238 = (1.0 +/- 0.5)% = 0.010 +/- 0.005 M(total Pu) = 38.6 +/- 2.9 grams.

f239 = (73.0 +/- 0.5)% For most plutonium samples, the dominant measure ment uncertainties will be in the 2 4 °pu effective mass f240 = (20.0 +/- 0.4)% = 0.200 +/- 0.004 and the 2 4 0 pU isotopic weight fraction, f24 0 . Thus good precision in M(total Pu) is achieved primarily through f241 = (4.0 +/- 0.2)% minimizing the uncertainties in these quantities.

5.34-7

VALUE/IMPACT STATEMENT -V

1. PROPOSED ACTION 1.3.3 Industry

1.1 Description Since industry is already applying the techniques discussed in the guide, updating these techniques should Licensees authorized to possess at any one time have no adverse impact.

more than one effective kilogram of plutonium are required in § 70.51 of 10 CFR Part 70, "Domestic 1.3.4 Public Licensing of Special Nuclear Material," to establish and maintain a system of control and accountability so No impact on the public can be foreseen.

that the standard error (estimator) associated with the inventory difference (SEID) ascertained as a result of a 1.4 Decision on Proposed Action measured material balance meets minimum standards.

The guide should be revised to reflect improvements Included in a typical material balance are containers in the technique and to bring the language of the of inhomogeneous scrap material that are not amenable guide into conformity with current usage.

to assay by the traditional method of sampling and chemical analysis. With proper controls, the nondestruc

2. TECHNICAL APPROACH

tive assay (NDA) technique of spontaneous fission detection is one acceptable method for the assay of Not applicable.

plutonium in containers of bulk scrap material. The use of spontaneous fission detection thus facilitates the

3. PROCEDURAL APPROACH

preparation of a complete plant material balance whose SEID meets established requirements. Of the procedural alternatives considered, revision of the existing regulatory guide was selected as the most advantageous and cost effective.

Regulatory Guide 5.34 was issued in June 1974 to describe procedures acceptable to the NRC staff for 4. STATUTORY CONSIDERATIONS

applying the NDA technique of spontaneous fission detection to plutonium in scrap. 4.1 NRC Authority Authority for this guide is derived from the safety

1.2 Need for Proposed Action requirements of the Atomic Energy Act through the Commission's regulations, in particular, § 70.51 of Improvements in technology have occurred since 10 CFR Part 70.

Regulatory Guide 5.34 was issued, and the proposed action is needed to bring it up to date. 4.2 Need for NEPA Assessment The proposed action is not a major action that may

1.3 Value/Impact of Proposed Action significantly affect the quality of the human environ ment and does not require an environmental impact

1.3.1 NRC Operations statement.

The improvements in technology that have occurred 5. RELATIONSHIP TO OTHER EXISTING OR

since the guide was issued will be made available for PROPOSED REGULATIONS OR POLICIES

the regulatory procedure. Using these updated tech The proposed action is one of a series of revisions niques should have no adverse impact.

of existing regulatory guides on NDA techniques.

1.3.2 Other Government Agencies 6. SUMMARY AND CONCLUSIONS

Not applicable. Regulatory Guide 5.34 should be updated.

5.34-8

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