Regulatory Guide 5.11

(Task SG 043-4), Revision 1, Nondestructive Assay of Special Nuclear Material Contained in Scrap and Waste

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Issue date:	04/30/1984
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Reg Guide 5.11, Rev 1, SG 043-4
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Revision 1*

U.S. NUCLEAR REGULATORY COMMISSION April 1984 REGULATORY GUIDE

OFFICE OF NUCLEAR REGULATORY RESEARCH

REGULATORY GUIDE 5.11 (Task SG 0434)

NONDESTRUCTIVE ASSAY OF SPECIAL NUCLEAR MATERIAL

CONTAINED IN SCRAP AND WASTE

I

A. INTRODUCTION

as absorption-edge densitometry and X-ray resonance fluorescence determine the elemental SNM concentration Section 70.5 1, "Material Balance, Inventory, and Records rather than the presence of specific isotopes. If isotopic Requirements," 10 CFR Part 70, "Domestic Licensing of radiation is measured, the isotopic composition of the Special Nuclear Material," requires licensees authorized material must be known or determined to permit a to possess at any one time more than one effective conversion of the amount of isotope measured to the kilogram of special nuclear material (SNM) to establish amount of element present in the container. Assays are and maintain a system of control and accountability to performed by isolating the container of interest to ensure that the standard error (estimator) of any inven permit a measurement of its contents through a compar tory difference (ID) ascertained as a result of a measured ison with the response observed from known calibration material balance meets established minimum standards. standards. This technology permits quantitative assays of The selection and proper application of an adequate the SNM content of heterogeneous materials in short measurement method for each of the material forms in measurement times without sample preparation and the fuel cycle is essential for the maintenance of these .without affecting the form of the material to be assayed.

standards. The proper application of this technology requires the understanding and control of factors influencing NDA

For some material categories, particularly scrap and measurements.

> waste, nondestructive assay (NDA) is the only practical, and sometimes the most accurate, means for measuring 1.1 Passive NDA Techniques SNM content. This guide details procedures acceptable to the NRC staff to provide a framework for the use of Passive NDA is based on observing spontaneously NDA in the measurement of scrap and waste components emitted radiations created through the radioactive decay generated in conjunction with the processing of SNM. of plutonium or uranium isotopes or of their radioactive Other guides detail procedures specific to the application daughters. Radiations attributable to alpha (a) particle of a selected technique to a particular problem. decay, to gamma ray transitions following a and beta

(8) particle decay, and to spontaneous fission have served Any guidance in this document related to information as the basis for practical passive NDA measurements.

collection activities has been cleared under OMB Clearance No. 3150-0009. 1.1.1 NDA Techniques Based on Alpha ParticleDecay

B. DISCUSSION

• Alpha particle decay is indirectly detected using calo rimetry measurements. (Note that additional contributions

1. APPLICABLE NDA PRINCIPLES are attributable to the (%decay of 2 4 1 Am and the $decay of 2 4 1 pu in plutonium calorimetry applications.) The The NDA of the SNM content of heterogeneous kinetic energy of the emitted a particle and the recoiling material forms is usually achieved through observing daughter nucleus is transformed into heat, together with either stimulated or spontaneously occurring radiations some fraction of the gamma ray energies that may be emitted from the isotopes of either plutonium or ura nium, from their radioactive decay products, or from The substantial number of changes in this revision has made some combination thereof. Some NDA techniques such it Impractical to indicate the changes with lines In the margin.

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emitted by the excited daughter nucleus in lowering its (Ref. 7) sources of stimulating radiation have been inves energy to a more stable nuclear configuration. The calor tigated. For a thorough discussion of active NDA tech imetric measurement of the heat produced by a sample niques, see Reference 10.

can be converted to the amount of a-particle-emitting nuclides present through the use of the isotopic abundance Stimulation with accelerator-generated high-energy and the specific power (W/g-s) of each nuclide (Refs. 1-3). neutrons or gamma rays is normally considered only Plutonium, because of the relatively high specific powers after all other NDA methods have been evaluated and of 2 3 8 pu and 2 4 0 pu, is amenable to assay by calorimetry, found to be inadequate. Operational requirements, with

241Am" possible complication from the presence of a-active including operator qualifications, maintenance, radiation shielding, and calibration considerations, normally require an inordinate level of support in comparison to the Another technique based on a decay involves the benefits of in-plant application.

interaction of high-energy a particles with some light nuclides (e.g., 7 Li, 9 Be, 1 0 B, 180, and 19 F) that may

2 3 3Neutron

2 35 bombardment

239 readily induces fissions of produce a neutron through an (a,n) reaction (Ref. 4). U, u, PU, and 2 4 1 Pu. Active NDA systems When the isotopic composition of the a-particle-emitting have been developed using spontaneous fission ( 2Cf)

nuclides is known and the content of high-yield (a,n) neutron sources, as well as (y,n) (Sb-Be) sources and a targets is fixed, the observation of the neutron yield variety of (a,n) (Am-Li, Pu-Li, Pu-Be) sources (Refs. 8, from a sample can be converted to the amount of SNM 9). Active techniques rely on one of the following three present. properties of the induced fission radiation to distinguish the induced radiation from the background and the

1.1.2 NDA Techniques Based on Gamma Ray Analysis stimulating radiation:

The gamma ray transitions that reduce the excitation "* High-energy radiation (neutrons with about 2 MeV

of a daughter nucleus following either a- or 0-particle energy and gamma rays with 1-2 MeV energy)

emission from an isotope of SNM occur at discrete energies (Refs. 5, 6). The known a- or 0-particle-decay "* Coincident radiation (simultaneous emission of two activity of the SNM parent isotope and the probability or more neutrons and about seven to eight gamma that a specific gamma ray will be emitted following the rays)

a- or 0-particle decay can be used to convert the measure ment of that gamma ray to a measurement of the amount "

of the SNM parent isotope present in the container being Delayed radiation (neutrons emitted from certain fission products with half-lives ranging from 0.2 to K

measured. High-resolution gamma ray spectroscopy is 50 seconds and gamma rays emitted from fission required when the gamma rays being measured are observed products with half-lives ranging from submicro in the presence -of other gamma rays or X-rays that, seconds to years. The usable delayed gamma rays without being resolved, would interfere with the measure are emitted from fission products with half-lives ment of the desired gamma ray (Ref. 5). similar to those of delayed-neutron-emitting fission products.)

1.1.3 NDA Techniques Based on Spontaneous Fission Examples of the use of these properties with the A fission event is accompanied by the emission of an types of isotopic neutron sources listed above are average of 2 to 3.5 neutrons (depending on the parent (1) fissions are induced by low-energy neutrons from a nucleus) and an average of about 7.5 gamma rays. A 124Sb-Be source, and energetic fission neutrons are total of about 200 MeV of energy is released,, distributed counted (Refs. 9, II); (2) fissions are induced by an among the fission fragments, neutrons, gamma rays, $ intense 2 5 2 Cf source, and delayed neutrons are counted particles, and neutrinos. Spontaneous fission occurs with after the source has been withdrawn (Refs. 9, 12-14);

sufficient frequency in 2 3 8Pu, 2 4 0 pu, 2 4 2 pU, and mar and (3) fissions are induced by single emitted neutrons ginally in 2 S Uto facilitate assay measurements through from an (a,n) source (Refs. 9, 15). Coincident gamma the observation of this reaction. Systems requiring the rays and neutrons resulting from the induced fission are coincident observation of two or more of the prompt counted by means of electronic timing gates (of less radiations associated with the spontaneous fission event than 100 microseconds duration) that discriminate against provide the basis for available measurement systems noncoincident events (Refs. 9, 13).

(Ref. 7).

2. FACTORS AFFECTING THE RESPONSE OF NDA

1.2 Active NDA Techniques SYSTEMS

Most active NDA is based on the observation of Regardless of the technique selected, the observed

/

radiations (gamma rays or neutrons) that are emitted NDA response depends on (1) the operational character from the isotope under investigation when that iso istics of the system, (2) the isotopic composition of the tope undergoes a transformation resulting from an interac SNM, (3) the amount and distribution of SNM, (4) the tion with stimulating radiation provided by an appropriate amount and distribution of other materials within the external source. Isotopic (Refa. 8, 9) and accelerator container, and (5) the composition and dimensions of

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the container itself. Each of these variables increases the The sensitivity to background radiations can be moni overall uncertainty associated with an NDA measurement. tored and controlled through proper location of the system and the utilization of radiation shielding, if The observed NDA response represents contributions required.

from the different SNM isotopes present in the container.

To determine the amount of SNM present, the isotopic 2.1.2 Uniform Detection Efficiency composition of the SNM must be known (except for cases in which the NDA system measures the isotopic For those NDA systems for which the sample or composition) and the variation in the observed response item to be counted is placed within a detection chamber, as a function of varying isotopic composition must be if the response throughout the detection chamber is not understood. The effects due to items(3), (4), and (5) uniform, positioning guides or holders may be utilized on the observed response can be reduced through to ensure consistent (reproducible) sample or item posi appropriate selection of containers, compatible segrega tioning. The residual geometric response dependence can tion of scrap and waste categories, and consistent use of be measured using an appropriate source that emits packaging procedures designed to improve the uniformity radiation of the type being measured. If the source is of container loadings. small with respect to the dimensions of the detection chamber, the system response can be measured with the

2.1 Operational Characteristics source positioned in different locations to determine the volume of the detection chamber that can be reliably The operational characteristics of the NDA system, used.

together with the ability of the system to resolve the desired response from a composite signal, determine the An encapsulated plutonium source can be used to ultimate usefulness of the system. These operational test gamma ray spectroscopic systems, active or passive characteristics include (I)operational stability, (2)uniform NDA systems detecting neutrons or gamma rays, or detection efficiency, (3)stimulating radiation uniformity calorimetry systems. Active NDA systems can be operated (for active systems), and (4)energy of the stimulating in a passive mode (stimulating source removed) to radiation. evaluate the magnitude of this effect. Rotating and scanning containers during assay is a recommended The impact of these operational characteristics on the means of reducing the response uncertainties attributable uncertainty of the measured response can be reduced to residual nonuniform geometric detection sensitivity.

through the design of the system, the use of radiation shielding (where required), and standardized packaging 2.1.3 Uniformity of StimulatingRadiation and handling (as discussed below and in Reference 16).

The stimulating radiation field (i.e., interrogating

2.1.1 OperationalStability neutron or gamma ray flux) in active NDA systems is designed to be uniform in intensity and energy spectrum The ability of an NDA system to reproduce a given throughout the volume of the irradiation chamber. The measurement may be sensitive to fluctuations in the residual effect can be measured using an SNM sample operational environment. Temperature, humidity, line that is small with respect to the dimensions of the voltage variations, electromagnetic fields, and microphonics irradiation chamber. The response can then be measured affect NDA systems to some extent. These effects may with the SNM sample positioned in different locations be manifested through the introduction of spurious within the irradiation chamber. If the same chamber is electronic noise or changes in the high voltage applied employed for irradiation and detection, a single test for to detectors or amplifiers, thereby changing the detec the combined geometric nonuniformity is recommended.

tion efficiency. To the extent that it is possible, a measurement technique and the hardware to implement Having both a uniform detection efficiency and a that technique are selected to be insensitive to changes uniform stimulating radiation field is the most direct routinely expected in the operational environment. approach and the recommended approach to obtaining a Accordingly, the instrument is designed to minimize uniform response for the combined effects. However, it environmental effects by placing components that operate is possible in some cases either to tailor the stimulating at high voltages in hermetically sealed enclosures and radiation field to compensate for deficiencies in the shielding sensitive components from spurious noise detection uniformity or, conversely, to tailor the detection pickup. In addition, electronic gain stabilization of the efficiency to compensate for deficiencies in the stimulat pulse-processing electronics may be advisable. As a final ing radiation field. An example of this combined approach measure, the instrument .environment can be controlled is the use of interrogating sources on one side of the (e.g., through the use of a dedicated environmental sample and placement of detectors on the other. A

enclosure for the instrument hardware) if expected environ combined uniform response in this example relies both mental fluctuations result in severe NDA response varia on material closer to the stimulating radiation source tions that cannot be eliminated through calibration having a higher fission probability but a lower induced and operational procedures. radiation detection probability and on material closer to

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the detector having a lower stimulated fission probability products that emit prolific and energetic gamma rays. It but a higher induced-fission radiation detection probability. should be noted that one of these daughter products is

228 This type of approach may be necessary when there are Th, and therefore the daughter products of 2 3 2 U

spatial constraints. When the measurement system is and 2 3 2 Th are identical beyond 2 28 Th.

optimized for these combined effects, a passive measure ment with such a system will have a greater uncertainty 2.2.2 Multiple Spontaneously FissioningPlutonium than would be obtained with a system having a uniform Isotopes detection efficiency.

In addition to the spontaneous fission observed from

240

Various methods have been used to reduce the response pu, the minor isotopes 2 3 8Pu and 2 4 2 pu typically uncertainty attributable to a nonuniform stimulating contribute a few percent to the total neutron rate observed radiation field, including rotating and scanning the con (Refs. 17-19). In mixtures of uranium and plutonium tainer, source scanning, distributed sources, and combina blended for reactor fuel applications, the spontaneous tions of these methods. fission yield from 2 3 8 U may approach one percent of the 2 4 °pu yield.

2.1.4 Energy of StimulatingRadiation

2.2.3 Multiple FissileIsotopes If the energy of the stimulating radiation is as high as practicable but below the threshold of any interfering In active systems, the observed fission response may reactions such as the neutron-induced fission in 2 3 8 U, consist of contributions from more than one isotope.

the penetration of the stimulating radiation will be For uranium, if the energy spectrum of the stimulating enhanced throughout the volume of the irradiation radiation extends above the threshold for 2 3 8 U fission, chamber. A high-energy source providing neutrons above that response contribution will be in addition to the the energy of the fission threshold for a fertile constituent induced 235U fission response.

such as 2 38 U or 2 3 2 Th can be employed to assay the fertile content of a container. In plutonium, the observed 'response will be the sum of contributions from the variable content of 2 3 9 pU and The presence of extraneous materials, particularly 241pu, with small contributions from the even plutonium those of low atomic number, lowers the energy spectrum isotopes.

of the interrogating neutron flux in active neutron NDA

systems. Incorporating a thermal neutron detector to When elements (e.g., plutonium and uranium) are monitor this effect and thereby provide a basis for a correction to reduce the response uncertainty caused by mixed for reactor utilization, the uncertainty in the K

response is compounded by introducing additional fissile this variable effect is recommended. components in variable combinations.

Active neutron NDA systems with the capability to moderate the interrogating neutron spectrum can provide 2.3 Response Dependence on Amount and Distribution of increased assay sensitivity for samples containing small SNM in a Container amounts of fissile material (<100 grams). This moderation capability should be removable to enhance the range of If a system has a geometrically uniform detection usefulness of the system. sensitivity and a uniform field of stimulating radiation (where applicable), a variation in the response per gram

2.2 Response Dependence on SNM Isotopic Composition of the isotope or isotopes being measured is generally attributable to one of the three causes described below.

The observed NDA response may be a composite of contributions from more than a single isotope of uranium 2.3.1 Self-Absorption of the Emitted Radiation Within or plutonium. Observed effects are generally attributable the SNM

to one of the three sources described below.

For a fixed amount of SNM, in a container, the

2.2.1 Multiple Gamma Ray Sources probability that radiation emitted by the SNM nuclei will interact with other SNM atoms increases as the Plutonium contains the isotopes 2 38 p.u through 2 4 2 pu localized density of the SNM increases within the in varying quantities. With the exception of 2 4 2 pu, these container. This is a primary source of uncertainty in isotopes emit many gamma rays (Refs. 5, 6). The observed gamma ray spectroscopy applications. It becomes increas plutonium gamma ray spectrum represents the contribu ingly important as the SNM aggregates into lumps and is tion of all gamma rays from each isotope, together with more pronounced for low-energy gamma rays.

the gamma rays emitted in the decay of 2 4 1 Am, which may also be present. 2.3.2 Multiplication of the Detected Radiation Gamma rays from 2 3 3 U and 2 3 SU are generally lower The neutrons given off in either a spontaneous or an in energy than those from 2 3 9Pu. However, 232U, which induced fission reaction can be absorbed in a fissile occurs in combination with 233U, has a series of daughter nucleus and subsequently induce that nucleus to fission,

5.11-4

resulting in the emission of two or more neutrons. called moderation. Low-atomic-weight elements have Multiplication affects the response of active NDA systems, greater moderating power than high-atomic-weight ele passive coincidence neutron or gamma ray detection ments and therefore reduce energetic neutrons to thermal systems (used to detect spontaneous fission), and passive energies with fewer collisions. Hydrogen has the greatest neutron systems used to count (a,n) neutrons. Multipli moderating power. Hydrogenous materials such as water cation becomes increasingly pronounced as the energy of or plastics have a strong moderating power because the neutrons traversing the container becomes lower or of their hydrogen content.

as the density of SNM increases within the container.

'For further details on multiplication effects, see Refer Low-energy neutrons have interaction characteristics ences 20 and 21. different from high-energy neutrons. If moderation of the stimulating neutron radiation occurs, the response

2.3.3 Self-Shielding of the StimulatingRadiation will be altered and the assay value could be in error.

Three effects arise from moderated neutrons. First, the Attenuation of incident radiation by the SNM, or fission probability for fissile isotopes increases with self-shielding, is particularly pronounced in active systems decreasing neutron energy. In this case, the response incorporating a neutron source to stimulate the fissile increases and, correspondingly, so does self-shielding.

isotopes of the SNM to fission. More of the incident Second, absorption by materials other than SNM also low-energy neutrons will be absorbed near the surface of increases. This absorption decreases the response of the a high-density lump of SNM, and fewer will penetrate system. Third, if isotopes with a fission threshold such deeper into the lump. Thus, the fissile nuclei located as 232Th or 238U are being assayed with high-energy deep in the lump will not be stimulated to fission at neutrons, moderation can lower the energy of the the same rate as the fissile nuclei located near the stimulating neutrons below the fission threshold. In this surface, and a low assay content will be indicated. This case, the response by these isotopes can be sharply effect is dependent on the energy spectrum of the reduced.

incident neutrons and the density of fissile nuclei It becomes increasingly pronounced as the energy of the Efforts to minimize moderation effects are particularly incident neutrons is decreased or as the density of the important if energetic neutrons are employed for the SNM fissile content is increased. The density of fissile stimulating radiation. Segregation of waste categories nuclei is increased when the SNM is lumped in aggregates according to their moderating characteristics and use of or when the fissile enrichment of the SNM is increased. separate calibrations for each category are direct steps to minimize moderation effects. Another step that can

2.4 Response Dependence on Amount and Distribution of be used with segregation, and sometimes independently, Extraneous Materials Within the Container is to monitor the stimulating neutron radiation and then correct the assay result. Because several effects are asso The presence of materials other than SNM within a ciated with moderation, this latter step may be difficult container can affect the emitted radiations in passive to implement. In some cases, it may be impossible.

and active NDA systems and can also affect the stimulat ing radiation in active assay systems. The presence of 2.4.3 Attenuation of the Emitted Radiation extraneoui materials can result in either an increase or a decrease in the observed response. Attenuation may range from partial energy loss of the emitted radiation (through scattering processes) to Effects on the observed NDA response are generally complete absorption of the radiation by the sample attributable to one of the four causes described below. material. This effect can be particularly severe for gamma ray assay systems; unless gamma ray attenuation

2.4.1 InterferingRadiations is fully accounted for by measurement or calculation, the assay value assigned to an unknown sample may be Interference arises when the material being assayed underestimated (Refs. 4, 22). The attenuation of gamma emits radiation that cannot be separated easily from the radiation increases with atomic number and material signal of interest. This problem is generally encountered density within the container. Also, systems that detect in gamma ray spectroscopy and calorimetry applications. emitted neutrons above a given energy (threshold) will In gamma ray assays, the problem is manifest in the observe fewer neutrons above the detection threshold form of additional gamma rays that must be separated when low-atomic-number (ie., highly moderating) mate from the desired radiations, often with high-resolution rial is added to the container and will thus produce a detection systems. In calorimetry, the decay daughters low assay.

of 2 4 1 pu, 2 3 8 U, and 2 3 2 U contribute additional heat that cannot be corrected for without detailed knowledge The attenuation of the emitted radiation may be of the isotopic composition of the sample. complete, as in the case of the absorption of neutrons in the nuclei of extraneous materia

l. The probability for

2.4.2 Interference to Stimulating Radiation this absorption generally increases as the energy of the incident neutron decreases. Hence, this effect is further Material lowers the energy of neutrons through colli aggravated when low-atomic-number materials are present sion processes. This lowering of the neutron energy is to reduce the energy of the emitted neutrons.

s.1i-5

2.4.4 Attenuation of the Stimulating Radiation uniform response from a lump of SNM positioned any where within a container. With increasing container size, This phenomenon is similar to the phenomenon of it becomes increasingly difficult to satisfy this criterion the preceding section. In this instance, some portion of and maintain a compact geometrically efficient system.

the stimulating radiation does not penetrate to the SNM For this reason, the assay of small-size containers is within the container and thus does not have the oppor recommended for the highest accuracy.

tunity to induce fission. The presence of neutron poisons (e.g., lithium, boron, cadmium, gadolinium) may atten If small containers are to be loaded into larger con uate the stimulating radiation to the extent that the tainers for storage or offsite shipment following assay, response is independent of the SNM fissile content. the size and shape of the inner and outer containers Most materials absorb neutrons. The severity of this should be chosen to be compatible.

absorption effect is dependent on the type of material, its distribution, the energy of the stimulating neutrons, Packaging in small containers will produce more and the relative neutron absorbing strength of the SNM containers to be assayed for the same scrap, and waste compared to the combined effect of the remaining generation rates. An offsetting benefit, however, is that material. the assay accuracy of an individual container should be significantly improved over that of large containers.

The presence of extraneous material can thus alter the observed response, providing either a high or a low 2.5.2 ContainerStructuralComposition SNM content indication. This effect is further aggravated by nonuniformity within the container of either the The structural composition of containers will affect SNM or the matrix in which it is contained. This the penetration of the incident or the emerging radia dependence of response on material distributions and tion. Provided all containers are uniform, their effect on matrix variations is severe. Failure to attend to its the observed response can be factored into the calibration ramifications through the segregation of scrap and waste of the system. The attainable assay accuracy will be categories and the utilization of representative1 calibra reduced when containers with poor penetrability or tion standards may produce gross inaccuracies in NDA varying composition or dimensions are selected.

measurements.

Uniform containers of the same composition, dimen

2.5 Response Dependence on Container Dimensions and sions, and wall thickness provide improved or best accuracy Composition (for a given material category). Variability in the wall thickness of nonhydrogenous containers usually is not The items identified as potential sources of uncertainty critical for neutron assays, but it can be a significant 11 in the observed response of an NDA system in Sections 2.1, factor for gamma spectroscopy applications when the

2.3, ý and 2.4 can be minimized or aggravated through container is constructed of relatively high-density mate the selection of containers to be employed when assaying rial or when low-energy (less than approximately 200-keV)

SNM contained in scrap or waste. gamma rays are being measured. However, when hydrog enous materials (such as polyethylene) are used in con

2.5.1 ContainerDimensions tainers, wall thickness variability can have a significant effect on neutron assay results.

The practical limitation on container size for scrap and waste to be nondestructively assayed represents a 3. NDA FOR SNM CONTAINED IN SCRAP AND

compromise of throughput requirements and the increas WASTE

ing uncertainties in the observed NDA response incurred as a penalty for assaying large containers. Radiations 3.1 NDA Performance Objectives emitted deep within the container must travel a greater distance to escape the confines of the container. There The measurement accuracy objectives for any material fore, with increasing container size, the probability that balance component can be estimated by considering the radiations emitted near the center of the container will amount of material typically contained in that component.

escape the container to the detectors decreases with The measurement performance required is such that, respect to the radiations emitted near the surface of the when the uncertainty corresponding to the scrap and container. This will result in large attenuation corrections waste material balance component is combined with the that can cause added uncertainty in the assay result. uncertainties corresponding to the other material compo nents, the constraints on the total standard error of the In active neutron NDA systems, a relatively uniform inventory difference (SEID) will be satisfied.

field of stimulating radiation must be provided through out the volume of the container that is observed by the 3.2 NDA Technique Selection detection system. This criterion is required to obtain a Factors that influence .NDA technique selection are IThe term "representative" is taken to mean representative the accuracy requirements for the assay and the type with respect to attenuation, moderation, multiplication, density, and range of scrap and waste categories to be encountered.

and any other properties to which the measurement technique is sensitive. No single technique appears capable of meeting all

5.11-6

requirements. When more than one type of information loadings, a well-moderated interrogating spectrum can be is required to separate a composite response, more than used to take advantage of the increased 2 3SU fission one NDA technique may be required to provide that probability for neutrons of low energy. In highly enriched information. uranium scrap . and waste (>20% 3 5 U), active NDA

featuring a high-energy stimulating neutron flux is

3.2.1 Plutonium Applications recommended.

The 185-keV transition observed in the decay of Calorimetry determinations are the least sensitive to

23SU is frequently employed in uranium applications.

matrix effects but rely on a detailed knowledge of the

241Am content and the plutonium isotopic composition The penetration of this 2 3 5U primary gamma ray is so to calculate grams of plutonium from the measured heat poor that the gamma ray NDA technique is not appli flux (Ref. 1). In addition, a calorimetry measurement cable with high-density nonhomogeneous materials in usually requires several hours in order to achieve or to large containers.

carefully predict thermal equilibrium.

Occasions arise when a passive enrichment determina Gamma ray spectroscopy systems complement the tion is practical through the measurement of the 185-keV

potential of other assay methods by providing the gamma ray. Enrichment assay applications for uranium capability

24 1 to verify or determine nondestructively the are the subject of Regulatory Guide 5.21, "Nondestruc Am content and the plutonium isotopic composition tive Uranium-235 Enrichment Assay by Gamma Ray (except 2 4 2 Pu). High-resolution gamma ray systems are Spectrometry."

capable of extracting the maximum amount of informa tion (elemental content, isotopic distributions, presence Calorimetry is not applicable to the assay of uranium of extraneous gamma ray sources) from an assay, but because of the low specific a activity. In 2 3 3 U applica content density severely affects the accuracy of quantita tions, the intense activity of the daughter products of tive predictions based on that assay method in large 232U imposes a severe complication on the use of calo samples. rimetry.

Passive coincidence detection of the spontaneous 3.3 Categorization and Segregation of Scrap and Waste for fission yield of plutonium-bearing systems provides an NDA

indication of the combined 238pu, 2 4 0pu, and 2 4 2 pu sample content. With known isotopic composition, the The range of variations in the observed response of plutonium content can be computed (Ref. 17 and an NDA system attributable to the effects noted in Sec Regulatory Guide 5.342). Neutron multiplication effects tions 2.3 and 2.4 can be reduced or controlled. Following become severe at high plutonium sample loadings an analysis of the types of scrap and waste generated in (Refs. 20, 21). conjunction with SNM processing, a plan to segregate scrap and waste at the generation points can be formu Combining passive and active measurements in a lated. Recovery or disposal compatibility is important in single system is a valuable approach for plutonium determining the limits of each category. Limiting the assay. Plastic scintillation coincidence detection systems variability of those extraneous NDA interference param have been designed in conjunction with active neutron eters discussed in Sections 2.3 and 2.4 is a primary interrogation source systems (Ref. 23). Delayed neutron means of improving the accuracy of the scrap and waste counting systems have an inherent active-passive counting assay. Once the categories are established, it is important capability (Refs. 9, 13, 14). Operated in passive and that steps be taken to ensure that segregation into active modes, such systems are able to provide an assay separate uniquely identified containers occurs at the of both the spontaneously fissioning content and the generation point.

fissile content of the sample. The spontaneous fission and (ca,n) backgrounds can be subtracted from an active NDA Category limits can be established on the basis of response to provide a yield attributable to the fissile measured variations observed in the NDA response of a SNM content of the container. container loaded with a known amount of SNM. The variation in extraneous parameters can then be mocked

3.2.2 Uranium Applications up and the resultant effect measured. In establishing categories, the following specific items are significant Active neutron systems can provide both high-energy sources of error.

and moderated interrogation spectra. Operation with the high-energy neutron source will decrease the density dependence and neutron self-shielding effects, significantly 3.3.1 Calorimetry enhancing the' uniqueness of the observed response. To extend the applicability of such a system to small fissile The presence of extraneous materials capable of

2 Regulatory Guide 5.34, "Nondestructive Assay for Plutonium absorbing heat (endothermic) or emitting heat (exothermic)

in Scrap Material by Spontaneous Fission Detection." A proposed will cause the observed response to be different from revision to this guide hasbeen Issued for comment as Task SG 046-4. the correct response for the plutonium in the sample.

5.11-7

3.3.2 Neutron Measurements order of decreasing probability of absorption of thermal neutrons. An estimate of the significance of the presence The presence of high-yield (a,n) target material will of one of these materials may be obtained from the increase the number of neutrons present in the sample. ratio of its absorption cross section to the absorption A fraction of these neutrons will induce fission in the cross section of the SNM present in the container:

fissile SNM isotopes and add another source of error to the measurement. These multiplication and self multiplication effects are discussed thoroughly in Refer R = Ni aa1 ences 4, 20, and 2

1. NSNM aaSNM

3.3.3 Gamma Ray Measurements where Gamma rays are severely attenuated in interactions with heavy materials. Mixing contaminated combustibles N1 the number of atoms per cubic centi with heavy, dense materials complicates the attenuation meter of material problem. Mixing of isotopic batches, mixing with radio active materials other than SNM, or lumps of SNM can absorption cross section of the extra also add to the complexity of the response. neous material (Table 1)

3.3.4 Fission Measurements NSNM f number of atoms of SNM present per cubic centimeter Scrap or waste having low-atomic-number materials will reduce the energy of the neutrons present in the container, which will significantly affect the probability aaSNM f absorption cross section of the SNM

(includes both fission and neutron of stimulating fission reactions. capture processes). Thermal neutron absorption cross sections for the follow Neutron-absorbing materials present in SNM scrap or ing

2 3 3 SNM isotopes 2 3of interest are:

waste may significantly affect the operation of NDA U, 537 barns; 'U, 678 barns;

systems. Table 1 identifies neutron absorbers in the 2 39 pu, 1015 barns; 1375 barns.

Table 1 NATURALLY OCCURRING NEUTRON ABSORBERS (Ref. 24)

Naturally Absorption Naturally Absorption Occurring Cross Section Occurring Cross Section Element Symbol (barns)* Element Symbol (barns)*

Gadolinium Gd 46,000 Terbium Th 46 Samarium Sm 5,600 Cobalt Co 38 Europium Eu 4,300 Ytterbium Yb 37 Cadmium Cd 2,450 Chlorine Cl 34 Dysprosium Dy 950 Cesium Cs 28 Boron B 755 Scandium Sc 24 Actinium Ac 510 Tantalum Ta 21 Iridium Ir 440 Radium Ra 20

Mercury Hg 380 Tungsten W 19 Protactinium Pa 200 Osmium Os 15 Indium In 191 Manganese Mn 13 Erbium Er 173 Selenium Se 12 Rhodium Rh 149 Praseodymium Pr 11 Thulium Tm 127 Lanthanum La 9 Lutetium Lu 112 Thorium Th 8 Hafnium Hf 105 Iodine I 7 Rhenium Re 86 Antimony Sb 6 Lithium Li 71 Vanadium -V 5 Holmium Ho 65 Tellurium Te 5 Neodymium Nd 46 Nickel Ni 5

• Cross section for thermal neutrons.

5.11-8

The magnitude of this effect is dependent on the the use of suitable auxiliary measurements. Calibration distribution of the materials and the energy of the neutrons by comparison of NDA and destructive analyses on present within the container. The relationship above is a randomly selected actual samples may be useful in cases

• gross approximation. For convenience in calculation, when well-characterized standards are not available or

- including only the primary fissile isotope is sufficient to are not practical for the measurements involved. How determine which materials may. constitute a problem ever, in view of the potential for greater errors with this requiring separate categorization for assay. In extreme calibration method, measurements based on this tech cases, it will be necessary either to seek methods for nique should be regarded as verifications rather than as measuring the content of the neutron absorber to careful quantitative assays.

provide a correction for the NDA response or to seek a different method for assay of that category. The relative difficulty in implementing one calibration scheme over the other depends on the type of facility

3.4 Packaging for NDA and available personnel. A steady operation with perhaps some initial set-up assistance might favor the correction NDA provides optimal accuracy when the packages to factor approach because only one calibration is used.

be assayed are essentially identical and when the calibra Often additional material categories can be assayed tion standards represent those packages in content and without preparing additional calibration standards. The form. Containers for most scrap and waste can be separate calibration scheme might be favored by facilities loaded using procedures that will enhance the uniformity that have well-characterized categories. A separate calibra of the loading within each container and from container tion is made for each category without the need for to container. For further discussion and recommendations establishing relationships among the categories.

on container standardization, see Reference 16.

The calibration of radiometric NDA systems is the

3.5 Calibration of NDA Systems for Scrap and Waste subject of Regulatory Guide5.53, "Qualification, Calibra tion, and Error Estimation Methods for Nondestructive To obtain an assay value on SNM in a container of Assay," which endorses ANSI N15.20-1975, "Guide to

3 scrap or waste with an associated standard error, the Calibrating Nondestructive Assay Systems."

observed NDA response or the predicted content must be corrected for background and for significant effects

C. REGULATORY POSITION

attributable to the factors described in the preceding parts of this discussion. Several approaches are available In the development of an acceptable framework for to correct an assay for effects that significantly perturb the incorporation of NDA for the measurement of SNM

the assay result. The first approach is to use a separate bearing scrap and waste, strong consideration should calibration for each material category that results in a be given to technique selection, calibration, and opera different assay response. The second approach is to tional procedures; to the segregation of scrap and waste make auxiliary measurements as part of the assay. The categories; and to the selection and packaging of con assay is then corrected according to a procedure developed tainers. The guidelines presented below are generally for interpreting each auxiliary measurement. A third acceptable to the NRC staff for use in developing such possible calibration technique is one in which a random a framework that can serve to improve materials account number of containers are assayed (by the NDA method ability.

to be used) a sufficient number of times (to minimize random error) and then destructively measured (in such a way that the entire container contents are measured). 1. ORIGIN OF SCRAP AND WASTE

A calibration curve depicting the relationship between destructive assay values and NDA response can then be The origin of scrap and waste generated in conjunction derived. This approach may give rise to relatively large with SNM processing activities should be determined as errors for individual items, but it can minimize the error follows:

associated with the total SNM quantity measured by the particular NDA method. This calibration procedure can a. Identify those operations that generate SNM-bearing also be used to confirm a calibration curve derived from scrap or waste as a normal adjunct of a process.

calibration standards.

b. Identify those operations that occasionally generate Each approach has its advantages and limitations. SNM-bearing scrap or waste as the result of an abnormal Separate calibrations are appropriate when (1)the perturb operation that renders the product unacceptable for ing effects are well characterized for each category, further processing or use without treatment.

(2) there are relatively few categories, and (3) the instru ment design will not allow collection of data suitable c. Identify those scrap and waste items generated in for making corrections. A calibration with auxiliary conjunction with equipment cleanup, maintenance, or measurements for correction factors is appropriate when replacement.

(1) the perturbing effects are variable within a material 3

> category, (2) the various categories are not reliably Copies may be obtained from the American National Standards Institute, 1430 Broadway, New York, New. York segregated, and (3) the measurement method facilitates 10018.

5.11-9

The quantities of scrap and waste generated during depend on the sensitivity of the specific NDA tech normal operations in each category in terms of the total nique, as shown in Table 3.

volume and SNM content should be estimated. Bulk measurement throughput requirements should be deter The means through which these interferences are mined to ensure that such assay will not constitute an manifested are detailed in Section B. When such effects operational bottleneck. or contents are noted, separate categories should be established to isolate the materials.

4. CONTAINERS

2.1 Technique

4.1 Size Constraints The performance objectives for the NDA system should be such that, when the uncertainty corresponding Scrap and waste should be packaged for assay in to the scrap and waste material balance component is containers as small as practicable consistent with the combined with the uncertainties corresponding to the capability and sensitivity of the NDA system. Discussion other material components, the quality constraints on of container standardization and recommendations for the total standard error of the inventory difference will NDA measurements can be found in Reference 16.

be satisfied.

To enhance the penetration of stimulating or emitted Techniques should be considered for implementation radiations, containers should be cylindrical If possible, in the order of precedence established in Table 2 of this the diameter should be less than 5 inches (12.7 cm) to guide. Often, techniques within a given instrument category provide for significant loading capability, ease in loading, in Table2 will have different accuracies, lower-limit reasonable penetrability characteristics, and where appli sensitivities, costs, availabilities, and sizes. Selection cable, compatibility with criticality-safe geometry require should be based on attainable accuracy with due con ments for individual containers.

sideration of the characteristics of the scrap and waste categories as well as cost, availability, and size. Containers having an outside diameter of 4-3/8 inches

(11.1 cm) will permit 19 such containers to be arranged

2.2 System Specifications in a cross section of a 55-gallon drum, even when that drum contains a plastic liner. Containers having an NDA systems for SNM accountability should be overall length equal to some integral fraction of the designed and shielding should be provided to meet the length of a 55-gallon drum are further recommended K

following objectives: when shipment or storage within such containers is to be considered. For normal operations, an overall length a. Performance characteristics should be essentially of either 16-1/2 inches (41.9 cm) (two layers or 38 con independent of fluctuations in the ambient operational tainers per drum) or 11 inches (27.9 cm) (three layers or environment, including: 57 containers per drum) is recommended.

(1) External background radiations, Certain objectives may be inconsistent with the above

(2) Temperature, size recommendations, such as the objective to limit

(3) Humidity, and handling, reduce cost, and keep waste volume to a mini

(4) Electric power. mum. It may therefore be necessary to package scrap and waste materials in containers of sizes that exceed b. Response should be essentially independent of these recommendations, and this may result in a signifi positioning of SNM within the scrap or waste container, cant impairment in the accuracy of NDA techniques on including effects attributable to: such samples. The relative merits of various NDA tech niques with samples of different sizes are addressed in

(1) Detector geometrical efficiency and Table2. With small containers (about 2liters), an accuracy

(2) Stimulating source intensity and energy. of 2 to 5 percent is routinely obtainable; with a 55-gallon drum a lower accuracy of 15 to 30 percent is to be Techniques to achieve these objectives are discussed expected. In cases of uniformly mixed well-characterized in Section B of this guide. material, a better accuracy may be possible. On the other hand, certain combinations of adverse circumstances

3. CATEGORIZATION AND SEGREGATION can lead to a considerably worse accuracy. The potential for an adverse measurement situation is greater with a Scrap and waste categories should be developed on larger container than with a smaller container, and the the basis of NDA interference control, recovery or consequences of that situation can lead to a greater disposal compatibility (Ref. 3), and relevant safety error with larger containers. Conditions leading to considerations. Categorization for NDA interfert.nce measurement errors are discussed in Section B.2,. arid control should be directed to limiting the range of they are listed as interferences in the column headings variability in an interference. Items to be considered of Table 3.

5.11-10

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Table 2

1 NDA TECHNIQUE SELECTION GUIDELINES

23 5 Plutonium 233u > 20% 5u -C 20% u

2 20 200 2 20 200 2 20 200

Volume (liters) 2 20 200

Technique NR2 NR NR NA 2 NA NA NA

NA NA

NA NA

NA

Calorimetry Ist* 3rds 3rd NR NA NA NA

NR NR NR NR

NR

NR NR 4th NR NR

1st NR NR 4th

3rd NR NR Ist 2nd Ist 1st 2nd Gamma ray Ist 1st 1st Ist

1st 1st 3rd SC SC SC SC SC

SC SC SC SC

SC 2 SC SC SC SC Sc SC SC

Singles SC SC Sc SC

SC SC SC

neutron SC

NR NR NR SC

NA NA SC

SC SC

2nd* lst* 2nd* NA NR NR NR SC

Coincidence NA NA NA

2nd* 2nd* lst*

neutron NR NR NR

Induced fission3 NR NR 2nd 2nd NR

NR NR 4th 3rd 3rd 3rd 3rd 3rd Gamma ray 5th* 3rd 3rd 3rd

4th* 4th* 4th* 3rd

1st 1st 1st 1st 1st

1st 1st Ist 1st

4th* 2nd* lst* 2nd 2nd 1st 2nd 2nd Neutron 2nd 2nd 2nd

3rd* 3rd* 2nd* 2nd NR NR 3rd NR NR

NR NR 3rd 4th

6th* NR NR 5th 4th 4th 4th 4th Both4 4th 4th 4th 4th

5th* 5th* 5th*

The upper recommenda- for low- and high-density samples

'For each technique and type of SNM, recommendations are given for three sizes3of containers and assumed to be above 0.5 g.

0.5 g/cm ). Fissile loading is tion is for high-density waste (> 0.5 g/cm ), the lower for low-density waste (<

3

2 Abbreviations: NR - Not recommended; NA - not applicable; SC - special case, use only well-characterized materials.

3 Neutron-induced fission with methods subdivided by detected radiation.

4 Neutrons and gamma rays are detected without distinguishing between the two radiation types.

• Isotopic data required.

Table 3 QUALITATIVE ASSESSMENT OF THE SENSITIVITY OF VARIOUS NDA TECHNIQUES TO INTERFERENCES

Combined Lumped Presence of Neutron Lumped vs.

Heat-Producing Mixed High-Yield Gamma Absorbers vs. Dist

r. SNM

or Absorbing Mixed Isotopic Misc. Radiationsa (a,n) Ray Neutron Neutron and Distr. Matrix Chemical Processes SNM Batches Gamma Ray Neutron Target Mat'L Absorbers Absorbers Moderators Moderators SNM Mat'L Form Calorimetry 3 3 3 1 1 0 0 0 0 0 0 0 0

Gamma ray 0 1 1 3 1 0 3 0 0 0 3 2 0

Singles 0 3 3 1 3 3 0 1 1 3 1 0 3 neutron Coincidence 0 3 3 1 2 1 1 0 1 2 3 1 0

neutron Induced neutronb High-energy 0 3 2 1 1 1 0 1 2 3 1 0 0

(> 1 MeV)

neutron interrogation Thermal- 0 3 1 1 1 1 0 3 1 3 3 0 0

energy neutron interrogation aEffect depends on intensity of the radiation. Key: 0 - No sensitivity.

bIf gamma rays are part of the detected signal, the gamma ray liabilities are 1 - Some sensitivity. Evaluate effect in extreme cases.

in addition to those listed. 2 - Marked sensitivity. Categorize and calibrate according to magni tude of observed effect. Correction factors will be useful.

3 - Strong sensitivity. Requires tight control of material categories and correction factors. May render the technique unacceptable in some cases.

( r -C

If unusual container sizes are necessary, it is often f. Compatible with subsequent recovery, storage, and useful to employ a second measurement method in a disposal requirements, as applicable.

comparative analysis to obtain a comparison of results.

The other measurement method should be more accurate In most NDA applications, uniformity of composition and one that is not sensitive to the interferences affect is more important than the specification of a particular ing the first measurement method. For example, if the material. Table 4 gives general recommendations in order first measurement is one that measures neutrons and is of preference for container structural materials.

affected by the amount of low-atomic-weight moderating material present (which is difficult to duplicate in the Table 4 standards), the second method should be one insensitive to the amount of moderator present. Or, if uncertainty SCRAP AND WASTE

in the calibration of the first method is due to geometry CONTAINER COMPOSITION

effects, the second method should be one that is insensi tive to those effects, e.g., through subdivision of the containers. Complete ashing, dissolution, sampling, and NDA Technique Container Composition chemical and mass spectrometric analysis of waste containers constitutes a useful second measurement Calorimetry Metal (aluminum, brass)

method in some cases.

Gamma ray analysis Cardboard, polyethylene The second, more accurate measurement method bottle, thin metal should be traceable to national standards 4 and should be employed to verify the calibration relationship of the Spontaneous or Metal, cardboard, primary method. Process items should be selected at stimulated fission polyethylene bottle random from the population of items being measured. A

sufficient number of items analyzed by the first method Gross neutron Metal, cardboard, should be selected to ensure, as a minimum, that a polyethylene bottle stable estimate of the population variance is obtained. If simple linear regression is applicable, the minimum number of items selected per material balance period 4.3 Container.Identification should be 17 in order to provide 15 degrees of freedom for the standard error of estimate and test for a propor To facilitate loading and assay within the segregation tional bias (Ref. 25). categories, containers should either be color-coded or carry color-coded identification labels. Identification of If a second NDA method is employed for compara categories should be documented, and operating personnel five analysis, the container size for the second method should be instructed to ensure compliance with established analyses should be consistent with the recommendations segregation objectives.

in this guide.

4.2 Structural Features

5. PACKAGING

Containers should be selected in accordance with Containers, where practicable, should be packaged normal safety considerations and should be: with a quantity of material containing sufficient SNM to ensure that the measurement is not being made at the a. Structurally identical for all samples to be assayed extremes of the performance bounds for that system.

within each category, Packaging procedures should be consistent with relevant safety practices.

b. Structurally identical for as many categories as practicable to facilitate loading into larger containers or storage facilities, Containers should be packaged in as reproducible a manner as possible, with special attention to the main c. Uniform in wall thickness and material composition, tenance of uniform fill heights. Low-density items should be compacted to reduce bulk volume and to d. Fabricated of materials that do not significantly increase the container SNM loading. Lowering the bulk interfere with the radiations entering or leaving the volume reduces the number of containers to be assayed sample, and generally improves the assay precision.

e. Capable of being sealed to verify postassay integrity, The sample containers should be loaded with SNM as and uniformly as possible. If significant variability in the distribution of container contents is suspected, rotating or scanning the container during assay will aid in improv

4 See Regulatory Guide 5.58, "Considerations for Establishing ing the accuracy of many NDA methods. An example Traceability of Special Nuclear Material Accounting Measurements." of this approach is described in Reference 26.

5.11-13

6. CALIBRATION comparison with predicted quantities is satisfactory.

Calibration of the system is not acceptable when the The calibration should be verified for each material NDA predicted value does not agree with the measured category. Within each category, the variation of inter value to within the value of the combined standard ference effects should be measured within the boundaries error.

defining the limits of that category. Calibration standards should employ containers identical to those to be employed Calibration data and hypotheses should be reinvestigated for the scrap or waste. Their contents should be mocked when this criterion is not satisfied. For a detailed dis up to represent the range of variations in the interferences cussion of calibration and measurement control proce to be encountered. To minimize the number of standards dures, see Regulatory Guide 5.53.

required, the calibration standards should permit the range of interference variations to be simulated over a range of SNM loadings. Assay values should be periodically checked through an independent measurement using a technique sufficiently Verification of the calibration should be made at the accurate to resolve the assay uncertainty. Periodically, a start of each assay section. If different calibrations are container of scrap or waste should be randomly selected to be used, each calibration should be independently for verification. Once selected, the NDA analysis should verified with material appropriate for that calibration. A be repeated a minimum of five times to determine the record should be kept of the verification measurements precision characteristics of the system. The contents of for quality assurance and to identify long-term instru that container should then be independently measured ment drifts. Verification measurements should be used using a technique sufficiently accurate to check the to periodically update the calibration data when the NDA.

I".

5.11-14

REFERENCES

1 F.A. O'Hare et al., "Calorimetry for Safeguards Nuclear Instruments and Methods, VoL 152, Purposes," Mound Facility, Miamisburg, Ohio, pp. 549-557, 1978.

MLM-1798, January 1972. 13. T. W. Crane, "Test and Evaluation Results of the

252 Cf Shuffler at the Savannah River Plant," Los

2. R. Sher and S. Untermeyer, The Detection of Fissionable Material by Nondestructive Means, Alamos National Laboratory, LA-8755-MS, March American Nuclear Society Monograph, 1980, and 1981.

references cited therein; also, C. T. Roche et al,

"A Portable Calorimeter System for Nondestruo 14. T. W. Crane, "Measurement of Pu Contamination at tive Assay of Mixed-Oxide Fuels," in Nuclear the 10-nCi/g Level in 55-Gallon Barrels of Solid Safeguards Analysis, E. A. Hakkila, ed., ACS Waste with a 2 S2 Cf Assay System," Proceedings of Symposium No. 79, p. 158, 1978, and references the InternationalMeeting ofPu-Contamination, Ispra, cited therein. Italy, J. Ley, Ed., JRC-1, pp. 217-226, September 25

28, 1979.

3. U.S. Nuclear Regulatory Commission, "Calorimetric Assay for Plutonium," NUREG-0228, 1977. 15. D. Langner etal., "The CMB-8 Material Balance System," Los Alamos Scientific Laboratory,

4. R. H. Augustson and T. D. Reilly, "Fundamentals LA-8194-M, pp.4-14, 1980.

of Passive Nondestructive Assay of Fissionable Material," Los Ahamos Scientific Laboratory, 16. K.'R. Alvar et al., "Standard Containers for SNM

LA-5651-M, 1974. Storage, Transfer, and Measurement," Nuclear Regulatory Commission, NUREG/CR-1847, 1980.

5. R. Gunnink et al, "A Re-evaluation of the Gamma Ray Energies and Absolute Branching Intensities of 17. R. Sher, "Operating Characteristics of Neutron

23 U, 238,239, 2 4 0 ,2 4 1 Pu, and 2 4 1 Am," Lawrence Well Coincidence Counters," Battelle National Livermore Laboratories, UCRL-52139, 1976. Laboratories, BNL-50332, January 1972.

6. J. E. Cline, R. J. Gehrke, and L D. Mclsaac, 18. N. Ensslin et al., "Neutron Coincidence Counters

"Gamma Rays Emitted by the Fissionable Nuclides for Plutonium Measurements," NuclearMaterials and Associated Isotopes," Aerojet Nuclear Co., Management, VoL VII, No. 2, p. 43, 1978.

Idaho Falls, Idaho, ANCR-1069, July 1972.

19. M. S. Krick and H. 0. Menlove, "The High-Level

7. L A. Kull, "Catalogue of Nuclear Material Safe Neutron Coincidence Counter (HLNCC): Users'

guards Instruments," Battelle National Laboratories, Manual," Los Alamos Scientific Laboratory, BNL-17165, August 1972. LA-7779-MS (ISPO-53), 1979.

8. J. R. Beyster and L. A. Kull, "Safeguards Applica 20. R. B. Perry, R. W. Brandenburg, N. S. Beyer, "The tions for Isotopic Neutron Sources," Battelle Effect of Induced Fission on Plutonium Assay National Laboratories, BNL-50267 (T-596), June with a Neutron Coincidence Well Counter,"

1970. Transactionsof the American Nuclear Society, Vol. 15, p. 674, 1972.

9. T. W. Crane, "Measurement of Uranium and Pluto nium in Solid Waste by Passive Photon or Neutron 21. N. Ensslin, J. Stewart, and J. Sapir, "Self-Multi Counting and Isotopic Neutron Source Interroga plication Correction Factors for Neutron Coinci tion," Los AlMmos Scientific Laboratory, LA-8294 dence Counting," Nuclear MaterialsManagement, MS, 1980. Vol. VIII, No. 2, p. 60, 1979.

10. T. Gozani, "Active Nondestructive Assay of Nu 22. J. L. Parker and T. D. Reilly, "Bulk Sample Self Attenuation Correction by Transmission Measure clear Materials," Nuclear Regulatory Commission, NUREG/CR-0602, 1981. ment," Proceedingsof the ERDA X- and Gamma-Ray Symposium, Ann Arbor, Michigan, Conf. 760639,

11. H.P. Filss, "Direct Determination of the Total p. 219, May 1976.

Fissile Content in Irradiated Fuel Elements, Water Containers and Other Samples of the Nuclear Fuel 23. N. Ensslin et al., "Description and Operating Manual Cycle," Nuclear Materials Management, Vol. VIH, for the Fast Neutron Coincidence Counter," Los pp. 74-79, 1979. Alamos National Laboratory, LA-8858-M, 1982.

> 12. H. 0. Menlove and T. W. Crane, "A

252 Cf Based 24. "Reactor Physics Constants," Argonne National Nondestructive Assay System for Fissile Material," Laboratories, ANL-5800, pp. 30-31, 1963.

5.11-15

25. U.S. Nuclear Regulatory Commission, "Methods 26. E.R. Martin, D.F. Jones, and J.L Parker, "Gamma of Determining and Controlling Bias in Nuclear Ray Measurements with the Segmented Gamma Materials Accounting Measurements," NUREG/ Scan," Los Alamos Scientific Laboratory, CR-1284, 1980. LA-7059-M, 1977.

SUGGESTED READING

American National Standards Institute and American D. R. Rogers, "Handbook of Nuclear Safeguards Meas Society for Testing and Materials, "Standard Test Methods urement Methods," Nuclear Regulatory Commission, for Nondestructive Assay of Special Nuclear Materials NUREG/CR-2078, 1983.

Contained in Scrap and Waste," ANSI/ASTM C 853-79.

This document provides further details on proce This book provides extensive procedures, with dures for assaying scrap and waste. references, for assaying scrap and waste.

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5.11-16

VALUE/IMPACT STATEMENT

1. PROPOSED ACTION 1.3.3 Industry

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

more than one effective kilogram of special nuclear material (SNM) are required in paragraph 70.58(f) of 1.3.4 Public

10 CFR Part 70 to establish and maintain a system of control and accountability to ensure that the standard No impact on the public can be foreseen.

error of any inventory difference (ID) ascertained as a result of a measured material balance meets established 1.4 Decision on Proposed Action minimum standards. The selection and proper applica tion of an adequate measurement method for each of The guide should be revised.

the material forms in the fuel cycle are essential for the maintenance of these standard

2. TECHNICAL APPROACH

Not applicable.

For some material categories, particularly scrap and waste, nondestructive assay (NDA) is the only practical,

3. PROCEDURAL APPROACH

and sometimes the most accurate, means for measuring SNM content. This guide details procedures acceptable 3.1 Procedural Alternatives to the NRC staff to provide a framework for the use of NDA in the measurement of scrap and waste Of the alternative procedures considered, revision of components generated in conjunction with the process the existing regulatory guide was selected as the most ing of SNM. advantageous and cost effective.

The proposed action is to revise Regulatory Guide 4. STATUTORY CONSIDERATIONS

5.11, originally issued in October 1973, which is still basically sound. 4.1 NRC Authority Authority for the proposed action is derived from

1.2 Need for Proposed Action the Atomic Energy Act of 1954, as amended, and the Energy Reorganization Act of 1974, as amended, and Regulatory Guide 5.11 was published in 1973. The implemented through the Commission's regulations.

proposed action is needed to bring the guide up to date with respect to advances in measurement methods 4.2 Need for NEPA Assessment as well as changes in terminology.

The proposed action is not a major action that may significantly affect the quality of the human environ

1.3 Value/Impact of Proposed Action ment and does not require an environmental impact statement.

1.3.1 NRC Operations

5. RELATIONSHIP TO OTHER EXISTING OR

The experience and improvements in technology PROPOSED REGULATIONS OR POLICIES

that have occurred since the guide was issued will be made available for the regulatory procedure. Using The* proposed action is one of a series of revisions these updated techniques should have no adverse of existing regulatory guides on nondestructive assay impact. techniques.

6. SUMMARY AND CONCLUSION

1.3.2 Other Government Agencies Regulatory Guide 5.11 should be revised to bring it Not applicable. up to date.

-.2

5.11-17

FIRST CLASS MAILt UNITED STATES POSTAGE & FEES PAID

NUCLEAR REGULATORY COMMISSION USNRC

WASH 3 C

WASHINGTON, D.C. 20555 PERMIT No j5..

OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, $300

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