Regulatory Guide 5.11
| ML13064A124 | |
| Person / Time | |
|---|---|
| Issue date: | 10/31/1973 |
| From: | US Atomic Energy Commission (AEC) |
| To: | |
| References | |
| RG-5.011 | |
| Download: ML13064A124 (16) | |
U.S. ATOMIC ENERGY COMMISSION
REGULATORY
DIRECTORATE OF REGULATORY STANDARDS
UIDE
REGULATORY GUIDE 5.11 NONDESTRUCTIVE ASSAY OF SPECIAL NUCLEAR MATERIAL
CONTAINED IN SCRAP AND WASTE
October 1973 USAEC REGULATORY GUIDES cap- of pabhw guide~s N.Y be oimism by r4 h~i thet divisions duIlud ms ti US. AsooAti GEmqy Communkilon. V~misgn. D4. 211MG.
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TABLE OF CONTENTS
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A. INTRODUCTION
....................................................... 5.11-1
B. DISCUSSION
.......................................................... 5.11.1
1. Applicable Nondestructive Assay Principles ................................... . 1
1.1 Passive NDA Techniques .............................................. . -1
1.1.1 NDA Techniques Based on Alpha Particle Decay ....................... -1
1.1.2 NDA Techniques Based on Gamma Ray Analysis ....................... -I
1.1.3 NDA Techniques Based on Spontaneous Fission ..........................- 1
1.2 Active NDA Techniques ............................................... -2
2. Factors Affecting the Response of NDA Systems ............................... -2
2.1 Operational Characteristics .............................................. -2
2.1.1 Operational Stability ............................................ -2
2.1.2 Geometric Detection Sensitivity ...................................... -2
2.1.3 Uniformity of StimulatingRadiation ........ ... ............. ........ -3
2.1.4 Energy of Stimulating Radiation ................................... -3
2.2 Response Dependence on SNM Isotopic Composition ........................ -3
2.2.1 Multiple Gamma Ray Sources ...................................... 3
2.2.2 Multiple Spontaneously Fissioning Pu Isotopes ........................ .3
2.2.3 Multiple Fissile Isotopes ........................................... 3
2.3 Response Dependence on Amount and Distribution of SNM in a Container ....... . 3
2.3.1 Self-Absorption of the Emitted Radiation Within the SNM ............... -4
2.3.2 Multiplication of the Spontaneous or Induced Fission ................... . -4
2.3.3 Self-Shielding of the Stimulating Radiation ........................ -4
2.4 Response Dependence on Amount and Distribution of Extraneous Materials Within the Container ....................................................... -4
2.4.1 Interfering Radiations ............................................ -4
2.4.2 Interference to Stimulating Radiation ................................ -4
2.4.3 Attenuation of the Emitted Radiation ................................ -4
2.4.4 Attenuation of the Stimulating Radiation ............................. -4
2.5 Response Dependence on Container Dimensions and Composition .............. -5
2.5.1 Container Dimensions ........................................... .5
2.5.2 Container Structural Composition .................................. .- 5
3. Nondestructive Assay for the Accountability of SNM Contained in Scrap and Waste .... -5
3.1 NDA Performance Objectives ............................................ -5
3.2 NDA Technique Selection ............................................. .5
3.2.1 Plutonium Applications .......................................... -5
3.2.2 Uranium Applications ............................................ -6
3.3 Categorization and Segregation of Scrap and Waste for NDA ................... -6
3.3.1 Calorim etry ................................................... -6
3.3.2 Neutron Measurements .............................. -6
3.3.3 Gamma Ray Measurements ......................................... -6
3.3.4 Fission Measurements ............................................ -7
3.4 Packaging for Nondestructive Assay ...................................... -8
3.5 Calibration of NDA Systems for Scrap and Waste ............................ -8 iii
C. REGULATORY POSITION
................................................... 5.11-8
1. Analysis of Scrap and Waste .............................................. . .8
2. N D A Selection ......................................................... -8
2.1 Technique ......................................................... -8
2.2 System Specifications .................................................. -8
3. Categorization .......................................................... -11
4. Containers ............................................................. -11
4.1 Size Constraints ..................................................... -1
4.2 Structural Features ................................................... 1
4.3 Container Identification ............. .................................. -1
5. Packaging ............................................................. -11
6. Calibration ............................................................ -12 REFERENCES ................................................................ 5.11-12 iv
NONDESTRUCTIVE ASSAY OF SPECIAL NUCLEAR MATERIAL
CONTAINED IN SCRAP AND WASTE
A. INTRODUCTION
Section 70.51, "Material Balance, Inventory, and decay, to gamma ray transitions following a and beta (6)
Records Requirements," of 10 CFR Part 70, "Special particle decay, and to spontaneous fission have served as Nuclear Material," requires licensees authorized to the bases for practical passive NDA measurements.
possess at a-, one time more than one effective kilogram of special nuclear material to establish and 1.1.1 NDA Techniques Based on Alpha Particle maintain a system of control and accountability such Decay that the limit of error of any material unaccounted for (MUF), ascertained as a result of a measured material Alpha particle decay is indirectly detected in balance, meets established minimum standards. The calorimetry measurements. (Note: a small contribution selection and proper application of an adequate is attributable to the 6 decay of 241Pu in plutonium measurement method for each of the material forms in calorimetry applications.) The kinetic energy of the the fuel cycle is essential for the maintenance of these emitted a particle and the recoiling daughter nucleus is standards. transformed into heat, together with some fraction of the gamma ray energies which may be emitted by the With proper controls, licensees may select nonde- excited daughter nucleus in lowering its energy to a structive assay (NDA) as an alternative to traditional more stable nuclear configuration. The calorimetric measurement methods. This guide details procedures measurement of the heat produced by a sample can be acceptable to the Regulatory staff to provide a converted to the amount of a-particle-emitting nuclides framework for the utilization of NDA in the present through the use of the isotopic abundance and measurement of scrap and waste inventory components the specific power [watts gm-f sec 1 I of each nuclide.'
generated in conjunction with the processing of special Plutonium, because of its relatively high specific power, nuclear materials (SNM). Subsequent guides will detail is amenable to calorimetry.
procedures specific to the application of a selected technique to a particular problem. The interaction of high-energy a particles with some light nuclides (e.g., 'Li, 'Be, 1Oe, 1 1 Be, 1 &O, and 19 F)
B. DISCUSSION
may produce a neutron. When the isotopic composition of the a-particle-emitting nuclides is known and the
1. Applicable Nondestructive Assay Principles content of high-yield (an) targets is fixed, the observation of the neutron yield from a sample can be The nondestructive assay of the SNM content of converted to the amount of SNM present..
heterogeneous material forms is achieved through observing either stimulated or spontaneously occurring 1.1.2 NDA Techniques Based on Gamma Bay radiations emitted from the isotopes of either plutonium Analysis or uranium, from their radioactive decay products, or from some combination of these materials. The isotopic The gamma ray transitions which reduce the composition must be known to permit a conversion of excitation of a daughter nucleus following either a or fl the amount of isotope measured to the amount of particle emission from an isotope of SNM occur in element present in the container. Assays are performed discrete energies. 2 3 The known a particle decay activity by isolating the container of interest to permit a of the SNM parent isotope and the probability that it measurement of its contents through a comparison with specific gamma ray will be emitted following the a the response observed from known calibration standards. particle decay can be used to convert the measurement This technology permits quantitative assays of the SNM of that gamma ray to a measurement of the amount of content of heterogeneous materials in short the SNM parent isotope present in the container being measurement times without sample preparation and measured. High-resolution gamma ray spectroscopy is without affecting the form of the material to be assayed. required when the gamma ray(s) being measured is The proper application of this technology requires the observed in the presence of other gamma rays or X-rays understanding and control of factors influencing NDA which, without being resolved, would interfere with the measurements. measurement of the desired gamma ray.
1.1 Passive NDA Techniques 1.1.3 NDA Techniques Based on Spontaneous Fision Passive NDA is based on observing spontaneously emitted radiations created through the radioactive decay A fission event is accompanied by the emission of Of plutonium or uranium isotopes or of their radioactive from 2 to 3.5 neutrons (depending on the parent daughters. Radiations attributable to alpha (a) particle nucleus) and an average of about 7.5 gamma rays. A
5.11-1
total of about 200 MeV of energy is released, distributed The observed NDA response represents primary among the fission fragments, neutrons, gamma rays, beta contributions from the different SNM isotopes present particles, and neutrinos. Spontaneous fission occurs with in the container. To determine the amount of SNM
sufficient frequency in 2 3 8 Pu, 2 4 0 Pu, 2 4 2 Pu, and 2 3 8 u present, the isotopic composition of the SNM must be to facilitate assay measurements through the observation known and the variation in the observed response as a of this reaction. Systems requiring the coincident function of varying isotopic composition must be observation of two or three of the prompt radiations understood. The effects due to items (3), (4), and (5)
associated with the spontaneous fission event provide above on the observed response can be reduced through the basis for available measurement systems. 4 appropriate selection of containers, compatible segregation of scrap and waste categories, and consistent
1.2 Active NDA Techniques use of packaging procedures designed to improve the uniformity of container loadings.
Active NDA is based on the observation of radiations (gamma rays or neutrons) which are emitted 2.1 Operational Characteristics from the isotope under investigation when that isotope undergoes a transformation resulting from an interaction The operational characteristics of the NDA system, with stimulating radiation provided by an appropriate together with the ability of the system to resolve the external source. Isotopic' and accelerator 4 sources of desired response from a composite signal, determine the stimulating radiation have been investigated. ultimate usefulness of the system. These operational characteristics include (I) operational stability, (2)
Stimulation with accelerator-generated high-energy geometric detection sensitivity, (3) stimulating radiation neutrons or gamma rays should be considered only after uniformity, and (4) energy of the stimulating radiation.
all other NDA methods have been evaluated and found to be inadequate. Such systems have been tested to assay The impact of the operational characteristics noted variable mixtures of fissile and fertile materials in large above on the uncertainty of the measured response can containers having a wide range of matrix variability. be reduced through the design of the system and the use Operational requirements,. including operator of radiation shielding (where required).
qualifications, maintenance, radiation shielding, and calibration considerations, normally require an 2.1.1 Operational Stability inordinate level of support in comparison to the benefits of in-plant application. The ability of an NDA system to reproduce a given measurement may be sensitive to fluctuations in the Fission is readily induced by neutrons in the 11 3 U operational environment. Temperature, humidity, and and 2 31 U isotopes of uranium and in the 2 3 9 Pu and line voltage variations affect NDA systems to some
24 ' Pu isotopes of plutonium. Active NDA systems have extent. These effects may be manifested through the been developed using spontaneous fission (e52 Cf) introduction of spurious electronic noise or changes in neutron sources, as well as (y,n) [Sb-Be) sources and a the high voltage applied to the detector(s) or amplifiers, variety of (an) [Am-Li, Pu-Li, Pu.Be] sources. 5 In the thereby changing the detection efficiency. The assay of scrap and waste, the neutron-induced fission environment can be controlled if such fluctuations result reactions are separated from background radiations in severe NDA response variations which cannot be through observing radiations above a predetermined eliminated through, calibration and operational energy level or through observing two or three of the procedures.
radiations emitted in fission in coincidence.
The sensitivity to background radiations can be The detection of delayed neutrons or gamma rays monitored and controlled through proper location of the has been employed using isotopic neutron sources to system and the utilization of radiation shielding, if induce fission, then removing either source or container required.
to observe the delayed emissions.
2.1.2 Geometric Detection Sensitivity
2. Factors Affecting the Response of NDA Systems The NDA system should be designed to have a Regardless of the technique selected, the observed uniform response throughout the detection chamber.
NDA response depends on (1) the operational The residual geometric response dependence can be characteristics of the system, (2) the isotopic measured using an appropriate source which emits composition of the SNM, (3) the amount and radiation of the type being measured. The source should distribution of SNM, (4) the amount and distribution of be small with respect to the dimensions of the detection other . materials -within the container, and (5) the chamber. The system response can then be measured composition and dimensions of the container itself. Each with the source positioned in different locations to of these variables contributes to the overall uncertainty determine the volume of the detection chamber which associated with an NDA measurement. can be reliably used.
5.11-2
An encapsulated Pu source can be used to test 2.2 Response Dependence on SNM Isotopic gamma ray spectroscopic systems, active or passive NDA Composition systems detecting neutrons or gamma rays, or calorimetry systems. Active NDA systems can be The observed NDA response may be a composite of operated in a passive mode (stimulating source removed) contributions from more than a single isotope of to evaluate the magnitude of this effect. Rotating and uranium or plutonium. Observed effects are generally Scanning containers during assay is a recommended attributable to one of the three sources described below.
means of reducing the response uncertainties attributable to residual nonuniform geometric detection 2.2.1 Multiple Gamma Ray Sources sensitivity.
242 Plutonium contains the isotopes 2.Pu 3 through
2.1.3 Uniformity of Stimulating Radiation pU in varying quantities. With the exception of
24 2 P.u, these isotopes emit many gamma rays. 2 3 The The stimulating radiation field (i.e.,. interrogating observed Pu gamma ray spectrum represents the neutron or gamma ray flux) in active NDA systmns contribution of all gamma rays from each isotope, should be designed to be uniform in intensity and energy together with the gamma rays emitted in the decay of spectrum throughout the volume of the irradiation 24 'Am, which may also be present.
chamber. The residual effect can be measured using an SNM sample which is small with respect to the Uranium gamma rays are generally lower in energy dimensions of the irradiation chamber. The response can than Pu gamma rays. Uranium-232, occurring in then be measured with the SNM sample positioned in combination with 2 3 3 U, has a series of prolific different locations within the irradiation chamber. If the gamma-ray-emitting daughter products which include
228 same chamber is employed for irradiation and detection, Th, with the result that daughter products of 2 3 2 U
a single test for the combined geometric nonuniformity and 2 3 2 Th are identical beyond 2281%.
is recommended.
2.2.2 Multiple Spontaneously Fissioning Pu Various methods have been investigated to reduce Isotopes the response uncertainty attributable to a nonuniform stimulating radiation field, including rotating and In addition to the spontaneous fission observed scanning the container, source scanning, distributed from 2 4 0 Pu, the minor isotopes 2 3 8Pu and 24 2Pu sources, and combinations of these methods. Scanning a typically contribute a few percent to the total rate rotating container with the detector and source positions observed. 6 In mixtures of uranium and plutonium fixed appears to offer an advantage in response blended for reactor fuel applications, the spontaneous uniformity and is therefore recommended. fission yield from 2 38 U may approach one percent of the 2 4 OPu yield.
2.1.4 Energy of Stimulating Radiation
2.2.3 Multiple Fissile Isotopes 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 enriched uranium, if the energy spectrum of the enhanced throughout the volume of the irradiation stimulating radiation extends above the threshold for
238 chamber. A high-energy source providing neutrons above U fission, that response contribution will be in the energy of the fission threshold for a fertile addition to the induced 2"U 3 fission response.
constituent such as 2 3a U or 23 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
24 1 Pu.
The presence of extraneous materials, particularly those of low atomic number, lowers the energy spectrum When elements (e.g., plutonium and uranium) are of the interrogating neutron flux in active neutron NDA mixed for reactor utilization, the uncertainty in the systems. Incorporating a thermal neutron detector to response is compounded by introducing additional fssile monitor this effect and thereby provide a basis for a components in variable combinations.
correction to reduce the response uncertainty caused by this variable effect is recommended. 2.3 Response Dependence on Amount and Distribution of SNM in a Container Active neutron NDA systems with the capability to moderate the interrogating neutron spectrum can If a system has a geometrically uniform detection provide increased assay sensitivity for samples containing sensitivity and a uniform field of stimulating radiation small amounts of fissile material (<100 grams). This (where applicable), a variation in the response per grain moderation capability should be removable to enhance of the isotope(s) being measured is generally attributable the range of usefulness of the system. to one of the three causes described below.
5.11-3
2.3.1 Self-Absorption of the Emitted 2.4.1 Interfering Radiations Radiation Within the SNM
This problem arises when the material emits a For a fixed amount of SNM in a container, the iadiation which cannot be separated from the desired probability that radiation emitted by the SNM nuclei signal. This problem is generally encountered in gamma will interact with other SNM atoms increases as the ray spectroscopy and calorimetry applications as the localized density of the SNM increases within the daughters of 2 41 Pu, 2 3 U, and 2 3 2 U grow in. In gamma container. This is a primary source of uncertainty in ray applications, the problem is manifested in the form gamma ray spectroscopy applications. It becomes of additional gamma rays which must be separated from increasingly important as the SNM aggregates into lumps the desired radiations. In calorimetry, the daughters and is more pronounced for low-energy gamma rays. contribute additional heat.
2.3.2 Multiplication of Spontaneous or 2.4.2 Interference to Stimulating Radiation Induced Fission Material lowers the energy of neutrons traversing a The neutrons given off in either a spontaneous or an container giving rise to an increase in the probability of induced fission reaction can be absorbed in a fissile inducing fissions. This problem becomes increasingly nucleus and subsequently induce that nucleus to fission, pronounced with low-atomic-number materials.
resulting in the emission of two or more neutrons. This Hydrogenous materials (e.g., water, plastics) have the multiplication results in an increased response from a strongest capability to produce this effect.
given quantity of SNM. Multiplication affects the response of all active NDA systems and passive 2.4.3 Attenuation of the Emitted Radiation coincidence neutron or gamma ray detection systems used to observe spontaneous fission. This effect becomes This effect may include the partial or complete loss increasingly pronounced as the energy of the neutrons of the energy of the emitted radiation. The detection of traversing the container becomes lower or as the density a reduced-energy radiation may mean that the radiation of SNM increases within the container. cannot be correctly assigned to its source. This effect can be severe for gamma ray system
s. The effect
2.3.3 Self-Shielding of the Stimulating increases with atomic number and the material density Radiation within the container. Also, systems which detect neutrons above a given energy will observe fewer This effect is particularly pronounced in active neutrons above the given energy when systems incorporating a neutron source to stimulate the low-atomic-number material is added to the container fissile isotopes of the SNM to fission. More of the and thus produce a low assay indication.
incident low-energy neutrons will be absorbed near the surface of a high-density lump of SNM, and fewer will The attenuation of the emitted radiation may be penetrate deeper into the lump. Thus, the fissile nuclei complete, as in the case of the absorption of neutrons in located deep in the lump will not be stimulated to the nuclei of extraneous material. The probability for fission at the same rate as the fissile nuclei located near this absorption generally increases as the energy of the the surface, and a low assay content will be indicated. incident neutrons decreases. Hence, this effect is further This effect is dependent on the energy spectrum of the aggravated when low-atomic-number materials are incident neutrons and the density of fissile nuclei. It present to reduce the energy of the emitted neutrons.
becomes increasingly pronounced as the energy of the incident neutrons is decreased or as the density of the
2.4.4 Attenuation of the Stimulating Radiation SNM fissile content is increased. The density of fissile nuclei is increased when the SNM is lumped in aggregates or when the fissile enrichment of the SNM is increased. This phenomenon is similar to that of the preceding section. In this instance, the stimulating radiation does
2.4 Response Dependence on Amount and not penetrate to the SNM within the container and thus Distribution of Extraneous Materials within the does not have the opportunity to induce fission. The Container presence of neutron poisons (e.g., Li, B, Cd, Gd) may attenuate the stimulating radiation to the extent that the The presence of materials other than SNM within a response is independent of the SNM fissile content. Most container can affect the emitted radiations in passive and materials absorb neutrons. The severity of this active NDA systems and can also aff.ct the stimulating absorption effect is dependent on the type of material, radiation in active assay systems. The presence of its distribution, and the energy of the stimulating extraneous materials can result in either an increase or a neutrons.
decrease in the observed response. The presence of extraneous material can thus alter the observed response, providing either a high or a low Effects on the observed NDA response are gener.lly SNM content indication. This effect is fuirther aggravated attributable to one of the four causes described below. by nonuniformiry within the container of either the
5.11-4
SN:.' or the matrix in which it is contained. This the penetration of the incident or the emerging dependence is severe. Failure to attend to its radiation. Provided all containers are uniform, their ramifications through the segregation of scrapand waste effect on the observed response can be factored into the categories and the utilization of representative calibration of the tvstem. The attainable assa" accr:
calibration standards may produce gross inaccuracies in will be reduced w en containers with poor penetraý
NDA measurements. or varying composition or dimensions are selected.
2.5 Response Dependence on Container 3. Nondestructive Assay for the Accountabilit) io.
Dimensi..j and Composition SNM Contained in Scrap and Waste The items identified as potential sources of 3.1 NDA Performance Objectives uncertainty in the observed response of an NDA system in Sections 2.1, 2.3, and 2.4 above can be minimized or The measurement accuracy objectives for any aggravated through the selection of containers to be inventory component can be estimated by considering employed when assaying SNM contained in scrap or the amount of material typically contained in that waste. inventory category. The measurement performance required is such that, when the uncertainty
2.5.1 Container Dimensions corresponding to the scrap and waste inventory component is combined with the uncertainties The practical limitation on container size for scrap corresponding to the other inventory components, the and waste to be nondestructively assayed represents a quality constraints on the total limit of error of the compromise of throughput requirements and the material unaccounted for (LEMUF) will be satisfied.
increasing uncertainties in the observed NDA response incurred as a penalty for assaying large containers. 3.2 NDA Technique Selection Radiations emitted deep within the container must travel a greater distance to escape the confines of the NDA technique selection should reflect a container. Therefore, with increasing container size, the consideration of the accuracy requirements for the assay probability that radiations emitted near the center of the and the type and range of scrap and waste categories to container will escape the container to the detectors be encountered. No single technique appears capable of
-decreases with respect to the radiations emitted near the meeting all requirements. When more tharl one type of surface of the container. information is required to separate a composite response, more than one NDA technique may be In active NDA systems, a relatively uniform field of recquired to provide that information.
stimulating radiation must be provided throughout that volume of the container which is observed by the 3.2.1 Plutonium Applications detection system. This criterion is required to obtain a uniform response from a lump of SNM positioned Calorimetry determinations are the least sensitive to anywhere within a container. It becomes increasingly matrix effects, but rely on a detailed knowledge of the difficult to satisfy this criterion and maintain a compact, 2"1 Am content and the plutonium isotopic composition geometrically efficient system with increasing container to transform the measured heat -flux to grams of size. For this reason, the assay of small-size containers is plutonium.'
recommended.
Gamma ray spectroscopy systems complement the To facilitate loading into larger containers for potential of other assay methods by providing the storage or offsite shipmen following assay, the size and capability
2 41 to nondestructively determine, or verify, the shape of the inner and outer containers should be chosen Am content and the piutonium isotopic composition to be compatible.
(except 2 41 2 Pu). High-resolution gamma ray systems are Packaging in small containers will produce more capable of extracting the maximum amount of containers to be assayed for the same scrap and waste information (isotopic composition, isotopic content, generation rates. An offsetting benefit, however, is that presence of extraneous gamma ray sources) from an the assay accuracy of an individual container should be assay, but content density severely affects the accuracy significantly improved over that of large containers. In of quantitative predictions based upon that assay addition, the total scrap and waste assay uncertainty method.
should be reduced through statistically propagating a larger number of random component uncertainties to Passive coincidence detection of the spontaneous determine the total uncertainty. fission yield of Pu-bearing systems provides an indication of the combined 2 38 Pu, 2 4 0 Pu, and 2 4 2 Pu sample
2.5.2 Container Structural Composition content. With known isotopic composition, the Pu content can be computed.' Neutron multiplication The structural composition of containers will affect effects become severe at high Pu sample loadings."
5.11-5
Plastic scintillation coincidence detection systems are equilibrium or its content is known. Enrichment meter often designed in conjunction with active neutron applications for uranium will be the subject of another interrogation source systems. Operated in passive and Regulatory Guide.
active modes, such systems are able to provide an assay of both the spontaneously fissioning and the fissile Calorimetry is not applicable to the assay ot content of the sample. The spontaneous background can uranium enriched in the 2 'U isotope because of the be subtracted from an active NDA response to provide a low specific a activity. In 2 3 3U applications, the intense yield attributable to the fissile SNM content of the activity of the daughter products of 2 32 U imposes a container. severe complication on the use of calorimetry.
Active NDA can be considered for plutonium scrap 3.3 Categorization and Segregation of Scrap and and waste applications after the potential Waste for NDA
implementation of the passive techniques has been evaluated. With the wide range of isotopic compositions The range of variations in the observed response of encountered, together with the mixture with various an NDA system attributable to the effects noted in enrichments of urax-um, the requirements to convert an Sections 2.3 and 2.4 above can be reduced or controlled.
observed composite response into an accurate assay of Following an analysis of the types of scrap and waste the plutonium and uranium fissile content become generated in conjunction with SNM processing, a plan to increasingly severe. segregate scrap and waste at the generation points can be formulated. Recovery or disposal compatibility is The application of these methods to the assay of important in determining the limits of each category.
plutonium-bearing solids and solutions are the subjects Limiting the range in variability in those extraneous of other Regulatory Guides. NDA interference parameters discussed in Sections 2.3 and 2.4 is a primary means of improving the accuracy of
3.2.2 Uranium Applications the scrap and waste assay. Once the categories are established, it is important that steps be taken to assure Active neutron systems can provide for both that segregation into separate, uniquely identified high-energy and moderated interrogation spectrum containers occurs at the generation point.
capabilities. Operation with the high-energy neutron source will decrease the density dependence and neutron Category limits can be established on the basis of sel f-shielding effects, significantly enhancing the measured variations observed in the NDA response of uniqueness of the observed response. To extend the container loaded with a known amount of SNM. T1, applicability of such a system to small fissile loadings, a variation in extraneous parameters can then be mocked well-moderated interrogating spectrum can be. used to up and the resultant effect measured. In establishing take advantage of the increased 2' sU fission probability categories, the following specific items are significant for neutrons of low energy. In highly enriched uranium sources of error.
23 scrap and waste (>20% sU), active NDA featuring a high-energy stimulating neutron flux is recommended. 3.3.1 Calorimetry The presence of extraneous materials capable of The number and energy of the gamma rays emitted absorbing (endothermic) heat or emitting (exothermic)
from the uranium isotopes (with the exceptions of the heat will cause the observed response to be less or minor isotopes 2 312 U and 2 3 'U) are generally lower than greater than the correct response for the Pu in the for the plutonium case. The 185-keV transition observed sample.
in the decay of 23 sU is frequently employed in uranium applications. The penetration of this 2 3 'U primary 3.3.2 Neutron Measurements gamma ray is so poor that the gamma ray NDA
technique is not applicable with high-density, The presence of high-yield (an) target material will nonhomogeneous matrices. increase the number of neutrons present in the sample.
A fraction of these neutrons will induce fission in the There arise occasions when a passive enrichment fissile SNM isotopes and add another error to the determination is practical through the measurement of measurement.
the 185-keV gamma ray. One criterion required for this application is that the contents be relatively 3.3.3 Gamma Ray Measurements homogeneous. This information can then be combined with an assay of the 38U content of the sample to Gamma rays are severely attenuated in interactions compute the total uranium and 2 3 sU sample content. with heavy materials. Mixing contaminated combustibles The 2 38 U sample content can be obtained either with heavy, dense materials complicates the attenuation through the detection of the 2 3 SU spontaneous fission problem. Mixing of isotopic batches or mixing wi'
neutron yield or through the assay of the 2 3 4Pa radioactive non-SNM can also add to the complexity daughter gamma activity, provided either the 2 34 Pa is in the response.
5.11-6
3.3.4 Fission Measurements where N, = the number of atoms per cubic Scrap or waste having low-atomic-number materials centimeter of material, will reduce the energy of the neutrons present in the container, significantly affecting the probability of Gal = absorption cross section of the stimulating fission reactions. extraneous material (Table B-I),
Neutron-absorbing materials present in SNM scrap NSNM = numbetiof atoms of SNM present per or waste may significantly affect the operation of NDA cubic centimeter, systems. Table B-I of this guide identifies neutron absorbers in the order of decreasing probability of OaSNM = absorption cross section of the SNM.
absorption of thermal neutron
s. An estimate of the
2 33 significance of the presence of one of these materials U oa = 573 barns may be obtained from the ratio of its absorption cross section to the absorption cross section of the SNM 23Su oa = 678 barns present in the container:
239 Pu oa = 1015 barns
2
4'Pu oa = 1375 barns R = N, Gal NSNM~aSNM (Thermal neutron values)
TABLE B-1 NATURALLY OCCURRING NEUTRON ABSORBERS 8 Naturally Absorption Naturally Absorption Occurring Cross Section Occurring Cross Sction Element Symbol (barns) * Element Symbol Iberns)*
Gadolinium .......... Gd 46,000 Terbium ............ Tb 46 Samarium. ........... Sm 5,600 Cobalt ............. Co 38 Europium ............ Eu 4,300 Ytterbium .......... Yb 37 Cadmium ............ Cd 2,450 Chlorine ............ a 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 Promethium ......... Pin 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
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The magnitude of this effect is dependent on the calibration, and operational procedures; to the distribution of the materials and the energy of the segregation of scrap and waste categories; and to the neutrons present within the container. The relationship selection and packaging of containers. The guidelines above is a gross approximation, and for convenience in presented below are generally acceptable to the calculation, including only the primary fissile isotope is Regulatory staff for use in developing such a framework sufficient to determine which materials may constitute a that can serve to improve materials accountability.
problem requiring separate categorization for assay. In extreme cases, either methods should be sought to 1. Analysis of Scrap and Waste measure the content of the neutron absorber to provide a correction for the NDA response or a different method The origin of scrap and waste generated in should be sought for the assay of that category. conjunction with SNM processing activities should be determined as follows:
3.4 Packaging for Nondestructive Assay a. Identify those operations which generate SNM-bearing scrap or waste as a normhal adjunct of a Nondestructive assay provides optimal accuracy process.
potential when the packages to be assayed are essentially b. Identify those operations which occasionally identical and when the calibration standards represent generate SNM-bearing scrap or waste as the result of an those packages in content and form. Containers for most abnormal operation which renders the product scrap and waste can be loaded using procedures which unacceptable for further processing or utilization will enhance the uniformity of the loading within each without treatment.
container and from container to container. Compaction c. Identify those scrap and waste items generated in and vibration are two means to accomplish this conjunction with equipment cleanup, maintenance, or objective. replacement.
3.5 Calibration of NDA Systems ior Scrap and The quantities of scrap and waste generated during Waste normal operations in each category in terms of the total volume and SNM content should be estimated. Bulk To obtain an assay value on SNM in a container of measurement throughput requirements should be scrap or waste with an associated limit of error, the determined to assure that such assay will not constitute observed NDA response or the predicted content must an operational bottleneck.
be corrected for background and for significant effects attributable to the factors described in the preceding 2. NDA Selection parts of this discussion.
2.1 Technique The calibration of radiometric nondestructive assay systems is the subject of another Regulatory Guide.* The performance objectives for the NDA system should be derived as discussed in Section B.3.1.
One procedure for referencing NDA results to Techniques should be considered for implementation in primary standards is the periodic selection of a container the order of precedence established in Table C-I of this at random from a lot submitted for assay. That guide.Selection should be based on attainable accuracy, container should then be assayed a sufficient number of factoring into consideration the characteristics of the times to reduce the random uncertainty of the scrap and waste categories. The application of such measurement to a negligible value. The SNM content of techniques will be the subjects of other Regulatory that container can then be determined through a Guides.
different technique having an accuracy sufficient to verify the stated performance of the NDA syste
m. This
2.2 System Specifications reference method. should be traceable to primary standards. High-integrity "recovery of the contents, NDA systems for SNM accountability should be followed by sampling and chemical analysis is one designed and shielding should be provided to meet .the recommended technique.
following objectives:
a. Performance characteristics should be essentially
C. REGULATORY POSITION
independent of fluctuations in the ambient operational environment, including:
In the development of an acceptable framework for
(!) External background radiations, the incorporation of nondestructive assay for the
(2) Temperature, measurement of SNM-bearing scrap and waste, strong
(3) Humidity, and consideration should be given to technique selection,
(4) Electric power.
b. Response should b~e essentially independent c
- To be based on ANSI N15.20, which is currently in positioning of SNM within the scrap or waste containe development. including effects attributable to:
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TABLE C-1 NDA TECHNIOUE SELECTION
TECHNIQUE Pu S"SU ;20% "'aU <20% asU
(1) ]st (1+2)* 3rd NA NA
CALORIMETRY
NR NR NA NA
(2) 3rd 2nd 2nd Ist (2+5)
GAMMA RAY
1st lIt 1st Ist
(3) 2nd (3+2) NA NR 3rd (3+2)0*
SPONTANEOUS
FISSION 2nd (3+2) NA NR MR
(4) 4th 1st 1st 2ad STIMULATED
FISSION 3rd 2nd 2nd 2nd
(5) NR NM mR (5+2) MR (S42)
GROSS NEUTRON
NR Mt MR Mt
- Above wommeadation reten to h0hdinty, m m rns. Lowe remmmnmntion rfas to ow4enmsty, *4I M .
"Spontaneous fuson of " 'OU.
NR-NOT RECOMMENDED-Technique =maima for dd allimtimb.
NA-NOT APPLICABLE.
MN-NOT INDEPENDENTLY bea.,.- o a* mai do with a cmplmeatury amy method.
TABLE C-2 NDA INTERFERENCE CONTROL
Presnce of Heat Producing Mixted High.Yield Ganne Neutron Lumped vs. Lumped vs.
or Absorbing Mixed Isotopic Miscellaneous (a,ni Target Ray Neutron Moderating Distributed Distribured NDA Technique Process SNM Retches Radletions Material Absorbers Absorbers Materials SNM Matrix Mat0
Calorimetry xxx xxx -
Gamma Ray Spectroscopy - x x- xxx - xxx xx Spontaneous Fission Detection - xx xxx .... xb xxc xx xx X
Stimulated x xb xxt . xxxC xxd d a Fission Detection -x
0h jXXe Xe :.
"
Key: - No apparent sensitivity.
x Some sensitivity. Evaluate effect in extreme cases.
xx Marked sensitivity. Categohize and calibrate according Notes: a - Effect depends on type and nature of radiation detected.
to magnitude of observed effect. b -Effect less pronounced in coincidence detection systems.
xxx Strong sensitivity. Requires correction to imy. May c - Same as a, additional effect due to neutron multiplication.
render technique unacceptable in extreme cases if d - Moderated-neutron stimulating source.
correction not possible e - High-energy stimulating source.
(1) Detector geometrical efficiency, and interfere' with the radiations entering or leaving the
(2) Stimulating source intensity and energy. sample, Techniques to achieve these objectives are discussed in e. Capable of being sealed to verify post-assay Section B of this guide. initegrity, and f. Compatible with subsequent recovery, storage, and
3. Categorization disposal requirements, as applicable.
Scrap and waste categories should be developed on In most NDA applications, uniformity, of the basis of NDA interference control, recovery oor conposition is .more important than the specification of disposal compatibility, 9 and relevant safety ,- particular material. Table C-3 gives general considerations. Categorization for NDA interference recommendations for container structural materials.
control should be directed to limiting the range of variability in an interference. Items to be considered depend upon the sensitivity of the specific NDA
technique, as shown in Table C-2. TABLE C-3 The means through which these interferences are SCRAP AND WASTE
manifested are detailed in Section B. When such effects CONTAINER COMPOSITION
or contents are noted, separate categories should be established wherein the materials are isolated.
NDA Technique Container Composition
4. Containers Calorimetry metal (aluminum, brass)
4.1 Size Constraints Gamma Ray Analysis cardboard, polyethylene Scrap and waste should be packaged for assay in bottle, thin metal containers as small as practicable, consistent with the capability and sensitivity of the NDA system. Spontaneous or thin metal, cardboard, Stimulated Fission polyethylene bottle To enhance the penetration of stimulating or emitted radiations containers should be cylindrical. The: Gross Neutron thin metal, cardboard, diameter should be less than five inches to provide for polyethylene bottle significant loading capability, ease in loading, reasonable penetrability characteristics, and compatibility with criticality-safe geometry requirements for individual containers, where applicable. 4.3 Container Identification Containers having an outside diameter of 4-3/8 To facilitate loading and assay within the inches will permit nineteen such containers to be segregation categories, containers should either be arranged in a cross section of a 55-gallon drum, even. uniquely color-coded or carry unique color-coded when that drum contains a plastic liner. Containers identification labels. Identification of categories should having an overall. length equal to. some integral fraction be documented and operating personnel instructed to of -the length of a 5.5-gallon drum -are further assure compliance with established segregation recommended when shipment or storage within such objectives.
containers is to be. considered. For normal operations, an overall length. of either 1.6-1,/2 inches (two layers or 38 5. Packaging containers per drum) or 11 inches (three layers or 57 containers per drum) is therefore recommended. Containers, where practical, should be packaged with a quantity of material containing sufficient SNM to
4.2 Structural Features assure that the measurement is not being made at the extremes of the performance . bounds for that system.
Containers should be selected in accordance with Packaging procedures should be consistent with relevant normal safety considerations and should be: safety practices.
a. Structurally identical for all samples to be assayed within each category, Containers should be packaged in as reproducible a b. Structurally identical for as many categories as. manner as possible. Low-density items should be practicable to facilitate loading into larger containers or compacted to reduce bulk volume and to increase the storage facilities, container SNM loading. Lowering the bulk volume c. Uniform in wall thickness and material composition, reduces the number of containers to be assayed and d. Fabricated of materials that do not significantly generally improves the assay precision.
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If assay predictions are significantly affected by the the system. The contents of that container should then variability in the distribution of the container contents, be independently measured using one of the following compacting or vibrating the container on a shake table techniques:
to settle the contents should be used to enhance the a. Recovery of the contents, followed by sampling and assay accuracy in conjunction with rotating and scanning chemical analysis, the container during assay. b. High-accuracy calorimetry (Pu only) with isotopic sample taken from contents and determined through
6. Calibraion standard techniques.
c. Small-sample screening followed by selective The NDA system(s) should be independently chemical analyses. This technique is applicable to cases calibrated for each category of scrap or waste to be in which the contents consist of a collection of similar assayed. items. Each item should be assayed in a small-sample Within each category, the variation of interference system capable of an accuracy greater than or equal to effects should be measured within the boundaries that of the system being calibrated. No less than five defining the limits of that category. Calibration items should then be selected for chemical analysis.
standards should employ containers identical to those to Those items should be chosen to span the range of be employed for the scrap or waste. Their contents observed responses in the screening assay.
should be mocked up to represent the range of variations in the interferences to be encountered. To minimize the number of standards required, the calibration standards Verification measurements -should be used to should permit the range of interference variations to be periodically update calibration data when the
.simulated over a range of SNM loadings. comparison with predicted quantities is satisfactory.
Calibration of the system is not acceptable when the Calibration relationships should be verified at NDA predicted value does not agree with the measured intervals sufficiently frequent to detect deviations from value to within the value of the combined limits of the expected response in time to make corrections error:
before the containers are processed or shipped.
Assay values should be periodically verified through INDA-VER 14 (LEIDA + LEER)1/2 an independent measurement using a technique sufficiently accurate to resolve NDA uncertainty. Calibration data and hypotheses should be Periodically, a container of scrap or waste should be reinvestigated when this criterion is not satisfied.
randomly seleted for verification. Once selected, the NDA analysis should be repeated a minimum number of The calibration of NDA systems will be the subject
.five times to determine the precision characteristics of of another Regulatory Guide.
REFERENCES
1. F. A. O'Hra et al., Calorbmetry for Safieswd Applications for Isotopic Neutron Sources, Pwposes, MLM-l 798 (January 1972). BNL-50267 (T-596) (June 1970).
2. R. Gunnink and R. J. Morrow, Gwnma Ray 6. R. Sher, Opeiting Oanclmtfics of Neutron Well E .iesad AbaWue
2 Awnhft intemitni for Cobsedmee Countat, BNL-50332 (January 1972).
224,23,240,. 61Pu .d "'Am, ECRL-SIO7 (July 1971). 7. R. B. Perry, R. W. Brandenburg, N. S. Beyer, The Effect of Induced Fmion on Plutonium Asay with
3. J. E. Cline, R. .. Gehrke, and L. D. Mcsuac, Gwnnv a Neutron Coiddumce Well Coutmer, Trans. Am.
Rays Emitted by the Ftosonable Nudlda and Nucl. Soc., 15 674 (1972).
Assciated Isotopes. ANCR-1069 (July 1972).
g. Reactor Physics Constants, ANL-580D (1963).
4. L A. Kull, Catalogueof Nucw MaerialSafieguard Istrument, BNL-17165 (August 1972).
9. Regulatory Guide 5.2, Classjcationof Unibndiated
5. J. R. Deyster and L. A. Kull, Sqauds Plutonium wad 1wisum *-w.
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