ASTM C1316-2001 Standard Test Method for Nondestructive Assay of Nuclear Material in Scrap and Waste by Passive-Active Neutron Counting Using a 252 Cf Shuffler《使用a252Cf的被动-主动中子计数法在.pdf

1、Designation: C 1316 01Standard Test Method forNondestructive Assay of Nuclear Material in Scrap andWaste by Passive-Active Neutron Counting Using a252CfShuffler1This standard is issued under the fixed designation C 1316; the number immediately following the designation indicates the year oforiginal

2、adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the nondestructive assay ofscrap and waste

3、for uranium and plutonium content using a252Cf shuffler. Shuffler measurements provide rapid results andcan be applied to a variety of matrix materials in containers aslarge as 208-litre drums. Corrections are made for the effects ofmatrix material. This test method has been used to assay itemsconta

4、ining uranium, plutonium, or both. Applications of thistest method include measurements for safeguards, accountabil-ity, TRU, and U waste segregation, disposal, and processcontrol purposes (1,2,3).21.1.1 This test method uses passive neutron coincidencecounting to measure238Pu,240Pu, and242Pu. It ha

5、s been used toassay items with plutonium contents between 0.03 g and 1000g. It could be used to measure other spontaneously fissioningisotopes. It specifically describes the approach used with shiftregister electronics; however, it can be adapted to otherelectronics.1.1.2 This test method uses neutr

6、on irradiation with amoveable californium source and counting of the delayedneutrons from the induced fissions to measure235U. It has beenused to assay items with235U contents between 0.1 g and 1000g. It could be used to assay other fissionable isotopes.1.2 This test method requires knowledge of the

7、 relativeisotopic composition to determine the mass of the differentelements.1.3 This test method may give biased results for measure-ments of containers that include large quantities of hydrogen.1.4 The techniques described in this test method have beenapplied to materials other than scrap and wast

8、e. These otherapplications are not addressed in this test method.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the appl

9、ica-bility of regulatory limitations prior to use. Specific precau-tionary statements are given in Section 8.2. Referenced Documents2.1 ASTM Standards:C 859 Terminology Relating to Nuclear Materials3C 986 Guide for Developing Training Programs in theNuclear Fuel Cycle3C 1009 Guide for Establishing a

10、 Quality Assurance Pro-gram for Analytical Chemistry Laboratories Within theNuclear Industry3C 1030 Test Method for Determination of Plutonium Isoto-pic Composition by Gamma-Ray Spectrometry3C 1068 Guide for Qualification of Measurement Methodsby a Laboratory Within the Nuclear Industry3C 1128 Guide

11、 for Preparation of Working Reference Mate-rials for Use in the Analysis of Nuclear Fuel CycleMaterials3C 1133 Test Method for Nondestructive Assay of SpecialNuclear Material in Low Density Scrap and Waste bySegmented Passive Gamma-Ray Scanning3C 1156 Guide for Establishing Calibration for a Measure

12、-ment Method Used to Analyze Nuclear Fuel Cycle Mate-rials3C 1207 Test Method for Nondestructive Assay of Plutoniumin Scrap and Waste by Passive Neutron CoincidenceCounting3C 1210 Guide for Establishing a Measurement SystemQuality Control Program for Analytical Chemistry Labo-ratories Within the Nuc

13、lear Industry3C 1215 Guide for Preparing and Interpreting Precision andBias Statements in Test Method Standards used in theNuclear Industry32.2 ANSI Documents:ANSI 15.20 Guide to Calibrating Nondestructive AssaySystems41This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel

14、Cycle and is the direct responsibility of Subcommittee C26.10 on Nondestruc-tive Assay.Current edition approved June 10, 2001. Published September 2001. Originallypublished as C 1316 95. Last previous edition C 1316 95.2The boldface numbers in parentheses refer to a list of references at the end oft

15、his test method.3Annual Book of ASTM Standards, Vol 12.01.4Available from American National Standards Institute, 11 W. 42nd St., 13thFloor, New York, NY 10036.1Copyright ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.ANSI N15.36 Nondestructive Assay Measurement Controla

16、nd Assurance43. Terminology3.1 DefinitionsTerms shall be defined in accordance withTerminology C 859.3.2 Definitions of Terms Specific to This Standard:3.2.1 accidentals (a), nthe number of neutrons detected inthe (a) gate interval following the initial detection of eachneutron during the selected c

17、ount time, t. These neutrons comefrom many sources and are not physically correlated with theinitial neutron.3.2.2 active mode, ndetermines total fissile mass in theassayed item through neutron interrogation and counting of thedelayed neutrons from induced fissions.3.2.3 benign matrix, na matrix tha

18、t has negligible effectson the neutron transport. A benign matrix includes very littleneutron moderator or neutron absorber.3.2.4 coincidence gate length, nthe time interval follow-ing the detection of a neutron during which additional neutronsare considered to be in coincidence with the original ne

19、utron.3.2.5 coincident neutrons, nneutrons emitted simulta-neously from a single event. Two or more coincident neutronsare correlated in time with the occurrence of one event, such asfissioning of a nucleus.3.2.6 die-away time, nthe average lifetime of a neutronfrom the time of emission until the ne

20、utron is detected. Theaverage lifetime is the time required for the neutron populationto drop to 1/e of the original value. Die-away time is a functionof several parameters including the detector design, the assayitem characteristics, and the neutron energies.3.2.7 effective240Pu mass (meff), nthe m

21、ass of240Pu thatwould produce the same coincidence response in the instru-ment as the assay item. It is a function of the quantities of theeven-mass isotopes of plutonium and fundamental nuclearconstants. It is specific to the type of coincidence circuitry used(4).3.2.8 flux monitors, ndetectors in

22、the measurement cham-ber that measure the interrogating neutron flux.3.2.9 item, nthe entire scrap or waste container beingmeasured and its contents.3.2.10 lump, nthat contiguous mass of nuclear materialthat is sufficient to affect the measured signal.3.2.11 lumps, nin the context of the active meas

23、urementmode, have a dimension larger than the mean free path of aninterrogating neutron and consequently exhibit self-shielding.3.2.12 lumps, nin the context of the passive measurementmode, have a dimension larger than the mean free path of afission neutron and consequently exhibit multiplication.3.

24、2.13 matrix, nthe material that comprises the bulk of theitem, except for the special nuclear material and the container.This is the material in which the special nuclear material isembedded.3.2.14 matrix-specific calibration, nuses a calibration ma-trix similar to the waste matrix to be measured. N

25、o matrixcorrection factors are used; this calibration is generally notappropriate for other matrices.3.2.15 neutron absorbers, nmaterials that have relativelylarge absorption cross sections for thermal neutrons. Absorberswith the largest cross sections are commonly known as neutronpoisons. Some exam

26、ples are lithium, boron, cadmium, andgadolinium.3.2.16 neutron coincidence counting, na technique usedto measure the rate of coincident neutron emission in themeasured item. Fig. 1 shows the probability of detecting aneutron as a function of time.3.2.17 neutron moderators, nthose materials that slow

27、fast neutrons through elastic scattering. Materials containinghydrogen are the primary example.3.2.18 neutron multiplication, nthe fractional increase inthe number of second-generation neutrons emitted, followingspontaneous fission, due to self-induced fissions in the itembeing measured.3.2.19 passi

28、ve mode, ndetermines the total spontaneouslyfissioning mass in the measured item through the detection ofcoincidence neutrons. The coincident neutrons are promptneutrons.3.2.20 predelay, nthe time interval immediately after thedetection of the initiating neutron. This time is selected toallow the el

29、ectronics to recover and detect subsequent neu-trons.3.2.21 prompt and delayed neutrons, nneutrons occurringas a result of fissions. Approximately 99 % are prompt neu-trons, emitted directly from fission within 1013s after fissionbegins. The remainder are delayed neutrons, the result ofneutron decay

30、 by some of the fission products. Delayedneutrons appear seconds or minutes after the fission begins.3.2.22 (a, n) reactions, noccur when energetic alphaparticles collide with low atomic number nuclei, such as O, F,or Mg, producing single neutrons. Neutrons produced in thismanner are not correlated

31、in time and are a source of “singles”in passive neutron counting and a source of background inactive neutron counting.3.2.23 reals (r), nthe number of real coincident neutronsin the (r + a) gate interval following the initial detection ofeach neutron during the selected count time, t. This quantity

32、isderived from the two measured quantities, r + a and a.3.2.24 reals plus accidentals (r + a), nthe number ofneutrons detected in the (r + a) gate interval following theinitial detection of each neutron during the selected count time,t. These events are due to neutrons that are coincident with thein

33、itial neutron (reals) and to neutrons that are not correlatedwith the initial neutron (accidental coincidences). This is ameasured quantity.3.2.25 shift-register-based coincidence circuit, nan elec-tronic circuit for determining totals (t), reals plus accidentals(r + a), and accidentals (a) in a sel

34、ected count time (t). Fig. 1illustrates the time relationship between the measured quanti-ties.3.2.26 shuffler technique, nan active-neutron nondestruc-tive assay technique that moves a252Cf source close to theassay item to irradiate the fissile material, then counts delayedneutrons from the induced

35、 fissions after the source is with-drawn. Fig. 2 illustrates the measurement concept, and the twosource positions that the source “shuffles” between.C 131623.2.27 totals (t), nthe total number of individual neu-trons detected during the selected count time, t. This is ameasured quantity.3.2.28 trans

36、uranic waste (TRU waste), n defined by theUnited States Department of Energy as any waste containingalpha-emitting isotopes with atomic number greater than 92and half-life greater than 20 years, with a activity concentra-tions greater than 100 nCi per gram of bulk waste.3.3 volume weighted average r

37、esponse, nan estimate ofthe count rate that would be obtained from a drum containinga uniform distribution of special nuclear material. It is aweighted average calculated from a series of measurements asfollows:3.3.1 The drum is divided into 15 or so volume elements,3.3.2 A point source is centered

38、in one of the volumeelements and measured,3.3.3 The point source is moved to the next volume elementand measured, and3.3.4 Each response is weighted by the size of the corre-sponding element. (See Appendix X1 for a more detailedexplanation.)4. Summary of Test Method4.1 This test method consists of t

39、wo distinct modes ofoperation: passive and active. The instrument that performs theactive mode measurement is referred to as a “shuffler” due tothe motion of the252Cf source. This test method usually relieson passive neutron coincidence counting to determine theplutonium content of the item, and act

40、ive neutron irradiationfollowed by delayed neutron counting to determine the ura-nium content.4.1.1 Passive Neutron Coincidence Counting ModeTheeven mass isotopes of plutonium fission spontaneously. Ap-proximately two prompt neutrons are emitted per fission. Thenumber of these coincident neutrons de

41、tected by the instrumentis correlated to the quantity of even mass isotopes of pluto-nium. The total plutonium mass is determined from the knownisotopic ratios and the measured quantity of even massisotopes. This test method refers specifically to the shiftregister coincidence counting electronics (

42、see Ref 4 and TestMethod C 1207).4.1.2 Active Neutron (Shuffler) ModeFissions in235U canbe induced by bombarding uranium with neutrons. Approxi-mately 1 % of the neutrons per fission are delayed, beingemitted from the fission products for several minutes after thefission event. The active mode consi

43、sts of several irradiate-count cycles, or shuffles, of the252Cf source between thepositions illustrated in Fig. 2. Californium-252 emits a fissionneutron spectrum. During each shuffle, a252Cf source is movedclose to the item for a short irradiation, then moved to ashielded position while the delayed

44、 neutrons are counted. Thenumber of these delayed neutrons detected by the instrument iscorrelated with the quantity of235U. The total uranium mass isdetermined from the known isotopic ratios and the measuredquantity of235U.4.2 Either corrections are made for the effects of neutronabsorbers and mode

45、rators in the matrix, or a matrix-specificcalibration is used. The effect that needs correction is theincrease or decrease in the neutron signal caused by the matrix.4.3 Corrections are made for electronic deadtime, neutronbackground, and the252Cf source decay.NOTE 1Curve (a) is a simplified probabi

46、lity distribution showing the decay, as a function of time, for detecting a second neutron from a fission event.The probability for detecting an uncorrelated neutron is constant with time. Typical coincidence timing parameters are shown in (b).FIG. 1 Probability of Neutron Detection as a Function of

47、 TimeC 131634.4 The active mode also induces fissions in plutonium if itis present in the assay item. The passive measurement ofplutonium can be used to correct the active measurementof235U for the presence of plutonium.4.5 Calibrations are based on measurements of well docu-mented reference materia

48、ls. The method includes measurementcontrol tests to verify reliable and stable performance of theinstrument.5. Significance and Use5.1 This test method is used to determine the uranium andNOTE 1The two main features of the active technique are shown. The shuffler measurement consists of several cycl

49、es. Each cycle includes anirradiation of the item by the242Cf source for about 10 s, followed by a counting period of about 10 s while the source is stored in a shield.FIG. 2252Cf Shuffler Measurement PrincipleC 13164plutonium content of scrap and waste in containers. Measure-ment count times have been 100 to 1000 s. The following limitsmay be further restricted depending upon specific matrix,calibration material, criticality safety, or counting equipmentconsiderations.5.1.1 The passive measurement has been applied to benignmatrices in 208-litre d