1、Designation: E854 14Standard Test Method forApplication and Analysis of Solid State Track Recorder(SSTR) Monitors for Reactor Surveillance, E706(IIIB)1This standard is issued under the fixed designation E854; the number immediately following the designation indicates the year oforiginal adoption or,
2、 in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes the use of solid-state trackrecorders (SSTRs) for neu
3、tron dosimetry in light-water reactor(LWR) applications. These applications extend from lowneutron fluence to high neutron fluence, including high powerpressure vessel surveillance and test reactor irradiations as wellas low power benchmark field measurement. (1)2This testmethod replaces Method E418
4、. This test method is moredetailed and special attention is given to the use of state-of-the-art manual and automated track counting methods to attainhigh absolute accuracies. In-situ dosimetry in actual highfluence-high temperature LWR applications is emphasized.1.2 This test method includes SSTR a
5、nalysis by bothmanual and automated methods. To attain a desired accuracy,the track scanning method selected places limits on theallowable track density. Typically good results are obtained inthe range of 5 to 800 000 tracks/cm2and accurate results athigher track densities have been demonstrated for
6、 some cases.(2) Track density and other factors place limits on the appli-cability of the SSTR method at high fluences. Special caremust be exerted when measuring neutron fluences (E1MeV)above 1016n/cm2(3).1.3 Low fluence and high fluence limitations exist. Theselimitations are discussed in detail i
7、n Sections 13 and 14 and inRefs (3-5).1.4 SSTR observations provide time-integrated reactionrates. Therefore, SSTR are truly passive-fluence detectors.They provide permanent records of dosimetry experimentswithout the need for time-dependent corrections, such as decayfactors that arise with radiomet
8、ric monitors.1.5 Since SSTR provide a spatial record of the time-integrated reaction rate at a microscopic level, they can be usedfor “fine-structure” measurements. For example, spatial distri-butions of isotopic fission rates can be obtained at very highresolution with SSTR.1.6 This standard does n
9、ot purport to address the safetyproblems associated with its use. It is the responsibility of theuser of this standard to establish appropriate safety and healthpractices and determine the applicability of regulatory limita-tions prior to use.2. Referenced Documents2.1 ASTM Standards:3E418 Test Meth
10、od for Fast-Neutron Flux Measurements byTrack-Etch Techniques (Withdrawn 1984)4E844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E 706 (IIC)3. Summary of Test Method3.1 SSTR are usually placed in firm surface contact with afissionable nuclide that has been deposited on a pure
11、 nonfis-sionable metal substrate (backing). This typical SSTR geom-etry is depicted in Fig. 1. Neutron-induced fission produceslatent fission-fragment tracks in the SSTR. These tracks maybe developed by chemical etching to a size that is observablewith an optical microscope. Microphotographs of etch
12、ed fis-sion tracks in mica, quartz glass, and natural quartz crystals canbe seen in Fig. 2.3.1.1 While the conventional SSTR geometry depicted inFig. 1 is not mandatory, it does possess distinct advantages fordosimetry applications. In particular, it provides the highestefficiency and sensitivity wh
13、ile maintaining a fixed and easilyreproducible geometry.3.1.2 The track density (that is, the number of tracks per unitarea) is proportional to the fission density (that is, the numberof fissions per unit area). The fission density is, in turn,proportional to the exposure fluence experienced by the
14、SSTR.The existence of nonuniformity in the fission deposit or the1This test method is under the jurisdiction ofASTM Committee E10 on NuclearTechnology and Applications and is the direct responsibility of SubcommitteeE10.05 on Nuclear Radiation Metrology.Current edition approved July 1, 2014. Publish
15、ed October 2014. Originallyapproved in 1981. Last previous edition approved in 2009 as E854 03(2009). DOI:10.1520/E0854-14.2The boldface numbers in parentheses refer to the list of references appended tothis test method.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact
16、ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO B
17、ox C700, West Conshohocken, PA 19428-2959. United States1presence of neutron fluence rate gradients can produce non-uniform track density. Conversely, with fission deposits ofproven uniformity, gradients of the neutron field can beinvestigated with very high spatial resolution.3.2 The total uncertai
18、nty of SSTR fission rates is comprisedof two independent sources. These two error components arisefrom track counting uncertainties and fission-deposit massuncertainties. For work at the highest accuracy levels, fission-deposit mass assay should be performed both before and afterthe SSTR irradiation
19、. In this way, it can be ascertained that nosignificant removal of fission deposit material arose in thecourse of the experiment.4. Significance and Use4.1 The SSTR method provides for the measurement ofabsolute-fission density per unit mass. Absolute-neutron flu-ence can then be inferred from these
20、 SSTR-based absolutefission rate observations if an appropriate neutron spectrumaverage fission cross section is known. This method is highlydiscriminatory against other components of the in-core radia-tion field. Gamma rays, beta rays, and other lightly ionizingparticles do not produce observable t
21、racks in appropriate LWRSSTR candidate materials. However, photofission can contrib-ute to the observed fission track density and should therefore beaccounted for when nonnegligible. For a more detailed discus-sion of photofission effects, see 14.4.4.2 In this test method, SSTR are placed in surface
22、 contactwith fissionable deposits and record neutron-induced fissionfragments. By variation of the surface mass density (g/cm2)ofthe fissionable deposit as well as employing the allowablerange of track densities (from roughly 1 event/cm2up to 105events/cm2for manual scanning), a range of total fluen
23、cesensitivity covering at least 16 orders of magnitude is possible,from roughly 102n/cm2up to 5 1018n/cm2. The allowablerange of fission track densities is broader than the track densityrange for high accuracy manual scanning work with opticalmicroscopy cited in 1.2. In particular, automated and sem
24、i-automated methods exist that broaden the customary trackdensity range available with manual optical microscopy. In thisbroader track density region, effects of reduced countingstatistics at very low track densities and track pile-up correc-tions at very high track densities can present inherent li
25、mita-tions for work of high accuracy. Automated scanning tech-niques are described in Section 11.4.3 For dosimetry applications, different energy regions ofthe neutron spectrum can be selectively emphasized by chang-ing the nuclide used for the fission deposit.4.4 It is possible to use SSTR directly
26、 for neutron dosimetryas described in 4.1 or to obtain a composite neutron detectionefficiency by exposure in a benchmark neutron field. Thefluence and spectrum-averaged cross section in this benchmarkfield must be known. Furthermore, application in other neutronfields may require adjustments due to
27、 spectral deviation fromthe benchmark field spectrum used for calibration. In anyevent, it must be stressed that the SSTR-fission densitymeasurements can be carried out completely independent ofany cross-section standards (6). Therefore, for certainapplications, the independent nature of this test m
28、ethod shouldnot be compromised. On the other hand, many practicalapplications exist wherein this factor is of no consequence sothat benchmark field calibration would be entirely appropriate.5. Apparatus5.1 Optical Microscopes, with a magnification of 200 orhigher, employing a graduated mechanical st
29、age with positionreadout to the nearest 1 m and similar repositioning accuracy.A calibrated stage micrometer and eyepiece scanning grids arealso required.5.2 Constant-Temperature Bath, for etching, with tempera-ture control to 0.1C.5.3 Analytical Weighing Balance, for preparation of etchingbath solu
30、tions, with a capacity of at least 1000 g and anaccuracy of at least 1 mg.6. Reagents and Materials6.1 Purity of ReagentsDistilled or demineralized waterand analytical grade reagents should be used at all times. Forhigh fluence measurements, quartz-distilled water and ultra-pure reagents are necessa
31、ry in order to reduce backgroundfission tracks from natural uranium and thorium impurities.This is particularly important if any pre-irradiation etching isperformed (see 8.2).6.2 Reagents:6.2.1 Hydrofluoric Acid (HF), weight 49 %.6.2.2 Sodium Hydroxide Solution (NaOH), 6.2 N.6.2.3 Distilled or Demin
32、eralized Water.6.2.4 Potassium Hydroxide Solution (KOH), 6.2 N.6.2.5 Sodium Hydroxide Solution (NaOH), weight 65 %.6.3 Materials:6.3.1 Glass Microscope Slides.6.3.2 Slide Cover Glasses.7. SSTR Materials for Reactor Applications7.1 Required PropertiesSSTR materials for reactor appli-cations should be
33、 transparent dielectrics with a relatively highionization threshold, so as to discriminate against lightlyionizing particles. The materials that meet these prerequisitesFIG. 1 Typical Geometrical Configuration Used for SSTR NeutronDosimetryE854 142most closely are the minerals mica, quartz glass, an
34、d quartzcrystals. Selected characteristics for these SSTR are summa-rized in Table 1. Other minerals such as apatite, sphene, andzircon are also suitable, but are not used due to inferior etchingproperties compared to mica and quartz. These alternativeSSTR candidates often possess either higher impe
35、rfectiondensity or poorer contrast and clarity for scanning by opticalmicroscopy. Mica and particularly quartz can be found with theadditional advantageous property of low natural uranium andthorium content. These heavy elements are undesirable inneutron-dosimetry work, since such impurities lead to
36、 back-ground track densities when SSTR are exposed to high neutronfluence. In the case of older mineral samples, a background offossil fission track arises due mainly to the spontaneous fissiondecay of238U. Glasses (and particularly phosphate glasses) areless suitable than mica and quartz due to hig
37、her uranium andthorium content. Also, the track-etching characteristics ofmany glasses are inferior, in that these glasses possess higherbulk etch rate and lower registration efficiency. Other SSTRmaterials, such as Lexan5and Makrofol6are also used, but areless convenient in many reactor application
38、s due to thepresence of neutron-induced recoil tracks from elements suchas carbon and oxygen present in the SSTR. These detectors arealso more sensitive (in the form of increased bulk etch rate) tothe and components of the reactor radiation field (13). Also,they are more sensitive to high temperatur
39、es, since the onset oftrack annealing occurs at a much lower temperature for plasticSSTR materials.7.2 Limitations of SSTR in LWR Environments:7.2.1 Thermal AnnealingHigh temperatures result in theerasure of tracks due to thermal annealing. Natural quartzcrystal is least affected by high temperature
40、s, followed bymica. Lexan and Makrofol are subject to annealing at muchlower temperatures. An example of the use of natural quartzcrystal SSTRs for high-temperature neutron dosimetry mea-surements is the work described in Ref (14).7.2.2 Radiation DamageLexan and Makrofol are highlysensitive to other
41、 components of the radiation field. As men-tioned in 7.1, the bulk-etch rates of plastic SSTR are increased5Lexan is a registered trademark of the General Electric Co., Pittsfield, MA.6Makrofol is a registered trademark of Farbenfabriken Bayer AG, U. S.representative Naftone, Inc., New York, NY.NOTE
42、 1The track designated by the arrow in the mica SSTR is a fossil fission track that has been enlarged by suitable pre-irradiation etching.FIG. 2 Microphotograph of Fission Fragment Tracks in MicaE854 143by exposure to and radiation. Quartz has been observed tohave a higher bulk etch rate after irrad
43、iation with a fluence of41021neutrons/cm2, but both quartz and mica are veryinsensitive to radiation damage at lower fluences (1021neutrons/cm2).7.2.3 Background TracksPlastic track detectors will reg-ister recoil carbon and oxygen ions resulting from neutronscattering on carbon and oxygen atoms in
44、the plastic. Thesefast neutron-induced recoils can produce a background of shorttracks. Quartz and mica will not register such light ions and arenot subject to such background tracks.7.2.4 Thermal Stability of Fissionable Material FoilsUranium foils habe been observed to completely convert tooxide d
45、uring high temperature irradiation.8. SSTR Pre- and Post-Irradiation Processing8.1 Pre-Irradiation Annealing:8.1.1 In the case of mica SSTR, a pre-annealing proceduredesigned to remove fossil track damage is advisable for workat low neutron fluences. The standard procedure is annealingfor6hat600C (l
46、onger time periods may result in dehydra-tion). Fossil track densities are so low in good Brazilian quartzcrystals that pre-annealing is not generally necessary. Anneal-ing is not advised for plastic SSTR because of the possibility ofthermal degradation of the polymer or altered composition,both of
47、which could affect track registration properties of theplastic.8.2 Pre-Irradiation Etching:8.2.1 MicaUnannealed fossil tracks in mica are easilydistinguished from induced tracks by pre-etching for a timethat is long compared to the post-etching conditions. In thecase of mica, a 6-h etch in 48 % HF a
48、t room temperature resultsin large diamond-shaped tracks that are easily distinguishedfrom the much smaller induced tracks revealed by a 90-minpost-etch (see Fig. 2).8.2.2 Quartz CrystalsPre-etching is needed to chemicallypolish the surface. Polish a crystal mechanically on the 001 or100 plane so th
49、at it appears smooth under microscopicalexamination, etch for 10 min in 49 % HF at room temperature,then boil in 65 % NaOH solution for 25 min. Examine thecrystal surface microscopically. If it is sufficiently free of pits,select it for use as an SSTR.8.2.3 Quartz GlassIf the glass has been polishedmechanically, or has a smooth surface, then pre-etch in 49 %HF for 5 min at room temperature. Upon microscopicalexamination a few etch pits may be present even in good-quality quartz glass. If so, they will be larger than tracks due tofission fragments reveal
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