1、Designation: E 854 03Standard 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 E 854; the number immediately following the designation indicates the year oforiginal adoption o
2、r, 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 describes the use of solid-state trackrecorders (SSTRs) for
3、neutron 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) This testmethod replaces Method E
4、 418. 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 SS
5、TR analysis 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
6、 for 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 High fluence limitations exist. These limitations arediscussed in detail in Section 1
7、3 and in references (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 radiometric monitors
8、.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 not purport t
9、o 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:E 418 Method for Fast-Neutr
10、on Measurements by Track-Etch Techniques2E 844 Guide for Sensor Set Design and Irradiation forReactor Surveillance, E706 (IIC)33. Summary of Test Method3.1 SSTR are usually placed in firm surface contact with afissionable nuclide that has been deposited on a pure nonfis-sionable metal substrate (bac
11、king). 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 etched fis-sion tracks in mica, quartz gl
12、ass, 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 while maintaining a fixed and easilyrep
13、roducible 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 SSTR.The existence of nonuniformity i
14、n the fission deposit or thepresence of neutron flux gradients can produce non-uniformtrack density. Conversely, with fission deposits of provenuniformity, gradients of the neutron field can be investigatedwith very high spatial resolution.3.2 The total uncertainty of SSTR fission rates is comprised
15、of two independent sources. These two error components arisefrom track counting uncertainties and fission-deposit mass1This test method is under the jurisdiction of ASTM Committee E10 on NuclearTechnology and Applicationsand is the direct responsibility of SubcommitteeE10.05on Nuclear Radiation Metr
16、ology.Current edition approved Feb. 10, 2003. Published March 2003. Originallyapproved in 1981. Last previous edition approved in 1998 as E 854 98.2Discontinued; see 1983 Annual Book of ASTM Standards, Vol 12.02.3Annual Book of ASTM Standards, Vol 12.02.1Copyright ASTM International, 100 Barr Harbor
17、 Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.uncertainties. For work at the highest accuracy levels, fission-deposit mass assay should be performed both before and afterthe SSTR irradiation. In this way, it can be ascertained that nosignificant removal of fission deposit mate
18、rial 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 SSTR-based absolutefission rate observations if an appropriate neutron spectrumaverage
19、 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 tracks in appropriate LWRSSTR candidate materials. However, photofission can contrib-ute
20、 to the observed fission track density and should therefore beaccounted for when nonnegligible. For a more detailed discus-sion of photofission effects, see 13.4.4.2 In this test method, SSTR are placed in surface contactwith fissionable deposits and record neutron-induced fissionfragments. By varia
21、tion 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 fluencesensitivity covering at least 16 orders of magnitude is possible,from roughly 102n/cm
22、2up to 5 3 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 semi-automated methods exist that broaden the customary trackdensity range available wit
23、h 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 limita-tions for work of high accuracy. Automated scanning tech-niques are described in
24、 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 for neutron dosimetryas described in 4.1 or to obtain a composite neutron detectione
25、fficiency 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 spectral deviation fromthe benchmark field spectrum used for calibration. In anyeven
26、t, it must be stressed that the SSTR-fission densitymeasurements can be carried out completely independent ofany cross-section standards (6). Therefore, for certain applica-tions, the independent nature of this test method should not becompromised. On the other hand, many practical applicationsexist
27、 wherein this factor is of no consequence so that bench-mark field calibration would be entirely appropriate.5. Apparatus5.1 Optical Microscopes, with a magnification of 200 3 orhigher, employing a graduated mechanical stage with positionreadout to the nearest 1 m and similar repositioning accuracy.
28、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 solutions, with a capacity of at least 1000 g and anaccuracy of at least 1 mg.6. Re
29、agents 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 necessary in order to reduce backgroundfission tracks from natural uranium and thorium
30、 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 Demineralized Water.6.2.4 Potassium Hydroxide Solution (KOH), 6.2 N.6.2.5 Sodium Hyd
31、roxide 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 transparent dielectrics with a relatively highionization threshold, so as to d
32、iscriminate against lightlyionizing particles. The materials that meet these prerequisitesmost closely are the minerals mica, quartz glass, and quartzcrystals. Selected characteristics for these SSTR are summa-rized in Table 1. Other minerals such as apatite, sphene, andzircon are also suitable, but
33、 are not used due to inferior etchingproperties compared to mica and quartz. These alternativeSSTR candidates often possess either higher imperfectiondensity or poorer contrast and clarity for scanning by opticalmicroscopy. Mica and particularly quartz can be found with theadditional advantageous pr
34、operty of low natural uranium andthorium content. These heavy elements are undesirable inFIG. 1 Typical Geometrical Configuration Used for SSTR NeutronDosimetryE854032neutron-dosimetry work, since such impurities lead to back-ground track densities when SSTR are exposed to high neutronfluence. In th
35、e case of older mineral samples, a background offossil fission track arises due mainly to the spontaneous fissiondecay of238U. Glasses (and particularly phosphate glasses)are less suitable than mica and quartz due to higher uraniumand thorium content. Also, the track-etching characteristics ofmany g
36、lasses are inferior, in that these glasses possess higherbulk etch rate and lower registration efficiency. Other SSTRmaterials, such as Lexan4and Makrofol5are also used, but areless convenient in many reactor applications due to thepresence of neutron-induced recoil tracks from elements suchas carbo
37、n and oxygen present in the SSTR. These detectors arealso more sensitive (in the form of increased bulk etch rate) tothe b and g components of the reactor radiation field (13).Also, they are more sensitive to high temperatures, since theonset of track annealing occurs at a much lower temperaturefor
38、plastic SSTR 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 temperatures, followed bymica. Lexan and Makrofol are subject to annealing at muchlower
39、 temperatures. An example of the use of natural quartzcrystal SSTRs for high-temperature neutron dosimetry mea-surements is the work described in reference (14).7.2.2 Radiation DamageLexan and Makrofol are highlysensitive to other components of the radiation field. As men-tioned in 7.1, the bulk-etc
40、h rates of plastic SSTR are increasedby exposure to b and g radiation. Quartz has been observed tohave a higher bulk etch rate after irradiation with a fluence of4 3 1021neutrons/cm2, but both quartz and mica are veryinsensitive to radiation damage at lower fluences (1021neutrons/cm2).7.2.3 Backgrou
41、nd TracksPlastic track detectors will reg-ister recoil carbon and oxygen ions resulting from neutronscattering on carbon and oxygen atoms in 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
42、 such background tracks.4Lexan is a registered trademark of the General Electric Co., Pittsfield, MA.5Makrofol is a registered trademark of Farbenfabriken Bayer AG, U. S.representative Naftone, Inc., New York, NY.NOTE 1The track designated by the arrow in the mica SSTR is a fossil fission track that
43、 has been enlarged by suitable preirradiation etching.FIG. 2 Microphotograph of Fission Fragment Tracks in MicaE8540338. 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
44、 for workat low neutron fluences. The standard procedure is annealingfor6hat600C (longer 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 t
45、he possibility ofthermal degradation of the polymer or altered composition,both of which could effect 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 c
46、ompared to the post-etching conditions. In thecase of mica, a 6-h etch in 48 % HF at 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 chemi
47、callypolish the surface. Polish a crystal mechanically on the 001 or100 plane so that 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
48、 pits,select it for use as an SSTR.8.2.3 Quartz GlassIf the glass has been polished me-chanically, or has a smooth surface, then pre-etch in 49 % HFfor 5 min at room temperature. Upon microscopical examina-tion a few etch pits may be present even in good-quality quartzglass. If so, they will be larg
49、er than tracks due to fissionfragments revealed in the post-etch, and readily distinguishedfrom them.8.2.4 Plastic-Track RecordersIf handled properly, back-ground from natural sources, such as radon, will be negligible.Consequently, both preannealing and pre-etching should beunnecessary.8.3 Post-Irradiation Etching:8.3.1 MicaCustomary etching is for 90 min in 49 % HF atroom temperature. Both the etch time and temperature may bevaried to give optimum track sizes for the particular type ofmica used. Except for work at the highest accuracy levels,precise control of the tem
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