1、Designation: C 1308 08Standard Test Method forAccelerated Leach Test for Diffusive Releases fromSolidified Waste and a Computer Program to ModelDiffusive, Fractional Leaching from Cylindrical WasteForms1This standard is issued under the fixed designation C 1308; the number immediately following the
2、designation indicates the year oforiginal adoption or, 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 provides
3、procedures for measuring theleach rates of elements from a solidified matrix material,determining if the releases are controlled by mass diffusion,computing values of diffusion constants based on models, andverifying projected long-term diffusive releases. This testmethod is applicable to any materi
4、al that does not degrade ordeform during the test.1.1.1 If mass diffusion is the dominant step in the leachingmechanism, then the results of this test can be used to calculatediffusion coefficients using mathematical diffusion models. Acomputer program developed for that purpose is available as acom
5、panion to this test method (Note 1).1.1.2 It should be verified that leaching is controlled bydiffusion by a means other than analysis of the leach testsolution data. Analysis of concentration profiles of species ofinterest near the surface of the solid waste form after the test isrecommended for th
6、is purpose.1.1.3 Potential effects of partitioning on the test results canbe identified through modeling, although further testing andanalyses are required to determine the cause of partitioning (forexample, if it occurs during production of the material or as aresult of leaching).1.2 The method is
7、a modification of other semi-dynamictests such as the IAEA test (1)2and the ANS 16.1 Leach Testwherein elevated temperatures are used to accelerate diffusiverelease to an extent that would only be reached after very longtimes at lower temperatures. This approach provides a mecha-nistic basis for cal
8、culating diffusive releases at repository-relevant temperatures over long times, provided that theleaching mechanism does not change with temperature.1.2.1 Tests can be conducted at elevated temperatures toaccelerate diffusive release and provide a mechanistic basis forcalculating diffusive releases
9、 that would occur at lower tem-peratures over long times. Tests conducted at high temperaturesallow the temperature dependence of the diffusion coefficientto be determined. They also demonstrate that the diffusionmechanism is rate-limiting through the measured extent ofdiffusive release.1.2.2 Releas
10、es at any temperature can be projected up to thehighest cumulative fractional release value that has beenmeasured for that material (at any temperature), provided thatthe mechanism does not change. The mechanism is consideredto remain unchanged over a range of temperatures if thediffusion coefficien
11、ts show Arrhenius behavior over that range.NOTE 1A computer program in which the test results are evaluatedusing three diffusion models is briefly described in Annex A1 and in theAccelerated Leach Test Method and Users Guide for the “ALT” Com-puter Program (2). The data are fit with model equations
12、for diffusion froma semi-infinite solid, diffusion from a finite cylinder, and diffusion withpartitioning of the species of interest to determine effective diffusioncoefficients and quantify the goodness of fit. The Users Guide containsseveral typographical errors; these are identified in Annex A1.1
13、.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 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
14、-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C 1220 Test Method for Static Leaching of MonolithicWaste Forms for Disposal of Radioactive WasteD 1193 Specification for Reagent Water2.2 ANSI/ANS S
15、tandard:ANSI 16.1 Measurement of the Leachability of Solidified1This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.07 on WasteMaterials.Current edition approved Dec. 1, 2008. Published January 2009. Originallyapp
16、roved in 1995. Last previous edition approved in 2001 as C 1308 95 (2001).2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annu
17、al Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Low-Level Radioactive Wastes by a Short-Term TestProcedure43. Terminology3.1
18、 Definitions:3.1.1 cumulative fraction leachedthe sum of the fractionsof a species leached during all sampling intervals prior to andincluding the present interval divided by the amount of thatspecies in the test specimen before the test.3.1.2 diffusion coeffcient (diffusivity)an intrinsic propertyo
19、f a species that relates (1) its concentration gradient to its fluxin a given medium (Ficks first law), (2) its spatial rate ofchange in the direction of the concentration gradient to the timerate of change in its concentration in a given medium (Fickssecond law), or (3) its mean square displacement
20、 to time in agiven medium (the Einstein equation).3.1.3 effective diffusion coeffcient (De)the diffusion coef-ficient as modified by other processes (for example, adsorp-tion) or physical constraints (for example, tortuosity andconstrictivity).3.1.4 finite cylinder (finite medium)a bounded body forw
21、hich Ficks diffusion equation can be solved.3.1.5 incremental fraction leachedthe amount of a speciesleached during a single sampling interval divided by theamount of that species in the test specimen before the test.3.1.6 leachantthe initial solution with which a solid iscontacted and into which th
22、e solid dissolves or is leached.3.1.7 leachatethe final solution resulting from a test inwhich a solid is contacted by a solution and leaches ordissolves.3.1.8 leachingthe preferential loss of components from asolid material into solution leaving a residual phase that isdepleted in those components,
23、 but structurally unchanged.3.1.9 leaching intervalthe length of time during which agiven volume of leachant is in contact with a specimen.3.1.10 leaching mechanismthe set of processes that con-trols the rate of mass transport of a species out of a specimenduring leaching.3.1.11 matrix materialthe s
24、olid material used to immobi-lize the waste or species of interest.3.1.12 reference leach testa leach test conducted underdefined conditions, the results of which are used as a standardagainst which the results of other leach tests are compared. Inthis test method, a reference leach test is one that
25、 is conductedat 20C using demineralized water.3.1.13 semi-dynamic leach testa leach test method inwhich the specimen is exposed to fresh leachant on a periodicschedule.3.1.14 semi-infinite mediuma body having a single planarsurface and extending infinitely in the directions parallel to thesurface an
26、d in one direction normal to the surface.3.1.15 source termin this test method, the concentrationof a species of interest in a specimen prior to leaching.3.1.16 specimen volumefor purposes of this test method,the volume of a monolithic specimen calculated from macro-scopic measurements of its dimens
27、ions by assuming a simplegeometric shape, such as a right circular cylinder.3.1.17 surface areafor purposes of this test method, thegeometric surface area of a monolithic specimen that iscalculated from macroscopic measurements of its dimensionsby assuming a simple geometric shape, such as a right c
28、ircularcylinder.3.1.18 waste formthe waste material and any encapsulat-ing or stabilizing matrix in which it is incorporated.4. Summary of Test Method4.1 This test method is a semi-dynamic leach test in whicha cylindrical specimen is immersed in a leachant that iscompletely replaced after specified
29、intervals. The concentra-tion of an element of interest in the recovered test solution ismeasured after each exchange; this is referred to as theincremental fraction leached (IFL). The accumulated amountof the species of interest in the intervals prior to and includingthe interval of interest is ana
30、lyzed to determine if the releasefrom the solid can be described using a mass diffusion model.The amount accumulated through a particular test duration isreferred to as the cumulative fraction leached (CFL).4.2 Tests at a single temperature are adequate to comparethe leaching behaviors of different
31、materials.4.3 The results of tests at repository-relevant temperaturescan be extrapolated to long times if data from tests run atelevated temperatures and data from tests run at the referencetemperature (20C) can be modeled using a diffusion modeland the diffusion coefficients show Arrhenius behavio
32、r.4.3.1 Elevated temperatures are used to accelerate the re-lease of a species of interest and collect enough data to showthat the release is controlled by diffusion and determine thevalue of the diffusion coefficient.4.3.2 Tests must be performed at a minimum of threetemperatures to verify that the
33、 leaching mechanism does notchange over that temperature range.4.3.3 By generating data over a range of temperatures, anArrhenius plot can be produced to interpolate values of thediffusion coefficient within the temperature range that wastested. Values cannot be extrapolated to temperatures that are
34、higher or lower than the temperature range spanned by thetests.4.3.4 A computer program that plots the experimental dataand a regression curve calculated using a finite cylinder model(2) is available from ASTM (see Note 1). The programprovides the value of the effective diffusion coefficient, themod
35、eled IFL and CFL values, and a measure of the goodnessof fit of the model.4.4 If the data from the accelerated tests, the reference test,and the fit of the modeled curve agree within defined criteria,the leaching mechanism can be taken to be diffusion-controlledand a diffusion model can be used to c
36、alculate releases fromfull-scale waste forms for long times.4.4.1 The accelerated leach test provides the maximumcumulative fractional release to which the modeled data can beextrapolated. The maximum cumulative fractional release mea-sured represents the maximum extent of reaction for which thecons
37、istency of the mechanism has been verified for thatmaterial.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.C13080824.4.2 Because the cumulative fraction leached is a functionof the specimen surface area-to-volume ratio,
38、the results oftests with the small-scale specimens used in the ALT directlyrepresent leaching from large-scale waste forms having thesame aspect ratio.4.4.3 The effective diffusion coefficient can be used tocalculate diffusive releases from waste forms with othershapes.4.5 If the diffusion model doe
39、s not fit the data within definedcriteria, no extrapolation can be made in time or specimen size.However, other models can be applied to the data to evaluatethe leaching process.4.5.1 A model including diffusion with partitioning of thespecies of interest between phases having different releasebehav
40、iors is included in the computer program (2).4.5.2 The possibility of a solubility-limit to the release ofthe species of interest is addressed in the computer program(2).4.6 If the data cannot be fit with a diffusion model within thedefined criterion, then graphical comparisons of the data arerecomm
41、ended for added insight: For example, a plot of thecumulative fraction leached (CFL) from ALT conducted at anelevated temperature against the CFL from ALT conducted atthe reference temperature can be used to verify that theaccelerated data are consistent with the reference data and thatthe accelerat
42、ed test appropriately accelerates the release, eventhough the release is not diffusion-limited.5. Significance and Use5.1 This test method can be used to measure the release ofa component from a cylindrical solidified waste form intowater at the reference temperature of 20C and at elevatedtemperatur
43、es that accelerate the rate and extent of leachingrelative to the values measured at 20C.5.2 This test method can be used to:5.2.1 Compare releases of waste components from varioustypes of solidification agents and formulations.5.2.2 Determine the diffusion coefficients for the release ofwaste compo
44、nents from waste forms at a specific temperature.5.2.3 Promote greater extents of reaction than can beachieved under expected service conditions within a laboratorytime frame to provide greater confidence in modeled diffusivereleases.5.2.4 Determine the temperature dependence of diffusiverelease.5.3
45、 Fitting the experimental results with a mechanisticmodel allows diffusive releases to be extrapolated to long timesand to full-scale waste forms under the following constraints:5.3.1 Results of this test method address an intrinsic prop-erty of a material and should not be presumed to representrele
46、ases in specific disposal environments. Tests can be con-ducted under conditions that represent a specific disposalenvironment (for example, by using a representative ground-water) to determine an effective diffusion coefficient for thoseconditions.5.3.2 Projections of releases over long times requi
47、res thatthe waste form matrix remain stable, which may be demon-strated by the behavior of the specimen in ALTs at elevatedtemperatures.5.3.3 Extrapolations in time and scale are limited to valuesthat correspond to the maximum CFL value obtained in anaccelerated test.5.3.4 The mechanism must be the
48、same at all temperaturesused in the extrapolation. The same model that describes theresults of tests conducted at elevated temperatures must alsodescribe the results of tests run at the reference temperature of20C.6. Apparatus6.1 A forced-air environmental chamber or a circulatingwater bath capable
49、of controlling leachant temperatures towithin 1C of the target test temperature shall be used.6.2 BalanceThe balance shall be accurate to 0.1 % of thetest load.7. Reagents and Materials7.1 LeachantThe leachant can be selected with regard tothe material being tested and the information that is desired.Demineralized water, synthetic or actual groundwaters, orchemical solutions can be used. The effects of the leachantsolution on the species of interest (that is, the species for whichthe diffusion coefficient is to be measured) and the solid mustbe cons
