1、Designation: C1308 08 (Reapproved 2017)Standard 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 C1308; the number immediatel
2、y following the 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
3、method provides 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 applicab
4、le to any material 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 a
5、vailable as acompanion 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 isre
6、commended for this 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.
7、2 The method is 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-nist
8、ic basis for calculating 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 di
9、ffusive releases 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 relea
10、se.1.2.2 Releases 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 thediffu
11、sion coefficients showArrhenius 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 mo
12、del equations 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
13、 in Annex A1.1.3 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 e
14、stablish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C1220 Test Method for Static Leaching of Monolithic WasteForms for Disposal of Radioactive Waste1This test method is under the jurisdic
15、tion ofASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.13 on Spent Fueland High Level Waste.Current edition approved Jan. 1, 2017. Published January 2017. Originallyapproved in 1995. Last previous edition approved in 2008 as C1308 08. DOI:10.1520/C1308-08
16、R17.2The 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 Annual Book of ASTMStandards volume information, refer to the standards Do
17、cument Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on
18、 Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1D1193 Specification for Reagent Water2.2 ANSI/ANS Standard:ANSI 16.1 Measurement of the Leachability of SolidifiedLow-Level Radioa
19、ctive Wastes by a Short-Term TestProcedure43. Terminology3.1 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.
20、1.2 diffusion coeffcient (diffusivity)an intrinsic propertyof 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 m
21、edium (Fickssecond law), or (3) its mean square displacement 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 andconstrictivi
22、ty).3.1.4 finite cylinder (finite medium)a bounded body forwhich 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 initi
23、al solution with which a solid iscontacted and into which the 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 l
24、eaving a residual phase that isdepleted in those components, 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
25、out of a specimenduring leaching.3.1.11 matrix materialthe solid 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 comp
26、ared. Inthis test method, a reference leach test is one that 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 exte
27、nding infinitely in the directions parallel to thesurface and in one direction normal to the surface.3.1.15 source termin this test method, the concentration ofa species of interest in a specimen prior to leaching.3.1.16 specimen volumefor purposes of this test method,the volume of a monolithic spec
28、imen calculated from macro-scopic measurements of its dimensions 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 dimen
29、sionsby assuming a simple geometric shape, such as a right circularcylinder.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 immers
30、ed in a leachant that iscompletely replaced after specified 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 int
31、ervals prior to and includingthe interval of interest is analyzed 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
32、 are adequate to comparethe leaching behaviors of different 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 diffusio
33、n modeland the diffusion coefficients show Arrhenius behavior.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 pe
34、rformed at a minimum of threetemperatures to verify that the 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 waste
35、sted. Values cannot be extrapolated to temperatures that arehigher 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 programprovi
36、des the value of the effective diffusion coefficient, themodeled IFL and CFL values, and a measure of the goodnessof fit of the model.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.C1308 08 (2017)24.4 If the data from th
37、e 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 calculate releases fromfull-scale waste forms for long times.4.4.1 The accelerated leach test prov
38、ides 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 theconsistency of the mechanism has been verified for thatmaterial.4.4.2 Because the cumulative fraction
39、 leached is a functionof the specimen surface area-to-volume ratio, 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 relea
40、ses from waste forms with othershapes.4.5 If the diffusion model does 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
41、 thespecies of interest between phases having different releasebehaviors 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 th
42、edefined criterion, then graphical comparisons of the data arerecommended 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 theaccelerat
43、ed data are consistent with the reference data and thatthe accelerated 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 int
44、owater at the reference temperature of 20C and at elevatedtemperatures 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.
45、2 Determine the diffusion coefficients for the release ofwaste components 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 diffusiverelease
46、s.5.2.4 Determine the temperature dependence of diffusiverelease.5.3 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
47、 prop-erty of a material and should not be presumed to representreleases 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
48、 thoseconditions.5.3.2 Projections of releases over long times requires 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 v
49、alue obtained in anaccelerated test.5.3.4 The mechanism must be the 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 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.
