ASTM C1308-1995(2001) Standard Test Method for Accelerated Leach Test for Diffusive Releases from Solidified Waste and a Computer Program to Model Diffusive Fractional Leaching fro.pdf

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1、Designation: C 1308 95 (Reapproved 2001)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 C 1308; the number immediat

2、ely 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This te

3、st method provides a method for accelerating theleach rate of solidified waste and determining if the release isdiffusion-controlled. This test method is applicable to anymaterial that does not degrade, deform, or change leachingmechanism during the test.1.1.1 If diffusion is the dominant leaching m

4、echanism, thenresults of this test can be used to model long-term releases fromwaste forms. Diffusion can be confirmed as the leachingmechanism through the use of a computerized mathematicalmodel for diffusion from the finite cylinder (Note 1).1.1.2 The leaching mechanism should be verified asdiffus

5、ion-controlled by a means other than analysis of the leachtest data. For this purpose, analysis of post-leaching concen-tration profiles within the solid waste form is recommended.NOTE 1The computer program and the models are briefly describedin Annex A1 and in the Accelerated Leach Test Method and

6、Users Guidefor the “ALT” Computer Program (1).1.2 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 applica-bility of regul

7、atory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:E 632 Standard Practice for Developing Accelerated Teststo Aid Prediction of the Service Life of Building Compo-nents and Materials2D 1193 Standard Specification for Reagent Water32.2 ANSI/ANS Standard:ANSI 16.1 Measurement of

8、the Leachability of SolidifiedLow-Level Radioactive Wastes by a Short-Term TestProcedure43. Terminology3.1 cumulative fraction leachedthe sum of the fractions ofa species leached during all sampling intervals calculated asCFL = (an/AOand assuming no radioactive decay, where anisthe quantity of a spe

9、cies in the leachate during any interval andAOis the quantity of that species originally present in thesample.3.2 diffusion coeffcient (diffusivity)based on Ficks Lawsfor diffusion, the diffusion coefficient is the ratio of the rate oftransfer of a diffusing substance through the unit area of asecti

10、on to the concentration gradient measured normal to thesection.3.3 effective diffusion coeffcient (effective diffusivity)thediffusion coefficient that results from diffusion as it is modifiedby other processes (for example, adsorption) or physicalconstraints (for example, tortuosity and constrictivi

11、ty).3.4 finite cylinder (finite medium)a bounded body forwhich Ficks diffusion equation can be solved.3.5 incremental fraction leachedthe fraction leached of aspecies of interest during a single sampling interval calculatedas IFL = an/AOand assuming no radioactive decay.3.6 leachantthe liquid that c

12、ontacts the specimen during aleach test or contacts a waste form in the disposal environment.3.7 leachatethe leachant after contacting the specimen orthe waste form.3.8 leachingthe process (or processes) by which masstransport from a solid to a liquid takes place.3.9 leaching intervalthe length of t

13、ime during which agiven volume of leachant is in contact with a specimen.3.10 leaching mechanismthe process that controls the rateof mass transport out of a specimen during leaching.3.11 reference leach testa leach test conducted underdefined conditions, the results of which are used as a standardag

14、ainst which the results of other leach tests (for example,accelerated) are compared. In this test method a reference leach1This 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 a

15、pproved Sept. 10, 1995. Published April 1996.2Annual Book of ASTM Standards, Vol 14.02.3Annual Book of ASTM Standards, Vol 11.01.4Available from American National Standards Institute, 11 W. 42nd St., 13thFloor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, Wes

16、t Conshohocken, PA 19428-2959, United States.test is one that is conducted at 20C.3.12 semi-dynamic leach testa leach test method thatexposes the specimen to fresh leachant on a periodic schedule.3.13 semi-infinite mediuma body used in diffusion theorywhose outer boundary is effectively at an infini

17、te distance fromthe inner region.3.14 source termthe original concentration, prior to leach-ing, of a species of interest in a specimen or a waste form.3.15 surface areafor purposes of this test method, surfacearea is defined as the geometric surface area of a specimencalculated from macroscopic mea

18、surements of its dimensions.3.16 volumefor purposes of this test method, volume isdefined as the volume of a specimen calculated from macro-scopic measurements of its dimensions.3.17 waste forma stable, solid body composed of thewaste and a solidification agent.4. Summary of Test Method4.1 This test

19、 method is a semi-dynamic leach test, that is,the leachant is sampled and replaced periodically. It is based onearlier semi-dynamic tests such as the IAEA test (2) and theANS 16.1 Leach Test.4Elevated temperatures, large volumesof leachant, frequent leachant changes, and small specimensize are used

20、to obtain accelerated releases. This is a short-termtest, requiring sampling on each of eleven or more successivedays. Tests must be performed to demonstrate that the leachingmechanism does not change at the elevated test temperature.This may be done by performing leach tests at a minimum ofthree te

21、mperatures to ascertain that the mechanisms andstructural controls of leaching do not change with increasingtemperature. If the test is to be used only for making compari-sons among specimens, then testing at a single temperature isadequate.4.2 The results of this accelerated test can be extrapolate

22、d tolong times if the data from tests run at elevated temperaturesand the tests run at the reference temperature (20C), and canbe modeled by diffusion. A computer program that plots theexperimental data and a curve calculated from an effectivediffusion coefficient for diffusion from a finite cylinde

23、r (Fig. 1)is available from ASTM. If the data from the accelerated tests,the reference test, and the modeled curve fit within definedcriteria, the leaching mechanism is taken to be diffusion. In thiscase, the model can be used to project releases from full-scalewaste forms and to long times. The acc

24、elerated test provides ameasure of the maximum fractional release to which themodeled data can be extrapolated. By generating data over aspecified temperature range, an Arrhenius plot can be producedallowing projections to be made at temperatures other thanthose tested. If the diffusion model cannot

25、 fit the data, othermodels (for example, diffusion plus partitioning and solubilitylimited leaching) contained in the computer program can beused to indicate the leaching mechanism that controls releases.No extrapolations are allowed with these models. If no modelfits the data, then an alternative g

26、raphical comparison of thedata is recommended. A linear plot of modeled CFL plottedagainst experimental CFL verifies that the accelerated data iscomparable to the reference data, showing that the acceleratedtest is appropriate. With this technique, no extrapolation of datacan be made.5. Significance

27、 and Use5.1 This test method measures mass transport from a cylin-drical solidified waste form into water under conditions thataccelerate leaching. Test parameters, such as the volume ofleachant and the frequency at which the leachant is changed,have been optimized to eliminate experimental effects

28、(forexample, saturation effects that can complicate modeling of thenet forward diffusion rate).5.2 This test method can be used to:5.2.1 Provide diffusion coefficients for waste forms;5.2.2 Obtain higher fraction releases than can be achievedwith expected service conditions for greater confidence in

29、waste form properties;5.2.3 Obtain measurable leachate concentrations from ma-terials that have very low release rates under service condi-tions; and5.2.4 Compare releases from various types of solidificationagents and formulations.5.3 Modeling the experimental observations obtained in thetest allow

30、s the extrapolation of leaching results to long timesand to full-scale waste forms under the following constraints:5.3.1 Results of this test method cannot be taken to apply toreleases in specific disposal environments unless tests areconducted to determine the leaching mechanism under thoseconditio

31、ns.5.3.2 Projections of releases require the long-term stabilityof the waste form, which may or may not be indicatedadequately by short-term tests.5.3.3 Extrapolations are limited to the maximum CFLobtained with the accelerated test.5.3.4 The leaching mechanisms observed in tests conductedat elevate

32、d temperatures must be the same as the mechanismsobserved in the tests run at the reference temperature.6. Apparatus6.1 A forced-air environmental chamber or a circulatingwater bath capable of controlling leachant temperatures to61C shall be used.6.2 BalanceThe balance shall be accurate to 0.1 % of

33、thetest load.FIG. 1 A Schematic of the Concepts Used in This Test Method toCombine Experimental and Modeling ApproachesC 130827. Reagents and Materials7.1 LeachantThe leachant shall be distilled or deionizedwater meeting or exceeding standards for types II or III reagentwater as specified in Specifi

34、cation D 1193.7.2 ContainersLeaching containers shall be made of amaterial that does not react with the leachant/leachate and thespecimen. It is particularly important to select materials thatallow very little plate-out of radionuclides from solution. Highdensity polyethylene has been found to be a

35、suitable containermaterial. The top of the container shall fit tightly to minimizeevaporation. This fit must be checked at test temperatures toensure that evaporative losses are less than 1 % over 24 hours.7.3 Specimen SupportsSupports for the specimens shallbe made of a material that does not react

36、 with the leachant/leachate or the specimen and does not allow plate-out onto thesupport. The method of support should not impede leaching byobstructing the surface area of the specimen by more than 1 %.Moreover, it should not interfere with replacement of theleachate. It is often convenient to susp

37、end the waste form fromthe cover of the leaching container using monofilament string.7.4 Sample ContainersContainers to hold aliquots ofleachate for storage prior to analysis should not allow anyplate-out of radionuclides. The containers should be checked toascertain that evaporation over long times

38、 is acceptably small.7.5 StirrersStirrers that are long enough to reach thebottom of the leaching containers are required. Wood or plastictongue depressors are adequate.7.6 Filtration EquipmentIf particulates are present in theleachate, filtration is necessary. Tests must be conducted toensure that

39、the filter and the filtration apparatus do not adsorbthe species of interest. The filter medium should be capable ofremoving particulates that are 0.45 m in diameter. Disposablesyringe filters are recommended.8. Specimens8.1 Right circular cylindrical specimens shall be used with adiameter-to-height

40、 ratio between 1:1 and 1:2. A convenient sizeis 2.5 cm diameter by 2.5 cm height. Smaller sizes should beavoided to preclude problems of mixing and producing non-homogeneous samples.8.2 Specimens shall be representative of the full-scalesolidified waste form. Particular attention should be paid toen

41、suring that the laboratory specimen is homogeneous. Thespecimens should be prepared using the same techniques asthose used to produce full-scale waste forms. Curing condi-tions, especially the temperatures experienced by the largewaste forms, should be duplicated for laboratory-scale speci-mens. Car

42、e should be taken to ensure that surfaces of thelaboratory specimens reflect the structure of surfaces of largewaste forms. This refers to surfaces that are cast againstcontainer walls as opposed to free or cut surfaces.8.3 A minimum of three specimens should be tested at anygiven temperature.8.4 Th

43、e dimensions, weight, composition, and curing his-tory shall be recorded for each specimen. Accurate determina-tion of the source term (A0), that is, the amount of the speciesof interest in the specimen at the start of the leach test, shall bemade and recorded.9. Procedure9.1 Removal of Specimen fro

44、m MoldAfter removing thespecimen from its container or mold, any excess materialshould be removed prior to weighing the specimen. The moldshould be rinsed in a volume of water equal to the volume ofthe specimen. If the quantity of the species of interest con-tained in this rinse water represents mor

45、e than 0.5 % of thetotal quantity in the specimen, the value should be subtractedfrom the source term (A0).9.2 Leachant VolumeThe leachant volume used for eachinterval is 100 3 the surface area of the specimen as calculatedbelow:Leachant volume cm3!Specimen surface area cm2!5 100 cm 6 2 % (1)This ra

46、tio requires a large volume of water, for example, a2.5 cm 3 2.5 cm specimen has a surface area of approximately30 cm2, giving a leachant volume of 3000 mL. Specimens thatare much larger than this will require volumes of water thatneed more sophisticated means of wastewater handling (suchas peristal

47、tic pumps for draining the containers), since largevolumes are too unwieldy for pouring.NOTE 2Some waste form materials, such as glass, have such lowleach rates that a volume-to-surface area ratio of 100 cm is not necessary.In some cases, such a large volume of leachant can make analysischallenging,

48、 even for major constituents of the specimen. Under thesecircumstances, the volume-to-surface area ratio may be reduced to 10 cm.9.3 TemperatureFor materials and formulations that havenot been tested previously, leach tests shall be conducted at aminimum of three temperatures to establish that leach

49、ingincreases systematically with higher temperatures. One tem-perature must be 20C. The recommended maximum tempera-ture is 50C, which is below the threshold of anomalousreleases observed so far (3). Temperatures above 50C can beused if it is demonstrated that releases follow the trendobserved at low temperatures, that is, that the leaching mecha-nism has not changed.9.4 Leachant ReplacementLeachant replacements shalltake place at the time intervals shown in Table 1. The time atwhich the specimen is first placed in the leachant should benoted. Th