ASTM C1308-08(2017)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:C1308 −08 (Reapproved 2017)
Standard Test Method for
Accelerated Leach Test for Diffusive Releases from
Solidified Waste and a Computer Program to Model
Diffusive, Fractional Leaching from Cylindrical Waste
Forms
This standard is issued under the fixed designation C1308; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.2.1 Tests can be conducted at elevated temperatures to
acceleratediffusivereleaseandprovideamechanisticbasisfor
1.1 This test method provides procedures for measuring the
calculating diffusive releases that would occur at lower tem-
leach rates of elements from a solidified matrix material,
peraturesoverlongtimes.Testsconductedathightemperatures
determining if the releases are controlled by mass diffusion,
allow the temperature dependence of the diffusion coefficient
computing values of diffusion constants based on models, and
to be determined. They also demonstrate that the diffusion
verifying projected long-term diffusive releases. This test
mechanism is rate-limiting through the measured extent of
method is applicable to any material that does not degrade or
diffusive release.
deform during the test.
1.2.2 Releasesatanytemperaturecanbeprojecteduptothe
1.1.1 If mass diffusion is the dominant step in the leaching
highest cumulative fractional release value that has been
mechanism,thentheresultsofthistestcanbeusedtocalculate
measured for that material (at any temperature), provided that
diffusion coefficients using mathematical diffusion models. A
the mechanism does not change.The mechanism is considered
computer program developed for that purpose is available as a
to remain unchanged over a range of temperatures if the
companion to this test method (Note 1).
diffusioncoefficientsshowArrheniusbehavioroverthatrange.
1.1.2 It should be verified that leaching is controlled by
diffusion by a means other than analysis of the leach test
NOTE 1—A computer program in which the test results are evaluated
using three diffusion models is briefly described in Annex A1 and in the
solution data. Analysis of concentration profiles of species of
Accelerated Leach Test Method and User’s Guide for the “ALT” Com-
interestnearthesurfaceofthesolidwasteformafterthetestis
puterProgram (2).Thedataarefitwithmodelequationsfordiffusionfrom
recommended for this purpose.
a semi-infinite solid, diffusion from a finite cylinder, and diffusion with
1.1.3 Potential effects of partitioning on the test results can
partitioning of the species of interest to determine effective diffusion
be identified through modeling, although further testing and coefficients and quantify the goodness of fit. The User’s Guide contains
several typographical errors; these are identified in Annex A1.
analysesarerequiredtodeterminethecauseofpartitioning(for
example, if it occurs during production of the material or as a
1.3 The values stated in SI units are to be regarded as
result of leaching).
standard. No other units of measurement are included in this
standard.
1.2 The method is a modification of other semi-dynamic
tests such as the IAEA test (1) and the ANS 16.1 Leach Test
1.4 This standard does not purport to address all of the
wherein elevated temperatures are used to accelerate diffusive safety concerns, if any, associated with its use. It is the
release to an extent that would only be reached after very long
responsibility of the user of this standard to establish appro-
times at lower temperatures. This approach provides a mecha- priate safety and health practices and determine the applica-
nistic basis for calculating diffusive releases at repository-
bility of regulatory limitations prior to use.
relevant temperatures over long times, provided that the
2. Referenced Documents
leaching mechanism does not change with temperature.
2.1 ASTM Standards:
C1220TestMethodforStaticLeachingofMonolithicWaste
ThistestmethodisunderthejurisdictionofASTMCommitteeC26onNuclear
Forms for Disposal of Radioactive Waste
Fuel Cycle and is the direct responsibility of Subcommittee C26.13 on Spent Fuel
and High Level Waste.
Current edition approved Jan. 1, 2017. Published January 2017. Originally
approved in 1995. Last previous edition approved in 2008 as C1308–08. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/C1308-08R17. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1308−08 (2017)
D1193Specification for Reagent Water 3.1.14 semi-infinite medium—a body having a single planar
surface and extending infinitely in the directions parallel to the
2.2 ANSI/ANS Standard:
surface and in one direction normal to the surface.
ANSI 16.1Measurement of the Leachability of Solidified
Low-Level Radioactive Wastes by a Short-Term Test
3.1.15 sourceterm—inthistestmethod,theconcentrationof
Procedure
a species of interest in a specimen prior to leaching.
3.1.16 specimen volume—for purposes of this test method,
3. Terminology
the volume of a monolithic specimen calculated from macro-
3.1 Definitions:
scopic measurements of its dimensions by assuming a simple
3.1.1 cumulative fraction leached—the sum of the fractions
geometric shape, such as a right circular cylinder.
of a species leached during all sampling intervals prior to and
3.1.17 surface area—for purposes of this test method, the
including the present interval divided by the amount of that
geometric surface area of a monolithic specimen that is
species in the test specimen before the test.
calculated from macroscopic measurements of its dimensions
3.1.2 diffusion coeffıcient (diffusivity)—an intrinsic property
by assuming a simple geometric shape, such as a right circular
ofaspeciesthatrelates (1)itsconcentrationgradienttoitsflux
cylinder.
in a given medium (Fick’s first law), (2) its spatial rate of
3.1.18 waste form—the waste material and any encapsulat-
changeinthedirectionoftheconcentrationgradienttothetime
ing or stabilizing matrix in which it is incorporated.
rate of change in its concentration in a given medium (Fick’s
second law), or (3) its mean square displacement to time in a
4. Summary of Test Method
given medium (the Einstein equation).
3.1.3 effective diffusion coeffıcient (D )—the diffusion coef- 4.1 This test method is a semi-dynamic leach test in which
e
ficient as modified by other processes (for example, adsorp-
a cylindrical specimen is immersed in a leachant that is
tion) or physical constraints (for example, tortuosity and completely replaced after specified intervals. The concentra-
constrictivity).
tion of an element of interest in the recovered test solution is
measured after each exchange; this is referred to as the
3.1.4 finite cylinder (finite medium)—a bounded body for
incremental fraction leached (IFL). The accumulated amount
which Fick’s diffusion equation can be solved.
of the species of interest in the intervals prior to and including
3.1.5 incremental fraction leached—theamountofaspecies
the interval of interest is analyzed to determine if the release
leached during a single sampling interval divided by the
from the solid can be described using a mass diffusion model.
amount of that species in the test specimen before the test.
The amount accumulated through a particular test duration is
3.1.6 leachant—the initial solution with which a solid is
referred to as the cumulative fraction leached (CFL).
contacted and into which the solid dissolves or is leached.
4.2 Tests at a single temperature are adequate to compare
3.1.7 leachate—the final solution resulting from a test in
the leaching behaviors of different materials.
which a solid is contacted by a solution and leaches or
dissolves. 4.3 The results of tests at repository-relevant temperatures
can be extrapolated to long times if data from tests run at
3.1.8 leaching—the preferential loss of components from a
elevated temperatures and data from tests run at the reference
solid material into solution leaving a residual phase that is
temperature (20°C) can be modeled using a diffusion model
depleted in those components, but structurally unchanged.
and the diffusion coefficients show Arrhenius behavior.
3.1.9 leaching interval—the length of time during which a
4.3.1 Elevated temperatures are used to accelerate the re-
given volume of leachant is in contact with a specimen.
lease of a species of interest and collect enough data to show
3.1.10 leaching mechanism—the set of processes that con-
that the release is controlled by diffusion and determine the
trols the rate of mass transport of a species out of a specimen
value of the diffusion coefficient.
during leaching.
4.3.2 Tests must be performed at a minimum of three
3.1.11 matrix material—the solid material used to immobi-
temperatures to verify that the leaching mechanism does not
lize the waste or species of interest.
change over that temperature range.
3.1.12 reference leach test—a leach test conducted under
4.3.3 By generating data over a range of temperatures, an
defined conditions, the results of which are used as a standard
Arrhenius plot can be produced to interpolate values of the
against which the results of other leach tests are compared. In
diffusion coefficient within the temperature range that was
this test method, a reference leach test is one that is conducted
tested. Values cannot be extrapolated to temperatures that are
at 20°C using demineralized water.
higher or lower than the temperature range spanned by the
tests.
3.1.13 semi-dynamic leach test—a leach test method in
which the specimen is exposed to fresh leachant on a periodic
4.3.4 A computer program that plots the experimental data
schedule.
and a regression curve calculated using a finite cylinder model
(2) is available from ASTM (see Note 1). The program
provides the value of the effective diffusion coefficient, the
modeled IFL and CFL values, and a measure of the goodness
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. of fit of the model.
C1308−08 (2017)
4.4 If the data from the accelerated tests, the reference test, 5.3 Fitting the experimental results with a mechanistic
and the fit of the modeled curve agree within defined criteria, modelallowsdiffusivereleasestobeextrapolatedtolongtimes
theleachingmechanismcanbetakentobediffusion-controlled and to full-scale waste forms under the following constraints:
and a diffusion model can be used to calculate releases from 5.3.1 Results of this test method address an intrinsic prop-
full-scale waste forms for long times.
erty of a material and should not be presumed to represent
releases in specific disposal environments. Tests can be con-
4.4.1 The accelerated leach test provides the maximum
cumulativefractionalreleasetowhichthemodeleddatacanbe ducted under conditions that represent a specific disposal
environment (for example, by using a representative ground-
extrapolated.Themaximumcumulativefractionalreleasemea-
sured represents the maximum extent of reaction for which the water) to determine an effective diffusion coefficient for those
conditions.
consistency of the mechanism has been verified for that
material. 5.3.2 Projections of releases over long times requires that
the waste form matrix remain stable, which may be demon-
4.4.2 Because the cumulative fraction leached is a function
strated by the behavior of the specimen in ALTs at elevated
of the specimen surface area-to-volume ratio, the results of
temperatures.
tests with the small-scale specimens used in the ALT directly
5.3.3 Extrapolations in time and scale are limited to values
represent leaching from large-scale waste forms having the
that correspond to the maximum CFL value obtained in an
same aspect ratio.
accelerated test.
4.4.3 The effective diffusion coefficient can be used to
5.3.4 The mechanism must be the same at all temperatures
calculate diffusive releases from waste forms with other
used in the extrapolation. The same model that describes the
shapes.
results of tests conducted at elevated temperatures must also
4.5 Ifthediffusionmodeldoesnotfitthedatawithindefined
describe the results of tests run at the reference temperature of
criteria,noextrapolationcanbemadeintimeorspecimensize.
20°C.
However, other models can be applied to the data to evaluate
the leaching process.
6. Apparatus
4.5.1 A model including diffusion with partitioning of the
6.1 A forced-air environmental chamber or a circulating
species of interest between phases having different release
water bath capable of controlling leachant temperatures to
behaviors is included in the computer program (2).
within 1°C of the target test temperature shall be used.
4.5.2 The possibility of a solubility-limit to the release of
the species of interest is addressed in the computer program
6.2 Balance—The balance shall be accurate to 0.1% of the
(2). test load.
4.6 Ifthedatacannotbefitwithadiffusionmodelwithinthe
7. Reagents and Materials
defined criterion, then graphical comparisons of the data are
recommended for added insight: For example, a plot of the
7.1 Leachant—The leachant can be selected with regard to
cumulative fraction leached (CFL) from ALT conducted at an the material being tested and the information that is desired.
elevated temperature against the CFL from ALT conducted at
Demineralized water, synthetic or actual groundwaters, or
the reference temperature can be used to verify that the chemical solutions can be used. The effects of the leachant
accelerated data are consistent with the reference data and that
solutiononthespeciesofinterest(thatis,thespeciesforwhich
the accelerated test appropriately accelerates the release, even the diffusion coefficient is to be measured) and the solid must
though the release is not diffusion-limited. be considered. For example, the leachant should not degrade
the host solid. In general, the leachant should be devoid of the
speciesofinteresttominimizesolutionfeedbackandsolubility
5. Significance and Use
limit effects. If the leachant does contain a non-negligible
5.1 This test method can be used to measure the release of
amount of the species of interest, blank tests should be
a component from a cylindrical solidified waste form into
conducte
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