ASTM C1308-95(2001)

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

SIGNIFICANCE AND USE
This test method measures mass transport from a cylindrical solidified waste form into water under conditions that accelerate leaching. Test parameters, such as the volume of leachant and the frequency at which the leachant is changed, have been optimized to eliminate experimental effects (for example, saturation effects that can complicate modeling of the net forward diffusion rate).
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 achieved with expected service conditions for greater confidence in waste form properties;
5.2.3 Obtain measurable leachate concentrations from materials that have very low release rates under service conditions; and
5.2.4 Compare releases from various types of solidification agents and formulations.
Modeling the experimental observations obtained in the test allows the extrapolation of leaching results to long times and to full-scale waste forms under the following constraints:
5.3.1 Results of this test method cannot be taken to apply to releases in specific disposal environments unless tests are conducted to determine the leaching mechanism under those conditions.
5.3.2 Projections of releases require the long-term stability of the waste form, which may or may not be indicated adequately by short-term tests.
5.3.3 Extrapolations are limited to the maximum CFL obtained with the accelerated test.
5.3.4 The leaching mechanisms observed in tests conducted at elevated temperatures must be the same as the mechanisms observed in the tests run at the reference temperature.
SCOPE
1.1 This test method provides a method for accelerating the leach rate of solidified waste and determining if the release is diffusion-controlled. This test method is applicable to any material that does not degrade, deform, or change leaching mechanism during the test.
1.1.1 If diffusion is the dominant leaching mechanism, then results of this test can be used to model long-term releases from waste forms. Diffusion can be confirmed as the leaching mechanism through the use of a computerized mathematical model for diffusion from the finite cylinder (Note 1).
1.1.2 The leaching mechanism should be verified as diffusion-controlled by a means other than analysis of the leach test data. For this purpose, analysis of post-leaching concentration profiles within the solid waste form is recommended.
Note 1—The computer program and the models are briefly described in and in the Accelerated Leach Test Method and User's Guide for the "ALT" Computer Program (1).
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 09-Sep-1995
• ICS: 13.030.10 - Solid wastes
• Technical Committee: C26 - Nuclear Fuel Cycle

Relations

• Replaced By: ASTM C1308-08 - 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
• Effective Date: 01-Dec-2008
• Referred By: ASTM D7031-11(2019) - Standard Guide for Evaluating Mechanical and Physical Properties of Wood-Plastic Composite Products
• Effective Date: 10-Sep-1995

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: C 1308 – 95 (Reapproved 2001)
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 C 1308; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope Low-Level Radioactive Wastes by a Short-Term Test
Procedure
1.1 This test method provides a method for accelerating the
leach rate of solidified waste and determining if the release is
3. Terminology
diffusion-controlled. This test method is applicable to any
3.1 cumulative fraction leached—thesumofthefractionsof
material that does not degrade, deform, or change leaching
a species leached during all sampling intervals calculated as
mechanism during the test.
CFL = (a /A and assuming no radioactive decay, where a is
n O n
1.1.1 If diffusion is the dominant leaching mechanism, then
the quantity of a species in the leachate during any interval and
resultsofthistestcanbeusedtomodellong-termreleasesfrom
A is the quantity of that species originally present in the
O
waste forms. Diffusion can be confirmed as the leaching
sample.
mechanism through the use of a computerized mathematical
3.2 diffusion coeffıcient (diffusivity)—based on Fick’s Laws
model for diffusion from the finite cylinder (Note 1).
for diffusion, the diffusion coefficient is the ratio of the rate of
1.1.2 The leaching mechanism should be verified as
transfer of a diffusing substance through the unit area of a
diffusion-controlledbyameansotherthananalysisoftheleach
section to the concentration gradient measured normal to the
test data. For this purpose, analysis of post-leaching concen-
section.
tration profiles within the solid waste form is recommended.
3.3 effective diffusion coeffıcient (effective diffusivity)—the
NOTE 1—The computer program and the models are briefly described
diffusion coefficient that results from diffusion as it is modified
inAnnexA1 and in theAccelerated Leach Test Method and User’s Guide
by other processes (for example, adsorption) or physical
for the “ALT” Computer Program (1).
constraints (for example, tortuosity and constrictivity).
1.2 This standard does not purport to address all of the
3.4 finite cylinder (finite medium)—a bounded body for
safety concerns, if any, associated with its use. It is the
which Fick’s diffusion equation can be solved.
responsibility of the user of this standard to establish appro-
3.5 incremental fraction leached—the fraction leached of a
priate safety and health practices and determine the applica-
species of interest during a single sampling interval calculated
bility of regulatory limitations prior to use.
as IFL = a /A and assuming no radioactive decay.
n O
3.6 leachant—the liquid that contacts the specimen during a
2. Referenced Documents
leachtestorcontactsawasteforminthedisposalenvironment.
2.1 ASTM Standards:
3.7 leachate—the leachant after contacting the specimen or
E 632 Standard Practice for Developing Accelerated Tests
the waste form.
to Aid Prediction of the Service Life of Building Compo-
3.8 leaching—the process (or processes) by which mass
nents and Materials
transport from a solid to a liquid takes place.
D 1193 Standard Specification for Reagent Water
3.9 leaching interval—the length of time during which a
2.2 ANSI/ANS Standard:
given volume of leachant is in contact with a specimen.
ANSI 16.1 Measurement of the Leachability of Solidified
3.10 leaching mechanism—theprocessthatcontrolstherate
of mass transport out of a specimen during leaching.
1 3.11 reference leach test—a leach test conducted under
This test method is under the jurisdiction ofASTM Committee C26 on Nuclear
defined conditions, the results of which are used as a standard
Fuel Cycle and is the direct responsibility of Subcommittee C26.07 on Waste
Materials.
Current edition approved Sept. 10, 1995. Published April 1996.
2 4
Annual Book of ASTM Standards, Vol 14.02. Available from American National Standards Institute, 11 W. 42nd St., 13th
Annual Book of ASTM Standards, Vol 11.01. Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 1308
against which the results of other leach tests (for example,
accelerated)arecompared.Inthistestmethodareferenceleach
test is one that is conducted at 20°C.
3.12 semi-dynamic leach test—a leach test method that
exposes the specimen to fresh leachant on a periodic schedule.
3.13 semi-infinite medium—a body used in diffusion theory
whose outer boundary is effectively at an infinite distance from
the inner region.
3.14 source term—theoriginalconcentration,priortoleach-
ing, of a species of interest in a specimen or a waste form.
3.15 surface area—for purposes of this test method, surface
area is defined as the geometric surface area of a specimen
calculated from macroscopic measurements of its dimensions.
3.16 volume—for purposes of this test method, volume is
defined as the volume of a specimen calculated from macro-
FIG. 1 A Schematic of the Concepts Used in This Test Method to
scopic measurements of its dimensions.
Combine Experimental and Modeling Approaches
3.17 waste form—a stable, solid body composed of the
waste and a solidification agent.
comparable to the reference data, showing that the accelerated
4. Summary of Test Method
testisappropriate.Withthistechnique,noextrapolationofdata
4.1 This test method is a semi-dynamic leach test, that is,
can be made.
theleachantissampledandreplacedperiodically.Itisbasedon
earlier semi-dynamic tests such as the IAEA test (2) and the
5. Significance and Use
ANS 16.1 Leach Test. Elevated temperatures, large volumes
5.1 This test method measures mass transport from a cylin-
of leachant, frequent leachant changes, and small specimen
drical solidified waste form into water under conditions that
sizeareusedtoobtainacceleratedreleases.Thisisashort-term
accelerate leaching. Test parameters, such as the volume of
test, requiring sampling on each of eleven or more successive
leachant and the frequency at which the leachant is changed,
days.Tests must be performed to demonstrate that the leaching
have been optimized to eliminate experimental effects (for
mechanism does not change at the elevated test temperature.
example, saturation effects that can complicate modeling of the
This may be done by performing leach tests at a minimum of
net forward diffusion rate).
three temperatures to ascertain that the mechanisms and
structural controls of leaching do not change with increasing
5.2 This test method can be used to:
temperature. If the test is to be used only for making compari-
5.2.1 Provide diffusion coefficients for waste forms;
sons among specimens, then testing at a single temperature is
5.2.2 Obtain higher fraction releases than can be achieved
adequate.
with expected service conditions for greater confidence in
4.2 Theresultsofthisacceleratedtestcanbeextrapolatedto
waste form properties;
long times if the data from tests run at elevated temperatures
5.2.3 Obtain measurable leachate concentrations from ma-
and the tests run at the reference temperature (20°C), and can
terials that have very low release rates under service condi-
be modeled by diffusion. A computer program that plots the
tions; and
experimental data and a curve calculated from an effective
5.2.4 Compare releases from various types of solidification
diffusion coefficient for diffusion from a finite cylinder (Fig. 1)
agents and formulations.
is available fromASTM. If the data from the accelerated tests,
the reference test, and the modeled curve fit within defined
5.3 Modeling the experimental observations obtained in the
criteria,theleachingmechanismistakentobediffusion.Inthis
test allows the extrapolation of leaching results to long times
case, the model can be used to project releases from full-scale
and to full-scale waste forms under the following constraints:
waste forms and to long times. The accelerated test provides a
5.3.1 Results of this test method cannot be taken to apply to
measure of the maximum fractional release to which the
releases in specific disposal environments unless tests are
modeled data can be extrapolated. By generating data over a
conducted to determine the leaching mechanism under those
specified temperature range, anArrhenius plot can be produced
conditions.
allowing projections to be made at temperatures other than
5.3.2 Projections of releases require the long-term stability
those tested. If the diffusion model cannot fit the data, other
of the waste form, which may or may not be indicated
models (for example, diffusion plus partitioning and solubility
adequately by short-term tests.
limited leaching) contained in the computer program can be
5.3.3 Extrapolations are limited to the maximum CFL
used to indicate the leaching mechanism that controls releases.
obtained with the accelerated test.
No extrapolations are allowed with these models. If no model
fits the data, then an alternative graphical comparison of the 5.3.4 The leaching mechanisms observed in tests conducted
data is recommended. A linear plot of modeled CFL plotted at elevated temperatures must be the same as the mechanisms
against experimental CFL verifies that the accelerated data is observed in the tests run at the reference temperature.
C 1308
6. Apparatus 8.3 A minimum of three specimens should be tested at any
given temperature.
6.1 A forced-air environmental chamber or a circulating
8.4 The dimensions, weight, composition, and curing his-
water bath capable of controlling leachant temperatures to
tory shall be recorded for each specimen. Accurate determina-
61°C shall be used.
tion of the source term (A ), that is, the amount of the species
6.2 Balance—The balance shall be accurate to 0.1 % of the
of interest in the specimen at the start of the leach test, shall be
test load.
made and recorded.
7. Reagents and Materials
9. Procedure
7.1 Leachant—The leachant shall be distilled or deionized
9.1 Removal of Specimen from Mold—After removing the
watermeetingorexceeding standards for types II orIIIreagent
specimen from its container or mold, any excess material
water as specified in Specification D 1193.
should be removed prior to weighing the specimen. The mold
7.2 Containers—Leaching containers shall be made of a
should be rinsed in a volume of water equal to the volume of
material that does not react with the leachant/leachate and the
the specimen. If the quantity of the species of interest con-
specimen. It is particularly important to select materials that
tained in this rinse water represents more than 0.5 % of the
allow very little plate-out of radionuclides from solution. High
total quantity in the specimen, the value should be subtracted
density polyethylene has been found to be a suitable container
from the source term (A ).
material. The top of the container shall fit tightly to minimize
9.2 Leachant Volume—The leachant volume used for each
evaporation. This fit must be checked at test temperatures to
interval is 100 3 the surface area of the specimen as calculated
ensure that evaporative losses are less than 1 % over 24 hours.
below:
7.3 Specimen Supports—Supports for the specimens shall
Leachant volume ~cm !
be made of a material that does not react with the leachant/
5 100 cm 6 2 % (1)
Specimen surface area ~cm !
leachate or the specimen and does not allow plate-out onto the
support. The method of support should not impede leaching by
obstructing the surface area of the specimen by more than 1 %.
This ratio requires a large volume of water, for example, a
Moreover, it should not interfere with replacement of the
2.5 cm 3 2.5 cm specimen has a surface area of approximately
leachate. It is often convenient to suspend the waste form from
30 cm , giving a leachant volume of 3000 mL. Specimens that
the cover of the leaching container using monofilament string.
are much larger than this will require volumes of water that
7.4 Sample Containers—Containers to hold aliquots of
need more sophisticated means of wastewater handling (such
leachate for storage prior to analysis should not allow any
as peristaltic pumps for draining the containers), since large
plate-outofradionuclides.Thecontainersshouldbecheckedto
volumes are too unwieldy for pouring.
ascertain that evaporation over long times is acceptably small.
NOTE 2—Some waste form materials, such as glass, have such low
7.5 Stirrers—Stirrers that are long enough to reach the
leach rates that a volume-to-surface area ratio of 100 cm is not necessary.
bottom of the leaching containers are required.Wood or plastic
In some cases, such a large volume of leachant can make analysis
tongue depressors are adequate.
challenging, even for major constituents of the specimen. Under these
7.6 Filtration Equipment—If particulates are present in the circumstances, the volume-to-surface area ratio may be reduced to 10 cm.
leachate, filtration is necessary. Tests must be conducted to
9.3 Temperature—For materials and formulations that have
ensure that the filter and the filtration apparatus do not adsorb
not been tested previously, leach tests shall be conducted at a
the species of interest. The filter medium should be capable of
minimum of three temperatures to establish that leaching
removing particulates that are 0.45 µm in diameter. Disposable
increases systematically with higher temperatures. One tem-
syringe filters are recommended.
perature must be 20°C. The recommended maximum tempera-
ture is 50°C, which is below the threshold of anomalous
8. Specimens
releases observed so far (3). Temperatures above 50°C can be
8.1 Rightcircularcylindricalspecimensshallbeusedwitha used if it is demonstrated that releases follow the trend
diameter-to-heightratiobetween1:1and1:2.Aconvenientsize
observed at low temperatures, that is, that the leaching mecha-
is 2.5 cm diameter by 2.5 cm height. Smaller sizes should be nism has not changed.
avoided to preclude problems of mixing and producing non- 9.4 Leachant Replacement—Leachant replacements shall
homogeneous samples. take place at the time intervals shown in Table 1. The time at
8.2 Specimens shall be representative of the full-scale which the specimen is first placed in the leachant should be
solidified waste form. Particular attention should be paid to noted. The leachant shall be brought to the test temperature
ensuring that the laboratory specimen is homogeneous. The
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