Compatibility of packaging components with simulant mixed waste Page: 2 of 5
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Standardized test methods were used to cut, condition, and test the materials. The geometry of the
material samples was specified by the test method. The samples were cut using an expulsion press
and dies manufactured by Testing Machines Inc., Amityville, NY. The use of the press and dies
permitted the cutting of multiple samples of uniform dimensions. When attempting to cut out the
harder materials such as HDPE, PP, and Kel-F with the expulsion press, considerable difficulty was
encountered requiring machining to specifications. The individual samples were visually checked to
assure that none had nicks or other imperfections prior to their use. As recommended by ASTM
D618, the plastics were conditioned at a standard temperature of 23 C and relative humidity of 50%
for at least 24 hours prior to the testing process.
The above mentioned samples were exposed to gamma radiation from an underwater "Co source at
SNL. These samples were loaded into a metal basket in the same configuration as was used to
condition the samples, i.e., the samples were stacked atop each other and separated by a metal spiral.
The basket was then inserted into a water-tight stainless steel canister (volume -4 L). The canister
was sealed and lowered into the pool to a depth of 6 feet, purged with slow steady flow (- 30
mL/min) of dry air, and allowed to come to thermal equilibrium at either ambient, 50, or 60 C. Once
thermal equilibrium was obtained, the canister was lowered into its irradiation location in the pool and
the exposure time was started to obtain the desired radiation dosage. The highest dose rate available at
the Low Intensity Cobalt Array (LICA) Facility was -2 kGy/hr. Thus for irradiations where a
gamma-ray dose of 1.43 kGy was required, the samples were exposed for approximately 0.75 hours.
For doses of -3, 6, and 40 kGy, the corresponding longer exposure times were needed. After the
samples received the calculated radiation dosage, the canister was removed from the pool and the
samples were again placed in the conditioning chambers.
Sample Exposure to Chemicals
The general exposure protocol for all tests involved placing specimens of each plastic material into a
container (cell), and exposing them to the specific testing conditions. Care was taken to ensure that
sufficient simulant waste was present to expose the entire surface area of all the samples. After
adding the liquid simulant waste, the plastic lid was attached to the jar and tightened. The cells were
placed in the respective enviromental chambers maintained at 18, 50, and 60 C. The cells were kept
in these environmental chambers for 7, 14, 28, and 180 days.
The material properties that should be evaluated to assess the suitability of potential liner materials in
mixed waste packaging designs are mass, dimensional and density changes, hardness, modulus of
elasticity, tensile strength, elongation, and stress cracking in polyethylene materials. Since the
measurement of all these material properties was expected to be costly and time-consuming, screening
tests with relatively severe exposure conditions such as high temperatures and high radiation levels
were implemented to quickly reduce the number of possible materials for full evaluation. The
screening criteria used were density changes for liners and vapor transport rates for elastomers.
From this screening study, it was found that all of the selected liner materials had passed the screening
criteria in the aqueous simulant mixed waste. This then resulted in the testing of five materials that
were exposed to a matrix of four radiation doses, three temperatures, and four times in the simulant
waste. These parameters were evaluated using standardized test methods such as those developed by
the American Society for Testing and Materials (ASTM). For specific gravity changes, ASTM D792
was used. In evaluating dimensional changes, ASTM D471 was used. For hardness changes, ASTM
D2240 was used. In evaluating stress cracking in polyethylene materials, ASTM D1693 was used.
Finally, for evaluating tensile property changes, ASTM D638 was used.
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Nigrey, P. J. & Dickens, T. G. Compatibility of packaging components with simulant mixed waste, report, April 1, 1996; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc666714/m1/2/: accessed October 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.