Chelant screening and refinement tests - Phase I, Task 2. Topical progress report, December 1993--June 1994 Page: 12 of 236
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These results showed that the metal surface area to solvent volume ratio must be factored into
solvent formulation as it is tailored for a specific application.
A secondary part of the refinement testing was to evaluate the feasibility of applying the
selected solvents in the foam state. A paste of uranium dioxide was dried onto coupons, which
were subsequently exposed to the foamed EDTA/carbonate/peroxide solvent. The tests showed
that U02 could be dissolved by the solvent in the foam state; however, a significant portion of
the deposit was dissolved after it had dislodged from the coupon and dropped into the liquid.
Further testing of foamed solvent with more appropriate test samples (material contaminated in-
service, if available) should be performed.
In the final phase of refinement testing, process application testing, various application
scenarios were simulated to evaluate their effect on dissolution and corrosion. The results of
these final tests were used to develop the recommended process for the bench scale and pilot
scale testing. Based on the results of testing, the following process application scenario was
chosen for application in bench- and pilot-scale testing:
(1) Two hours at room temperature
(2) Heatup to 93*C and hold for four hours
(3) Cool to room temperature and inject peroxide
(4) Two hours at room temperature.
The rationale for this application scenario is that readily available uranium will be dissolved
during the initial low temperature exposure. The four-hour 93*C exposure will result in
corrosion of the base metal, thereby releasing contamination trapped in grain boundaries. This
released contamination will be dissolved by the final low temperature exposure.
Using this application sequence for the EDTA/carbonate/peroxide solvent, 100% of the
available U02 was dissolved and a carbon steel corrosion rate of 1.4 mils in four hours was
achieved. These results exceeded the established success criteria for the solvent developed in
this task, those being 90% dissolution of uranium present in the system in less than eight hours,
and capability of a carbon steel corrosion rate greater than two mils per eight hours.
The conclusions drawn from Task 2 chelant screening and refinement testing were as
(1) None of the chelant-only solvents (including proprietary and commercially
available formulations) tested at high temperature (93*C) effected acceptable
uranium dioxide dissolution.
(2) The two solvents found to exhibit targeted uranium dissolution effectiveness (90%
in eight hours) when applied at room temperature were:
(a) ammonium carbonate/hydrogen peroxide at pH 9.0 with NH40H, and
(b) EDTA/ammonium carbonate/hydrogen peroxide at pH 9.0 with NH40H,
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Chelant screening and refinement tests - Phase I, Task 2. Topical progress report, December 1993--June 1994, report, July 1, 1995; United States. (https://digital.library.unt.edu/ark:/67531/metadc680875/m1/12/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.