Use of Modeling for the Prevention of Solids Formation During Canyon Processing of Legacy Nuclear Materials at the Savannah River Site Page: 3 of 11
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AIChE Spring Conference, March 30-April 3, 2002
neutron poison for criticality control. This processing need required development of a thermodynamic
speciation program for predicting multiple fluoride species equilibrium concentrations in representative
plant solutions. As a result of the SS&C campaign issues, the INEEL model was used to predict nuclear
material residue dissolution using calcium fluoride in the presence of boric acid and to predict the
corrosion potential of the stainless steel dissolver vessel. However, the INEEL speciation program
thermodynamic data are applicable at ionic strength conditions for the INEEL process solutions, i.e., do
not have activity coefficient data. Therefore, application to SRS solutions with high ionic strength
requires that the INEEL model be improved with specific chemical species information. Therefore, the
INEEL speciation computer program is being updated with new basic chemical data in order to better
predict and avoid the precipitation of undesirable solids in aqueous process solutions at SRS.
The objective of the project is to incorporate activity coefficients into the speciation program that
has been developed to calculate individual component concentrations in acidic aqueous fluoride systems.
The incorporation of relevant activity coefficients into the program will enable accurate predictions of
solubilities of potentially precipitating species in plant solutions and provide the ability to calculate
solution adjustments to assure stability. In order to do this, solubility and activity coefficient data must be
fitted to a suitable activity coefficient model and its ion interaction parameters must be determined.
Subsequently, the fitted model can be used to calculate the activity coefficients for process solution
compositions. The computer program has potential applications at DOE sites working with EM materials
in aqueous solutions.
MODELING TO ADDRESS PRECIPITATION IN THE CANYON DISSOLVER
In laboratory tests to support the Sand, Slag, and Crucible (SS&C) campaign and the Mark 42
Fuel Tube campaign, the presence of high concentration of fluoride ions in boric acid/nitric acid solutions
led to the formation of a white solid (see Table 1). The white solids were collected from laboratory
flowsheet simulations, and were identified as KBF4.
Table 1. Identification of KBF4 Precipitate in SRS Dissolver Simulation Tests.
[HNO3]0 [F-]o [B]o**
Date Test (M) (M) (g/L) Observation
Dec. 1997 SS&C - simulation 9.3 0.30 2.5 Unidentified
May 1998 SS&C - simulation 1.0 0.23 1.7 White solid,
Nov. 1998 SS&C - test 1 8.8 0.32 1.6 No solids
SS&C - test 2 8.6 0.40 2.2 KBF4 (s)
Feb. 1999 Mark 42 - simulation 1.0 0.40 2.5 No solids
[Al] = 0.44 M 1.0 0.50 2.5 KBF4 (s),
1.0 0.60 2.5 KBF4 (s),
*Added as KF. **Added as H3B03
Without known KBF4 activity coefficients at the conditions evaluated, the INEEL program under predicts
the saturation of KBF4, as shown in Table 2.
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Rhodes, W.D. Use of Modeling for the Prevention of Solids Formation During Canyon Processing of Legacy Nuclear Materials at the Savannah River Site, article, January 29, 2003; South Carolina. (digital.library.unt.edu/ark:/67531/metadc736750/m1/3/: accessed August 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.