MEASUREMENT AND PREDICTION OF RADIOLYTIC HYDROGEN PRODUCTION IN DEFENSE WASTE PROCESSING SLURRIES AT SAVANNAH RIVER SITE Page: 13 of 16
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WSRC-STI-2006-00114 Rev. 1
2.6E-07 moles per liter of the sludge slurry. The total predicted rate for the sludge slurry is then
7.2E-07 moles per hour per liter of the sludge slurry.
Predicted Rate of Radiolytic of H2 Production for the SB3 SRAT Slurry
For the SRAT slurry the predicted H2 production rates were again calculated separately for both
beta/gamma and alpha radiation. However, the values of GH fformate have to be included for
both beta/gamma and alpha radiation.
For the first of the two G values in Equation 8, the effect of nitrate and nitrite in the supernate on
GH2 was calculated using Equations 5 and 6. In the supernate of the SRAT slurry the measured
concentrations of N03- and NO2 ions were 0.512 M and 0.018 M, respectively, giving a value of
0.521 for NOeg . When this is substituted into Eq. 5 the G value for beta/gamma radiation is
lowered to 0.15 molecules/100 eV. When this is substituted into Eq. 8 along with the value for k
from Eq. 4 and the watts per liter of absorbed beta/gamma radiation for the SRAT slurry from
Table V, the predicted rate of radiolytic H2 production based the first G value in Eq.8 is 4.2E-07
moles of H2 per hour per liter of the sludge slurry for beta/gamma radiation. For alpha radiation
the G value is lowered to 0.64 molecules per 100 eV using Eq. 6 and the predicted rate of
radiolytic H2 production is 2.6E-07 moles per hour per liter of the sludge slurry. The total
predicted rate based on the first G value in Eq. 8 is then 6.8E-07 moles per hour per liter of the
SRAT slurry. Note that this is very similar to the predicted rate for the sludge slurry.
The contribution of the radiolytic production of H2 from Reaction 4 will now be estimated.
Measurements by ion chromatography on the supernate of the SRAT slurry indicated that the
concentration of formate in the supernate was 0.980 M. Based on the following discussion, it can
be concluded that in the SRAT slurry ~94% of the H atoms produced by radiolysis react with the
formate anions to produce H2 rather than reacting with nitrate or nitrite ions and not producing
H2.
Radiolytically produced H atoms can react with both formic acid and with formate anions. Rate
constants have been measured for both reactions and the rate constant for the reaction with formic
acid is ~ 450 times lower than the constant for the reaction with formate ions. [10] Also, the pH
of the SRAT product measured by pH paper was -6; therefore, based on the acid dissociation
constant for formic acid (1.8E-04 M [12]), essentially all of the formic acid that was added in the
SRAT process is dissociated into formate ions. The H+ ions reacted with the caustic in the slurry.
Rate constants for the reaction of H atoms with formate, nitrate and nitrite anions have been
measured and reported in the radiation chemistry literature. [10] The fractions of H atoms
reacting with formate ions rather than nitrate or nitrite ions can be calculated using these rate
constants and the concentrations of the respective anions in the supernate. These fractions are the
ratio of the reactivity of H atoms to formate ions compared to their reactivity for the nitrate or
nitrite ions in the slurry. The reactivity for each anion is the product of the concentration of the
anion concentration times its rate constant for reacting with the H atom. Table VI presents
measured rate constants for the reaction of H atoms with these anions, the concentrations of the
anions in the supernate of the SRAT product and the calculated reactivities for the H atoms with
these anions in the SRAT product. The last column of Table VI presents the fraction of H atoms
reacting with nitrate or nitrite ions relative to formate. Only 0.3% of the H atoms formed by the
radiolysis react with nitrate rather than formate and only 6% of the H atoms react with nitrite
rather than formate in the two slurries. The results indicate that in the SRAT product slurry 94%
of the radiolytic H atoms react with the formate anion to produce H2.PAPER FOR WM'07
Page 12 OF 15
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Bibler, N; John Pareizs, J; Terri Fellinger, T & Cj Bannochie, C. MEASUREMENT AND PREDICTION OF RADIOLYTIC HYDROGEN PRODUCTION IN DEFENSE WASTE PROCESSING SLURRIES AT SAVANNAH RIVER SITE, article, January 10, 2007; [Aiken, South Carolina]. (https://digital.library.unt.edu/ark:/67531/metadc885839/m1/13/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.