Management of Commercially Generated Radioactive Waste - U.S. ...

K.29
TABLE K.3.4 Retention Time Ranges on 1-m Barriers for
Several Radionuclides (Neretnieks 1977)
Retention Time, Years
10% Bentonite/
Radionuclide 90% Quartz Clinoptilolite
90Sr 30 600 to 1,400
137 Cs 20 to 30 2,200 to 5,200
226Ra 40 to 50 600 to 1,400
229 Th 50 to 300 unknown
237Np 2.1 x 106 unknown
239Pu 2.4 x 104 unknown
241Am 458 1,000 to 30,000
9 Tc 1 1
1291 1 1
TABLE K.3.5 Barrier Depth (m) Required to Retard Various
Radionuclides 30 Half-Lives (Neretnieks 1977)
30 Half-Lives Barrier Depth, m
10% Bentonite/
Radionuclide 90% Quartz Clinoptilolite
Sr 1 0.2
Cs 1 0.1
2 26 Ra 40 1.5
241Am 1 0.1 to 0.7
If the reduced or oxidized species is less soluble than the original radionuclide solu-
tion species, an oxidation-reduction (redox) reaction may be used to retard the mobilities
of certain radionuclides. Very little work has been done using redox controlling materials
as migration retardants. An example of redox control is the use of wustite (FeO) to surround
the waste form. The oxidation of ferrous to ferric ion would reduce technetium in the
highly mobile pertechnetate ion (TcO 4 ) from Tc(VII) to Tc(IV). (Latimer 1952 and Pourbaix
1966). Tc(IV) is a much less mobile form of technetium than Tc(VII).