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

K.27
TABLE K.3.1. Predominant Solution Species of Elements Without Organic Ligands
(Karn-Bransle-Sakerhet 1978)
Little Affected by
Elements Oxidation-Reduction In an Oxidizing Environment In a Reducing Environment
Am Am 3 + , AmSo4 , 2 +
Am(OH)
Sb HSb02 0 , Sb(OH) 3 , SbOF 0 , SbO+
Ce Ce 3+ +
, CeSO4 Cs Cs +
Co Co 2+ , Co(OH)2 +
Cm Cm 3 + , CrmH 2 + , Cm(OH)2 +
Sb(OH) 4
Eu Eu 3+ , EuS04 + 2
, Eu2 P20 7 +
I I, 103- I
Np Np02 + , Np02HP04-, NpOH 3 + 4 +
, Np
Pu
NpO2HCO 3
Pu02+
Pm Pm 3 P 2
Ra
Ra 2+
Ru Ru(OH)2 + , Ru04-, Ru04 2
Sr
Sr 2+
2
Pu0 2 +, PuO 2 (CO3 )(OH) 2 -, PuOH 2 +, Pu 3 +
Tc TcO 4 - TcO 2
Th ThF 3 + , Th(OH) 3 +
3 H H + , 3 H-O-H
SUO" , UO2F+, UO (OH2)o ,
0 3 +
Zr Zr(OH) 4 , Zr(OH)5, ZrF
uo2(co 3 ) -
Ru0 4
2
U02 (C0 3 )
, UOH 3 + , U2
Examples of inorganic sorption materials are given in Table K.3.3. Chabazite, erionite
and clinoptilolite are zeolites that occur in large depos-its of sedimentary origin (Hay
1966) and montmorillonite is the main clay mineral in bentonites. Thermal and hydrothermal
stabilities generally are acceptable for the intended use. The thermal conductivities of
both clay minerals and zeolites are comparatively low. The zeolites are quite permeable to
ground-water while sodium-based montmorillonites show low permeabilities (Jacobsson 1977).
Pusch (1978) has suggested that varying amounts of quartz sand be added to bentonite
and that it be compacted to improve its load-bearing and thermal conductive characteristics
while retaining some of its cation exchange properties. Through the use of simple relation-
ships between diffusion or solution flow-controlled migration and equilibrium distribution
coefficients, Neretnieks (1977) determined the retention time in years in 1-m-10%
bentonite/90% quartz and clinoptilolite sorption barriers as shown in Table K.3.4.
The barrier depths (in meters) required to retard various radionuclides for 30 half-
lives are shown in Table K.3.5. Clinoptilolite is a better sorption barrier, but it is more
permeable and.has less bearing strength than the bentonite-quartz mixture. For use within
the canister, the clay minerals and zeolites can be dehydrated at just below their stability
temperatures.