SEPARATION OF TRITIATED WATER FROM WATER USING COMPOSITE MEMBRANES Page: 4 of 7
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temperatures and pressures, the hydrophobic membrane gave enhanced separation compared
to a cellulose acetate membrane. Preliminary engineering calculations have been reported for
the separation of D20 from H20 using the PTFE membranes in counter-current cascades .
Polyphosphazenes were chosen as the polymeric material for the membranes in the current
investigation because they have been shown to possess excellent isothermal stability to 320*C
 and selected types, especially poly[bis(phenoxy)phosphazene] or PPOP, were permeable
to alcohols . Furthermore, these polymers are chemically resistant to various solvents and
are film-forming thermoplastics . Of interest to the current research, polyphosphazenes
with aryloxy side groups provided very low scission or cross-linking yields when exposed to
gamma-radiation,  especially if no halogen or alkyl-groups were substituted on the aryl-
The FY-95 effort at PNNL has shown that the poly[bisphenoxy]phosphazene based
membrane can consistently achieve 30% reduction, single pass, from a challenge of 3 gCi/L
(KE-Basin water). The FY-96 effort is directed primarily at a basic understanding of the
HTO separation. Thus, a series of mass balance experiments will be conducted to confirm
the preliminary FY-95 results. Experiments will follow statistically experimental parameters.
Designed experiments will also examine factors which might impact the HTO separation,
such as pH, ion type/concentration, and temperature. Assistance is expected from the
University of Idaho and the University of Washington for spectroscopic data concerning the
possible mechanism of the HTO separation. Similarily, we shall be assisted by SpinTek
Membrane Systems in the study of water permeation through the membranes. Several
critical factors must be determined if the system is to be modulized. We expect to examine
N-Basin water (39 pCi/L) during FY-96 as well as water with a much higher tritium content.
The experiment(s) with water in the mCi/L or higher range will require considerable
coordination with other PNNL (regulatory and technical) personnel as well as the possibility
of other DOE sites. The data from this experiment is crucial since it will allow us to
determine further design parameters for the staged array system. Once most of the
mechanism information and membrane property data is obtained, we shall calculate the
hypothetical separation of the isotopomeric water in the cascade.
The major milestones of this project are directed at several issues which need resolution.
These include a statistical approach to experimental design and mass balances, calculations
from a designed module staged array, and a determination of the mechanism of the HTO
separation. A statistical design of experiments has been accomplished and work toward
providing the necessary information is underway. Thus, we have deionized and distilled 10
gallons of KE-Basin water (3 Ci/L) and used that HTO for initial experiments. Twenty
gallons of N-Basin water (39 gCi/L) will also be prepared for similar use.
Experiments were conducted with 10% carboxylated poly(diphenoxy)phosphazene and
poly(diphenoxy)phosphazene, unannealed, using distilled KE-Basin water (3 pCi/L). The
experiments indicated that HTO separation is quite variable and reached 18% depletion with
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JB, DUNCAN & DA, NELSON. SEPARATION OF TRITIATED WATER FROM WATER USING COMPOSITE MEMBRANES, article, December 18, 1995; Richland, Washington. (digital.library.unt.edu/ark:/67531/metadc893834/m1/4/: accessed June 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.