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by removing some uranium from the fuel salt and replacing it wieh fresh
feed. If onlgr 1% of the uranium inventory were removed each year and con-
signed to waste or to off-site recovery, the in-plant isotopic composition
would reach equilibrium within 300 yearss and the fuel cycle could be con-
tinued indefinitely. faTa even more attractive choice would be to remove
some of the uranium, strip out part of the 238U, and return the remainder
to the reactor plantr To examine this case, we assumed that 2% of the re-
actor inventory would be treated each year and that the returning uranium
would contain one-half the original 23*U or enough for denaturing which-
ever was greater.
tion.) The calculation showed that this approach also would allow indefi-
nite operation and would require less feed material (see the following
discussion) than the other options.
(Only 238U was extracted in this preliminary calcula-
4.1.3 Partial fission-product removal
Although the reference fission-product pr~cessf~g concept could
strongly affect the very long-term viability of DMSRs, the fission-product
process would require substantial time and effort for commercial develop-
ment, and, even then, it might not be a market success. Consequently,
considering alternative processes might be useful
A variety of alternative separations procedures have been examined
over the years in the ORNL MSR program for possible application in fuel
reprocessing operations. Possible recovery of protaetintm, uranium, and
other actinides by selective precipitation of oxides has been examined,
though most methods have preferred removal of uranium isotopes by fluo-
rination to volatile UF6. Attempts to remove the lanthanides (the most
important parasitic absorbers of neutrons) have included processes based
on ion exchange, precipitation of intermetallis compounds, and even vola-
tilization at low pressure of the other melt constituents" to leave tihe
very nonvolatile lanthanide trifluorides behind. All such processes re-
quire solids handling, and many also have other disadvantages. None was
* Such a separation wight be feasible, after fluorination of the
uranium, for a. fuel consisting only of LiF, BeF2, and W4, but inclusion
of considerable TkF4 Cas in a DMSR fuel) defeats such a process.