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Table 8.2. Chemical Analyses af MSRE Flush Salt Specimens
Run No.
Average Uranium
Found
Number of Samples
(ppm) Analyzed
FP-3 (final)
FP-4 (initial)
FP-8 (initial)
FP-8 (final)
FP-9 (final)
FP-11 (final)
FP-12 (initiao
FP-13 (initial)
195
218
160
616
840
930
'7 99
1186
lmplicotions of Current Experience
in Future Operations
Currently, the MSRE is entering its final period
of operation with 235U fuel salt. It is planned
that the MSRE: will operate with 233U fuel in
1968,' as will the MSBE later, and that the concentration
of uranium tetrafluoride in those fuels
will be only one-fouith that employed in the MSRE
Several inferences rnay be drawn from the experience
developed during previous -operation
which have significant implications regarding
operation of the MSKE when it is charged with
2 3 3 fuel, ~ as well as for larger molten-salt reactors.
In general, we must conclude that if
chemical analyses are to function as operational
controls, appreciably greater precision than is
now available must characterize the methods for
deterniiriing the concentration of uranium as well
as the U3+ fraction in the total uranium.
The overall composition of the present fuel salt
may be determined in routine chemical analysis
with a precision of 0.2 to 0.3 wt % (Fig. 8.1).
Precision in the determination of the uranium concentration
is considerably better, k0.02 wt % on a
statistical basis (Fig. 8.2). Such precision in the
determination of the uranium concentration is,
however, only one.-tenth that which is obtained in
routine computations of reactivity balance. The
........................ ............
1
6
3
Average Increase in
Uranium far Flush
(ppm)
19s
218
230
205
210
186
160
197
L_
Overall average = 200 ppm
__I .
high sensitivity in the reactivity balance to varia-
tions in uranium concentration vitiates applica-
tion of periodic batch analysis of fuel as a sig-
nificant control parameter in reactor operations;
such analyses have come to function primarily as
an independent basis for cross-checking burnup
and inventory computations. It is anticipated that
when the reactor is fueled with 233U, the pre-
cision of the reactivity balance will be improved
by a factor of at least 4,3 while the precision of
the chemical assay of uranium will fall in pro-
portion to the uranium concentration as it is re-
duced from 0.83 to 0.20 mole %. The limitations
on the present methods of analyzing the MSRE
fuel indicate, therefore, that it will be necessary
to develop improved methods for determining fuel
composition, In reactor systems in which fre-
quent or nearly continuous chemical reprocessing
is carried out, composition of the fuel and blanket
syslems will undergo constant change. Un-
questionably, composition determination will then
be necessary by way of on-line techniques sup
plemented by methods which have high intrinsic
accuracy.
The intrinsic corrosion potential of the fuel
salt is proportional to the UF, concentration,
which, to date, has been determined directly only
by an intricate and difficult method which is
probably near its limit of capability with salt of
'P. N. Haubanreich et a1. to R. B. Briggs, private 3J. R. Engel to R. E. Thoma, private cornmunica-
communication, Dec. 19, 1966. tion, April 28, 1967.