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the salts are currently in essentially as pure
condition as when charged into the reactor.
Fuel Salt
MSRE runs 11 and 12 were completed within the
current report period During this period, small
amounts of beryllium metal were dissolved into
the fuel salt to adjust the oxidation-reduction
potential of the salt. The total concentration of
uranium in the fuel was also increased by addition
of 7LiF-235UF, to the circulating salt Currently,
the uranium concentration of the fuel salt is
approximately 4 590 wt 76, of which the U3’ frac-
tion of the total uranium is 1 5%. The effects of
the beryllium and 7LiF-23sUF, additions are
evident in the results of the chemical analyses of
the fuel salt shown in Table 8 1. A refinement of
analytical procedure was introduced during run 11;
preliminary values for the determination of ura-
nium concenttations were confirmed by a second
group of analysts before final values were re-
ported. Continuous control methods were em-
ployed by both groups. This innovation in pro-
cedure resulted in a significant improvement in
precision. Average scatter was reduced from
+0.5% to +0.4% of the value, corresponding to
t0.03 and ‘0.02 wt % uranium.
MSRE fuel salt is analyzed by IIF-H, purge
methods €or evidence of oxide contamination. The
results of analyses obtained during runs 11 and 12
indicated that the fuel salt does not contain more
than 50 to 60 ppm of oxide, that is, it is currently
as free of oxide as when it was originally charged
into the MSRE.
Coolant Salt
When run 12 was terminated in August 1967, the
coolant salt had circulated in the MSRE for a
period of 12,047 hr. Coolant salt specimens were
submitted at onsmonth intervals during 1967.
Results of those analyses show the composition
and purity of the salt to be
Li Be F Fe Cr Ni 0
(wt W) (PPd
___
13.04 9.47 76.30 63 27 12 “’200
103
as compared with the composition and purity it
was known to possess a year ago:
Li Be F Fe Cr Ni 0
.--.-
(wt X) (PPd
13.03 9.46 76.16 58 36 16 Q’200
The two compositions are not differentiable with-
in the precision of the analytic methods. The
constancy of the trace concentrations of the
impurities attests to the fact that the cover gas,
which is supplied to both the fuel and coolant
circuits from a common source, has been main-
tained in a state of high purity throughout tfie
entire operational period.
Flush Sait
Whenever the MSRE fuel circuit is flushed with
flush salt, there is cross mixing uf fuel and flush
salts by residues which remain in the reactor
after each is drained. We need to know the
amounts of material transferred betwcen the fuel
and flush salts because they enter into the calcu-
lation of the book-value concentration of uranium
in the fuel salt. Sufficient analytical data are
now available to enable us to deduce the average
mass of these rcsidues.
The concentration of uranium in the flush salt
appears to change in neatly equal increments
during each flush operation, as shown in Table
8.2. These data indicate that fuel salt which
remains in the fuel circuit after drainage of the
fuel increases the uranium concentration of the
flush salt by 200 ppm each time the drained re-
actor is cleaned with flush salt. An increase of
200 ppm of uranium corresponds to the addition of
approximately 850 g of uranium to the flush salt.
This is the amount of uranium in 19.20 t 0.10 kg
of fuel salt in which the uranium concentration is
between 4 570 to 4 622 wt % U, the range for the
MSRE during the period considered.
On filling the MSRE with fuel salt, 7L.iF-BeF2
(66-34 mole %) flush salt residue is incorporated
in the fuel salt, diluting its concentration of UF,
and %rF4 slightly. This dilution is reflected in
the uranium and zirconium analyses shown in Fig.
8.1 The decrease in zirconium concentration of
the fuel salt from a mean value of 11 33 wt % to
10.85 wt ;“o corresponds to dilution of the fuel by
12.7 kg of salt on each drain-flush-fill cycle.