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Fig. 15.8. Inner Surface of Core Shell in Contact with Graphite Core of In-Pile Loop 2. 250~.
These equations permit the calculation of activity
if flux is given, or of flux if activity has been
measured.
The Ys F term is the chain production rate at a
given flux or power density for the quantity of
material under consideration. It was useful to
treat the Y. F term in the case of fissioning as a
product of fission yield Y, a standard fission
rate F" per gram of uranium (at a given flux), a
uranium inventory for the interval j (from salt
inventory actually under irradiation, w ., times
I
uranium concentration U .), and the irradiation
I
intensity factors, p. and q., relative to full re-
1 1
actor power and fully inserted position. Thus for
any set of intervals, for example,
-A, * t -A .t
- (1-e 'j). (e ' dj)
A similar expression can be written for the
daughter isotope (such as the 35-day 5Nb daughter
of 65-day "Zr).
The term on the right may be computed for any
given isotope from a knowledge of decay rate,
irradiation, and inventory history. The term on
the left represents the count to be expected,
divided by the saturation value from 1 g of uranium
at full power.
In practice, the total loop inventory was corrected
for the amount of salt not under irradiation,
at the time, in sample lines and the purge tank.
The activity withdrawn with each removal and that
remaining in the loop were calculated. The total
activity (at reference time) of a given isotope
produced during the experiment was thus estimated.
As mentioned in an earlier section, it appears
reasonable to use the activities of certain fission
products in the salt samples, in particular 37Cs,
'44Ce, and "Zr, as internal standards to estimate
the flux. A mean flux to the salt of 0.88 x
10' was thus estimated from activities measured