ORNL-4191 - the Molten Salt Energy Technologies Web Site

Table 6.2, Temperature Coefficients of Reactivity
Component
Coefficient
1 dk
("K)-'
_I
k dI
Moderator +1.66 x
Fertile salt -t 2.05
Fuel salt --8.0s x
Overall -4.34 x
tions. It is particularly worthy of note that the
moderator coefficient appears to be quite insensitive
to uncertainties in the energy dependence
of the 233U cross sections in the energy range
below 1 ev; that is, reasonable choices of cross
sections based on available experimental data
yield essentially the same coefficicnt.
The fertile-salt reactivity coeffment comprises
a strong positive component due to salt expansion
(and hence reduction in the tiumbpr oE fertile atoms
per unit core volume) and an appreciable negative
component due to temperature dependence of the
effective resonance-absorption cross sections, so
that the ovcrall coefficient, though positive, is
less than half as large as that due to salt expansion
alone.
The fuel salt coefficient comes mainly from expansion
of the salt, which of course reduces the
average density of fuel in the core. Even if all
core components should undergo equal temperature
changes, the fuel-salt coefficient dominates, and
in transients in which the fuel temperature change
is far larger than that of the other components, the
fuel coefficient is even more controlling.