ORNL-1816 - the Molten Salt Energy Technologies Web Site

clean reactor at a low power for a 1-hr period and
then withdrawing a fuel sample and taking a count
of the sample. This calibration was attempted
first at an estimated power of 1 w and then at
10 w. The fuel activity from the I-whr run was
too low for an curate count to be made, but
that from the 10-whr run indicated a power of
13.5 w. The nuclear instrumentation was cali-
brated on the basis of this power determination.
It developed later that almost all the volatile, as
well as the gaseous, fission products were ap-
parently continuously removed from the fuel at
the pump, and consequently the actual power was
probably much greater than that indicated by the
Attempts were made to measure the temperature
ient when the reactor was subcritical and
ain during the low-power operation. In both
instances it was established that the coefficient
was negative, , in the latter case, it was
determined that the magnitude was approximately
5 x lo-’ Ak/oF. A more accurate determination
of the magnitude of the temperature coefficient
was deferred until the high-power runs were made.
As a part of the low-power operation, the shim
rods were calibrated in terms of the regulating
rod. Each of the three shim rods had approxi-
mately 0.15% Ak/in. for most of their 36 in. of
travel.
Hi gh-Power Experiments
The reactor was finally taken to high power
(estimated at 1 Mw from the nuclear instrumen-
tation) at 6:20 PM, November 9, some six days
after it first became POW
was attained of 0
durinq - which t
power levels of 10,
Deration with
pressures and remotely exhausting the pit gases
to the atmosphere.
-I . _- ~
.
. ..- . . ... . .
PERIOD ENDING DECEMBER 70,1954
Once high power was attained, the reactor was
operated at various power levels during the next
several days, as required, to complete the desired
tests. These tests included measuremeni of the
temperature coefficient of reactivity, a power cal i-
bration from the process instrumentation, and a
determination of the effect of large increases in
reactivity, and they were concluded by a 25-hr
run at full power to determine whether thc =re was
a detectable buildup of xenon.
The temperature coefficient of reactivity was
determined simply by placing the regulating rod
on the flux servo and then increasing the speed
of the blower cooling the fuel. The change of
rod position (converted into reactivity) divided by
the change in the reactor mean temperature determined
the reactor temperature Coefficient. The
absolute value of this coefficient was initially
quite large, and it decreased after 2 min to a
relatively constant value of -5.5 x lo-’% Ak/OF.
Further analysis of the data is under way to
ascertain the precise value of the instantaneous
fuel temperature coefficient, which is, of course,
the most important characteristic affecting the
control of a power reactor. It is certain that this
coefficient was considerably larger than was expected
and that the reactor was exceptionally
stable.
In this, as in any potential power reactor, the
reactor behavior as a result of large increases
in either reactivity or power demand is of particular
interest. With a circulating-fuel reactor
operating to produce power, insertion of the safety
rods reduces the reactor mean temperature. The
power level, on the other hand, is controlled by