ORNL-1816 - the Molten Salt Energy Technologies Web Site

for more than 0.6 Mw in the sodium, which result
in a total reactor power in excess of 2.5 Mw. The
temperature differences quoted were obtained from
the fuel pipe temperatures to and from the reactor
at the time the reactor inlet and outlet core tube
temperatures (as shown in Fig. 1.3) recorded a
AT of only 25OOF. While there are several
possible phenomena which could contribute to
these low core tube temperatures (external cooling,
surface layers, radiation, etc.), there were 10 to
15 thermocouples on the inlet and outlet pipes
which gave consistent readirigs. The outlet pipe
temperature was at an equilibrium of 1580°F and
was in excess of 160OOF during transients.
The last scheduled experiment to be conducted
on the reactor was a measurement of the xenon
buildup during a 25-hr run at high power. The
amount of xenon buildup was observed by the
amount of regulating rod which had to be with-
drawn in order to maintain a constant power level.
However, during the 25-hr power run the regulating
rod had been withdrawn only 0.3 in., or one-
thirtieth the amount calculated on the assumption
that the xenon would remain in the fuel.
The scheduled tests were completed by 8:OO AM,
November 12. The reactor operation was then
demonstrated for all those who attended the ANP
Information Meeting on Friday, November 12.
During the 12-hr period of 8:OO AM to 8:OO PM,
the reactor power was cycled 21 times. The
resulting temperature cycling was probably as
severe as that to which an aircraft reactor would
be subiected. At 8:OO PM, November 12, with
the scheduled experimental program completed and
over 100 Mwhr of operation logged, the reactor
was made subcritical, but circulation of the fuel
and sodium was continued. The following morning,
the fuel umped into
their respective dump tanks.
Mathematical Analysis of Approach .. to Critical
Wh
it was observed that the
ultiplication constant)] vs
uranium concentration incr ed, at first, very
is observed in many reactors, but the ARE ex-
hibited the effect to an unusual degree. In order
--
PERIOD ENDING DECEMBER 70, 7954
to explain this, the ORACLE three-group, three-
region code was modified so that flcx shapes at
successive fuel additions could be calculated.
Group constants were obtained by flux weighting
with fluxes from an Eyewash calculation on the
ARE.
Figure 1.4 shows the space distribution of the
thermal flux for no fuel and for runs 2 through 6.
The effect of the reflector as fission neutrons
become more numerous can be seen. Figure 1.5
compares experimental and calculated startup
curves for the fission chambers whic1.l were
located in the reflector as indicated in Fig. 1.4.
In the calculation,
CR - Of,+, + Of$ + Of$ I
where CR is the counting rate of the fission
chamber, u is the fission cross section for group
fi
i, and +i is the group i flux. For the ARE startup
CRi
where m is the multiplication constant, CR. is
I
the counting rate on run j, and CRo is the counting
rate with no fuel. It seems, then, that the unexpected,
rapid initial rise in the counting rate of
the fission chamber and the [l - (l/m)] curve is
due not only to the general rise in flux level but
also to the formation of the thermal-flux maximum
near the fission chambers. Once the shape of
spatial distribution of the thermal neutron flux
is set up, the fission chambers register only the
general increase in flux level and the count rate
increases slowly.
OPERATION OF ARE PUMPS
W. G. Cobb A. G. Grindell
h. R. Huntley
Aircraft Reactor Engineering Division
The operation of the ARE pumps during the
prenuclear and nuclear phases of the experiment
can be regarded as
of operation at hig
with the sodium sy
. The latter total include$, 169 hr
with fuel carrier, 2 hr with critical fuel but no
heat removal, and 73 hr with heat removal.
The preoperation check of the ARE pumps
consisted in a functional check of he seal gas-
15
i
I