ORNL-1816 - the Molten Salt Energy Technologies Web Site

ANP QUARTERLY PROGRESS REPORT
reactor fuel systems because it is essential that
the exact amount of fuel in the reactor be known
at all times. One good way of measuring the
quantity of liquid in the tank would be to support
the tank on two Hogan Thrustorq units. This
should give an instantaneous measure of the weight
of the tank to an accuracy of 1% of full-scale
reading.
Design work is under way on a system to fill the
a bove-s peci f ied requirements. Complete tests of
mockups of proposed designs will be made before
the final design is chosen.
DESIGN PHYSICS
W. K. Ergen
Reactor Engineering Division
The compari son between mu ltigroup calculations
and critical experiments on three-region reflector-
moderated reactors has shown a certain amount of
discrepancy, which must be overcome by adjusting
the constants used in the calculations. Investi-
gations were made with the ultimate aim of ob-
taining simpler expressions for the critical mass
and power distribution for reflector-moderated
reactors. This was done in the hope that these
simpler expressions could be fitted to the experi-
ments by adjusting of constants and that this
fitting might be as satisfactory as theone employed
for the multigroup calculations. The three-group
ORACLE calculations of the approach to criti-
cality of the ARE (see Sec. 1) gave a satisfactory
explanation of the strange results observed during
the experiment. An example of the calculations
performed for the ART is the following calculation
of the activation of the lnconel core shells.
Activation of the lnconel Core Shells
H. W. Bertini
Aircraft Reactor Engineering Division
An attempt was made to estimate the activity of
the lnconel core shells on the inside of a 60-Mw
reflector-moderated reactor after the reactor had
been operating for 1000 hr. The activity will
come from two main sources: the activity of the
cobalt in the lnconel and the activity of the fission
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fragments that strike the lnconel and remain there.
The method described below for obtaining the
estimate gives an order of magnitude of the total
activity. Reasonable approximations are used to
simplify the calculations, and, in this way, many
of the details that a more complete analysis would
require are circumvented, and yet the required
accuracy of the calculations is maintained.
To obtain the activity due to the cobalt, the
total flux at the surface of the lnconel is obtained.
This flux is multiplied by the product of the
microscopic cross section of cobalt times the total
number of cobalt atoms in the core shells. This
gives the total number of cobalt atoms being
activated per second. Multiplication of this
number by 1000 hr gives the total number of cobalt
atoms activated during the reactor lifetime. Since
the half life of cobalt is so long (5 years) com-
pared with the reactor lifetime, the decay of the
excited cobalt atoms can be assumed to be con-
stant, and therefore the disintegration rate can be
taken as AN, where A is the decay constant of
cobalt, and N is the total number of cobalt atoms
activated during the lifetime of the reactor.
The following values were used for the calcula-
tions:
Reactor power = 6 x lo7 w
Total mass of U235 in the core = 2,5 x lo4 g
Density of lnconel = 8 g/cm3
Weight per cent of cobalt in the lnconel = 0.1%
Half life of cobalt = 5 years
Average flux at the surface of the reactor,
- -
+s=2 x $reactor
1 curie = 3 x 10" decays/rec
0: = 550 barns
= 35 barns
The total mass of lnconel in the core shells of
the reactor is approximated by the mass of two
spherical lnconel shells, one with a 15-cm radius
and the other with a 25-cm radius, each shell
being 0.3 cm thick. Then,
I
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