ORNL-2106 - the Molten Salt Energy Technologies Web Site

CRITICAL EXPERIMENTS FOR THE
COMPACT-CORE REFLECTOR-MODERATER
REACTOR
E. Demski’ J. J. Lynn
W. 3. Fader’
D. A. Harvey’
D. Scott
4.4. CRITICAL EXPERIMENTS
D. E. McCarty
E. V. Sandin’
The study of the NDA2-proposed, sodium-cooled,
reflector-moderated reactor with solid fuel element~~
has been completed. In the critical assembly
the fuel region contained 0.004-in.-thick
uranium sheets interleaved between aluminum and
stainless steel sheets. This fuel region was
separated from the beryllium of the island and
of the reflector by stainless steel shells. As
described previo~sly,~ additional uranium, in the
form of 0.01-in.-thick disks, was added in one
section of the fuel region to provide excess reactivity
for other measurements. An evaluation
of the effect of this local nonuniform fuel distribution
on the reactivity was made by replacing
2636 g of U235 in 0.004-in.-thick sheets with
2678 g of U235 in 0.01-in.-thick disks in another
section of the core. With the other materials
unchanged, there was a reactivity loss of only
19 cents.
Evaluation of Stainless Steel Shell
The loss in reactivity caused by the stainless
steel shells was determined by substituting alumi-
num shells of the same dimensions, The exchange
of 4.4 kg of aluminum for 11.9 kg of stainless
steel resulted in a gain in reactivity of $4.20,
‘A. D. Calli hon et al., ANP Qwr. Prog. Re March 10,
1956, ORNL-2061, p 64; Dec. IO, 1955, gkNL-2012,
p 73.
A. D. Callihan
PERIOD ENDING JUNE IO, 1956
over the 28t-in. length of the outer reflector and
comprised 70% of the outer cylindrical layer re-
sulted in a loss in reactivity of $2.39.
Measurements of Gamma-Ray Heating in Beryllium
Capacitive ionization chambers were used to
measure the distribution of gamma-ray heating in
the beryllium of the island and the reflector of the
critical assembly by a method developed at the
Knolls Atomic Power Laboratory.’ The chambers
are constructed of beryllium and have a 10-mil-
thick annular cavity T6 in. OD and s/s in. deep,
The results are expressed as power dissipated as
heat in a unit volume per unit reactor power. The
reactor power was determined from a calibration
based on the intensity of a fission-product gamma
ray from an irradiated uranium foil.6
A plot of the data obtained from radial traverses
C and 107 in. from the mid-plane of the reactor is
’6
given in Fig. 4.4.1. Three longitudinal traverses,
one along the axis of the reactor and the others
45/16 and 73/16 in. from the‘ axis, are plotted in
Fig. 4.4.2. These data have not been corrected
for the ionization resulting from the (n,p) reaction
in the air-filled chambers and may overestimate
the heating adjacent to the fuel by as much as
25%, an estimate based on the work at KAPL.
An attempt was made to measure this error by
filling the chambers with CO, but it was apparent
that they were not gas-tight during these experiments.
It may be possible to make a correction
to these data by using the results of similar
measurements in another assembly.
A layer of beryllium, 2% in. thick, was removed
from the top of the reactor, and one traverse was
repeated with this thinner reflector. The heating
was observed to be unaffected in the region between
the fuel and a point 3 in. from the surface
of the modified reflector, In this outer 3-in. layer
the heating decreased to a value, at the surface,
about 35% less than it was at the same distance
from the fuel in the thicker reflector.
’C. A. Rich and R. f. Slovacek, Gamma-Ray Heating
Measurements in the SIR PPA-18, KAPL-866 (Jan. 7,
1953).
6S. Snyder, Absolute Determination of Power Prodwed
in a Nominally Zero Power Reactor, ORNL-2068 (May
15, 1956).
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