ORNL-2106 - the Molten Salt Energy Technologies Web Site

NEUTRON SHIELD MATERIAL FOR
HIGH-TEMPERATURE USE
M. R. D'Amore J. H. Coobs
The neutron shield designed for the ART, as
discussed previ~usly,~ incorporates a double layer
of boron-containing materials which have a total
boron density of 1.2 g/cm2. A stainless-steel-clad
copper-B,C cermet layer 0.100 in. thick is to be
used nearest to the neutron source to absorb radiation
damage. The second layer consists of B,C
ceramic tiles 0.265 in. thick contained in stainless
steel cans.
Ceramic B,C Tiles
The evaluation of the B,C ceramic tiles sub
mitted by the Norton Company and by the Carborun-
dum Company was completed. Two sets of four
sample tiles each were received from the Carborun-
dum Company during the quarter. The tiles were
bonded with silicon and fabricated by a casting
and sintering process. Radiographs of the first set
of four tiles revealed large voids. The macro-
porosity was eliminated in the second set of tiles
by a revision in the manufacturing process. The
boron densities of the eight tiles, as determined by
chemical analysis, varied between 0.889 and 1.15
g/cm3. The minimum boron density of 1.26 g/cm3
specified for the tiles appears to be difficult to
achieve in a cast and sintered B,C-Sic tile.
The Norton Company submitted tiles of both
technical-grade and high-purity B,C that had been
hot pressed to densities of 1.9 to 234 g/cm3. A
high-purity B,C tile with a density of 2.0 g/cm3
was found by analysis to contain 1.48 g of boron
per cubic centimeter, rather than the minimum of
1.33 g/cm3 guaranteed by the Norton Company.
The Norton Company has guaranteed to produce
finished tiles of high purity with a minimum boron
content of 1.7 g/cm3,
Representative specimens cut from sample tiles
submitted by each company were irradiated in the
LiTR for a six-week period. A cursory examination
of the irradiated specimens indicated that the
ability to withstand radiation dmage is equal for
both materials at less than 3% burnup of the B'O
atoms. No cracking of the specimens or gas evolu-
tion was observed after irradiation. The hot-
pressed B,C tiles are preferable for ART applice
7H. Inouye, ANP Quat. Prog. Rep. March 10, 1956,
ORNL-2061, p 151.
PERIOD ENDING JUNE 10, 1956
tion, since the higher boron concentrations attain-
able by this fabrication method will result in a
more effective reduction in neutron activation of
the NaK heat exchanger circuit.
Copper-B 4C Cermets
The shield plates made from a stainless-steel-
clad copper-B4C cermet are to be 0.100 in. thick
and to have the following cross-sectional configu-
ration:
8 to 10 mils of type 430 stainless steel
cladding
1 to 3 mils of copper diffusion barrier
80 mils of 16 VOI 95 B,C particles dispersed
in copper
1 to 3 mils of copper diffusion barrier
8 to 10 mils of type 430 stainless steel
c I adding
The maximum plate size is to be &out 8 in. square.
Bonding of the components by hot-roll cladding in
an evacuated picture frame has been moderately
successful. Bonding of the copper barrier material
to the type 430 stainless steel cladding is difficult
to achieve at moderate intermediate reductions.
Reductions of 20% per pass cause a bulging of the
B4C-copper core at each end which ruptures the
cladding. A more promising method of manufac-
turing the clad cermet plates consists in bonding
the components by hot pressing at temperatures be-
tween 1800 and 19OOOF and then cold rolling the
plates to the final thickness. The plate uniformity
can be controlled to close tolerances by this
method, and good bonding of the components is
achieved.
Small plates have been successfully fabricated,
and the process is being scaled up for the manu-
facture of larger plates. Radiation-damage speci-
mens of the clad cermet have been prepared and
will be irradiated in the LITR and in the MTR.
Boride Particle Dispersions in a Metallic Matrix
Dispersions of BN and CaB, particles in iron
and nickel were investigated as possible substi- r
tutes for copper-8,C cermets. Compacts containing
21 vol % CaB, dispersed in iron and 30 vol % BN
dispersed in nickel were successfully fabricated
by cold pressing, sintering, and coining the powder
mixtures. The coined compacts were encapsulated
in a type 304 stainless steel picture frame and
rolled at 200OOF to a total thickness reduction of
85%. After hot rolling, the CaB,-Fe and BN-Ni
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