ORNL-1816 - the Molten Salt Energy Technologies Web Site

ANP QUARTERLY PROGRESS REPORT
conduit shaped around a 9-in. core. After removal
of the core, the ducts were stiffened by Fiberglas
wrapping. The projected length of each duct along
the z axis was 46.5 in., and the duct arrays were
arranged so that there was 5 in. between the duct
center I ines.
Thermal-neutron measurements beyond a single
duct and a 3-duct array in a water medium were
reported previously.6 Measurements made beyond
the 35-duct array in both a water medium and a
gamma-shield medium are shown in Fig. 13.6. The
gamma shield consisted of steel Raschig rings
(35 vol %) and water borated to 1% by volume.
For both mediums the array was contained in a
4-ft-long iron tank (t-in.-thick walls) which had
'/,-in.-thick iron windows in each end. The
windows were 29 in. in diameter and were slightly
Fig. 13.6. Thermal-Neutron Flux Beyond Various
Arrays of GE-ANP Helical Air Ducts (3 in. in
Diameter, 46.5 in. Long).
1 54
larger than, and concentric with, the LTSF source
plate. The measurements were made behind the
tank in the LTSF water.
As indicated in Fig. 13.6, the presence of the
35 ducts in the gamma shield increased the
thermal-neutron flux by a factor of approximately
3000. In the medium of plain water, the flux was
increased by a factor of 300. For the water
medium the increase in flux seems to be consistent
with a calculation which takes into account only
the reduced density of the attenuating medium.
For the case in which the ducts were in the gamma
shield, the neutron streaming in the ducts appears
to be relatively more important. The latter is not
surprising, since the addition of the steel in-
creases the attenuation of the medium to neutrons
as well as to gamma rays.
The fast-neutron dose rates beyond the 35-duct
array both in a medium of water and in the Raschig
ring-borated water medium are shown in Fig. 13.7.
The gamma-ray dose rate beyond the gamma shield
without the ducts is compared in Fig. 13.8 with
that beyond the shield with the 35 ducts. The
presence of the ducts increased the gamma dose
rate by a factor of approximately 160.
2
10-2
Fig. 13.7. Fast-Neutron Dose Rate Beyond 35
GE-ANP Helical Air Ducts (3 in. in Diameter,
46.5 in. Long).
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