ORNL-2106 - the Molten Salt Energy Technologies Web Site

thermocouple lead wires which failed had, in-
advertently, been clamped rigidly to the end of the
outer wall of the double-walled heat exchanger.
This could have resulted in strains on the thermo-
couple wire from the thermal expansion of the
pipes. The loop design has been modified to
correct this condition.
As with loop No. 3, both the bearing-housing and
the pump-sump purge outlets plugged. The bearing
purge outlet plugged five days after startup, and
the sump purge outlet plugged four days later.
The cause of this plugging is still being investi-
gated. The fission-gas absorption traps from loop
No. 3 have been sectioned. An extensive black
deposit was found in the inlet of one and a brownish
film was found in the other. This black deposit,
believed to have come from the pump lubricating
oil in the bearing housing, is to be given radio-
assay and spectrographic analysis to determine
its composition (see Chap. 4.2, "Radiation
Damage"). It is planned to operate future loops
with little or no purging of the bearing housing
and reduced purging of the pump sump to minimize
the probability of plugging. Previously, the higher
purging rates were considered necessary to mini-
mize hydraulic-motor-oi I contamination. Experience
indicates that, although some contamination results
from operating with the purges plugged, such con-
tamination is not a serious problem during dis-
assembly.
Other major difficulties encountered were a leak
in the pump bulkhead, probably through a glass
heater or thermocouple-wire seal, and an excessive
radiation level in he cubicle after shutdown. A
new type of electrical seal for the pump bulkhead
is being investigated. The excessive activity of
the cubicle after shutdown was caused by the
deposition of material on the purge-outlet-tube
walls during operation. Radiation levels as hi&
as 50 rhr were measured on the \-in. pump-purge-
outlet tube. This caused considerable difficulty
in loop removal because it necessitated a relatively
large amount of preparatory wak. The design has
76
now been modified so that all tubes may be pinched
leak-tight, cut, and removed remotely to make
possible the removal of the activity prior to the
entry of personnel into the cubicle. The only work
which will require entry to the cubicle will be the
removal of the air and water lines.
Loop No. 5
D. M. Haines
In-pile loop No. 5 was completed and inserted
in the MTR, but could not be filled. This loop
was to have operated for the duration of two
MTR operating cycles with a maximum fuel tem-
perature of 1600OF and a temperature differential
of 200OF. The improved thermocouple installa-
tion mentioned above was used in the fabrication
of this loop, and the rear section was modified to
simplify removal and to provide a second hermetic
seal to back up the seal at the intermediate bulk-
head to prevent fission-gas leakage. The loop is
being returned to ORNL for salvage.
Horizontal-Shaft Sump Pump for In-Pile Loops
W. S. Karn3
An improved prototype (Mark II) of the horizontal-
shaft sump pump designed for in-pile loop operation
completed 1000 hr of a 2000-hr endurance test at
4500 rpm and 1500OF. The test was terminated by
shaft seizure, and disassembly showed that the
seizure was caused by the buildup of zirconium
fluoride on the shaft slinger. This was the first
pump operated at 1500°F, the previous pumps being
operated at 1400OF. The vapor pressure of zir-
conium fluoride in the fuel mixture (No. 44) NaF-
ZrF4-UF, (53.5-40.6.5 mole %) used in this test
is 2 mm Hg at 1400OF and 4.5 mm Hg at 1500OF.
The increase in vapor pressure is considered to
have been the cause of the buildup of zirconium
fluoride on the slinger. A new pump is to be built
with increased clearances at the slinger.
30n assignment from Prott & Whitney Aircraft.