ORNL-1771 - Oak Ridge National Laboratory

that will permit remote, momentary flooding of the
impeller eye and the labyrinth behind the impeller.
A turbine-type impeller is used instead of the
conventional centrifugal i mpel ler.
It has been experimentally determined, with
water, that the turbine type of impeller will prime
itself if the inlet and outlet are placed at the
bottom of the pump and the fluid is maintained at
a level about half way between the bottom of the
impeller and the impeller center. The horizontal
sump pump principle is used, with the sump having
a minimum volume that acts merely as an expansion
chamber and a reservoir to replace and catch the
fluid leaking past the labyrinth seal. Excessive
impeller end clearances are necessary for this
type of pump because of the severe temperature
gradients present. However, estimated available
pump heads (25 ft at 4500 rpm and 1.5 gpm) are
greater than the estimated requirements. Hydraulic
efficiency of the pump will be low but performance
will be reliable.
Further work has been done on centrifugally
sealed and frozen-fluoride-sealed pumps, and it
has been established that the centrifugally sealed
pump requirestoo greata volume of fluid for sealing
for it to be considered for in-pile use and that the
leakage rate of the frozen-fluoride-sealed pump is
excessive. However, the centrifugally sealed
pump, which will be useful for other applications,
has been modified to include a system that makes
the pump self-priming and deaerating. By con-
trolling the seal level and using a proper venting
PERIOD ENDING SEPTEMBER 10, 1954
sequence, the pump can be easily stopped and
restarted. A pilot model of the pump, similar to
the pump previously described,2 has been designed
that incorporates these features (Fig. 3.1) and an
integral sump tank connected by a passage to the
seal cavity.
In Operation, the system would be filled to the
full level. The seal cavity and sump tank would
then be pressurized through the gas inlet tube to
the predetermined pressure necessary to obtain a
positive pump inlet pressure during operation, and
the pump would be started. The centrifugal force
would cause the liquid in the seal cavity to form a
rotating annulus. The annulus of fluid would
develop a small pressure and thus pump fluid into
the discharge tube, through the loop, and back to
the pump. The small bleed hole from the pump
discharge to the sump tank would permit deaeration
by bypassing aerated fluid from the pump into the
sump. The bypassed fluid would be replaced by
clear fluid from the seal. When the pump was
primed and deaerated, a continuous flow of fluid
would pass from the bleed hole to the sump to
remove any accumulation of gas. Throughout this
operation, fluid entering the loop from the seal to
either fill the loop or replace the bleed flow would
be replaced by fluid from the sump, and sufficient
fluid would thus be in the seal for sealing. There-
fore there is a lower limit on the run level in the
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