Nuclear Plant Journal, July-August 2014 NuclearPlantJournal.com
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controlling the leakage through the seal
between 1.0 and 5.0 gallons per minute
(gpm). Normal operational leakage is
about of 2.5 gpm. Without the hydrostatic
seal, the RCS water would leak through
this area at a very high rate.
The hydrostatic seal operates with
two separate sources of cooling water
that cools the RCS water going through
the seal. These cooling sources cool the
RCS water from 572° F to 140°F. If both
of these sources of cooling are lost, the
572° F RCS water would enter the seal
cavity and cause the hydrostatic seal to
fail.
During an event with a loss of all
cooling, the hot reactor coolant seal water
enters the RCP seal cavity and subjects
it to these higher temperatures. Under
these higher temperatures, the fuse spacer
transforms from a hardened state to a
softer state and is no longer able to keep
the wave spring compressed. When the
wave spring is decompressed, it pushes
a piston ring upward, which causes a
sealing ring to begin to constrict around
the pump shaft/sleeve to eventually seal
off the leakage path. Multiple tests have
proven the reliability of the triggering
mechanism to actuate the PSDS when it
is needed. Limiting the leakage through
the seal lessens the need for additional
makeup capacity by helping to maintain
the existing reactor coolant system
inventory, reduces the load to existing
makeup systems, and reduces cleanup
and associated radiation dose, all of
which contribute to improved safety at
the plant.
AREVA specifically developed the
PSDS for use in U.S. pressurized water
reactors using the Westinghouse Model
93A, 93A1 and 100 reactor coolant
pumps with hydrostatic seal designs.
International utilities using similar
hydrostatic RCP seal designs can also use
the PSDS. Currently, theAREVA PSDS is
installed and in operation in a model 100
RCP at a U.S. utility site and is scheduled
to be installed in a French nuclear plant in
the first quarter of 2015. After a full cycle
of operation, AREVA will remove the
PSDS from the current U.S. reactor pump
and perform an actuation test to confirm
that the seal is operating properly after
being actively used during an operating
cycle.
In addition, AREVA is working
with the NRC to review the design and
qualification program in order to gain the
agency’s certification of the PSDS as a
low leakage seal. AREVA will then work
with a utility on the low leakage assurance
in the probabilistic risk assessment and
core damage frequency calculations
under Extended Loss of All Power, NFP
805, Mitigating Systems Performance
Index and other programs.
AREVA’s PSDS is one of many
examples of how the industry is innovating
to improve the safety and reliability of
the existing fleet, especially in relation to
emergency event preparedness. Through
experience feedback and a thorough
Three stage hydrostatic seal arrangement and location of PSDS.
understanding of the needs of nuclear
plant operators, AREVA is working to
secure the future of nuclear electricity
generation in the United States.
Contact: Mary Beth Ginder, AREVA
Inc., 1 International Plaza, Suite 210,
Philadelphia, Pennsylvania 19113;
telephone: (301) 841-1703, email:
.
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