ties available in the industry, creating a
production chokepoint.
Solenoid Operated Valves (SOVs).
The process solenoid valves discussed in
this article are not part of a valve or
equipment actuator system but instead
are actually welded into the process
piping. The nuclear industry has SOVs
as large as 6 inches installed in nuclear
safety-related systems. Initially, one of
the key elements promoting the use of
SOVs in nuclear plants was that such
valves have no stem. Dynamic stem
seals are prone to leakage every time
the valve moves. For applications handling highly radioactive fluid, this is not
acceptable. Solenoid valves have a
static pressure boundary and contain all
moving parts inside, eliminating this
escape path, and, as such, are considered hermetically sealed.
Later plant designs have expanded
their use after recognizing the additional
benefits of small-size, small-weight, electric actuation and quick operation with
no friction factors.
PLENTY OF PAPERWORK
Probably every type of traditional valve
technology is used in the massive
machine that is a nuclear power plant,
including gates, globes, butterflies,
checks, safety/relief valves and ball
valves. Married to these is a wide array
of actuation, including diaphragm actuators, piston actuators, motor operators
and hydraulic actuators.
What sets these valves and actuators
apart from their industrial cousins is
the amount of quality verification
paperwork needed to install them into a
nuclear safety application. The ASME
Code and customer specifications are
very detailed in these matters. Codes
and specifications associated with supplying a nuclear plant address nondestructive examination (NDE)
requirements on specific valve parts,
detailed material specifications verified
through certified testing, minimum wall
thicknesses, analytical design reports,
seismic analysis and testing, environmental qualification and extensive pro-
duction testing. In the nuclear industry,
a valve is not ready to ship until the
paperwork weighs at least as much as
the valve.
This paperwork significantly
increases the price of valves at a time
when the nuclear renaissance is already
threatened by significant increases in
cost estimates for building a plant and
difficult construction financing challenges. The valve industry can help by
assisting plant designers in the careful
specification and selection of valves
focusing on cost optimization. This can
be accomplished in several ways, a few
of which are discussed in this article.
LESSONS LEARNED
First, one of the lessons learned in the
Generation II plants is that valves were
too frequently over-specified. Plant
designers are often not knowledgeable
in valve sizing, and as a result, there
are many oversized valves installed in
the industry. The use of the latest sizing
programs makes sizing of control valves
