The Daring Dufas wrote:
....

I have some understanding of the work you've been involved in enough to
know how important it is to the safety of nuclear plants especially when
it comes to predicting failure of the infrastructure. Tell me if I'm
wrong in assuming that some of the testing involves actually sort
of listening to the pipes to ascertain the condition? A good pipe has
a particular (sound) or characteristic reaction to fluid flow when it's
in good shape? I've worked with vibration sensors to monitor bearings in
chiller plants before so the early signs of failure could be detected
and equipment could be shut down and repaired before a failure
could cause catastrophic damage. I'm also wondering about the types of
failure that could be caused by high pressure, high velocity fluid flow
in pipes in a plant that's running 24/7? You mention turbulence so I
guess cavitation would be another concern? Do the high frequency
vibrations cause stress fractures in the metal of the pipes, flanges
and welds?

TDD

That particular work wasn't terribly related to each other -- the
pressure vessel samples are chunks of the reactor vessel material that
are placed in special specimen holders designed into the vessels on
initial installation and then removed after a specified set of intervals
and tested. The primary test for these samples is for ductility
(testing against radiation-induced embrittlement) to, as you inferred
correctly, determine that the vessel and other high pressure components
have not undergone excessive degradation so as to still be capable of
withstanding operating pressures and temperatures.

The accelerometer measurements in piping I referred to earlier were for
the pulverized coal flow distribution pipes in coal-fired boilers, not
nuclear plants. These are fairly low pressure but high air flow volume
pipes and the air is both for coal transport and is also a major
fraction of combustion air. Since it isn't liquid fluid flow and is
blown not pumped, cavitation isn't an issue there. The turbulence noise
here is simply a byproduct of the transport system that we were using w/
the characteristics that fluid transport/flow isn't stochastic but
chaotic to find information regarding coal and air flow rates buried in
that ultrasonic signal we could pick up via the accelerometer. It had
the major advantage of being non-invasive as coal dust is extremely
abrasive so it's a major hassle to try to keep instrumentation alive
that can survive inside a pipe. Being as how there is no free lunch,
the counter problem was that the processing was quite intensive.

Back to your question regarding flow noise and measurements in nuclear
plants -- in general, the answer is "yes, stuff like that is done" and
is done routinely as you're familiar with for preventive maintenance and
other various mechanical systems. If you've worked in the area much at
all you've probably come across my last employer that I mentioned above,
CSI (Computational Systems, Inc) in Knoxville, TN, now a subsidiary of
Emerson Electric in the Rosemount catalog of instrumentation.

As for other similar measurements in reactors, the secondary piping and
so on wasn't particularly my area of expertise. I'll note, however,
though, that other than the reactor itself, the rest of the plant is
really no different than are the other large generation plants in
pressures and/or flow; in fact, super-critical fossil boilers run at
much higher pressures and temperatures than do pressurized water
reactors. The containment of such fluids was pretty much routine long
before commercial nuclear power came along.

There is routine monitoring of primary reactor coolant pumps for such
problems as you would expect. As a complete sidelight, interestingly,
the reason the TMI accident progressed to the point it did was that the
operators misinterpreted some pressure/temperature data and fearing
cavitation in the RCPs turned them off, thus cutting off forced
circulation in the core for several hours. The accident sequence was
brought under control and began to be stabilized when the SRO of the
subsequent shift recognized the issue and had the pumps restarted as
well as the HPI (high pressure injection) system and recovered the core
and reestablished core cooling. If the first crew had simply kept their
hands in their pockets and let the safety systems and control systems
"do their thing" there would have been no event other than a reactor
trip and a manual reset of the PORVs and the plant would have gone back
to normal operation in a week or so after some routine maintenance. A
case where an event can be turned into a major one by a combination of
mistakes after a mechanical failure (which wasn't terribly uncommon nor
is unexpected, particularly, for a PORV to not automatically reclose
which not being manually closed after it failed to reseat and not being
recognized was open was the source of the primary coolant loss).

Some of the things that are unique to nuclear units that are done to
monitor for early signs of failure or mechanical problems in the reactor
include "loose parts monitors" and "neutron noise analysis". The first
of these uses a group of accelerometers mounted in various places on the
reactor vessel and primary coolant piping and "listen" for impact noises
that could be the result of some reactor internals failure or similar.
They are tied into systems that use a triangulation method on time of
arrival for impacts to try to localize where within the plant any
particular noise might actually be coming from. Did do the software for
a prototype one of these systems for TVA way back when, too...just after
the REMOTEC work. Unfortunately, then was about the time TVA was
pulling back so only the one prototype was ever finished and by the time
things picked up again, technology (and I) had moved on...

"Neutron noise" is a very interesting and intellectually and
computationally challenging area -- it uses the small fluctuations in
the signal of the excore neutron detectors and signal processing to
infer things about reactor internals such as the movement of the core
inner liner or fuel assembly vibrations. As the inner barrel moves
slightly (on order of tens of mils), the change in water density owing
the that slight change in thickness is discernible in a very small
fluctuation in the neutron flux at the detector. By monitoring this in
time, if something were to happen to one of the studs that holds the
barrel in place, one could detect a larger amplitude of barrel motion
(this has happened at at least on reactor I'm aware of). By knowing
this before either the next outage or larger damage became apparent, one
can monitor the situation and determine when or if an early shutdown
would be required.

There are any number of other monitoring systems and instrumentation
besides for almost all systems and certainly for those that are directly
safety related.

Again, undoubtedly, far more than one might care about in ahr...

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