ing assessment. However, there is not a one-stop checklist
that you can use to determine whether a reactor should be
repaired or retired.
There may be some reprieve on the horizon, but not as
near-term as you might hope. I understand that API 934-I
and API 934-H covering an inspection standard and a repair
standard are actively in the works. While these documents
are under development, I understand that they are not imminent, and the timeframe suggested to me may be another
2 or 3 years. Also, they will likely be issued as a technical
report rather than a recommended practice. We do not expect failure, but reactors can degrade if not operated and
maintained correctly. On my next slide, I introduce the concept of reactor life management. Through life management,
we are trying to accomplish two things. First, we are trying
to limit thermal cycles, which is a fatigue issue. The intent is
to maximize plant reliability and extend cycles, where possible, in order to extend the life of reactors and other pressure vessels. If you have to pull a unit offline, you should try
to minimize the thermal cycling.
The second issue to be managed is minimizing post-weld
heat-treating cycles because this can lead to derating. Minimizing post-weld heat-treating is accomplished by managing crack and defect repairs. We use the following process to
manage repairs. Cracks and defects are evaluated by highly
trained specialists who make a determination about whether
these cracks can be left and monitored or require immediate
repair. I understand that cracks within the cladding do not
generally represent a serious risk and can usually be left and
monitored for propagation.
Cracks and defects in the base metal will raise a higher
level of concern. However, even these can sometimes be left
in place. Usually they are not left as a crack; rather, they are
ground out to transform them into a local thin area rather
than a high-stress crack. This is how we approach reactor
life management.
While we have not had many failure or forced retirement
issues, we are currently evaluating the economic replacement of one reactor. We have a 1960s-vintage reactor that
has recurring cracks in the closure ring grooves and in the
internal attachment welds, and these are all time-consuming
to repair. They have added work and extended every recent
shutdown. So there is an ongoing cost associated with the
condition of this reactor. However, this cost is not sufficient
to justify replacement. We can repair each of the defects so
that the overall condition is still good enough for it to pass
an FFS engineering assessment.
We are now in the process of developing additional econom-
ic incentives to determine if replacement is justified. For exam-
ple, the reactor we are evaluating is old, and older reactors tend
to have a high minimum pressurizing temperature (MP T). High
MPT translates into startup-shutdown risk and time, so there is
an economic value that can be assigned to replacement with a
lower-MPT vessel. The design of the reactor internals is dated,
Our view on reactor replacement is that we have
experienced very few failures. We do not expect reactors to
fail. We expect to be able to repair them as needed and op-
erate them indefinitely. We are operating reactors that we
have had in service since the mid 1960s. In one case, we are
considering a replacement, but this would be an economic
replacement. Generally, even for older reactors, we do not
manage them as though they have a fixed end of life. We
replaced two reactors that were affected by adjacent fires. We
do not have much of a case history where a reactor incident
or defect caused us to remove it from service. In fact, we have
repaired significant cracks, bulges, and other defects. While
issues are uncommon, they are generally with older reactors.
We have no expectation of issues with newer reactors.
Reactor age is not just calendar age. Cycles can significantly affect a reactor’s condition. We have some ongoing
issues associated with high-cycle reactors. In addition, older
calendar-age reactors can be less reliable and may require
ongoing repairs to keep them in service due to material quality, design, and fabrication issues. However, improvements
in each of these areas have significantly improved reliability
for newer reactors.
There have also been design improvements. For example,
nozzle design and location has improved. On older reactors,
nozzles are considered to be a potential weak point and are
closely monitored. We seem to have fewer concerns with
newer nozzles.
There have been significant improvements in materials
technology such as cladding, for example. Bonding methods and the degree to which cladding is bonded to the base
metal is significantly superior in newer reactors.
Fabrication methods have also improved. Welds are an
example. Historically, the heat-affected zone around the
weld has been an area of concern. Now, welds are implemented and geometrically designed to minimize the heat-affected zone, which has improved reliability.
For full-disclosure purposes, I mentioned that I am not
a trained materials engineer. I also have no specific training
in pressure vessel mechanical design, so treat my comments
for this next slide as an informed third party. Unfortunately,
for those who are responsible for pressure vessel inspection
and reliability, there is no industry standard that specifically
addresses reactor retirement. There are standards around
high-pressure equipment; most notably, the FFS engineer-
