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NuclearPlantJournal.com Nuclear Plant Journal, May-June 2015
Fukushima
Lessons-
Learned
By Jack Davis and Jeremy Bowen,
Nuclear Regulatory Commission.
Jack Davis
Jack Davis is Director of the Japan
Lessons Learned Division in the NRC’s
Office of Nuclear Reactor Regulation.
Mr. Davis oversees the staff focused
on enhancing the
U.S. commercial
nuclear fleet’s ability
to safely deal with
beyond-design-basis
extreme natural
phenomena.
Mr. Davis’s more
than 24 years of
nuclear experience
include senior NRC
leadership positions
in nuclear reactors,
nuclear fuel cycle,
high-level waste,
nuclear security
and corporate
infrastructure.
Mr. Davis holds a bachelor’s in Nuclear
Engineering from Penn State University.
An interview by Newal Agnihotri, Editor
of Nuclear Plant Journal, at the Nuclear
Regulatory Commission’s Regulatory
Information Conference in North
Bethesda, Maryland on March 10, 2015.
1.
What are the different mitigation
strategies to cope with beyond design
basis events?
Jack Davis:
After Fukushima,
the Commission put out an Order for
mitigation strategies, the EA-12-049
order,
Order to Modifying Licenses with
Regard to Requirements for Mitigation
Strategies for Beyond-Design-Basis
External Events
. The U.S. NRC also
put out a request for information, the
50.54(f) letter,
Request for Information
Pursuant to Title 10 of the Code of
Federal Regulations 50.54(F) Regarding
Recommendations 2.1,2.3, and 9.3, of the
Near-term Task Force Review of Insights
from the Fukushima Dai-ichi Accident
,
for seismic and flooding re-evaluations.
Then the commission started the
rulemaking process to codify this for the
agency. So, what’s being put into the
rulemaking is really all of the things that are in
the mitigation strategy
order. All the nuclear
plants are required to
be in compliance with
the order by December
31, 2016. They’re on
a staggered submittal
to the agency based
upon their outages.
The plants are allowed
to have two outages to
come into compliance.
All of the plants have
submitted
interim
information for us to
complete our interim
safety
evaluation.
They’re now completing
that work, and they will
all be done by 2016.
Jeremy Bowen:
The only exceptions to
the December 31, 2016, date is that there are
a few plants that have to make a modification
to their venting system to comply with
the EA-13-109 order,
Order to Modify
Licenses with Regard to Reliable Hardened
Containment Vents Capable of Operation
Under Severe Accident Conditions
. There
are a select few plants that asked to align
their schedules. The venting portion of
their mitigating strategies to comply with
the mitigating strategies order goes past
2016. All the other equipment, all the
other modifications will comply with the
mitigating strategies order and will still be in
place by the end of 2016.
The
post-Fukushima
venting
strategy is for boiling water reactors with
Mark I and Mark II containments. It’s a
venting capability for the containment,
not anything to do with the reactor vessel
and the primary coolant system. This is a
way to vent those containments, because
one of the lessons learned from the
Fukushima accidents was that there was
vulnerability in those containments, that
if you didn’t vent the containment within
a certain time frame, it could actually
make the accident sequence worse.
Then the commission issued an
Order in March 2012, to install all this
venting capability. As the staff and
industry were working through how to
implement that, we determined that we
wanted to provide a level of defense-in-
depth by making that venting capability
severe accident-capable. So, the NRC
issued a subsequent Order. The first
Order was EA-12-050,
Issuance of
Order to Modify Licenses with Regard to
Reliable Hardened Containment Vents
,
and we rescinded that Order and issued
a new order, EA-13-109, that basically
added additional requirements to the
venting capability so that it would be
severe accident-capable.
There’s another tier 3 activity to
evaluate other types of containments to
see whether additional activities might be
needed to enhance the safety of those, but
that’s yet to be evaluated.
Jack Davis:
Mitigation strategies,
the way they’re designed is pre-core
damage. So, the plant has a capability
to deal with an ELAP, an extended loss
of AC power. And then the commission
said we still want you to have a severe
accident-capable venting system, which
means that all of the mitigation strategies
would have failed, and now the plant is in
a post-core damage state, and it would be
venting at that point. So, that’s the reason
for rescinding the 2012 Order and then
putting the 2013 Order in its place. So,
it’s defense-in-depth if you will.
Whatever this event is, whatever
has caused the station to have an ELAP,
mitigation strategies are designed to deal
with that situation and keep the core cool,
keep the spent fuel pool cool and keep
containment intact. The strategies, the way
the plant is designed, should do that very
effectively. There’s three phases to that
order. Phase 1, you realign your installed
