UNITED STATES OF AMERICA
NUCLEAR REGULATORY COMMISSION
BRIEFING ON SPENT FUEL POOL STUDY
Nuclear Regulatory Commission
11555 Rockville Pike
Thursday, November 14, 1996
The Commission met in open session, pursuant to
notice, at 2:05 p.m., the Honorable SHIRLEY A. JACKSON,
Chairman of the Commission, presiding.
SHIRLEY A. JACKSON, Chairman of the Commission
KENNETH C. ROGERS, Member of the Commission
GRETA J. DICUS, Member of the Commission
NILS J. DIAZ, Member of the Commission
EDWARD McGAFFIGAN, Member of the Commission
STAFF AND PRESENTERS SEATED AT THE COMMISSION TABLE:
ANDREW BATES, Acting Secretary
MARTY G. MALSCH, Deputy General Counsel
JAMES TAYLOR, EDO
ED JORDAN, AEOD
ERNIE ROSSI, AEOD
JOSE G. IBARRA, AEOD
GARY HOLAHAN, NRR
P R O C E E D I N G S
CHAIRMAN JACKSON: Good afternoon, ladies and
The purpose of this meeting is for the NRC staff
to brief the Commission on the results of its assessment of
the likelihood and consequences of an extended loss of spent
fuel pool cooling inventory.
As you all are aware, fuel handling and spent fuel
pool issues have been the subject of considerable recent
attention and has highlighted the need to better understand
issues such as spent fuel pool design, fuel handling
practices and the contribution of the spent fuel pool to
overall plant risk. This assessment is one part of our
ongoing effort to enhance our performance in these areas and
we look forward to hearing the results of your study.
I understand copies of the presentation slides are
available at the entrances to the room.
Do any of my fellow commissioners have any
comments at this point? If not, Mr. Taylor, please proceed.
MR. TAYLOR: Good afternoon.
With me at the table are Ed Jordan, Ernie Rossi,
Jose Ibarra from the Office of AEOD and Gary Holahan from
As the Commission may be aware, earlier in August
of this year the staff presented the NRR Spent Fuel Storage
Pool Action Plan, which covered the issues outlined at the
beginning by the Chairman but, to provide an independent
assessment of this issue of spent fuel cooling, also earlier
this year I asked AEOD to perform an independent study of
the likelihood and consequences of loss of spent fuel
cooling and this assessment was provided to the Commission
on October 3.
The staff will now present that information.
Ed Jordan will continue.
MR. JORDAN: The AEOD study and the August 1
briefing are complementary since the action plan was design
and requirements based and the focus of the AEOD assessment
was a collection and analysis of operating experience
related to fuel pool cooling.
Our assessment attempts to characterize what is
happening at reactor sites as it impacts fuel cooling. Our
findings are based on site visits to specific plans, a
probablistic risk assessment of a single plant and the
operating experience collected from all plants.
The summary of the lessons that you will hear
through this are that, first, a loss of spent fuel
inventory, the pool inventory, may be more important than
previously thought. And, second, that operator actions for
both prevention and mitigation are of primary importance in
spent fuel events.
The assessment was a team effort by members of the
reactor analysis branch of AEOD. Jose Ibarra was the team
leader and will make the presentation.
MR. IBARRA: Thank you, Mr. Jordan.
In February of this year, the Executive Director
for Operation requested that AEOD perform an independent
assessment of loss of spent fuel pool cooling. We formed a
team to do this assessment.
All through this assessment, we were in contact
with NRR. We wanted to make sure NRR understood what we
were doing but, more important or equally important, we
wanted to get the latest information that was available from
The assessment itself had six major tasks.
Slide number 2, please.
MR. IBARRA: The first of the major tasks was we
had to deal with 74 different configurations and we
developed two generic configurations, one for a pressurized
water reactor and then one for an ordinary water reactor.
And another of our important tasks was to review our over 12
years of operating experiments and in doing this we reviewed
about 700 separate documented operating events. In addition
to this, we also looked at the foreign experience.
A very important task was to go to the licensees
and to gather information and we were interested in looking
at the physical configuration of the pools and understanding
the practices and procedures that the licensees were doing
and we conducted six site visits.
In addition to this, we conducted two more
additional trips to interview two individuals who had
formerly submitted a Part 21 on Susquehanna.
We reviewed the regulations. Basically, this is
reviewing the standard review plan and going through 10 CFR
50, Appendix A, to identify the general design criteria and
we also identified the applicable regulatory guides.
Now, when we talk about the spent fuel pool
cooling, loss of cooling, there is a lot of calculations
involved in this and we felt it was important for us to do
our own independent assessment and we did this for the
electrical system, the instrumentation system, we performed
some heat load calculations and also radiation levels.
And then one of the last major tasks was to assess
the risk of losing spent fuel pool cooling and for this we
contracted with Idaho National Engineering Labs to assist
Slide number 3.
MR. IBARRA: Like I mentioned before, we had to
deal with 74 different designs that covers 109 operating
plants. Basically all the designs are a little bit
different so we developed two generic diagrams and what we
have in front of us is the pressurized water reactor. This
was a basis for our assessment in the sense that we had to
identify the important components and how they relate to
loss of spent fuel pool cooling.
I would like to point out some of the important
features. For the pressurized water reactor, let's start
off with the right-hand side.
The reactor is in a separate building from the
spent fuel pool. On the reactor side important components
are refueling cavity seal. And then you have the fuel
manipulation area and then the fuel transfer tube.
In a separate building adjacent to the containment
building would be the spent fuel pool. They usually call
this the fuel handling building or the auxiliary building.
Here we have a fuel transfer canal, we have the gates, the
pool structure itself with a liner. The pool structure is
reinforced concrete. And then we have the fuel racks. The
fuel racks are basically under 20 feet of water. And then
on the left-hand side, we have the forced cooling, the
components consisting of the spent fuel pumps and a head
Also we have various sensors. This includes the
temperature, the level and the radiation.
A very important component for us is the connected
systems. Connected systems would be like the purification
system, the make-up sources and the reactor itself when it
is undergoing refueling.
When we talk about plant differences, what are
some of those differences? Well, the dimensions of the pool
sometimes vary and then the number of pumps varies, number
of heat exchangers varies, number of loops within that
varies. We have different make-up sources.
Some licensees have a different number of transfer
tubes and then, if this wasn't enough within, outside the
structure itself of the spent fuel pool, we might have
equipment that varies with the different plants.
Slide number 4.
MR. IBARRA: What we have here now is the generic
boiling water reactor configuration and basically the left-
hand side is what we saw in the pressurized water reactor.
There are some differences and one of the major differences
is that the reactor and the spent fuel pool are in the same
building, one difference from the pressurized water reactor.
And some other differences are we have two gates.
When they actually do refueling, they will flood the reactor
side up to the level of spent fuel pool and then they will
remove those gates.
In order to simplify our assessment of losing
cooling, we had to break it up into two different areas,
loss of inventory and loss of cooling. And loss of
inventory would be the connected systems, we have the gates
and then we have the structure itself, the pool structure.
For loss of cooling, we are talking about the
coolant flow and the heat sink.
Next slide, slide number 5, please.
MR. IBARRA: We reviewed over 12 years of
operational experience. This is looking at the licensee
event reports. We looked at 5072 reports, inspection
reports, industry reports and basically any other document
that described operational events. This included looking at
700 separate documented operational experiences and we were
able to screen these down to about 260 events.
This is in addition to looking at the
international community to find out how they were doing and
they are consistent with our operating experience.
What we have a slide here of is a table of where
the events would fall. And we have two columns. The actual
one, one named actual and one precursor. And I will explain
a little about what we mean by precursor.
If we look at the -- under inventory, structure or
liner, precursor column, we have 35 events. One of these
events was a report to us from a licensee that stated that
under certain temperatures the liner could buckle and, if
buckled enough, it would cause coolant loss. In contrast to
the eight on the actual column and there we do have leaks in
Slide number 6, please.
MR. IBARRA: This is a final breakdown of a loss
of inventory and you can see once again the different
categories of where the events would fall. Some numbers I
would like to point out is the configuration control.
That's 16 of the 20 of the connected systems would be
configuration control and we found this was mostly due to
CHAIRMAN JACKSON: You mean gates being open?
MR. IBARRA: Gates being open and so forth, wrong
Under gates and seals, it's mostly the gate seals
that have failed there or that have leaked and in pool
structure or liner, like I mentioned in the slide before,
there was leaks, actual leaks to the liner. And, of course,
we haven't had any earthquakes or any seismic events and
there has never been any failure due to that nature.
Another number that sort of stands out is the 32
under precursor under load drops and what we see there are
tech spec violations, the licensee moving heavy loads over
Slide number 7.
COMMISSIONER ROGERS: Excuse me, before you leave
MR. IBARRA: Sure.
COMMISSIONER ROGERS: Would the precursor data
MR. IBARRA: No.
COMMISSIONER ROGERS: No? You wouldn't treat an
allegation as a precursor?
MR. IBARRA: No.
COMMISSIONER ROGERS: Unless it was substantiated
in some way?
MR. IBARRA: We do find like a lot of precursor
like analysis where they determine something can go wrong
but it actually has not gone wrong but allegations, no.
MR. ROSSI: Well, I think it would include an
allegation if, as a result of the allegation, the licensee
then filed a report of some sort based on what he really
found. So in that respect, if the allegation was
substantiated and then it was put in one of the reports that
we researched then it would be included. But an allegation,
in and of itself --
COMMISSIONER ROGERS: Yes, just a raw allegation.
MR. ROSSI: No, it would not constitute a
MR. IBARRA: Slide number 7.
MR. IBARRA: Now, a lot of the events and times,
we were not able to extract sufficient information to do
plots but we were able to extract some level decreases here
from some of the events and we feel the most significant of
the events. None of these have led to fuel uncovery.
CHAIRMAN JACKSON: What is there about 12 to 60
MR. IBARRA: That is just the way we broke it up,
even though I think one foot is pretty substantial.
If you go look at the spent fuel pools, they have
a gauge there and you could see that. A few inches, you
probably couldn't see. So, you know --
CHAIRMAN JACKSON: I guess what I am really
looking at is this big bump in the one to five feet level
MR. IBARRA: That's just the way they fell.
CHAIRMAN JACKSON: But you are saying already the
12 inches is significant.
MR. IBARRA: You could see that. Yes, you could
see that visually.
MR. ROSSI: Again, there is a lot of water over
the fuel, before you get down.
CHAIRMAN JACKSON: I know, it's about 20 feet.
MR. ROSSI: About 20 feet.
CHAIRMAN JACKSON: But still, five, if you get up
to five and you didn't break it down, that's a lot of water.
MR. ROSSI: Yes.
MR. IBARRA: We would be concerned, of course,
anything over a foot but here we have two events that are
really of concern, they went over five feet.
One of them was Hatch in 1986. It was an
inflatable seal. Then River Bend, 1987, this was a
configuration control problem and there we lost from 60 to
We calculated the frequency of losing more than a
foot of water from our operating experience to be one --
COMMISSIONER DIAZ: Excuse me, why this range, 60
MR. IBARRA: We couldn't nail it down. We just
knew it was within this range.
COMMISSIONER DIAZ: Within five feet?
MR. IBARRA: More than five feet.
We calculated the frequency now of losing over one
foot of water, of coolant, is about one occurrence in 100
Slide number 8.
MR. IBARRA: Once again, we were able to plot the
duration of some of these events and we would be
CHAIRMAN JACKSON: Basically, this one per 100
reactor years, Commissioner Dicus points out, is essentially
one per year, right?
MR. IBARRA: Yes.
COMMISSIONER DICUS: That's an easier way to look
MR. IBARRA: Yes.
On slide number 8, what we have now, we plotted
duration and the -- of concern to us, of course, any
duration that is not picked up right away. But eight hours
is important to us because, at that point, some pools can
start boiling. And we have two -- three incidents here that
lasted over eight hours. Two in particular lasted over 24
hours. We had Wolf Creek in '87, configuration control
problem, that lasted 72 hours. And then we had Hatch, 1986,
an inflatable seal problem, over 24 hours.
Slide number 9.
CHAIRMAN JACKSON: Did the water boil in either of
MR. IBARRA: No.
COMMISSIONER ROGERS: But that comment about eight
hours, that depends on how long the fuel has been allowed to
cool in the vessel before it is brought in.
MR. IBARRA: Surely, it is more critical when you
are doing refueling than when you are in normal operations.
Normal operations, you have lots of time, right.
COMMISSIONER ROGERS: Well, you could have lots of
time in refueling if you wanted to.
MR. IBARRA: In slide number 9, now we are
plotting loss of cooling and temperatures increase. And of
concern to us would be the one that increased 50 degrees and
this occurred in Farley in 1983. A configuration control
And we calculated now for a frequency of
occurrence that would increase the temperature over 20
degrees would be two to three in 1,000 reactor years.
Slide number 10.
MR. IBARRA: And the other one, you know, we were
able to cut off at zero.
Slide number 10, we are plotting loss of cooling,
now, duration again. Once again, eight hours to us is an
important point. We do have here three events that went
over eight hours. Hadden Neck in '86, a pump failure that
went 32 hours. River Bend in 1989, a configuration control
problem, 30 hours. And then Seabrook in '94 went 24 hours
and Seabrook was a configuration control problem also.
Slide number 11.
MR. IBARRA: We did six site visits. We visited
North Anna --
COMMISSIONER ROGERS: Excuse me, if I could just
go back to loss of cooling event?
MR. IBARRA: Yes.
COMMISSIONER ROGERS: What is the meaning of those
hours? I mean, when did the clock start ticking to measure
those hours, from the time that the loss of cooling took
place, started, whatever, failed or whatever, or until it
MR. IBARRA: Well, it's from the point of noted
until the point of being corrected.
COMMISSIONER ROGERS: But it could be longer than
MR. IBARRA: The end point we know; the beginning
point might be a little bit -- you know, the information is
not there, we don't know. But we do know within certain,
you know, limits.
COMMISSIONER ROGERS: What I am really trying to
get at was how alert was the licensee to the fact that this
took place and are these just simply measures of how long it
took to correct the problem after they discovered it or does
it also include some time when they should have known it?
MR. IBARRA: Well, a little bit of both. You
know, it does take time to correct the problem once you
COMMISSIONER ROGERS: Right.
MR. IBARRA: And, of course, that would be in
there. But in our opinion, of course, it was too long.
COMMISSIONER DIAZ: When you said loss of the
coolant pump, you mean both coolant pumps were inoperable
because these all have redundant systems?
MR. IBARRA: It would be loss of a pump.
COMMISSIONER DIAZ: One pump?
MR. IBARRA: One pump.
COMMISSIONER DIAZ: And the other pump was
MR. IBARRA: In some cases, one pump is more than
enough for cooling.
COMMISSIONER DIAZ: I know that it is more, but
they normally have two pumps, right?
MR. IBARRA: Or three.
COMMISSIONER DIAZ: Right. So we didn't lose
complete cooling capability; we just lost one pump?
MR. IBARRA: In some cases you lost one pump, yes.
MR. JORDAN: My understanding of the study was
that this is a case when no pump was available. Whether the
other pump was operable, it wasn't connected. You have to
manually back these up; there is no automatic transfer.
That's how you're normally running, with one pump and one
heat exchanger and if there is a failure then you have to
first detect it and then you have to take manual actions to
valve the other pump in and start it.
COMMISSIONER DIAZ: Actually you lost coolant
because one pump that was operating, was not operating and
the other pump which should come and be switched was not
MR. JORDAN: Not yet switched.
MR. ROSSI: Jose, is that --
MR. IBARRA: That's correct.
COMMISSIONER ROGERS: Well, that still doesn't
totally give me the full picture. Namely, what this 32
hours, say, in that particular instance, I don't care
whether it is 30 or 32, but how -- what portion of this time
was there no cooling available and what portion of the time
was there ordinary cooling not available?
MR. IBARRA: Well, the --
COMMISSIONER ROGERS: Do you know what I'm saying?
If they had to switch over, was the 32 hours -- did that
include the time in which -- was that the time in which
there was no pump available at all to get switched over to
MR. IBARRA: That's correct. Time without
COMMISSIONER ROGERS: Thirty-two hours?
MR. IBARRA: From the --
COMMISSIONER ROGERS: You could fly in from the
West Coast in that time.
MR. IBARRA: Yes, a lot of it is being aware that
MR. ROSSI: The biggest part of the time, I
believe, was the time to detect that they were without
COMMISSIONER ROGERS: Well, that was what I was
asking. How much of the time was the time they didn't know
they had the problem?
MR. ROSSI: The biggest amount of the time is the
time it took to detect they had no cooling.
That, I believe, is the biggest time in all these
cases because once they know they have lost the cooling then
I think it is reasonably quick to start cooling. They catch
it real quick, after they know they have the problem.
COMMISSIONER DICUS: Do we know how quick that is?
MR. IBARRA: Some of the LER, you know, do not
give you enough detail to be able to gather some of that
information but it is true that once you find it, the
correction is rather quick, versus, you know, the time to
detect that it was occurring.
MR. ROSSI: There is one other thing I think I
will see if I can clarify and that is that there is the
question of pumps being available and then there is the
question of pumps running and I believe what you have here
is a situation where these are the number of hours that no
pump was running. But there might have been a pump
available to run and, as a matter of fact, I think in most
cases there was. It was a matter of someone turning that
These are the times when no pump was running and
the majority of this time is the time to detect that fact
and then once you have detected it, you can then turn a
pump -- another pump on or restart the pump that had been
turned off and available. Let me just make sure I am clear
on that. "Available" means that even though it may not be
running, you can turn it on if you want to. It's not torn
down for maintenance or a seized bearing or anything of that
CHAIRMAN JACKSON: But detection of when the
pump -- the availability of the pump is by inference or some
back-calculation. If they didn't know it was not running,
they didn't know it was not running so there was some, you
know, going back to infer or try to calculate that loss.
MR. ROSSI: That is basically correct. I am not
sure it would be a calculation. I think if it had not been
available because it was broken in some way, that would
generally have been included in the report --
CHAIRMAN JACKSON: Right, but what I am trying to
say is what we have been talking about for the last few
minutes had to do with the fact of most of the time that we
see reflected here being the time to detect that there is no
MR. ROSSI: That's correct.
CHAIRMAN JACKSON: So I am saying if one had not
detected that the pump is not running, then that means there
is some period of time before I came and looked and said,
oh, this pump is not running. Then you have to go back and
try to figure out --
MR. ROSSI: Yes, you have to deduce when it
probably started. Right.
CHAIRMAN JACKSON: That is what I am saying.
MR. JORDAN: That will be reflected when we get to
the end, in terms of part of the corrective action may be
CHAIRMAN JACKSON: Okay.
MR. JORDAN: There is not a great deal of active
instrumentation indicating the condition of the pumps.
COMMISSIONER DIAZ: Most of the systems did not
have an automatic switchover --
MR. JORDAN: That's correct.
COMMISSIONER DIAZ: -- from one pump to the other
pump is what you're saying. I know that some do but a lot
of them did not have them.
MR. IBARRA: It's not typical.
So the six site visits included North Anna, South
Texas project, Susquehanna, River Bend, TMI and Calvert
Cliffs and basically this covers all the reactor vendors,
big and small architect engineers, single and shared pools
and you have old and new plants.
And we were interested in looking at the physical
configuration of the pools when trying to understand the
practices and procedures that the licensees were using in
And one thing I would like to point out, the
information that NRR had was a tremendous amount of
information that assisted us in doing our assessment. It
would have caused us problems if we wouldn't have had that
information. But, by the same token, the NRR information
were dealing with information and compliance and our focus
was on operating experience. So we needed to go talk to the
licensees and we talked to them at length, we sat down for
two days and talked to anybody that touched upon the spent
fuel pool activities.
This included talking to the reactor operators,
talking to the analysts, all sorts of engineers. We even
talked to the outage planners and basically anybody that had
anything to do with spent fuel pool activities.
Slide number 11.
MR. IBARRA: There was a good lot of good
practices that we saw. There was one utility that had a
loss of coolant event in 1987 and they learned very well
from this experience.
Right now in the control room, they have a diagram
that shows all the different alignments, all the different
ways that spent fuel coolant could be aligned and nobody is
allowed to make changes to that alignment until they come
into the control room and discuss these alignments with the
control room operator.
CHAIRMAN JACKSON: Where was this?
MR. IBARRA: This is River Bend.
CHAIRMAN JACKSON: Did they also have good
MR. IBARRA: From what we gathered, yes. River
Bend was one of the better plants that we had that included
a lot of these good operating practices. However, I must
mention that not everybody had one of each of these.
Another important thing that we saw, a positive
step, was risk assessments, spent fuel pool risk assessments
that are included in their outage plant and several
licensees had formal classroom training and similar training
prior to refueling.
Also, a very important point to us was to get
information to the operator that he could easily read. A
lot of licensees had good graphs that you could quickly look
and determine time to boil.
Several had very effective programs for analyzing
their problems, plus analyzing what's been happening in the
industry. One plant in particular had almost 11 years ago
-- over 10 years ago done an analysis on their own to
determine all the different pathways that you can lose
coolant in the spent fuel pool.
COMMISSIONER ROGERS: I have a question on the
simulator training. Is it possible to simulate total fuel
transfer from the reactor to the spent fuel racks on the
MR. JORDAN: Not to my knowledge.
COMMISSIONER ROGERS: What aspects of simulator
training then would be --
MR. IBARRA: Well, a lot of the aspects is being
able to provide backup power, being able to go through all
these procedures they would have to do the realignment of
the spent fuel pool and then allowing they still had higher
level operating procedures.
MR. IBARRA: We've reviewed the regulations and
this included reviewing the standard review plan, going
through 10 C.F.R. Part 50, Appendix A and identifying the
general design criteria. Also, we identified the applicable
Like I mentioned before, we did our own
engineering assessments. The first thing we looked at was
the electrical system and we wanted to determine what kind
of power supplies were being provided to the spent fuel pool
We determined that about 80 percent of them have
safety-related power going to the pump safety -- spent fuel
pumps, but these loads are shed when there is a loss of
outside power, so you have to manually reload them, manual
We wanted to determine what kind of parameters are
being monitored and where they're being monitored. We
determined that there was temperature level radiation,
coolant flow and leaked detection being monitored and they
were monitored either locally or in the control room.
When they are monitored in the control room, they
are usually grouped together to one enunicator window and
when that window alarms, then you have to send the control
room operator down the local panels to determine which of
the signals triggered this.
Now, some of the licensees do separate temperature
and levels from that grouping and then some of them even go
farther and put it to a meter or to an instrument. We feel,
though, it's very important for the operator to continuously
know where these temperature levels are. Some utilities do
not have that.
For radiation levels, here we compiled a bunch of
calculations from the licensees themselves to determine what
kind of levels, radiation levels we're going to see in the
spent fuel pool when the coolant decreases.
We found that at 1 foot, we have about 900 rem per
hour. This is one 1 foot above the fuel. We covered that
with about 8-1/2 feet, that drops down to about 20 milirem
Then one of the more important calculations was
the heat load calculations. We performed a calculation for
a pressurized reactor and a boiling water reactor. The time
to boil on a pressurized water reactor is about 12 hours;
for a boiling water reactor, it's about 7.4 hours.
This is just to the point that the coolant starts
to boil. You still have room on top of the fuel. To boil
to the top of the fuel, we calculated for a pressurized
reactor to be about 80 hours and about 50 hours for a
boiling water reactor. These calculations are consistent
for the industry.
MR. IBARRA: This is a slide that dramatically
shows what can happen when you offload sooner into the
outage. This was actual data we were able to compile from
Nine Mile Point, Unit 2.
In their outage Number 1, we see they had about
108 hours to boil, but this is when they offloaded in 23
days. Their last outage was Outage Number 4 and that 108
had dropped down to 8 hours. This was due to the fact that
now they offloaded in 5 days. This is very crucial because
all utilities are now going to shorter refueling outages.
COMMISSIONER ROGERS: Before you leave that slide,
where did these numbers come from.
MR. IBARRA: These numbers, we got them from Nine
COMMISSIONER ROGERS: I mean are they calculated
MR. IBARRA: They are actual numbers from their
MR. ROSSI: I'm sure they're calculated.
MR. IBARRA: They're calculated. I'm sorry, they
COMMISSIONER ROGERS: Then I think there's
something wrong with them because in the first place, I
think it's the wrong way to plot them. The interesting
number is the days to offload and hours to boil, not the
If you look at them, you can see that there is
something wrong here with this Outage 3 number or the Outage
4 because there's just too big a difference between the days
to offload and the hours to boil.
There ought to be a nice, smooth curve, and it
looks deceptively smooth by the way you plotted it, but if
you plot it up the hours to boil versus days to offload, you
see there's a big discontinuity. That number 29 doesn't fit
on there very well at all, so there's something odd about
MR. IBARRA: This data was from Nine Mile Point,
MR. JORDAN: But it's just a weaker curve --
COMMISSIONER ROGERS: I understand. Something is
MR. JORDAN: I'm agreeing with you.
COMMISSIONER ROGERS: With one of those numbers.
MR. JORDAN: It's a fundamental curve that we all
have in the textbook. We'll verify the number and get back
COMMISSIONER ROGERS: It looks like the 29 is the
one that's off.
CHAIRMAN JACKSON: You say the qualitative trend.
MR. IBARRA: What we wanted to point out there was
the fact that if you offload in 5 days, there's a tremendous
difference from offload in 23 days.
COMMISSIONER ROGERS: Yes, I think the point is an
important one, but the details of it, I suggest you go back
and look at again because there's something wrong.
MR. ROSSI: That we will do, we will recheck it.
MR. JORDAN: But the real point of this is that
the time is reducing at plants with outages.
COMMISSIONER ROGERS: Sure. Oh, absolutely.
MR. JORDAN: So it's a big pressure on the
COMMISSIONER ROGERS: The sensitivity to it is
because they are starting to work right down towards where
these times are very short, so you really want to be sure
MR. TAYLOR: Generally, that's happening as they
COMMISSIONER ROGERS: Qualitatively, it's right;
quantitatively, it doesn't look right to me.
CHAIRMAN JACKSON: You can use it at an outage
MR. HOLAHAN: I suspect there are other elements
to this. For example, for the fourth outage, the fuel from
the third outage is still in the pool. That's a nonlinear
effect and the operating history probably changes from cycle
to cycle. So these are probably actual experience. I think
if you were to use the same assumptions and do a
calculation, you'd get --
MR. JORDAN: Numbers of fuel assemblies that they
offload changes. We'll provide the data.
COMMISSIONER ROGERS: But I think it's worth
looking at little more closely because there may be
something in there particularly when you're going down to
the low end here.
MR. JORDAN: Yes.
CHAIRMAN JACKSON: It's almost as if there's
another axis which has to do with the load existing.
MR. ROSSI: There clearly would be another one.
It depends on how much fuel is there and how much is
offloaded in each refueling, so that is indeed the case.
CHAIRMAN JACKSON: So it exists in peak load is
the missing element.
MR. TAYLOR: The constant is usually the level of
the coolant and you know, how much it can absorb.
MR. IBARRA: Slide 14, please.
MR. IBARRA: We contacted with Idaho National
Engineering Lab to assist us in the risk assessment. INEL
looked at existing PRAs but they concentrated on a PRA that
was done by Pacific Northwest Laboratory on Susquehanna.
This PRA was funded by NRR.
This PRA actually was the starting point of our
assessment, so PNL had calculated near boiling frequencies.
Let me explain what near boiling would mean. It would be
the point before boiling where there's substantial number of
substantial vapor being generated.
INEL looked at the PNL work and they did some
corrections, both in methodology and in updating the data.
Some corrections in methodology was to account for common
cost failure and they also used a better human reliability
The updated data actually comes from us. As we
were doing our assessment, we were feeing them the
information, especially the frequency data on loss of
CHAIRMAN JACKSON: How does the concept of near
boiling frequency relate to some other measure of risk like
for damage frequency?
MR. IBARRA: Well, I'm about to get to that.
CHAIRMAN JACKSON: Okay.
MR. IBARRA: It's a lot easier to calculate near
boiling frequency than it is damage to the fuel. We did not
progress beyond the near boiling frequency, but we feel very
confident that to the magnitude of this. Let me point out,
this is just Susquehanna.
From the near boiling frequency, the risk of
damage to the fuel and the spent fuel pool due to spent fuel
pool accident is one to two orders of magnitude below the
core damage frequency due to reactor accident.
If we look at this from the previous work and the
current work, we see that the total near boiling frequency,
the risk increases by 2-1/2 times. Then the two major
components of the total near boiling frequency is loss of
offset power and inventory losses according to the INEL
The Loop increased a risk factor of 3, but the big
factor here is loss of inventory. We have a jump of about
twentyfold. Part of that is due to the updated data from
our operating experience to what we're feeding to INEL. The
methodology, we can account for common cause failure and
human reliability modeling.
MR. IBARRA: There was another important aspect
coming out of the Susquehanna PRA. PNL was able to do
calculations on the configuration before and after they did
some modifications. There were some modifications done by
Susquehanna on instrumentation procedures and training. The
calculation shows there is a risk reduction of a factor of 4
according to their improvements.
Another important factor coming out of the PRA, it
showed vulnerability of an operating unit from a defueled
unit. What we have in Susquehanna are two different units,
two different pools that can be connected and basically you
can have like one body of water.
If you have a situation where one unit is
operating and the other one is in an outage situation, and
that happens to boil, that could affect the operating unit.
That's what we mean by that bullet.
MR. IBARRA: Our findings and conclusions we have
divided this into likelihood and consequences, prevention
and response. The consequences of actual events have not
severe. That is according to our review of the upper end
One thing I must point out, all these events we
looked at were very slow developing events, so we didn't
have like rapid drain down. The primary cause has been
configuration control and this is mainly due to human error.
According to our near boiling frequency
calculations, the relative risk of fuel damage is low
compared to other reactor events. We find that the
likelihood and consequences are highly dependent on the
human and on the various plant designs.
We calculated the frequency of losing coolant that
is greater than 1 foot. It would be 1 per year, per reactor
year, for 100 reactor years. The frequency of loss of
coolant down that results in an increase greater than 20
degrees would be two to three occurrences in 1,000 reactor
CHAIRMAN JACKSON: If you went back to Slide 6
where you looked at the loss of coolant inventory event and
you pointed out that these actual events were not ones where
you had rapid loss of inventory, which of these event types
would be the ones -- did you look at which ones are the ones
that would have the highest probability of causing what you
would call a rapid loss of coolant?
MR. IBARRA: Well, none has occurred, but we have
-- when we're talking about cavity seals, that can be
dramatic loss of coolant right away. We haven't had any of
those, but that would be a very drastic event.
CHAIRMAN JACKSON: The reason one asks is because
in principle, what one wants to look at is where the
greatest vulnerabilities are.
MR. TAYLOR: I think that is where it is. We've
had some of those leak significantly in some of these
events. If that goes completely, you lose water fairly
CHAIRMAN JACKSON: Are those seals subject to any
kind of catastrophic failure over time or you don't know?
MR. TAYLOR: I guess I can't answer that. Some of
them are inflatable.
MR. HOLAHAN: The worst event in this category, I
think it is also referred to in the report, was a problem at
Hadden Neck in 1984. I remember sitting in Mr. Jordan's
office the next day writing a bulletin to have all the
plants rereview their seals for the potential for gross
failures. I think there have been a number of improvements
back in that time frame.
MR. HOLAHAN: That pretty well drained the
transfer canal. Unfortunately, there was fuel in it.
MR. IBARRA: 200,000 gallons.
MR. HOLAHAN: Yes.
CHAIRMAN JACKSON: So, in some sense, then on
Slide 16 when you talk about frequency of coolant loss, then
that is based on your actual -- the database from the study
that you used, is that correct?
MR. IBARRA: Operational type.
MR. JORDAN: Yes.
MR. ROSSI: There is one other thing I'm not sure
has been pointed out and that is that the geometry of the
spent fuel pools a lot of times is such so that you can
drain down to a certain point where there is a Weir or
something of that sort that makes it more difficult to boil
down before that, so in order to get down below the top of
the fuel, you have to drain down to this Weir and then from
then on, you would boil-down. So it's not like -- many of
them -- I don't know that I can say every one -- but many of
them are such that for things like gates, cavity seals and
that kind of stuff, you wouldn't just go right down --
MR. TAYLOR: Yes, you would still have some water
MR. ROSSI: You'd have water and then you'd have
MR. TAYLOR: There's a ledge.
MR. ROSSI: Now, there are situations that have to
be looked at in terms of siphoning-down below the Weir
because if the antisiphoning device does not work, then
there's a mechanism for perhaps going down.
Again, as Jose pointed out, all of these things
are quite plant specific, exactly what exists at each plant.
Different plants have different things.
CHAIRMAN JACKSON: I understand. So I guess then
the follow-on question would be, as you point out, these are
very much plant-specific. What did you come away with in
terms of the understanding then by the plant operators, the
licensees, of where their greatest vulnerabilities are?
You talked about some good practices, but the
question is how uniform is the knowledge or appreciation for
the given plants of where their greatest vulnerability is?
MR. IBARRA: Well, we feel that there needs to be
-- an issue or an awareness of what can happen. In our
trips, we did find some licensees had a good understanding
and awareness of the configuration and what can happen, but
we still feel that industrywide, that needs to occur. You
need training and procedures.
MR. ROSSI: There were differences from plant to
plant, I believe, in terms of the knowledge of the actual
people that were dealing -- would have to deal with the
events. I believe you went to at least one site where they
had done a lot of good engineering work to determine how
long it might take to boil and so forth, but some of that
information had not been conveyed on to the operators that
would be the ones responsible for doing it, which is why, as
Jose will go on, training and procedures can be very, very
important because just making people aware of the kinds of
things that can happen and the things they already have
within the plant to deal with those things can perhaps do a
CHAIRMAN JACKSON: Are any of the events that you
discuss on page six a surprise? Did anything jump out at
MR. IBARRA: Well, what jumped out at us, because
it's interesting when you compile the data and look at it,
there were some things that jumped out like the number of
tech-spec violations. Licensees were still moving heavy
loads over fuel, so there's a potential for a drop and
damaging the fuel. But some of them know, there were not
surprises, and some were surprises.
CHAIRMAN JACKSON: Thank you.
MR. IBARRA: Slide 17.
MR. IBARRA: For prevention, we believe
configuration control improvement can prevent or mitigate
spent fuel pool accidents. We believe evaluations may be
needed at some multiunit sites for potential spent fuel pool
boiling effects and safe shutdown. This is the Susquehanna
For a response, we believe there has to be
attention paid to time to boil now that the licensees are
doing shorter outages. We believe improved procedures and
training may be needed, and improvement to instrumentation
and power supplies.
In particular, instrumentation, we believe that
the operators need to know at all times where the level and
temperature are and for power supplies, as I mentioned
before, 20 percent would not have reliable power supplies.
MR. IBARRA: The followup to our assessment and
what we're going to be doing, we do plan to put an
information notice out to the industry to let them know what
the findings were from our assessment that is ongoing right
We will be making our study into a NUREG. I think
this lends a little bit of visibility to the study. In
addition, we're going to be making the INEL risk assessment
a NUREG. In the international community, we will be
submitting a report to the instant reporting system, so the
International Committee knows what we're doing in our
assessment. We will continue to work with NRR in
implementing whatever we come up with in our report.
CHAIRMAN JACKSON: Thank you. Let me ask you two
quick questions. You mentioned the surprise at the number
of tech-spec violations and there is this whole issue about
differences between actual fuel handling practices and say
Did you find any correlation between the plants
that actually had the spent fuel pool events or precursors
and those that had the tech-spec violations or these
nonconformances relative to the FSAR?
MR. IBARRA: No, we didn't follow that.
CHAIRMAN JACKSON: You didn't specifically look at
MR. IBARRA: No.
CHAIRMAN JACKSON: Okay. Let me ask you this
punitive question. I understand that to compensate for
degraded boron flex, that some PWR licensees are considering
amendments to technical specifications for spent fuel pool
shutdown reactivity margins that would allow a credit for
If we were to then grant these amendments, how
would that complicate a licensee's recovery from an
inventory loss in a spent fuel pool?
Then, sort of the follow-on question is, would
existing borated water sources be sufficient to compensate
for worse case loss of spent fuel pool inventory under this
scenario where we would have allowed amendments to take
credit for soluble boron relative to reactivity margins?
MR. HOLAHAN: I could give that a try.
MR. IBARRA: Well, we didn't look at any
reactivity, so our report did not cover that at all.
CHAIRMAN JACKSON: This is a favorite kind of
question of mine because it's a linked kind of thing.
MR. HOLAHAN: Yes. The staff has or was the
recipient of a topical report from Westinghouse proposing a
generic approach to taking some credit for soluble boron in
spent fuel pools. That report was recently reviewed with
the CRGR because it was really a new staff position. It
would be a change in a standard we have established for many
We've made some modifications to the Westinghouse
approach, but the staff still is inclined to accept some
credit for soluble boron and the way we've done that is to
assure that -- we've reduced our standard in the effect that
says previously it was necessary to show that the fuel
remained 5 percent subcritical with no credit for boron.
Now what we're saying is, we would allow
sufficient credit for boron, so that the reactor only needed
to remain subcritical -- not 5 percent subcritical, but
subcritical with a high degree of confidence -- we're asking
for a 95/95 type of statistical analysis to show that if the
boron were not in the pool or, for example, what's of most
concern is if you were responding to an event by putting
fire water or service water or some other water into the
spent fuel pool, you could lose boron to the point of
approaching but never going critical, so it would give some
credit but never so much credit that it was necessary to
keep the subcritical.
CHAIRMAN JACKSON: I guess the question I'm asking
in evaluating this proposal, was it explicitly evaluated
relative to the kinds of scenarios we're talking here,
particularly the rapid loss of coolant?
MR. HOLAHAN: Yes, very much so. We looked at the
boiling in the pool and our first conclusion was that boron
is not loss if you boil the water down in the pool. It
tends to stay --
CHAIRMAN JACKSON: You're talking about the
MR. HOLAHAN: The catastrophic draindown is the
one of concern because probably something like one-half to
two-thirds of the water could be replaced with unborated
water and we found even if all the water was replaced with
unborated water, the fuel in the pool would not go critical,
had a very high confidence.
So we felt that we were reducing our requirement
but still maintaining a very safe level.
CHAIRMAN JACKSON: Is that something that has a
time factor associated with it, the amount of soluble boron
is a function of time relative to say the further
degradation of the boroflex?
MR. HOLAHAN: It would allow some credit for the
boroflex that's existing in the spent fuel pools. I think
it wouldn't change that. The licensee would still take
credit for the amount of boroflex that they could show was
CHAIRMAN JACKSON: Well, you understand what
happens to boroflex?
MR. HOLAHAN: Yes.
CHAIRMAN JACKSON: It's throughout the pool as a
suspension or something like that, if it breaks off or
MR. HOLAHAN: Yes, and it can -- there have been
such problems. There's been some loss --
CHAIRMAN JACKSON: So if the Commission gets some
anonymous letter, we can have confidence that you guys have
evaluated all of these scenarios? That's what I'm trying to
MR. HOLAHAN: Yes.
CHAIRMAN JACKSON: Okay. This is November the --
MR. HOLAHAN: I believe we're being recorded.
MR. JORDAN: I would add that the CRGR review
process did, in fact, bring this experience from this work
into that meeting, so it was part of the basis for bringing
back some of the conservatism into that review.
CHAIRMAN JACKSON: Okay. Thank you. Mr. Rogers.
MR. JORDAN: I would add that the CRGR review
process did in fact bring this experience from this
CHAIRMAN JACKSON: Into that --
MR. JORDAN: -- into that meeting.
CHAIRMAN JACKSON: Okay.
MR. JORDAN: And so it was part of the basis for
bringing back some of the conservatism into that review.
CHAIRMAN JACKSON: Okay, thank you. Commissioner
COMMISSIONER ROGERS: Just you say that went to
MR. JORDAN: Yes.
COMMISSIONER ROGERS: So that is one good reason
to have CRGR, isn't it?
MR. JORDAN: Yes.
COMMISSIONER ROGERS: Do you expect anything
beyond recommendations to come out of this? Do you expect
any new requirements to emerge from this study?
MR. JORDAN: No.
COMMISSIONER ROGERS: No specific requirements?
MR. JORDAN: We are not recommending any specific
COMMISSIONER ROGERS: When you say attention to
timed boil you are not thinking about setting some time
limits or things of that sort?
MR. HOLAHAN: What I would add is I think this
study supports the conclusions in NRR's August or July study
and August presentation to the Commission, so to the extent
that we said we were going to go ahead with the ten general
areas to study for potential backfits, I think this is
COMMISSIONER ROGERS: Consistent with that.
MR. HOLAHAN: Right -- and I think it adds
emphasis in some areas to focus our review to some extent.
CHAIRMAN JACKSON: That's good. Commissioner
COMMISSIONER DICUS: No.
CHAIRMAN JACKSON: Commissioner Diaz?
COMMISSIONER DIAZ: Yes, I have a couple of
I think this is a very good start on this area,
which is of concern, but is the event frequency analysis you
did that was based on 12 years' experience, is an effort
made to correlate the frequency of the events with plant age
or plant configuration or any other possible indicator that
you are actually going to have a degraded condition? Are
there correlations available?
MR. IBARRA: We didn't attempt to do that.
COMMISSIONER DIAZ: That brings me to the next
question then. How do we know that there are not some
plants out there which are a lot less safer than what this
seems to indicate, that there's some plants that might have,
you know, some plant configurations, age, or other
particular indicators that might put them in a category in
which they are, quote, "less safe," than what the report
seems to indicate?
MR. JORDAN: I guess maybe I would comment on
It is true that the risk or the issues are
dependent on the design very largely and that some of the
designs are less forgiving than others, and so that is a
reason for causing the utilities to do the review against
the experience and see where their design may be weaker.
For instance, if they have no alarms and
instrumentation and only one train and you have to rely on
repairs then they are in much worse shape than a utility
that has two trains and alarms or if there is a greater
susceptibility to a seal failure, for instance, so they are
very, very design dependent and the designs are so
COMMISSIONER DIAZ: I know they are design
dependent. Shouldn't then we make an effort in really
determining which ones are really more vulnerable because
there might be some plans that have higher vulnerability
because of the design configuration?
MR. JORDAN: The sequence I hope would be that we
communicate to the utility. The utilities then are
responsible for doing the review against the experience and
then we follow up through our inspection programs to see
that in fact utilities are using that experience.
MR. HOLAHAN: I think you should also be aware
that the earlier report done in July of this year was based
on, I would say, a much broader scope but less depth and
detail when compared to the AEOD study, but there was a
survey done of all the plants to look at the design features
with respect to spent fuel pools, anti-siphon devices,
whether they were seismically qualified, how many pumps were
available, size of the pool.
There was a considerable amount of information
collected for every plant and the project managers and the
resident inspectors put that information into a survey-type
vehicle, and then the technical staff looked over that to
identify potential outliers, plants which had an unusual
features that might lead to a concern, and that is what led
to the ten categories of -- that we want to follow up on, so
there is an ongoing program to identify plants with
COMMISSIONER DIAZ: Based on that, if, you know,
since I think we require all spent fuel pools to have
redundant cooling systems, and based on the fact that human
error or lack of, you know, instrumentation information
seems to be major causes, would that justify at least
indicating that plants should operate their instrumentation
to prevent early notification of degradation of the systems?
MR. HOLAHAN: I think that is a fair statement.
We did identify both temperature and level
instrumentation as potential areas for improvement on a
number of plants.
Whether when we look at those plants in detail we
can justify a specific change or not remains to be seen and
I think also what the AEOD study does is it clarifies the
issue a little bit in the context that if there is
information that there is an ongoing event it looks like
these events are not so difficult to recover from, in most
cases, and so when we go through these issues and look at
the plants we will be focusing on instrumentation and
recovery type actions.
COMMISSIONER DIAZ: Except that there are no
catastrophic issues in here and of course there could be,
you know, from an earthquake -- in which case the
probability to rapidly recover or initiate another system
action will become imperative.
MR. HOLAHAN: Yes. Well, we do look at the
seismic capability of the pools, but I think probably that
the most important contribution from the AEOD study in my
view is focusing on the cavity seals.
I am not prepared to endorse the two times ten to
the minus five number, but it is clear that when you think
about that event the rapidity of the event and the
difficulty of recovering in the high radiation environment,
et cetera, makes it an important event to follow up on, so
we'll pick that up as part of our plant-specific reviews.
COMMISSIONER DIAZ: All right.
MR. ROSSI: But that is one that we have sent out,
as you indicated before, a bulletin at one point in time, to
have it looked at --
COMMISSIONER DIAZ: Yes.
MR. ROSSI: -- across the industry, so --
MR. HOLAHAN: Well, we have been talking a little
bit about maybe going back and making sure about the
effectiveness of the bulletin.
It's been more than 10 years.
COMMISSIONER DIAZ: Yes.
CHAIRMAN JACKSON: Also I think that there is
another piece that I heard you talk about, and that does
have to do with the human performance aspect of this, you
know, what people do.
If you are moving heavy loads over the spent fuel
pool, that's people doing that. That doesn't have to do
with degraded cavity seals. That's people lifting heavy
loads, so we can't lose sight of that.
COMMISSIONER McGAFFIGAN: If I could just ask one
question, as I understand it there are certain plants --
Oconee is one -- where the spent fuel inventory is used in
certain event scenarios. I guess you pull down the
inventory in the spent fuel pond to deal with something
worse happening somewhere else.
How many cases are there like that?
MR. HOLAHAN: I believe all of the big power
plants, Oconee, Maguire, and Catawba, have various
arrangements in which they have put what is put a safe
shutdown facility -- that is, if a plant has a complete loss
of offsite power with the diesels not working for a station
blackout, and I think they also use it to cover fire
protection type concerns that could broadly affect the
plant, they have a separate facility which provides water to
the steam generators for decay heat removal and it also
provides injection of water for the reactor coolant pump
seals, and because they want clean purified water for that
reason, they draw water off the spent fuel pool.
That is generally something like maybe 30 gallons
COMMISSIONER McGAFFIGAN: Okay.
MR. HOLAHAN: So that is not, if it is working
properly, that is not a big concern, although we will look
at the potential for a pipe break or something that would
inadvertently drain water out of the pool, but we have
identified those plants for some follow-up.
COMMISSIONER McGAFFIGAN: And the other event that
was called to my attention was Dresden I some years back, a
Is there a problem with the shutdown condition,
you know, that we have to be wary of?
MR. HOLAHAN: Yes. I'll have to do the Dresden
one from memory but my recollection is that the Dresden I
facility was -- I think it would be fair to say -- ignored
by Commonwealth Edison for some period of time, and I
believe they had some commitment to heating of the system,
which had fallen by the wayside at some point, and they had
an event with freezing in the pipes, and what we realized --
it didn't actually occur, but we realized that there were
pipes which could freeze and for which, if they were to
fail, would drain water from the spent fuel pool.
I believe we issued a bulletin to the
decommissioned plants to address two things -- to address
the configuration, to look for areas in which because these
are generally very old plants not meeting sort of current
standards, they might have a pipe that could drain in the
spent fuel pool, so look at both the configurations and also
look into the concern that there may be an important piece
of the facility that is not getting our proper attention.
So I believe all those plants got a bulletin,
responded, and I believe all of them had been inspected a
year or two ago.
COMMISSIONER McGAFFIGAN: Thank you.
CHAIRMAN JACKSON: Commissioner Diaz?
COMMISSIONER DIAZ: Yes, I guess I have one more
comment on the issue that since there's so significant a
difference between plants and although the risk is much
lower than a reactor accident, we all agree with that and it
should be and it is and that's why they don't have a
containment or a way of injecting pressurized water into the
systems. Still it seems like, you know, we should make a
further attempt to determine whether there are unacceptable
risks to the public or the workers from, you know, accidents
in which those plants don't have the appropriate
configuration or the appropriate detection system, and I
believe that might be something that the Staff could look
CHAIRMAN JACKSON: Any other comments?
CHAIRMAN JACKSON: Well, I would like to thank the
Staff for this very informative briefing. It was very good.
Today you presented a great deal of information to us on
spent fuel pool operating events and their implications in
terms of risk.
As we have been discussing, we understand that you
will take the findings and conclusion of this in your other
earlier reviews to determine what additional action may be
I think as you see as we formulate future actions
in this area, we do need to consider, as Commissioner Diaz
has said, the wide variations in spent fuel pool
configurations in specific circumstances against our limited
database of spent fuel pool events, and so I think we have
to guard against, on the one hand, imposing industry-wide
changes that, though beneficial at one facility result in
only a marginal improvement in risk at another, or vice
versa, do not capture the vulnerabilities and risks on a
So unless my fellow Commissioners have any further
comments, I think we are adjourned.
[Whereupon, at 3:15 p.m., the briefing was