David,
I can respond to your second question.
BVPS-1 & 2 have RCS loop stop valves so we do not need to drain down below
the reactor pressure vessel flange by more than one foot (except when the
fuel is removed from the reactor vessel).
The time to boiling volumes we credit are in accordance with NUREG-1269,
“Loss of Residual Heat Removal System”: 100% of core volume, 100% of upper
plenum volume, 100% of reactor head volume (as applicable), 10% of vessel
downcomer volume (above the lower core plate), a portion of the hot leg
volumes (to the closed loop stop valves), and the specific heat capacity of
the core fuel assemblies. No other credit is given in the draindown
configuration and the local boiling temperature of 210.6 degrees F is
applied.
When the PRZR is filled to the operating minimum of at least 22% (and no
other RCS vent exists), then the PRZR surge line volume and 22% level in
the PRZR is credited in the time to boiling. Also the static head with
volume in the PRZR (> 22%) results in an increased core boiling temperature
of approximately 238 degrees F.
We are hoping to do some detailed analysis using MAAP5, but that is still
in the future.
Michael Unfried
BVPS Staff Nuclear Engineer
724-682-5993
Anthony R
Burger/FirstEner
gy To
Michael
10/07/2009 08:21 Unfried/FirstEnergy@FirstEnergy
AM cc
Subject
Fw: [Pwrrm] RCS time to boil
Mike,
Jay deferred to you. See email below.
AR
----- Forwarded by Anthony R Burger/FirstEnergy on 10/07/2009 08:21 AM
-----
James D
Lutz/FirstEnergy
To
10/07/2009 07:25 Anthony R
AM Burger/FirstEnergy@FirstEnergy
cc
Subject
Re: Fw: [Pwrrm] RCS time to boil
(Document link: Anthony R Burger)
Unfried is your best bet.
Anthony R
Burger/FirstEner
gy To
James D Lutz/FirstEnergy@FirstEnergy
10/06/2009 02:49 cc
PM
Subject
Fw: [Pwrrm] RCS time to boil
Jay,
I know your probably busy, but I received the following request from DC
Cook regarding time to boil. I've got the answer for the first part on
decay heat, however could you provide information on the second item - sink
term? Or would Mike Unfried be the person?
AR
----- Forwarded by Anthony R Burger/FirstEnergy on 10/06/2009 02:46 PM
-----
ddgoff(a)aep.com
Sent by:
pwrrm(a)retaqs.com To
pwrrm(a)retaqs.com
cc
09/30/2009 09:07
AM Subject
[Pwrrm] RCS time to boil
Please respond to
PWR Reactivity
Management
<pwrrm(a)retaqs.com
>
I'd like to know how others are handling decay heat projections. Our Ops
procedures here at Cook were recently changed to link containment closure
time requirements to RCS time-to-boil projections. Our operators are
asking for more realistic, less conservative (.i.e., longer) times.
First, the source term. We are still using the old Branch Technical
Position paper ASB 9-2 that was part of earlier NUREG-0800 revisions. The
latest NUREG-0800 now references ANSI/ANS-5.1-2005 for calculating decay
heat. We would start using that; however, we cannot find a defensible
value for R ("atoms of U-239 produced per second per fission per second
evaluated for the reactor composition at the time of shutdown; the value of
R shall be supplied and justified by the user") for the heavy element
contribution in section 4. The examples in the appendices use R=0.6. What
are you using for decay heat calcs?
Second, the sink term. We have no heat transfer modeling of our vessel and
RCS. Rather, we make some very conservative assumptions about vessel
internal volumes and then credit only the water volume within the vessel
for cases when the cavity is not flooded. Now, we know that there is metal
and air and concrete as well as natural circulation within the RCS that
will act as the decay heat sink. We just can't model all that. How do you
model the decay heat sink for time-to-boil calcs?
Thanks.
David Goff
Reactor Engineer
Donald C. Cook Nuclear Plant
269-465-5901 x1465
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