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@aep.com Sent by: pwrrm@retaqs.com To pwrrm@retaqs.com cc 09/30/2009 09:07 AM Subject [Pwrrm] RCS time to boil

Please respond to PWR Reactivity Management <pwrrm@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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