ML071510338

Draft RAI Questions for Discussion in a Telecon

ML071510338
Person / Time
Site:	Cook
Issue date:	05/31/2007
From:	Tam P NRC/NRR/ADRO/DORL/LPLIII-1
To:	Scarpello M, Simpson S, Steinmetz H Indiana Michigan Power Co
References
TAC MD5297
Download: ML071510338 (3)

Text

From:

Peter Tam To:

Scarpello, Michael; Simpson, Sue; Steinmetz, Keith Date:

05/31/2007 11:42:41 AM

Subject:

D.C. Cook Unit 1 - Draft RAI re. SBLOCA Reanalysis (TAC MD5297)

Keith:

We are reviewing your 3/29/07 submittal (Accession No. ML071000431) on this subject. Our reviewer Leonard Ward has written the following draft RAI questions that we would like to discuss with you in a conference call. Please contact me to set up the call.

1.

Table 1 on page 9 identifies the calorimetric uncertainty as 1.0034%. However, the text on page 3 quotes the full power analysis value of 100.34%. Please explain the discrepancy.

Also, please also provide the reference for the calorimetric uncertainty determination.

2.

Please provide the results of the severed ECC injection line case that utilizes the degraded ECC injection into the intact lines.

3.

Does the reduced HPSI impact the timing for precipitation and the switch time to simultaneous injection? Please explain. Please also provide the boric acid vs. time for the limiting large-and smal-break LOCA and identify the time to switch to simultaneous injection.

4.

The NOTRUMP version employed in the evaluation utilized the COSI steam condensation model. While the staff has previously approved this model, there have been no integral experiments validating this modification. Please provide the results of the COSI condensation model to integral smal-break LOCA experiments with long-term core uncovery.

5.

Please explain the cause of the abrupt change in the core two-phase level which suddenly remains constant from 800 to 1000 seconds in Fig. 6, for the 3.25-inch break. Since this is a boil-off process, and the broken loop seal has cleared earlier, the abrupt termination of the level decrease during the boil-down and uncovery period is not understood. Please provide the core inlet and outlet mass flow rates and the core liquid mass vs time for this break.

6.

The PCT turns over at about 1500 seconds for the 3.25-inch break in Fig. 14, at which time the heat transfer coefficient peaks during steam cooling shown in Fig. 15. At 1800 - 2000 seconds the heat transfer coefficient drops below the value that produced the earlier heatup from 800 to 1500 seconds, yet the clad temperature continues to decrease. Please explain.

7.

Please explain the termination in the core two-phase level for the 3-inch break from 1000 to 1300 seconds in Fig. 28 for the 3-inch break. The 2.5-inch break has a similar behavior from 1200 to 1500 seconds in Fig. 25 as does the 2.5-inch break from 1100 to 1600 seconds in Fig.

22. Please explain the abrupt deviation from the boil-down and initial rapid loss of level behavior for these breaks. The froth-up behavior for the 2.5-inch break terminates and cools the hot spot during this period and does not appear physical. Please also provide the liquid mass and core inlet flow rates vs. time for these breaks.

8.

The hot spot begins heatup at about 100 seconds in Fig. 29, when the level drops to about 21 feet. The clad heat-up is terminated at 200 seconds when the level increases from the minimum of 15 to 16 feet. Why does the PCT turn around at level of 16 feet when heat up of the hot spot begins at a level of 21 feet or less during the earlier portion of the event? How is the heat transfer at the hot spot during steam cooling calculated? Please provide the reference and

briefly describe the correlations used to determine the heat transfer at the hot spot.

9.

For each break size, please identify the timing for and the location of the loop seals that clear of liquid. Please provide plots of the liquid levels in the vertical sections of the loop seals.

10.

Please explain why the hot spot location at 9.5 feet does not produce the highest PCT and rupture location, since Table 5 identifies the PCT elevation as 11.75 ft, which has a local linear power level of about 6 kw/ft versus 12.5 kw/ft at 9.5 ft.

11.

Upon drainage of the RWST, are HPSI pump flows also interrupted for 5 minutes?

What is the impact of the 5 minute RHR delay on the 8.75-inch break? What is the impact on the limiting large-break LOCA? Please explain.

12.

Were time step studies performed on the limiting small break? Please explain and provide the results of the time step study.

13.

Were any modifications made to the ECCS licensing models subsequent to the latest NRC approval and applied to the D.C. Cook SBLOCA analyses? Please identify any changes.

This e-mail aims solely to prepare you and others for the proposed conference call. This e-mail is not a formal RAI, unless you accept it as such later. This e-mail does not convey a formal NRC staff position.

Peter S. Tam, Senior Project Manager Plant Licensing Branch III-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation e-mail: pst@nrc.gov Tel.: 301-415-1451 CC:

Ward, Leonard Mail Envelope Properties (465EECF1.C99 : 12 : 35330)

Subject:

D.C. Cook Unit 1 - Draft RAI re. SBLOCA Reanalysis (TAC MD5297)

Creation Date 05/31/2007 11:42:41 AM From:

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PST@nrc.gov Recipients Action Date & Time aep.com Transferred 05/31/2007 11:42:49 AM kasteinmetz (Keith Steinmetz) mkscarpello (Michael Scarpello) sdsimpson (Sue Simpson) nrc.gov TWGWPO04.HQGWDO01 Delivered 05/31/2007 11:42:43

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