NSD-NRC-98-5510, Forwards W Responses to FSER Open Items on AP600.Summary of Encl Responses Is Provided in Table 1,including FSER Open Item Number,Associated Oits Number & Status to Be Designated in W Status Column

Forwards W Responses to FSER Open Items on AP600.Summary of Encl Responses Is Provided in Table 1,including FSER Open Item Number,Associated Oits Number & Status to Be Designated in W Status Column

ML20198G763
Person / Time
Site:	05200003
Issue date:	01/06/1998
From:	Mcintyre B WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:	Quay T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NSD-NRC-98-5510, NUDOCS 9801130110
Download: ML20198G763 (6)

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- xy .l Westinghouse Energy Systems Ba355 Pittsburgh Pennsylvarda 15230 0355

' Electric Corporation _

. DCP/NRCl205 NSD-NRC-98-5510 Docket No.: 52-003 .,

January 6,1998 Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555 ATfENTION: T. R. QUAY

'SullJECT: AP600 RESPONSE TO FSER OPEN ITEMS

Dear Mr. Quay:

Enclosed with this letter are the Westinghouse responses to FSER open items on the AP600. A summary of the enclosed responses is provided in Table 1. Included in the table is the FSER open item number, the associated OITS number, and the status to be designated in the Westinghouse status co! imn of OITS.

The NRC should review the enclosure and inform Westinghouse of the status to be designated in the "NRC Status" column of OITS.

Please contact me on (412) 374-4334 if you have any questions cor.cerning this transmittal, w%

11rian A. McIntyre, Manager Advanced Plant Safety and Licensing jml ( ,

Enclosure ec: W. C. Iluffman. NRC (Enclosure) '

. T. J. Kenyon, NRC (Enclosure)

J. M. Sebrosky, NRC (Enelosure)

D. C. Scaletti, NRC (Enclosure)

N. J. Liparuto, Westinghouse (w/o Enclosure) 900113o11o 9e0106  :^~

PDR ADOCK 05200003 E PDR .

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NSD NRC-98 5510 - January 6,1998 Table 1 List of FSER Open Items Included in Letter DCP/NRCl205 FSER Open item OITS Number Westinghouse status in OITS 410.400F - 6427 Action N 720.45SF 6484 Action N-720.459F 6485 Confirm W l

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Enclosure to Westinghouse .

Letter DCP/NRCl205 January 6,1998 a

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410.400F (OITS #6427)

Where restraints are used to ensure protecticon of safety related equipment from the dynamic effects of pipe failure, Westinghouse should provide justification why separation and protective structures were not used.' (OI 3416) 1 Responses :

To the maximum extent practical, safety related equipment is separated from the location of the postulated pipe b*ca':s. When potential interactior between the pipe break and essential equipment was possible, pipe whip restraints were used (see SSAR table 3.6-3). Protective structures, in the form

- of barriers or shields, are used when neither separation nor pipe whip restraints are practical.= ne design philosophy of separating safety related systems and components from pipe break hazards

- minimizes the need for pipe whip restraints. De pipe rupture hazard analysis identifies equipment that may need to be protected by the use of whip restraints or jet shields. These results are included in Table 3.6-3. The specific locations of barriers or shields is not identifiM as part of the certified

' design.

SSAR Revision: NONE 1

UD 410.400 1

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NRC TSER OPEN ITEM Question: 720.458F (OITS #6484)

WEC needs to identify the operating mode assumed for each of the five plant damage states or accident c' u. t used in the level 2 analysis.

Response

As a result of updating the shutdown PRA to incorporate the containment sump recirculation function,in response to open item 720.431F. one additional accident class (LP-3BL) is identified for events at shutdown. Therefore, the six accident classes for events at shutdown, their descriptions and associated technical specification operating modes are as follows:

Accident Operating Class Description Mode (s)

LP-l A No RCS depressurization 4, 5 LP-3D Partial RCS depressurization . 5 LP 3BR Full RCS depressurization, core damage caused by insufficient or late 4, 5 core reflood LP 3bE Full RCS depressurization, failure of gravity injection 4, 5 LP 3BL Full RCS depressurization, failure of long-term core cooling 5 LPCBP Core damage initiated by containment bypass 4, 5 PRA Revisions: None.

720. m W westinghouse 1

6 NRC.FSER OPEN ITEM y

1 Question: 720.459F (OITS #6485)

In the level 2 analysis provided by letter dated September 17,1997. WEC indicates that the split fractions assigned to the phenomena nodes of the shutdown CETs were based on the scalar values from the ht-po ver CETs for the corresponding accident classes. WEC needs to demonstrate that the at-power splot fractions are appropriate for shutdown conditions, and are not impacted by differences in plant conditions, system alignments, or system / component availability allowed by technical specifications (TSs) at shutdown.

4

Response

The at power phenomenological probability values are conservative with respect to values expected at shutdown.

Decay heat rates for shutdown events are substantially lower than at-power events. For in-vessel retention of molten core debris via caternal cooling of the reactor vessel, the lower decay heat rate translates to a lower volumetric power density in the lower head, ne heat fluxes predicted for the at-power scenarios bound the heat fluxes expected at shutdown and therefore the results are conservative.

For hydrogen generation and combustion phenomena, containment failure is dominated by early detonation. De release location and the hydrogen generation rate are the important phenomena that affect detonation. Shutdown -

accidents are dominated by reduced inventory cases which fail core cooling. 71.e release location is to the steam generator compartments, which participate in containment mixiag. Hydrogen release to the dead-ended compartments is limited so at power detonation probability bounds with respect to shutdown. Hydrogen generation rates are also reasonably predicted. He core heat up rate at shutdown is slower than at-power due to the lower decay heat, but once cladding oxidation begins, the heat of reaction dominates the process and the progression is sin,ilar, if the oxidation reaction is not steam limited, the hydrogen generation rate is similar to the at power rates, if the reaction is steam limited, the at power generation rates bound the shutdown rates. Herefore, the at-power phenomenological probability estimates are conservative for the shutdown analysis.

PRA Revisions: PRA section 54B.3 of Attachment 54B willinclude the above two paragraphs under a subsection discussing the phenomena node failure probabilities.

720.459F 3, Westinghouse