ML11105A168

OL - Component Cooling System RAI 9.2-CSS-6

ML11105A168
Person / Time
Site:	Watts Bar
Issue date:	03/11/2011
From:	Office of Nuclear Reactor Regulation
To:	Division of Operating Reactor Licensing
References
Download: ML11105A168 (4)

Text

WBN2Public Resource From: Lyon, Fred Sent: Friday, March 11, 2011 12:19 PM To: garent@tva.gov; wdcrouch@tva.gov Cc: Poole, Justin; Milano, Patrick; Raghavan, Rags

Subject:

Component Cooling System RAI 9.2-CSS-6 Attachments: RAI 9.2-CSS-6.docx Attached fyi is a request for information regarding the component cooling system. Please provide a response by letter within 15 days.

Thanks, Fred Lyon (301-415-2296) 1

Hearing Identifier: Watts_Bar_2_Operating_LA_Public Email Number: 329 Mail Envelope Properties (A56E37EC1CBC8045910287CEF5E7AE6CA8DB922C7A)

Subject:

Component Cooling System RAI 9.2-CSS-6 Sent Date: 3/11/2011 12:19:22 PM Received Date: 3/11/2011 12:19:24 PM From: Lyon, Fred Created By: Fred.Lyon@nrc.gov Recipients:

"Poole, Justin" <Justin.Poole@nrc.gov>

Tracking Status: None "Milano, Patrick" <Patrick.Milano@nrc.gov>

Tracking Status: None "Raghavan, Rags" <Rags.Raghavan@nrc.gov>

Tracking Status: None "garent@tva.gov" <garent@tva.gov>

Tracking Status: None "wdcrouch@tva.gov" <wdcrouch@tva.gov>

Tracking Status: None Post Office: HQCLSTR01.nrc.gov Files Size Date & Time MESSAGE 177 3/11/2011 12:19:24 PM RAI 9.2-CSS-6.docx 20851 Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

Recipients Received:

REQUEST FOR ADDITIONAL INFORMATION REGARDING FSAR SECTION 9.2.2, COMPONENT COOLING SYSTEM (CCS)

TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 2 DOCKET NO. 50-391 By letter to the U.S. Nuclear Regulatory Commission (NRC) dated March 4, 2009 (ADAMS Accession No. ML090700378), the Tennessee Valley Authority (TVA) submitted an update to its application for a facility operating license for Watts Bar Nuclear Plant (WBN), Unit 2. The NRC staffs review of the information provided by TVA, as supplemented by amendments to the WBN Unit 2 Final Safety Analysis Report (FSAR), and TVAs responses to the staffs requests for additional information, is in progress. The NRC staff requests the following additional information to complete its review of the proposed application.

Request for Additional Information (RAI)

RAI 9.2-CCS-6:

In its letter dated December 10, 2010, TVA provided Enclosure 3, Summary Heat Load and Flow Tables for RAI 9.2-CCS-4. These tables show component cooling system (CCS) heat loads and flows for (1) loss of offsite power (LOOP) with loss of Train B, and (2) LOOP with loss of Train A (1A and 2A). It appears that loss of Train A is the worst case single failure, because in the safety injection (one unit) and cold shutdown (other unit) mode only one CCS pump is operating; whereas, in the loss-of-coolant accident (LOCA) recirculation (Recirc) mode (one unit) and cold shutdown (other unit), two CCS pumps are running with the C heat exchanger.

Loss of Train A appears to be the worst case scenario, because there is more CCS flow and there are more available heat exchangers for the same modes when the single failure is loss of Train B.

TVA also stated in its letter dated December 10, 2010, in response to RAI 9.2-CCS-1, that, The project has performed calculations which demonstrate that there is sufficient ERCW and CCS capability to bring the non-accident unit to Cold Shutdown within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> from entry into the Hot Standby mode. It is not clear to the staff whether or not this ability includes assuming the worst case single failure, as described above. Therefore, the staff requests TVA provide responses to the following questions.

1. Is loss of Train A the worst case single failure for the CCS system, as described above?

If not, then what is the worst case single failure for the CCS?

2. From the CCS flow and heat load in the worst single failure scenario, explain whether or not the remaining CCS equipment, which is not affected by the single failure, can perform its safety function for the LOCA unit and provide an orderly shutdown and cool down of the nonaccident unit. Provide the approximate time to reach cold shutdown for the nonaccident unit, and explain whether or not this meets the requirements of GDC 5 for shared systems.

3. Does the 72-hour cold shutdown capability described above include assuming the worst case single failure? Explain why or why not.

2