ML14168A613

NRR E-mail Capture - RAI 1 for Csst LAR

ML14168A613
Person / Time
Site:	Watts Bar
Issue date:	06/02/2014
From:	Dion J Watts Bar Special Projects Branch
To:	Arent G Tennessee Valley Authority
References
MF2549
Download: ML14168A613 (3)

Text

NRR-PMDAPEm Resource From: Dion, Jeanne Sent: Monday, June 02, 2014 2:46 PM To: Arent, Gordon <garent@tva.gov> (garent@tva.gov); rhbryan@tva.gov; tahess@tva.gov Cc: Poole, Justin; Lingam, Siva

Subject:

RAI 1 for CSST LAR Please see the below clarification for RAIs associated with CSST LAR (TAC MF2549).

Jeanne Dion Project Manager Watts Bar Special Projects Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation 301-415-1349 From: Matharu, Gurcharan Sent: Monday, June 02, 2014 1:45 PM To: Dion, Jeanne Cc: Lingam, Siva; Poole, Justin; Zimmerman, Jacob; Mathew, Roy

Subject:

RE: RAI 1 for CSST LAR Here is a clarification to my RAI:

BACKGROUND: Assuming Watts Bar Unit 1 and Unit 2 are operating in mode 1, the current Licensing basis of the plant is:

The Class 1E power system is normally supplied from offsite power through CSSTs C and D. For flexibility, there is also a maintenance feed available from CSSTs A and B to the Class 1E power systems to be used only when the unit is in cold shutdown.

The CSST C and D are each capable of powering shutdown loads during events such as:

a) Dual-unit trip as a result of an abnormal operational occurrence; b) Accident in one unit and concurrent shutdown of the second unit; c) Accident in one unit and spurious Engineered Safety Feature (ESF) actuation in the other Unit Following a dual unit trip the plant alignment would result in the following configuration as described in the UFSAR :

1. CSST C will supply 6.9 KV Shutdown Board 1A-A and 2A-A. Shutdown Boards 1B-B and 2B-B will be supplied by CSST D

2. This arrangement provides two immediate sources to redundant trains of Units 1 and 2 and EACH source provides assurance that specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded (a GDC 17 requirement) because there is adequate capacity in each source AND no delay in providing power to plant shutdown loads.

3. As a defense-in-depth measure, the plant design affords a transfer to the alternate path (with fast transfer) through CSST D (if CSST C is unavailable) or CSST C (if CSST D is unavailable). This configuration results in a SINGLE immediate source to redundant trains of Units 1 and 2 and is not in 1

compliance GDC 17 requirements. Hence a dual unit plant LCO is imposed by Technical specifications.

RAI questions 1 and 6 The LAR proposes to revise TS 3.8.1 and TS Bases 3.8.1 to add an allowance to use CSST A or B to meet the requirements of limiting conditions for operation (LCO) 3.8.1, with respect to qualified offsite circuits that satisfy GDC 17 requirements i.e. to compensate for item 3 above. CSST A (or CCST B) is considered the delayed second source for GDC 17 source.

RAI Questions 1 and 6 are related to the time delay associated with using CSST A and B as GDC 17 source.

GDC 17 requires two sources of offsite power, one immediate source and one source can be delayed. The GDC does not define the requirement for allowable delay time in the second source. However, the GDC states that The safety function for each system (assuming the other system is not functioning) shall be to provide sufficient capacity and capability to assure that (1) specified acceptable fuel design limits (SAFDLs) and design conditions of the reactor coolant pressure boundary are not exceeded as a result of anticipated operational occurrences and (2) the core is cooled and containment integrity and other vital functions are maintained in the event of postulated accidents.

The LAR proposes CSST A (or CCST B) to be available but not connected to the shutdown busses. The staff has noted that CSST A and B have adequate capacity to support safe shutdown of the WNB units. The staff requested information on how this proposed delayed path with CSST A (or B) in available mode is able to support GDC 17 requirements (a) and (b) noted above. The RAI responses in letter dated April 21, 2014 did not provide a clear answer related to the proposed delay in the second GDC 17 source.

SUMMARY

The staff is concerned that the proposed amendment would deviate from the current license basis because sources would not be immediately connected to safe shutdown busses. Allowing the delayed AC sources to be unconnected for a period of 14 days, as stated in the LAR, would not meet GDC 17.

NOTE: The staff considers the proposed change to be non conservative when compared to the current licensing basis as indicated in the RAIs based on

1. the time delay associated with CSST A and B

2. CSSTs A and B are not automatically aligned to the shutdown busses,

3. CSSTs A and B do not have the capacity to supply loads on both units during limiting Design Basis Events,

4. CSSTs A and B cannot be aligned to more than one shutdown bus for dual unit shutdown.

2

Hearing Identifier: NRR_PMDA Email Number: 1383 Mail Envelope Properties (0B8884532E5C074E972B443F6E8F592E7DE6017122)

Subject:

RAI 1 for CSST LAR Sent Date: 6/2/2014 2:46:21 PM Received Date: 6/2/2014 2:46:00 PM From: Dion, Jeanne Created By: Jeanne.Dion@nrc.gov Recipients:

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

Tracking Status: None "Lingam, Siva" <Siva.Lingam@nrc.gov>

Tracking Status: None "Arent, Gordon <garent@tva.gov> (garent@tva.gov)" <garent@tva.gov>

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

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

Tracking Status: None Post Office: HQCLSTR01.nrc.gov Files Size Date & Time MESSAGE 4814 6/2/2014 2:46:00 PM Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

Recipients Received: