BVY 08-050, Response to RAIs Related to Degraded Grid Protection Ontechnical Specifications Proposed Change No. 273, Supplement 1

Response to RAIs Related to Degraded Grid Protection Ontechnical Specifications Proposed Change No. 273, Supplement 1

ML082490165
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	08/28/2008
From:	Ted Sullivan Entergy Nuclear Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
BVY 08-050, TAC MD8011
Download: ML082490165 (7)

Text

Entergy Nuclear Operations, Inc.

Vermont Yankee P.O. Box 0250 vpw-wEnterV 320 Governor Hunt Road Vernon, VT 05354 Tel 802 257 7711 August 28, 2008 BVY 08-050 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Reference:

(a) Letter, VYNPS to USNRC, 'Technical Specification Proposed Change No. 273 Instrumentation Technical Specifications," BVY 08-001, dated February 12, 2008 (b) Letter, USNRC to VYNPS, "Vermont Yankee - Request for Additional Information Regarding Technical Specification Change Relating to Degraded Grid Protection System Instrumentation (TAC No. MD801 1)," NVY 08-066, dated July 2, 2008

Subject:

Vermont Yankee Nuclear Power Station License No. DPR-28 (Docket No. 50-271)

Technical Specifications Proposed Change No. 273, Supplement 1 Response to RAIs Related to Degraded Grid Protection

Dear Sir or Madam,

In Reference (a), Entergy Nuclear Operations Inc. (ENO) submitted a proposed change to the instrumentation sections of the Vermont Yankee Operating License Technical Specifications. This letter is in response to your staffs request for additional information (RAI) related to degraded grid protection system instrumentation that were provided in Reference (b). Attachment 1 to this submittal provides ENO's response to each of the RAI questions.

This supplement to the original license amendment request does not change the scope or conclusions in the original application, nor does it change ENO's determination of no significant hazards consideration.

There are no new regulatory commitments being made in this letter.

Should you have any questions or require additional information concerning this submittal, please contact Mr. David J. Mannai at (802) 451- 3304.

I declare under penalty of perjury, that the foregoing is true and accurate.

Executed on August 28, 2008 Since ely, Ted A. WIlivan Site Vice President Vermont Yankee Nuclear Power Station Attachment cc listing (next page)

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BVY 08-050 / page 2 of 2 cc: Mr. Samuel J. Collins Regional Administrator, Region 1 U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406-1415 Mr. James S. Kim, Project Manager Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop 0 8 C2A Washington, DC 20555 USNRC Resident Inspector Entergy Nuclear Vermont Yankee, LLC 320 Governor Hunt Road Vernon, Vermont 05354 Mr. David O'Brien, Commissioner VT Department of Public Service 112 State Street - Drawer 20 Montpelier, Vermont 05620-2601

Docket 50-271 BVY 08-050 Attachment 1 Technical Specification Proposed Change No. 273 Vermont Yankee Nuclear Power Station Response to Request for Information

BVY 08-050 / Attachment 1/page 1 of 4 Technical Specification Proposed Change No.273 Vermont Yankee Nuclear Power Station Response to Request For Additional Information RAI No. 1 Confirm whether the Emergency Core Cooling Systems (ECCS) loads are started simultaneously or through a load sequencer on receiving a safety injection (SI) signal when there is no loss of offsite power. Provide a logic diagram or explain how the degraded voltage protection system interfaces with the starting of various ECCS loads on receipt of SI signal when the ECCS loads are fed from (a) offsite power, (b) emergency diesel generator (EDG).

Response to RAI No. 1 The ECCS loads are started simultaneously on receiving an accident signal when there is no loss of offsite power.

The degraded voltage relays for each safety division are configured in a 2-out-of-2 logic arrangement with a ten second time delay. If the degraded voltage relays sense a sustained low voltage (> 10 seconds) they will separate the emergency buses from the offsite power supply by initiating a loss of offsite power signal which trips the tie breaker between the non-safety-related 4 kV buses and the Class 1E buses. Tripping the tie breaker initiates bus load shedding, automatic EDG start and loading of the ECCS loads on the EDG in a pre-determined sequence. Vermont Yankee (VY) does not have a load sequencer. VY has load sequencing relays on each ECCS pump.

When the emergency buses are supplied from the EDG, the actuation of the degraded voltage relays have no impact on the safety loads; that is, they are bypassed and will not cause further load shedding or cause re-sequence of loads on the EDG.

RAI No. 2 When the 4160 V safety-related buses are powered from the offsite power source at the minimum grid voltage, confirm the following during the sequencing of ECCS loads (or block load if applicable):

(1) Minimum steady state voltage assumed at the switchyard (offsite source),

and the basis for this minimum switchyard voltage; (2) Minimum steady state voltage at the 4160 V safety-related buses; (3) Minimum (worst case) transient voltage at the motor control center starter for the farthest load - whether adequate to pickup the starter/contactor; (4) Minimum (worst case) transient voltage at the starting motor (farthest load) -

whether adequate to provide requisite torque to start the load; and (5) Minimum (worst case) transient voltage at the already running downstream Class 1E load terminals - whether adequate so that the load will not drop due to undervoltage at the downstream load.

BVY 08-050 / Attachment 1/page 2 of 4 Technical Specification Proposed Change No.273 Vermont Yankee Nuclear Power Station Response to Request For Additional Information Response to RAI No. 2 When the 4160 V safety related buses are powered from offsite power source at the minimum grid voltage:

(1) The minimum steady state voltage assumed at the switchyard is 115 kV at the 115 kV bus. This value was established as the "minimum anticipated voltage" after trip of the VY unit under stressed grid conditions. It was established by VY and grid operator ISO-New England using a series of sensitivity studies of grid conditions to determine the minimum expected voltage.

(2) The minimum steady state voltage at the 4160 V safety related buses after addition of the accident loads taken from VY calculation VYC-1088, R4, "Vermont Yankee 4160 V / 480 V Short Circuit / Voltage Study", is 3923 V for 4160 V bus 3 and 3944 V for 4160 V bus 4.

(3) The minimum transient voltage at the safety related motor control center starter for the farthest load adequate to pickup the starter / contactor is 377 V.

(4) The minimum transient voltage at the starting motor adequate to provide requisite torque to start the load is 3498 V for 4000 V motors (required starting voltage is 3200 V) and 368 V for a 460 V motor.

(5) The minimum transient voltage at the already running downstream class 1E load terminals adequate so that the load will not drop due to undervoltage at the downstream load is 3538 V for a 4000 V motor and 360 V for a 460 V motor.

RAI No. 3 In Section 8.5 of Final Safety Analysis Report (FSAR) of Vermont Yankee Nuclear Power Station (VYNPS), when the safety-loads are fed from the EDG, the licensee states that "a voltage drop limit of 40% is established as a maximum voltage variation to occur during the starting of any load group shown in the starting sequence of Tables 8.5-1 A and 1 B, 8.5.2A and 2B, and 8.5.3A and 3B."

NRC Safety Guide 9 and Regulatory Guide 1.9 recommend that: At no time during the loading sequence should the frequency and voltage decrease to less than 95 percent of nominal and 75 percent of nominal, respectively. During sequencing of the ECCS loads from the EDG at Vermont Yankee, confirm the following:

(1) Minimum (worst case) transient voltage profile at the 4160 V safety-related buses; (2) Minimum (worst case) transient voltage at the motor control center starter for the farthest load - whether adequate to pickup the starter/contactor;

BVY 08-050 / Attachment 1/ page 3 of 4 Technical Specification Proposed Change No.273.

Vermont Yankee Nuclear Power Station Response to Request For Additional Information (3) Minimum (worst case) transient voltage at the starting motor (farthest load)

- whether adequate to start the load; and (4) Minimum (worst case) transient voltage at the already running downstream Class 1E load terminal - whether adequate so that the load will not drop due to undervoltage at the downstream load.

Response to RAI No. 3 The VY FSAR describes a voltage drop limit of 40% when the safety loads are fed from the EDGs. This description has been relatively unchanged since the original FSAR and this statement represents the NRC approved licensing basis for VY. VY is not committed to Safety Guide 9 or Regulatory Guide 1.9. Although the voltage dips to a value close to the 40% criteria stated in the original FSAR, the voltage dip is only momentary and voltage recovers to near nominal values rapidly. The EDG is capable of accelerating the required loads as demonstrated by procedures that are performed to meet Technical Specification (TS) surveillance requirement 4.10.A.1 .c.

(1) The minimum (worst case) transient voltage dip at the 4160 V buses is calculated to be 2580 V during the first step (start of the 1000 hp RHR pump) by the latest version of VYC-1860, "Emergency Diesel Generator Dynamic Voltage and Frequency Analysis." Once each operating cycle VY Procedure OP 4100, "Integrated ECCS Test" simulates the transient loading of the diesel generator (TS requirement 4.10.A.1.c) and demonstrates the capability of the diesel generator to start and accelerate the accident mitigating loads. Results of the last surveillance test document that the large ECCS pumps successfully started and accelerated their loads within the time required.

(2) The minimum (worst case) transient voltage at the motor control center starter for the farthest load is estimated to be 305 V based on extrapolation of results from VYC-1860 and VYC-1088, "4160 V and 480 V Voltage Regulation and Short Circuit Calculation." This value may be momentarily less than the minimum pickup voltage for a 460 V contactor; however, during EDG loading, voltage recovery to above the pickup value is rapid and the testing performed by OP 4100 documents that all required loads start successfully.

(3) The minimum (worst case) transient voltage at the starting motor (farthest load) adequate to start the load is 2538 V which is the terminal voltage of the RHR pump during the first step of the load profile. The RHR pump is analyzed to be able to accelerate its load at 70% of rated voltage or 3400 volts. The transient voltage dip to 2538 V lasts less than 0.1 seconds and voltage quickly recovers.

The motor successfully accelerates the load as documented in the Integrated ECCS Test Results.

BVY 08-050 / Attachment 1/page 4 of 4 Technical Specification Proposed Change No.273 Vermont Yankee Nuclear Power Station Response to Request For Additional Information (4) The minimum (worst case) transient voltage at the already running downstream Class 1E load terminal adequate so that the load will not drop due -to undervoltage at the downstream load is considered to be 307 V. This voltage is considered to occur during the start of the second large load on the diesel generators because when the first RHR pump starts onthe initial step when all loads are considered to be accelerating. Dropout voltage for contactors in the 460 V system is between 40% and 60% of rated voltage. The VY analysis uses the maximum 60% value or 288 V; therefore contactors do not drop out during the transient voltage dips. The Integrated ECCS Test Results confirm that contactor dropout is not a problem.

RAI No. 4 The proposed TS Table 3.2.8 ACTION Note 3 states in the end: If the Action and associated completion time of Note 3.a or 3.b are not met, initiate increased voltage monitoring of the associated 4.16 kV emergency bus(es).

Describe in detail what is meant by increased voltage monitoring (i.e., logging requirements and time intervals).

Response to RAI No. 4 VY monitors the 4160 V bus voltage twice per shift (every six hours) by logging the voltage reading in the operators rounds as a heightened surveillance. This frequency is based on:

1) Safety Bus 3 and 4 voltage indication is on CRP 9-8, a control room front panel that is routinely monitored by the operator at the controls; and

2) Low Bus 3 and 4 voltage is annunciated in the control room and responded to in accordance with Alarm Response Procedure 8-J-9.