ML020580385
| ML020580385 | |
| Person / Time | |
|---|---|
| Site: | North Anna  (NPF-004, NPF-007) |
| Issue date: | 02/18/2002 |
| From: | Hartz L Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 01-560B, TAC MB1451, TAC MB1452 | |
| Download: ML020580385 (8) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 February 18, 2002 U.S. Nuclear Regulatory Commission Serial No.:
01-560B Attention: Document Control Desk CM/RAB RO Washington, D.C. 20555-0001 Docket Nos.:
50-338 50-339 License Nos.:
NPF-4 NPF-7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)
NORTH ANNA POWER STATION UNITS I AND 2 PROPOSED IMPROVED TECHNICAL SPECIFICATIONS REQUEST FOR ADDITIONAL INFORMATION ITS 3.7.9 BEYOND SCOPE ISSUE (TAC NOS. MB1451 AND MB1452)
This letter transmits our response to the NRC's request for additional information (RAI) regarding the North Anna Power Station (NAPS) Units 1 and 2 proposed Improved Technical Specifications (ITS). The North Anna ITS license amendment request was submitted to the NRC in a December 11, 2000 letter (Serial No.00-606). The NRC requested additional information regarding ITS 3.7.9, "Ultimate Heat Sink," in a letter dated September 6, 2001 (TAC Nos. MB1439, MB1440, MB1451, and MB1452). On November 19, 2001, Dominion submitted responses to the NRC's RAIs (Serial Number 01-560). In a subsequent telephone call with members of your staff, Dominion agreed to revise one response and to submit additional information to address certain questions in the September 6, 2001 letter. The revised response and the additional information were transmitted in a letter dated January 25, 2002 (Serial Number 01-560A). In a letter dated February 11, 2002, the NRC requested further information on the North Anna reservoir. This letter provides the requested information.
If you have any further questions or require additional information, please contact us.
Very truly yours, Leslie N. Hartz Vice President - Nuclear Engineering Attachment Commitments made in this letter: None I
cc:
U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW Suite 23T85 Atlanta, Georgia 30303-8931 Mr. Tommy Le U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 12 H4 Rockville, MD 20852-2738 Mr. M. J. Morgan NRC Senior Resident Inspector North Anna Power Station Commissioner (w/o attachments)
Bureau of Radiological Health 1500 East Main Street Suite 240 Richmond, VA 23218 Mr. J. E. Reasor, Jr. (w/o attachments)
Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Blvd.
Suite 300 Glen Allen, Virginia 23060
SN: 01-560B Docket Nos.: 50-338/339
Subject:
RAI - Proposed ITS 3.7.9 COMMONWEALTH OF VIRGINIA
) )
COUNTY OF HENRICO
)
The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Leslie N. Hartz, who is Vice President - Nuclear Engineering, of Virginia Electric and Power Company. She has affirmed before me that she is duly authorized to execute and file the foregoing document in behalf of that Company, and that the statements in the document are true to the best of her knowledge and belief.
Acknowledged before me this 18th day of February, 2002.
My Commission Expires: March 31, 2004.
"""tNotary Public (SEAL)
Attachment Proposed Improved Technical Specifications Revised Response to Request for Additional Information ITS 3.7.9, "Ultimate Heat Sink" Virginia Electric and Power Company (Dominion)
North Anna Power Station Units I and 2
North Anna Improved Technical Specifications (ITS) Review Comments Ultimate Heat Sink (UHS)
(TAC Nos. MB1451 AND MB1 452)
NRC Letter dated February 11, 2002 RAI 1, QUESTION 1:
When "steam dump" is referred to in the submittal, does this refer to the use of the turbine by-pass valve to route steam directly into the condenser?
RESPONSE
Yes. The steam dumps are turbine bypass valves, and provide a direct line from the steam generators to the condenser.
RAI 1, QUESTION 2:
Describe the system, sequence of events, success criteria, and automatic/manual operations required for short term decay heat removal using the Decay Heat Release Valve (DHRV).
RESPONSE
Each unit has a single, normally isolated DHRV.
Downstream of its manual isolation, it is fed by each of the three main steam lines through non-return valves from taps upstream of the trip valves. It provides an alternate means of releasing steam to the atmosphere without using the steamline PORV's.
During a steam generator tube rupture, the operators will enter 1(2)-E-3.
This procedure requires the operators to identify and isolate the ruptured SG. Afterward, the operators are instructed to cool down the RCS by releasing steam from the two intact generators. The first choice for cooldown is the steam dump system, which sends all of its steam to the condenser.
If the dumps are not available, the procedure directs cooldown via the main steam PORV's or the DHRV. The DHRV is placed in service by opening its single upstream isolation valve and the non return valves on the lines from the non-ruptured loops. The action is successful when the two intact loops can vent through the DHRV.
RAI 1, QUESTION 3:
After short term heat removal is successful using the DHRV, is long term heat removal initiated in the same way and under the same plant conditions as following other short term heat removal scenarios (i.e., condenser cooling using circulating water)?
RESPONSE
Yes. Steam relief from the main steam system provides cooling until the Reactor Coolant System is below 350 degrees and 450 psig, after which the Residual Heat Page 1 of 4
North Anna Improved Technical Specifications (ITS) Review Comments Ultimate Heat Sink (UHS)
(TAC Nos. MB1451 AND MB1452)
NRC Letter dated February 11, 2002 Removal System will be placed in service for long term cooling. This sequence is followed no matter which steam relief path was used.
RAI 1, QUESTION 4:
If DHRV cooling was incorporated into the PRA, how would the PRA need to be modified to accurately model the scenario of events, plant states, and required supporting equipment?
RESPONSE
Currently, the PRA model includes the steam dumps and the PORVs as illustrated below. The model does not credit the DHRV for steam release.
In order to incorporate the DHRV into the model, an additional gate in the secondary cooling fault tree would be added that reflects the failure probability of the DHRV and the manual action.
The DHRV would be assigned a failure rate of approximately 2E-2. The human error term for a simple, procedurally controlled operation, with reasonable allowance for time, would be approximately 1E-2 or less. (The human error term for use of the SG PORVs, HEP-1ES1:2-S2, is 8.5E-4.) The combined effect would be a DHRV unavailability of well below 1.OE-1.
RAI 1, QUESTION 5:
If the DHRV is not modeled in the PRA but a reduction in the Risk Achievement Worth (RAW) for the North Anna Reservoir is estimated, describe how the magnitude of the anticipated reduction in the RAW was estimated.
RESPONSE
Table 1 lists the top cutsets for the case in which Lake Anna is unavailable. Nine of the top ten cutsets are initiated by a tube rupture, followed by a failure of the steam PORVs on the intact loops to release steam. The result is a release of steam from the ruptured loop, including any radionuclides from the primary-to-secondary leakage.
Page 2 of 4
North Anna Improved Technical Specifications (ITS) Review Comments Ultimate Heat Sink (UHS)
(TAC Nos. MB1451 AND MB13452)
NRC Letter dated February 11, 2002 Table 1 Top Ten Cutsets with Lake Anna Unavailable Number of cut sets in equation
= 5781 Top event unavailability (rare event) = 5.245E-006 Reference Run NOAL304 Cutset LERF Basic Events 1
4.08E-007 LERF-25 IE-T7B 1MSRV--23-101AC 2
4.08E-007 LERF-25 IE-T7C 1 MSRV--23-101AB 3
4.08E-007 LERF-25 IE-TCA 1MSRV--23-101BC 4
3.66E-007 LERF-25 IE-T7A 1MSRV--C3-101ABC 5
3.66E-007 LERF-25 IE-T7B 1MSRV--C3-101ABC 6
3.66E-007 LERF-25 I E-T7C 1MSRV--C3-101ABC 7
2.39E-007 LERF-24 IE-VX 8
1.99E-007 LERF-25 I E-T7B 1MSRV--FC-101A 1MSRV--FC-101C 9
1.99E-007 LERF-25 I E-T7A 1MSRV--FC-101B 1MSRV--FC-101C 10 1.99E-007 LERF-25 IE-T7C 1MSRV--FC-101A 1MSRV--FC-101B If we credit the DHRV as an alternate means of secondary heat removal, it would add an extra basic event to every cutset except #7 in the table above.
The additional basic event would reduce the LERF contribution of these cutsets by at least a factor of ten (reflecting the DHRV unavailability of <0.1). This reduction would decrease the top event unavailability by 50%, just due to the improved modeling for these nine cutsets alone.
The Risk Achievement Worth for this scenario would also diminish by the same 50%, taking the RAW from 2.9 to below 1.5.
RAI 2
How long can North Anna Power Station continue to operate at full power if the temperature of the North Anna reservoir exceeds 95 degrees or if the water level of the reservoir falls below 244 feet Mean Sea Level? If the plant cannot operate at full power under the above conditions, can it operate at reduced power and, if so, at what power level?
RESPONSE
Generally, the ability to operate North Anna Power Station would be impacted if the temperature of the North Anna reservoir exceeded 950F or if the water level fell below 244 feet Mean Sea Level, due to the effect these two parameters have on condenser performance. Both parameters could affect condenser pressure, and plant procedures require the unit to shut down if condenser pressure is Page 3 of 4
North Anna Improved Technical Specifications (ITS) Review Comments Ultimate Heat Sink (UHS)
(TAC Nos. MB1451 AND MB1 452)
NRC Letter dated February 11, 2002 unacceptable. Condenser pressure is not a nuclear safety issue, but it does affect the ability to operate the plant.
If the North Anna Reservoir temperature exceeded 950F, the increase in main condenser pressure would be the critical parameter of concern. Condenser performance curves indicate that with a Circulating Water (CW) supply temperature of 950F, pressure is predicted to be in the range of 3.5 to 3.8 inches mercury (Hg), which is below the turbine trip setpoint of 5.5 inches Hg. A Control Room annunciator alarm for low vacuum has a setpoint of approximately 5.0 inches Hg, which is expected to occur when the CW supply temperature increases above 1050F. Abnormal Procedure 1(2)-AP-14, "Low Condenser Vacuum," requires a plant trip when condenser pressure is unacceptable. Also, it should be noted that it is very unlikely that the North Anna Reservoir temperature would exceed 95 0F.
If the level in the North Anna Reservoir decreased below 244 feet, the capability to maintain power operation would begin to be challenged. In particular, the lower water level would begin to adversely affect pump submergence and net positive suction head for the various types of pumps located at the CW Intake Structure.
The screenwash pumps would be impacted first, as their submergence requirements would not be satisfied if level decreased a few inches below 244 feet. A loss of the screenwash function may ultimately lead to the shutdown of the CW pumps as the differential level increases across the screens. Therefore, it is not expected that the main condenser would be available indefinitely to support plant power operation with level below 244 feet. The time duration that power operation could continue would be dependent on the rate of fouling of the travelling screens. Abnormal Procedure 0-AP-40, "Abnormal Level in North Anna Reservoir (Lake)," would be entered if the level fell below 247 feet. Also, as stated above, 1(2)-AP-14 would require a plant trip when condenser pressure is unacceptable.
Based on the previous discussion, operation of North Anna Power Station would be limited by the impact that the North Anna reservoir temperature and level have on condenser pressure.
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