ML20128E318
| ML20128E318 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 02/01/1993 |
| From: | Tremblay L VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BVY-93-12, NUDOCS 9302100379 | |
| Download: ML20128E318 (5) | |
Text
.
- VERMONT YANKEE NDCLEAR POWER CORPORATION rys Ferry Road. Brattleboro VT 05301-7002 ENGINE I OFFICE N
~
580 MAIN STREET DOLTON. M A 01740 608? 779-671*
February 1,1993 BVY 93-12 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Weashington, D.C. 20'555
References:
a)
License No. DPR-28 (Docket No. 50-271) b)
%CFR 50.63, " Loss of All Alternating Current Power" c)
Letter USNRC to VYNP'., Vermont Yankee Station Blackout Analysis, NVY 91-98, dated June 5,1991 d)
Letter VYNPC to USNRC, Vermont Yankee Response to Station Blackout Safety Evaluation Report, BVY 91-69, dated July 17,1991 e) letter VYNPC to USNRC, Supplement to Response to Station Blackout 3t'e, BVY 90-038, dated March 30,1990 f)
LottLr USNRC to VYNPC, Supplemental Safety Evaluation of Vermont Tatt.ee Nuclear Power Station, Station Blackout Rule (t005R 50.6H (TAC %..MGL6'20), dated September 1,1992
Subject:
Response to Ststion Blac'ont SSL'l
Dear Sir:
In Reference c), the USNRC provided comments aun.n initial Gafety Evaluation Report (SER) on Vermont Yankee's submittal to meet the Station Blackout Rule, Reference b).
Vermont Yankee responded to the comments in the initial SER in References d) and e). The USNRC issued a Supplemental Safety Evaluation Refrar+ (SSFRNr th9 Station Blackout Rule in Reference f). The SSER provided acceptance, con 6npant uren several recommendations regarding Vermont Yankee's proposed method for meeting the requirements of Reference b).
It also roquested that Vermont Yankee keep the NRC informed about any key developments in the implementation of the rule. The purpose of this letter is to respond to issues raised in the SSER and to provide an update of progress in implementing the requirements of the rule.
050053 3l 9302100379 Y30201 iT d
PDR ADOCK 05000271 A
l P
PDR l'
)
VERMONT YANKEE NUCLEAR POWER CORPOR ATION o
U.S. Nuclear Regulatory Commission February 1,1993 Page 2 Periodic Testing Recommendation in Reference f) the NRC staff acknowledges that a combination of the simulator testing and load testing of the AAC source is acceptable but recommends that load testing "be done initially after the Vernon Hydro upgrade and tio line upgrade is completed and once overy refueling outage thereafter, or more often."
n VY Response Vermont Yankee believes that performing a load capacity test once per refueling outage or more often is unnecessary. The AAC source for Vermont Yankee is unlike most other AAC sources used for SBO. Most AAC sources are standby sources such as on-site gas turbines or non-safety diesel generators. These sources tsf power are tested to assure that they can start and carry loads; similar testing is not required for transformers. Gas turbine or diesel generators can easily.be paralleled to power systems at nuclear plants at any time.
The Alternate AC source for Vermont Yankee is a normally operating adjacent hydroelectric station. It is a "run of the river" station which generates continuously and whose loci capacity is continuously being demonstrated. Vermont Yankee is connected to the station by a normally energized cable and transformer. Voltage indication for the line and station output in MW is providet 5 the Vermont Yankee control room at all times. Unlike other standby sources, because of the inability to control power flow, it is not possible to parallel the Vernon Hydro Station with Vermont Yankee. Control of power flow (voltage, VARs, or phase angle) is not available. AdditiMally, absent an.SBO event, Vermont Yankee cannot connect full emergency load to the hydro station and the full capacity of the tie line cannot be readily tested. Connection of the hydroelectric station to Vermont Yankee currently requires complete deenergizing of a vital 4160 V bus because of existing electrical interlocks. These interlocks ensure that the Vernon tie line transformer can only be loaded with the load available from one emergency bus. The load available during a refueling outage may be limited and would not be enough to load the line and transformer to full capacity as recommended by NUMARC 87-00.
Nevertheless, the hydro station has been shown to be a reliable source of power for about 90 years ano its availability and capacity is continuously monitored and tested. The load carrying capacity of the line and transformer does not vary with time nor is this arrangement susceptible to active failures such as diesel generator failures to start Routine electrical tests are performed on the transformer and cable to detect any degradation. In addition, extensive testing is planned on the new transformer and cable to be installed during tie line modifications. This testing is discussed in Attachment A.
VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclear Regulatory Commission February 1,1993 Page 3 Because of the difficultyin performing o " load capability" test, Vermont Yankee plans to continue to connect the hydro station to tne plant buses once every 5 years (about every third refueling outage) and tast the tie line with the loads available during the refueling outage (~ 400 kW). This hvel of testing and routine electrical tests have demonstrated a very high level of reUability of the tie line to Vermont Yankee over the past 20 years.
Steam Tunnel Habitability RecomnMndation The Supplemental Safety Evaluation Report- (Reference f) for the. Station -
Blackout Rule (10Cf-R50.63)- required Vermont Yankee to "... verify that the main-steam tunnelis habitable for the operator to perform the manual operations if required during an SBC event (Section 2.3.1 of the SSER)."
VY Resoonse A review of the SBO submittals and documentation was initiated to ensure that i
no credit had been taken for operator action in the main steam tunnel during an SBO event. This review has been completed and has confirmed-that no credit has ever been assumed for habitability of the tunnel area.
S During this review, we attempted to determine whv the NRC may have believed manual action in the tunnel area was required. The only statement which may have been understood to require that action was found in Reference j). In this submittal VY stated, "... the HPCI, RCIC and Main Steam Tunnel areas were not considered dominant areas of concern. Although equipment located:in these areas will be-automatically initiated or used as the operators follow the emergency procedures...
(emphasis added)". _ This statement may have been understood as requiring action in --
l the tunnel, but what the statement was really identifying was that HPCI and RCIC would probably autn initiate, or if not, be used as identified in emergency procedures.
There is no equ;pment in the steam tunnel which requires manual operation during an' SBO event and no credit is taken for habitability of_the main steam tunnel area.
Current Schedule for SBO Modifications As stated above, Reference f) requested VY.to keep the staff informed about the. progress of modifications.
Reference f) considered the two' yoar clock for i
completing modifications to comply to the SBC rule to have begun upon the receipt of the SSER.
p u
.x v
3
= w-
VERMONT YANKEE NUCLEAR POWER CORPORATION r
e U.S. Nuclear Regulatory Commission February 1,1993 Page 4 i
As stated in previous submittals, the schedule for coming into full compliance l
with the rule depends heavily on the schedule of modifications to the hydroelectric station. At this time, major electrical modifications are scheduled to commence in the first quarter of 1993. These modifications will require the existing connection for Vermont Yankee to be removed from the 2.4 kV generation bus. This bus is being modified and the existing circuit breaker is being removed. Current plans call for Vermont Yankee's existing overhead line to be supplied from a temporary connection in the hydro station 13.2 kV switchyard and a temporary transformer. Testing planned for this interim temporary configuration is discussed in Attachment A.
e While modifications are made within the' power station, the new underground feeder will be constructed. Construction should take plr ;e in spring - fall of 1993. A new permanent 13.2 / 4.16 kV transformer will be installed on Vermont _ Yankee i-property to connect the underground cable from the temporary connection at the hydro i
station twitchyard; to the existing underground 4.16 kV cable that connects.to j
Vermont Yankee's emergency switchgear.
Af ter the completion o'f electricst installation at the hydro station, the temporary conacction at the hydro station 13.2 kV switchyard will be transferred to a permanent circuit breaker This connection is anticipated to be made in late 1993 -'early 1994.~
At this time Vermont Yankee anticipates all modifications will he comploted within the two year time frame. However, we expect that:the status is going to change as installation progresses and we will keep the staff informed on a periodic basis.
We trust this information is satisfactory for resolution of the recommendations j
i contained in Reference f), and will be sufficient to demonstrate that VY's proposed method of coping with an S30 meets the requirements of the SBO Rule,10 CFR 50.63. However, l
should you have any additional questions or. require additional information please do not hesitate to contact this office, i
Very truly yours, VERMONT YANKEE NUCLEAR POWER CORP.
N W Ci V y.WyA_ M,\\(/i.
. ( f'y Leonard A. Tremblay, Jr.
N Senior Licensing Engineer Attachment cc:
. USNRC Region i Administrator USNRC Resident inspector - VYNPS USNRC Project Manager _ - VYNPS
~
VERMONT YANKEE NUCLEAR POWER CORPORATION 4
Attachment A Factory and Installation Testing i
Factory Testina Vermont Yankee will perform routine factory acceptance testing of cable and transformers used for the new tie line equipment. The testing for the transformer will be in accordance with ANSI /IEEE C57.12.90 and willinclude the following:
Resistance of all windings on all tap connections Polarity and phase relationship Ratio of all windings on all tap positions No load losses and excitation current -
Impedance at all tap positions Temperature rise.
Hi potential testing induced voltage testing insulation resistance test The cable will be subjected to hi potential testing and insulation sesistance testing at 4
the factory.
Installation Testina For the temporary connection of the tie line and the permanent installation of tie line equipment routine field acceptance testing such as insulation resistance, high potential testing -
I will be performed. Transformer testing will include testing such as power factor testing, i
insulating fluid testing, winding resistance, insulation. resistance, and phase relationship testing. Cable testing willinclude field hi potential testing, insulation resistance testing and -
continuity and ground testing.
Because Vermont Yankee will be operating at the time of the temporary connection and will most likely be-operating 'when intermediate. and final configuration of 'the line is established,icad testing of the line itself will not be performed. Vermont Yankee will perforrn a load test at the first refueling following the' completion of the permanent installation. The load test will use the available load from one safety bus because of the constraints described above.
.-r%1.
..,m1 yg y
lm.
.