ML18153C280
| ML18153C280 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 06/29/1990 |
| From: | Varga S Office of Nuclear Reactor Regulation |
| To: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| References | |
| RTR-REGGD-01.155, RTR-REGGD-1.155 NUDOCS 9007060110 | |
| Download: ML18153C280 (7) | |
Text
I' e
UNITED STATES e
NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 Docket Nos. 50-280 and 50-281 Mr. W. L. Stewart Senior Vice Pr~sident - Nuclear Virginia Electric and Power Company 5000 Dominion Blv~.
Glen Allen, Virginia 23060
Dear Mr. Stewart:
June 29, 1990
SUBJECT:
SURRY UNITS 1 AND 2 - VEPCO MARCH 30, 1990 SUPPLEMENTAL RESPONSE (88-414B) TO STATION BLACKOUT (SBO) RULE 10 CFR 50.63 Our review of the subject letter indicates, as you have stated, that a variance*
exists between the staff's and VEPCO's interpretations of the documents*
related to Station Blackout (10 CFR 50.63, Regulatory Guide (RG) 1.155, and NUMARC 87-00) in the areas you identified. These areas are:,
(1) acceptable designs for electrical crossties between units at multi-unit sites to facilitate use of existing emergency diesel generators
{EDGs) as alternate AC {AAC) sources
{2) criteria for qualifying existing EDGs as AAC sources {question of load shedding to make available "excess capacity")
{3)
EDG reliability The basic NRC position on the use of EDGs as AAC sources is provided in the letter from William T. Russell (NRC) to William Rasin (NUMARC) dated June'6, 1990 (Enclosure).
We appreciate your desire to fully comply with 10 CFR 50.63, RG 1.155 and NUMARC 87-00. Therefore, to facilitate your understanding of the staff's position, we provide the following explanations relative to the above items.
{1)
Your understanding that Figure C of NUMARC 87-00, Supplemental Questions and Answers, dated December 27, 1989, presents a crosstie configuration which*is unacceptable to the staff is correct.
The basic criteria governing the connectability of an AAC power source are contained in 10 CFR 50.2 (the AAC source should be connectable to but normally not connected to the offsite or onsite emergency AC power systems),
10 CFR 50.63 {SBO should not_assume a concurrent single failure or design basis acc,dent), and Appendix A of 10 CFR Part 50 {the single failure criterion and the independence requirements apply to the non-blackout
[NBO] unit)~. Therefore, in a one-unit site, as a minimum, an AAC source
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Mr. W. need only be connectable to one set of safe shutdown equipment, regardless of whether that equipment is part of a safety train or not, or whether the AAC source is an excess-redundancy EDG or an independent power source.
However, at a two-unit site where two EDGs per unit are provided and qualify as an AAC source, one intertie circuit between units is acceptable provided it is separately connectable to each safety (EDG) bus in both *
- units. This follows from the*application of the above criteria and the assumptions that an SBO can occur in either unit and that the single failure in the NBO unit can be on either one of its EDGs or on its respective safety bus.
(2) Your presumption of the acceptability of load shedding in the NBO unit to make*available "excess capacity" to qualify an existing EOG in the NBO unit to satisfy the SBO rule requirements in another unit is at variance with the staff position.
The guidance on the use of existing EDGs as AAC power sources is documented in the SBO Rule~ 10 CFR §50.63, RG 1.155 Position C.3.3.5 and NUMARC 87-00 (Section 2.3.1(3)). This guidance is further explained in NUMARC 87-00, Supplemental Questions and Answers, dated December 27, 1989, under questions 3.4.and*B.3. The SBO Rule states:
"At multi-unit sites, where the combination of emergency ac power sources exceeds the minimum redundancy requirements for safe shutdown (non,;,,DBA) of all units, the remaining emergency ac power sources may be used as alternate ac power sources provided they meet the applicable*
requirements.".
The rule statement requires minimum redundancy. This means that in order to qualify as an AAC source, there must be an EOG available in the NBO unit that is in addition to the number of EDGs required to meet the minimum EDG redundancy requirement for powering a normal safe shutdown for a loss of offsite power (LOOP) event. Thus, the EDGs in a two-unit site with two dedicated EDGs per unit would not qualify as AAC sources because the two EDGs per unit just meet the minimum redundancy requirement, i.e.,
there is no excess EDG.
However, there are some plants at two-unit sites which meet the minimum redundancy requirement and where each EDG is of sufficient capacity to fully power all the normal LOOP loads of the NBO unit, and also has sufficient excess capacity for powering the required safe shutdown loads of the SBO unit. Recognizing this type of situation, the staff has interpreted the excess EDG redundancy requirement of the SBO rule to allow EDGs just meeting the minimum EOG redundancy requirements to qualify as AAC sources on the* basis of excess capacity, provided the other applicable requirements for AAC sources are also met.
l Mr. W. The NRC's basic position on the use of EDGs as AAC power sources on the basis of excess capacity is that such excess capacity should not be attained by any load shedding in the NBO unit which results in a degradation of its normally available safe shutdown capability for the LOOP condition.
Any actions that would add to the burden of operators that ar~ already iri a high stress environment, such as load switching or disablement of information readouts or alarms in the control room, are considered to be a degradation of normal safe shutdown capability for LOOP'. in the NBO unit.
The staff position is, therefore, that the normal equipment complement should remain available with adequate EOG capacity for use should it become necessary.
The NBO unit should have the capability for hot shutdown/
hot standby forced cooling, cooldown and depre*ssurization as required.
While idditional events are not explicitly postulated, it is not prudent to diminish the capability of the NBO unit to mitigate problems should they arise.
It is not in the interest of safety to reduce the capability to handle various eventualities in one unit for the purpose of meeting the SBO rule in another unit. Each unit must meet the SBO rule on its own merits without reducing another unit's capability to respond to its own potential problems *.
Therefore, a multi-unit site with the dedicated EDGs just meeting the minimum redundancy requirement but not having the excess capacity defined above for qualifying as an AAC source does not meet the SBO rule require-ments.
Further measures are required, such as a separate AAC source or a coping analysis which shows the plant can cope with and recover from an SBO for the required duration.
(3}
- With regard to diesel generator target reliability, as you have accurately stated, the target reliabilities chosen for each plant are to be maintained.
However, it is the staff's position that an EOG reliability program should be developed in accordance with the guidance in RG 1.155, Section 1.2.
We believe that the staff positions, as stated above, are sufficiently clear to allow you to appropriately modify your response to the SBO rule and to proceed expeditiously with the planning to implement any necessary plant modifications.
Mr. W. June 29, 1990 Should your have any further questions or desire to discuss these issues further, please contact Bart Buckley at 301-492-1452.
Enclosure:
As stated cc w/enclosure:
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MS i n ku 1 e R II FRosa 7/E/4 AThadani 8/E/2 Sincerely, en A.
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Division of Reactor Pro* ts - I/II Office of Nuclear Reactor egulation NAME /......-* "'7'N.r r ffl DATE
e Mr. W. L. Stewart Virgini,a El~ctric and Power Company cc:
Michael* W. Maup~n, Esq.
Hunton and Williams Post Office Box 1535 Richmond, Virginia 23212 Mr. Michael R. Kansler, Manager Surry Power Station Post Office Box 315 Surry, Virginia 23883 Senior Resident Inspector*
Surry Power Station U.S. Nuclear Regulatory Commission Post Office Box 166, Route 1 Surry, Virginia 23883 Mr. Sherlock Holmes, Chairman Board of Supervisors of Surry County Surry County Courthouse Surry, Virginia 23683 Mr. W. T. Lough.
Virginia Corporation Commission Division of Energy Regulation Post Office Box 1197 Richmond, Virginia ?3209 Regional Administrator, Region II U.S. Nuclear Regulatory Commission.
101 Marietta Street N.W., Suite 2900 Atlanta, Georgia 30323 C. M. G. Buttery, M.D., M.P.H.
Department of Health 109 Governor Street Richmond, Virginiar 23219 Surry Power Station Attorney Genera 1
- Supreme Court Building -
101 North ath Street Richmond; Virginia 23219 Mr. E. Wayne Harrell Vice President - Nuclear Operations Virginia Electric and Power Company 5000 Old Dominion Blvd.
Glen Allen, Virginia 23060 Mr. J. P. O'Hanlon Vice President -*Nuclear Services Virginia Electric and Power Company 5000 Old Dominion Blvd.
Glen Allen, Virginia. 23060 Mr. R. F. Saunders Manager - Nuclear Licensing
~
Virginia Electric. and Power* ComRany*.*.
5000 Old Dominion Blvd.
~
Glen Allen, Virginia. 23060
- e UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 Mr. William Rasin, Director
. Technical Division
~l'JI v*~,1 Nuclear Management and Resources Council (NUMARC) 1776 Eye Street, N.W., Suite 300 Washington, D.C.
20006-2496
SUBJECT:
STATION BLACKOUT
Dear Mr. Rasin:
e ENCLOSURE Mr. Alex Marion's letter to Mr~ Ashok Thadani dated May 7, 1990, (Enclosed) proposed an alternate position on the use of existing emergency diesel generators (EDGs) as alternate AC (AAC) sources at multi-unit sites for the purpose of meeting the requirement (AAC option) of the station *blackout (SBO) rule.
Mr. Marion's letter indicates that our staffs have not been able to reach agree-ment on the definition of the 11excess EDG capacity 11 requi_red for qualifying EDGs as an AAC.source at multi-unit sites where the EDGs just meet the minimum EOG redundancy requirement.
The NRC's long-held position is that such excess capacity should not be attained by load shedding in the non-blackout (NBO) unit which results in a degradation of its normally available safe shutdown capability for the loss-of-offsite-power (LOOP) condition.
Any actions that would add to the burden of operators that are already in a high stress environ-ment, such as load switching or disablement of information readouts or alarms in the control room, are considered to be a degradation of normal safe shutdown capability for LOOP in the HBO unit.
Each unit must meet the SBO rule.on its own merits without reducing another unit's capability to respond to its own potential problems.
The NUMARC position, on the other hand, would permit load shedding which may degrade the ability of the non-blackout unit to safely shut down.
- "Excess EOG capacity" is difficult to define generically because of the diversity of site and plant design features that must be considered.
So it is not unexpected that our staffs would fail to reach agreement on this issue.
I believe the net effect of the NRC/NUMARC coordination *in regard to SBO has been a positive one and has been effective in reaching agreement on generic resolution of many aspects of SBO rule implementation.
Wi11iam Rasin 2
The staff review of 1icensee responses to th~ SBO ru1e which propose to use 11 excess EOG. capacity" wi11 continue based on the NRC position and the previously issued guidance (i.e., R.G. 1.155, NUMARC 87-00, and the NUMARC Supplemental Guidance dated December 27, 1989).
Enclosure:
Letter ftom A. Marion (NUMARC) to.
A. Thadani (NRC) dated May 7, 1990,
Subject:
Station Blackout - TAC 40577 Sincerely,
/s/
Wil.liam T. Russell, Associate Director for Inspection and Technical Assessment Office of Nuclear Reactor Regulation