ML20210K111
| ML20210K111 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Millstone |
| Issue date: | 04/04/1986 |
| From: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Asselstine, Palladino, Roberts NRC COMMISSION (OCM) |
| Shared Package | |
| ML082401831 | List: |
| References | |
| FOIA-86-263, FOIA-86-80 NUDOCS 8604110703 | |
| Download: ML20210K111 (3) | |
Text
r APR 0 41986 MEMORANDUM FOR:
Chairman Palladino Commissioner Roberts Comissioner Asselstine
- Comissioner Bernthal Comissioner Zech FROM:
Victor Stello, Jr.
Executive Director for Operations
SUBJECT:
EFFICACY OF INTERCONNECTING SOURCES OF EMERGENCY AC POWER AT SITES WITH MORE THAN ONE UNIT Your memorandum of February 7, 1986 noted that, during the discussion _on issuance of a full power license for Millstone 3, the Commission was advised by the Acting EDO that the staff would examine the efficacy of interconnecting sources of emergency AC power (both safety grade and nonsafety-grade) at sites with more than one unit. The Acting EDO further advised that the staff would per-form a generic analysis on check valves. !lere following are our coments on the efficacy of interconnecting power sources. The generic analysis on check valves will be addressed in a separate memorandum.
Prior to answering the question we should differentiate between shared power sources and interconnections between power sources. A power source is considered to be shared between units when it is required by each unit in order to meet the single-failure criterion of GDC 17 for each unit during one or more design basis events. An example of a shared power source is a diesel gener-ator that can swing between either of two units, each of which has an additional single dedicated diesel. However, a power source is not considered to be shared between units simply because it might have an interconnection to the other unit.
An example of such a configuration would be a two unit installation with independent, redundant diesel generators in each unit and an electrical intertie between units. The distinction is that for the station with two units and two emergency diesels per unit the intertie is not required in order to meet the single failure criterion during design basis events.
GDC 5, which addresses sharing, does not prohibit sharing provided "....it can be shown that such sharing will not significantly impair their ability to per-form their safety functions, including, in the event of an accident in one unit, an orderly shutdown and cooldown of the remaining units." Regulatory Guide 1.81, however, does recomend against sharing of emergency onsite power systems at multi-unit nuclear power plants for which the construction permit application was made on or after June 1,1973. This does not preclude having interties available as noted above, with appropriate interlocks and administrative con-trols such that manual action could allow the emergency power sources of one unit to power emergency loads of the other or both units under abnormal
Contact:
J. Lazevnick X24864 3
(op$ll@7$3Xft1Nf J
1
1 The Commissioners
- 7 circumstances (e.g., Byron /Braidwood designs provided an intertie between onsite power sources of two units to improve the reliability of the auxiliary feedwater system in both units).
The above discussion has primarily dealt with the interconnection of safety-grade AC power sources. With regard to nonsafety grade AC power sources, the interconnection of these power sources between units are reviewed only to the extent that they not degrade systems which are safety grade. The only exception to this is the preferred offsite power sources which must also meet the require-ments of GDC 17 and GDC 5.
An example of a nonsafety grade AC source would typically be a-gas turbine generator that is connected to the offsite power sys-tem and utilizes the normal offsite power circuits to deliver power to the plant in an abnormal situation. Gas turbine generators have been accepted as alter-nate power sources for exposure-fire type events.
With respect to Millstone 3 spectfically, the Probabilistic Risk Assessment of the facility shows that the risk of core melt is dominated by station blackout (loss of offsite power and failure of the unit's two emergency diesel genera-tors).
Interties may, if properly implemented, reduce the predicted core melt frequency.
Such interties are permitted by current regulations as previously
~
discussed.
In summary therefore, the present staff position recommends against the sharing of safety grade power sources between nuclear units. This does not, however, prevent the use of appropriately designed electrical interties to allow a power source normally dedicated to one unit from also supplying power to another unit during abnormal situations, such as loss of all AC power in one unit.
Nonsafety-grade power sources may be connected between units provided their intercon-nections do not violate the normal design criteria for safety grade systems to which they may be connected.
Original signed by James H. Sniezek blictorStello,Jr.
1
' Executive Director for Operations gE:Y cc:
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- SEE PREVIOUS CONCURRENCE EICSB/DPA*
SL/EICSB/DPA*
BC/EICSB/DPA*
EICSB/ DBL
- PEICSB/DPB*
JLazevnick:ct JEKnight FRosa MSrinivasan OParr 3/18/86 3/18/86 3/18/86 3/18/86 3/18/86 AD/DPA*
ACT.D/DPA*
NRR*
D/DSR0 D/NRR CERossi TMNovak DEisenhut TSpeis HDenton 3/18/86 3/ 24 /86 3/ 27 /86 4/01/86 4/02/86 ELD
- EDO GHCunningham VStello 3/ 27 /86 3/
/86 0FFICIAL RECORD COPY
1 The Commissioners Distribution:
Central Files EICSB Rdg.
J.Lazevnick(PF)(2)
J. E. Knight F. Rosa M.'Srinivasan
- 0. Parr C. E..~Rossi T. Novak H. Denton G. H. Cunningham V. Stello EDO Rdg.-
D. Eisenhut B. Sheron T. Speis t.
J. Roe T. Rehm J. Sniezek J. Taylor C. Heltemes PWR-A Rdg. (2)(P. Baker)
D. Mossburg (WITS #860043)
PPAS T. Murley M. Bridges (#860043)
.