ML17262A867
| ML17262A867 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 04/13/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17262A865 | List: |
| References | |
| NUDOCS 9205280250 | |
| Download: ML17262A867 (10) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20666
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SAFETY ALUAT ON REPO T
EVALUATION OF USE OF BUS TIE BREAKE G
NN UCLEAR POWER OCKET NO. 50-4 Back round The Special Inspection Branch performed a Service Water System Operational Performance Inspection (SWSOPI) for Rochester Gas and Electric (RG&E) Corporation at Ginna nuclear power plant (GINNA).
The inspection team identified that if either emer'gency diesel generator (EDG) failed during a recirculation phase of design basis accident (DBA) the bus tie breaker would be used to connect the redundant safety buses in order to supply power from the remaining EDG.
This is needed in order to obtain two service water (SW) pumps required under the licensing basis and Technical Specification
(>S).
The project directorate requested that the Electrical Systems Branch evaluate whether the use of the tie breaker is appropriate under this condition and whether it conforms with the guidance provided in Generic Letter (GL) 91-11 regarding interlocks and LCOs for Class 1E tie breakers.
Evaluatio The safety bus system for GINNA consists of four Class 1E 480 v buses (14, 16, 17, and 18).
Emergency power to buses 14 and 18 is provided by EDG 1A, and emergency gower to buses 16 and 17 is provided by EDG 1B.
Buses 17 and 18 can be connected by closing the bus tie breaker (52/BT 17-18).
Similarly buses 14 and 16 can be connected by closing the bus tie breakers (52/BT 14-16).
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l configuration is part of the licensing basis of the GINNA plant (Newer designs have been required to provide two bus tie breakers in series)
Buses 17 and 18 each supply power to two SW pumps (total of four SW pumps).
Our review of TS 3.3.4.1.a indicates that two SW pumps (one from each of the redundant buses 17 and
- 18) are required to be operable for reactor conditions above cold shutdown.
The licensing basis (table 9.2-5 of Updated FSAR) also requires a minimum of two SW pumps during the recirculation phase.
The licensing basis also requires conformance of the design to the single failure criterion (see Recommended Action IV of GL 89-13, Service Water System Problems Affecting Safety-Related Equipment).
With only one pump per bus operable the single failure criterion is met for failure of an EDG through use of the bus tie breaker (52/BT 17-18).
However, this criterion is not met for a bus fault type of failure because the bus tie breaker cannot be used in this case (both passive and active electrical failures must be assumed see footnote (2) in 10 CFR 50, Appendix A).
The argument posed by the licensee in the UFSAR that GINNA was designed for conformance to the criteria that preceded the GDC and that these criteria precluded consideration of passive electrical failures is not valid; and in any event, this argument is irrelevant since the catastrophic failure of a breaker (an active component) on the bus must be considered a bus fault which would prevent use of the tie breaker.
- Also, a
failure of one of the two available pumps would not meet single failure even though power to both buses would be available.
The bus tie breakers require special consideration (such as administrative controls to remove breakers from their cubicles or otherwise lock them open)
- because, when left closed, they could compromise the independence of the redundant safety-related buses and may prevent loading of both EDGs.
Over the years, the staff has found that in some plants the tie breaker had been left
C
closed inadvertently for a substantial period of time.
To resolve this concern, under the resolution of Generic Issue GI-49 "INTERLOCKS AND LCOs FOR CLASS 1E TIE BREAKERS" and pursuant to 10 CFR 50.54(f),
GL 91-11, the staff requested all licensees to provide a written response to certify whether procedures exist which contain time limitations and surveillance requirements for tie breakers.
By letter dated February 3,
- 1992, RG6E provided its response regarding how tie breakers at GINNA conform to GL 91-11 guidance.
Based on the above response, SELB has evaluated the appropriateness of using the tie breaker (52/BT 17-18) at GINNA during a
SW recirculation phase of DBA.
The licensee's response.
states that:
1 ~
the above tie breaker is maintained in the test position which would prevent its closure electrically and mechanically to the bus.
With the breaker racked in (connected to the bus),
the control scheme is designed such that: the bus tie breaker can only be closed if either bus 17 or 18 is de-energized from its normal and emergency sources.
Once the tie breaker is closed, the diesel generator breaker and normal supply breakers of the previously de-energized bus can not be closed without first
-opening the tie breaker.
2 ~
the current Specification 3.7.2.1.a.2 of TS requires that the tie breaker remains open when the plant is not in cold shutdown condition (above 200 degree F).
Also the TS surveillance 4.6.3.a.3 requires that the tie breaker be verified at least once per 7 days that it remains open when the plant mode is above 200 degree F.
3.
the continuous monitoring of the tie breaker position is annunciated in the control room.
conclusion Based on our review of the licensee's submittal, we find that adequate time limitations and surveillance requirements exist at GINNA for the proper use of the tie breakers on occurrence of loss of offsite power and failure of one
On this
- basis, we conclude that the use of the tie breaker (52/BT 17-18) during the recirculation phase of a DBA is acceptable.
Additionally, the plant does not meet its design basis in regard to the single failure criterion.
However, this issue can be resolved by (1) revising the TS to require that two SWS pumps be operable on each Class 1E bus, or (2) verifying by analysis that only one SWS pump is required for the recirculation phase of a DBA.
,(
S LP F CILITY NAME:
R.
E. Ginna Nuclear Plant S
RY OF REVIEW:
The Special Inspection Branch performed a Service Water System Operational Performance Inspection (SWSOPI) for Rochester Gas and Electric Corporation at Ginna nuclear power plant (GINNA).
The inspection team identified that if either emergency diesel generator (EDG) failed during a design basis accident (DBA) the bus tie breaker would be used to connect the..redundant safety buses in order to supply power from the remaining EDG.
We have evaluated the use of tie breaker issue raised during the SWSOPI inspection.
We find that adequate time limitations and surveillance requirements exist for the proper use of the tie breakers and that this is consistent with the guidance provided in GL 91-11.
We conclude that the use of tie breaker in this mode is acceptable.
NARRATIVE DISCUSSION OF LICENSE PER ORMANC FUNCTIONAL AREA:
NG NEERING EC SU 0
0 The licensee's response to GL 91-11 was not intended to respond to the SW system concerns raised during Service Water Operational Performance inspection.
However, the licensee response to GL 91-11 identified all pertinent procedures and Technical Specifications that the staff used in the evaluation of the tie breaker without any additional interactions with the licensee.
We find that the licensee's overall performance on this issue is adequate.
~ut or: P.
Kang Date:
3/25/92