ML20040D599
| ML20040D599 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 01/26/1982 |
| From: | Widner W GEORGIA POWER CO. |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20040D600 | List: |
| References | |
| TAC-10026, TAC-11262, TAC-47044, TAC-47045, TAC-47876, TAC-47877, NUDOCS 8202020070 | |
| Download: ML20040D599 (4) | |
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't"Cl aus January 26, 1982 AUanta G4:umit 30'iO2 Georgia Power W. A. Widner Vu PrePt und G< riera: Maaat;er k OSI.d and b'y'ff 0 benefabOU
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Director of Nuclear Reactor RegulE. tion U. S. Nuclear Regulatory Commission FEB 11982> To Washington, D. C.
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EDWIN I. HATCH NUCLEAR PLANT UNITS 1, 2 EMERGENCY POWER SYSTEMS Gentlemen:
In your letter dated December 10, 1981, you discussed the failure of the Hatch Unit 1 emergency power diesel-generators to energize the 4160 volt emergency engineered safety features buses during a simulation of total loss of offsite power to Unit 1 as reported by LER 50-321/1981-026.
The failure was caused by misoperation of two non-Class lE undervoltage relays which are part of the preferred offsite power system.
You stated that the present design of these relay circuits does not comply with applicable requirements of IEEE-279-1971.
The December 10, 1981 letter requested that Georgia Power Company (GPC) provide a schedule for implementing improvements in the design of the undervoltage relay circuits and provide a submittal date for the modified design.
In Appendix 1, the modified design is outlined and a schedule for its implementation is given.
Additionally, you requested that until the modified design is implemented, GPC should propose Technical Specifications which include surveillance of the undervoltage relays and associated components.
Our previous Unit 1 proposed Technical Specifications for the disconnection from offsite power in the event of loss of offsite power or a sustained degraded system voltage at the interconnection to offsite power were submitted on July 22, 1977, and amended on May 21, 1981, October 2, 1981, and December 2, 1981. Our submittal is again amended to reflect the requirements imposed by your December 10, 1981, letter.
For clarity and completeness, all proposed amended pages are included in Appendix 2.
Additional proposed Technical Specifications for Unit 2 are not required at this time.
The relays in question are functionally tested once per operating cycle (a minimum of once per 18 months) per a Hatch Unit 2 procedure used to meet Unit 2 Technical Specification 4.8.1.1.2.C.8.
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Georgia Pbwerd Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission January 26, 1982 Page Two The - Plant Review Board and the Safety Review Board have reviewed and approved the proposed change to the Technical Specifications and have determined that the probability of occurrence or the consequences of an accident or malfunction of equipment important to safety are not increased since the proposed changes impose additional requirements to assure proper operation of the onsite power system.
The possibility of an accident or malfunction of a new or different type than those previously analyzed is not created since the undervoltage relays would be tested under actual loss of voltage conditions on the IC start-up transformer.
Loss of offsite power conditions have been previously analyzed.
While the relays are being tested a loss of the ID start-up transformer (normal power supply) would result in the emergency diesels being tied to their respective buses.
Hence, the margin of plant safety is not reduced and no safety limits defined in the Technical Specifications will be affected.
If you have any questions, please contact this office.
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W. A. Widner states that he is Vice President of Georgia Power Company and is authorized to execute this oath on behalf of Georgia Power Company, and
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that to the best of his knowledge and belief the facts set forth in this letter are true.
GEORGIA POWER COMPANY By:
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a W. A. Widner to and subscribed be ore me this 26th day of Januag.jppg Swo Notary Pubhc. Gsorgia, o My Commission Empires Sept 20.1983
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Notary Public DLT/mb Enclosure xc:
M. Manry R. F. Rogers, III
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APPEtOIX 1 Undervoltage Relay Circuit Design 5
Question:
(Reference TEC letter of 12-10-81)
The present design does not comply with the applicable requirements of IEEE-279-1971.
From discussions between our staffs we understand that GPC is replacing the failed design with components which satisfy IEEE-279 requirements.
We regard these components, including the relays, potential transformers, associated auxiliary relays and their power supplies as safety-related equip:aent.
Response
During a simulated loss of offsite power (LOSP) test, the three onsite diesel generators failed to supply power to their respective class 1E 4KV buses.
The failure was attributed to two malfunctioning undervoltage (W) relays which monitor the availability of power on the second (alternate) of two offsite power sources.
Specifically, the malfunctioning W relays prevented the tripping of all three LOSP lockout relays.
The tripping of the lockout relays effectively locks out the offsite power source circuit breakers and provides permissives to close the diesel generator circuit breakers.
At present the lockout relays are tripped on a loss of bus voltage (indicative of a loss of the first or primary offsite pcwer source) concurrent with the loss of voltage of the alternate offsite power source.
The failure of the diesel generator breakers to close was a result of the malfunctioning of both W relays.
After the failure, our review of the logic design indicated that changes in the LOSP logic were warranted.
To correct this problem, GPC proposes a design change which will remove the dependency of the diesel generator loss of offsite power lockout relay circuit on the subject undervoltage relays.
Currently, the W relays that sense voltage on the IC transformer control two undervoltage auxiliary relay contacts which are in the lockout relay circuits.
The new design will use redundant time delay relays (2 per emergency bus) to control these contacts in the lockout relay circuit. The new time delay relays will be of the time delay to pickup type and will be controlled by the existing bus undervoltage auxiliary relays located in the diesel generator switchgear room.
For a loss of' bus voltage condition the new time delay relays will allow necessary circdit operation to occur which is required to close the 4160V bus alternate supply breaker.
Such action will be initiated before the time delay relay contacts are closed to trip t
the loss of offsite power lockout relay.
With th6 closure of the alternate supply breaker and re-energization of the 4160V emergency bus the time delay relays will reset.
If the bus is not re-energized, the time delay relays l
will close their contacts to trip the loss of offsite power lockout relay which will give the diesel generator supply breaker a permissive for auto closure and will trip the 4160V bus alternate supply breaker.
Two time This delay relays in parallel will be used in each circuit for redundancy.
i design will meet IEEE standard 279-1971.
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l APPENDIX 1 (Continued)
The existing undervoltage auxiliary relay contacts will remain in the diesel generator system test circuits and the automatic closure circuits for the emergency busses alternate supply breakers.
The function of the contacts in these circuits has been evaluated and determined not to degrade the capability of the standby diesel generator system to perform its required function for all postulated accident conditions.
Therefore, it is GPC's position that the design of the diesel generator test circuits and automatic closure circuits for the emergency busses alternate supply breakers meet the intent of IEEE standard 279-1971.
The design effort' has already begun to change this LN rela ing so that it meets the requirements of IEEE 279-1971.
This change will be implemented at the first opportunity following receipt of an soproved design package and parts.
GPC anticipates that the work on Unit 2 can be completed during the upcoming Spring 1982 outage.
Work on Unit 1 should be completed before the end of the Fall 1982 Unit 1 outage.
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