ML17222A699
| ML17222A699 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 02/28/1989 |
| From: | Conway W FLORIDA POWER & LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| L-89-74, NUDOCS 8903080035 | |
| Download: ML17222A699 (4) | |
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'ccp~~TED DI~BUTlON DEMOÃs~04 SY) TEM
'EGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
ACCESSION NBR:8903080035 DOC.DATE: 89/02/28 NOTARIZED: NO FACIL:50-335 St. Lucie Plant, Unit 1, Florida Power
& Light Co.
50-389 St. Lucie Plant, Unit 2, Florida Power
& Light Co.
AUTH.NAME AUTHOR AFFILIATION CONWAY,W.F.
Florida Power
& Light Co.
RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
SUBJECT:
Forwards addi info.requested re anticipated transients w/o scram.'ISTRIBUTION CODE:
A055D COPIES RECEIVED:LTR ENCL SIZE:
TITLE: OR/Licensing Submittal:
Salem ATWS Events GL-83-28 NOTES:
DOCKET 05000335 05000389 RECIPIENT ID CODE/NAME PD2-2 LA NORRIS,J INTERNAL: ACRS NRR LASHER,D NRR/DEST/ICSB 7
NRR/DLPQ/QAB 10
,S-STRACT REPTILE 01 EXTERNAL: LPDR NSIC COPIES LTTR ENCL 1
0 1
1 6
6 1
1 1
1 1
0 1
1 1
1 1
1 1
1 RECIPIENT ID CODE/NAME PD2-2 PD ARM/DAF/LFMB NRR/DEST/ESB 8D NRR/DEST/PSB 8D NRR/DOEA/GCB 11 OGC/HDS2 RES/DS IR/EIB NRC PDR COPIES LTTR ENCL 3
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NOIR 'IO ALL "RIDS" RECIPZEÃIS:
PLEASE HELP US 'IQ REMKZ WASTE.'GNI'ACT 'IHE DOCUMENI'ONGEAL DESK, ROOM Pl-37 (EXT. 20079)
KO ELOHI2QQP. 'YOUR NME FROM DISXVUBVTIGN LXSTS FOR DOCUMENIS KKJ DGNiT NEEDt TOTAL NUMBER OF COPIES REQUIRED:
LTTR 25 ENCL 19
P.O. Box14000, Juno Beach, FL 33408-0420 FEBRUARY. 2 8 ]989 L-89-74 10 CFR 50.62 U. S. Nuclear Regulatory Commission Attn:
Document Control Desk Washington, D.
C.
20555 Gentlemen:
Re:
St. Lucie Units 1 and 2
Docket Nos.
50-335 and 50-389 Request for Additional Information Antici ated Transients Without Scram ATWS By letter dated May 18, 1988 (E.
G. Tourigny to W. F. Conway), the NRC requested additional information concerning the Florida Power Light Company (FPL) plant-specific ATWS Diverse Scram System (DSS) conceptual
- design, submitted by letter L-87-301 dated July 15, 1987.
By letter L-88-343 dated August 15,
- 1988, FPL provided a partial response to this request for additional information.
Attached is the response to Question 4.
This completes FPL's response to this request for additional information.
Should there be further questions, please contact us.
Very truly yours,
~W. F.
Seni nway ice President Nuclear WFC/EJW/gp Attachment cc:
Malcolm L. Ernst, Acting Regional Administrator, Region II, USNRC Senior Resident. Inspector, USNRC, St. Lucie Plant 8903030035 890223 PDR ADOCK 05000335 P
l4
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l 4 v
PAGE 1 OF 2 FLORIDA POWER
& LIGHT COMPANY ST I,UCIE PIANT -UNITS 1 & 2 ATWS - RESPONSE TO NRC QUESTION 04 BREAKER DIVERSITY l.
Introduction -
On July 15, 1987, the Conceptual Design for a Diverse Scram System (DSS) was issued by FPL to describe how FPL was going to meet the requirements of the ATWS Rule, 10CFR50.62, "Requirements for Reduction of Risk from Anticipated Transients Without Scram (ATWS) Events for Light-Water-Cooled Nuclear Power Plants".
In the conceptual
- design, the Control Element Assembly (CEA) Motor~nerator (MG) set output breakers were selected as the final actuating devices for the DSS.
By opening both MG set output breakers with a signal from the DSS logic, voltage to the reactor trip switchgear buses and consequently to the CEA drive mechanisms would be removed, causing a Unit shutdown.
Both St Lucie Units 1 and 2 function similarly.
Upon review of the conceptual
- design, the NRC expressed concern for the degree of diversity between the MG set output breakers and the reactor trip switchgear breakers, prompting FPL to examine that portion of the conceptual design for an alternate method of DSS actuation.
This concern was expressed in Question 84 of the NRC Request For Additional Information, May 18, 1988 and is answered herein.
24 estion
& Res onse Question 84:
Using circuit breakers from different manufacturers is generally not considered sufficient to provide the required diversity for interruption of control rod power.
In general, circuit breakers from different manufacturers are considered susceptible to common mode failure (CMF) because of common design features such as mechanical linkage (consisting of springs, pivots, latches,
- pins, cams, etc.) that are sub)ect to binding/malfunction from a number of causes (e.g., dirt, corrosion, improper lubrication, etc.) as has been demonstrated through operating experience.
Please provide information 'that demonstrates physical hardware diversity of the CEA drive MG set output breakers from the reactor trip breakers actuated by the RPS.
Response
Due to the NRC's concern for diversity between the reactor trip breakers and the CEA drive MG set output breakers, FPL conducted an investigation of alternate methods for ATWS actuation, including the use of MG set output contactors
.and interruption of the MG set generator field.
0727I
PAGE 2 OF 2, It was determined that interrupting the MG set field was not a satisfactory method of de-energizing the reactor trip switchgear due to output voltage decay rates, potential damage to the MG sets, high residual output voltage after decay, and eventual tripping of the MG set output breakers, (making the output breakers the final actuation devices).
The investigation into the use of a contactor installed at the output of each MG set showed that this was a satisfactory method of de-energizing the reactor trip switchgear and met the diversity requirements.
Some interlocks between the HG set control circuits and the contactors may be necessary, although there will be no detrimental effects to the reliability of the HG sets or the safety functions of the reactor trig switchgear.
3.
Conclusion FPL proposes as part of their conceptual design, to de-energize the reactor trip switchgear to initiate a diverse scram by opening a load contactor at the output of each MG set.
The installation of the contactors will meet the diversity requirement without compromising the functions of the MG sets or the reactor trip switchgear.
4.
References 10CFR50.62 Requirements for Reduction in Risk from Anticipated Transients Without Scram (ATWS) Events for LightWater-Cooled Nuclear Power Plants (ATWS Rule)
FPL letter L-87-301 dated July 15, 1987 Conceptual Design for a Diverse Scram System and the Reactor Trip System/Auxiliary Feedwater Actuation Diversity Study 0727I