ML18024A726
| ML18024A726 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/09/1979 |
| From: | Gilleland J TENNESSEE VALLEY AUTHORITY |
| To: | Stello V Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7903140246 | |
| Download: ML18024A726 (5) | |
Text
REGUL
'RY INFORr>ATION OISTRIBUT I SYSTE<<(RIDS)
ACCESSION NBR:7903140246 OOC.DATE: 79/03/09 NOTARIZED: Nu FACIL:50-259 BROGANS FERRY iVUCLEAR POnER
- STATION, UiVIT 1, TEiVNESSEE O~'iNS FERRY VUCLEAR POAER STAT ION UNIT 2
TENNESSEE 50 29b 0>'rNS F E<H Y NUCLEAR PO'iiER ST A T I ON t UNI T 3 t TENNt SSEE AU
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A U 1'HOR AFFILIATION GILL LAlVOiJ.E.
TE4iVESSEE VALI EY AUTnORI TY REC IP.lvAME SEC IP IENT AFF ILIAT ION STELLOiV~
DIVISION OF OPERATING REACTORS DOCKET 05000259 05000260 05000296 SUB JECT
~
SUBillTS FOLLO'<>
UP REP T REQUIRED B Y IE BULLETIN 79 0 1 RE EiVVIRONrlENTAL QUALIF ICATION OF HSIV LI>IT S"i ITCHES ~ 0 ISCUSSES opEHAB ILI T Y REQUIRE'<ENTs rli coNGLUDEs QUALIF IG AT IDN UNNECESSARY AS OPERATION NOT REAUIHED OUH IiVG LOCA ~
DISTRIBUTION CODE:
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TITLE: GENERAL DISTR IBUT IOiV FOR AFTER ISSUANCE OF OPERATING L IC NOTES; i'>Z>:
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TOTAL NUblBER OF COPIES REQUIRED:
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500C Chestnut Street Tower II
~1arch 9
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. Victor Stello, Director Division of Operating Reactors Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
Dear Mr. Stello:
By my letter of February 23,
- 1979, we informed you that stem-mounted limit switches on the MSIV's on all three Browns Ferry units are of the type referenced in IE Bulletin 79-01.
Enclosed is the required 14-day followup report which discusses the operability requirements of the MSIV limit switches in the LOCA environment.
We have concluded that environmental qualification of the subject switches is unnecessary since their operation is not required during the LOCA.
Very truly yours, jIJ.
E. Gilleland Assistant Manager of Power Enclosure cc:
Mr. James P. O'Reilly, Director (Enclosure)
Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Region II Suite 3100 101 Mi rietta Street Atlanta, Georgia 30303 7908 r4029@
ENCLOSURE FOLLOWUP REPORT REQUIRED BY IE BULLETIN 79-01 REGARDING ENVIRONMENTAL QUALIFICATION OF MSIV LIMIT SWITCHES BROWNS FERRY NUCLEAR PLANT (
REFERENCES:
J.
P. O'REILLY'S LETTER TO H.
G.
PARRIS OF FEBRUARY 8 j 1979 AND J
~
E ~ GILLELAND S LETTER OF FEBRUARY 23,
- 1979, TO V. STELLO)
The inboard and outboard MSIV's on the Browns Ferry units have stem-mounted limit switches, model NAMCO SL3-B2W which are earlier versions of the type model EA-700.
These two models are essentially the same and are intended for general purpose application.
The contacts on the switches serve two pertinent purposes.
The first function is to display the open/close indication of the valves.
The second funct on involves reactor protection system input (scram logic) in case of simultaneous MSIV closure.
The subject switches have no control function with regard to the valve's actual operation und also do not interface the containment isolation logic in any manner.
During a postulated LOCA, only the inboard MSIV switches would be exposed to the accident environment, potentially failing.
However, reactor scram will be initiated by high drywell pressure or low vessel level, not iMSIV closure.
In fact, these same signals not only scram the reactor but also initiate the actual MSIV closure.
The only other possible deleterious condition is loss of position indication on the inboard MSIV's.
- However, it should be noted that the automatic closure signal to both the inboard and outboard MSIV's will be sealed in as a primary containment isolation signal and the valves will remain closed during the LOCA.
Therefore, position indication of the inboard valves is not required.
Position indica-tion of the outboard valves is not lost.
We have considered the various physical failure modes of the switches and have determined that the worst case would be a short to ground, blowing the power fuses in each contact circuit.
For the position indicating circuits, the result would be a loss of position indication for the inboard MSIV's.
Blown fuses on the reactor protection system circuit result in an additional scram signal being present since the scram relays are fail-safe; i.e., loss of power to trip.
Based on the evaluation presented
- above, we conclude that the MSIV limit switches do not have to be environmentally qualified since their postulated failure would not perturb the reactor system's response to a postulated LOCA.
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