05000309/LER-1990-001, :on 900207,failure of Environ Qualified Limit Switch Occurred.Caused by Moisture Entering Limit Switch,Due to Inadequate Sealing of Conduit & Corroded Terminal.Switch Replaced W/Identical Model
| ML20059H314 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 09/05/1990 |
| From: | Nichols S, Oesterling L Maine Yankee |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LER-90-001, LER-90-1, MN-90-88, SEN-90-253, NUDOCS 9009170104 | |
| Download: ML20059H314 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(1) |
| 3091990001R00 - NRC Website | |
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MaineYankee 4uitgygE[Tirr63Riijs]EwR33 EDISON OR!VE
- AUGUSTA. MAINE 04336 ? (207) 622 4868
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l September 5, 1990 MN-90-88 SEN-90-253 i
UNITED STATES NUCLEAR REGULATORY COMISSION Attention: Document Control Desk Washington, DC 20055
References:
(a) License No. DPR-36 (Docket No. 50-309)
(b) Maine Yankee Letter to USNRC dated March 9, 1990 (MN-90-25) -
LER 90-001-00 Subject: Maine Yankee Licensee Event Report 90-001 Failure of Environmentally Qualified Limit Switch Gentlemen:
Please find enclosed Maine Yankee Licensee Event Report 90-001-01.
This report is submitted in accordance with the requirements of 10 CFR 50.73(a)(2)(ii) and supplements that information previously provided with Reference (b).
Very truly yours,.
SEddh S. E. Nichols Licensing Section Head SEN:SJJ Enclosure c:
Mr. Thomas T. Martin Mr. Eric J. Leeds i
Mr. Charles S. Marschall
- - Mr. Patrick J. Dostie 1
a W'l*& WEN N
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NRC Form 366 U.S. Nuclear Regulatory Comission (9-63)
Approved OM8 No. 3150-0104 LIC[N5([ [ VENT RtPORT (LtR)
Expires: 8/31/85 i
c facility Name(l)
Docket Number (2)
Panef31 Maine Yankee Atomic Power Company 0 15 10 10 10 13 10 19 1 lofl31
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11tle(4)
FAf tuRE or (NylRONMf NTALLY OUALIFit0 I fMIT $ WITCH
[ vent Datef51 lER Numbertf.)
Reoort Datef7)
Other Fact 11tien involvedf B)
Month Day Year Year Sequential Revision Month Day Year Facility Names Docket Number (s, huber Number ilIIl1!
0 1 0 11 0 !
1__ 0 19 0 15 910 li1l1Il
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Of P 01 7 9 0 910 Ihts Report is Submitted Pursuet to the R64uirements of 10 CFR 6 Operating 7
ftheck one or more of the fol%rino) fil)
Mode 9) 20.402(b) 20.405(c) 50.73(a)(2)(lv) 73.71(b)
Power 20.405(a)(1)(1) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c) level 0
9 8
to.405(a)(1)(11) 50.36(c)(2) 50.73(a)(2)(vil)
Other (5pecify in fle) 20.40$(a)(1)(11t) 50.73(a)(2)(1) 50.73(a)(2)(vlii)(A)
Abstract below t. 20.405(a)(1)(lv)
& $0.73(a)(2)(11) 50.73(a)(2)(vlit)(B) and in Text. NRC 1
P0.a05falft)(v) 50.73falff)fiti) 50.73falfPlfr)
Forn 366A)
LICENSEE CONTACT FOR THIS LER (IP' NAME Teleobone Number Lisa Oesterling, Nuclear Safety (ngineer AreaCodel
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P I 0 1 7 18 18 12 16 13 f f,,j.L 00MPLE1[ ONI LINE FOR E ACH COMPONEN' F AllURF DEstR BED IN "His REPORT (13)
Com-Manufac-Reportable Com-Manufac-Reportable Cause $votem nonent i urer to NPROS Cause Syntem nonent urer to NPRDS o
Sunclemental Report Fxceeted fla)
Expected Month Day Year Submission (If yes, complete Expected Date(15)
! Yes Sutsission Date)
XI No l
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ABSTRACI (Limit to 1400 spaces, i.e., approximately fifteen single space typewritten lines) (16) t While operating at 98% power, Maine Yankee identuied a failed environmentally quallfled ([Q) limit switch located inside the containment. The limit switch provides main control board position indication of an isolation valve for the primary sampling system. The valve closes on a 5afety Injection or Containment Isolation signal, or may be operated from the main control board.
Investigation revealed that moisture entered the limit switch, due to inadequate sealing of the conduit, and corroded a terminal. The limit switch provides position indication only and does not affect valve operation. The valve remained operable at all times.
The switch was replaced with an identical model. The new switch and conduit were bench assembled and sealed to ensure proper construction. The conduit orientation was changed to enter below the limit switch and holes were drilled in the conduit such that any colstura in the conduit would drain out.
Maine Yankee subsequently upgraded thirty-six EQ limit switch conduit seals with new pre-sealed
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connector assemblies during the 1990 Refucting Outage. Fourteen of these thirty six seals had
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previously been made in the same time period as the one found failed in February 1990; the second )
switch for that valve was not reworked as it had been inspected and found satisfactory. Two of
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the thirty-six seals were found to have been improperly installed.
1 The remaining (Q limit switches have been inspected ano found satisfactory. The seals for these
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and the two on the primary sampling systee valve will be upgraded during the 1991 Refueling
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Outage.
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U.S. kuclear Regulatory Casunission '(9-83)
Approved OMB No. 3150-0104 Expires: 8/41/85 LICENSEE EVENT REP F, (LER) TEXT CONT]NUATION b
facility Name(l)
Doctet Number (2)
LER Number (M Panof3)
~
Year Sequential Revision Maine Yankee Atom M Power Company Ntsnber Nam iber Ol5'01010131019 910 0 l 0 1 1-0
_1 2
of 31
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TEXT (if more space is required, use additional NRC Form 366A's) (17).
On February 7,1990, while operating at 98% pccr, Maine Yankee detemined that an l;
environmentally quellfled (EQ) limit switch (33) located inside the contalment had failed due to 4
a moisture corroded terminal inside the limit kwitch. Motsture entered the limit switch due to inadequate sealing of the conduit (CND). The failed limit switch provides main control board position indication for the priinary sampling system A train isolation valve (ISV), PS-A 20.
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The valve automatically closes on a Safety injection or Containment Isolation signal, or may be operated f rcan the main control board. The failed limit switch provides main control board position indication only, and does not affect valve operation. Tne v.Ive remained operable at 4
all times, and alternate indication was available via a second limit switch. Keine Y(nkee Emergency Procedures direct the operator to manually close the valve in the case of incorrect (or T
f ambiguous) indicated position. The valve is normally in the cirmed position.
The NAMCO Model EA 180 limit switch conduit is t cled with 3M Scotchcast #9 conduit sealer (potting compound), a two part epoxy. The epoxy is injected into the conduit in I? quid fom and contairad with a dem while curing. In the case of this failed seal, voids we e present in the cured epoxy, leaving the conduit unsealed. Motsture entered through a fittin and e
collected in the limit switen, eventually corroding a terminal and causing the switch failure.
The conduit orientation with respect to the switch aggravated the problem; th* en!uit da vertically down to the limit switch, such that any moisture in the conduit wo h "tlect in the switch should the seal f ail.
The switch was replcced with an identical model. The new switch and conduit were bent assembled and sealed to ensure proper construction. The conduit orientation was changed to ente below the limit switch and holes were drilled in the conduit such that any moisture in the condui would drain out. The se o nd PS-A 20 limit switch was unaffected, but was inspected for moisture
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intrusion and found satisfactory.
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In 1987, environmentally quallfled limit switches were inspected and sixteen (16) of 64 limit switches (including the two on PS-A-20) were noted to h ve conduit seal discrepanctr.s.
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k The condults were resealed tr, place using a corrective action procedure which was developed to
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repair the potential seal problems. Subsequently, a procedure was generated for future
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mi.intenance, and new installations, of EQ limit switches; this new procedure requires a low point drain in the condult.
The connections for fourteen of.the fifteen additional EQ limit switches, which had conduit seal
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discrepancies in 0 87 similar tn PD A-20, were upgraded with new NAMCO Hodel EC 210 pre-sealed
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connector assemh tes during the 1990 Refueling Outage; the second switch on PS-A 20 was not
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rewe r*ed, as it had been inspected and found satisfactory. The new installattens included
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a low point d%1n in the condult. An additional twenty-two limit switch conduit seals were
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a upgraded w1" the new NAMCO connector assembiles. The remaining EQ limit switches on the
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current Eter List (40) were inspected for moisture intrusion and found satisfactory,
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~aU.S. Nuclear Regulatory Consission (9-83)'
Approved OMB No. 3150-0104 Expires:-8/31/85 LICENSEE EVENT REP'1RT (LER) TEXT CONTINUATION Facility Name(!)
Docket Number (!)
LER Number M)
Panof3)
Year Sequential Revision Malne Yankee Atomic Power Company Number Nunber 015101010131019 910 010i1 0
1 3
of 3I J-TEXT (if more space is required, use additional NRC Form 366A's) (17)
During the upgrade work performed during the 1090 Refueling Outage, two additional limit switch
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conduit sesis were found to have been improperly installed. The first was on the high pressure
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drain cooler outlet isolation valve, DR-A-6.
The second was on PCC-A 270, the control element
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i drive mechanism cooler isolation valve. Both valves operate automatically on a Contalrnent
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Isolation / Safety injection Actuation (C1/SIA) signal to isolate their respective coolers.
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These limit switches provide main control-board position indication only, lhe limit switch
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conduit seals were replaced with the new NAMCO connectors.
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1 The limit switch foi DR A-6 was found to be missing Scotchcast resin potting compound in the
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EYS conduit fitting. Further inspection revealed that the EYS fitting had probably been -
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installed without a des or potting compound. No moisture or corrosion was found within the
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limit switch. During dycle 11, the valve operation indicated properly, but probably would have
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4 falled to indicate vahe position during a design basis event. However, this would not have
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prevented the valve frce operatig un 3 CI/SIA signal during a design basis event.
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The limit switch for N C-A-270 was found one-quarter filled with Scotchcast resin potting
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compound. Thit result ad because the danning material had not been properly installed. Even
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though corroshn was evident inside tne limit switch due to moisture intrusion, the malt. control
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1 board position indication worked properly during Cycle 11. Since this limit switch provides
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position indication only for PCC-A-270, the valve would have operated as required during a design ]
basis event.
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In order to ensur; the continued integrity of EQ limit switches, Maine Ya.nkee plans to upgrade
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the remaining fod.-" c Scotchcast #9 conduit seals (includes the two on PS-A-20) with NAMCO'
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connector assemblie. auring the 1991 Refueling Outage.
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