ML20046C558

LER 93-008-00:on 930706,possibility of MOV W/Brakes Failing to Perform Safety Function Under Degraded Voltage Conditions Due to Lack of Engineering Review.Identified & Reviewed MOV W/Motor Brakes for Safety significance.W/930804 Ltr

ML20046C558
Person / Time
Site:	Crystal River
Issue date:	08/04/1993
From:	Boldt G, Froats E FLORIDA POWER & LIGHT CO., FLORIDA POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
3F0893-03, 3F893-3, LER-93-008, LER-93-8, NUDOCS 9308110149
Download: ML20046C558 (5)

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Florida Power CORPORATION-

. Crystal River Unit 3 Docket No. 50-302 August 4, 1993.

3F0893-03  !

1 U. S. Nuclear Regulatory Commission  ;

Attention.: Document Control Desk l Washington, D. C. 20555 t

Subject:

Licensee Event Report (LER) 93-08 ,

Dear Sir:

Enclosed is Licensee Event Report (LER) 93-08 which is submitted in 1 accordance with 10 CFR 50.73. ..

.i Sincerely, ,  ;

8-l lheL '

l G. L. Boldt Vice: President l Nuclear Production .

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. Enclosure  !

xc: Regional Administrator, Region 11 ,

Project Manager, NRR  :

Senior NRC Resident Inspector-.

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100044 . , 1 9308110149 930804

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A Florida Progress Company 1 e

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l OdMane U.lL NUCLEAR KCJLATORY COMMISSION APPROVED OM8 NO. 3150-0104 EXPIPIS 6/31/96 N ATK)N C L ET . HOURS.

LICENSEE EVENT REPORT (LER) gggago,sVRDgETju,A;E g ig g AN O 1E APE E D T" CT 04).

OFFICE OF MANAGEMENT AND BUDOET, WASHIN TON DC 20603.

FAC1fTV NANC (1) DOCKET NUMBER (2) PAGE (3)

CRYSTAL RIVER UNIT 3 (CR-3) 01510 l 0 l 013 l 0 l 2 1 loFl 0 l 4 TTTLE (4)

Due to a Lack of Engineering Review, Motor Operated Valves With Brakes Could Fall to Perform Their Safety Function Under Degraded Voltage Conditions EVENT DATE (6) LER NUMBER (s) KPORT DATE F) OTHER FACILITIES INVOLVED (s)

SEQUENTIAL - - REVISION FACILfrY NAMES DOCKET NUMBER (S)

MONTH DAY YEAR YEAR HUMBER  : NUMBER MONTH DAY YEAR N% 0l5l0l0l0l l l 0l7 0l6 9 3 9l3 -

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0l0 0l8 0l4 9l3 N/A 0l5l0l0l0l l l OPERATING THIS REPORT IS SUBurTTED PURSUANT TO THE KQUIREMENTS OF 10 CFR $: (CHEC4 ONE OR MORE OF THE Fot. LOWING) (11)

MODE (9) 1 20.402(b) 20.405(c) 60.73(aV2Xiv) 73.71(b)

POWLll 20.405(aXIXI) 50.36(cXI) 60.73(aX2Xv) 73.71(c)

(10) l1 l 0l 0 20.406(aX1X10 50.36(cK2) 60.73(aX2Xvil)

CTHERf a see 20.405(aX1)(lil) 50.73(aX2)(I) 50.73(aX2XvillXA) spaaf 20.405(aX1Xiv) X 50 73(aX2XII) 60.73(aX2Xviii)(B) 20.406(aX1Xv) 60.73(aX2Xiii) 60.73(aX2Xx)

UCENSEE CONTACT FOF4 THis LER(12)

NAME TELEPHONE NUMBER AREA CODE E. E. Froats, Manager, Nuclear Compliance 9l0l4 $l 6 l 3 l- l 4l 7 l 0 l 5 COMPLETE ONE UNE FOR EACH COMPONENT FAILURE IN THtS KPORT (13)

CAUSE SYSTEM COMPONENT MANUFAC. REPORTABLE  : > -

CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLE TURER TO NPRDS TURER TO NPRDS t

I l I I I I I I I I I I I I U '

I I I I I I I l l l l l l l BUPPLEMENTAL KPORT EXPECTED (14) EXPECTED MONTH DAY YEAR SUBMISSION

] YES f#r e sonques EXPECTED #v8wspoND47D NO DATE (16) l l l AssiRACT Am.n so noe spee . a... wa== aHr m w c. trp-m Ni (te)

On July 6,1993, Crystal River Unit 3 (CR-3) was in Mode 1 (POWER OPERATION) at ,

100% Rated Thermal Power producing 859 Megawatts. A High Pressure' Injection

• suction valve was determined to be inoperable. An earlier concern had been raised for the operability of sefety related Limitorque motor operated valves (MOV) with an electrical motor brake option installed. Minimum operating voltages were found to be different for a valve motor versus the motor brake. A 1991 calculation showed that under degraded voltage conditions,- valve motors -

will have sufficient voltage to accelerate their load. However, MOVs with motor brakes installed may not receive sufficient voltage to release the brake. The motor will attempt to operate the valve, but valve movement may be prevented by the brake. The valve therefore may not be capable of performing its safety function. This is a condition outside the design basis. The cause was a lack of engineering review for the motor brake' voltage requirements. Seven safety ,

related valves have been identified with this condition. Four of the valves are locked in position during plant operation. One valve with one type of brake was successfully tested. The remaining two valves have had the brakes removed.

NRc F- = ,w

NHCfCHM3e&A U.S. NCLEAR Gout.ATC?tY COMMISSION CPPROVED OM8 NO. 3160-4104

- EXPIGS 6/31/96 LICENSEE EVENT REPORT (LER) g T,r;D 4nDr g g g g g g g TEXT CONTINUATION gg7gggg Tge y,cg E $ sS ATP RV "Hi P b 1 L OFHCE OF MANAGEMENT AND BUDGET, WASHIN TON DC 20603, f A011TYNAME(1) DOCKET NUMDER(2) (Dt NUMBER (t0 PAGE (3)

SEQufNTIAL REVISCN CRYSTAL RIVER UNIT 3 (CR-3) ol 5l ol 0] ol 3l ol 2 el3 -

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ol0 o l 2 lOFl o l 4 TEXT (# more am a seeded use ai* stores uc perm assa e (17)

EVENT DESCRIPTION:

On June 6,1993, Crystal River Unit 3 (CR-3) was in Mode 1 (POWER OPERATION) at 100% Rated Thermal Power producing 863 Megawatts. During the process of reviewing the draft dedication and seismic qualification plan for a spare motor and brake assembly for FWV-28 [SJ,ISV] a Limitorque motor operated valve (MOV), a discrepancy was identified between the acceptance criteria for the electrical brake minimum operating voltage versus the valve motor minimum voltage acceptance criteria. A review was conducted to determine the design requirements for the brakes and to identify other safety related MOVs with similar brakes. Six other safety related valves were found with this condition. ,

On June 28, 1993, a concern was then identified for the operability of these i valves. A calculation performed in 1991 showed that under degraded voltage conditions, valve motors will have sufficient voltage to accelerate their load.

However, the motor brakes did not receive degraded voltage operation review. The ,

brake function is to protect the valve from excessive mechanical thrust by stopping l motor and valve inertia after power cut off. The brake coil [CL] is connected in parallel to the motor. The braking action is released with the energizing of the brake coil. Upon power cut off, the coil is deenergized and the brake clamps onto the valve motor shaft. The motor brake has a more restrictive operating range of j 460 VAC +/- 10 percent than analyzed for the valve operator. This more restrictive  !

motor brake operating voltage range results in the possibility the MOVs may be exposed to voltages within design operating ranges but lower than required to operate the brake coil. With insufficient voltage to release the brake coil, the valves could be unable to perform their safety function.

Limitorque Maintenance Update 92-2, Section 7 " Significance of Motor Brakes on Actuator Motors" indicates that the brake does not substantially minimize the inertial overshoot of the valve drive train for this type of valve. The. vendor confirmed this type of valve will function properly without brakes.

On July 6,1993, CR3 was in Mode 1 at 100 percent Rated Thermal Power producing 859 Megawatts. At 1700 on that day, MUV-58 [BQ,ISV], the normally closed High Pressure Injection (HPI) [BQ] suction valve from the Borated Water Storage Tank (BWST)

[BP,TK], was declared inoperable and the Action Statement for Technical .

Specification (TS) Limiting Condition for Operation (LCO) 3.5.2, ECCS Subsystems -

Tava > 280*F, was entered. The TS was exited on July 7,1993 at 0405 upon removal of the stationary and rotating discs for MVV-58 which permanently de-coupled the motor from the brake assembly. The electrical power connections to the brake were also removed. This modification was performed on MUV-73 [BQ,ISV), the normally open BWST suction valve, as well.

This is a condition outside design basis and is reported in accordance with 10 CFR 50.73(a)(2)(ii)(B).

NHC Form 386A (649)

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( ORM aneA U.S. NUCLEAR GOUT 4TCM COMMESION APPfC>>ED OMB NO.3150-0104 E%PKIB 6/31/96 ' '

LICENSEE EVENT REPORT (LER) (s,TgTgD rnDE g w g s,r g g g r gN TEXT CONTINUATION gggagogugNyggTgEgcgg NYo*THSAF Fd T Pi IJ 1 104),

omCE OF MANAGEMENT AND BUDGET, WASH N TON DC 20603.

FAC3.HY NAME (1) DOCKET NUMHER f4 LEH NUMBER (6) PAGE (3)

SEQUENT W MVISON CRYSTAL RIVER UNIT 3 (CR-3) ol 5l cl 0l 0l 3l ol 2 sl3 -

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CAUSE:

The cause of the condition is considered to be a lack of engineering review for the motor brake voltage requirements. Although the motor brake symbols appear on relevant drawings, the voltage requirements for the motor brakes were not determined when degraded voltage calculations were being performed. In CR3's configuration, the brake is wired in parallel with two phases of the three phase 460 VAC power feed to the valve operator electric motor. As such, the brake was considered part of the motor and did not receive a separate review.

EVENT EVALUATION:

Seven safety related valves were identified with motor brakes installed. Four valves are locked in their safety function position during plant operation and are not a concern. One valve with a motor brake manufactured by Sterns was tested and is operable with voltages above 75 percent (345 VAC). The remaining two valves (MUV-58 and MUV-73) have motor brakes manufactured by Dings Dynamic Group.

The event of concern involves a postulated low voltage condition in the 230 kV switchyard above the Second Level Undervoltage Relays (SLURS) [27] setpoint coupled with an Engineered Safeguards (ES) actuation and subsequent block loading. With switchyard voltage at the low end of the SLURS setpoint and with accident loads applied via block loading, during BLOCK 1 MUV-73 and MUV-58 receive 377.1 VAC and 381.2 VAC respectively.

The vendor for these motor brakes has indicated that the brake coil could fail at a +/- 10 percent voltage differential. This places the lower limit for motor brake voltage at 414 VAC. If voltage remains above the SLURS setpoint, the Emergency Diesel Generator (EDG) [EK,DG] does not connect to the bus to restore adequate voltage. And, as long as voltages remain below 414 VAC, insufficient voltage to release the brake coil may exist and the valves could be unable to perform their safety function.

These valves provide HPI suction to the Makeup Pumps (MVP) [BQ,P] from the BWST during accident conditions and are required to open on an HPI signal. Normal plant configuration is for one of these valves to be open and the other closed. Upon an HPI signal with voltages above the SLURS setpoint, the MOVs with motor brakes will be block loaded to the degraded hus. If the closed valve fails to open, the operating MVP will not be realigned to the BWST and will rapidly draw down the Makeup Tank (MUT) [CB,TK]. Damage to that MUP will occur if suction pressure is lost. At that point, and under an assumed simultaneous single active failure of the other ES selected MVP to start, HPI would be unavailable until operator action can align and start the third MVP.

The event could also be mitigated by operator action to supply the ES buses with power from the EDGs. .

l NfC Form 366A (6-80)

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omcE oF MANAGEMENT AND BUDGET. ton Oc 20503.

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SEQUENTIAL .

AfvimON CRYSTAL river UNIT 3 (CR-3) 0l 5l 0l 0l 0l 3l 0l 2 9l3 -

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0l0 0 l 4 lOFl 0 l 4 TEXT tv mee spese e i end use amoresas; one rw. seam'e (17)

CORRECTIVE ACTIONS:

All safety related MOVs with motor brakes have been identified and reviewed for safety significance. MUV-58 and MUV-73 have had their motor brakes removed.

Applicable drawings will be revised to more accurately reflect the motor brake option. The lack of a separate engineering review for these valve operator subcomponents is considered an isolated event due to the manner in which they were wired as part of the motor. Engineers will be advised of this occurrence to increase the awareness for vendor supplied subcomponents when performing operability reviews or preparing design packages.

PREVIOUS SIMILAR EVENTS:

There have been three previous Licensee Event Reports (LER) generated due to potentially inadequate voltage to safety related components, two of which included degraded grid voltage concerns (LER 92-007, LER 92-010 and LER 92-020).

NRc Fwm 386A(649)

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