ML18150A171

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LER 87-011-00:on 870516,low Flow Reactor Trip Occurred. Caused by Hot Leg Loop Stop Valve Stem Failure Permitting Disc to Drop,Blocking Loop Flow.Procedure Revised to Reduce Stress on Valve stem.W/870612 Ltr
ML18150A171
Person / Time
Site: Surry Dominion icon.png
Issue date: 06/12/1987
From: SAUNDERS R F
VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
87-013, 87-13, LER-87-011-01, LER-87-11-1, NUDOCS 8706230353
Download: ML18150A171 (4)
v • d • e


Text

POW 28-06-01 *.* -NIIC Form 391} U.S. NUCLEAR REGULATORY COMMISSION 19-83) APPROVED OMII NO. 3150-0104 LICENSEE EVENT REPORT (LER) EXPIRES: 8/31185 FACILITY NAME 11) I DOCKET NUMBER 121 I PAG~ 131 Surrv Power Station. Unit 1 o I 5 I o I o I o I 2 I R In 1 OF n I -:i TITLE 1'1 Reactor Trip on Low RCS. Flow Due to Failure of Loop Stop Valve. EVENT DATE 16) LER NUMBER 161 REPORT DATE 171 OTHER FACILITIES INVOLVED (Ill MONTH* DAY YEAR YEAR /{ SEQUENTIAL

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    • 20.40llloll1 llvl &0.73(oll2lliiil 60.73(oll211xl LICENSEE CONTACT FOR THIS LER (121 NAME TELEPHONE NUMBER AREA CODE R. F. Saunders, Station Manager 0 1 o, q 3 I 51 7 I -13 I 1 I 8 14 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (131 MANUFAC-REPORTABLE . ;.;;.;. .*.**.; . ;,;.;.*.*
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SUPPLEMENTAL REPORT EXPECTED 114) MONTH DAY YEAR EXPECTED h NO SUBMISSION lxl YES (If yos, compl*r* EXPECTED SUBMISSION DATE/ DATE 1151 018 310 817 ABSTRACT (Limit to 1400 SPIJCSs. i,tJ,, *PfJroxim,ttJly fifts6n singts-spacs typswrirrsn lim,s} (16) On May 16, 1987 at 0824 hours0.00954 days <br />0.229 hours <br />0.00136 weeks <br />3.13532e-4 months <br />, with Unit 1 at 100% power, a low flow reactor trip occurred when "A"loop reactor coolant system (RCS) {EI IS-AB} flow decreased to 47%. Following the reactor trip, the source range channels {EIIS-DET}

did not automatically reinstate.

All other protection and control systems functioned properly.

Operators followed appropriate plant procedures and stabilized the plant following the reactor trip. This event occurred when the. II A" hot leg loop stop valve (EIIS-ISV}

stem failed, permitting the disc to drop, partially blocking loop flow. A detailed metallurgical analysis is being performed to determine the failure mode and mechanism of the valve stem. The preliminary report indicates that failure was due to stress or fatigue. To reduce the stress on the valve stem, the operating procedure is being revised to normally operate the valves*off the backseat.

The failure of source range channels to reinstate was due to the under compensation of the intermediate range channel NI-36. The source range channels were manually reinstated, and technicians readjusted the intermediate range compensating voltage. Itl'-,..,;.., 8706230353 870612 \ ( \ PDR ADOCK 05000280 s PDR NRC Form 386 19-83)

NRC l'orm 366A * (9-83) FACILITY NAME (1) POW 28-06-01 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION U.S. NUCLEAR REGULATORY COMMISSION APPROVED 0MB NO. 3150--0104 EXPIRES: 8/31/88 DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) YEAR ::::::::::

SEQUENTIAL

REVISION *::::::::::

NUMBER .'."."."." NUMBER Surry Power Station, Unit 1 o 1s Io Io Io I 2 I 81 O 81 7 -011 I 1 -0 I O Ol 2 OF O I 3 TEXT '" more IP"C9 i& "'flUired, U&tl *dditiona/

NRC Form 36flA '&/ (17) NAC FOAM 366A (9-83) 1.0 Description of the Event On May 16, 1987 at 0824 hours0.00954 days <br />0.229 hours <br />0.00136 weeks <br />3.13532e-4 months <br />, with Unit 1 at 100% power, a low flow reactor trip occurred when "A" loop reactor coolant system {EIIS-AB} (RCS) flow decreased to 47%. Following the reactor trip, the source range channels {EIIS-DET}

did not automatically reinstate.

All other protection and control systems functioned properly.

Operators followed appropriate plant procedures and stabilized the plant following the reactor trip. 2.0 Safety Consequences and Implications The low flow reactor trip automatically trips the reactor to maintain sufficient margin above a DNBR of 1.3 with a loss of RCS flow. The complete loss of flow in one loop from a reactor power of 100% (2441 MWt) with three loops operating is an analyzed event. During the event, "A" loop flow was maintained at approximately 47% and total core flow remained at 84%. A confirmatory analysis performed by Nuclear Engineering concluded that DNBR was maintained above the accident analysis value of 1.3. In addition, all other safety related systems remained operable during the event, and plant parameters remained well within the bounds of the accident analysis.

Therefore this event did not constitute

  • an unreviewed safety ques*tion and the health and safety of the public were not affected.

3.0 Cause The cause of this event was a failure of the "A" RCS hot leg loop stop valve (MOV-1590)

{EIIS-ISV}.

The valve stern failed, permitting the disc to drop, partially blocking the loop flow. The valve stern is being analyzed for failure mode and mechanism.

A supplemental LER will be submitted when this analysis is completed.

The preliminary report indicates that failure was due to fatigue or stress. The failure of the source range channels to reinstate was due to the under compensation of the intermediate range channel NI-36.

NRC Form 366A. (9-831 FACILITY NAME (1) POW 28-06-01 LICENSEE EVENT REPORT (LER) TEXT CONTINUATION U.S. NUCLEAR REGULATORY COMMISSION APPROVED 0MB NO. 3150-0104 EXPIRES: 8/31 /88 Dq<:KET NUMBER (2) YEAR LER NUMBER (6) ::::::::::

SEQUENTIAL

REVISION ::::::::::

NUMBER ::::::::::

NUMBER PAGE (3) Surry Power Station, Unit 1 0 1s101010121a10 817 -01111-olo oh °Fo 1~ TEXT /ff more /J/NJCl1 is n,quired, U/ltl 11dditionsl NRC Form 3lil!iA '*) (17) NRC FORM 366A (9-83) 4.0 Inunediate Corrective Action The Operators performed all appropriate emergency procedures and function restoration procedures to ensure the plant was returned to a stable condition.

This included manually reinstating the source range channels.

Also, the STA performed the critical safety function status tree review to ensure specific plant parameters were noted and that those parameters remained within safe bounds. 5.0 Additional Corrective Actions The unit was placed in the cold shutdown condition and the stem of the hot leg loop stop valve was replaced.

The stems of the other five Unit 1 loop stop *valves were ultrasonically tested and found to be satisfactory.

Technicians readjusted the intermediate range compensating voltage. 6. O Actions Ta-ken to Prevent Recurrence A detailed metallurgical analysis is being performed to determine exact cause of the valve stem failure. To reduce the stress on the valve stem, the operating procedure is being revised to normally operate the valves off the backseat.

7.0 Similar Events A similar failure occurred on the Unit 1 "B" loop Hot Leg Isolation Valve on December 1, 1973. 8.0 Manufacturer/Model Number Anchor Darling/Drawing nos. 95-11778 and 95-11779.

  • June 12, 1987 U.S. Nuclear Regulatory Commission Document Control Desk Oi6 Phillips Building Washington, D.C. 20555 Gentlemen:

e VIRGINIA ELECTRIC AND POWER COMPANY Surry Power Station P. 0. Box 315 Surry, Virginia 23883 Serial No.: Docket No.: Licensee No.: 87-013 50-280 DPR-32 Pursuant to Surry Power Station Technical Specifications, Virginia Electric and Power Company hereby submits the following Licensee Event Report for Surry Unit 1. REPORT NUMBER 87-011-00 This report has been reviewed by the Station Nuclear Safety and Operating Committee and will be reviewed by Safety Evaluation and Control. Very truly yours, R. F. Saunders Station Manager Enclosure cc: Dr. J. Nelson Grace Regional Administrator Suite 2900 101 Marietta Street, NW Atlanta, Georgia 30323 _._J

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