ML20043H384

LER 90-009-00:on 900517,RHR Sys B HX Bypass Valve Failed to Reposition on Demand,Rendering RHR Sys Train Operable for Containment Spray Cooling Mode of Operation.Caused by Failure of Valve Stem Nut.Stem Nut replaced.W/900618 Ltr

ML20043H384
Person / Time
Site:	Perry
Issue date:	06/18/1990
From:	Hegrat H, Lyster M CENTERIOR ENERGY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-009, LER-90-9, PY-CEI-NRR-1190, NUDOCS 9006250338
Download: ML20043H384 (4)

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6200 00k1ree Boulevard Mod Acatess-IndependenceOH PO Box 94661 216-44T3100 Cleelona. 04 441014661 June 18, 1990 PY-CEI/NRR-1190 L U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20535 Perry Nuclear Power Plant Docket No. 50-440 LER 90-009 Dear Sirt f Enclosed is Licenseo Event Report 90-009 for the Perry Nuclear Power Plant.

Sincerely, W,Awh <N Michael D. Lyster i Vice President, Nuclear - Perry MDL:njc Enclosuret LER 90-009 I

cc: T. Colburn '

NRC Resident Inspector U.S. Nuclear Regulatory Commission 799 Roosevelt Road Clen Ellyn, Illinois 60137 i

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DJ l i I I I I I I I l l l l 1 eu tew=va6.. at amerso n. Mo v. e, viaa svaasistion tt9149 von tempoeen ik99CitO $v0n093890N De tti 8e0 l l l ASST A ACT lemut to f 800 assem # # . appr.eameery hrssoa esa,9 eppet fyppWHf89# &#SSI DOI On May 17, 1990 at 1930, the "B" Residual Heat Removal (RilR) system heat exchanger bypass valve failed to reposition on demand, rendering this train of RHR system inoperable for the Containment Spray and Suppression Pool cooling modes of operation. At this time, the "A" train of the RHR system was also out of service due to surveillance testing. Operators then terminated the surveillance and restored operability of the A train of the RHR system at 1945.

The root cause of this event is component failure. The valve stem nut failed due to excess wear, possibly caused by inadequate stem lubrication. Two days previous to the event, the normal preventive maintenance task to inspect and lubricate the stem was completed. During this activity it was observed that the stem lubrication was minimal. During stem nut replacement, valve inspection, retest, and Motor Operator Valve Analysis and Testing System testing, no other valve problems were identified.

Corrective actions taken at the time of the event included replacing the stem nut, conducting a valve inspection to determine the cause of failure and performing the Technical Specification operability surveillance. A monitoring schedule has been developed to visually inspect the valve for degradation of the stem nut on a periodic basis, until such time that system engineering personnel confirm that the problem is not recurring. The "A" RHR heat exchanger bypass valve was inspected and no anomalies were identified. All licensed operators will be trained on the lessons learned from this event.

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Ol0 0 12 vixt . .ac manonn On May 17, 1990 at 1930, the "B" Residual Heat Removal [BO) (RHR) system heat  ;

exchanger bypass valve [20] failed to reposition on demand, rendering this train of the RHR system inoperable for the Containment Spray and Suppression Pool Cooling modes of operation. At this time, the "A" train of the RHR system was also out of service due to surveillance testing. At the time of the event, the

[ plant was in Operational Condition 1 (Power Operation) with reactor power at '

approximately 100 percent of rated thermal power. The Reactor Pressure Vessel

[RPV) was at saturated conditions at approximately 1020 psig.

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F On May 17, 1990 at 1930 while operators were attempting to line up the "B" RHR ,

system to the Suppression Pool Cooling mode of operation, the heat exchanger by-pass valve failed to go to the full closed position on demand. This valve failure rendered the "B" RHR train inoperable for the Containment Spray and Suppression Pool Cooling modes of operation. At the time of the event, the "A" RHR system was out of service for surveillance testing; therefore, both, loops of the RHR system designed for Containment 9eray and Suppression Pool Cooling were inoperable. At 1945, the "A" RHR system ("A" Containment Spray and Suppression Pool Cooling) was restored to service. Visual inspection of the failed heat

, -exchanger bypass valve revealed that the stem nut was stripped, resulting in the failure of the valve stem to move when the motor operator was energized. The valve stem was inspected for damage and the stem nut was replaced. After two stroke time tests were completed to ensure valve operability, the "B" RHR system  !

was declared operable on May 19, 1990 at 0900. I The root cause of this event is equipment malfunction due to excessive wear of the valve stem nut (Limitorque valve operator model number SMB-3). The stem nut j was found to have approximately 60 percent of the threads worn off and the <

remaining damaged. A possible mode of failure has been determined to be inadequate stem nut lubrication. Two days previous to the event, the normal f preventive maintenance task to inspect and lubricate the stem was performed.

4 During this activity it was observed that the lubrication on the visible portions of the valve stem was evenly distributed, but minimal. No other evidence of valve degradation was noticed; however the valve stem nut is not visible for external inspection. The stem was then properly lubricated as prescribed by vendor recommendations. A review of the maintenance records indicates that the valve stem has been lubricated as prescribed by the vendor recommendations  ;

throughout its operation. Valve lubrication is an eighteen month preventive i maintenance activity. During the repair activities, no additional problems with the valve could be identified. Since no other failures under similar circumstances have occurred at Perry, this is considered to be an isolated event.

The Containment Spray system consists of two 100% capacity loops, each with three spray rings located at different elevations about the inside circumference of the containment. RHR pump A supplies one loop and RHR pump B supplies the other.  ;

Dispersion of the flow of water is effected by 345 nozzles in each loop, enhancing the condensation of water vapor in the containment volume and preventing overpressurization after a Loss of Coolant Accident (LCOA). The heat exchanger bypass valve is automatically closed upon initiation of containment ce..m ...

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TLET W mere spese s soewses, was emneow AMrs Aspen Jme sA 1971 spray, allowing heat to be rejected from the containment to the Emergency Service Water (ESW) [B1] system. In the event both Containment Spray loops become inoperable, Technical Specification 3.6.3.2, action b requires the operator to restore one loop to operable status within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> or be in at least Hot Shutdown within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in Cold Shutdown within the following 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

h The Suppression Pool Cooling function is a mode of the RHR system and functions 1 as part of the containment heat removal system. The purpose of the system is to fa ensure containment integrity following a LOCA by preventing excessive containment pressures and temperatures. The Suppression Pool Cooling modo is designed to limit the long term bulk temperature of the pool to 185 degrees F considering all of the post-LOCA energy additions. The Suppression Pool Cooling trains, being an integral part of the RHR system, are redundant, safety-related component systems that are initiated following the recovery of the reactor vessel water level by ECCS flows from the RHR system. Heat rejection to the Emergency Service Water System is accomplished in the RHR heat exchangers. In the event both loops of Suppression Pool Cooling becoming inoperable, Technical Specification 3.6.3.3, action b requires the plant ;.o be in at least Hot Shutdown within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in Cold Shutdown within et.e next 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

During this event, the Containment Spray and Suppression Pool Cooling modes of RHR loop A were restored to operability 15 minutes after the discovery of the RHR B heat exchanger bypass valve failure, well within the time allowed by either one of the above described Technisal Specification. Therefore, this event is not considered to be safety signifl cant.

One previous similar event occursed on June 26 1987 when it was identified that a gate valve, RHR Return to Suppresidon Pool test valve, became inoperable due to the failure of a stem nut. The valce stem nut became stripped due to a bent C valve stem. The valve stem was modit!ed and the stem nut was replaced. Previous ji corrective actions would not have been axpected to prevent the event on May 17,

& 1990.

Corrective actions were taken at the time of the event included replacing the failed stem nut, conducting a valve inspection and performing the Technical Specification operability surveillance, Surveillance Instruction (SV1-E12-T2002)

"RHR B Pump and Valve Operability Test", so as to verify operability. A monitoring schedule has been developed so that this valve will be visually inspected for degradation of the stem nut on a periodic basis until such time that system engineering personnel confirm that the problem is not recurring. On June 12, 1990 Motor Operated Valve Analysis and Testing System (MOVATS) testing was conducted, and no additional problems were identified. The "A" RHR heat exchanger by pass valve was inspected On June 1 and no anomalies were identified.

All licensed operators will be trained on the lessons learned from this event through normal requalification training.

Energy Industry Identification System Codes are identified in the text as [XX].

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