Information Notice 2003-01, Failure of a Boiling Water Reactor Target Rock Main Steam Safety/Relief Valve
| ML030140543 | |
| Person / Time | |
|---|---|
| Issue date: | 01/15/2003 |
| From: | Beckner W D NRC/NRR/DRIP/RORP |
| To: | |
| Billings, Danny, NRR/OES/ROR, 415-1175 | |
| References | |
| TAC M6480 IN-03-001 | |
| Download: ML030140543 (8) | |
January 15, 2003
NRC INFORMATION NOTICE 2003-01:FAILURE OF A BOILING WATER REACTORTARGET ROCK MAIN STEAM SAFETY/RELIEF VALVE
Addressees
All holders of operating licenses or construction permits for nuclear power reactors, exceptthose that have permanently ceased operations and have certified that fuel has been permanently removed from the reactor.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alertaddressees to a recent failure of a main steam safety/relief valve on a boiling water reactor (BWR). The NRC anticipates that recipients will review the information for applicability to their facilities and consider taking appropriate action However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response is required.
Description of Circumstances
In April 2002, following a Unit 1 refueling outage at the Hatch Nuclear Plant, the safety/reliefvalve (S/RV) in the 1J location began leakin In an effort to stop the assumed pilot valve leakage, the licensee cycled the S/RV at rated pressure and temperatur The valve failed to fully open and then failed to resea The licensee continued the startup to allow identification of potential balance-of-plant leakag During the balance-of-plant startup, the associated S/RVvacuum breaker failed due to repeated cycling, resulting in high unidentified drywell leakage. The plant was shut down when the leakage exceeded the technical specification allowableleakage (reference LER 50-321/2002-002). The S/RVs installed in Unit 1 are Target Rock two-stage S/RV The main stage valve internals(shown in attached Figure 1) are assembled by screwing the main piston onto the main stem so that the piston moves inside the guide, installing a locking tab washer, and installing the stem nut against the washer's locking ta The piston is torqued to 100 ft-lbs, the stem nut is torqued to 50 ft-lbs, and the locking tab is bent to capture the stem nu During the S/RV inspection after the April 2002 shutdown, the failed valve was found to have a .003-inch clearance between the main disc and its sea When the valve was disassembled, the stem nut and the piston were found to be loos The stem nut was removed by hand and the piston was alsounthreaded by hand from the ste However, the threads on the stem were severely damage The piston was unthreaded by working it up to the good threads under the stem nut and threading it onto this portion of the ste The inside of the guide was heavily grooved and was also worn by the piston edge wearing on the guid The piston was visibly cocked on the valve ste In an earlier event in 1999, the licensee had a different S/RV fail on the test stan This failureoccurred during the fourth valve actuation when the stem nut fell off the stem and jammed in the preload spring coil The resulting uneven force caused the piston to cock in the guid The stem nut had lost torque and came unscrewed from the stem threads in spite of the locking ta Following this failure, the licensee instituted a program to check the torque on both the stem nut and the pisto The licensee found in most cases, both the stem nut and the piston had lost torque.Following the failure of the 1J S/RV, the licensee closely examined three valves which had beenremoved during the April 2002 refueling outag The stem nuts and pistons of all three valves had lost torque, the stems of two of the valves showed significant wear on the valve threads, and one valve exhibited some thread wea All three valves showed signs of damage on the stem shoulder, which is designed to contact the pisto In October 2002, the licensee removed three additional S/RVs from Unit 1 for testing, disassembly, and inspectio All three valves successfully stroked with steam pressure but when disassembled and inspected, were found to have lost torque on both the stem nut and the pisto Two valves had fairly good threads and the final valve (1F) had significant thread damage and a visibly cocked pisto All three valve stems showed varying degrees of damage in the shoulder area.The licensee believes the loss of torque and damage of the valve internals can be attributed tothe manufacturing tolerances of the valve stem and piston and to the lengthy service time without adequate inspection and maintenanc The valve is designed so the valve stem screws into the pisto The stem has a shoulder that seats against the piston shoulde For the valves that show little to no thread damage, the stem apparently seats properly against the piston and most of the valve actuation force is carried by the stem and piston shoulder For the valves with thread damage, the licensee believes that the end of the lead thread of the piston contacts the fillet that is machined into the shoulder of the valve ste As shown in Figure 1, when this occurs, the shoulder of the stem does not properly seat against the shoulder of the piston.
Thread damage starts with the first actuation on the test stand, resulting in a loss of torqu Over time, vibration from normal plant operations causes fretting and wear of the valve stem shoulder and thread The piston rocks in the guide and wears grooves where the piston rings contact the guid Eventually the piston could significantly cock on the stem and wedge in the guide during valve actuation, which would prevent proper opening or closing of the valv The licensee has not been able to determine the time in operation required to damage a valve to the point of failur The licensee believes the failed 1J valve and the damaged 1F valve were in service for approximately 20 years without maintenanc The licensee is currently removing several S/RVs during each plant outage to ensure that all installed S/RVs are inspected and maintained at least every 6 year There are 11 S/RVs installed in each uni DiscussionAs the result of the 1J valve failure, the licensee performed a root cause analysis following theevent and contracted an independent engineering firm to perform a separate root cause analysi The licensee believes that the failure of the S/RV is related to the manufacturing tolerances of the valve stem and piston assembly and to the lengthy service time without adequate inspection and maintenanc The independent root cause analysis determined that the lead thread of the piston was contacting the fillet of the shoulder, preventing shoulder-to- shoulder contac Since the piston was not adequately attached to the stem, operational vibration and valve actuation caused thread damage and eventual valve failur The valve vendor (Curtiss Wright Flow Control Corporation) has developed changes to the inspection and refurbishment procedures to ensure proper shoulder-to-shoulder contact during valve assembl The BWR vendor (GE Nuclear Energy) is issuing a Service Information Letter (SIL)
to address the degradation found in the Hatch S/RVs.The above-described circumstances emphasize the importance of periodic inspection of S/RVmain stage components to identify deficiencies and necessary corrective action All Target Rock two-stage and three-stage S/RVs have similarly designed main stage component Currently 11 BWR plants in the U.S. have two-stage S/RVs, and 11 BWR plants have three- stage S/RVs.The above described problems found in the main stages of Target Rock S/RVs are not relatedto the problems found previously in the pilot stages of the S/RVs that were discussed in Regulatory Issue Summary 2000-12, "Resolution of Generic Safety Issue B-55." This information notice requires no specific action or written respons If you have anyquestions about the information in this notice, please contact one of the technical contacts listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager./RA/William D. Beckner, Program Director Operating Reactor Improvements Program Division of Regulatory Improvement Programs Office of Nuclear Reactor RegulationTechnical Contacts:Norman Garrett, Region IICharles G. Hammer, NRR(912) 367-9881(301) 415-2791 Email: nxg@nrc.govEmail: cgh@nrc.govDanny Billings, NRR(301) 415-1175 Email: deb1@nrc.gov
Attachments:
Figure 1 - Target Rock Safety/Relief Valve List of Recently Issued NRC Information Notices As the result of the 1J valve failure, the licensee performed a root cause analysis following theevent and contracted an independent engineering firm to perform a separate root cause analysi The licensee believes that the failure of the S/RV is related to the manufacturing tolerances of the valve stem and piston assembly and to the lengthy service time without adequate inspection and maintenanc The independent root cause analysis determined that the lead thread of the piston was contacting the fillet of the shoulder, preventing shoulder-to- shoulder contac Since the piston was not adequately attached to the stem, operational vibration and valve actuation caused thread damage and eventual valve failur The valve vendor (Curtiss Wright Flow Control Corporation) has developed changes to the inspection and refurbishment procedures to ensure proper shoulder-to-shoulder contact during valve assembl The BWR vendor (GE Nuclear Energy) is issuing a Service Information Letter (SIL)
to address the degradation found in the Hatch S/RVs.The above-described circumstances emphasize the importance of periodic inspection of S/RVmain stage components to identify deficiencies and necessary corrective action All Target Rock two-stage and three-stage S/RVs have similarly designed main stage component Currently 11 BWR plants in the U.S. have two-stage S/RVs, and 11 BWR plants have three- stage S/RVs.The above described problems found in the main stages of Target Rock S/RVs are not relatedto the problems found previously in the pilot stages of the S/RVs that were discussed in Regulatory Issue Summary 2000-12, "Resolution of Generic Safety Issue B-55." This information notice requires no specific action or written respons If you have anyquestions about the information in this notice, please contact one of the technical contacts listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager./RA/William D. Beckner, Program Director Operating Reactor Improvements Program Division of Regulatory Improvement Programs Office of Nuclear Reactor RegulationTechnical Contacts:Norman Garrett, Region IICharles G. Hammer, NRR(912) 367-9881(301) 415-2791 Email: nxg@nrc.govEmail: cgh@nrc.govDanny Billings, NRR(301) 415-1175 Email: deb1@nrc.gov
Attachments:
Figure 1 - Target Rock Safety/Relief Valve List of Recently Issued NRC Information NoticesDISTRIBUTION:ADAMS IN File ADAMS ACCESSION NUMBER: ML030140543 DOCUMENT NAME: G:\RORP\OES\Staff Folders\Info\Hatch SRV\Billings\Hatch SRV\Hatch SRV IN.rev2.wpdOFFICEOES:RORP:DRIPTech EditorEMEB:DEEMEB:DENAMEDBillingsPKleeneBRBonserCGHammer DATE12/12/200212/04/200201/09/200312/18/2002OFFICERegion IIRegion IISC:OES:RORP:DRIPPD:RORP:DRIPNAMENPGarrettBRBonserTReisWDBeckner DATE12/20/2002 / /200201/13/200301/15/2003OFFICIAL RECORD COPY Attachment 1 ______________________________________________________________________________________OL = Operating License CP = Construction PermitAttachment 2 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICES_____________________________________________________________________________________InformationDate of Notice N SubjectIssuanceIssued to_____________________________________________________________________________________2002-35Changes to 10 CFR Parts 71and 72 Quality Assurance Programs12/20/2002All holders of 10 CFR Part 71quality assurance program approvals and all 10 CFR Part 72 licensees and certificate holders.2002-34Failure of Safety-RelatedCircuit Breaker External Auxiliary Switches at Columbia Generating Station11/25/2002All holders of operating licensesor construction permits for nuclear power reactors.2002-33Notification of PermanentInjunction Against Neutron Products Incorporated of Dickerson, Maryland11/21/2002All teletherapy and radiationprocessing licensees. 2002-29(Errata)Recent Design Problems in Safety Functions of Pneumatic Systems11/06/2002All holders of operating licensesor construction permits for nuclear power reactors.2002-32Electromigration onSemiconductor Integrated Circuits10/31/2002All holders of operating licensesfor nuclear power reactors except those who have ceased operations and have certified that fuel has been permanently removed from the reactor vessel.2002-31Potentially Defective UF6Cylinder Valves (1-inch)10/31/2002All licensees authorized topossess and use source material and/or special nuclear material for the heating, emptying, filling, or shipping of uranium hexafluoride (UF6) in 30- and 48-inch cylinders.2002-30Control and Surveillance ofPortable Gauges During Field Operations10/30/2002All NRC licensees authorized topossess, use, transport, and store portable gauges.Note:NRC generic communications may be received in electronic format shortly after they areissued by subscribing to the NRC listserver as follows:To subscribe send an e-mail to <listproc@nrc.gov >, no subject, and the followingcommand in the message portion:subscribe gc-nrr firstname lastname