IR 05000338/1989007

Insp Repts 50-338/89-07 & 50-339/89-07 on 890313-17.No Violations or Deviations Noted.Major Areas Inspected: Inservice Insp Work Observation,Inserice Insp Data Review & Licensee Recovery Efforts from 890225 Hot Leg Plug Failure

ML20245C645
Person / Time
Site:	North Anna
Issue date:	04/11/1989
From:	Blake J, Glasman M NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
To:
Shared Package
ML20245C644	List: IR 05000338/1989007 ML20245C641
References
50-338-89-07, 50-338-89-7, 50-339-89-07, 50-339-89-7, NUDOCS 8904270307
Download: ML20245C645 (9)

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Report Nos.: 50-338/89-07 and 50-339/89-07 Licensee: Virginia Power Company Glen Allen, VA 23060 1 l Docket No and 50-339 License Nos.: NPF-4 and NPF-7  ; i Facility Name: North Anna 1 and 2 Inspection Conducted March 13 - 17, 1989 Inspector: cA hw d 4 S9 Micha'el M.Glasman Date Signbd Approved by: M k Jerome J. Blake, Thief Date' Signed Materials and Processes Section Engineering Branch Division of Reactor Safety SUMMARY Scope This routine unannounced inspection was conducted in the areas of inservice inspection work observation, inservice inspection data review, and observation of the licensee's recovery efforts from the February 25, 1989, hot leg mechanical plug failure and subsequent tube rupture in Unit 1, steam generator

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Results This inspection documents an effective inservice inspection (ISI) progra Management involvement in assuring quality was evident in that the ISI program was well-documented, and procedures examined were technically sound and well-written. Another feature of the Licensee's program is contractor NDE personnel must demonstrate competence by passing method examination (s) administered by the licensee. This adds confidence that contract personnel are qualified and competent. The inspectors contacted and observed during this inspection were well-trained, and experienced individuals. At the time of this inspection, the licensee also determined that a mechanical plug on the hot leg side of steam generator (S/G) "C" had failed in such a way that the upper portion of the plug accelerated under reactor coolant system (RCS) pressure, exited the tube at the U-bend transition, struck and dented an adjacent tube above, then came to rest in its original tube. For a summary of events leading up to this event, refer to NRC Report Nos. 50-338, 339/89-03. The plug, its exit point and the adjacent dented tube were observed via remote video equipmen [[3 pgg hag PDa ADOCK O - - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

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, i Licensee personnel were very respon:;ive to the inspector's initiatives in that l information was provided in a timely manner, and personnel in contact with the inspector were knowledgeable and well-informed. In addition, the recovery efforts relative to the mechanical tube plug failure in Unit I were ' well-organized; daily information sheets and action plans were issued each morning. The licensee's efforts in the recovery effort were augmented by strong Westinghouse support in the removal and failure analysis of the failed plug, as well as assisting in support of the NRC inspector's initiative ( )

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I a REPORT DETAILS Persons Contacted

  ' *R. Driscoll, Manager, Quality Assurance
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  . *S.;Hamill, Inservice Inspection Engineer
  *G. Kane,-Station Manager
  *J.-Leberstien,'. Licensing Enginee '*E. Smith, Nuclear Operations Support L. ' Spain, Metallurgist Power Engineering-Services
  '*H.'.Travis, Supervisor, Nondestructive Evaluation Westinghouse Employees
  *R'. Andersen, Westinghouse Site,, Service Manager R. Easterling, Westinghouse Program Manager, Virginia Power Steam-
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Generator Maintenance Agreement NRC ResidentEInspectors J. Caldwell.. Senior Resident In'spector

  -*L. King, Resident Inspector
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  * Attended Exit. Interview Inservice Inspection (ISI) Units I and 2 The' inspector examined documents, procedures, records, and observed work to determine whether ISI was being conducted in accordance with applicable procedures, regulatory' requirements and licensee commitment The-
  ' applicable code of record for both Units 1 and 2-is American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME B&PV),

Section XI,1974 Edition, Summer 1975 Addend Units.,1 and 2 are in the 3rd period of the first 10 year ISI interva Inservice inspection is performed both by contractors and Virginia Power personnel under. the Virg+nia Power Quality Assurance (QA) progra Contract personnel performing NDE were from Westinghouse and Virginia Corporation of Richmond. In addition, contract NDE personnel must pass

  . tests administered by Virginia Power and, in most cases, use Virginia Power procedure Virginia Power procedures for NDE vendor / contractor surveillance also require review and sign-off on all test result Observation of Work and Work Activities, Unit 2 (73753)

L The inspector was limited in the amount of ISI work activity that could be observed because a decision was made to close Unit 2 containment for a full day for decontamination work, and ISI was not  ; in progress in Unit I at the time of the inspection. In additio Health Physics (HP) coverage required by the applicable Radiation Work Permit for the ISI-NDE activities in the containment was not always available in a timely manner. This caused considerable delay __ - _ __ -_ - ___ _- _ _ _ _ _ ___ _ _- _ ______-__-__=_ - _ _ _ - __ -__-- - _ _ ___ _ - _ -

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For the methods observed, the inspector verified that: An approved procedure for the activity was in use Examination personnel were knowledgeable in the examination method, and operation of the test equipment

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Examination personnel with proper level of qualification and certification were performing the various examination activities, including designation of examination methods to be used; equipment calibration; examination; and interpretation; evaluation; and acceptance of test results Applicable procedures and travelers clearly specified the test proced"re, and a copy of the test procedure was available in the work area Acceptance limits were specified and were in accordance with the applicable ASME Code Examination reselts, evaluation of results, and any corrective actions / repairs / replacements were being recorded as specified in the ISI program and NDE procedures The ISI-NDE work observed by the inspector is listed below: System / Location / Component Line N Weld N Drawing Method RHR 10"-RHR-414 05 VGB-1-4303 R0 UT RHR 10"-RHR-414 06 VGB-1-4304 R0 UT SI Accum Disc 12"-SI-469 06 VGB-1-4302 R0 UT RCP "B" Flywheel N/A Peripheral N/A UT RCP "B" Flywheel N/A Shaft Hole N/A PT and Keyways

 , The inspector noted that the lower portion of the Reactor Coolant Pump (RCP) "B" Flywheel shaf t hole was damaged by what appeared to be misalignment between the flywheel and RCP shaft during installation or removal. The damage cot,31sted of gouges and deep score marks which showed up as indications during the Liquid Penetrant (PT) test.

L At the time of the inspection, it was not possible to determine if the indications were relevant because additional preparation in the area of the indications was required due to the presence of galled and lapped-over surfeces.

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The inspector also noted that prior to this inspection, an item relative to the assembly procedure for the RCP flywheel was opened, 50-339/86-12-01, "RCP Flywheel Assembly Procedure." The inspector of record indicated that the Virginia Power assembly procedure did not include sufficient detail to enable the craf t to remove / replace the flywheel without reference to the pump manufacturer's procedure. The subject item was closed in Report No. 50-339/87-07 when the licensee revised the assembly procedure to include the necessary instruction Relative to this inspection, it should be noted that the "B" RCP was dissambled/ assembled using the previous revision of the subject procedur Certification and calibration records for the UT equipment used in the above examinations were also reviewed by the inspector. The inspector verified that the UT instrument was within its current calibration interval, that certification records were on file for the transducers used, and the couplant certifications stated conformance to ASTM D-129, and D-108 for sulphur and halogen conten The certification records for the following were reviewed by the inspector: Item Serial No. or Batch Transducer, KB-A 2.25 mHz 41030 0.5" dia UT Instrument, Sonic MX I 11223E Couplant, Ultragel 8557 b. Review of Procedures, Units 1 and 2 (73052) The inspector reviewed the procedures indicated below to determine if they were consistent with regulatory requirements and licensee commitment The procedures were also reviewed to determine if requirements for NDT personnel were specified; equipment and supplies were appropriately certified and/or calibrated; accept / reject levels were specified;- data recording requirements were specified; proper review, approval, and concurrence was indicated; and if applicable, division of responsibility existed between licensee and contractor personnel.

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 ' Procedur,_e  Title NDE 6.2 R2 -"Review of Contractor Nondestructive Examination l    Interpretation 'by' Virginia Power Company Personnel" NDE 7.3 R0 _" General Requirements for ISI Nondestructive Examination" NDE PT-301 R0 " Liquid Penetrant Examination" NDE UT_-301 R0 " Manual Ultrasonic Examination of Piping Welds" (1)- Technical Review, Liquid Penetrant Procedure-The inspector reviewed Procedure NDE PT-301 R0 to asc?rtain
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conformance ' with ASME Code, Section V, Article 6, in the following areas: specified . method; penetrant material identification; penetrant; test materials analyzed for sulphur and total halogen content; acceptable pre-examination test surfaces;- test . temperature; cleaner application method and drying time; method of penetrant application; test piece temperature; solvent removal and drying time; type of developer and application technique; evaluation technique; light level;

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and procedure requalificatio (2) Technical Review, Ultrasonic Procedure The inspector reviewed Procedure "DE UT-301 R0 to ascertain conformance with ASME Code, Section V, Article 5, in the following areas: Method specified; apparatus specified; linearity and signal attenuation accuracy requirements; beam coverage / angle; scan rate / direction;- scan technique; calibration before and after examination; calibration block requirements, including size and location of _ defects within the block; sizes and frequencies of search units specified; methods of distance-amplitude correction techniques specified and consistent with equipment used; reference level for scanning; methods of demonstrating penetration and coverage; levels for evaluation of defects specified; methods for recording significant indications; and acceptance limits specifie ; c. Inservice Inspection Data Review and Evaluation, Unit 2 (73755) Records of completed nondestructive examinations were selected and reviewed to ascertain whether: the method (s) technique, and extent of the examination complied with the ISI plan and applicable NDE procedures; findings were properly recorded and evaluated by _=_ - .

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qualified personnel; programmatic deviations were recorded as required; personnel , instruments, calibration bl ocks , and NDE materials (PT materials, couplant) were. designate Records selected for this review are. listed below: System Line Weld / Location Drawing Method b SI 6" 62 VGB-2-2526 R0 UT SI 8" SI-440 1 VGB-2-2531 R0 UT SI- 8" SI-440- 3 VGB-2-2531 R0 UT SI 8" SI-440- 4 VGB-2-2531 RO UT CH -8" CH-60 WS-1 VGB-2-2532 R0 P MAIN STM 32" SHP-601 BPL-104 3C-90 PT MAIN STM' 32" SHP-457-601 BPL-335 3C-90 PT L MAIN STM - 32" SHP-459-601 BPL-200 3C-90 PT MAIN STM 6" SHP-438 WS-1 VGB-2-2202 R1 MT Within this area. of inspection, no violations or deviations were identifie . Mebhanical Tube Plug Failure, Steam Generator "C", Unit 1 On . February 25,1989, Unit 1 experienced a trip following a loss of feedwater when the "C" Main Feedwater Regulating Valve close Shortly after the trip, primary-to-secondary leakage was detected in the "C" steam generator (S/G). For additional details regarding the events surrounding the trip and response to the transient, refer to NRC Inspection Report Nos. 50-338, 339/89-0 Remote visual examination of S/G "C" revealed a leaking hot leg plug at row 3, column 60 (R3060) with the steam generator filled to approximately 58% on the wide range instruments. This corresponds to the region above the 7th support plate. Historical eddy current data, however, indicated that the tube R3C60 was not plugged for through-wall indications. Discussion of historical eddy current data relative to this event may be found in NRC Report Nos. 50-338, 339/89-0 Preliminary video examination using a Welch Allyn (W/A) video probe revealed that the top of the plug had become separated from the body of

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the plug; the bottom section of the plug was firmly in place, along with the mechanical expander, however, the top was missing. Subsequent W/A video examination located the missing plug section above the 7th support plate, on the hot leg side, and lodged in a semi-inverted position above a jagged tear in the extrados at the transition between the straight and U-bend portion of tube R3C60. The tear appeared to be about 3" long. In addition, the tube above, and adjacent to tube R3C60, R4C60, was dented in three adjacent locations. These dents were clearly visible through the hole torn in R3C60.

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Shortly after the inspector viewed the failed lower section of the R3C60 and plug plugsrecovered from Unit from tube R24C8, 1, it, also fromalong S/Gwith

      "C",theUnit coldI were leg R3C60 plug shipped to (W)

laboratories in Pittsburgh for analysis; plug R24C8 was observed to be dripping, however, this plug reportedly was not fabricated from a heat known to be susceptible to PWSCC. Preliminary information returned from Pittsburgh indicated that this plug had also failed due to PWSC Within the areas inspected, no violations or deviations were identifie . Action on Previous Inspection Findings (92701) Inspection was not conducted in this are . Exit Interview The inspection scope and results were summarized on March 17, 1989, with those persons indicated in paragraph 1. The inspector described the areas inspected and discussed in detail the inspection results. Although reviewed during this inspection, proprietary information is not contained in this report. Dissenting comments were not received from the licensee.

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During the inspection, the inspector was able to view the lower section of the failed plug which was recovered from the S/G, as well as the intact cold leg plu These plugs were visually examined in the Unit I l

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containment by the inspector, and a licensee metallurgist. The following observations were made: The lower section of the plug exhibited a flat circumferential fracture at the root of the second sealing lan The fracture was approximately perpendicular to the axis of the plug and covered with an undisturbed, evenly-distributed layer of brown colored oxid There was no indication of mechanical rubbing, fretting, or other .

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disturbance to the oxide laye No evidence of a ductile fracture, such as a shear lip, or necking in the region of the fracture was evident to the unaided eye. In addition, there was no evidence of cracking transverse to the main fracture, or significant branching of the main fractur The above remote video observations and examination of the fracture surface of the mechanical plug strongly indicate that the plug failed prior to the February 25, 1989 tri This is supported both by the presence of undisturbed oxide on the fracture face, and the lack of ductile fracture indicators. At the time of the inspection, the licensee was not able to say with certainty what mechanism was responsible for keeping the fractured plug tip in place prior to the tri Following the trip, the now separated plug tip was accelerated up the bore of tube R3C60, with considerable reactor coolant system (RCS) pressure as the driving force. This was sufficient to impart sufficient energy to the plug tip such that it was able to penetrate the tube wall (and damage tube R4C60) instead of following the bend in the tub ' The failed plug was machined from thermally treated Alloy 600 barstock, from heat 3962. This heat, and heat 3513 were both identified as material susceptible conclusion was to based Primary onWater Stress information Corrosion from Cracking Westinghouse (W . )(PWSCC).

WestinghouseThis indicated that these these heats did not receive adequate thermal treatment, resulting in a discontinuous to semi-continuous carbide network in the grain boundaries. PWSCC resistance is enhanced when a continuous network of grain boundary carbides is present in Alloy 600. Both of the above heats are used in North Anna's S/Gs. The licensee is currently trying to locate these plugs as part of their recovery effort While at the site, the inspector reviewed a proprietary (W) Research and Development report which described the analysis of a leaking hot leg mechanical plug removed from North Anna, Unit 2. The particular plug was l also fabricated from heat 3962. This plug was removed from Unit 2 "A" S/G l during the 1985 outage. The report indicated that the plug contained axial and circumferential cracking, which was intergranular in nature, and caused by stress corrosion. Further, the axial cracks initiated from the inside, or primary side of the plug. An initiation site / direction could not be determined for the circumferential crack.

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