IR 05000249/1991026
| ML17174B009 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/02/1991 |
| From: | Jeffrey Jacobson, Schapker J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML17174B008 | List: |
| References | |
| 50-249-91-26, NUDOCS 9112060044 | |
| Download: ML17174B009 (7) | |
Text
U. S. NUCLEAR REGULATORY COMMISSION
REGION III
Repqrt No. 50-249/91026(DRS)
Docket No.:
50-249 License No.:
DPR-25 Licensee:
Commonwealth Edison Company 1400 Opus Place Downers Grove, IL 60515 Facility Name:
Dresden Nuclear Power Station - Unit 3 Inspection At:
Morris, IL 60540 Inspection Conducted:
September 9-12, 16, 18-19, October 7-8, 2 -31, and November 12, 1991 Inspector:
1.21~111 Date'
Approved l )....-:L.-'I (
Date Section Inspection Summary Inspection on September 9-12, 16, 18-19, October 7~8. 29-31, and November 12, 1991 (Report No. 50-249/91-026CDRS))
Areas Inspected:
Routine unannounced inspection of inservice inspection (ISI) activities including review of program (73051),
procedures (73052), observation of work activities (73753), data review and evaluation (73755), and of licensee action regarding reactor vessel ~losure head studs (92700).
Results:
No violations or deviations of NRC requirements were identifie ISI activities were accomplished within the guidelines of ASME Code Section XI requirement The licensee's augmented inspection of reactor vessel closure studs demonstrated a positive commitment to safet The licensee has demonstrated the ability to properly implement the ISI Program, including augmented inspection of intergranular stress corrosion cracking (IGSCC) susceptible piping.
Yll~U6UU44 ~llLVZ F_;DR ADOCK 05000249
- DETAILS Persons Contacted Commonwealth Edison Company (CECo)
- K. Peterman, Regulatory As~urance Superintendent
- G. Whitman, ISI Coordinator
- J. Kotowski, Production Superintendent
- L. Gerner, Technical Superintendent
- J. Harrington, NQP Maintenance Group Leader M. Harbaczewski, Technical Staff Group Leader Lambert. MacGill and Thomas. Inc. CLMT)
w. Thomas, ISI Inspector, Level II J. Newgurd, ISI Inspector, Level II R. May, ISI Inspector, Level II u. s. Nuclear Regulatory Commission CNRC)
D. Hills, Resident Inspector D. Liao, Reactor Inspector Other licensee personnel were contacted as a matter of course during this inspectio *Denotes those present. at the exit interview conducted November 12, 199.
Inservice Inspection CISI) Unit 3 {73051, 73052, 73753, and 73755) General {73051)
This was the second outage of the third period in the second ten year pla The licensee contracted with Lambert, MacGill, and Thomas, Inc. (LMT) to perform ultrasonic (UT), magnetic particle (MT), and liquid penetrant (PT) examination The licensee's System Materials Analysis Department (SMAD) nondestructive examination (NDE) section assisted with those examinations and performed independent examinations using UT and MT during the outag Examinations were performed in accordance with ASME Section XI, 1977 Edition, Summer 1979 Addend The procedures utilized for NDE were reviewed and approved by an EPRI certified CECO Level III.
2 ISI Procedure Review (73052)
The NRC inspector reviewed the following NOE procedures:
0
0
0
0 CECo, Nondestructive Testing (Inservice Inspection) OAP 11-8, Revision CECo, "Preservice and Inservice Ultrasonic Inspection of Similar and Dissimilar Metal Pipe Welds at Nuclear Stations," NDT-C-2, Revision 1 CECo, "Ultrasonic Inspection of the Vessel Inner Radii at Nuclear Stations," NDT-C-10, Revision 1 CECo, "Ultrasonic Examination of Reactor Vessel Welds to NRC Regulatory Guide.1.150 for Boiling Water Reactors," NDT-C-30-79, Revision CECo, "Beam Spread and Refracted Angle Determination to NRC Regulatory Guide 1.150 for Boiling Water Reactors," NDT-C-31-79, Revision CECo, "Nonaqueous Red Dye Liquid Penetrant Examination for Section XI Class IWB and IWC Components for Nuclear Stations," NDT-D-2, Revision CECo, "UT of Dissimilar Metal Safe-End to Nozzle Welds with Inconel 182 Buttering and Filler Meta CECo, "Visual Examination - Welds, Pressure Retaining Bolting, and Component Internals," VT-1-1, Revision CECo, "Visual Examination - System Hydrostatic and Leak Tests," VT-2-1, Revision CECo, "Visual Examination -
Component Supports,"
VT-3-1, Revision CECo, "Magnetic Particle Examination for ASME Section XI Class IWB and IWC Components for Nuclear Stations," NDT-B-1, Revision Review of ISI Data, Material, Equipment, NOE Personnel Certifications and Audits/ (73753, 73755)
The NRC inspector reviewed the following documents and determined that the applicable QA/QC requirements were met:
- 0 ISI Data Reports; Ultrasonic instruments, transducers, and couplant certifications; Liquid penetrant, cleaner, and developer certifications; Magnetic particle materials and equipment; and NOE personnel certifications compliance to SNT-TC-lA requirements and EPRI certifications for IGSCC examination Observations of Work and Work Activities (73753)
The NRC inspector observed the following work activities in progress:
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Ultrasonic examination (UT) of:
Reactor vessel (RV) flange to shell weld, isolation condenser piping welds**, recirculation piping welds, core spray piping welds, shutdown cooling piping welds, and high pressure coolant injection (HPCI) safe-end weld Liquid penetrant examination (PT) of isolation condenser welds and shutdown cooling piping weld Magnetic particle examination (MT) of core spray piping weld Visual examination of RV internals*.
- Visual examination of jet pump restrainer clamp bolt keepers was performed utilizing the "bump" method to verify that the keepers tack welds were intac The NRC inspector observed this examination in progress (via video camera).
During the examination, one keeper weld was observed to have faile The bump method uses a crows foot type device which is manipulated to lift or jar the keeper to detect whether the tack weld is soun The tack weld is not visually accessible for inspection in some cases and it is not always possible to discern the soundness of the weld, therefore, the bump method was devised to inspect for security of the keepe The bolt keeper was repair welded and reinspected for adequac **The isolation condenser safe-end to nozzle welds are comprised of a stainless steel safe-end welded to a carbon steel nozzle that has been buttered and cladded
- *
with stainless stee The licensee fabricated two mockups (8" and 12 11 diameters) to determine the best ultrasonic technique for the examinatio Through the use of these mockups it was determined that the Refracted-Longitudinal Wave (RL) technique, using both 45* and 60° angles, provided the best examination Ultrasonic procedure NDT-C-2, Revision 18, with some modifications, was used as the governing procedure. A two-inch depth range was established using the 10% and 50% deep axial notches in the respective mockup The sensitivity was established by setting the 1/8 11 diameter 3/4 T side drilled hole to 80% full screen heigh The scan gain was adjusted to maintain a 10 to 30 percent noise level as required by the procedure and recorded on the data sheet The NRC inspector observed the UT examination and calibration checks, no defects were identifie A PT *examination of the safe-end to nozzle weld detected an indication located in the safe-end material at the toe of the weld to the nozzl The indication was surface oriented with no appreciable dept The maximum length was.3 inche Due to the nature of the indication, the licensee contacted SMAD to perform field metallography which revealed numerous discontinuous cracks not connected to the main indicatio The cracks contained no oxide and appeared to be sharp with no evidence of bluntin Subsequently, SMAD removed the indication (boat sample)
for laboratory analysi The sample was prepared, mounted and etched with a 10% oxalic acid to accommodate viewing the indication in tQe radial directio The area surrounding the PT indicatio contained the discontinuous cracks which etched differently than that of the base or weld meta From this, it was apparent that the indication was directly adjacent to the field weld, but was not part of the field wel The maximum depth of the indication
measured.030 inc A longitudinal cross section through the PT indication exhibited a dendritic microstructur The cracking observed was interdendriti The cracks did not extend into the base material and terminated at the interface between the dendritic structure and the base meta Semi-quantitative chemical analysis was performed using the energy dispersive x-ray spectrometer (EDS).
Results of the analysis revealed that the base metal appeared typical of a stainless steel *(SS) type 304, and the weld metal appeared typical of SS type 30 The area containing the indications. revealed a composition of approximately 53% nickel, which is
- typical of Inconel material. It is possible that a thermocouple or other type of attachment weld was the cause of the foreign materia During solidification of the tack weld, interdendritic cracks may have developed in the area of dilutio The NRC inspector observed the initial PT and UT examinations, the boat sample removal and subsequent UT examination after repair weldin Review of the repair documentation was performed with no discrepancies note The licensee conservatively exceeded the ASME Code requirements to assure the root cause of the cracking was identifie No violations or deviations were identifie.
Inspection of Reactor Vessel Studs (92700)
In the spring outage of 1989 for Unit 2, ultrasonic examinations performed as part of the Section XI Inservice Inspection (ISI) Program identified cracks in the lower threaded portion of two reactor vessel (RV) head closure*
stud The two studs were removed and replaced with spare studs during that refueling outag Subsequently, a metallurgical evaluation on a sample from one of the cracked studs determin.ed the cracking mechanism to be Intergranular Stress Corrosion cracking (IGSCC), and that the material toughness:of the stud was lower than previously reported in the original Certified Material Test Repor Due to the possibility of stud cracking in. other CECo BWR units, the licensee elected to perform augmented inspections of (1.00%)
of the RV studs at each of the six BWR units, utilizing* an enhanced end-shot ultrasonic technique (enhanced from the original UT procedure which identified the cracks).
In addition, further metallurgical evaluations are being performed by the licensee and General Electric Company.*
During the current outage for Dresden Unit 3, all RV studs were examined via the enhanced UT end shot metho In addition, a sample of 16 studs were removed and magnetic particle examined (wet fluorescent) with no cracking identifie The NRC inspector observed the UT calibration for the end shot stud U The licensee fabricated a new calibration stud assembly made from material similar to the actual stud material, to duplicate the acoustic propertie The NRc*inspector observed that during the *initial calibration attempts, a high amplitude sign'al was interfering in obtaining a clean UT setup to perform the examination to procedure requirement The licensee changed
- equipment to lower the pulse repetition rate which was causing the nonrelevant signal due to the length and geometric configuration of the stu With the change of the UT equipment, the nonrelevant signal was still present but the amplitude was reduced so that the calibration was achievabl During the examination of the RV studs, identical nonrelevant signal responses of lower amplitudes were detecte These signals were recorded per procedure requirement No cracking was detected during the examination of the RV head closure stud The licensee's augmented inspection program for the RV studs along with the metallurgical analysis and evaluations as to the root cause of the cracked studs, demonstrates a positive attitude to assuring the safe operation of the plant No violations or deviations were identifie.
Exit Meeting The NRC inspector met with licensee representatives (denoted in Paragraph 1) at the conclusion of the inspection on November 12, 199 The inspector summarized the scope and findings of the inspection activitie The licensee acknowledged the inspection finding The inspector also discussed the likely informational content of the inspection report with regard to documents or processes reviewed by the inspecto The licensee did not identify any such documents/processes as proprietar