ML14216A347
| ML14216A347 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 07/28/2014 |
| From: | Swift P M Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML14216A347 (7) | |
Text
V APaul M. Swift wDirector
-Site Engineering Exeon enera on P.O. Box63 Lycoming, NY 13093 (315) 349-5208 Paul.Swift@exeloncorp.com July 28, 2014 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Nine Mile Point Nuclear Station, Unit 2 Renewed Facility Operating License No. NPF-69 Docket No. 50-410
Subject:
Submittal of Post Extended Power Uprate Steam Dryer Inspection Results in Accordance with Operating License Condition 2.C.(20)(f) and 2.C.(20)(g)
References:
(1) Letter from R. V. Guzman (NRC) to K. Langdon (NMPNS), dated December 22, 2011, Nine Mile Point Nuclear Station, Unit No. 2 -Issuance of Amendment RE: Extended Power Uprate (TAC No. ME1476)By letter dated December 22, 2011 (Reference 1), the NRC issued Amendment No. 140 to Renewed Facility Operating License No. NPF-69 for Nine Mile Point Unit 2 (NMP2). The amendment authorized an increase in the maximum steady-state reactor core power level for NMP2 to 3,988 megawatts thermal (MWt). This letter provides the steam dryer inspection results in accordance with the following NMP2 license conditions associated with the issuance of Amendment No. 140: License Condition 2.C.(20)(f)
-"During the first two scheduled refueling outages after reaching 120 percent OLTP conditions, a visual inspection shall be conducted of all accessible, susceptible locations of the steam dryer in accordance with BWRVIP-139 inspection guidelines.
In addition, a visual inspection of all accessible welds that were analyzed using embedded models shall be conducted.
In addition, a visual inspection of the existing indications in the upper support ring, the drain channel to skirt weld, the tie bar-to-hood weld heat affected zone, and vertical support plates shall be conducted." License Condition 2.C.(20)(g)
-"The results of the visual inspections of the steam dryer shall be reported to the NRC staff within 90 days following startup from the respective refueling outage." The inspection results for the first refueling outage (RFO) post Extended Power Uprate (EPU)required by the license conditions above are summarized in the attachment to this letter.There are no regulatory commitments contained in this letter.Should you have any questions regarding the information in this submittal, please contact Theresa Darling, Acting Manager -Site Regulatory Assurance, at (315) 349-2221.A-0N!
U. S. Nuclear Regulatory Commission July 28, 2014 Page 2 Sincerely, Paul M. Swift Director -Site Engineering, Nine Mile Point Nuclear Station PMS/BTV
Attachment:
Steam Dryer Inspection Results -First RFO Post EPU (N2R14)cc: Regional Administrator, Region I, USNRC Project Manager, USNRC Resident Inspector, USNRC ATTACHMENT STEAM DRYER INSPECTION RESULTS -FIRST RFO POST EPU (N2R14)
ATTACHMENT STEAM DRYER INSPECTION RESULTS -FIRST RFO POST EPU (N2R14)1.0 Purpose This report provides the results of the visual inspections of the steam dryer as required by the Nine Mile Point Unit 2 Renewed Facility Operating License No. NPF-69 (Reference
- 1) License Conditions 2.C.(20)(f) and 2.C.(20)(g) as issued by Amendment No. 140 (Reference 2). The scope of the steam dryer inspections are defined in License Condition 2.C.(20)(f), which states: "During the first two scheduled refueling outages after reaching 120 percent OLTP conditions, a visual inspection shall be conducted of all accessible, susceptible locations of the steam dryer in accordance with BWRVIP-139 inspection guidelines.
In addition, a visual inspection of all accessible welds that were analyzed using embedded models shall be conducted.
In addition, a visual inspection of the existing indications in the upper support ring, the drain channel to skirt weld, the tie bar-to-hood weld heat affected zone, and vertical support plates shall be conducted." 2.0 Inspection Summary The required steam dryer inspections were completed during N2R14, which ran from March 24, 2014 through April 29, 2014. The full steam dryer inspection results are documented in the Westinghouse Refuel Outage N2R14 Inspection report G9M12-N2R14-320812 (Reference 3)and in the associated IDDEAL video database.
The steam dryer inspection included a total of 323 exams. In summary the inspections included 100 horizontal and vertical welds, 37 Tie Bars, 25 Cam/Nut and Washer tack welds, 40 Hood Support Welds, 9 Reinforcement Bank welds, 4 hood reinforcement bank welds, 8 closure plate reinforcement welds, 8 reinforcement strip welds, 8 mass plate welds, 12 drain channel and pipe welds, 6 perforated plate welds, 44 lifting rod welds, 16 high stress areas, 6 upper support ring exams (100% circumference), 2 lower guide welds, 1 manway cover weld, and 4 impingement areas. The scope included as found and as left inspections of both center closure plate stiffener brackets installed in N2R14.3.0 Inspection Results The inspections show no cracking associated with the locations analyzed with the embedded models, no cracking associated the BWRVIP-139 inspections, no change in the intergranular stress corrosion cracking (IGSCC) associated with support ring locations, no new cracking, and no change in the drain channel to skirt weld locations.
Section 2.2.6.1.1 of the Safety Evaluation Report (SER) included in Reference 2 discusses existing steam dryer cracking flaw evaluations.
The SER section discusses the IGSCC flaw evaluations for the upper ring, the tie bars and the steam dryer hood support vertical cracks.The SER accepted the flaw evaluation basis which concluded that EPU conditions would create sufficient alternating stress to cause fatigue crack growth of the existing IGSCC cracks and that the existing hood support plate vertical weld cracks would remain bounded by the flaw evaluation without repair.1 of 4 ATTACHMENT STEAM DRYER INSPECTION RESULTS -FIRST RFO POST EPU (N2R14)The flaw assessment for the hood support vertical cracks concluded that these fatigue cracks would not grow vertically longer than 2 to 3 inches under EPU service condition and therefore repair of these locations was not required for EPU service. In the 2012 pre-EPU outage diver access to the hood supports was obtained.
Based on diver access to these locations in 2012, NMP performed a best effort flaw removal grind out and re-weld/ weld overlay to provide additional margin. The re-inspection of the hood supports locations identified that 4 of the repair locations show repeat cracking.
The most likely cause of the cracking was the crack was not completely removed and therefore the crack remained active. The 2014 inspection shows the vertical cracking remains bounded by the flaw evaluations noted in the SER assessment.
A horizontal indication was identified at one location below a vertical weld repair location.
Review of the 2010 inspection video has shown that this indication was present in 2010 and not considered relevant.
The 2014 video is improved quality and the indication was judged relevant requiring review. The comparison between the 2010 and 2014 video shows the length is essentially unchanged from 2010. The flaw evaluation for the hood support location bounds the horizontal crack and no growth is anticipated under EPU service conditions.
The EPU steam dryer modifications included installation of eight mass plates in 2012: four 10 lb plates installed on the middle section of the inner hoods, four 15 lb plates on the middle section of the middle hoods. Each plate is attached with an upper and lower 3/16" fillet weld. The inspection identified two indications associated with a weld stop cavity defect. No other indications were identified for the mass plate attachment welds. The review of the attachment weld QA records and inspection photos show the weld cavity defect and evidence of a pre-existing indication.
Review of the 2014 inspection showed no other significant stop cavities with similar potential crack initiation risk. The flaw analysis of these two locations shows for these locations have an alternating stress below the crack initiation and crack growth thresholds.
As a conservative measure a 3/8" stop drill was performed to provide margin to prevent crack growth.The stop drill method is a method considered effective in BWRVIP-139.
The previously identified tie bar to hood IGSCC locations and the steam dryer support ring IGSCC locations showed no evidence of fatigue crack growth. The inspection scope included all 37 tie bar locations last inspected in 2004. This re-baseline identified one tie bar with IGSCC indications previously not identified.
The review of the 2004 video show that this indication was likely present in 2004 and was not identified.
The tie bar IGSCC cracking remains essentially unchanged and remains bounded by the previous flaw evaluations.
The inspection scope included re-inspection of previously identified cracks associated with the lifting lug anti-rotation tack welds and the steam dryer vane bank tie rod cam nut anti-rotation tack welds. These tack weld cracks were being monitored prior to EPU service. The tack weld cracking is not structurally significant as these welds are anti-rotation tack welds and adequate redundancy exists. The EPU load definition showed no change in the expected loads associated with these tack welds and repair was not required.In the 2012 pre-EPU outage, NMP installed additional redundant tack welds to both the cam nuts and the lifting lug to add additional margin. The 2014 inspection showed no new cracking in 2 of 4 ATTACHMENT STEAM DRYER INSPECTION RESULTS -FIRST RFO POST EPU (N2R14)the repaired cam nut tack weld locations.
The 2014 100% re-baseline identified one new location with a cam nut tack weld crack. For this location the anti-rotation function was not degraded as redundant tack welds exist and adequate engagement exists to prevent rotation.The 2014 100% baseline identified two of the lifting lugs with tack weld cracks. These cracks were found in similar locations to the pre-EPU baseline cracking.
The anti-rotation function was not degraded based on adequate integrity of the weld / interference and redundancy of the tack welds.4.0 Acoustic Circuit Model Vendor Non-Conformance In October 2013, Continuum Dynamics Inc. (CDI), issued a preliminary notice of investigation into an issue associated with the CDI Acoustic Circuit Model (ACM) version 4.1 used to assess the NMP2 acoustic loads on the steam dryer. CDI determined that the software used for the NMP2 steam dryer evaluation was run with an option activated that was not consistent with the ACM computer software used to define the ACM 4.1 benchmark bias and uncertainties.
The resolution of NC-0343 was evaluated in the NMP corrective action program (CR-2013-008411). The corrected ACM load definition as documented in CDI Report No.14-09P (Reference 4), and the stress re-evaluation is documented in CDI Report No.14-08P (Reference 5), conclude that the top of the center closure plate inner weld location is a high stress location.
The inspection of this location was expanded to include both the outer and inner weld high stress region a total of 4 locations.
The inspection showed no cracking.The corrected steam dryer loads and stress re-evaluation determined the best long term solution for the new center closure plate high stress location was the installation of a stiffener bracket that eliminated the end plate vibration mode and the high stress condition.
The stiffener bracket (5" width x 29" length) was installed in April 2014 and is bolted to the upper end plate (center line 13.5" below the top of the end plate attached with 6 %" diameter bolts). The modification conforms to the BWRVIP-84 and BWRVIP-181A requirements.
The inspection included the BWRVIP-139 required baseline inspection for the stiffener bracket.The stress re-evaluation (Reference
- 5) has confirmed that all steam dryer locations maintain the recommended margin of 2.0 during EPU 100% power normal operations and with the Reactor Core Isolation Cooling (RCIC) drain trap out alternate lineup (described as drain trap out of service off-normal condition).
The resolution of the NC-0343 issue has determined that the off-normal condition when the RCIC isolation valve is closed satisfies all required level I and level 2 acceptance criteria; however, the minimum stress ratio is below the recommended ratio of 2.0 assuming continuous operation (high cycles > 1011 cycles). This operating condition is an off-normal condition.
The closure of the RCIC isolation valve causes the system to become inoperable and for NMP2 to not meet Limiting Condition for Operation (LCO) 3.5.3, "RCIC System". The action required for the RCIC system inoperable is to immediately verify that the High Pressure Core Spray system is Operable and to restore the RCIC system to Operable status within 14 days. Subsequently, if the RCIC system is not restored within 14 days, the unit must enter MODE 3 (cold shutdown) within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and reduce reactor steam dome pressure to < 150 psig within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. When the short operating time is considered, the analysis in CDI 3 of 4 ATTACHMENT STEAM DRYER INSPECTION RESULTS -FIRST RFO POST EPU (N2R14)Report No.14-04P (Reference
- 6) has demonstrated that the equivalent minimum stress ratio is maintained above the recommended ratio of 2.0 for all locations.
5.0 Conclusion
The inspections completed during N2R14 did not identify any EPU related service induced cracking.
The NMP2 steam dryer remains qualified for EPU service conditions.
The resolution of NC-0343 identified that the center closure plate upper inner weld as a high stress location.
The inspection of these welds confirms no cracking and adequate alternating stress margin for EPU conditions.
The installation of the center end plate stiffener bracket improved the margin for this new high stress location and eliminates the end plate resonant frequency that was identified to correspond with the revised steam dryer load.6.0 References
- 1. Nine Mile Point Unit 2 Renewed Facility Operating License No. NPF-69 2. Letter from R. Guzman (NRC) to K. Langdon (NMPNS), "Nine Mile Point Nuclear Station, Unit No. 2 -Issuance of Amendment RE: Extended Power Uprate (TAC NO.ME1476)," December 22, 2011 3. Westinghouse Report No. G9M12-N2R14-320812, "Refuel Outage N2R14 Inspection report" 4. CDI Report No.14-09P "Acoustic and Low Frequency Hydrodynamic Loads at 115%CLTP Target Power Level on Nine Mile Point Unit 2 Steam Dryer to 250 Hz Using ACM 4.1R" 5. CDI Report No.14-08P "Stress Re-Evaluation of Nine Mile Point Unit 2 Steam Dryer at 115% CLTP" 6. CDI Report No.14-04P "Computation of the Cumulative Usage Factor for the 115%stress Re-Evaluation of Nine Mile Point Unit 2 Steam Dryer at 115% CLTP power level at Nine Mile Point Unit 2 with the Inboard RCIC valve closed" 4 of 4