ML13154A506
| ML13154A506 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 06/03/2013 |
| From: | Jack Giessner Reactor Projects Region 3 Branch 4 |
| To: | Entergy Nuclear Operations |
| References | |
| Download: ML13154A506 (9) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION REGION III 2443 WARRENVILLE ROAD, SUITE 210 LISLE, IL 60532-4352 June 3, 2013 LICENSEE:
Entergy Nuclear Operations, Inc.
FACILITY:
Palisades Nuclear Plant
SUBJECT:
SUMMARY
OF THE MAY 29, 2013, MEETING REGARDING PALISADES NUCLEAR PLANT SAFETY INJECTION REFUELING WATER TANK (SIRWT) LEAK On May 29, 2013, at 10:00 a.m. EDT, the U.S. Nuclear Regulatory Commission (NRC) held a Conference Call Meeting with members of the Palisades management team at both parties request. The purpose of the call was to discuss the current repair and inspection plan related to the SIRWT. Palisades was shut down on May 5, 2013, in response to leakage from the SIRWT of 90 gallons per day which exceeded a leak rate limit of 38 gallons per day established in the NRC confirmatory action letter (CAL EA 12-155; ADAMS No. ML12199A409). Specific discussion topics included:
- 1. SIRWT repair plan;
- 2. Status of leak causal evaluation; and
- 3. Code compliance related to the tank repair and design changes.
Status of Causal Evaluation The licensee stated that the causal evaluation was to be approved by the plants Corrective Action Review Board (CARB) on Thursday, May 30, 2013. The cause of the leak, as determined by the Babcox &Wilcox (B&W) laboratory report, from the analysis of the F east nozzle crack sample, is a lack of fusion in the weld, i.e., failure of a poorly performed weld. The final B&W report was provided to the NRC resident inspectors.
The NRC asked the licensee if they plan to evaluate the flaw against the critical flaw and stresses before starting up the plant. The NRC stated that the reason for this question was, if the tank did have future leakage, the NRC will want to ensure that all the flaws reviewed by the licensee were bounded in accordance with Code Case 705, stresses were lower than the limit, flaw size was smaller than the critical size and structural integrity was not challenged.
The licensee stated that they were updating their structural integrity calculation and understood the NRC position. The previous analysis assumed a nozzle flaw, with higher stresses, and it
Entergy Nuclear Operations, Inc.
appeared to be bounded. The licensee said that if they started up and had a leak, their analysis will have to conform to Code Case N-705. The licensee stated that Lucius Pitkin Inc. (LPI) was conducting the analysis related to the most recent flaw to confirm their assessments.
The licensee said that the most of the concerns raised by the NRC during the previous conference call were no longer applicable due to the change in repair plans related to the tank.
The liner option was not going to be pursued.
Nozzle Repairs The licensee discussed nozzle repairs related to the SIRWT as follows:
- 1. In 1988, the G and H nozzles were bored out of the concrete floor below the tank and replaced as a result of certain issues related to these nozzles.
- 2. In 2012, during the SIRWT leakage event, nozzles K, L and M were bored out to be freed from the concrete, replaced and reinforced through reinforcing plates at the nozzle penetrations. Nozzles J and N were also severed from the tank bottom and patch plates were installed over the tank plating. Eight nozzles remained in service after the SIRWT repairs related to the 2012 leak. Three nozzles, F east, F west and E remained locked in the concrete structure below the tank.
- 3. During the repairs related to the current leak (May, 2013), the remaining nozzles will be freed from the concrete. F east, F west and E nozzles have been bored out of the concrete to reduce stresses on the nozzle to floor plate weld joint, and replaced.
G and H nozzles are also being replaced.
So, by the end of this outage, all nozzles would have been replaced in the last year and removed from concrete encasement, or removed from service permanently.
Tank Bottom Repair The licensee stated that they will replace most of the tank plating at the bottom of the tank and replace all inner tank welds at the bottom of the tank. This will be accomplished by removing the old plating at the bottom of the tank out to a radius within the tank that leaves a plate remnant of approximately 14 inches from the shell wall. This remnant bottom plate allows a new plate to be welded onto it. During the plate removal activity, the licensee inspected the area under the plate to determine the extent of grout ring which supports the outer shell of the tank as shown on plant drawings. This lead to the discovery that the drawing did not accurately represent components in the field in that there is no grout ring and the tank was constructed on the circular slab foundation in its entirety. During the plate removal, the licensee also discovered there was no sand underneath the tank with the exception of areas where sand was injected during the 2012 repair efforts. There was no evidence of any coating between the concrete area and the bottom aluminum plates. As a result of these discoveries, the licensee will be providing a layer of asphalt impregnated fiber board between the concrete slab and new aluminum plating which will extend to the periphery of the remnant plate. The licensee stated
Entergy Nuclear Operations, Inc.
that they will be installing a felt type paper, similar to roofing material, underneath the fiber board and remnant plate. Both the asphalt impregnated fiber board and the felt paper will provide the separation between the aluminum and the concrete. This practice was recommended by the code document for the SIRWT, B96.1 to provide a suitable cushion as recommended by Appendix E of B96.1. The licensee stated that the fiber board will be permanent and is not required to be replaced.
The NRC asked the licensee if they planned to perform a separate cause analysis based on the absence of the sand and grout ring underneath the tank to explain factors that could be related to previous leakage, concrete to aluminum interaction, water squeezing effect from the sand, etc. The licensee stated that these items were being reviewed and incorporated into the tank design evaluation, including stresses and impacts caused by design irregularities. The NRC asked the licensee if they planned to perform a cause evaluation related past leakage and past cause evaluations to determine if the lack of sand and grout ring changes any conclusions. The NRC noted that there could be a potential change to the CAL and/or commitments. The licensee stated that their expectation is that the tank will not leak when the plant starts up. The NRC and site noted there was further discussion needed on the CAL. The NRC said that the correlation with tritium, at best, is weak, unless a tracer can be shown to work. If there is any leakage from the tank, short of some analysis, the NRC will assume that the tank is leaking and if the licensee can make a Code Case assessment, the NRC will review it. The licensee agreed with the NRC and stated that they were in the process of looking for a good tracer and they will inform the NRC if they arrive at a decision regarding this matter.
When the NRC asked the licensee if they planned on replacing the weld between the side and the bottom of the tank because of concerns related to previous root causes pointing to potential tank flexing, the licensee stated that all the welds, including the circumferential weld inside the tank, will be new - these welds will be ground out and re-welded. The licensee stated that all the lap welds and corner joints for the bottom plates, including the plates interfaced with the shell, will also be ground out and renewed. The licensee said that there will be no old welds on the bottom two feet inside the tank with the exception of the vertical weld on the side wall of the tank, i.e., all the floor welds and the floor-to-wall welds will be new. The circumferential weld outside the tank will not be renewed.
The NRC asked the licensee for the details of the material being used for the welds. The licensee said that they will inform the NRC once the material was confirmed.
The NRC asked the licensee how much overlap of the remnant plate they planned to leave in place and if they had the results of any inspections they had conducted on the remnant plates.
The licensee stated that the new plate will overlap the old plate in varying dimensions around the tank circumference primarily due to guidance provided in industry standards with respect to installing lap joints a certain distance away from other joints that have plates lapped together.
They said that some of the new plates will be 6 inches from the inside shell wall, other locations will be 12 inches from the inside wall and the transitions between these two locations will be in a smooth radius. The NRC asked how this design relates to the identified thinning in certain areas of the old plate that were discovered through ultrasonic testing (UT). The licensee said that the intent was to overlap the new plate over the thinned material that was found. In addition, the licensee stated that they are working with LPI to perform an analysis of the thinned area to determine the acceptable plate thickness for this region of the tank to ensure the
Entergy Nuclear Operations, Inc.
installed thickness exceeds the requirement. The NRC asked if the licensee had identified the cause of the plate thinning. The licensee said that they did not know the cause; however, the known phenomenon, previously discussed, of concrete-aluminum interaction, if combined with certain conditions such as moisture, can lead to a pitting effect. The licensee stated that placing the fiber board and felt paper in between the aluminum surface and concrete should address future corrosion. Since the concrete-aluminum interaction occurred on a couple of nozzles in the past, the NRC noted a follow-on preventative inspection based on a certain frequency may be needed. The licensee said that there wasnt widespread corrosion or pitting throughout the tank. They said that there were nine small areas identified that were bean shaped and varied in size between 3x3 and 3x1 and that the amount of corrosion identified was within any projected corrosion rate of aluminum. They said that the tank floor was in good shape with the exception of the above mentioned nine load spots that were above minimum wall code thickness and were negligible compared to the size of the tank.
The NRC asked if the licensee was planning to address the issue related to the missing grout ring underneath the tank. The licensee stated that B96.1 allows tanks to rest on a concrete slab as long as a suitable cushion was established. The licensee stated that that they will be meeting this requirement by using the 3/8 inch fiber board and (felt) paper material. The fiber board will be installed next to the annulus ring. The code does not require a grout ring.
When the NRC asked the licensee if they plan to install a liner, the licensee stated that they did not plan to install one and hence, the relief request will be withdrawn since the coating will not be applied.
The licensee stated they plan to improve their ability to encourage any future leakage (which they expect not to occur) from the bottom plates to migrate to the penetrations where the F nozzles reside by scoring shallow grooves on the top surface of the concrete slab. The licensee said that this will enable them to collect and quantify any potential future leakage and should prevent leakage to the roof.
The NRC asked if there was a possibility for the leakage to bypass the F east and F west nozzle penetrations or goes undetected. The licensee stated that the channel system will direct the leakage to the desired location in the catacombs for collection. The NRC asked if the licensee planned to perform any repairs to the roof based on what was discovered. The licensee said that they are still evaluating this issue. The licensee stressed their intention, regardless of their leakage plans, is to startup with no leakage.
Code Compliance The licensee stated that all the work related to the tank was expected to be compliant with the original code requirements for the tank, i.e., B96.1. ASME IWA 4000 series requires code suitability reconciliation for the plate material being used. The licensee plans to use aluminum 5086 as opposed to the originally installed aluminum 5454. The licensee will include a section in their Engineering Change (EC) document per IWA 4000 to evaluate the suitability of the changes being made during this repair/replacement activity.
The NRC asked the licensee for the basis behind the use of aluminum 5086. The licensee stated that this material was commonly used in the marine industry and was more suitable to the current application compared to the initially proposed aluminum 6061 material. The licensee
Entergy Nuclear Operations, Inc.
stated that the reinforcing plate will also be fabricated from aluminum 5086 material. These details were still being validated.
Schedule The NRC asked for the licensees schedule related to the repairs. The licensee said that they were working on installing retaining collars for the nozzles, the fiber board was cut and in place and the new aluminum plates were being fabricated outside the tank (which was delayed due to high winds and lightning conditions). During the next several days, they anticipated installing the plates and weld for approximately 3-4 days. Finally, they plan to conduct extensive non-destructive examinations (NDE) on the new welds.
Post Maintenance Testing The NRC asked if the licensee had arrived at a means to detect the lack of fusion, as it occurred during the recent crack and what corrective actions were being incorporated into the post maintenance testing. The licensee stated that the post maintenance testing for all the lap joints in the tank and the corner joints around the circumference will include a visual examination with vacuum box testing to satisfy the B96.1 code. They will also be conducting Testex electromagnetic field testing to identify any sub-surface defects. A visual inspection, vacuum box testing, dye-penetrant examination and Testex electromagnetic field testing will be conducted on the welds between the reinforcing plate and the floor plate. Dye-penetrant examination will be conducted at the locations where the nozzle pipes penetrate the reinforcing plate. The licensee stated that they were working with Testex to optimize the technique to identify subsurface defects. They were planning to ship the welding sample coupons to Testex to enhance their testing techniques. The licensee stated that Testex was not a code approved methodology and that it was only a quality assurance method for the licensee since this was the best available testing methodology for the application. There were no plans to approve the Testex method per the code. Post maintenance testing involved visual VT-2 examinations and ongoing inspections to include pressure test requirements of ASME Code Section XI to identify any evidence of leakage under normal operating pressure and temperature. In addition, detailed training of welders was taking place.
The NRC concluded the conference by suggesting the licensee update their commitments, even though not required by code, with the results of the sand samples, periodic inspections and information related to roof drains. The NRC wanted to ensure the revised CAL was established.
The NRC said that it will request another conference call as and if things change. The licensee said they will request another conference call next week to discuss the technical aspects of the tank repair.
Entergy Nuclear Operations, Inc.
The call lasted about an hour. Enclosure 1 is a list of attendees for the meeting.
Sincerely,
/RA/
John B. Giessner, Chief Branch 4 Division of Reactor Projects Docket Nos. 50-255 and 72-007 License No. DPR-20
Enclosure:
- 1. List of Meeting Attendees for the May 29, 2013, Conference Meeting cc w/encl: Distribution via List ServTM
LIST OF MEETING ATTENDEES FOR THE MAY 29, 2013 CONFERENCE MEETING NRC Attendees John Giessner, Chief, Division of Reactor Projects, Branch 4 David Hills, Chief, Division of Reactor Safety, Engineering Branch 1 Vijay Meghani, Reactor Inspector, Division of Reactor Safety, Engineering Branch 1 Thomas Taylor, Palisades Senior Resident Inspector April Scarbeary, Palisades Resident Inspector Swetha Shah, Reactor Engineer, Division of Reactor Projects, Branch 4 Mahesh Chawla, Project Manager, Division of Operating Reactor Licensing Licensee Attendees Barry Davis, Engineering Director Otto Gustafson, Licensing Manager Jeff Erickson, Palisades Engineering Licensing Jody Haumersen, Palisades Manager of Engineering Systems Kevin OConner, Palisades Design Engineering Manager Tom Fouty, Palisades System Engineering Supervisor David MacMaster, Palisades Design Engineering Supervisor Kent Novotney, Sargent & Lundy Project Manager
Entergy Nuclear Operations, Inc.
The call lasted about an hour. Enclosure 1 is a list of attendees for the meeting.
Sincerely,
/RA/
John B. Giessner, Chief Branch 4 Division of Reactor Projects Docket Nos. 50-255 and 72-007 License No. DPR-20
Enclosure:
- 1. List of Meeting Attendees for the May 29, 2013, Conference Meeting cc w/encl: Distribution via List ServTM DOCUMENT NAME: Palisades Meeting Summary May 29, 2013 Publicly Available Non-Publicly Available Sensitive Non-Sensitive To receive a copy of this document, indicate in the concurrence box "C" = Copy without attach/encl "E" = Copy with attach/encl "N" = No copy OFFICE RIII RIII NAME JGiessner for Swetha:rj JGiessner DATE 06/03/13 06/03/13 OFFICIAL RECORD COPY
Letter to Entergy Nuclear Operations, Inc. from J. Giessner dated June 3, 2013
SUBJECT:
SUMMARY
OF THE MAY 29, 2013, MEETINGS REGARDING PALISADES NUCLEAR PLANT SAFETY INJECTION REFUELING WATER TANK (SIRWT) LEAK DISTRIBUTION:
Doug Huyck RidsNrrPMPalisades Resource RidsNrrDorlLpl3-1 Resource RidsNrrDirsIrib Resource Chuck Casto Cynthia Pederson Steven Orth Allan Barker Carole Ariano Linda Linn DRPIII DRSIII Patricia Buckley Tammy Tomczak ROPassessment.Resource@nrc.gov