ML120481708

Summary of Meeting with Exelon, LLC to Discuss Approach to Unrestrained Stack-Up Operations at the Upcoming Loading Campaign at Byron Nuclear Station (Byron), Enclosure 1 - Meeting Attendees, Enc 2- Agenda

ML120481708
Person / Time
Site:	Byron
Issue date:	02/17/2012
From:	Garcia-Santos N NRC/NMSS/SFST
To:	Michael Waters, Boland A NRC/NMSS/SFST, Division of Nuclear Materials Safety III
Garcia-Santos N, NMSS/SFST 492-3290
Shared Package
ML120481631	List: ML120481708 ML120520125
References
TAC L24611
Download: ML120481708 (8)

Text

February 17, 2012 MEMORANDUM TO: Michael Waters, Acting Deputy Director Division of Spent Fuel Storage and Transportation, NMSS Anne T. Boland, Director Division of Nuclear Material Safety, Region III FROM: Norma Garcia Santos, Project Manager /RA/

Rules, Inspections, and Operations Branch Division of Spent Fuel Storage and Transportation, NMSS

SUMMARY

OF JANUARY 10, 2012, PUBLIC MEETING WITH EXELON, LLC TO DISCUSS APPROACH TO UNRESTRAINED STACK-UP OPERATIONS AT THE UPCOMING LOADING CAMPAIGN AT BYRON NUCLEAR STATION [BYRON]

Background

A public meeting was held on January 10, 2012, in Rockville, Maryland, at the request of the Exelon Generating Company, LLC (Exelon) to discuss Exelons plans to support unrestrained stack-up operations for the upcoming dry fuel storage campaign at Byron.

The meeting was noticed on December 21, 2011(ML113550591). The meeting was open to the public. Exelon provided presentation slides on January 9, 2012 (ML120090302). The meeting attendance list is provided as Enclosure 1. The meeting agenda and meeting logistics are provided as Enclosure 2. Exelons presentation slides are provided as Enclosure 3. Additional handouts provided by Exelon at the public meeting are provided as Enclosure 4. A summary of additional comments discussed at the meeting are provided as Enclosure 5.

Discussion The discussion generally followed the agenda (Enclosure 2). The primary reason for the meeting was to discuss Exelons assumptions and calculations to support unrestrained stack-up operations for the upcoming dry fuel storage campaign at Byron. No regulatory decisions were made at this meeting. Exelon was seeking feedback on its planned analysis and at the same time to understand the Unites States Nuclear Regulatory Commissions (NRCs) position regarding unrestrained stack-up operations during loading campaigns. Currently, NRC staff from the Division of Spent Fuel Storage and Transportation (SFST) as well as regional inspectors had asked questions about unrestrained stack-up operations during loading of spent fuel into dry storage cask systems due to seismic concerns (i.e., tip over, rocking, etc.). During inspections, NRC staff has asked licensees to provide justification for why restraints are not needed to prevent tip over or rocking of a cask system, if an earthquake occurs during spent fuel loading operations. Staff from the Office of Nuclear Reactor Regulation (NRR) as well as Office of New Reactors (NRO) attended the meeting as well as representatives from the nuclear industry and the press.

M. Waters Exelon explained that no analytical evaluations or tests had yet been performed to validate the analyses or simulations performed using the ANSYS and LS-DYNA computer codes. The NRC staff also noted that the assumptions of the analysis should be clearly supported. The staff noted that when using analytical methods, it is important to properly benchmark the model in order for staff to have confidence in the modeling techniques.

Technical Discussion The licensee mentioned that the LS-DYNA stack-up model incorporated nonlinear material properties and friction sliding contact at the base, and that the model's free rocking response was the basis for determining the coefficient of restitution (COR). The calculated COR was then converted to equivalent viscous damping, which was assigned to the contact elements at the base of the ANSYS stack-up model. Friction sliding contact was also included in the ANSYS model. The staff commented that this meant that frictional energy dissipation (damping) had been "double counted" by friction having been included in determining the COR from the LS-DYNA model, from which the damping for the ANSYS contact elements was calculated, and also having been included again in the ANSYS model.

The staff noted that the sliding and rocking of a stack-up exhibit many elements of chaotic behavior, and as such, the final results may be significantly altered by small changes in initial conditions. The staff mentioned that recent tests on the free rocking of concrete blocks on different surfaces conducted at the University of Auckland in New Zealand, in which the blocks had been restrained from sliding, had confirmed Housner's original equation for calculating the rocking COR. The staff commented that, in the absence of physical evidence to the contrary, a COR computed from an LS-DYNA model, which is restrained from sliding should be no less than Housner's value. The staff also mentioned that the equivalent viscous damping of 9% that had been calculated from the LS-DYNA COR result and used in the ANSYS model appeared to be too high.

The licensee commented that the average of the five real earthquake time history spectra used in the ANSYS analysis enveloped the 2 percent (%) damped floor response spectra. The staff commented that the average of the time history spectra should envelope the undamped floor spectra. The staff noted that on slide 12 of the licensees presentation, seismic loads are input to ANSYS in the form of velocity time histories (and not the acceleration time histories). The licensee would need to verify if the velocity and acceleration time histories will provide the same response.

The staff noted that the gap between the interior of the transfer cask and the canister was 3/16-inch, which was less than the gap of 1/2-inch mentioned by the staff at the Technical Exchange. SFST staff explained that the 1/2-inch gap was based solely on engineering judgment. NRO staff mentioned that the licensee needed to verify that the 3/16-inch gap would not have a significant influence on the sliding or rocking of the stack-up.

Slide 24 of the licensee's presentation showed the allowable sliding distance of the stack-up to be 29.75 inches. Based on the geometry of the shims and LPT shown on slide 8, the staff commented that the allowable distance was too large, because it would allow the stack-up to extend over the edge of the LPT and shims by almost 2.5 feet, which would not only change the COR but also increase the possibility for greater rocking response of the stack-up.

M. Waters The licensee was asked if testing had been performed to demonstrate that the cask system would not rock or slide in the longitudinal direction during a seismic event. The licensee mentioned that they had performed some tests for Dresden Station, but no specific tests were conducted at Dresden for longitudinal motion (i.e., rolling) of the LPT. However, HOLTEC commented that they had, in the past, performed numerical simulations for other licensees, using VisualNastran, to quantify the amount of LPT rolling in the longitudinal direction.

The staff asked if the calibrated low friction material (CLFM) would be reused. The licensee replied that it would be reused. The staff suggested that the CLFM be tested before each use to ensure that the coefficient of friction (COF) had not increased with time or wear, because an increase in COF could lead to increased rocking.

While discussing the structural methodology, Exelon mentioned that if resolution was reached between Exelon and NRC on concerns raised during this meeting, it would develop a 10 CFR 50.59 evaluation, finalize the analysis, and provide it to Region III ISFSI staff for inspection during Byrons upcoming loading campaign. At the end of the meeting, Exelon mentioned that this timeline may be delayed given the feedback provided by NRC staff during this public meeting.

Finally, the staff discussed the possibility for HOLTEC, Exelons cask system vendor, to submit a topical report for NRCs review, because of the generic applicability of this issue. This approach would provide a higher level of closure than an inspection report, even though it would not be the end state. Moreover, the staff mentioned that the general license process has advantages, but it requires the vendor to demonstrate that the cask system would not tip over with a high degree of certainty.

The loading campaign at Byron is scheduled for February 2012.

Docket Nos. 50-454, 50-455, 72-68 TAC No. L24611

Enclosures:

1. Meeting Attendees

2. Agenda and Meeting Logistics

3. Presentation Slides (Public Meeting)

4. Supporting Material (Provided by Exelon at the Public Meeting)

M. Waters The licensee was asked if testing had been performed to demonstrate that the cask system would not rock or slide in the longitudinal direction during a seismic event. The licensee mentioned that they had performed some tests for Dresden Station, but no specific tests were conducted at Dresden for longitudinal motion (i.e., rolling) of the LPT. However, HOLTEC commented that they had, in the past, performed numerical simulations for other licensees, using VisualNastran, to quantify the amount of LPT rolling in the longitudinal direction.

The staff asked if the calibrated low friction material (CLFM) would be reused. The licensee replied that it would be reused. The staff suggested that the CLFM be tested before each use to ensure that the coefficient of friction (COF) had not increased with time or wear, because an increase in COF could lead to increased rocking.

While discussing the structural methodology, Exelon mentioned that if resolution was reached between Exelon and NRC on concerns raised during this meeting, it would develop a 10 CFR 50.59 evaluation, finalize the analysis, and provide it to Region III ISFSI staff for inspection during Byrons upcoming loading campaign. At the end of the meeting, Exelon mentioned that this timeline may be delayed given the feedback provided by NRC staff during this public meeting.

Finally, the staff discussed the possibility for HOLTEC, Exelons cask system vendor, to submit a topical report for NRCs review, because of the generic applicability of this issue. This approach would provide a higher level of closure than an inspection report, even though it would not be the end state. Moreover, the staff mentioned that the general license process has advantages, but it requires the vendor to demonstrate that the cask system would not tip over with a high degree of certainty.

The loading campaign at Byron is scheduled for February 2012.

Docket Nos. 50-454, 50-455, 72-68 TAC No. L24611

Enclosures:

1. Meeting Attendees

2. Agenda and Meeting Logistics

3. Presentation Slides (Public Meeting)

4. Supporting Material (Provided by Exelon at the Public Meeting)

Distribution:

NRC Attendees G:\SFST\Garcia\Public Meetings NGS\Meetings-ngs\SFST-Stackup\Exelon Approach-Byron\Exelon Mtg-Concurrence Pkg ML120481631 OFC NMSS\SFST NMSS\SFST NRR NRO NAME NGarcia-Santos GBjrkman KManoly BJain DATE 1/25/2012 1/27/2012 1/27/2012 1/26/2012 OFC NMSS\SFST NMSS\SFST Region III NMSS\SFST NAME WWheatley CAraguas CLipa MWaters DATE 1/31/2012 2/16/2012 2/17/2012 C" = Copy without attachment/enclosure "E" = Copy with attachment/enclosure "N" = No copy OFFICIAL RECORD COPY

January 10, 2012, Public Meeting Between Exelon, LLC and the Nuclear Regulatory Commission MEETING ATTENDANCE LIST Name Organization Doug Weaver NRC Gordon Bjrkman NRC Anne T. Boland NRC Christine A. Lipa NRC Blair Spitzberg NRC Vincent Everett NRC John Bozga NRC Vijay Meghani NRC Jim Neurauter NRC Robert Carrion NRC Marc Ferdas NRC John Nicholson NRC Eric Benner NRC BP Jain NRC D. Ibana NRC John Goshen NRC Rhex Edwards NRC David Tarantino NRC David Tang NRC Bob Tripathi NRC Jon Woodfield NRC Bob Martin NRC Breda Mozafari NRC Ray Wharton NRC David Pstrak NRC Natreon Jordan NRC Alexis Sotomayor NRC Jimmy Chang NRC Kamal Manoly NRR Norma Garcia Santos NRC Lucieann Vechioli NRC Terry Sides Southern Nuclear John Schrage Exelon David Gullot Exelon Enclosure 1

January 10, 2012, Public Meeting Between Exelon, LLC and the Nuclear Regulatory Commission MEETING ATTENDANCE LIST Name Organization Kevin Donovan Exelon Ed Blodin Exelon Gary Voss Exelon Tom Bortolini Exelon Ken Hunter Exelon M Kassar Exelon Adam Levin Exelon Stefan Anton HOLTEC Tammy Morin HOLTEC Chuck Bullard HOLTEC Venkat Prabhala HOLTEC Zhihua Yue HOLTEC Anveshan Bommareddi HOLTEC Pierre Oneid HOLTEC Marc Nichol NEI George Abadallah DTE, Fermi Bruce F. Henley, PE & PMP Luminant Power Ken Spates TVA/RRC Stephenie Pyle Entergy - Arkansas Nuclear One Robert Clark Entergy - Arkansas Nuclear One Jay G. Wellwood; Nuclear Services Westinghouse Glenn Schwartz, P.E. PSEG Nuclear Fuels Sam Hassoun Fermi 2 Nuclear Power Plant Zita Martin Tennessee Valley Authority John Pfabe D.C. Cook Nuclear Plant Ben Spiesman FirstEnergy Nuclear Operating Company Jeff Fox FENOC Jim Veglia FENOC Donna Haviland FENOC Paul Wilson FENOC Lloyd Zerr FENOC Ted Hilston FENOC Kevin Koski FENOC Maureen Conley Platts/McGraw Hill Nuclear Publications Carlyn Greene Ux Consulting Enclosure 1

Public Me eeting with Exelon, LLC January 10, 2012 Agenda Opening remarks Norma Garcia a Santos Anne Boland Doug Weaverr Introductions All Exelons Approach Exelon Break All Open Discussion . All Parking Lot Parking Lot Summary Norma Garcia a Santos Opportunity for Public Comm ment Public Closing Remarks Anne Boland Doug Weaverr E

Enclosure 2

Public Meeting with Exelon, LLC January 10, 2012 Logistics Executive Boulevard Building (EEB) Complex Cafeteria Flag Pole Snack Building 6002 Shop Building 6003 st Conference Room 1 Floor Lobby L

M Road Ladies Room Mens Room Water Fountain Door(s)

Reminders

• You will need an escort at all times while in EBB 6003.

• You will need an identification to access EBB 6002 and 6003.

• Building evacuation - Meet at the flag pole.

• Return your provisional badge when you leave this building.

• Please fill out the Public Meeting Feedback Form at the end of the meeting or send it by mail (NO Postage necessary).

Enclosure 2