L-PI-17-014, Summary of Public Meeting and Plan for NRC Request for Additional Information Regarding License Amendment Request for Spent Fuel Pool Criticality Technical Specification Changes (CAC Nos. MF7121...

Summary of Public Meeting and Plan for NRC Request for Additional Information Regarding License Amendment Request for Spent Fuel Pool Criticality Technical Specification Changes (CAC Nos. MF7121...

ML17109A485
Person / Time
Site:	Prairie Island
Issue date:	04/19/2017
From:	Conboy T Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CAC MF7121, CAC MF7122, L-PI-17-014
Download: ML17109A485 (9)

Text

Prairie Island Nuclear Generating Plant Xcel Energy 1717 Wakonade Drive East Welch, MN 55089 L-PI-17-014 Apri119, 2017 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant, Units 1 and 2 Dockets 50-282 and 50-306 Renewed License Nos. DPR-42 and DPR-60 Summary of Public Meeting and Plan for NRC Request for Additional Information Regarding License Amendment Request for Spent Fuel Pool Criticality Technical Specification Changes (CAC Nos. MF7121 and MF7122)

References:

1) Letter from Kevin Davison (NSPM) to NRC (Document Control Desk),

"License Amendment Request for Spent Fuel Pool Criticality Technical Specification Changes," dated November 17, 2015 (ADAMS Accession No. ML15327A244)

2) Email from Robert Kuntz (NRC) to Glenn Adams (NSPM), "Official Use Only- Proprietary Information Enclosed- Request for Information Related to the Prairie Island SFP Criticality Analysis License Amendment Request (CAC Nos. MF7121 and MF7122)", dated October 31, 2016

3) Letter from Scott Northard (NSPM) to NRC (Document Control Desk),

"Response to NRC Request for Information- License Amendment Request for Spent Fuel Pool Criticality Technical Specification Changes (CAC Nos. MF7121 and MF7122," dated February 16, 2017 (ADAMS Accession No. ML17047A454)

4) Letter from Robert Kuntz (NRC) to NSPM, "Summary of March 9, 2017, Meeting with Northern States Power Company, Doing Business as Xcel Energy, Related to the Spent Fuel Pool Criticality License Amendment Request (CAC Nos. MF7121 and MF7122)," dated April 6, 2017 (ADAMS Accession No. ML17093A601)

In a letter to the U.S. Nuclear Regulatory Commission (NRC) dated November 17, 2015 (Reference 1), the Northern States Power Company, a Minnesota corporation doing business as Xcel Energy (hereafter "NSPM"), requested an amendment to the Technical Specifications (TS) for Prairie Island Nuclear Generating Plant (PINGP).

Specifically, NSPM proposed to revise Technical Specification (TS) 3.7.16, "Spent Fuel Storage Pool Boron Concentration," and TS 4.3.1, "Fuel Storage Criticality," to allow spent fuel pool (SFP) storage of nuclear fuel containing a boron-based neutron

Document Control Desk Page 2 absorber in the form of zirconium diboride (ZrB 2 ) Integral Fuel Burnable Absorber (IFBA).

The IFBA-Gd spent fuel pool criticality analysis submitted by Reference 1 followed published NRC guidance (DSS-ISG-201 0-01 ), utilized NRC approved methods, and was consistent with the Prairie Island Licensing Basis. To complete their review, the NRC staff provided a second request for additional information (RAI)- Reference 2.

The NRC requested that the reactivity effect of fuel position eccentricity be treated differently than the method utilized in the approved 2013 criticality analysis and that a new reactivity effect of spacer grid growth be considered in the criticality analysis.

In Reference 3, NSPM deferred response to the Reference 2 RAis until the merits of those RAis could be discussed with NRC Staff.

At a public meeting held on March 9, 2017, NSPM sought to understand the basis for these RAis relative to the additional conservatisms that potentially result in unnecessary spent fuel movement and adverse safety impact. NSPM requested that NRC Staff reconsider the need for the RAis. To promote continued engagement to resolve the situation prior to the 2-year review metric, NSPM agreed to submit a summary of the public meeting and a proposed markup of the RAis based on its understanding from the discussions at the March 9, 2017 public meeting. To that end, NSPM provides a meeting summary (Enclosure 1) and a markup to the RAis (Enclosure 2).

In Reference 4, NRC provided its summary of the meeting.

NSPM will continue to work with the NRC's Licensing Project Manager to schedule further engagement with NRC Staff to resolve the scope of the RAis and separate engagement with technical staff to discuss any revised models and methods that the licensee may require to address the revised RAis.

If there are any questions or if additional information is needed, please contact Glenn Adams at 612-330-6777.

Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.

Thomas Conboy Director Site Operations - Pra* re Island Nuclear Generating Plant Northern States Power Company - Minnesota

Enclosures:

1. Meeting Summary- Public Meeting 3/9/2017

2. Markup of RAis

Document Control Desk Page 3 cc: Regional Administrator, Region Ill, USNRC Project Manager, Prairie Island Nuclear Generating Plant, USNRC Resident Inspector, Prairie Island Nuclear Generating Plant, USNRC State of Minnesota

L-PI-17-014 Enclosure 1, Meeting Summary- Public Meeting 3/9/2017 Page 1 of 4 Date: 3-9-2017 Time: 9:00am- 11:30 pm ET Location: One White Flint North, Rockville, MD (OWFN-12B4)

Participants:

NRC NSPM Rob Kuntz, Project Manager (DORL) Marty Murphy Katherine Brock, Deputy Division Director, DORL Tom Conboy Bob Lukes, Branch Chief (NRR/DSS/SNPB) Glenn Adams Amrit Patel (NRR/DSS/SNPB) Darius Ahrar Scott Krepel (NRR/DSS/SNPB) by phone Sean Martin Kent Wood (NRR/DSS/SNPB) Mark Brossart Hank Hoelscher (phone)

Gene Eckholt (phone)

Westinghouse Mike Wenner Doug Sipes Andrew Blanco NEI Kris Cummings No members of the public appeared in person or identified themselves by phone.

Topic

Introduction:

The purpose of this meeting is for the NRC staff and NSPM to discuss NRC staff's request for additional information as requested by NSPM letter dated February 16, 2017 (ADAMS Accession No. ML17047A454). The presentation slides were provided to NRC Staff two days prior to the meeting.

Main Points of Discussion:

Rob Kuntz provided preliminary administrative remarks about the meeting, and opening remarks including that no regulatory decisions would be made during the meeting.

NSPM presented slides to describe its project team, and the project principles and objectives. The project principles focused on maintaining adequate safety margins in analysis while also preserving nuclear safety by avoiding unnecessary fuel moves. The meeting objectives were outlined to explain the regulatory and technical basis for the Requests for Additional Information (RAis) and request their reconsideration. The second set of objectives was focused on the scope and schedule for an alternate approach to addressing the RAis (if still warranted after reconsideration of the RAis).

L-PI-17-014 Enclosure 1, Meeting Summary- Public Meeting 3/9/2017 Page 2 of 4 NSPM presented the plant's criticality analysis licensing history from 1997 to current time; a series of amendments that have progressively increased conservatism to align with the evolving regulatory guidance, from an approved Westinghouse topical methodology, through the Kopp Letter, to the Interim Staff Guidance (DSS-ISG-201 0-01 ). NSPM explained how the license amendment request under review was submitted with an analysis using the analysis methodology that NRC approved in 2013, and still aligned with the IS G. NRC Staff pointed out that one of the license amendment requests (approved in 1997) used a topical methodology that was later found to be non-conservative, so the increase in burn up requirements shown on the curve did not fully represent conservatism due to regulatory changes.

NSPM discussed its concerns with RAI-6, which relates to eccentric fuel positioning within a storage cell. The RAI requested that the analysis be corrected to treat the effect as a bias rather than an uncertainty. The stated justification for this RAI was: (1) an NEI agreement to support this treatment in draft NEI 12-16, and (2) the large reactivity impact on the Prairie Island spent fuel pool. The draft NEI12-16 document is not currently endorsed by the NRC.

NSPM stated their desire to understand how the RAis (RAI 6 and 7) were necessary to .

support the Staff's safety determination and were interested to understand why these RAis had not been identified during the pre-application meeting, acceptance review, or first round RAis. NSPM conveyed its concern of constantly changing and expanding criteria for an acceptable criticality analysis. NRC Staff conveyed that these RAis represented actual phenomena (eccentricity and grid growth) that have been known to have a potential reactivity effect and have been included in the draft NEI 12-16 guidance and previous RAis.

The NRC indicated that it was not its intent to specify that NSPM had to follow the NEI document and treatment as an uncertainty would be acceptable with adequate justification. NRC staff identified that precedent alone (i.e., historical treatment as an uncertainty) was not sufficient, yet did not provide insight regarding what would be considered adequate justification.

NEI was concerned that NRC Staff was referencing unapproved draft guidance in NEI 12-16 to justify an RAI. The draft guidance has not been endorsed by NRC, and the licensee has not committed to it. NEI clarified that the draft guidance only identifies that it is conservative to treat the effect as a bias, but does not limit approaches to treatment in this conservative manner.

NSPM discussed its concerns with RAI-7, which related to spacer grid growth due to irradiation. The stated justification for this RAI was: (1) a general concern for grid growth, (2) the identification of the issue in the draft NEI12-16 guidance, and (3) an internal NRC sensitivity study of uniform pin pitch changes that resulted in significant reactivity increase. NRC staff identified it had performed an internal study of the phenomena and had reviewed grid growth data, but it was highly varied and challenging to accurately estimate its reactivity effect. NSPM suggested that the data and

L-PI-17-014 Enclosure 1, Meeting Summary- Public Meeting 3/9/2017 Page 3 of 4 phenomena be better understood before used as an RAI basis. NSPM asked if the internal NRC study and supporting information had been made publicly available as the RAI basis and to support an understanding of the concern and associated analysis.

The NRC stated that it had not released the information.

NSPM did present information on the grid growth phenomenon for the Zirlo grids used at PINGP. However, the method of determining the grid growth and its statistical treatment is not established. Further, the NSPM preliminary analysis suggests that assuming uniform grid growth (axial and radial) would be overconservative.

NSPM then described the results of the "preliminary" analysis that was completed in January 2017 to address the RAis. In short, the increase in burnup requirements due to the RAis would result in a significant number of fuel moves in the spent fuel pool.

NSPM stressed its priority was ensuring nuclear safety and its concern that potentially unneeded fuel movement to address excessive conservatism added via the RAis (without clarity for the RAI safety basis and understanding of aggregate impact) was not aligned with that priority and was not in the best interest of safety. To support a continuation of the technical review in case that the RAis are ultimately determined to be valid, NSPM presented an alternate approach to address eccentricity and grid growth that would be less limiting than the "preliminary" approach, but still address the RAis.

For eccentricity, NSPM described the analog controls and indicators and the manual operations that provided them confidence that fuel placement was truly random and could be modeled as a 2x2 array surrounded by concentric fuel. NRC Staff raised concerns with proving randomness and offered some phenomena that should be addressed, including rack levelness and rack bottom plate sag. NRC Staff did not challenge the two statistical approaches offered by the licensee, but stated that modeling the location of a fuel assembly as concentric had to be "credible". However, the Staff provided no insights to quantify a level of credibility.

For grid growth, NSPM described using a median value of grid growth rather than a 95/95 maximum growth value. NRC Staff questioned whether treatment in this manner would also require additional consideration of an uncertainty for the deviation in growth.

NRC Staff thought it would be worthy of reviewing in a future meeting.

NSPM also suggested use of recent EPRI papers to reduce depletion uncertainty from five percent to three percent. This approach was offered as an alternative in the draft of NEI 12-16. NRC Staff stated concern with applying these papers because NEI 12-16.

was not approved guidance and these papers would have to be reviewed separately.

The NEI representative stated that these EPRI papers were getting their own separate reviews as stand-alone topical reports.

In summary, the safety basis and drivers for the RAis are not readily apparent relative to existing safety margins available in the regulation (1 0 CFR 50.68) and achieved through use of existing guidance and precedent for criticality analyses. NSPM believes that

L-PI-17-014 , Meeting Summary- Public Meeting 3/9/2017 Page 4 of 4 these RAis and associated phenomena should be assessed with an aggregate understanding of the available safety margin to preclude potential adverse safety impacts resulting from overconservative analysis causing unnecessary spent fuel movement. Lastly, NSPM finds it challenging as these RAis appear to be new concerns that the NRC staff is addressing solely through the RAI process and has not made the supporting information publicly available prior to issuance of the RAis.

NSPM requests the NRC staff reconsider and review the need for the RAis in light of the public meeting discussion. In the event the RAis are determined to be necessary, it was agreed that NSPM would summarize its understanding of the RAis and provide these to the NRC. (To that end, NSPM's revised understanding of the RAis is captured in Enclosure 2.)

L-PI-17-014 , Markup of RAis Page 1 of 2 RAI 6 - Proposed Markup Draft guidance document, NEI 12 16, "Guidance for Performing Criticality ,A,nalyses of Fuel Storage at Light VVater Reactor PO\ver Plants," is in the process of being finalized.

HovJever, the NRC technical staff has reached agreement vvith NEI on many aspects of the document without exception. One of these aspects is in regards to accounting for the reactivity effect of ((proprietary text)). The NRC staff did not identify that this accounting practice 'A'aS not implemented during its initial revie\3,f of vvc.a,p 17400 P, Supplement 1, Revision 1, "Prairie Island Units 1 and 2 Spent Fuel Pool Criticality Safety Analysis: Supplemental Analysis for the Storage of IFBA Bearing Fuel," and consequently it vvas not identified in the corresponding requests for additional information issued on April 12, 2016.

In order for the NRC staff to complete its revie'N of \'VCAP 17400 P, Supplement 1, Revision 1, please correct the accounting of the ((proprietary text)) to align with the current NRC and industry understanding of this phenomena to ensure that the 10 CFR 50.68(b)(4) requirements are met. The NRC staff believes this correction is particularly necessary in this case because of the large reactivity effect specific to Prairie Island spent fuel pool storage conditions.

Please provide technical justification for treating the reactivity effect of eccentric fuel positioning as a bias or uncertainty.

RAI 6 Proposed Retyped Version Please provide technical justification for treating the reactivity effect of eccentric fuel positioning as a bias or uncertainty.

L-PI-17-014 , Markup of RAis Page 2 of 2 RAI 7 Proposed Markup A concern was recently brought to the attention of the NRC staff regarding the potential for fuel assembly spacer grid growth during irradiation and its impact on spent fuel pool criticality safety analyses. This concern has also been identified and is being addressed as part of NEI 12 16 guidance development. Please explain the extent of grid growth known to occur in the types of materials used in the Prairie Island nuclear fuel inventory.

The fuel assembly grids have been shown to expand over the course of their utilization in the reactor (see Figure 4 of Ref. 1). How does this affect the Prairie Island spent fuel pool criticality safety analysis in WCAP-17 400-P, Supplement 1, Revision 1 and the ability to meet 10 CFR 50.68(b)(4) requirements? The NRC staff has performed studies sho,Ning that the effect of uniform pitch changes of 0.5% and 1% under spent fuel pool storage conditions can result in reactivity effects of approximately 500 pcm and 1000 pcm, respectively. The NRC staff has performed studies showing that the effect of uniform pitch changes of 0.5% and 1% under spent fuel pool storage conditions can result in reactivity effects of approximately 500 pcm and 1000 pcm, respectively.

Reference

[1] Janga, Young Ki, et al. "/>,n Investigation on Irradiation induced Grid \Aiidth Gro*lJth in Advanced Fuels." (2011).

RAI 7 Proposed Retyped Version A concern was recently brought to the attention of the NRC staff regarding the potential for fuel assembly spacer grid growth during irradiation and its impact on spent fuel pool criticality safety analyses. Please explain the extent of grid growth known to occur in the types of materials used in the Prairie Island nuclear fuel inventory. How does this affect the Prairie Island spent fuel pool criticality safety analysis in WCAP-17400-P, Supplement 1, Revision 1 and the ability to meet 10 CFR 50.68(b)(4) requirements?