RA21-016, Netco Rack Insert 10-year Surveillance Report

Netco Rack Insert 10-year Surveillance Report

ML21105A035
Person / Time
Site:	LaSalle
Issue date:	04/15/2021
From:	Washko J Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RA21-016
Download: ML21105A035 (7)

Text

LaSalle County Station Exelon Generation ,~ 2601 North 21 st Road Marseilles IL 61341 815-415-2000 Telephone www.exeloncorp.com RA21-016 April 15, 2021 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 LaSalle County Station, Units 1 and 2 Renewed Facility Operating License Nos. NPF-11 and NPF-18 NRC Docket Nos. 50-373 and 50-374

Subject:

Netco Rack Insert 10-year Surveillance Report

References:

1. "Additional Information Supporting License Amendment Request Regarding the Use of Neutron Absorbing Inserts in Unit 2 Spent Fuel Pool Storage Racks,"

Exelon letter to NRC, RS-11-008, dated January 24, 2011

2. NRC Safety Evaluation for Amendment No. 199 to Facility Operating License No.

NPF-11 and Amendment No. 186 to Facility Operating License No. NPF-18, dated January 28, 2011 The attached report is submitted in accordance with Reference 1, which made a one-time regulatory commitment to submit the results of the first 10-year surveillance of the NETCO-SNAP-IN rack inserts within 60 days following completion. The subject report indicates that the insert appeared to have no wear from duty, the results were deemed acceptable, and no further evaluation was required. The insert was re-installed in its original location.

There are no additional regulatory commitments contained in this letter. Should you have any questions concerning this letter, please contact Mr. Daniel Mearhoff, Regulatory Assurance Manager, at (815) 415-2800.

Respectfully,

.,,)..--L---'

Joh hko Site ice resident LaSalle County Station Attachments: (1) Netco Rack Insert 10-year Surveillance Report cc: Regional Administrator - NRC Region Ill NRC Senior Resident Inspector- LaSalle County Station

Attachment 1 Netco Rack Insert 10-year Surveillance Report Engineering Change (EC)

Evaluation 633708

EC EVAL 633708-000 N ETCO Rack Insert 10-year Surveillance Report Reason for Evaluation/Scope LaSalle station installed NETCO Snap-in rack inserts in 2011 due to the ongoing degradation of the previous neutron absorber in the Unit 2 spent fuel pool, Boraflex. Surveillance programs were put in place to ensure the rack inserts remained able to maintain the pool sufficiently subcritical (i.e., fast-start coupon surveillance and a long-term coupon surveillance program). As part of the license amendment process, LaSalle station agreed to perform an additional surveillance test every 10 years to ensure that items being placed in to and out of rack cells containing inserts did not see excessive wear. Specifically, from Exelon's response to the rack insert amendment requests for additional information states (Reference 1):

A region of high duty spent fuel storage rack cell locations will be identified for surveillance activity. These locations will be monitored for fuel insertion and removal events to ensure that their service bounds that of the general population of storage locations. Once every 10 years, an insert will be removed from this region and will be inspected for thickness along its length in a minimum of 10 locations.

This collection of measurements will then be compared with the as-built thickness measurements of the removed insert to determine whether it has sustained uniform wear over its service life.

This technical evaluation is being performed to document the acceptance criteria used as well as the results from thickness testing performed at LaSalle for the installed inserts.

Page 1 of 5

EC EVAL 633708-000 Detailed Evaluation Acceptance Criteria In Reference 1, Exelon had estimated that up to 8 mils of wear was tolerable, but this did not take in to account the potential range of as-built insert thicknesses versus the nominal thickness (the assumed thickness in the Reference 1 was 67 mils). Therefore, it was determined that there would be multiple criteria, and subsequent action, if any, would be based on the difference between as built and as found thickness for the measured insert. Per Reference 2, rack insert thickness is 0.065" with a tolerance of 0.005".

• The minimum acceptable thickness is either the lowest acceptable as-built thickness during manufacturing (0.065" - 0.005" or 0.060") OR 8 mils less than the selected insert's as-built thickness, whichever is higher. If the insert fell into this category, no additional evaluations would be required.

• If the as-found thickness was within 8 mils but lower than 0.0060" versus as-built, then an evaluation showing that the as-found thickness corresponded to an acceptable areal density would be performed.

• In the most severe scenario, if the as-found thickness was more than 8 mils less than the as-built thickness, then an operability evaluation would have to be performed for the entire SFP (potentially limiting operable cells), and a detailed analysis would have to follow on how to continue using these inserts.

Additionally, the insert would be visually inspected for any local wear. Photos would be sent back to the vendor for dispositioning obvious imperfections. The vendor specifically requested that any imperfections greater than 0.3" x 0.3" be included for disposition.

Insert Selection Reference 1 states that an insert from a high duty region would need to be measured. LaSalle used fuel and component movement data since the inserts were installed to determine which cells in the spent fuel pool had seen high duty. A list was generated that ranked all inserts in the spent fuel pool, and then one was selected based on duty and accessibility.

The insert selected was from cell H-61 (ID 3758). It had 43 total inserts/withdrawals, approximately 10 times the average duty of inserts in the spent fuel pool. Per NETCO manufacturing records, the insert had an as-built thickness of 0.068" (Reference 3). Therefore, the acceptance criterion for this particular insert was to be greater than 0.060".

Testing Method Reference 1 stated that the insert would need to be tested at a minimum of 10 locations along its length. LaSalle selected 10 locations - 5 at the midpoint on each insert wing - spaced evenly inside where the active fuel length would be for a fuel bundle sitting inside a rack cell. Specifically at 7", 44",

81", 118", and 155" from the bottom of the insert. A sheet metal outside micrometer was used to perform the measurements (reported accuracy of 0.0005").

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EC EVAL 633708-000 Conclusions/Findings At every location measured, the insert measured greater than 0.068" (Reference 4). Therefore, no notable wear has occurred over the lifetime of the insert. Additionally, the insert looked visually sound, with no obvious imperfections (large scraping, gouges, etc.) along the length of the insert. Slight imperfections were noted on the top edge of the insert; however, these are far above the active fuel length and above the large holes used for insertion/removal of the insert and were deemed acceptable.

The vendor was contacted to look at the photos and agreed with the site's assessment. See Attachment 1 for photos. Because the insert appeared to have no wear from duty at all, the results were deemed acceptable, and no further evaluation was required. The insert was re-installed in its original location.

References

1. RS-10-102, Additional Information Supporting License Amendment Request Regarding Use of Neutron Absorbing Inserts in the Unit 2 Spent Fuel Storage Racks

2. LaSalle Drawing 8601-74, ALCAN BWR INSERT

3. NETCO Manufacturing Records for Insert #3758

4. WO 4802173-01, U2 Testing of the SFP High-Duty Rack Cell Locations

5. NRC SE for Amendment No. 199 to Facility Operating License No. NPF-11 and Amendment No.

186 to Facility Operating License No. NPF-18.

Approval uo-Preparer:

2021-04-05 11: 18-05:00 Reviewer:

~~

Rash, Eric J 2021-04-05 11 :48-05:00 Approver:

Shea,Joshua fk-L- 2021-04-05 16:28-05:00 Page 3 of 5

EC EVAL 633708-000 - As-found photos Page 4 of 5

EC EVAL 633708-000 Page5of5