ML23222A187

Univ. of California, Davis, 14-Day Written Follow-up to Call Made to the HOO (EM 56643) on July 28th 2023

ML23222A187
Person / Time
Site:	University of California-Davis
Issue date:	08/10/2023
From:	Frey W McClellan Nuclear Research Center
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
Download: ML23222A187 (1)

Text

UNIVE RSITY OF CALIFO RNIA, DAVIS

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McCLELLAN NUCLEAR RESEARCH CENTER 5335 PRICE AVENUE, SUITE 258 MCCLELLAN, CALIFORNIA 95652 WESLEY D. FREY TELEPHONE:

DIRECTOR (916) 614-6200 FAX: (916) 614-6257 E-MAIL: wesfrey@ucdavis.edu August 10, 2023 Document Control Desk U.S. Nuclear Regulatory Commission 1 White Flint North 11555 Rockville Pike Rockville, MD 20852

Subject:

14-Day Written Follow-up to Call Made to the HOO {EM# 56643) on July 28th 2023.

Reference:

Docket No. 50-607, Facility Operating License No. R-130 This notification is being made per the requirements of UC Davis MNRC technica l specification 6.7.2 1hand is the 14-day written follow up to a call made to the HOO (EM# 56643) on July 28th 2023.

During the facility's routine 2023 fuel inspection on July 27 th , a stainless steel clad standard TRIGA 20/20 element did not pass its visual inspection. The visual inspection of the element

, made via an underwater camera with approximately 2 times optical magnification, showed inward pitting and unusual discoloration in the cladding of the fueled and non-fueled section of the element. The elongation and transvers bend of the element were measured and were within toleranc e per the facility's technical specifications. The cause of this pitting is unknown. The pitting may be due to a manufacturing defect in the element, though this cannot be verified. The element has been permanently retired from service and placed in an in-tank fuel storage rack. No unusual radiation readings were observed leading up to the inspection or during the inspection. Therefo re, it is very likely that the integrity of the cladding has not been compromised and no fission products have escaped as a result of the pitting. The element (serial number 10873) was at approxim ately 23% U-235 burnup when it failed inspection.

Though not required by the facility's technical specifications, MNRC staff conduct ed the inspection of all adjacent fuel elements and all other standard elements that have not been inspected within the last year. This inspection corresponds to approximately 85% of all in-core element

s. The inspection has been completed and has not identified any other elements that failed the inspection criteria called out in MNRC's technical specifications.

The root cause of the pitting in the element and when the degradation in the cladding began will likely never be identified with 100% certainty. Under MNRC's old license (prior to 11/21/22) only "lead elements" had to be inspected on an annual basis. Due to a lack of fuel shuffles

, the same

~20% of the core was inspected annually for nearly 20 years and other non-lead elements were rarely inspected during these 20 years. Under MNRC's current license, a 100%

core inspection is required every 5 years. This 5-year inspection requirement will likely identify fuel elements of concern so that they can be removed from service proactively prior to failing inspecti on.

MNR C intends to inspect the remaining 11 standard elements during the 2024 fuel inspection.

Thes e elem ents have been inspected every year for the last 25 years and have neve r had any issues. Also, during the 2024 fuel inspection the 2 IFEs and any of the new replacement elements introduced this year are scheduled for inspected.

This will complete MNR C's first 5 years fuel inspection surveillance requirement.

Please direct any questions to Wesley Frey at 916-6 14-6200 or wesfrey@ucdavis.edu .

I declare under penalty of perjury that the foregoing is true and correct executed on August 10th 2023 .

Sincerely, i:::;D ~ PhD Director, McClellan Nuclear Research Center cc:

Linh Tran, U.S. NRG Geoffrey Wertz, US NRG