05000186/LER-2024-003, University of Missouri Research Reactor, Specification Deviation from Technical Specification 3.2.g.21

University of Missouri Research Reactor, Specification Deviation from Technical Specification 3.2.g.21

ML24299A074
Person / Time
Site:	University of Missouri-Columbia
Issue date:	10/25/2024
From:	Sanford M Univ of Missouri - Columbia
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
LER-2024-003-00
Download: ML24299A074 (1)

LER-2024-003, University of Missouri Research Reactor, Specification Deviation from Technical Specification 3.2.g.21

Event date:
Report date:
1862024003R00 - NRC Website

text

Research Reactor University of Missouri October 25, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 REFERENCE:

Docket No. 50-186 MU Research Reactor 1513 Research Park Drive Columbia, MO 65211 PHONE 573-882-4211 WEB murr.missouri.edu University of Missouri-Columbia Research Reactor Renewed Facility Operating License No. R-103 SUBJECT:

Written communication as required by University of Missouri Research Reactor Technical Specification 6.6.c(3) regarding a deviation from Technical Specification 3.2.g.21 The enclosed document provides the University of Missouri-Columbia Research Reactor (MURR)

Licensee Event Report (LER) for an event that was discovered on October 14, 2024, and resulted in a deviation from MURR Technical Specification 3.2.g.21 If you have any questions regarding this report, please contact Ronald M. Astrino, the facility Reactor Manager, at (573) 882-5118.

Sincerely, Matthew R. Sanford Facility Director MRS Enclosure cc:

Reactor Advisory Committee Reactor Safety Subcommittee Ms. Jessica Lovett, U.S. Nuclear Regulatory Commission Mr. Edward Helvenston, U.S. Nuclear Regulatory Commission Mr. Andrew Waugh, U.S. Nuclear Regulatory Commission

Enclosure U.S. Nuclear Regulatory Commission October 25, 2024 Licensee Event Report No. 24 October 14, 2024 University of Missouri Research Reactor Introduction On October 14, 2024, while performing reactor pre-startup checks, one switch of the Fluxtrap Irradiations Reactivity Safety Trip (FIRST) device failed its operational check. This switch was last verified operating correctly prior to reactor startup on October 7, 2024. The reactor operated from October 7, 2024, until shutdown the night of October 13, 2024. Since the time of failure cannot be accurately determined, this condition could have existed during that period of reactor operation. That is a deviation from Technical Specification (TS) 3.2.g.21.

TS 3.2.g states, "The reactor safety system and the number (N) of associated instrument channels necessary to provide the following scrams shall be operable whenever the reactor is in operation. Each of the safety system functions shall have a 1/N logic where N is the number of instrument channels required for the corresponding mode of operation."

TS 3.2.g.21 states for the Center Test Hole, the number of required instruments is the two switches associated with the FIRST device.

If the flux trap starts to eject from the core, each switch sends a scram signal to the reactor protection system. The switches act independently from each other. Only one signal is needed to scram the reactor.

Reactor pre-startup checks performed on October 14, 2024, confirmed that the second FIRST device switch was functioning. Based on that, the reactor would have automatically scrammed had the flux trap become dislodged at any point while the reactor was operating during the week of October 7, 2024.

Detailed Event Description MURR's reactor flux trap sits in the center tube of the core. Material intended for irradiation is loaded into the flux trap. To provide protection in the event of a large reactivity transient initiated due to the ejection of the flux trap from the center test hole, MURR uses the FIRST device. There are two switches which are closed when the flux trap is seated into this device/loaded into the core. If either switch opens due to the flux trap starting to lift from the core, a scram signal is sent to the reactor protection system and the reactor automatically scrams.

At 2200 October 13, 2024, the reactor was shut down and the flux trap was removed. Routine maintenance was performed through the night with no abnormalities. At approximately 1330 on Monday, October 14, 2024, the FIRST device switch associated with the yellow leg failed to actuate when tested during execution of pre-startup checks using the Long Form Startup Checksheet (FM-57). MURR reactor protection system trips are processed through one of two circuits. These circuits are designated the "yellow leg" and the "green leg." The switch associated with the green leg responded properly, indicating that the reactor protection system would have issued a reactor scram if that switch opened in response to the flux trap leaving the seated position it the center test hole.

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Enclosure U.S. Nuclear Regulatory Commission October 25, 2024 Management was informed. Troubleshooting determined that the problem was either the switch itself or the associated wiring in the reactor pool coming from the device. Both switches and their pool wiring were replaced. The failed switch and wiring did not display any obvious failure mode.

Plant conditions for reactor startup were re-established and startup checks were performed.

Post maintenance testing performed at 1658 confirmed both FIRST device switches functioned properly.

Permission was received from the acting Facility Director and a reactor startup was performed on the evening of October 14, 2024, with the reactor reaching full power at 2109.

In accordance with MURR's Event Review Procedure (AP-RR-026), an event review was conducted on October 18, 2024, to review performance and identify any problems. The event review is documented with the associated Corrective Action Program entry (CAP 24-0388) for this problem.

Safety Analysis Since one of the two FIRST device switches would have opened and sent a scram signal to the reactor protection system, the reactor would have automatically shut down via a scram if the flux trap started to eject from the center test hole.

Amendment 35, RAI Round-2 responses from MURR, letter dated January 31, 2011, on page 18 addresses the question from the NRC (italics) and MURR's response to that question, regarding a possible closed circuit failure of the system.

"How would the reactor operator become aware of a closed circuit failure? How long could a closed circuit failure exist without the reactor operator not being aware of the failure? If this type of failure could exist for more than a short period of time, please justify the time period an undetected failure could exist.

In addition to the semiannual surveillance Compliance Check Procedure and the quarterly physical inspection Preventative Maintenance Procedure, an operability check will be performed prior to each reactor startup to ensure that a closed circuit failure has not occurred. The means used to accomplish this are detailed in the answer to Question 4 of this RAI. This condition in a single channel of the proposed instrument could exist for a maximum of one week without the operator becoming aware of the failure. During this time, the other instrument channel would continue to provide proper indication and be capable of performing its intended function. Also during this time, the root variable being detected, namely a change in reactivity, will be indirectly measured and protected against by the Nuclear Instrumentation and its independent input to the reactor safety system."

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Enclosure U.S. Nuclear Regulatory Commission October 25, 2024 Corrective Actions

1. Both FIRST device switches and associated pool wiring were replaced and retested satisfactorily.

2. Based on previous failures (all in the open position, this being the first closed failure) MURR will establish a maintenance item to change out these switches at a two-year frequency.

3. MURR is performing a failure analysis on the switch and associated wiring to determine the cause of failure. Results will be documented in MURR CAP 24-0388.

If there are any questions regarding this LER, please contact me at (573) 882-5118. I declare under penalty of perjury that the foregoing is true and correct.

ENDORSEMENT:

Sincerely, Ronald M Astrino Reactor Manager Reviewed and Approved,

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Matthew R Sanford Facility Director Page 3 of 3 State of Missouri County of Boone Subscribed and sworn before me this SHARON KAY PAULSELL Notary Pubtlc

• Notary Seal

&TATE OF MISSOURI Boone County

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Commission Expires: Jan. 23, 2027 CommlssiOn #04552028