ML24344A113
| ML24344A113 | |
| Person / Time | |
|---|---|
| Site: | University of Missouri-Columbia |
| Issue date: | 12/06/2024 |
| From: | Sanford M Univ of Missouri |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| LER 24-04 | |
| Download: ML24344A113 (1) | |
Text
(!) University of Missouri December 6, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
REFERENCE:
Docket No. 50-186 University of Missouri-Columbia Research Reactor Renewed Facility Operating License No. R-103 MU Research Reactor Division of Research. Innovation & Impact 1513 Research Park Drive Columbia, MO 65211 PHONE 573-882-4211 WEB murr.missouri edu
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.a The enclosed document provides the University of Missouri-Columbia Research Reactor (MURR)
Licensee Event Report (LER) for an event that was discovered on November 25, 2024, and resulted in a deviation from MURR Technical Specification 3.2.a.
If you have any questions regarding this report, please contact Russell W. Gibson, the facility Interim Reactor Manager, at (573) 882-0342.
Sincerely, Matthew R. Sanford Facility Director MRS:rwg 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 December 6, 2024 Licensee Event Report No. 24 November 25, 2024 University of Missouri Research Reactor Introduction On November 25, 2024, with the reactor operating at 50 KW, the Reactor Operator Trainee (ROT), under the direction of the Lead Senior Reactor Operator (LSRO), attempted to select control blade 'C' using the five-position ("A-B-C-D-Gang") Control Rod Selector switch (1 S3). While attempting to perform a routine control blade shimming evolution to bank all four control blades for 50 KW startup data, the ROT noted the operation of three-position ("In-Normal-Out") Control Rod Operate switch (1 S4) failed to cause movement of control blade 'C' in either the inward or outward direction. A manual scram was immediately initiated by the LSRO due to the inability to operate the control blade. The LSRO completed all Immediate and Subsequent Actions ofreactor emergency procedure REP-2, "Reactor Scram," and verified all control blades were fully inserted. Failure of the I S4 switch to operate control blade 'C' resulted in a deviation from Technical Specification (TS) 3.2.a, which states, "All control blades, including the regulating blade, shall be operable during reactor operation."
Description of the Rod Control System As described in Section 7.5, Rod Control System, of the MURR Safety Analysis Report (SAR), the reactivity of the reactor is controlled by five (5) neutron absorbing control blades. Each control blade is attached to a Control Rod Drive Mechanism (CRDM) by means of a support and guide extension (offset mechanism). Four (4) of the control blades, referred to as the shim blades, are used for coarse adjustments to the neutron density of the reactor core. The fifth control blade is a regulating blade. The low reactivity worth of this blade allows for very fine adjustments in the neutron density in order to maintain the reactor at the desired power level. The nominal speed of the shim control blades is one (I) inch per minute in the outward direction and two (2) inches per minute in the inward direction. Nominal speed of the regulating blade is 40 inches per minute in both the inward and outward directions. The four (4) shim control blades are actuated by electromechanical CRDMs that position, hold, and scram each shim blade. Each CRDM consists of a 0.02-HP, 115-volt, one-amp, single-phase, 60-cycle motor connected to a lead screw assembly through a reduction gearbox.
The reactor is operated from the reactor control console in either of two (2) control modes: manual or automatic. Manual control is used for reactor start-up, changes in power level, and steady-state operation for short periods of time. Automatic control is selected only after a minimum power level has been attained and is used for long-term steady-state operation.
Control blade movements, interlocks and bypasses, and control modes are managed by the Rod Control System. The Rod Control System is a relay and switch logic system used to prohibit accidental or incorrect operation which could result in an unsafe condition. A three-position ("Off-Test-On") keylock Master Control Switch and a two-position ("Off-On") Magnet Current Switch located on the reactor control console controls power to the Rod Control System. The Master Control Switch and the Magnet Current Page I of3
Enclosure U.S. Nuclear Regulatory Commission December 6, 2024 Switch, designated as 1 S 1 and 1 S 14 respectively, must both be in the "On" position to provide current to the shim control blade electromagnets.
The shim and regulating blades are withdrawn or inserted manually by three-position ("In-Nonnal-Out")
switches located on the reactor control console. The switches are spring return to the mid-position
("Nonna!") when released. A five-position ("A-B-C-D-Gang") selector switch enables the reactor operator to select the shim blades individually or as a group. The Control Rod Selector switch is designated 1 S3 and the withdrawal-insertion switches for the shim and regulating blades are designated 1 S4 and 1 S5, respectively. Two (2) push button switches located on the reactor control console allow the regulating blade to be "jogged" inward and outward for fine adjustment ofreactor power level in the manual control mode. Note: Switch 1 S3 is designated as the "Control Rod Selector" switch, which is identified as Item No. 34 on Table 7-2, "Reactor Control Console Control Equipment," of the MURR SAR.
The Rod Run-In System, which initiates the automatic insertion of the control blades at a controlled rate should a monitored parameter exceed a predetennined value, is also part of the Rod Control System.
Detailed Event Description On November 25, 2024, at 14:41, during a nonnal reactor startup with the reactor operating at 50 KW in the manual control mode, while establishing a 50 KW banked height, it was discovered that shim control blade 'C' would not shim in the inward or outward direction when Control Rod Operate Switch 1S4 was manipulated. The LSRO then immediately shut down the reactor by initiating a manual scram. The LSRO completed all immediate and subsequent actions ofreactor emergency procedure REP-2, "Reactor Scram,"
and verified all shim control blades were fully inserted.
Not being able to shim the control blade resulted in a deviation from TS 3.2.a, which states, "All control blades, including the regulating blade, shall be operable during reactor operation." TS 1.15, Operable, states, "Operable means a component or system is capable of performing its intended function."
Furthermore, TS 1.1, Abnonnal Occurrence, states, "An abnormal occurrence is any of the following which occurs during reactor operation.... b. Operation in violation of Limiting Conditions for Operations established in Section 3.0."
After the reactor was shut down and secured, troubleshooting efforts revealed that Control Rod Selector switch 1 S3 had failed - the internal spring that provides pressure to the detent contacts for each position had broken. The switch spring within 1 S3 was replaced and post maintenance testing was conducted satisfactorily, which included verifying inward and outward movement of all four ( 4) shim control blades.
Authorization was received from the Reactor Facility Director, as required by TS 6.6.c.(4), to restart the reactor and resume 10 MW operation.
Safety Analysis The basis for TS 3.2.a is to ensure that the normal method ofreactivity control is used during reactor operation (Ref. Section 4:5 of the SAR). When performing a reactor startup, shim control blades are Page 2 of3
Enclosure U.S. Nuclear Regulatory Commission December 6, 2024 manually shimmed in the inward and outward directions to increase and stabilize power at prescribed intervals (50 KW, 5 MW and 10 MW). While the ability to manually insert and withdraw the shim control blades was unavailable for approximately 5-10 seconds, the ability to either manually or automatically scram the reactor was retained. Switch 1 S3 is not a part of the Reactor Safety System, nor is it relied upon to perform any safety function otherwise. This failure would not have prevented the Rod Run-In System from functioning normally. As a result, there was no safety impact due to this condition.
Corrective Actions
- 1. When the LSRO discovered that switch 1 S3 was inoperable, they immediately initiated a reactor scram and completed all actions of reactor emergency procedure REP-2, "Reactor Scram," to ensure the reactor was in a safe shutdown condition. All four (4) shim control blades were verified to be fully inserted.
- 2. Troubleshooting efforts identified that the spring within switch 1 S3 had failed. The 1 S3 spring was replaced and retest was conducted satisfactorily, which included verifying inward and outward movement of all four ( 4) shim control blades.
- 3. MURR is performing a failure analysis on the spring to determine the cause of failure. Results will be documented in MURR CAP 24-0438.
If there are any questions regarding this LER, please contact me at (573) 882-0342. I declare under penalty of perjury that the foregoing is true and correct.
ENDORSEMENT:
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Russell W. Gibson Interim Reactor Manager Reviewed and Approved,
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Matthew R. Sanford Facility Director Page 3 of3 State of Missouri County of Boone Subscribed and sworn before me this 6111 day of December, 2024.
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KATHLEEN WESSLER NOTARY PUBLIC* NOTARY SEAL STATE OF MISSOURI MY COMMISSION EXPIRES JUNE 1, 2025 BOONE COUNTY c_oM_M_1s_s1_o __
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