ML20111A113
| ML20111A113 | |
| Person / Time | |
|---|---|
| Site: | University of Utah |
| Issue date: | 04/02/2020 |
| From: | Lund M Univ of Utah, Salt Lake City |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML20111A113 (4) | |
Text
THEU UNIVERSITY OF UTAH Utah Nuclear Engineering Program 50 5. Central Campus Drive, Suite 2298 Salt Lake City, Utah 84112 801-581-4188 Fax 801-585-5477 April2,2020 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention:. Document Control Desk
Subject:
Facility License No. R-126, Docket No. 50-407 Special Report
Dear Nuclear Regulatory Commission:
In accordance with the University of Utah TRIGA Reactor (UUTR) Technical Specifications (T.S.) 6.7.2.1.5 to Operating License R-126, Docket No. 50-407 this written report identifies a component malfunction that affects T.S. 3.2.1.2.
Report No: 50-407/ 2020-1 Report Date: April 2, 2020 Date of Identification: March 31, 2020 Facility: University of Utah TRIGA Identification of Occurrence:
On March 30, 2020, facility staff completed the monthly inspection and began a reactor run to test all systems and began a reactor run to test the reactor. During testing at 12:17, the RO tested the safety rod by cutting magnet power, but the rod failed to drop. The RO drove the rod down manually to 98%, when the rod started dropping on its own to the fully inserted position.
Conditions Prior to Occurrence:
Historically the safety control rod dropped in under <1.1 seconds from 100% withdrawn.
Also, during the reactor pre-startup checklist, the safety rod is withdrawn to 20% and scrammed by inserting a test signal into the linear channel to test the scram, causing the channel to exceed 100% indicated power in test mode. During all these tests, the safety rod always dropped as expected within -1 second. AO Z I) xE2- tJfcf(
THEU UNIVERSITY OF UTAH Utah Nuclear Engineering Program 50 S. Central Campus Drive, Suite 2298 Salt Lake City, Utah 84112 801-581-4188 Fax 801-585-5477 The safety rod drop time during the semi-annual control rod calibration has been increasing since 6/7118 with the following rod drop times:
- 6/7/18 1.35 seconds
- 9/24/18 1.43 seconds
- 2/27/19 1.32 seconds
- 10/14/19 2.0 seconds - The rod was visually inspected and the rod continued to drop within expected time.
- 2/13/20 1.66 seconds Since the rod drop times were increasing, facility staff were planning on fully inspecting the rod and rebuilding drive components during the fuel inspection in May of 2020. On 3/18/2020 at 7:09 MDT, a large 5.7 magnitude earthquake occurred- 14 miles away from the facility, while the reactor was shutdown and secured. A thorough visual inspection of the facility was completed that afternoon with no damage noted to any system. All control rods appeared normal and the f~cility was secured. The RS ordered the reactor to remain shutdown until the monthly inspection was completed and all systems checked during startup in two weeks after the aftershocks decayed.
Description of the Occurrence:
On March 30, 2020, facility staff completed the monthly inspection with all system performing normally. At 11 :08, a RO, SRO, and RS began going through the startup and termination checklist to test all systems after the earthquake. All system tested correctly including safety rod dropping from 20% by linear power scram as expected. At 11 :58, after completing checklist and verifying all systems functioned correctly, the safety rod was withdrawn to 100% and the reactor was brought slowly up to 2 watts. At 12:09, RS directed staff to insert shim and regulating rod in order to test each rod independently from 100% for full rod drop time. The reactor was shutdown by shim and regulating rod by 12:15p.m.
At 12:17, the safety rod magnet power was cut to the safety rod, but the rod did not drop.
The rod was then manually driven by the drive down to 98% when the rod dropped on its own to the fully inserted position. The rod drive was then visually inspected, limit switches checked with the rod fully inserted, and the drive was functioning correctly. The rod was then raised to 20% at 12:38 and dropped normally. The rod was then raised and dropped from 50% at 12:39, 70% at 12:41, and 90% at 12:45 with the rod dropping normally. Then at 13:00, the safety rod was raised to I 00%, at which the safety rod hesitated then dropped. The run was immediately terminated and reactor secured.
Description of the Apparent Cause of the Occurrence:
THEU UNIVERSITY OF UTAH Utah Nuclear Engineering Program 50 S. Central Campus Drive, Suite 2298 Salt Lake City, Utah 84112 801-581-4188 Fax 801-585-5477 The exact cause is unknown until the rod can be removed for detailed inspection; however, from listening to and watching the safety rod drop from I 00% during the final drop, it sounds as if the control rod is sticking at the barrel between 90-100% fully withdrawn. This could potentially be due to debris build up that was exacerbated by the earthquake.
Analysis of the Occurrence:
- a. Condition during event- The reactor was shutdown with shim and regulating rod fully inserted.
- b. Equipment malfunction- Safety control rod drive failed to drop from 100% without driving the rod down by 2% manually.
- c. Operator error-None.
- d. Potential damage to systems, components, and structures- The safety control rod connecting rod is sticking between 98-100% withdrawn at either barrel or control rod guide tube at core.
- e. Personnel injuries- None, there was no injuries.
- f. Personnel exposures- None, there was no radiation exposure.
- g. Radioactive materials released- None, there was no radioactive release.
- h. Consequence or potential consequences to public health- None, the other 2 control rods remained functional and able to shutdown the, reactor. The safety rod was fully inserted by manually driving the rod. Also, a cadmium rod was available if needed to shutdown the reactor.
Immediate Actions Taken:
Immediately the RS terminated the reactor run and ordered the reactor to remain shutdown until the rod is repaired during fuel inspection.
Cause Investigation Activities- After approval by reactor safety committee (RSC), the control rod inspection procedure will be followed to inspect and repair the rod. The following will be done:
- The rod drop times for the shim and regulating rod will be tested to verify within TS.
- The shim rod, instead of the safety rod, will be withdrawn while monitoring reactor power with the other two rods fully inserted. A cadmium plug will be inserted into the A-ring to verify the reactor is sub-critical according to the fuel inspection procedure.
- With cadmium plug in A ring, the B ring and partially the C-ring will be de-fueled by moving one fuel element at a time according to the fuel inspection procedure into the storage rack.
- All rods will be fully inserted into the core, then the safety control rod will be removed according to the control rod inspection for inspection and performance of any needed repair.
THEU UNIVERSITY OF UTAH Utah Nuclear Engineering Program 50 5. Central Campus Drive, Suite 2298 Salt Lake City, Utah 84112 801-581-4188 Fax 801-585-5477
- After inspection and calibration, the safety control rod will be tested to verify drop time meets historical values .
- After which fuel inspection will continue as normal.
Corrective Action to Prevent Repetition of Occurrences- The following changes will be made to prevent future occurrences:
- Control rod drive inspection procedure will include checking for debris, binding, rubbing, or misalignment of control rod drive that prevents the rod from dropping.
- Emergency plan procedures for earthquakes will require the rod drop times to be tested before operations continue.
- Direction will be added to the semi-annual control rod drop procedures to check with historical rod drop times and resolve any discrepancy or complete an inspection before continuing operation.
- The new ThermoFisher control console will contain a rod drop analog timing drawer to record rod drop times to improve accuracy and track data over time.
Failure Data:
The drive is a General Atomics TRIGA control rod drive. The serial number appears to be F-101, but the number on the side of the drive have been worn away from years of use. The safety rod limit switches were adjusted on 4/5/2000 and 12/18/2005. The rod was removed to repair the union between the connecting rod and piston in the barrel onl/24/2008, due to failing screws that were replaced. This connection was fixed again on 2/15/2013, tightening the connection. During this repair, rust was observed on the rod inside the barrel.
Matthew Lund
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Interim Director and Reactor Supervisor University of Utah TRIGA Reactor 50 S. Central Campus Dr~, Rm 1206 Salt Lake City, Utah 84112