ML24145A126
| ML24145A126 | |
| Person / Time | |
|---|---|
| Site: | Oregon State University |
| Issue date: | 05/21/2024 |
| From: | Reese S Oregon State University |
| To: | Michael Balazik Office of Nuclear Reactor Regulation |
| References | |
| EN 57113 | |
| Download: ML24145A126 (1) | |
Text
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Oregon State V' University U.S. Nuclear Regulatory Commission C/O Michael Balazik Document Control Desk Washington, DC 20555
Reference:
Oregon State University TRIGA Reactor (OSTR)
Docket No. 50-243, License No. R-106 Event Report 57113 Radiation Center Oregon State University 100 Radiation Center Corvallis, Oregon 97331 P 541-737-2341 F 541-737-0480 radiationcenter.oregonstate.edu May 21, 2024
Subject:
Self-Reporting of a Potential Violation of a Technical Specification Involving Minimum Staffing Mr. Balazik:
We would like to respectfully report a potential violation of T.S. 6.1.3.a.1 The minimum staffing when the reactor is not secured shall be a reactor operator or the senior reactor operator on duty (Duty SRO} in the control room.
Reason for the Violation On May 7, 2024, at approximately 2:25PM, the Reactor Operator shut down the reactor as they normally would by driving the control rods down and removing the console key. During that process, the SHIM control rod drive was observed driving up. Upon observation of this, an attempt was made to run the SHIM control rod drive down to the bottom again and it was observed that it could only go down to 1%, rather than 0% which indicates that the rod is full down. This occurred with the key out, which means that magnet power was off and the control rod was not connected to the control rod drive. The operator pressed the CONT/ON button a few times, assuming that the button may have been stuck, but still the rod would not indicate 0.0%. They assumed this was a repeat of a limit switch issue seen in the past.
This time, however, there was something preventing the motor from driving down all the way.
This phenomenon of the run up ofthe drive has been seen before. The windings on the motor are set with slightly different voltages to compensate for the weight of the control rod.
OSU Failure to Maintain Minimum Staffing Page 2 of4 However, when the weight is not on it and power is still on, the difference will cause the drive to raise the carrier and eventually reach the top. Normally, an interlock, called the footswitch, can mechanically sense when the control rod is at the bottom and through inference know that the control rod and drive are connected. We have seen cases where the position of the switches associated with the footswitch are slightly out of alignment, causing the motor to drive up in a way nearly identical as was observed on May 7. What was different with this particular situation on May 7 is that the drive could go no further than 1% when driven down.
The Development Engineer was contacted. After verifying that the reactor appeared shut down by the co~sole key being removed from the console (eliminating magnet power) and visually checking the core camera that the rods appeared fully inserted, the Reactor Operator and the Development Engineer went onto the reactor top to investigate at approximately 2:28PM. The Development Engineer found that the footswitch was not engaged by the control rod armature. At approximately 2:32PM, the Development Engineer was able to manually lift the rod slightly and set it back down with his finger on the footswitch, and this time the rod fully engaged with the foot switch. This indicates.that the rod was actually
- slightly off the bottom (1% = 0.15"), which prevented the motor from being driven down.all the way (i.e., not a footswitch misalignment issue). There was nothing visibly caught on the rod, armature, or any other component of the SHIM rod or drive. The Reactor Supervisor was then notified of the situation.
The next morning (May 8, 2024), the SHIM rod drive barrel was inspected, and it showed that the small nylon seat at the bottom of the barrel had, after 57 years of use, broken into several parts. This seat is designed to cushion the control rod armature as it reaches the bottom. It appears that one of the broken pieces configured themselves in a way that the control rod armature could not reach the bottom. Furthermore, the seat is held down from underneath by four small screws. These screws were missing. The seats for the other two control rods of similar design (REG and SHIM control rods) were inspected as well. The REG control rod seat looked in good order. The SAFE control rod seat was intact but showing wear and had its screws missing. General Atomics was contacted and they provided the sub-part engineering drawing for the seat. The Development Engineer made three new seats out of Delrin instead of Nylon and replaced all three. Using cameras, the staff was unable to locate the missing screws.
The staff was unable to determine the location of the missing screws nor when the screws were no longer connected to the nylon seats. Pictures from 2008 and 2013 indicate that all of the screws were intact at that time. These screws are items that aren't typically inspected during biennial control rod inspections. Pictures from 2002 (50.59 Evaluation 00-11), show different screws on the SAFE and SHIM rods from what are installed on the REG rod. The REG rod assembly is also machined differently (particularly, different numbers of dash pots), which indicates that the assembly may be newer than the SAFE and SHIM rod assemblies (the condition of the nylon seat would also seem to confirm this).
OSU Failure to Maintain Minimum Staffing Page 3*of 4 However,. during the approximately 5 minutes when the Reactor Operator went with the Development Engineer to investigate the footswitch linkage alignment on the reactor top, the reactor was not secured because the SHIM rod was at 1%, or 0.15" off the bottom. There are several requirements for the reactor to be considered secured but one of the requirements is that all control rods are fully inserted. As such, there should have been an operator at the console. This was a potential violation of T.S. 6.1.3.a.l.
Corrective Actions On May 8, 2024, a report was made to the NRC Headquarters Operation Center at approximately 11:30AM Pacific (Event# 57113) of the potential violation and both our NRC Program Manager and Inspector were informed later that day. The Reactor Operations Committee was notified via email later that* day as well.
All of the seats on the.safety, shim and regulating rods were replaced with Delrin seats and secured with stainless steel socket-head screws (50.59 Screen 24-04). The rods were tested for operability per OSTROP 16.IV.
All licensed operators were reminded that.if the rods do not all indicate 0.0% withdrawn at the console, they will need to stay at the console until full rod insertion can be assured through confirming fully inserted indication on the console. Furthermore, the Duty-SRO should be the first person contacted in unusual circumstances with respect to the reactor.
Corrective Actions to Prevent Reoccurrence The replacement of nylon seats to Delrin should provide more long-term protection for the control rods ~s well as the seats.
Operations staff shall inspect the control rod assemblies during biennial inspections to ensure that the four screws are still intact. Checks will be added to the biennial control rod inspections (OSTROP 12} to check the condition of the Delrin seats and screws.
Conclusion In* summary, we have discovered that after reviewing our Technical Specifications, we potentially violated TS 6.1.3.a.l. We believe we have incorporated corrective actions to solve the issue.
Should there be questions regarding the information in this report or should you require more information, please do not hesitate to contact me.
- OSU Failure to Maintain Minimum Staffing Page 4 of 4 I declare under penalty of perjury that the foregoing is true and correct.
Executed on: __
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Sincerely,
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Steven R. Reese Director Enclosure cc:
Andrew Waugh, USNRC Maxwell Woods, ODOE Dr. lrem Turner, OSU