IR 05000150/1993003
| ML20035A600 | |
| Person / Time | |
|---|---|
| Site: | Ohio State University |
| Issue date: | 03/19/1993 |
| From: | Cox C, Mccormick J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML20035A595 | List: |
| References | |
| 50-150-93-03, 50-150-93-3, NUDOCS 9303290068 | |
| Download: ML20035A600 (3) | |
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U.S. NUCLEAR REGULATORY COMMISSION
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REGION III
Report No. 50-150/93003(DRSS)
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Docket No. 50-150 License No. R-75
Licensee: Ohio State University
Facility Name: Ohio State University Research Reactor
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f Inspection At: Nuclear Reactor Laboratory, Columbus, Ohio j
Inspection Conducted: March 9, 1993
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Inspector:
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C. Cox Date
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Approved By: O /M /d k-be t[Mb 3 (4. W. McCormick-Barger,' Chief Date l
Non-Power Reactor Section
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Inspection Summary
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Inspection an March 9. 1993 (Report No. 50-150/93003(DRSS))
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Areas Inspected:
Reactive, announced inspection to review actions on the recent licensee event report concerning the March 5,1993 failure of Shim
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Safety Rod No. I to drop following a manual scram signal (92700).
Results: No violations or deviations were identified. The licensee's immediate response to the event was appropriate and the corrective actions
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were thorough.
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DETAILS 1.
Persons Contacted
Ohio State University
- R. D. Myser, Associate Director
- J. M. Hatch, Senior Reactor Operator
- Denotes those attending the exit meeting on March 9, 1993
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General
l This inspection, which was held on March 9, 1993, was conducted to
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review the failure of Shim Safety Rod No. I to drop following initiation
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of a manual scram signal during a routine shutdown on March 5,1993.
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The inspector examined the safety rods and burnt circuits, examined
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schematics of the involved circuitry, interviewed personnel, and
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discussed corrective actions.
l 3.
Licensee Event Reports (92700)
(0 pen) LER 93-01:
Failure of Shim Safety Rod to drop following the initiation of a manual scram signal, j
On March 5, 1993, during a routine shutdown, the senior reactor operator
(SRO) initiated a manual scram. When the SR0 noticed that Shim Safety
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Rod No. I failed to drop, he used the rod drive mechanism to insert the rod. The other two safety rods had inserted and were able to bring the reactor subcritical immediately after the manual scram.
The SR0 also
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noted that the magnet current for Shim Safety Rod No. I did not drop to i
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zero amps after the manual scram was initiated.
i Trouble shooting was initiated on March 6,1993. The licensee i
determined that a short developed between the 120 vac in the engage
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limit switch circuit and the 18 vdc Shim Safety Rod No. I circuit. That
short was apparently caused by close proximity of the connectors for j
both circuits in the magnet coil and corrosion causing the wires to come
loose at the connectors. The short damaged the comparator circuit used
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in the slow scram circuit to de-energize the slow scram relay. The i
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manual scram signal was supposed to de-energize.that relay, but with the j
damaged comparator circuit, the relay remained energized and therefore l
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the magnet coil also remained energized. That condition explained the amp reading that the SRO noted after the manual scram on March 5,1993.
The immediate corrective actions were to repair the damage caused by the short circuit, examine the other two shim safety rods for similar corrosion, repositioning the connectors for both circuits to allow greater physical separation, and revising procedure OM-1, " Reactor Power
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Changes," to instruct operators to observe the shim safety rod's magnet current after a slow scram signal to ensure the magnets are
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de-energized.
If the magnet current has not dropped to zero amps, the
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procedure requires the operator to turn off the power to the magnet.
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Long term corrective actions that were planned were to develop a quarterly preventive maintenance (PM) item to examine the magnet coil
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connectors and engage circuit wires for corrosion, to develop a monthly PM item for electrically checking for grounds in the circuits, to review the current PM program to determine if any additional safety related items requires expanding the PM program, consider drilling ventilation
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holes in the cover for the drive mechanism to reduce condensation on the
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coil, and to evaluate and redesign the magnet current amplifier circuit.
Reactor operations were planned to resume sometime during the week of
March 15, 1993. This LER will remain open until a follow-up on the long
term corrective actions is completed.
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4.
Exit Interview (30703)
The inspector met with'the licensee representatives denoted in
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Paragraph I at the conclusion of the inspection on March 9,1993. The inspector summarized the scope and results of the inspection and
discussed the likely content of this inspection report.
The licensee
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acknowledged the informa"'n and did nat indicate that any of the
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information disclosed du
.g the inspection could be considered i
proprietary in nature.
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