05000483/LER-1985-025, :on 850506,reactor Trip,Feedwater Isolation & Auxiliary Feedwater Actuation Occurred During Startup.Caused by Faulty Switch on ex-core Neutron Monitoring Channel SE-NI-36.Switch Replaced
| ML20198B352 | |
| Person / Time | |
|---|---|
| Site: |  |
| Issue date: | 10/29/1985 |
| From: | Miltenberger S, Naslund C UNION ELECTRIC CO. |
| To: | NRC OFFICE OF ADMINISTRATION (ADM) |
| References | |
| LER-85-025, ULNRC-1194, NUDOCS 8511060457 | |
| Download: ML20198B352 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 4831985025R00 - NRC Website | |
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On 5/6/85 at 2115 CDT a Reactor Trip, Feedwater Isolation, and Auxiliary Feedwater Actuation occurred during a reactor startup.
The plant was in Mode 2, Startup, at 0% power at the time of the event.
The Reactor Trip was initiated by a spurious Intermediate Range Hi Flux Signal that was caused by a blown fuse in the ex-core neutron monitoring channel SE-NI-36.
The spurious Hi Flux signal also initiated an automatic transfer of charging pump suction from the Volume Control Tank to the Refueling Water Storage Tank. The fuse was replaced and by 0947 on 5/7/85 normal reactor startup was commenced.
Westinghouse Electric Corporation has determined that a leak path existed for an alternating current to be superimposed onto the direct current in the Log Amplifier due to a faulty switch. The resultant current flow could then be sufficient to blow the control power fuse.
The SE-NI-36 drawer was replaced with a spare drawer which had a new switch installed. No further problems have been experienced since the drawer was replaced.
Final corrective actions are pending identification of other sources of alternating current and determination of the switch failure mode.
There was no damage to plant equipment or release of radioactivity as a result of this incident. This event has in no way affected the health Ng or safety of the public.
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Nne wsu.nm On 5/6/85 at approximately 2115 CDT a Reactor Trip, Feedwater Isolation, and Auxiliary Feedwater Actuation occurred during a plant startup following the Reactor Trip reported in LER 85-024-00 transmitted via ULNRC-1103, dated 5/31/85. The plant was in Mode 2, Startup, at 0%
power at the time of the event. This event is classified as reportable per 10 CFR 50.73(a)(2)(iv).
The Reactor Trip was initiated by an Intermediate Range Hi Flux Signal that was caused by a blown 5 ampere control power fuse in the ex-core neutron monitoring channel SE-NI-36 (IEEE Standard 805-1983 system-lG).
The spurious Fi Flux signal also initiated an automatic transfer of charging pump suction from the Volume Control Tank to the borated Refueling Water Storage Tank.
The blown fuse was replaced and by 0947 on 5/7/85 normal reactor startup was commenced with the reactor becoming critical at 1045.
Union Electric Company is presently evaluating the cause of the event with Westinghouse Electric Corporation. A similar event was discovered to have occurred at the Indian Point 3 plant, NRC Docket No. 50-286, through the INPO Operating Plant Experience Report OE 1308.
The investigation has determined that there existed a leakage path for an alternating current through the Operation Selector Switch (S201) to the Log Amplifier in the intermediate range nuclear instrumentation circuitry. The alternating current could then be superimposed onto a direct current resulting in a current flow which under certain conditions is sufficient to blow the control power fuse.
Westinghouse has determined that the Operation Selector Switch (Manufacturer - Grayhill, Part #44N30-D6-1-10-S) is contributing the major portion of the alternating current which is amplified by the Log Amplifier. The switch manufacturer has been contacted to determine the I
failure mode of the switch. Also, another switch manufacturer is being evaluated by Westinghouse to potentially supply the replacement switch.
Final corrective actions are pending identification of other sources of alternating current and determination of the failure mode of the switch.
Since the switch has been isolated as the major contributor of alternating current, no further supplemental reports will be submitted on this issue.
As a result of this incident a temporary change to operating procedure OTG-ZZ-00002,~ Reactor Startup, was made which directed technicians to unplug the test signal to the Log Amplifier on both intermediate range channels during a reactor startup. This action failed to correct the problem. Oscillations about the P-6 permissive (permissive which c,omu 3 sea m
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ass.uiin blocks source range trips when the intermediate range is greater than IE-10 amps) caused by the alternating current in the intermediate range circuit were observed. The temporary change to OTG-ZZ-00002 was therefore deleted.
The intermediate range drawer of nuclear instrumentation for channel 36 was replaced on 7/18/85 as a result of problems experienced after reactor trips on 6/7/85 and 7/18/85. These problems were also associated with the alternating current in the circuit and are described in LER 85-026-00 (ULNRC 1130 dated 7/8/85) and LER 85-034-00 (CLNRC 1156 dated 8/16/85). During calibration of the spare drawer in preparation for installation, it was noted that abnormal alternating current was leaking through the Operation Selector Switch. The switch was replaced and no abnormal alternating current was detected. The replacement switch was manufactured by the same company and was the same model as the original switch. No further problems have been experienced since the drawer was replaced.
The safety function of the internediate range nuclear instrumentation, i.e. Reactor Trip Protection, was not impaired by the presence of the alternating current. All safety systems responded as designed and there
.was no damage to plant equipment or release of radioactivity as a result of thin event. Based on this the event in no way affected the health or safety of the public.
Previous occurrences
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UNION ELECTRIC COMPANY Cc!!away Plant October 29, 1985 U. S. Nuclear Regulatory Cenmiission Document Control Desk Washington, DC 20555 ULNRC-1194 Gentlemen:
DOCKET NUMBER 50-483 CALLAWAY PIANT UNIT 1 FACILITY OPERATING LICENSE NPF-30 LICENSEE EVENT REPORT 85-025-02 INTERMEDIATE RANGE HI FLUX REACTOR TRIP Ref. 1) LER 85-025-00, via ULNRC 1106 dtd 6/3/85
- 2) LER 85-025-01, via ULNRC 1184 dtd 9/27/85
- 3) LER 85-026-00, via ULNRC 1130 dtd 7/8/85
- 4) LER 85-034-00, via ULNRC 1156 dtd 8/16/85 The enclosed Licensee Event Report (LER) is submitted to amend LER 85-025-01, which concerned a spurious Reactor Trip caused by a blown fuse in an ex-core neutron monitoring channel. As stated in references 1 through 4, a supplemental report was to be submitted to provide the results of the investigation of the ex-core neutron monitoring channel.
The enclosed supplemental report describes the findings of the investigation and the actions to be taken.
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S. E. Miltenberger Manager, Callaway Planc o-jAC s
CDNfJWK/drs Enclosure cc: Distribution attached Mailing Address: RO. Box 620. Futton, MO 65251
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cc distribution for ULNRC-1194 Mr. James G. Keppler Regional Administrator Office of Inspection & Enforcement U.S. Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen E11ya, IL 60137 American Nuclear Insurers c/o Dottie Sherman, Library The Exchange Suite 245 270 Farmington Avenue Farmington, CT 06032 Records Center Institute of Nuc1 car Power Operations Suite 1500 1100 circle 75 Parkway Atlanta, GA 30339 Mr. Nicholas A. Petrick Executive Director, SNUPPS 5 Choke Cherry Road Rockville, Maryland 20850 Mr. J. H. Smith Bechtel Pcwer Corporation SNUPPS Project 15740 Shady Grove Road Gaithersburg, Maryland 20877-1454 NRC Resident Inspector D. F. Schnell J. F. McLaughlin J. E. Davis (Z40LER)
D. W. Capone /R. P. Wendling F. D. Field R. L. Powers A. C. Passwater/D. E. Shafer/D. J. Walker G. A. Hughes V. R. Robinson (QA Record)
J. M. Price C. D. Naslund R. A. McAleenan S. L. Auston (470)(NSRB)
Merlin Williams, Wolf Creek SEM Chrono 3456-0021.6 3456-0260 Z40ULNRC G56.37 N. Date