RBG-34290, Special Rept:On 901201,loose Parts Monitoring Channel 8 Detector Module Illuminated,Indicating Channel Low Background Noise.Caused by Fault within Cable.Failed Portion of Channel Will Be Repaired or Replaced

Special Rept:On 901201,loose Parts Monitoring Channel 8 Detector Module Illuminated,Indicating Channel Low Background Noise.Caused by Fault within Cable.Failed Portion of Channel Will Be Repaired or Replaced

ML20066D615
Person / Time
Site:	River Bend
Issue date:	01/10/1991
From:	Odell W GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RBG-34290, NUDOCS 9101150233
Download: ML20066D615 (2)

Text

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al I1[ Ilil January 10, 1991 RBG- 34290 File Nos. G9.5, G9.25.1.4 U. S. Nuclear Regulatory Ccomission Cocumnt Control Desk Washington, D. C. 20555 Gentlemn:

River Bend Station Unit 1 Docket No. 50-458 i

Enclosed is Gulf States Utilities Ccrqnny's Special Report concerning an inoperative loose-part detection system channel.

'Ihis report is subttitted pursuant to River Bend Station 'Ibchnical Specifications 3.3.7.9 and 6.9.2. This report also serves as a supplement to a previous report, dated 7/12/90, on another failure of the sann loose parts nonitoring channel.

Sincerely,

[ 4 2 fl W. h. Ocell Manager-Oversight River Bend Nuclear Group cc: U. S. Nuclear Regulatory Camission Region IV i 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 NRC Resident Inspector Post Office Box 1051 St. Francisville, IA 70775 Enclosure 9101150233 910110 PDR ADOCK 05000458 ggy S

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,, SPE'IAL RITORP RFIORTED CONDITION On 12/01/90, during nonal surveillance testing, the light providing failure indication of the loose parts nonitoring (UN) channel 8 detector nodule was illuminated, indicating channel low background noise. Since this UN channel is inoperable, this Special Report is subnitted pursuant to 'Ibchnical Specification 3.3.7.9. This report also serves as the supplcnnnt to a previous Special Report, dated 7/12/90, on an earlier failure of the same IIM channel.

INVESTICATION AND CORRECTIVE ACTION Troubleshooting by plant staff personnel has located the failure inside the drywell structure which is inaccessible during power operations. This sane channel was reported failed during the last operating cycle (RBG-33189, dated 07/12/90) and was repaired during the recent refueling outage.

Previous troubleshooting had determincd that the problem was either in the accelermeter or in the cable leading to the accelerometer. The accelermeter was replaced on 11/17/90 and channel 8 was returned to operable status. Channel 8 functioned properly during startup but failed again on 12/1/90. Based on this second failure, it is now believed that a fault within the cable is causing the channel to be inoperative.

GSU will repair or replace the failed portion of the loose parts nonitoring channel during the next planned outage, currently scheduled for September, 1991. GSU will issue a supplenental report within 30 days following ompletion of the outage. This supplemental report will provide the cause and corrective actions taken to restore the channel to operable status.

SAFETY ASSESShDTP The low background problem caused the channel 8 failure indication light to illuntinate, indicating a malfunctioning channel. There has been no indication of a loose part in the reactor vessel and thus the health and safety of the public and plant safety are not affected by this condition.

In addition, the problem does not affect the capability of the remaining channels to detect loose parts in the reactor vessel since a comton annunciator is initiated when any of the ISM channels detects an impact signal.

Note that both channels 7 and 8 are designed to detect loose parts in the upper portion of the reactor vessel. Thus, even with channel 8 inoperable, channel 7 remains available in the event that a loose part appears in the i upper port. ion of the vessel.

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