RBG-35-704, Suppl 1 to Special Rept:On 901201,failure Indication Received That Loose Parts Monitoring Channel 8 Detector Module Inoperable.Initially Reported on 910110.Caused by Degraded Softline Cable.Mod Scheduled in Mar 1992

Suppl 1 to Special Rept:On 901201,failure Indication Received That Loose Parts Monitoring Channel 8 Detector Module Inoperable.Initially Reported on 910110.Caused by Degraded Softline Cable.Mod Scheduled in Mar 1992

ML20079G588
Person / Time
Site:	River Bend
Issue date:	09/30/1991
From:	Odell W GULF STATES UTILITIES CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RBG-35-704, NUDOCS 9110090178
Download: ML20079G588 (2)

Text

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GULF ST/aTES UTXLITXES COMPJA N Y

, ,,, o s m s w n ,, , . r n,u m , m.m u ; o A fu A [ C :4$M t J! t W4 ir f- 81 f i September 30,1991 RilG- 3 5,704 File Nos. G9.5, G9.25.1.4 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555 Gentlemen:

River Bend Statiot - Unit 1 Docket NoJCL4J8 Enclosed is supplement I to Gulf States Utihties Company's Special Report concerning an inoperative loose-part detection system channel. The original report was submitted on January 10, 1991 pmsuant to River llend Station Technical Specifications 3.3.7.9 and 6.9.2. This suoplement provides the results of further investigation and corrective actions to resl ore the loose-part detection system channel to operable status.

Sincerely, f /

W.H Gilell Manager ' Oversigh:

River Bend Nuclear Group

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1/PDG/ GAB /DiH/DEJ/kvm Enclosure cc: U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, TX 76011 NRC Resident inspector P.O. Ilox 1051 6 St. Francisville, LA 70775 /^ h.

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k,e7pp9o 9110090178 910930 PDR ADOCK 050004".9 {i s PDR

SPECI Al, REPOltT RElDlGED CONDin0N On 12/01/90, during normal surveillance testing, the light providing failure indication of the loose parts monitoring (1.Pht) channel 8 detector module was illuminated, indicating channel low background noise. This supplement provides the results of further investigation and corrective actions to restoic the loose part detection system channel to operable status.

IXYEFTIGATION AND COBR)Il1YE ACTION Troubleshooting by plant staff personnel has located the failure inside the drywell structure which is inaccessible during power operations. This same channel was reported failed during the last operating cycle (RilG-33189, dated 07/12/90) and was repaired during the recent refueling outage. Previous troubleshooting had determined that the problem was either in the accelerometer or in the cable leading to the accelerometer. The accelerometer was replaced on 11/17/90 and channel 8 was returned to operable status. Channel 8 functioned properly during startup but failed again on 12/01/90. Ilased on this second failure, it is now believed that a fault within the cable is causing the channel to be inoperative.

After further investigation it was discovered that the softline cable for LPhi Nill!41) (channel

8) has degraded due to high temperature in the drywell overhead. Due to this degradation channel 8 is inoperative. A modification (h1R-91-0085) is being designed that corrects this problem. This modification will be worked during the fourth refueling outage scheduled to begin in hiarch 1992. A supplemental report will be issued by GSU within 30 days following completion of h1R-91-0085. This supplemental repert will provide the corrective actions taken to restore the channel to operable status.

SAFETY ASSESShihXf The low background problem caused the channel 8 failure indication light to illuminate, indicating a malfunctioning channel. Th:re has becn 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 resctor vessel since a commor, annunciator is initiated when any of the LPhi 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 upper portion of the vessel.

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