05000346/LER-1979-122-03, /03L-0:on 791201,reactor Protection Sys Channel 2 Thorium Indication Failed Low.During 791203 Investigation of Failure,Water Found in Termination Box.Caused by Failed Extension Piece on Resistance Temp Detectors

/03L-0:on 791201,reactor Protection Sys Channel 2 Thorium Indication Failed Low.During 791203 Investigation of Failure,Water Found in Termination Box.Caused by Failed Extension Piece on Resistance Temp Detectors

ML19257A361
Person / Time
Site:	Davis Besse
Issue date:	12/28/1979
From:	Werner J TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19257A351	List: 05000346/LER-1979-122, Forwards LER 79-122/03L-0 05000346/LER-1979-122-03, /03L-0:on 791201,reactor Protection Sys Channel 2 Thorium Indication Failed Low.During 791203 Investigation of Failure,Water Found in Termination Box.Caused by Failed Extension Piece on Resistance Temp Detectors
References
LER-79-122-03L, LER-79-122-3L, NUDOCS 8001030821
Download: ML19257A361 (2)

LER-1979-122, /03L-0:on 791201,reactor Protection Sys Channel 2 Thorium Indication Failed Low.During 791203 Investigation of Failure,Water Found in Termination Box.Caused by Failed Extension Piece on Resistance Temp Detectors

Event date:
Report date:
3461979122R03 - NRC Website

text

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8 LJ b1 DOCK E T NU'.iBER bd 63 EVENT DATE 74 13 HEPORT DATE 80 EVENT DESCRIPTION AND PRC9 ABLE CONSEQUENCES h l On 12/1/79 at 1125 hours0.013 days <br />0.313 hours <br />0.00186 weeks <br />4.280625e-4 months <br />, it was discovered that the Reactor Protection System (RPS) l 0

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40 41 42 43 44 41 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h lilcj l The occurrence was caused by a failed extension piece on the RTDs (resistance tempera--l ture detectors) which allowed a small primarv leak to the wiring which shorted out t t,d Li j t J l clement. The extension was cracked when thermal expansion caused an attached Furman- !

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-79-139 DATE OF EVENT: December 1,1979 FACILITY: Davis-besse Unit 1 IDENTIFICATION OF OCCURRENCE: Reactor Coolant Th Resistance Temperature Detector (RTD) failure Conditions Prior to Occurrence: The unit was in Mode 2 with Power (MWT) = 30 and Load (Gross MWE) = 0 on December 1,1979; The unit was in Mode 3 with Power (MRT)

= 0 and Load (Cross MWE) = 0 on December 3,1979.

Description of Occurrence:

On December 1, 1979 at about 1125 hours0.013 days <br />0.313 hours <br />0.00186 weeks <br />4.280625e-4 months <br /> while performing ST 5099.01, " Miscellaneous Instrument Shif t Checks", it was discovered that the Reac-tor Protection System (RPS) Channel 2 Th indication was failed low.

This put the unit in the action statement of Technical Specification 3.3.1.1 which required that the inoperable channel be placed in a tripped condition. RPS Channel 2 was tripped at about 1137 hours0.0132 days <br />0.316 hours <br />0.00188 weeks <br />4.326285e-4 months <br />.

On December 3, 1979 with the unit in Mode 3 to investigate the RPS Th failure under Maintenance Work Order (MRO) IC-537-79 at about 1815 hours0.021 days <br />0.504 hours <br />0.003 weeks <br />6.906075e-4 months <br /> the cap on the head of the RTD was removed and water was found in the termination box, apparently a pressure boundary leak through the RTD assembly. This placed the unit in Action Statement "a" of Technical Specification 3.4.6.2 which required the unit be in cold shutdown within 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. Cooldown of the plant was immediately initiated.

Designaticn of Apparent Cause of Occurrence:

Failure was apparently due to component failure of the RTD extension piece resulting in a small primary leak to the wiring causing one element to open and shorting out the other element. The extension piece was cracked by a bending force caused by a Furmanite enclosure, installed to stop a gasket leak which came into contact with a seismic pipe whip restraint due to thermal expansion. The leakage was not a primary pressure boundary leak but leakage through the gasket joint to the RTD Analysis of Occurrence: There was no danger to the health and safety of the public or to station personnel.

Reactor protection functions were available through redun-dant channels at all times.

Corrective Action

Following the unit shutdown on December 3,1979, and the subsc-quent drain down, all four direct immersion Th RTDs were removed, including the failed RTD,and new well-type RTDs were installed per FCR 79-349. The installation of the well-type RTD and removal of the Furmanite enclosure should prevent ac/

similar failure in the future. The bosses for the wells for three of the icur RTDs were also replaced due to damage on two bosses incurred by the Furmanite enclosure and due to thread damage from galling on the third boss.

Failure Data: There have been no previous occurrences of this type.

k LER #79-122