ML20003A394

LER 80-033/03L-0:on 801227,one of Four Loops Indicating Pressurizer Pressure & Feeding Thermal Margin/Low Pressure Calculator of Reactor Protection Sys Channel & Safety Injection Actuation Channel,Failed Low.Caused by Blown Fuse

ML20003A394
Person / Time
Site:	Fort Calhoun
Issue date:	12/29/1980
From:	Core M OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20003A395	List: ML20003A394
References
LER-80-033-03L, LER-80-33-3L, NUDOCS 8102030608
Download: ML20003A394 (4)

Text

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60 61 DOCAET NUVSER 68 63 EV ENT DATE 74 76 REPOH T OATE 84 EVENT DEiCRIPTioN AND PROB ABLE CONSEQUENCES h tol2ll Durink power operation, one of four current loops indicating pressurizer pressure andl

) io i3i I feeding the thermal margin / low pressure calculator of one Reactor Protective System I o 4 l channel and one Safety Injection Actuation channel failed low, placing the SIAS in 1 I F5Ts1 l half trip and tripping one Ti1/LP channel of the RPS. The RPS "B" channel wculd not l i,

iO is i ! have tripped on high pressurizer pressure. The RPS was placed in two-out-of,-three l j l O 171 [ logic by bypassing the "B" channel TM/LP bistable. Technical Specification 2.15 l 1Otai I applies. I 80 y g 9 C DE CODE S SC E COMPONENT CODE SUB DE SU DE l0l9l l Il Al(U) [Ej@ W@ ll IN lS lT lR lu l@ LPl@ 18 19 _

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h j [1Lo ] l After investination. it was discovered that the current 1000 fuse in the CE/MAC lilil l Type 570 power supply for the B/ PIA-102Y loop had blown. The fuse was roolaced and I i,i,ii the loop returned to normal after comparing the loop current with the other three I gl loop currents measuring the same process.  !

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LER 80-033 i Omaha Public Power District Fort Calhoun Station Unit No. 1 -

Docket No. 05000285 ATTACHMENT N0. 1 Safety Analysis The Reactor Protective System is designed in such a manner that no-t single failure will prevent it from performing its design function. The failure of the B/P-102Y loop placcd the "B" channel-Thermal Margin / Low i Pressure trip bistable in the trip condition and was immediately by- t passed, placing the RPS in two-out-of-three logic. Further, the failure 4 of the loop rendered the "B" channel High Pressurizer Pressure trip bistable inoperative. However, during the time the "B" loop was in-operable, the other three channels-of the RPS were operable and wo.'d have performed the design function of the RPS; that is, trip the re-4 actor. Further, the Safety Injection Actuation Signal logic was in half 3- trip, as it should have been with the failure of the instrument loop, j and was, therefore, conservative.

At all times, the minimum degree of redundancy conditions were met.

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LER 80-033 1

Omaha Public Power District i Fort Calhoun Station Unit No.1 7

Docket No. 05000285 ATTACHMENT NO. 2 f

Corrective Action 4

After troubleshooting the loop for malfunction, it was discovered l that the loop current fuse in the power supply, a GE/MAC Type 570, had

. blown, thus opening the current loop. The loop fuse was replaced and the loop returned to service. The RPS & SIAS circuitry was verified to be reset and the bypass keys removed, placing the RPS into its normal two-out-of-four logic. No further corrective action is anticipated.

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. w LER No.80-033 Omaha Public Power District Fort Calhoun Station Unit No.1 Docket No. 05000285 ATTACHMENT NO. 3 Failure Data This is the first reportable occurrence of this type in loop 102Y at the Fort Calhoun Station. Other fuses in GE/MAC Type 570 power supplies have failed; however, these failures have always been in the conservative direction (failed safe) or involved non-safety related equipment.