ML20086S576

AO-S2-74-07:on 740810,summator TM-2-412G Drift Allowed Overpower Trip Setpoint to Be Approx 5% High.Caused by Defective Summator.Summator Removed & Replaced & Module Calibr

ML20086S576
Person / Time
Site:	Surry
Issue date:	09/26/1974
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
AO-S2-74-07, AO-S2-74-7, NUDOCS 8403020445
Download: ML20086S576 (5)

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O O VxnoinzA Ex.r.cTrtic Awo Powr:re Co>ri Any 4 RecnnoNo.VinotNrA 23201 September 26, 1974 Mr. Norman C. Moseley, Director Serial No. 287 Directorate of Regulatory Operations P0faf/JTB:clw United States Atomic En'ergy Commission Region II - Suite 818 Docket No. 50-281 230 Peachtree Street, Northwest License No. DPR-37 Atlanta, Georgia 30303

Dear Mr. Moseley:

Pursuant to Surry Power Station Technical Specification 6.6.B.1, the Virginia Electric and Power Company hereby submits forty -(40) copies of Abnormal Occurrence Report No. A0-S2-74-07.

The substance of this report has been reviewed by the Station Nuclear

• Safety and Operating Committee and will be placed on the agenda for the {

next oceting of the System Nuclear Safety and Operating Committee. -

t Very truly yours,

0. NNf C. M.,Stallings f Vice President-Pouar' Supply and Production Operations Tnclosures 40 copics of A0-S2-74-07 .

cc: Mr. K. R. Coller, Assistant Director M[gf Y*&

for Operating Rcactors O- Q U I O 'l s v 7I ll Gr'

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B ABNORMAL OCCURRENCE REPORT REPORT NO. A0-S2-74-07 FAILURE OF THE OVERPOWER AT SETPOINT SUMMATOR TM-2-412G AUGUST 29, 1974 DOCKET NO. 50-281-

. LICENSE NO. DPR SURRY POWER STATION.

VIRGINIA ELECTRIC AND' POWER COMPANY i

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r 9 O I. INTRODUCTION In accordance with Technical Specification 6.6.B.1 for Surry Power Station, Unit No. 2, Operating License Number DPR-37, this report describes an abnormal occu'trence which occurred on August 10, 1974. The Directorate of Regulatory Operations, Region II, was notified on August 10, 1974.

The occurrence reported herein is classified as an abnormal occurrence

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pursuant to Technical Specification 1.0.I.1 which states that "An abnormal occurre'nce is defined as: Any unit condition that results in exceeding a safety limit or that results in safety system settings less conservative than the limiting safety system settings delineated in these Technical Specificntions."

The occurrence described herein involved a summator which drifted high causing an incorrect overpower AT trip setpoint.

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SUMMARY

OF OCCURRENCE On August 10, 1974, Periodic Test 2.1, " Reactor Coolar. Temperature Protection Instrumentation" was being performed. At approximately 1030 hours0.0119 days <br />0.286 hours <br />0.0017 weeks <br />3.91915e-4 months <br />, with the unit at 100 per cent of rated power, it was found'that summator TM-2-412G had drifted allowing the overpower AT trip setpoint to be~ approx-imately five (5) per cent high. The defective summator was removed and replaced, and the replacement module was calibrated.

III. ANALYSIS OF OCCURRENCE Summator TM-2-412G is a Hagan model _ III, assembly' number. 4111084-004.

The T,yg signal is transmitted to lead-lag controller TM-2-412L and summator-3 TM-2-412M. The outputs of ' TM-2-412L and TM-2-412M are. transmitted to summator -

~TM-2-412G where.they are summed'Nith the flux signal output of function l'

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generator NM-2-412B. Summator TM-2-412G develops the overpower trip set-point signal which is equal to a constant minus the characterized T avg signal, minus a T,yg deviation signal, and minus a function of the flux difference signal. The output of the overpower trip setpoint computer TM-2-412G is transmitted to input module TM-2-412G/R which provides an input to signal comparator TC-2-412B. The dual comparator TC-2-412B provides an overpower AT rod stop, turbine runback, and an overpower AT reactor trip signal to protection channel 1.

Summator TM-2-412G drifted high resulting in a trip setpoint of 111 per cent in lieu of 106 per cent. After its removal, the summator was subjected to extensive bench testing. Transistor Q4 was found to be heat sensitive, causing faulty operation of the input amplifier section of the module.

Failure of electronic components such as that experienced is expected and has occurred before. However, the occurrence reported herein is the first to result in exceeding a safety setting.

IV. CORRECTIVE ACTION TO PREVENT RECURRENCE The failure of transistor Q4 was a random electronic failure. After the replacement of transistor Q4, the failed summator operated satisfactorily after being subjected to the previous series of tests. No further corrective action is deemed necessary.

V. ANALYSIS OF SAFETY IMPLICATIONS OF THE OCCURRENCE The overpower AT reactor trip protects the reactor against excessive power density. It trips the reactor on coinci3ence of two out of the three channels, with one channel per loop.

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The safe operation of the station was not affected, since the remaining two overpower AT protection channels were operating properly.

VI. CONCLUSIONS The licensee concludes that:

1. The occurrence described herein was caused by a faulty transistor in the overpower AT summator.

2. The occurrence reported herein did not affect the safe operation of the station.

3. The occurrence described herein did not adversely affect the health of the general public.

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