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s esRC Form 3ge U S. NUCLEa0 REGULf TORY COhml10SION APPROVE 3 Oede NO. 31to-s104
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LICENSEE EVENT REPORT (LER)
FACILITV NAAe6 (1)
DOCKET NUedSER (2)
FAGE G Browns Ferry - Unit 3 0 1s!o10101 21916 1 lOFl0 l2 TITLE ten Hismatch of Reactor Water Level Indicators EVENT DATE tel LER NUMAER (S)
REPORT DATE 176 OTHER FACILITIES INVOLVED (4)
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During the startup of unit 3, a mismatch between water level indicators developed while et low pressure and subsequently diminished.
Since the event, training has been received by operators, plant management and shift technical advisors to enable them to more rapidly diagnose water level indication problems during startup operations. The unit was shutdown on March 9, 1985, to inspect instruments and instrument lines for any problems which could cause a loss of water in the reference leg.
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Brawns Ferry - Unit 3 015 lo 1010 l 2l 916 81 5 01016 0 l0 0 l2 oF 0l2 rm n -.
, -,,nn Unit I was in normal operation at 95 percent power, unit 2 was in a refueling outage, cnd unit 3 was in a startup from cold shutdown. Only unit 3 was affected by this cvent.
On February 13, 1985, at 2130, unit 3 was returning to service from a cold shutdown.
The unit had been critical since 2058, and reactor pressure was approximately 20 pais.
At this time, the unit operator noticed the B GEMAC water level indicator, LI-3-60, was indicating approximately 17 inches less than A and C GEMACs, LI-3-53 and LI-3-206.
At 2136, a half scram was initiated by LIS-3-203D. The unit operator immediately raised water level which cleared the half scram.
By 2230, all three control room indicators were indicating the same level. Operability checks on LIS-3-203C and LIS-3-203D verified operability of redundant low water level scram switches.
The apparent cause of the event was a partial loss of water in the A GEMAC (see attached cketch) reference leg causing LI-3-53 and LI-3-206 to indicate erroneously. The reference leg refilled as the efficiency of the headpot increased with increased reactor pressure.
Post event review indicated that similar phenomena have been cbserved at several BWR facilities and was usually due to a small leak in associated valves or pressure gauges.
This deviation would introduce a corresponding error in the setpoints of the levels switches on the affected instrument leg.
Redundant level switch instrumentation was cperable as well as LI-3-60 and the 2 Yarway indicators which monitor this range of interest.
Since the event, training has beenJ rovided to operators, shift technical advisors, and p
plant management (plant manager, plant superintendents, engineering group supervisor, compliance supervisor, reactor engineering supervisor, shift technical advisor unit cupervisor) to enable them to more rapidly diagnose water level indication problems that may occur during startup and normal operation and take appropriate technical cpecification action. The major problem in the event was a training deficiency in that Cperators and shift technical advisors had not been thoroughly trained in the behavior cf all level indicators in off-rated conditions.
The unit was shutdown on March 9, 1985, so a thorough inspection of the instrument lines could be performed. This inspection should identify any leaks or air bubbles.in the instrument line that could have caused the partial loss of the reference leg.
A follow-up report will be provided discussing the results of these inspections.
Responsible Plant Section - N/A Previous Events - BFRO-50-296/81027, 50-260/7711 g eo n..
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, TENNESSEE VALLEY AUTHORITY Browns Ferry Nuclear Plant P. O. Box:2000 Decatur, Alabama 35602 March 15, 1985 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D. C.
20555
Dear Sir:
TENNESSEE VALLEY AUTHORITY - BROWNS FERRY NUCLEAR PLANT (BFN) UNIT 3 -
DOCKET No. 50-296 - FACILITY OPERATING LICENSE DPR REPORTABLE OCCURRENCE REPORT BFRO-50-2%/85006 The enclosed report provides details concerning the mismatch of reactor water level indicators. This report is submitted in accordance with 10 CPR 50.73 (a)(2)(iv) and (vii).
Very truly yours, TENNESSEE VALLEY AUTHORITY h&O O. T. Jones Plant Manager Browns Ferry Nuclear Plant Enclosures oc (Enclosures):
Regional Administrator INPO Records Center U. S. Nuclear' Regulatory Commission Suite 1500 Office of Inspection and Enforcement 1100 Circle 75 Parkway Region II Atlanta, Georgia 30339 101 Marietta Street, Suite 2900
' Atlanta, Georgia 30303 NRC Resident Inspector, BFN l
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An Equal Opportunity Employer
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