ML19347F499

LER 81-041/03X-1:on 810323,pressurizer Level Channels 1-L-68-339,1-L-68-325C & 1-L-326C Declared Inoperable.Caused by Erroneous Indications Due to Condensate Reservoir Mod Resulting in Increased Static Head in Common Sense Line

ML19347F499
Person / Time
Site:	Sequoyah
Issue date:	05/15/1981
From:	Harding M, Wilkey A TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19347F496	List: ML19347F495 ML19347F499
References
LER-81-041-03X, LER-81-41-3X, NUDOCS 8105190448
Download: ML19347F499 (2)

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Ulal lWith Unit I at 97% newer. oressurizer level channels 1-L-68-339, 1-L-68-325C. and o l 31 l l-L-326C declared inoperable when erroneous indications were observed. On 4/2/81, o 14 I l 1-LI-68-339 was again declared inoperable. On 4/17/81, 1-LI-68-325C ahd 1-LT-68-326C

, o I 5 I l were again declared inoperable. On each occasion, the plant entered the applicable

. o is 1 I action statement: LCO 3.3'.1.1 (7) and LCO 3.3.3.5 (a). There was no effect upon 0171 l oublic health or safety. No previous occurrences.

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i i 1 o 3 lThe ' apparent cause of the error was an' increased static head in a ' common sense line due li1 lto a condensate reservoir modification made under ECN L5392. When corrective actinnn

,;y; ltaken (work plan 9117) failed to correct the conditions, the instrument sense line _

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• Sequoyah Nuciscr Fitnc LER SUPPLEMENTAL INFORMATION SQRO-50-327/81041 REVISION 1 During a channel check performed on March 23, 1981, pressurizer level loop 1-L-68-339 was discovered to be indicating approximately 15% lower than r redundant channels. The loop was declared inoperable and the associated reactor protection bistable was tripped in accordance with action 7 of LCO 3.3.1.1. Since auxiliary control room loops 1-L-68-325C and 1-L-68-326C shared a common sensing line with 1-L-68-139, they were also checked. After verifying that the two auxiliary control loops were also indicating approx-

"a" of LCO 3.3.3.5.

imately 15% low, the plant entered action statement The error was diagnosed as an increased static head in the common reference leg for the loop transmitters. A modification to this leg had been performed (ECN L5392) to improve the performance of the condensate pot in the reference leg to ensure that the reference leg was maintained'. The 15% error was attributed to an accumulation of water in the tubing added by ECN L5392.

To compensate for the increased static head, the pressurizer high level In addition, temporary trip bistable setpoint was shifted from 92% to 76%.

scales were installed on main control room indicators to enable operators to obtain direct readings. The auxiliary control room loops were retubed to the sensing line for 1-L-68-335, which did not have the sense line modification (ECN L5392).

On April 2, 1981, a channel check of 1-L-68-339 revealed that loop to be indicating approximately 8% high. Since this indicated that previous corrective action was not adequate, the loop was declared inoperable and the associated bistable tripped in accordance with action statement 7 of LCO 3.3.1.1. A return to the premodification configuration was planned .

for the next unit outage.

On April 17, 1981, auxiliary control room loops 1-L-68-325C and 1-L-326C 4

were observed to be reading approximately 15% high. The plant again entered action statement "a" of LCO 3.3.3.5.

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During the subsequent unit outage, the sense lines for 1-L-68-339, 1-L-68-325C, 1-L-68-326C were returned to their premodification configuration. Since_this I

configuration is susceptible to variations in the reference leg staticSince head, losses

! the loops will be monitored closely and refilled as necessary.

of condensate in the reference leg result in higher (than actual) pressurizer level signals, the limiting safety system setting of 693% will not be compromised. .

A design change request has been initiated for a permanent solution to the condensate pot deficiencies for the pressurizer loops.

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