05000327/LER-1981-050-03, /03L-0:on 810504,w/unit at 60% Rated Thermal Power,Pressurizer Level Pressure Channel Declared Inoperable When Indicator Read Higher than Redundant Channels.Caused by Error in Senseline Tubing to Condensate Pot

/03L-0:on 810504,w/unit at 60% Rated Thermal Power,Pressurizer Level Pressure Channel Declared Inoperable When Indicator Read Higher than Redundant Channels.Caused by Error in Senseline Tubing to Condensate Pot

ML20004D072
Person / Time
Site:	Sequoyah
Issue date:	05/29/1981
From:	Harding M, Wilkey A TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20004D071	List: 05000327/LER-1981-050, Forwards LER 81-050/03L-0 05000327/LER-1981-050-03, /03L-0:on 810504,w/unit at 60% Rated Thermal Power,Pressurizer Level Pressure Channel Declared Inoperable When Indicator Read Higher than Redundant Channels.Caused by Error in Senseline Tubing to Condensate Pot
References
LER-81-050-03L, LER-81-50-3L, NUDOCS 8106080306
Download: ML20004D072 (3)

LER-1981-050, /03L-0:on 810504,w/unit at 60% Rated Thermal Power,Pressurizer Level Pressure Channel Declared Inoperable When Indicator Read Higher than Redundant Channels.Caused by Error in Senseline Tubing to Condensate Pot

Event date:
Report date:
3271981050R03 - NRC Website

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1. 4 69 EVE NT DATE 74 76 REPORT DAT E to EvfNT DESCRIPTION AND PROD A8LE CONSEQUENCES h 10 l 2 l l With Unit I at 60% RTP. pressurizer level oressure channel 1-L-68-339 was declared I

inoperable at 0340 CST when the associated indicator was 3bserved to be reading higher [

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] o 1. t l than redundant channels. The trip b' stable was tripped per action statement Ioisl l LCO 3.3.1.1.

At 1505 CST, auxiliary control room channels 1-L-68-325C and 3260 were l

Io is l l also declared inoperable for the same reason, and action statement "a" of LCO 3.3.3.5 l

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Durine a subsequent inn i t outane. Instrn-not ~ocMnicn dincovernd gl an error in the sense line tubing to the condensate pot which accounted for the errors li13l l exnerienced with the instrument loops. The error was corrected and the loops have been.

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LSequoyah Nucis r Plant LER SUPPLEMENTAI. INFORMATION SQRO-50-327/31050 In February 1981, DCR-P1036 was submitted to modify the tubing to the condensate pot in the sense lines for pressurizer level loops 1-L-68-325C, 326C, and 339. -Tubing from'the condensate pot to the pressurizer vapor sample line was to be added to allcw noncondensable gases to escape from the pot so that the pot could function properly to maintain the required reference leg for the three level loops. This request was implemented by ECN L5392.

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 redundant citannels. 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-68-339, they were also checked. After verifying that the two auxiliary control loops were also indicating approx-tmately 15% low, the plant entered action statement "a" of LCO 3.3.3.5.

The error was diagnosed as an increased static head in the common reference leg for the loop transmitters. The 15% orror was attributed to an accumulation of water in the tubing added by ECN L5392.

To compensate for the in crease'd sqatic head, the pressurizer high level trip bintable setpcint was shifted f, rom 92% to 76%. In addition, temporary scales were installed on main control r~oom indicators to enable operatois to obtain direct readings. Ute auxiliary control room loops were recubed 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 indi-cating 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-68-326C were observed to be reading approximately 15% high. The pltnt again entered action statement "a" of LCO 3.3.3.5.

During the subsequent unit outage, the sense lines for 1-L-68-339, 1-L-68-325C, and 1-L-68-326C were returned to their premodification configuration. Since this configuration was susceptible to variations in the reference leg static head, the loops were monitored closely and refilled as necessary. Since losses of condensate in the reference leg resulted in higher (than actual) pressurizer level signals, the limiting safety system setting off 93% was not compromised.

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On'May 4, 1981, pressurizer level channels.1-L-68-339, 325C, and 326C were again d : lared low when they were observed ' to be reading higher than redun-dant channels. The reference legs were backfilled, calibration verified, and' the loops were returned to service that same day.

During a subsequent unit outage, instrument mechanics discovered that sense

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line tubing to the condensate pot for the instrument loops had been revarsed

- inside a wall-penetration. The line from the bottom of the condensate pet

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- was tubed to.the vent line and the line from the top.of the pot was tubed to the instrument loop transmitters. The tubing error had prevented proper opcration of the condensate pot which had resulted si erroneous-level indi-Cations.

1 The tubing error was corrected on May 13-14, 1981, and the loops were returned to'scrvice. A modification on the condensate pots has been requested (DCR-1120) to-improve their operation. A similar modification to the Unit 2 pressurizer loopu.was perforced and verified during-Unit 2 hot functional testing.

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