ML20154G084
| ML20154G084 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 05/20/1988 |
| From: | Richardson S NRC OFFICE OF SPECIAL PROJECTS |
| To: | |
| References | |
| PNO-OSP-88-007, PNO-OSP-88-7, NUDOCS 8805240211 | |
| Download: ML20154G084 (1) | |
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May 20, 1988 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE PN0-0SP-88-007 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance.
The infonnation is as initially received without verification or evaluation, and is all that is known by the OSP staff on this date.
FACILITY: Tennessee Valley Authority Licensee Emergency Sequoyah Unit 2 Classification:
Docket No. 50-328 Notification of Unusual Soddy-Daisy, Tennessee Event Alert Site Area Emergency General Emergency X
Not Applicable
SUBJECT:
SEQUOYAH UNIT 2 SCRAM At 2:14 p.m. on May 19, 1988, Sequoyah Unit 2 tripped from approximately 73%
power. The trip was initiated by "steam flow greater than feed flow coincident, withlow(25%)steamgeneratorlevel." At the time of the event, a steam generator (SG) level channel was in the tripped condition while maintenance work was in progress on a level transmitter cable splice. An automatic turbine runback to 70% occurred due to an indicated high level in the #3 feed heater drain tank. Shortly thereafter, the heater drain tank pumps tripped and the operator manually ran the turbine back to 50%.
When the runback began, the automatic level control system for SG 1 malfunc-tioned, and the unit operator took manual control of that SG's level control valve. The combination of the runback and manual feed of the SG caused level oscillations (shrink and swell). These level oscillations caused the auto feed valves for SGs 2, 3, and 4 to cycle and operators took manual control of feedwater on these SGs as well. While feeding in manual, SG levels were raised to 60% on all 4 SGs. This initiated feed line isolation to those SGs, which resulted in the steam flow greater than feed flow by more than 40% flow difference setpoint in SG 3.
With the level channel for SG 3 already tripoed, the reactor trip coincidence was made up and the reactor scrammed.
The operators took the requisite post-trip actions; the plant was stabilized in a hot standby condition and remains there while TVA conducts its post-trip root cause analysis and completes repairs. After completion of the post-trip review TVA will brief the NRC staff prior to restart.
CONTACT:
S.' Richardson (301) 492-3286 DISTRIBUTION:
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