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4 Docket No.950-275-.-}
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MEMORANDUM FOR:' H. Denton
.R. Houston L. Rubenstein D. Eisenhut
- D. Crutchfield-J. B. Youngblood J. Lyons J. Knight V. Noonan H. Thompson G. Lainas F. Miraglia T. Speis R. Bernero W. Russell T. Novak G. Holahan F. Schroeder G. Lear THRU:
Steven A. Varga, Director PWR Project Directorate #3 Division of PWR Licensing-A g
FROM:
Hans Schierling, Project Manager PWR Project Directorate #3 Division of PWR Licensing-A c.
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SUBJECT:
DAILY HIGHLIGHT Plant Name, Diablo Canyon Power Plant, Unit 1 With the plant at about 0.5% power, the reactor tripped on steam flow / feed ~
. flow mismatch coincident with steam generator low-level signal. The flow mismatch was a momentary upset caused by opening the turbine stop valves in
.r the process of latching the turbine.
With one steam generator level',
bistable tripped because the channel was out of service, the coincident' mismatch signal made up the logic for the reactor trip. Trip breaker. Train A opened but trip breaker Train B did not open. Both breakers have the shunt trip. attachment installed.
The licensee's review of the sequence of events indicated the trip signal-duration was.for one cycle, or 15 mil 1iseconds. Subsequent testing indicates that about 70 to 80 milliseconds are required for the breakers to actbate. Why the Train A breaker opened in light of this finding is still.under investigation. The licensee has verified the operability of the breakers, including the testing of the undervoltage trip attachment, and additional review of the event is still underway.
This information was received at 9:20 a.m. this date, from Bob Magruder,-
shift foreman at Diablo Canyon 2.
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WASHINGTON. D. C. 20555
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November 29, 1985
-Docket No. 50-275 MEMORANDUM FOR:
H. Denton R. Houston L. Rubenstein D. Eisenhut D. Crutchfield J
- 8. Youngblood J. Lyons J. Knight V. Noonan H. Thompson G. Lainas F. Miraglia T. Speis R. Bernero W. Russell T. Novak G. Holahan F. Schroeder G. Lear THRU:
Steven A. Varga, Director PWR Project Directorate #3 Division of PWR Licensing-A FROM:
Hans Schierling, Project Manager PWR Project Directorate #3 Division of PWR Licensing-A
SUBJECT:
DAILY HIGHLIGHT Plant Name Diablo Canyon Power Plant, Unit 1 With the plant at about 0.5% power, the reactor tripped on steam flow / feed flow mismatch coincident with steam generator low-level signal.
The flow,
mismatch was a momentary upset caused by opening the turbine stop valves in r
the process of latching the turbine.
With one steam generator level bistable tripped because the channel was out of service, the coincident.
mismatch signal made up the logic for the reactor trip. Trip breaker Train A opened but trip breaker Train B did not open. Both breakers have the l
shunt trip attachment installed, t
The licensee's review of the sequence of events indicated the trip signal duration was for one cycle, or 15 milliseconds. Subsequent testing indicates that about 70 to 80 milliseconds are required for the breakers to actuate. Why the Train A breaker opened in light of this finding is j
still under investigation.
The licensee has verified the operability of the breakers, including the testing of the undervoltage trip attachment, and additional review of the event is still underway.
This information was received at 9:20 a.m. this date, from Bob Magruder, shift foreman at Diablo Canyon 2.
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Hans Schie g,ProjectManagfr [g,j, e'~~Yh M Llh hg (p
PWR Project ire torate #3 Division of PWR Licensing-A L,/
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