ML19338C756
| ML19338C756 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 07/28/1980 |
| From: | Check P Office of Nuclear Reactor Regulation |
| To: | Scherer E FLORIDA POWER & LIGHT CO. |
| References | |
| NUDOCS 8009050029 | |
| Download: ML19338C756 (2) | |
Text
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d Nr-4 JUL 8 390 Mr. Ed Scherer Combustion Engineering Owners Group Florida Power and Light Company P. 0. Box 529100 Miami, Florida 33152
Dear Mr. Scherer:
SUBJECT:
VOID FORMATION IN VESSEL HEAD DURING ST. LUCIE NATURAL CIRCULATION C00LDOWN EVENT OF 6/11/80 On June 11, 1980, the St. Lucie reactor was shutdown due to a loss of component cooling water to the reactor coolant pump seals. This also required shutdown of the reactor coolant pumps and cooldown was accomplished by natural circulation.
At approximately 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> into the event, charging flow, which was initially being divided between the cold legs and the auxi.11ary pressurizer spray, was diverted entirely to the auxiliary spray to enhance the depressurization and reduce the system pressure on the pump seals. At this time, abncrmally rapid increases in pressurizer level were observed which could not be explained by the charging flow rate alone.
Detailed evaluation and follow-up analyses by the licensee and NSSS supplier have indicated that a steam void was probably formed in the upper head region of the reactor vessel and displaced water from the vessel into the pressurizer.
Continued alternating realignment of charging ficw between the cold legs and auxiliary spray line produced a "saw-tooth" pressurizer level behavior.
Relevant information and data available to the staff to date are provided in the enclosure.
It has been postulated that the steam void in the upper vessel was produced when the system pressure dropped belcw the saturation pressure corresponding to the temperature of the fluid in the upper head. Because the measured hot and cold leg temperatures at the time of voiding were highly subccoled 0
(-200 F), it appears that the fluid in the upper head was much hotter, relatively stagnant, and in poor mr"mication with the fluid exiting the core and in the
~
upper plenum.
In additfor., stored heat in the upper head structures most likely contributed to the voiding.
Because of the unexpected occurrence of the void, the failure of the operators to immediately recognize the void formation and take corrective action, and the questien of whether such void formation is properly accounted for in safety 8000050029
JUL r3 200,
analyses (Cnspter 15), we have sent a list of questions documenting our t
concerns to the licensee.
enclosure for your information.These questions are also provided in the We are presently evaluating the need to pursue this issue generically with all PWR licensees.
soliciting your technical opinion and advise regarding the potential fo void formation under similar circumstances in NSSS's designed by you.
Specifically, we need to know if you can %stify why the voiding phenomenon cannot occur in NSSS's designed by you f.or can confirm that such phenomena can be preparly predicted by your transient analysis models), and if it can occur, is sroperly accounted for in operating procedures (e.g., cooldown rates), operator guidelines, and operator training (including the simulator)
The urgency of this matter requires you~ advise us within fifteen (15) working days after receipt of this letter whether a supplemental information submittal by you on the subject would preclude the need to expeditiously pursue this issue generically with your customers, odc%rl @ bg Paul S. Check, Assistant Director for Plant Systems Division of Systems Integration bcc:
E. Case Office of Nuclear Reactor Regulation ACRS (16)
T. Murley L. Tong H. Sullivan G. McPherson L. Rubenstein DIST:
D. Eisenhut Central Files R. Mattson RSB Rdg. File C. Berlinger NRR Rdg. File C. Michelson,AE00 BSheron TSpeis PCheck RSlf*
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n 75peis PCheck 7/12, /S0 7/;c/80 7
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