ML19338C837
| ML19338C837 | |
| Person / Time | |
|---|---|
| Site: | Oconee, Indian Point  |
| Issue date: | 07/28/1980 |
| From: | Check P Office of Nuclear Reactor Regulation |
| To: | Taylor J DUKE POWER CO. |
| References | |
| NUDOCS 8009050343 | |
| Download: ML19338C837 (2) | |
Text
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t Mr. J. Taylor Babcock & Wilcox Owners Group Duke Power Company P. O. Box 2178 422 South Church Street Charlotte, North Carolina 28242
Dear Mr. J. Taylor:
SUBJECT:
VOID FORMATICN 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 ccolant pump seals. This also required shutdown of the reactor coolant pumps and cooldewn 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 auxiliary pressurizer spray, was diverted entirely to the auxiliary spray to enhance the depressurization and reduce the system pressure on the pump sL:1s. At this time, abnormally rapid increases in pressurizer level were cbserved 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 tne 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 subcooled 0
(-200 F), it appears that the fluid in the upper head was much hotter, relatively stagnant, and in poor communication with the fluid exiting the core and in the upper plenum.
In addition, 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 question of whether such void formation is properly accounted for in safety 8 009 0 503C S
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analyses (Chapter 15), we have sent a list of questions documenting our concerns to the licensee.
These questions are also provided in the enclosure for your information.
We are presently evaluating.the need to pursue this issue generically with all PWR licensees.
Prior to taking any definitive action however, we are soliciting your technical opinion and advise regarding the potential for void formation under similar circumstances in NSSS's designed by you.
Specifically, we need to know if you can justify why the voiding phencmenon cannot occur in NSSS's designed by you (or can confirm that such phenomena can be properly predicted by your transient analysis models), and if it can occur, is properly 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.
67Mm1 s! ped by!
Paul S. Check, Assistant Director for Plant Systems Division of Systems Integration Office of Nuclear Reactor Regulation bcc:
E. Case D. Eisenhut DIST:
ACRS (16)
R. Mattson Central Files T. Murley C. Berlinger RSB Rdg. File L. Tong C. Michelson, AE00 NRR Rdg. File H. Sullivan BSheren G. McPherson TSpeis y
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