ML17209A009
| ML17209A009 | |
| Person / Time | |
|---|---|
| Issue date: | 08/12/1980 |
| From: | Check P Office of Nuclear Reactor Regulation |
| To: | Anderson T WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| References | |
| TAC-47150, TAC-47151, TAC-47792, TAC-51994, NUDOCS 8008200025 | |
| Download: ML17209A009 (3) | |
Text
pe ~aCI, NUCLEAR REGULATORY COMMISSION
)<< F WASHINGTON, D. C. 20555 AUG 12 BBO Mr. Thomas Anderson, Manager Nuclear Safety Department Westinghouse Electric Corporation P. 0.
Box 355 Pittsburgh, Pennsylvania 15230
Dear Mr. Anderson:
SUBJECT:
VOID FORMATION IN VESSEL HEAD DURING ST.
LUCIE NATURAL CIRCULATION COOLDOllN EVENT OF 6/ll/80 On June ll, 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 auxiliary 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, abnormally 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 flow 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 I)rovided in the enclosure.
It has been postulated that the steam void in the upper vessel was pIoduced when the system pressure dropped below 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
("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 voi'd,forIIIation and take corrective action, and the question of whetheI such void formation is properly accounted for in safety
~"
Mr. Thomas Anderson AUG 1S 1980 analyses (Chapter 1S),
we have sent a list of questions documenting our concerns to the licensee.
These questions are also provided in the enclosure for your information.
He are presently evaluating the need to pursue this issue generically with all PHR 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 phenomenon 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 (1S) working days after receipt of'his letter whether a supplemental information submittal by you on the subject would'preclude the need to expeditiously pursue this issue generically with your customers.
Original Sip~cd bg Paul S. ChedC h
Paul S.
Check, Assistant Director for Plant Systems Division of Systems Integration Office of Nuclear Reactor Regulation cc:
E.
Ca'se ACRS (16)
T. Mur ley L. Tong H. Sullivan G. McPherson L. Rubenste'n D. Eisenhut R. Mattson C. Berlinger C. Michelson, AEOD DIST:
Central Files RSB Rdg. File NRR Rdg. File BSheron PCheck TSpeis on:dlr 8/
/80 C
S peis 8/1 /80 AD S/DSI PSC hack 8
/80
A I