ML17250B345
| ML17250B345 | |
| Person / Time | |
|---|---|
| Issue date: | 08/12/1980 |
| From: | Check P Office of Nuclear Reactor Regulation |
| To: | Taylor J BABCOCK & WILCOX CO. |
| References | |
| TAC-51994, NUDOCS 8008180173 | |
| Download: ML17250B345 (3) | |
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.Enclosure 1
PUG a2 I-SO Letter sent to PWR NSSS Vendors:
Westinghouse, Combustion Engineering and Babcock and Wilcox Dear I/r..
SUBJECT:
VOID FORI'ATION IN, VESSEL HEAD DURING ST.
LUCIE NATURAL CIRCULATION COOLDOWN 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 alsb'equired shutdo);n of the reactor coolant pumps and c oldown );as 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 );as initially being divided between the cold legs and the auxiliary p)-essu) izer spray,
),"as diverted entirely to the auxiliary spray to enhance the depressu) ization and reduce th 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 evalvation and follow-up analyses by the-licensee and NSSS svpplier have indicated that a steam void was probably formed in the vpper head region of the reactor vessel and displaced water from the vessel into the pressurizer.
Continved alter'nating realignment of charging flow between tt)e cold legs and auxiliary spray line produced a "sa>>-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 below the saturation pressure corresponding to the te-peratvre of the fluid in the upper head.
Because
'he measured hot'nd cold leg temperatures at the time of voiding were highly:svbcooled
( 200 F), it appears-.that the fluid in the upper head was much hoiter, relatively-
- stagnant, and in poor communication with the flvid exiting tl)e core and in the v'pper plenum.
In addition, stored heat in the vpper head st)-))ctures most likely contributed to the voiding.
'ecause of the unexpected occurrence of the void, the failu).e'f. the operators to immedia ely recognize the void for,ation and take corrective action, and the question of whether svch void formation is p)'opelly accounted for in safety
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analyses (Chapter 15), i'e have sent a list ~t>>g o" concerns to the licensee.
These questions a~-the enclosure for your information.
)!e are presently evaluating the need to purs~
a y
all PHR licensees.
'Prior to taking any dcfi~er soliciting your technical. opinion and advise4kPt'oid formation under similar circu...stances in~'y '"
Soecifically, tie need to 'knox, if you can just~ p"en "-" "
cannot occur in f!555's designed by you (Qr car h Phe".'" "
~ can be properly pi edicted by your transient ~
occur, is properly accounted for in operati~':
rates),
operator guidelines, and operator troche.simulator)
The urgency of this matter requires you advi~
~;orking days after receipt of this letter i;h~l information submittal by you on the subject i;ould precl~editiously pursue this issue generically v.ith your cust~'
Paul
.g
@+director. =or Plant ~"
Division~
Office of&Eegulation
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