ML20151U633

PNO-77-061:on 770419,cracking of 18-inch Thick Concrete at Containment Floor Level Was Observed in SGs B & C Cubicles. Cause Believed to Be Air Leakage & Air Buildup Under Containment Floor Metal Liner.Press Release Planned

ML20151U633
Person / Time
Site:	Farley
Issue date:	04/20/1977
From:	Gower G, Roy G, Thompson D NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
To:
References
PNO-77-061, PNO-77-61, NUDOCS 9809110088
Download: ML20151U633 (2)

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PRELIMINARY NOTIFICATION i

April 20, 1977 PRELIMINARY NOTIFICATION Or EVENT OR UNUSUAL OCCURRENCE--PNO-77-61

' This preliminary notification constitutes EARLY notice of an event of l POSSIBLE safety or public interest sicnificance. The information presented is as initially received without verification or evaluation

. and is basically all that is.known by IE staff on this date.

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Facility: ;AlabamaPowerCompay Farley Unit No. 1 DN 50-348)

Subject:

CRACKS IN CONCRETE FLOOR OF CONTAINMENT At 2:00 p.m. on April 19, 1977, cracking of the 18-inch thick concrete at containment floor level (elevation 105'-6") was observed in steam generators B and C cubicles. The cracking continued to progressively worsen until about t

5:00 p.m.. At that time, the largest crack was observed to be about 20 feet in length, have an opening of about 1/2 inch and one edge of the crack was elevated about 3/8 inch with respect to the other edge. The worst crack appeared to originate in SG "C" cubicle and progress in an outward direction to the biological shield wall (no cracking was visible in the biological shield) and continued on from the shield for an overall distance of 20 feet.

Cause of the cracking is believed to be air leakage and air buildup under the containment floor metal liner from local leak rate testing in progress on the concentric guard pipe and valve enclosure over the containment sump recircula-tion pipe. Air pressure on the guard pipe and valve enclosure was reported to

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" be about 28 lbs. at time of most severe cracking. When air pressure was re- -

duced, cracking was observed to subside.

Construction of the containment floor area is on a 9-foot thick concrete slab, inence a steel containment liner plate is placed over the slab, and an 18-inch thick concrete filler slab poured over the steel liner to form the containment floor. The recirculation pipe penetrates the floor of the containment. Where the pipe run is through concrete, a concentric guard pipe encloses the recirculation pipe. The guard pipe connects to an air tight enclosure that encloses the recirculation valve and terminates by seal welding the valve enclosure to the downstream side of the recirculation pipe. preliminary calculations indicate that an air pressure of about --

18 lbs,. under the liner plate could cause the phenomena observed.

Licensee was recuesting that an operating license be issued on 5/2/77. The -

delay associatec with this occurrence is not yet known.

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CONTINUED 9j $'

g91 88 770420

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, . l Continued April 20, 1977 -

Page 2 PNO-77-61

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Media interest has occurred, in that a local television station contacted the licensee. IE Headquarters has been contacted by a concerned citizen who learned of the cracking from plant employees. Licensee is making a press release of the occurrence. 4 Regien II received notification of this occurrence from onsite Region II )

inspectors at 10:00 p.m. on 4/19/77. .

Contact:

G'CGower, IE x27261 GWRoy, IE x27261 DThompson, IE x27541  !

~ Distribution: Transmitted H St //A** po- i Chairman Rowden C. C. Kammerer, CA G. F. Murphy, JCAE Commissioner Gilinsky S. J. Chilk, SECY H. H. Whiteside, SCNR H. R. Myers, HCEE Transmitted: MNBB/:Jd[ P Bldg /.'/f[,' SS Bldg /.' J//";

L. V. Gossick, EDO B. C. Rusche, NRR K. R. Chapman, NMSS S. H. Hanauer, ED0 H. K. Shapar, ELD J. A. Harris, PA W. G. Mcdonald, MIPC Luge (mail); E. Volgenau R. G. Ryan, OSP T. J. McTiernan, OIA Region f , IE/.A)[;

PRELIMINARY NOTIFICATION t

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