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N N SL7173CIE @@lPZPATT PHOENIX, ARIZON A 85o36 P. O. SoK 21666 November 10, 1977 ANPP-9720 U. S. Nuclear Regulatory Commission Office of Inspection and Enforcement s'vi !',
Region V
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Walnut Creek Plaza - Suite 202 g g y' '
f, 1990 North California Boulevard o-d 9,$.g i-Walnut Creek, California 94596 i
Attention: Mr. G. S. Spencer, Chief 6
e Reactor Construction and 0
Engineer Support Branch W"
dl 2' a File:
77-058-026
Dear Sir:
During the Region V, I&E Inspection of PVNCS on August 29 to September 2, 1977, Mr. Bob Pate requested further information relating to concrete voids that have been identified under the thickened liner plate of the Unit No. I containment basemat.
At the time of your inspection, these concrete voids had been documented by nonconformance reports which were in the normal process of evaluation and because the information relating to the cause and corrective action may be generic to the industry, Mr. Pate requested that this information be presented to I&E, Region V.
Our response to this request is contained in Attachment A, " Report on Voids Found in the Containment Basemat Concrete, Palo Verde Nuclear Generating Station Unit No.
1".
Very truly yours,
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E. E. Van Brunt, Jr.
APS Vice President Construction Projects ANPP Project Director EEVBJr/ JAR:ske Attachments cc:
R. L. Robb W. M. Petro 8508150610 050703 fem-ey-m J. M. Allen CH
-293 PDR A. C. Rogers R. L. Hand k
W. H. Wilson V C Rinoham
ii REPORT ON VOIDS FOUND IN THE CONTAINMENT BASEMAT CONCRETE
-PALO VERDE NUCLEAR GENERATING STATION UNIT No. 1 NCE No. C-226-- November 10, 1977 Introduction As per the request of NRC I&E, Region V, this report is submitted to describe the nature of the voids identified in the containment basemat concrete of Unic No. 1 because of the possible generic application to the industry.
Background
During the planning for the placement of the concrete for the Unit No. I containment basemet, it was recognized that difficulties might be encountered during the placement of concrete under the thickened liner plate sections that were welded to the vertical reactor pit liner. During this preplacement review, it was recog-nized that the configuration of the thickened plate and vertical liner plate permitted access from only one side and may entrap air during placement.
Consequently, it was determined that (1) concrete placement would begin at the junction of the pit liner and thickened plate, (2) the tramie would be carefully placed as far under the thickened plate as possible, and (3) extra care would be taken dur-ing placement and vibration to lessen the possibility of air entrap-ment.
l Since the preplacement planning for this pour had identified the potential for voids, a testing plan was prepared and carried out after the concrete placement was completed.
The testing plan, which included soundings and destructive testing, commenced prior to the concrete curing.
The testing indicated that in spite of the pre-
's cautions taken, voids had occurred in~the areas of concern. These conditions were reported on nonconformances and corrective action was initiated in accordance with the project quality assurance program.
Discussion l
After the containment basemat concrete cured, areas around the top i
of the reactor pit where voids were suspected to occur, as well as the other sections of thickened liner place, were sounded by tapping on the liner plate surface. The sounding technique determined that voids might exist in certain areas behind the vertical pit liner j
plate under the thickened basemat places.
Holes were cut in the pit liner place and the thickened plate where I
L the examination determined voids may occur. This enabled a visual examination and confirmed that voids did exist as indicated by the sounding technique.
1
.. _ _ _ -.. _. - ~. _. _ -, _, _ _ _ - -. -. - - - - - - - _ -. - - - - - -. - -
o MCR ::c. C-:::
November 10, 1977 2_
Three voids were found (see Attachment 1). The largest void had a maximum volume of approximately 18 cubic feet. The void was generally triangular in shape and ranged in cross-sectional area from % square foot to a maximum of 4 square feet. The void extended'for a distance of approximately 16 feet.
Corrective Action Corrective action for Unit No. I was to assure that all of the voids had been determined and correctly logged. This has been accomplished.
The voids were repaired in accordance with construction specification 13-CM-365.
Specific repair procedures are documented in Attachment 1.
For subsequent unito, the corrective action will utilize a method which creates a small finite void area under each thickened plate using expanded metal and then to thoroughly grout these void areas af ter placement of the containment basemat concrete using a non-shrink grout and an approved pressure grouting technique.
In addition, small observation ports will be cut into the top liner place to relieve any trapped air and to permit direct observation to assure,that no voids have occurred under the thickened liner plate sections after placement of the containment basemat concrete.
Conclusion The voids have all been satisfactorily repaired.
Subsequent tests indicate that all of the containment basemat chickened liner place is on sound concrete and no other voids exist. The nonconformance is accepted and closed out.
The corrective action described will provide assurance that voids will not occur in the containment basemat concrete of subsequent units.
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a ATTACMENT 1
. DESCRIPTION OF VOIDS
. REPAIR PROCEDURE FOR VOIDS i
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NCR No. C-226 Page 1 of 6
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