ML19309F330

Deficiency Rept Re Concrete Honeycombing in Steam Generator Compartment Walls of Unit 2 Reactor Containment Bldg. Consultant Survey Showed No Critical Internal Defects.Util to Repair Condition w/dry-pack Mortar,Grout & Concrete

ML19309F330
Person / Time
Site:	Comanche Peak
Issue date:	04/21/1980
From:	TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:
Shared Package
ML19309F329	List: ML19309F328 ML19309F330
References
NUDOCS 8004290254
Download: ML19309F330 (3)

Text

. 8 0 DA290 .;$ S.$P TXX-3124 ATTACHMENT April 21, 1980 Page 1 COMANCHE PEAK STEAM ELECTRIC STATION CONCRETE HONEYCOMBING UNIT 2 - STEAM GENERATOR COMPARTMENTS CONCRETE PLACEMENT N0. 201-4812-007 Description of the Deficiency The subject concrete placement was completed on June 21, 1979 between approximate Elevations 819' and 846'-6" and involved approximately 950 cubic yards of concrete. Due to construction s. gencing, formwork re-mainted in place until the first part of October '979 pending completion of subsequent concrete placements for the core wai:s to apprcximately Elev. 860.

Following form removal for the subject placement, routine Quality Control inspection efforts identified and documented areas of the exposed concrete surfaces which did not fully comply with the governing specification in that honeycombed conditions per CpSES procedural definitions were visible following form removal. The horizontal and perpendicular extent of the defects varied from relatively small areas of limited depth (suitable for repair by conventional dry pack techniques) to large areas (on the order of 150 sq.ft.) extending several feet into the walls, the maximum estimated volume of repair concrete being on the order of 3.5 cubic yards.

Following engineering review of the documented deficiencies, the construction forces were authorized in early December 1979 to begin repair of the concrete in one of the compartments. During the process of chipping to sound concrete, Engineering and Senior Quality Control personnel simultaneously -

expressed concern to site management over the integrity of the inaccessible portions of the placement, particularly that portion of the placement adjacent to the stainless steel liner for the refueling pool. Considering the diffi-culty of the placement and the results of the repair work to date, site management decided that some additional investigation was required to fully resolve the above stated concerns. The matter was then promptly verbally reported to the NRC Resident Inspector as an item under evaluation for formal reportability within the requiremenL of 10 CFR 50.55(e).

In early January 1980, the services of a consultant were retained for the purpose of microseismically evaluating the inaccessible Nrtions of the subject placement to identify and correct any internal defects which might be present and n,t visible from the compartment wans. The non-destructive method emplayed util'zes pulse echo and resonant frequency techniques and includes the foiloving basic eauinmer.t:

TXX-3124 ATTACHMENT April 21, 1980 Page 2 (1) Impactor for the creation of a mechanical stress wave and the energy for an air cavity standing wave.

(2) A piezoelectric / accelerometer transducer for converting the mechanical energy into electrical energy.

(3) A signal processor.

(4) A storage oscilloscope for data presentation and recording.

A series of measurements were taken over a four-day span on a grid pattern within the subject placement from both the liner face towards the exposed compartment walls and from the compartment walls toward the stainless steel liner. The results of these measurements were summarized and sub-sequently submitted for review by Engineering. Following review, Engineering directed some physical investigations to better ascertain the nature of certain anomalies revealed by the microseismic investigation. These in-vestigations included:

(1) Removal of small patches of thes stainless steel liner at locations determined to represent the more critical anomalies. -

(2) Coring of selected critical areas to evaluate the nature of minor internal defects thought to be present as the result of the mi'croseismic investigation.

On February 14, 1980 and following completion of the above mentioned physical investigations, the consultant returned to the site to review the results of those investigations and to obtain additional microseismic information in areas of Engineering concern. The results of all these investigations have been compiled in an Engineering Report relative to the subject placement, which is available for review at the CPSES site.

This report concludes that the inaccessible portions of the subject placement, excluding the honeycombed portions described separately above, meets or exceeds design requirements and contains no hidden internal defects which would be detrimental to the safety or utility of the structure.

TXX-3124 ATTACHMENT April 21, 1980 Page 3 Analysis of Safety Implications 4

3 Had the honeycombed conditions described previously gone uncorrected, the compartment walls would not have performed structurally under postulated loading conditions and would not have provided the necessary shielding

! inherent in the design of the compartment walls.

Corrective Action The honeycombed conditions described above have been or will be repaired using the following basic repair methods as appropriate to the conditions present at specific locations.

(1) Dry-Pack Mortar (2) Non-Shrink Grout (3) Replacement Concrete The repair work is currently scheduled for completion on or before May 2, 1980, s i

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