ML19323G645

Final Deficiency Rept Re Unacceptable Bending of Welded Stud Anchors on Embedded Plates.Testing Program Was Initiated. Bending of Studs Has No Significant Effect on Stud Capacity. Lists Guidelines for Max Bending of Stud Anchors

ML19323G645
Person / Time
Site:	Hartsville, Phipps Bend
Issue date:	06/02/1980
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML19323G628	List: ML19323G627 ML19323G645
References
NCR-HNP-A-064, NCR-HNP-A-64, PBNP-039, NUDOCS 8006060413
Download: ML19323G645 (3)

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, ENCLOSURZ HARTSVILLE AND PHIPPS BEND NUCLEAR PLANTS - ALL UNITS UNACCEPTABLE BENDING OF WELDED STUD ANCHORS l 10CFR50.55(e) REPORT NO. 2 (FINAL) l NCR'S HNP-A-064 AND PBNP-039 On August 30 and 31, 1979, TVA informed NRC-01E Inspector W. B. Swan, of a potentially reportable condition under 10CFR50.55(e) regarding unacceptable bending of welded stud anchors (studs) on embedded plates at the Hartsville Nuclear Plant and the Phipps Bend Nuclear Plant, respectively. .

This ic the final report on this deficiency.

Description of Deficiency l Construction personnel were bending welded stud anchors (Nelson studs, etc.) to varying angles in order"to clear interferences during the placement of embedments for concrete pours. No instructions from the design engineer on bending of these studs existed. Studs bent may have been designed to carry tension loads and the bending could possibly reduce the capability of embedments in tension. to perform as intended by the designer (due to potential of reduced capacity of the studs).

At the time o dentification of this problem (August 1979),

Hartsville CONbT was using a site guideline for STRIDE and BOP that the head of the bent stud had to be behind the rebar mat. On all

) STRIDE embedded plates, C. F. Braun had shown on their drawings oversized (longer and larger diameter than required by the design) i studs. Using the guideline above with the STRIDE stud length and i head size, the rebar mat location (3 inches into the wall), and rebar i

size, the maximum angle of bend would have been 51 (for the head to clear the rebar mat). Use of smaller studs (in BOP) would require a lower angle for the head to clear the rebar mat. Locations in {

STRIDE structures where a number of bends occurred were brought to I i

the attention of the C. F. Braun site representative for his approval, i

Phipps Bend had wry few embedded plates installed in safety-related areas at the time tr.is problem was identified. Those installed were floor places in STRIDE and some floor, ceiling, or wall plates in I

nonsafety areas of the BOP (turbine building). A general guideline was being employed for STRIDE installations of a maximum allowable l bend of approximately 30 degrees with the head of the stud being at 6

1 least 6 inches intu the wall after bending.

! All stud bending at both sites was subject to the visual inspection

} and approval of site civil engiceers and civil QC inspectors.

Cause of the Deficiency The cause of the deficiency is the construction forces not following design drawings due to lack of specific instruction ocing provided  !

by the design organizations to CONST on how to handle embeiner.t i interferences.

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Safety Implications Tests performed by TVA indicate no discernable loss of capacity due to the bending of welded stud anchors through angles as 1srge as 45 degrees (largest angle used in the test). Since practices at Hartsvilla indicate that studs which were bent before identification of the condition were required to extend behind the rebar mat (giving a maximum angle of 51 degrees for the oversized studs used on STRIDE) and since the practice at Phipps Bend was to use lower angle bends than 45 degrees, TVA has determined that no degradation of the design capacity of the welded stud anchors at the Hartsville and Phipps Bend Nuclear Plants has occurred.

Corrective Action Af ter this condition was identified in late August 1979, discussions-were held eithin TVA and with GE/C. F. Braun. C. F. Braun indicated that 30 bends for studs on STRIDE embedded plates were acceptable without case-by-case approval in an August 31, 1979, letter to TVA.

TVA (EN DES) issued a memo for Hartsville and Phipps Bend BOP allowing 15 bends on embedded plates (without requiring EN DES approval) on September 11, 1979, and C. F. Braun revised STRIDE instructions to agree with the TVA position on September 17, 1979. Interim instructions were issued by TVA (EN DES) in December 1979 to all TVA nuclear plant construction sites establishing limits (15 .

from the normal position) on the bending of studs on embedded plates.

A testing program was also initiated to determine what effects bending of the studs had on their capacity. TVA has completed the testing program on the welded stud anchors and concluded that the bending of the studs up to 45 has no significant effect on the capacity of the studs. Based on the conclusion from the testing program, TVA (EN DES) issued new criteria in March 1980 to TVA CONST establishing the following conservative guidelines for maximum bending

. of welded stud anchors:

1. Structural steel plates used for supporting structural members to concrete - The bending of the studs from the normal position on the pir.te shall not exceed 30 .

2. Plates used as framing around doors, penetrations, edge of slabs, curb angles, hatch openings, and any edge protection application -

Fifty percent of the studs may be bent up to 45 . -

3. Heavy-duty inserts - Fifty percent of the welded studs may be bent up to 45 provided:

(a) No more than three adjacent studs are bent. .

(b) The number of straight studs on the plate shall equal or exceed the number of bent studs in succession.

TVA (EN DES) has investigated other TVA nuclear plants with respect to bending of studs during construction and has not uncovered any problems concerning bending of studs.

, v e a Action to Prevent Recurrence Implementation of the criteria discussed above (see Corrective Action) should prevent recurrence of this condition at all TVA nuclear plants.

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