ML19294A777

Interim Rept Re Embedded Plate Assemblies Not Installed in Compliance W/Design Drawings

ML19294A777
Person / Time
Site:	Vogtle
Issue date:	02/22/1979
From:	GEORGIA POWER CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19294A776	List: ML19294A775 ML19294A777
References
REF-PT21-79-175-001 NUDOCS 7903220120
Download: ML19294A777 (2)

Text

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9 ALVIN W. V0GTLE NUCLEAR PLANT GEORGIA POWER COMPANY INTERIM REPORT

SUBJECT:

Embedded Plate Assemblies Description of Embedded Plate Assembly:

An embedded plate assembly consists of a plate of specified dimensions.

Heavy hexagonal nuts are welded on the plate. These nuts will be called

" plate" nuts. A 5" observation hole is drilled through the plate in alignment with the center line of the plate nut. A bolt is threaded through the plate nut until it is fully engaged. Engagement is defined by subtracting the plate thickness from the measured distance from the front of the plate to the end of the engaged bolt. To be fully engaged, this value is zero. Additionally, a washer and another nut (called "end" nut) are tack welded to the opposite end of the bolt. Bending of the bolts is permitted to accommodate rebar interference. The embedded assemblies are designed to support HVAC ducts, piping system, and structural steel.

Origin of the Issue:

In November 1978, Georgia Power Company personnel identified some embed assemblies not fabricated or installed in accordance with the design drawings. The discussion of findings are presented in the following section.

Description and Proposed Evaluation and Resolution of the Issue:

(A) The design drawings required the plate nuts to be heavy hexagonal nuts. All of the plate nuts were standard hexagonal nuts instead of heavy hexagonal nuts. It has been analyzed and determined that the use of the standard hexagonal nuts meets the design requirements.

(B) The design drawings require that the bolts be fully engaged with the plate nut. Some of the bolts for a given embedded plate assembly were not fully engaged with the plate nut. The lack of full engage-ment for each bolt has been measured by Georgia Power Company. It has been analyzed and determined that bolts with 80% or more of full engagement meet the design requirements. Bolts having less than 801 full engagement and more than approximately 40% full engagement will be plug welded. The purpose of plug welding is to restore the bolt to an equivalent full thread engagement. Bolts that are engaged less than approximately 401 (exact value will be determined later) will be abandoned and the embed capacity will be derated accordingly.

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Alvin W. Vogtle Nuclear Plant Georgia Power Company Interim Report Page 2 (C) The design drawings required the bolts to be tack welded to the plate nut to assure full engagement during construction. Some of the bolts were not tack welded as required. This is not a concern since the degree of engagement of the bolt has been determined by measurements performed through the inspection hole.

(D) The design drawings required that the bolt have washers tack welded either to the bolt or the end nut. Some of the bolts in a given embed plate assembly did not have washers. It has been analyzed and determined that the washers are not needed to meet embed design capacity requirements.

(E) The design drawings required that the washers be tack welded either to the bolt or end nut. The impact of not meeting this requirement was not evaluated due to the findings stated in (D) above.

(F) The design drawings required that the end nut be tack welded to the bolt. Some end nuts were not tack welded to the corresponding bolt.

A pull test will be conducted to verify the integrity of the bolt assemblies.

(G) The design drawings restricted bending of the bolts to 6 300 Some bolts were bent in excess of this specification. By ultrasonic testing, the bend angle of the bolt can be determined up to 250 As a conservative measure, any bolt bent greater than 200 was assumed cracked and not considered to contribute to the capacity of the embed assemblies.

(H) Previously Unreported Iten - The design drawings require a full fillet weld around the plate nut. This fillet weld around the plate nut was only partially made in several cases. An evaluation will be made to determine the strength of the fillet weld using the information obtained by ultrasonic testing.

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