ML20101U485

Interim Deficiency Rept 55-84-19 Re Nelson Studs Detaching from Embedment Plates.Initially Reported on 840828.Repair Design Developed Based on Welding Wing Plates to Existing Embedments

ML20101U485
Person / Time
Site:	Clinton
Issue date:	01/21/1985
From:	Hall D ILLINOIS POWER CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
55-84-19, U-10242, NUDOCS 8502070378
Download: ML20101U485 (4)

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lLLIN0/8 POWER COMPANY CLINTON POWER STATION. P.O. 80X 618. CLINTON. ILLINOl$ 61727 January 21, 1985 Docket No. 50-461 Mr. James G. Keppler Regional Administrator Region III U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, IL 60137

Subject:

Reportable 10CFR50.55(e) Deficiency 55-84-19:

Nelson Studs On Embedment Plates

Dear Mr. Keppler:

On August 28, 1984, Illinois Power Company notified Mr. F.

Jablonski, NRC Region III, (Ref: IP Memorandum Y-20790, dated August 28, 1984) of a aotentially reportable deficiency concern-ing Nelson Studs, whica have parted from the back of the '

embedment plates. This initial notification was followed by one

-- (1) interim report (ref: IP letter U-10204, D. P. Hall to J. G.

Keppler, dated October 1, 1984). Illinois Power's investigation into this matter has determined that this issue represents a reportable deficiency under the provisions of 10CFR50.55(e).

This letter represents an interim report in accordance with the requirements of 10CFR50.55(e). Attachment A provides the details of our investigation to date.

We trust that this interim report provides you sufficient background information to perform a general assessment of this reportable deficiency and adequately describes our overall approach to resolve the issue.

Sincerely yours,

%gS,g 8 p D. . Hall Vice President RLC/1r (NRC)

Attachment cc: NRC Resident Office, V-690 Director - Office of I&E, US NRC, Washington, DC 20555 Illinois Department of Nuclear Safety INPO Records Center jgg 281985

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ATTACHMENT A Illinois Power Company Clinton Power Station Docket No. 50-461 Reportable 10CFR50.55(e) Deficiency 55-84-19 Nelson Studs on Embedment Plates Interim Report ,

Statement of Reportable Deficiency / Background Nonconformance Report (NCR) No. 20031 was written to docu-ment a condition where an embedment plate on the outside of the drywell wall had pulled away from the concrete (AZ 128' el. 753',

S&L dwg. S27-1002-03A). To aid in dispositioning of this condi- l tion, the concrete was excavated along the edges of the plate to expose the embedded Nelson studs behind the plate. All seven (7) studs in the outer row were exposed. Six (6) of the seven (7) studs were found detached from the back of the plate. A second plate at AZ 140' was also excavated and found with two (2) of four (4) exposed studs parted from the back of the plate (NCR 21516).

Investigation Results There are four (4) embedment plates in the drywell outer wall (AZ 128*, 140*, 157*, 174*, el. 755') with eccentrically located beam connections. The end connections had been field modified due to a design change and required large fillet and penetration welds to be amplied to the embedment plates. NCR 20031 was written after these modifications to document the fact that the plate at AZ 128' had pulled away from the concrete. The ,

concrete on one side of this plate was excavated to expose the Nelson Studs behind the plate. Six (6) of seven (7) in the outer row were found parted from the embedment plate. Although the embedment plates at AZ 140*, 157*, 174* had not shown any obvious signs of distortion or concrete spalling, they were excavated to determine if any other studs were parted. The fact that beams were also attached to these embedment plates eccentrically (positioned off the centerline of the plate) gave reason to suspect that the modification welding near to the stud row may have caused thermal stresses and/or unobservable plate distortion sufficient to cause the stud failure.

The embedment pinte at AZ 140' was excavated on both sides.

Two (2) studs in the row of seven (7) closest to the welding area were found parted (NCR 21516). The side away from the welding areas had six '6) of the seven (7) studs exposed. All six (6) were still attached to the back of the embedment plate. The embedment plates at AZ 157* and 174* were excavated on the side near the weld areas. No studs on either plate were found parted.

IPQA has written Surveillance Reports to document the results of the excavations.

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ATTACHMENT A (continued)

Since the beams were eccentrically attached to the embedment plate, Sargent & Lundy (S&L) was requested to evaluate the possibility that the modification welding using large (7/8")

. fillets near the outer stud row was a plausible cause of the studs parting. S&L provided calculation 8.35.0-4A which shows that thermal stress and/or thermal. gradient are plausible causes for the studs parting.

The= review of the existing documentation for the embedment plates supplied by Rockwell Engineering has~ revealed no obvious discrepancies. The stud welding procedure used by Rockwell-(RECO 200-1) had been reviewed and accepted by S&L and Baldwin Associates. The inspection of the' stud weld fracture area behind the plate indicated the studs had been welded to the plates properly.' Repair travelers S-1331, 1332, 1334, 1335 required replacement of missing studs on four (4) of the five (5) plates in question. Although it is not precisely known which studs were

. replaced, the travelers S-1334 and 1335 required a visual-check of-the remaining studs.

- Since, 1) the excavations have shown the problem to be limited to the embedment plates at AZ 128' and 140* and only in-the area where.the fillet welds were applied near.the outer row of studs:12) calculations show welding induced stresses to be:

, sufficient to cause the stud failures and: 3) there is no 4 evidence of improper fabrications it is-concluded that the stud

. separations were caused by the stresses induced from the large

welds applied near the plate edge.

Corrective' Action The loading on the two1(2) embedment plates,with parted

- J studs'is such that repairs must'be made to. restore the fullt ~

~-1.e, the. total Design Basis Accident (DBA)

~

.designloadcapacitykeShutdown=

Lloading including Sa Earthquake (SSE)'andPoolSwell loads.. The broken studs:cannot be rewelded to the plates.

. Therefore, a repair. design has been developed based on welding Twing plates to the existing embedments. At:AZ'140*,sthe wing plate wil1~ be welded-to an existing,1 adjacent embedment plate. .

v' At-AZL128' the wing' plates top and bottom will~be' secured to!the.

drwell wall using Drillco' Maxi Bolts.; TheLexcavated concrete-

.will:be replaced with grout.

m Drillco Maxi Bolts have~not been used st CPS-in the past.

S&L issued an Engineering' Change Notice (ECN'4643)-against-1S>ecification K-2944, concrete and GroutLWork, authorizing use of tiis ene ' bolt. IPQA has initiated the evaluations required-to" Jadd Drillco' Devices'Ltd. to;the approved vendors list for CPS.

'<Baldwin Associates:will write construction / installation:

, iprocedures for,the'Drillco Maxi Bolts-

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s.

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3, ATTACHMENT A (continued)

~

Several-other NCRs have been written to describe cases of

.embedment plate: distortion. There is one known case where two (2) deformed wire anchors, welded to an embedment plate, have parted (ref: NCR 18764/25462). These are on the bottom row of an embedmentiplate that has 3 columns of 5 wire anchors each. The welding of-the beam seat to the embedment plate with a single bevel, partial penetration weld, has visibly distorted the plate on the bottom (ref: NCR 18764). Illinois Power and S&L will evaluate these recent developments for significance and whether any repairs'are required. To preclude any future parting of studs and. minimize the distortion of embedment plates, Sargent &

Lundy (S&L) has issued Engineering Change Notice (ECN) 4807 with

' instructions for welding structural steel on embedments. A note will be added to the general structural steel notes on drawing

.S21-1001 which gives criteria for when special caution applies

.for welding to embedments. 'Baldwin Associates Technical Services (BATS): is' preparing instructions, consistent with the

' requirements.of ECN 4807, that will be attached to travelers that

, require welding to embedments. These instructions will minimize

.the buildup of localized thermal stresses by controlling welding sequences and parameters.

Safety Implications / Significance Illinois-Power'has reviewed the findings of the investigation to date, and has determined that the matter of the broken studs represents a significant safety issue. S&L has determined that the loading on the-beams, (numbered 104 and 103),

attached to..the embedment plates at AZ 128' and 140* respectively uis'such that the capacity of:those-plates with brokennstuds is insufficient to' sustain the total Design Basis Accident loads.-

Repairs are. required and the1use'of.the special Drillco devices is r'equired due-to the high' reaction' loads. Beams 103 and 104 ~

are part,of the support forLthe. containment annulus deck at-elevation-755'. Safety.related: equipment is, in turn, supported

.by'the deck area. :Even without a rigorous analysis, postulated failure of these embedments and beams is considered unacceptable and represents'a significant safety issue. This issue is therefore consideredLreportable under the provisions of 10CFR50.55(e). -It:is. anticipated that approximately ninety (90)

. days ' will be required to complete the corrective action and ~ file La' final report.

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