ML19294C260

Final Deficiency Rept Re Discrepant Terminal Block Disconnect Links Discovered During Check of non-Class IE Startup Transformer OXO3A.Caused by Stress Corrosion Cracking.Insp Plan Developed.Search of Records Initiated

ML19294C260
Person / Time
Site:	Midland
Issue date:	03/03/1980
From:	Howell S CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:
References
HOWE-52-80, NUDOCS 8003070387
Download: ML19294C260 (6)

Text

Consumers

/ @4:="

f U Power (Q

) Qg Stephen H. Howell Senior Vice President General offices: 1945 West Pernall Road, Jackson, Michigan 49201 * (517) 788 0453 March 3,1980 Howe-52-80 Mr J G Keppler, Re6 1onal Director Office of Inspection and Enforcement US Nuclear Regulatory Commission Region III 799 Roosevelt Road Glen Ellyn,.IL 60137 MIDLAND NUCLEAR PLANT UNIT NO 1, DOCKET NO 50-329 UNIT NO 2, DOCKET NO 50-330 STATES TERMINAL BLOCKS, CRACKED DISCONNECT LINKS

References:

1) S H Howell letters to J G Keppler; Midland Nuclear Plant; Unit No 1, Docket No 50-329; Unit No 2, Docket No 50-330; States Terminal Blocks , Cracked Disconnect Links; a) Serial Howe-220-79, dated August 10, 1979 b) Serial Howe-2'(6-79, dated October 26, 1979 c) Serial Howe-8-80, dated January 18, 1980

2) H D Thornburg letter to S H Howell dated February 21, 1980 The Reference 1 letters were interim 50.55(e) reports on discrepant terminal block disconnect links. The enclosure provides the status of the investigation and corrective action co.icerning this matter. This letter is a final 50.55(e) report in that the corrective actions to assure the plant is in conformance have been scheduled. If it becomesnecessary to install jumpers across the terminal blocks, you vill be notified of this decision and the. schedule for accomplishment. .

Reference 2 requested that samples of the U-shaped clips be sent to Sandia Laboratories. Terminal blocks removed from equipment groupings, as described by the attachment to the enclosure, and terminal blocks direct from varehouse stock, vill be sent to Sandia by March 5,1980.

0 0//t/ lt W/, a  % 'l' WRB/1r /

// /

Enclosure:

Status Report; States Terminal Blocks, Cracked Disconnect Links; dated February 29, 1980 3 8003070 * ' k

~

2 Hove-52-80 CC: Director of Office of Inspection and Enforcement Att: Mr Victor Stello, USIIRC (15)

Director of Office of Management Information & Program Control, US?IFC (1)

W R Rutherford Office of Inspection & Enforcement, USIIRC (1)

Enclosure to Hove-52-80 STATUS REPORT STATES TERMINAL BLOCKS, CRACKED DISCONNECT LINKS Description of Discrepancy During the electrical checkout by CPCo of non-Class 1E startup transformer OX03A, 38 individual nickel plated brass disconnect links out of 156 were found to be cracked. The initial failure was identified when, in an attempt to reccnnect a circuit after testing, the link failed to tighten and make a good connection. Subsequent investigation by Bechtel on four cubicles in class lE h.16kV switchgear 2A06 revealed seven individual States terminal blocks with cracked disconnect links.

The subject terminal blocks are used extensively in all maj or electrical equipment, both Class 1E and non-Class 1E. The terminal blocks are supplied as appurtenances to the major equipment and, theref ore, a large number of equipment suppliers are involved.

Cause The narrow breaks, or flaws, are believed to be caused by stress corrosien cracking which propagated by both transgranular and intergranular cracking.

The stress corrosion is believed to be the result of excessive cold working of the brass and the subsequent exposure of the brass to a corroding agent during the nickel plating process. Also, refer to paragraphs k and 5 of

" Corrective Action."

Corrective Action

1) The terminal block manuf acturer and the maj or equipment suppliers were informed of the deficiency.

2) The terminal block manufacturer was supplied with a list of all the other equipment suppliers involved and was requested to evaluate and determine the probable cause (refer to paragraph h below) and to stipulate what corrective actions need to be taken to identify and correct the nonecnforming terminal blocks. The terminal block manufac-turer has replied that terminal blocks sold to equipment manufacturers '

are not traceable to any specific batch or period of manufacture and that only isolated instances of failures have been reported in the past. The terminal block manufacturer has, however, agreed to prcvide known good links to replace all cracked links, as required.

3) An inspection plan was developed for determining the extent of cracked links in the major equipment using States terminal blocks. The inspection activity has been completed. The attached swunary lists the results of this inspection.

2 Status Heport States Termin cd Blocks, Cracked Disconnect Links h) The terminal block manufacturer and CPCo independently conducted metallurgical failure analyses to determine the probable cause of the sliding link cracks. These metallurgical analyses have been reviewed and the cause has been deteruined to be as stated in the "Cause" section of this report.

5) A search was initiated of the operations records of CPCo facilities to identify.any other link failures of States terminal blocks. No extensive failure problems with the sliding links were found, only isolated cases.

6) The status of delivery of Class 1E equipment containing States terminal blocks was reviewed to determine which pieces of equipment have not yet been shippe'd to the jobsite. This review was intended to support considerations for potential in-process (ie, prior to shipment) cor-rective action that might reasonably be applied to equipment that has not yet been shipped. Since less than 10% of the equipment renains to be shipped, it is believed to be most cost effective to ship them to the jobsite, install them, and proceed as outlined in items 2 and 3 under " Planned Actions", below. Accordingly, in-process corrective action is not believed to be appropriate in this case.

Safety Implication The identified discrepancy is of a nature that would be suspe . to a f ailure mode; that is, one in which the screw does not hold the links in a tight position and thus dces not provide circuit continuity. The failure mode could cause an electrical circuit disruption and, therefore, depending en the circuit function, could be classified as a failure of the associated equipment to perform its intended function.

Report ability Based on the potential failure mode and possible safety implication, this discrepancy was considered to be reportuble in accordance with the Code of Federal Regulations, Part Su.55(c).

Planned Actions Construction and preoperational testing vili continue with the existing links based on the following conditions:

1. A review of operating history at other CPCo plants has indicated that no' generic problems are known to exist with the States sliding disconnect link terminal block.

2. All of the links in Class 1E circuits vill be exercised during pre-operational testing. Links that fail to provide an electrical

3 Status Report States Terminal Blocks, Cracked Disconnect Links connection or which are found to be broken vill be replaced with links which are known to be good.

3. CPCo will continue investigative efforts, including taking advantage of any industry information which may beccme available to determine long-term mortality statistics. If the links are determined to be un-acceptable for lcng-term operation, then suitable shunt / jumpers vill be installed on all Class lE circuits prior to fuel load.

WREird February 29, 1980 WRB/lr Attachment : Summary of Inspection Plan Results J

t Howc-52-80 Attachment to Status Report

SUMMARY

OF INSPECTION PLAN RESULTS -

Cracked Screw Did Not Group ' Description links Tested Links

• Tighten 30 16 0 I Q-Listed 480V Load Centers 178 11 3 II Q-Listed 460V Motor Control Centers III Q-Listed 4.16kV Switchgear 45 13 0 IV 120 11 4

. Q-Listed Main Control Panels V Q-Listed Auxiliary Control 44 11 1 Panels VI Q-Listed Miscellaneous Equipment 82 11 0 VII Non-Q-Listed Miscellaneous Equipment Totals 501 73 8

% of Total 15% 1.6%

• Cracks found by visual inspection under 10 power magnification with

~

high intensity lighting. Includes links where screws did not tighten.

• • Inspection not performed. Either equipment not delivered to jobsite as of date or equipment was found not to contain States terminal .

blocks.

.