ML20247H593

Advises That Util 890405 & 0501 Responses to CAL-RIII-89-07,Item 6 Re Reactor Trip & Sustained Loss of Sys Auxiliary Transformer Acceptable

ML20247H593
Person / Time
Site:	LaSalle
Issue date:	05/22/1989
From:	Davis A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:	Reed C COMMONWEALTH EDISON CO.
References
CAL-RIII-89-07, CAL-RIII-89-7, NUDOCS 8905310269
Download: ML20247H593 (2)

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e. Od MAY 22 2 Docket No. 50-373 Docket No. 50-374 Commonwealth Edison Company ATTN: Mr. Cordell Reed Senior Vice President Post Office Box 767 Chicago, IL 60690 Gentlemen:

On March 2, 1989, LaSalle Unit I sustained a reactor trip and Unit 2 sustained the loss of the System Auxiliary Transformer (SAT). On March 3 NRC established an Augmented Inspection Team (AIT) to independently assess the cause and significance of these events and any associated problems.

In addition, Confirmatory Action Letter (CAL) CAL-RIII-89-007 was. verbally issued on March 3, 1989, and formally issued on March 6, 1989, to document our understanding of the actions you would take in response to these events and that the startup of Unit I would only occur with the concurrence of the Regional Administrator or his designee.

On March 4, 1989, The AIT completed its assessment and conducted its exit meeting with the LaSalle station staff. The AIT determined that CECO had adequately evaluated the event and had satisfied the actions required by the CAL, with the exception of item 6, which required a formal report of your findings and conclusions within 30 days of receipt of the CAL. Therefore, I concurred with your decision to restart Unit 1 on March 5 and items 1 through 5 of the CAL were considered closed. This was documented in my letter to you dated March 8, 1989.

On April 5,1989, CECO provided the report requested by item 6 of the CAL.

That report indicated that the root cause of the March 2 events was attributed to the Unit 2 SAT C phase lightning arrester that developed an internal failure resulting in a Phase-to-Ground fault. You further indicated that the failed lightning arrester was being analyzed to determine what caused its failure. The results of this analysis were subsequently provided in a letter from W. E. Morgan to A. B. Davis dated May 1, 1989. The factory inspection determined that the C phase lightning arrester did not fault internally as had been initially thought. Further investigation indicated that an external C Phase-to-Ground flashover had occurred.

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' Commonwealth Edise L apany 2 22 3 We have completed our review of your responses (April 5 and May 1,1989) to item 6 of CAL-RIII-89-007 and have determined that you have provided an adequate evaluation of the event and have satisfied the action required by item 6. We therefore consider CAL-RIII-89-007 to be closed. Your May 1, i 1989, response to the unresolved items from the March 21, 1989, AIT inspection j report will be reviewed in a future inspection.

Should you have any questions, I would gladly discuss them with you.

Sincerely, Orginial Signed by C. E. Norelius A. Bert Davis Regional Administrator cc: T. Kovach, Nuclear Licensing Manager G. J. Diederich, Station Mansger DCD/C".B (RIDS)

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