ML20029D861
| ML20029D861 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 05/02/1994 |
| From: | Rogers K NRC COMMISSION (OCM) |
| To: | Dingell J HOUSE OF REP., ENERGY & COMMERCE |
| Shared Package | |
| ML19304C139 | List: |
| References | |
| NUDOCS 9405100321 | |
| Download: ML20029D861 (9) | |
Text
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,,8 Iog UNITED STATES 3
NUCLEAR REGULATORY COMMISSION n
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WASHINGTON, D. C. 20555
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May 2, 1994 CHAIRMAN 3
The Honorable John D. Dingell, Chairman Subcommittee on Oversight and Investigations Committee on Energy and Commerce United States House of Representatives Washington, D.C.
20515-6116
Dear Mr. Chairman:
On behalf of the Commission, I am responding to your letter of March 21, 1994, regarding the Fermi 2 turbine failure on December 25, 1993, and the NRC Augmented Inspection Team (AIT) report on the incirant issued on February 7, 1994.
Specific responses to your questions are provided in the enclosure.
At this time, the licensee has not completed its evaluation of the root cause for this event. The NRC staff is continuing to monitor the licensee's activities and will review the evaluation when it is complete. We will provide you the licensee's evaluation when we receive it and will also inform you of any subsequent actions taken by the NRC as a result of the staff's review.
If I can be of any further assistance, please let me know.
E" Sincerely, J
DLA. M1 L-Kenneth C. Rogers
Enclosures:
A.
Response to Questions B.
Enclosures (18) to Question 7 cc:
Rep. Dan Schaefer G
9 [ Ak mu (wa
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ENCLOSURE A RESPONSE TO CONGRESSIONAL QUESTIONS OVESTION 1.
According to a Preliminary Notification of Event or Unusual Occurrence Dated December 30, 1993, from the Region III NRC office on December 28, 1993 (PN0-III-93-69), Detroit Edison was to submit its investigation of the review of the incident to the NRC.
Was this submittal completed?
If so, has the NRC reviewed it and what were the findings?
AN5WER:
The licensee committed to submit its investigation plan to the NRC for review, quarantine equipment, and investigate fully the turbine and generator damage and related equipment failures to determine their causes.
These commitments were documented in the Region III Confirmatory Action Letter (CAL) of December 28, 1993.
Although preliminary discussions have occurred between the NRC and the licensee regarding the root cause for the turbine failure, t'ie licensee has not yet submitted its investigation of the root cause to the NRC for review. The licensee's commitment to complete its investigation and submit its report for NRC evaluation remains in effect as part of the CAL.
The NRC intends to review the licensee's root cause determination whun it is complete.
QUESTION 2.
The AIT report states that an inspector from the turbine manufacturer approved turbine blade #27 under the condition that it be changed at a scheduled refueling in September, 1992.
Instead, Detroit Edison decided to delay blade replacement for another cycle, until March of 1994. Has Detroit Edison offered an explanation for that decision to the NRC? Did the NRC concur with that determination? Was Detroit Edison in violation of NRC rules or an agreement with the turbine manufacturer when it decided to not replace the blades in 1992?
ANSWER:
The licensee stated that the decision not to change blade 27 or other eighth stage blades on low pressure turbine 3 (LP 3) until the fourth refueling outage (RF0 4), originally scheduled to commence in March 1994, was based on technical input from its staff and on information provided in a letter from the turbine manufacturer to Detroit Edison dated February 21, 1992.
The letter stated, in part, that they did not think that the reliability of the turbine would be affected as a consequence of not changing LP 3 stage 8 blades until RF0 4.
The letter contained a further recommendation that the licensee perform an inspection of the blades durina RF0 3 (September 1992). The licensee performed a visual inspection of the turbine blades during RF0 3 and concluded that the wear was of the same magnitude as observed during RF0 2.
The licensee did not record the wear since all blades were scheduled for replacement during RF0 4.
The NRC was not a party to decisions made regarding blade replacement by the licensee.
OVESTION 2.
(Continued) The turbine is not a component subject to NRC regulatory quality assurance requirements because it is not a component that can prevent or mitigate the consequences of an accident having significant implications to public health and safety. Therefore, it is unlikely that the licensee was in violation of NRC rules when it decided not to replace the blades in 1992. The NRC will evaluate the licensee's root cause analysis of the turbine blade failure, including a determination of whether the licensee was in violation of RC regulatory requirements or failed to comply with the turbine manufacturer's specifications.
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OVESTION 3.
The AIT report states that when the turbine manufacturer was informed of Detroit Edison's decision to not replace the blade in question, it requested that an inspection be performed during the September 1992 outage. Was the inspection required for operation? Did Detroit EC' nn perform the inspection?
If so, in your opinion was tL' inspection adequate?
ANSWER:
The licensee did perform an inspection of the turbine blades curing RF0 3.
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This inspection was at the request of the turbine manufacturer, and war.iot a t
requirement for plant operation. The NRC has not yet determined wheth the inspection performed was germane to the failure of the turbine, esper ally since blade 27 did not fail.' Until the NRC evaluation of the lice ae's root cause analysis is completed, the NRC cannot determine whether the inspection was adequate. A preliminary assessment of the licensee's visual inspection shows it to be of lesser scope than the more detailed measurement of turbine blade wear recommended by the turbine manufacturer.
' Based on visual inspection by NRC personnel.
h OVESTION 4.
According to the chronology of events in the AIT report, Detroit Edison first identified problems with the turbine blades during a routina outage in September 1989.
- Further, the AIT report states that at the time of the accident, the plant was operating at 93% power because Detroit Edison had identified problems with the turbine.
Detroit Edison clearly was aware that there was some difficulty with the turbine. Why did the company not address the problems and replace the blade?
In your assessment, could the accident have been avoided if the blade had been replaced?
ANSWER:
The problems associated with the licensee's decision to operate at 93-percent power before the turbine blade failure were not related to the blade problems but to vibration and oscillation problems with the turbine contr'l valves which admit steam to the turbine.
Given the results of the licensee's inspection in RF0 3 and the letter from the turbine manufacturer that the i
reliability of the turbine should not be affected, it is not yet clear that the licensee should have known that there was a problem with the turbine.
Until we have reviewed the licensee's root cause analysis, the NRC cannot evaluate the licensee's decision not to replace eighth stage blades on LP 3 during RF0 3 other than to note the licensee's statement that it believed the turbine could operate until RF0 4 without damage or blade failure during that operating cycle.
We will not know if the accident could have been avoided by replacing the turbine blades until we evaluate the root cause analysis for the turbine failure.
e OVESTION 5.
The AIT report states that "the root chase of this event and the full extent of damage to the turbine-generator system has not been deterri.ned." Since that document was prepared, has the NRC determined the cause of the.irbine-generator damage and the incidert? Has Detroit Edison Company?
ANSWER:
Since the AIT report was prepared, the licensee has been in the process of disassembling the turbine and generator and performing metallurgical and other examinations to identify the root cause.
The licensee made a presentation to several members of the NRC staff on April 7,1994, regarding Detroit Edison's evaluation of root cause based on information assembled as of that date.
However, the report has not yet been submitted to the NRC for review. An NRC determination will not be made until completion of our evaluation of that report.
The licensee currently plans.o complete repairs and restart the plant by October 1994.
The NRC staff plans to review the licensee's root cause analysis prior to restart.
l QUESTION 6.
I further understand that the NRC is awaiting a response from Detroit Edison Company on questions raised by the NRC in the Confirmatory Action Letter (CAL-3-93-018).
I would like to receive a copy of that response when it is prepared and would like to know what action, if any, the NRC decides to take as a result.
Based on the findings of the AIT report or other material is the NRC examining the incident for possible violations?
l-ANSWER:
We will be pleased, when we have received it, to send you a copy of the licensee's. response to questions contained in the CAL, including its completed investigation of the cause of the turbine failure. We will keep you apprised of our' actions taken as a result of our evaluation of these documents including any future enforcement action taken resulting from any violation of NRC regulations.
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QUESTION 7.
Additionally, please send me all relevant material on this accident, including b"t not limited to:
any interim reports prepared by the NRC; any correspondence between the l
manufad.urer of the blades and Detroit Edison; and any correspondence between the NRC and Detroit Edison in which the accident o' the initial discovery of turbine blade damage was discussed.
l ANSWER:
l Documents in response to your question are.provided in Enclosure B.
Portions l
of document numbers 11 and 12 (the turbine manufacturer's letters dated January 10, 1994 and January 14,1994) are marked as proprietary and are being
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withheld from public disclosure; we request that you preserve its confidentiality through restricting its access and use to the Members and staff of the Committee.
We have not included in Enclosure B a copy of the February 7, 1994 AIT report; the December 28, 1993 CAL; the revised AIT charter; appendix D to the AIT report; and NRC Inspection Report 50-341/94003 i
(which evaluated the water discharges to Lake Erie) as well as related Preliminary Notifications of Event or Unusual Occurrence.
It is our understanding that your office has already received these documents.
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