ML20207R678
| ML20207R678 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 03/11/1987 |
| From: | Andrews R OMAHA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20207R679 | List: |
| References | |
| LIC-87-065, LIC-87-65, NUDOCS 8703180016 | |
| Download: ML20207R678 (2) | |
Text
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Omaha Public Power District 1623 Harney Omaha. Nebraska 68102 2247 402/536 4000 March 11, 1987 LIC-87-065 Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C.
20555 I
References:
1.
Docket No. 50-285 2.
Letter from 0 PPD (W. C. Jones) to NRC (J. T. Collins) dated June 19, 1984 (LIC-84-196) 3.
Letter from NRC (J. T. Collins) to OPPD (W. C. Jones) dated June 22, 1984 4.
Letter from 0 PPD (R. L. Andrews) to NRC (J. T. Collins) dated July 17, 1984 (LIC-84-228) 5.
Letter from 0 PPD (R. L. Andrews) to NRC (R. D. Martin) dated February 2, 1985 (LIC-85-040) 6.
Letter from NRC (R. P. Denise) to OPPD (R. L. Andrews) dated March 27, 1985 7.
CE Report 0-MCC-86-007, Fort Calhoun Secondary Chemistry Review, dated December, 1986.
Gentlemen:
SUBJECT:
Notification of Raising the Currently Reduced Cold Leg Temperature (T ) f r Fort Calhoun Station c
The Omaha Public Power District, holder of Operating License DPR-40, plans to return T to normal operating temperatures presented in the USAR.
Subsequent to the sEeam generator tube rupture at Fort Calhoun Station, OPPD made a vol-untary commitment to operate at a reduced T of 537'F to avoid potential c
Coriou cracking while the relationship between T and tube cracking was investigated.
As presented in our Cycle 11 Reload Submittal, OPPD intends to resume the normal operating T value of 545*F when the plant is returned to c
power operation.
Combustion Engineering Report 0-MCC-86-007 (Reference 7) endorses this action.
The Omaha Public Power District notified the NRC by letter dated May 22, 1984 that a steam generator tube failure had occurred at the Fort Calhoun Station on May 16, 1984.
Subsequently, OPPD performed eddy current examinations of the accessible tubes in both steam generators and removed the failed section of tubing for metallurgical analysis.
The results of the examination and metal-lurgical analysis were provided to the NRC in References (2) and (4).
OPPD received Reference (3) which provided the Commission's safety evaluation of the incident and permission to restart Fort Calhoun Station.
Within Reference (3) was a requirement to conduct eddy current and profilometry examinations of the Fort Calhoun Station steam generators nine (9) months 8703180016 870311
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U. S. Nuclear Regulatory Commission LIC-87-065 Page 2 following resumption of power operation unless justification was provided that such inspections were not warranted.
Reference (5) provided the results of the ongoing investigations as required by Reference (3) and provided information on the programs implemented and planned which significantly reduced the probabil-ity of recurrence of intergranular stress corrosion cracking (IGSCC) and IGSCC induced steam generator tube failure.
Reference (6) provided the Commission's waiver of the mid-cycle steam generator tube inspection requirement.
Reference (5) outlined actions taken by 0 PPD in an effort to reduce the prob-ability of additional tube failures resulting from IGSCC. Along with commitments to remove contaminants from the steam generators, maintain conservative secondary chemistry limits and take prompt action if primary-to-secondary leakage was detected, there was also a commitment to operate at a reduced T. The commitment found on page 9 of Reference (5) reads as c
follows:
"One additional operational action which has been taken is a slight (8'F) reduction in T. There is limited laboratory data which indicates that c
the propagation rate of caustic-induced IGSCC can be reduced by reducing temperature.
This reduction in T results in a slight performance pen-c alty for the unit, which the District has decided to accept until such time as further contaminants are soaked from steam generator crevices."
OPPD has evaluated the merits of continuing operation at a reduced T -
c Coriou cracking results from a combination of temperature and stresses that exist during normal operation in a pure water environment.
Coriou cracking is a contributing factor to IGSCC. At the time Reference (5) was written, data on this subject for temperatures in the operating range of the Fort Calhoun Sta-tion could not be located.
The District chose the conservative alternative of operating at a reduced T, although there was insufficient evidence available c
to determine the benefit to be gained from this measure.
Further investigation has failed to produce additional evidence to indicate any benefits car: be achi-eved by continued operation at the reduced T -
c OPPD believes that operating at the lower temperature does not contribute to reducing the susceptibility of the steam generator tubes to cracking. There-fore, the normal operating T value of 545'F will be used for the ensuing c
fuel cycle.
Sincerely, AfhW R. L. Andrews Division Manager Nuclear Production RLA/rh Attachment c:
LeBoeuf, Lamb, Leiby & MacRae Mr. R. D. Martin, Regional Administrator - Region IV Mr. W. A. Paulson, NRC Project Manager Mr. P. H. Harrell, NRC Senior Resident Inspector s