ML20214L478
| ML20214L478 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 08/15/1986 |
| From: | Andrews R OMAHA PUBLIC POWER DISTRICT |
| To: | Thadani A Office of Nuclear Reactor Regulation |
| References | |
| LIC-86-411, NUDOCS 8609100182 | |
| Download: ML20214L478 (2) | |
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Omaha Public Power District 1623 Harney Omaha. Nebraska 68102-2247 402/536 4000 August 15, 1986 LIC-86-411 Mr. Ashok C. Thadani, Project Director l
PWR Project Directorate #8 Division of PWR Licensing - B Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, DC 20555
Reference:
Docket No. 50-285 l
Dear Mr. Thadani:
Appendix R Requirements for Inverters During the 1985 refueling outage, Omaha Public Power District replaced the safe-ty related inverters at the Fort Calhoun Station.
During a subsequent walkdown of Abnormal Operating Procedure (A0P) 6, it was discovered that the new confi-l guration of inverters C and D (EE-8K and L) with their associated instrument buses did not meet all of the requirements of Appendix R of 10 CFR 50.
This was discussed between OPPD personnel and NRC - Region IV personnel.
Appendix R requires that one train of equipment necessary to achieve hot shutdown from either the Control Room or Emergency Control Station must be main-tained free of fire damage by a single fire, including an exposure fire. The alternate shutdown panel (AI-185) is powered from inverter D via the emergency feedwater local control panel (AI-179). AI-179 is supplied with power from both inverters C and D.
Both panels (Al-179 and AI-185) are necessary to achieve a safe shutdown in the event that the Control Roon, is inaccessible.
In a postulated accident scenario in which a fire occurs in either the Control 4
Room or Cable Spreading Room, it is possible that the output cables for inver-ters C and D could short out or come in contact with other cables which are energized.
If this were to happen, the inverters would shut themselves off to prevent damage.
The old inverters had output breakers which the operators were instructed to open in the event of a fire in either the control Room or the Cable Spreading Room. When the output breakers were opened the inverters were isolated from the output cables.
The old inverters met the Appendix R re-quirements because the cables which supply power to AI-179 and AI-185 were terminated on the inverter side of the output breaker.
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Mr A. C. Thadani LIC-86-411 Page 2 The new inverters have no such output breaker and thus cannot be completely isolated from the Cable Spread Room and Control Room. When the discrepancy was discovered, a revision to A0P-6 was made and an hourly firewatch for the Cable Spreading Room was posted.
The revision to A0P-6 instructs the operator to sever the output cables for inverters C and D with tools provided in the switch-gear rooms and to restart the inverters in order to supply power to AI-179 and AI-185.
Elgar, the vendor for the inverters, has been consulted for suggestions of pos-sible means for meeting the Appendix R requirements.
The solution of choice is that OPPD will place a breaker on the output of the inverters. This solution would require a plant outage for installation. OPPD has determined that this solution is the most acceptable method of meeting the Appendix R requirements.
The required modifications will be made during the 1987 refueling outage under MR-FC-86-16.
This item was also noted by the NRC Resident Inspector during a routine walkdown on April 18, 1986.
OPPD believes that the interim measures established in A0P-6 and the hourly Cable Spread Room fire watch are adequate to assure continued safe operation of Fort Calhoun Station. Most circuit failures (grounds, shorts, etc.) on the 120 VAC instrument bus due to a fire will be cleared by the circuit protective 4
fuses and breakers. Only in the extremely remote case of a " smart fire" would the inverter operation be affected.
In this case, the operator would sever the inverter output cable as provided in A0P-6, thus assuring continued availabil-ity of panels AI-179 and AI-185.
If you have any further questions on this matter, please do not hesitate to contact us.
Sincerely, R. L. Andrews Division Manager Nuclear Production RLA/me cc: LeBoeuf, Lamb, Leiby & MacRae 1333 New Hampshire Ave., N.W.
Washington,'DC 20036 C
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