ML20127M331
| ML20127M331 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 11/23/1992 |
| From: | Gates W OMAHA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LIC-92-332, NUDOCS 9211300135 | |
| Download: ML20127M331 (3) | |
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I, Omaha Public Power District 444 South 16th Street Mall Omaha, Nebraska 68102-2247 November 23, 1992 LIC-92-332 U. S. Nuclear Regulatory Commission ATlN: Document Control Desk Mail Station Pl-137 Washington, DC 20555
References:
1.
Docket No. 50-285 2.
Letter from NRC (A. B.
Beach) to OPPD (W. G. Gates) dated October 22, 1992 Gentlemen:
SUBJECT:
NRC.'nspection Report No. 50-285/92-22 Reply to a Notice of Violation (NOV)
The subject report transmitted a NOV resulting from an NRC inspection conducted August 30 through October 10, 1992 at the Fort Calhoun Station. Attached is the Omaha Public Power District response to this NOV.
If you should have any questions, piease contact me.
Sincerely, W. G. Gates Vice President - Nuclear l
Attachment l
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LeBoeuf, Lamb, leiby & MacRae J. L. Milhoan, NRC Regional Administrator, Region IV R. P. Mullikin, NRC Senior Resident Inspector S. D. Bloom, NRC Project Manager l
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Attachment i
LIC-92-332 Page 1 REPLY TO A N0flCE OF VIOLATION ELO1A110N During an NRC inspection conducted on August 30 through October 10, 1992, a violation of NRC requirements was identified.
In accordance with the " General Statement of Policy and Procedure for NRC Enforcement Actions," 10 CFR Part 2 Appendix C, the violation is listed below:
1 1
10 CFR Part 50, Appendix 8, Criterion XVI, and the Fort Calhoun Quality Assurance Plan, Revision 3 Section 10.4, Paragraph 4.2.5, require, in part, that corrective actions associated with significant conditions adverse to quality shall preclude repetition.
Contrary to the above, the licensee's corrective action to preclude the loss of 480-Vac busses during an abnorir.a1 electrical alignment failed to 1
prevent recurrence.
On September 1, 1992, three 480 Vac busses were i
electrically tied together and supplied through one breaker, resulting in the breaker tripping open on an overload condition. One of the corrective actions from a similar event, on A)ril 12,1992 (monit:: ring the current on the busses), was inadequate in t1at the proceduralized maximum current monitored was the incorrect value to prevent a bus overload.
j This is a Severity Level I'l vi lation.
o
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OPPD Response 1.
Reason for Violation
)
A Root Cause Analysis (RCA)he root cause was determined to be that the was completed by Omaha Public Power District (0 PPD for this event.
admin)istrativecurrentlimitforthe was based on the Long Time Delay (LTC) primary side of transformer TIB-4C design trip setpoint (2240 amps on the secondary side of transformer TIB-4C) for breaker IB4C, while the LTD actual trip setpoint was calibrated using a nominal 1600 amps due to test equipment limitations.
As a result of this inconsistency, the administrative current limit of 200 amps primary side of transformer TlB-
- 40) was not low enough to preclude the br(eaker from tripping.
1 4
Either the administrative current limit needed to be lower or the breaker calibration needed to be performed using a higher test input current to ensure the LTD actual trip setpoint would be closer to the LTD design trip setpoint.
A similar event occurred on April 12, 1992 when power throu breaker IB3A was lost while in an abnormal electrical lineup. gh 480 VAC y
This event i
was described by NRC Inspection Report 50-285/92-09 and Licensee Event l
Report 92-15.
OPPD persoanel reviewed this event in April 1992 and 1
concluded that the breaker functioned properly and appeared to trip within i
the expected range. Therefore, deficiencies in the method of calibration were not suspected at that time.
1 i
Attachment LIC-92-332 Page 2 2.
Corrective Actions That Have Deen Taken The administrative current limit in procedure 01-EE-28 has been revised to 150 amps for the primary side of all six 4160/480 VAC transformers.
The basis for this change is the calioration input test current of a nominal 1600 amps corresponding to 173 amps at 4160 volts, providing a 23 amp margin prio(r trip) bus tripping during abnormal bus alignm for the 480 VAC supply breakers.
This change should preclude overload Operator training has been provided or. the circumstances of this event and the new limitations in 01-EE-28.
Design Engineering evaluated the worst case Design Basis Analysis (DBA) loading on the 480 VAC busses. For all breakers except IB3C and 1848, the load was calculated to be below 1500 amps and therefore was satisfactorily enveloped by the existing calibration method. Breakers 1830 and 1848 were determined to have a worst case Design Basis Analysis (DBA) loading of approximately 1600 amps. Following the September 1, 1992 event, breakers 183C and 184B were subsequently tested using the correct criteria.
The as-found condition verified that the trip points were above the projected DBA loads for buses IB3C and 184B.
The calibration procedures for 187.0 and 1848 were revised to specify a 1900-2000 amp test input to ensure tne LTD actual trip setpoint will be above the worst case DBA loading.
A generic implications analysis was performed aad concluded that the 480 VAC breaker calibration problems revealed by this event do not extend to the 4160 VAC breakers.
l 3.
Corrective Actions That Will Be Taken 1
Abnormal Operating Procedure A0P-32 has been revised to reflect the 01-EE-2B chances and will be implemented following completion of training. This i
will be completed by December 31, 1992.
l A memorandum will be sent to design engineers and system engineers I
describing this event and the associated RCA. The memorandum will discuss the need for using empirical or verified data versus unverified assumptions when performing analyses. This will be completed by December 15, 1992.
4.
Date of Full Comoliance OPPD is presently in full compliance.
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