ML20082H375
| ML20082H375 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 03/22/1995 |
| From: | Terry C NIAGARA MOHAWK POWER CORP. |
| To: | Martin T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| Shared Package | |
| ML20082H380 | List: |
| References | |
| NMP1L-0926, NMP1L-926, NUDOCS 9504170111 | |
| Download: ML20082H375 (2) | |
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MV NIAGARA H
H UMOHAWK NIAGARA b00 HAWK POWER CORPORATION /NINE MILE POINT NUCLEAR STATION P.O. BOX 63. LYCOMING. N.Y.13093 /TEL (315) 349 7263 C
_ FAX (315)3494753 5
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March 22,- 1995
' Nuciw Evm*g
' NMP1L 0926 1
Mr. Thomas T. Martin
. Regional Administrator, Region I ~
U. S. Nuclear Regulatory Commission j
475 Allendale Road D
- King of Prussia, PA 19406 RE: Nine Mile Point Unit'l 1
Docket No. 50-220 -
DPR-63 C
Subject:
Response to Requestfor Additional h fonnation Related to Special Team t
inspection 50-220/95-80 and 50-410/95-80 Gentlemen:
This letter provides Niagara Mohawk's response to the three issues identified in your letter of March 17,1995. _ These issues were related to the flow indications observed during the recirculation pump runback event which occurred at Nine Mile Point Unit 1 on February 1:,.
1995. Niagara Mohawk has concluded that the low flow indications were the result of
-instrument flow bias, and not an inappropriate low actual flow condition. We have
~ calculated the impact of the indication bias and made appropriate changes to the flow instrument calibration. The attachment to this letter restates your three issues and provides Niagara Mohawk's response.
Based upon our analysis and the actions taken, Niagara Mohawk is preparing to restart
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Unit 1 following completion of refueling outage activities. Startup of Unit 1 is currently-scheduled for March 29,1995.
Please contact Mr. W. D'Angelo at (315) 349-1948 should you hwe any additional questions-regarding this information.
Very truly yours,
'j.
C. D. Terry Vice President - Nuclear Engmeermg CDT/AFZ/Imc Enclosure xc:
Mr. L. B. Marsh, Director, Project Directorate I-1, NRR Mr. G. E. Edison, Senior Project Manager, NRR Mr. B. S. Norris, Senior Resident Inspector
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Records Management j/ [)
9504170111 950322
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PDR :ADOCK c3Ooo220
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v ATTACHMENT
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Issue 1
'"Detennine whether the indicated corepow observed during the event (below predicted nctaral cimulation pow) is the result ofinstrument inaccuracles,
' actual lowflow condidars or other causes. "
An engineering analysis indicates'that bias within the flow instrumentation resulted in an indication lower than actual recirculation flow during the pump runback event. The.
engineering analysis investigated two areas of potential flow bias in the low flow region.
The first area was the as found instrumentation loop calibration, and the second area was the recirculation flow differential pressure transmitter calibration. The review of the as found instrument loop calibration data determined that, in the low flow range, a negative error of approximately 1-2% existed. The review of the venturi installation and transmitter :
calibration revealed that the vertical installation of the venturi results in approximately a 24 inch height difference between the high and low pressure taps,= and in the low flow region this pressure bias is significant. The engineering calculation of the effect on the transmitter calibration is enclosed with this letter. When these two errors are combined and the tran'sient indicated end point flow of 16% is adjusted, the runback transient core flow (with 4 pumps) was determined to be approximately 22% of rated. This is consistent with the 1970 startup test data (i.e.,24-26% flow for 5 loops) as adjusted to reflect an approximate'4% reduction ~
for 4 loop operation as determined by. calculation. The flow from pumps at 10% ' speed has been determined to be essentially the same as natural circulation.
Issue 2 l
"In the event that the low indicatedpow is accurate, the inconsistencies between the FSAR safety (transient and accident) and stability analysis and the current plant design need to be resolved. "
Niagara Mohawk has concluded, as discussed above, that the low flow indicated during the evem was not accurate, and that actual flow during the event was consistent with the safety l
analysis and current plant design.
Issue 3
" Ensure thatpow instruments are properly calibratedfor lowflow regimes so that regions ofpotential thermal-hydraulic instability can be readily detected and properly acted upon. "
The calibration process has been modified to accommodate the instrument indication bias at low flow conditions so that the existing BWR Owners' Group interim corrective actions for stability are appropriately implemented. In addition, we will strengthen our operating procedures and provide appropriate operator training prior to standing watch during power operation to assure that clear direction is available to the operator for all regions of the power / flow map.
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