ML033640613

G20030763 - David Lochbaum Ltr. Re Apparent Flaw in Davis-Besse Root Cause Analysis

ML033640613
Person / Time
Site:	Davis Besse
Issue date:	12/18/2003
From:	Lochbaum D Union of Concerned Scientists
To:	Travers W NRC/EDO
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ML042510281	List: ML033640613
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G20030763
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EDO Principal Correspondence Control FROM: DUE: 01/12/04 EDO CONTROL: G20030763 DOC DT: 12/18/03 FINAL REPLY:

David Lochbaum Union of Concerned Scientists Travers, EDO FOR SIGNATURE OF : ** GRN ** CRC NO:

Travers, EDO DESC: ROUTING:

Apparent Flaw in Davis-Besse Root Cause Analysis Travers Norry Paperiello Kane Collins Dean DATE: 12/24/03 Burns/Cyr Caldwell, RIII ASSIGNED TO: CONTACT:

NRR Dyer SPECIAL INSTRUCTIONS OR REMARKS:

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Union of Concerned Scientists CMy end 8dfsM tr Enrorarmf Soludtio December 18, 2003 William D. Travers Executive Director for Operations U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

SUBJECT:

APPARENT FLAW IN DAVIS-BESSE ROOT CAUSE ANALYSIS

Dear Dr. Travers:

It appears to the Union of Concerned Scientists that the root cause analysis submitted by FirstEnergy for the control rod drive mechanism (CRDM) nozzle cracking is deficient. Specifically, the root cause analysis does not adequately examine the potential role played by the reactor vessel head vent through nozzle #14 and may underestimate the operating temperature used in related calculations.

It is our understanding that nozzle #14 is piped to the steam generator #2 upper primary hand hole and provides a continuous vent pathway. Its function is to remove non-condensible gases from the reactor vessel dome -during an accident. Nozzle #14 is in very close proximity to Nozzle'#2 and in close proximityto Nozzles #1 and #3. Nozzle #2 had the greatest number of, cracks (nine axial and one circumferential cracks). Nozzle #1 had nine axial cracks. Nozzle #3 had four axial cracks. Nozzles further away from Nozzle #14 had little or no crack indications.

This information may be relevant to the question of why Davis-Besse was so extensively degraded. It is our understanding that this vent configuration is unique to Davis-Besse - in other words, the other Babcock & Wilcox pressurized water reactors do not have this arrangement.

The cracked CRDM nozzles at other reactors appear almost randomly distributed. The worst nozzle cracking at Davis-Besse appears "clustered" close to nozzle #14. It could very-well be a coincidence. Or, it could be attributed to thermal effects resulting from the 6.9 pounds mass per hour flow rate predicted through nozzle #14 in B&W design calculation 86-1142171 -00.

The root cause analysis casually dismisses the potential impact of this unique configuration. It stated,

'"There is no evidence of thermal fatigue on this penetration [nozzle #14]." This is insufficient basis for dismissing the matter. Nozzle #14 was manufactured by B&W Tubular Products with heat no M4437.

Nozzle Nos. 1, 2, and 3 came from heat No. M3935 and are more vulnerable to cracking. Heat No.

M4437 had a higher annealing temperature (1850 to 19501F) compared to heat No. M3935 (1600 to 17000 F) making it more resistant to stress corrosion cracking. Thus, the fact that no evidence of thermal fatigue was identified on Nozzle #14 -does not, in itself eliminate this vent line configuration as being a contributing factor to damage experienced at nearby, less resistant nozzles.

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December 18, 2003 Page 2 of 2 In addition, the root cause analysis appears to have non-conservatively characterized the temperature used in calculations such as the time-at-temperature estimate. The root cause analysis used 605TF. I have actual operating data for Davis-Besse from June 29, 1999, through August 18, 1999, and am told that this data reflects that from periods before and after this snapshot. According to process computer points T719 and T720 for reactor coolant system loop I and computer points T728 and 1729 for reactor coolant system loop 2, the indicated loop 1 temperatures were consistently about 607.50 F at full power while the indicated loop 2 temperatures were about 604.10 F. I do not have the calibration information for these instruments and their computer points, but if the actual operating temperature was higher than the 6050 F value assumed in the time-at-temperature calculations, it would increase the effective degradation years (EDY) for Davis-Besse and move it towards, if not ahead, of Oconee.

Our concern is that the root cause analysis submitted by FirstEnergy casually dismissed the potential contribution of nozzle #14 to CRDM nozzle cracking and may have underestimated the temperature conditions. This concern has more than historical significance. If the unique vent line arrangement at

-Davis-Besse makes its CRDM- nozzles-nore -vulnerable to cracking than other B&W reactors, then the inspection scope and frequency for the CRDM nozzles on the replacement head may be inadequate to prevent future problems.

We request the NRC to reconsider the root cause analysis with this unique vent line configuration concern in mind. At this stage, we do not feel that our concern fits into allegation space or 2.206 petition space, although we could easily recrafl the concern if necessary to fit into either of these processes. We would hope that the NRC staff will look into this concern absent that effort.

If after doing so the NRC agrees with our contention that FirstEnergy has not adequately addressed this factor, we would expect that the NRC would take appropriate measures to cause the company to fix this deficiency. As a minimum, the company's root case analysis and responses to NRC bulletins on CRDM nozzle cracking supplemented.

Sincerely, DavidLochbaW Nuclear Safety Engineer