ML053460456

Update on Control Cell Friction

ML053460456
Person / Time
Site:	Susquehanna
Issue date:	12/08/2005
From:	Dyszel A Susquehanna
To:	Office of Nuclear Reactor Regulation
References
Download: ML053460456 (10)

Text

Susguehanna Steam Electric Station Update on Control Cell Friction Andrew Dyszel PPL Susquehanna, LLC Nuclear Fuels & Analysis

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Agenda

• Review October 12 NRC Meeting Discussion

- Unit 1 Operation with Control Cell Friction

- Plan for Mid-Cycle Maintenance Outage

- Preliminary Root Cause

- Exigent Tech Spec Change

• Update and Actions Going Forward

- Channel Measurements

• As-Found

• As-Left

• Impacts on Compensatory Actions and MCPR SL

- Probable Root Cause

- Unit 1 Cycle 15 MCPR SL Tech Spec Change

- Unit 2 Status 12/08/05 Page 2

Susquehanna Steam Electric Station (SSES)

• SSES Characteristics:

- "C" Lattice GE BWR 4

- 3489 MWth

- 764 Assemblies

- 185 Cruciform Blade Control Rods

- Full Core ATRIUM- I OTM (10 x 1O) Fuel 12108/05 Page 3 ppi *-

Overview of Channel Dimensional Measurements

• Purpose of Channel Measurements

- Characterize the amount of channel distortion in the Unit 1 Cycle 14 core.

- Determine the As-Left channel bow distribution in Unit 1 Cycle 14A core.

- Check measurement results against assumptions within MCPR SL.

- Confirm previously determined probable root cause.

Determine any possible trends.

• Material type (Zr-4 vs Zr-2)

• Neutronic parameters (e.g., controlled exposure, burnup) 12/08/05 Page 4 i.i

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UlC14 As-Found Channel Bow Results

• Compensatory Actions Implemented in July 2005

- Specific Analysis: MCPR OL increased by 0.04

- LHGR limit decreased by 3.9%

• Data taken for cells which experienced friction

- Represents upper end of the bow distribution

• Data on UlC14 fuel

- Fresh fuel (SQA-13) mean bow within FANP database

- Once-Burned fuel (SQA-12) mean bow - double FANP database mean value

- Twice-Burned fuel (SQA-l 1) mean bow within FANP database

• As-Found Condition

- UlC14 MCPR SL sensitivity analysis confirms MCPR OL increased < 0.04

- LHGR sensitivity analysis confirms that LHGR compensatory action conservative

-

Conclusion:

Compensatory Actions Conservative 12/08/05 Page 5 PPI

U1C14A As-Left Channel Bow Results

• Exigent Tech Spec Change Submitted

• U1C14A MCPR SL assumed Fresh Fuel (MCPR limiting fuel) and surrounding fuel had double the mean bow of the FANP database

• Measured bow distribution bounded by MCPR SL assumption

- Fresh Fuel (SQA-13) mean bow within the FANP database

- Once-Burned Fuel (SQA- 12) As-Left mean bow < 70% of the value used in MCPR SL (i.e., 2 x bow)

• 54 assemblies re-channeled 0 38 assemblies discharged

- Twice-Burned Fuel (SQA-l 1) & Thrice-Burned Fuel (SQA-IO) mean bow less than the value used in MCPR SL

Conclusion:

MCPR SL is valid for remainder of UIC14A 12108/05 Page 6 P____'

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Probable Root Cause

• Previously documented in our Corrective Action Process

• Probable Root Cause is Channel Deformation

- Shadow Corrosion induced bow

- Change from Zr-4 to Zr-2

• Visual inspections of Inoperable cells without fuel revealed no anomalies in control blade and fuel support piece

• Control Rod Drive testing showed normal drive performance without fuel in the cell

• Bow data substantiates our probable root cause

- Mean of Zr-4 channels was within FANP database

- Mean of Second Cycle Zr-2 channels was substantially higher than FANP database.

12/08/05 Page 7

UlC15 MCPR SL

• 1St application of SPCB CPR correlation at SSES

• Bow assumption is double FANP nominal mean value

• MCPR SL Assumptions

- Fuel that contributes to pins in BT (fresh and once-burned) and the surrounding fuel are assumed to have double the mean bow of the FANP database

- Control cell friction monitoring as a part of channel management program will proactively identify MCPR SL issues during U1C15

• Evaluating U 1C 15 channel management strategy

- Potential re-channeling & channel measurements during Unit 1 14t Reload and Inspection Outage 12/08/05 Page 8

SSES Unit 2 Current Status

• Unit 2 is not currently showing signs of control cell friction

• Bow assumption already includes double FANP nominal mean value

• Similarities to Unit 1

- Core Loading Philosophy

- Channel Design and Material Composition

- Hot Excess Reactivity and Control History

• Anticipated Performance

- Unit 2 may follow a similar friction trend to that observed in Unit 1

- Based on Unit 1 experience, signs of friction would not develop until first quarter of 2006 12/08/05 Page 9

END 12V0805 Page 10 i___