Jet Pump Degradation Management. · • BWR-4 jet pump assembly (Complete) – Full scale-full flow...

Jet Pump Degradation Managementg

Bob Carter

EPRI

EPRI-NRC Technical Exchange Meeting May 25-26, 2010

Contents

• BWR jet pump overview

• Examples of jet jump degradation

• Potential causes for jet pump degradation

• Jet pump degradation mitigation techniques

• BWRVIP jet pump inspection guidance

2© 2010 Electric Power Research Institute, Inc. All rights reserved.

BWR Vessel & Internals Project (BWRVIP)

BWRVIP jet pump inspection guidance

• International BWR riser crack/BWRVIP Response

• BWRVIP jet pump research program

• Summary

BWR Jet Pump Overview



Jet Pumps as Installed



Jet Pump Restrainer Bracket



Examples of Jet Pump Degradation

• Jet pump degradation is characterized by

– Wedge movement and wear

– Rod wear



Example of Wedge Wear



Example of Rod Wear



Potential Causes for Jet Pump Degradation

• Slip joint leakage flow (SJLF) instability

Slip joint

Mixer

Slip joint leakage flow



• Pressure pulsations from recirculation pumps at vane passing frequency

• Flow induced vibration from turbulent flow

Diffuser

Jet Pump Flow Induced Vibration (FIV) Mitigation Techniques

• Slip joint clamp

– Restricts movement of mixer relative to diffuser

• Slip joint labyrinth seal

– Restricts leakage flow through the slip joint reducing potential for flow instability



p y

• Set screw auxiliary wedges

– Restricts movement of mixer where set screw gaps exist

Conclusions from Operational Experience

• Jet pump degradation is persistent

• Degradation is predominately found in BWR/4-5 models and varies considerably by plant and within each loop

• Fuel designs can increase core resistance leading to increased slip joint leakage flow increasing susceptibility



to instability

• Slip joint labyrinth seals and/or clamps may not be universally effective in eliminating wedge wear

• Turbulence in the inlet mixer can contribute to wedge wear if three point contact is not maintained

• Current design does not appear to ensure three point contact at the restrainer bracket

BWRVIP Jet Pump Inspection Guidance

• BWRVIP-41 Rev. 2 “Jet Pump Inspection and Flaw Evaluation Guidelines,” July 2009

– Degradation mechanism assessment and failure consequences

– Inspection of key locations



– Reinspection frequencies

– Scope expansion

– Structural evaluation methodologies

International BWR

• Fatigue crack in riser pipe at riser brace weld identified in Fall 2008

• Crack extended 240 degrees around circumference of riser

• Substantial wedge damage to adjacent jet pump



International BWR – Riser Pipe Crack



International BWR

• Postulated cause (GEH SIL 660 issued May 19, 2009)– Large set screw gap appeared resulting in significant

loss of rigidity of mixer– Loss of rigidity resulted in high vibration due to both

slip joint leakage flow instability and turbulent flowExacerbated by high flexibility of jet pumps which is



– Exacerbated by high flexibility of jet pumps which is unique to this plant

BWRVIP Response to Event

• In light of this event, BWRVIP issued interim guidance for accelerated inspections to all BWRs on June 18, 2009

– Requires inspection of all riser pipe to riser brace welds and all jet pump wedges by completion of the first outage occurring after January 1, 2010



– Credit for inspections completed in the outage immediately preceding this outage is allowed

• No significant cracking identified based on inspections conducted to date

BWRVIP Jet Pump Research Program

• BWRVIP has initiated a jet pump degradation mitigation research program including– Sub-scale testing

• Phenomenological testing at 1/5th and 1/2 scale (Complete)

Full scale low flow jet pump testing to investigate slip



– Full scale-low flow jet pump testing to investigate slip joint leakage flow (SJLF) instability • BWR-4 jet pump assembly (Complete)

– Full scale-full flow jet pump testing of BWR-4 and 5 jet pump assemblies to evaluate the effectiveness of potential FIV mitigation hardware under worst case FIV loading

– Detailed evaluation of industry jet pump operational, repair/maintenance and degradation histories

Full Scale Jet Pump Testing

• Phase 1

– Full scale testing of a BWR-4 jet pump assembly up to 180oF at atmospheric pressure

• Flow through slip joint (SJ) only

– Products:

• Defined effects of:



Defined effects of:

– SJ gap

– SJ insertion depth

– Set screw gaps

– Beam tension

– SJ DP

– Diffuser flexibility

– Testing completed in August 2009

Full Scale Jet Pump Test Facility Overview



Test Vessel Design



Test Tank



Lowering Tank into Concrete Enclosure



Tank Installation Complete



BWRVIP Jet Pump Project Results to Date

• Significant insights/results to date

– Slip joint instability phenomenon reproducible at sub-scale at low temperature

– Slip joint gap and insertion depth influence instability

– Damping changes as critical ΔP for slip joint instability



p g g p j yis approached

– Flexibilities of diffuser and mixer have strong influence on slip joint instability

– Full scale testing at reduced temperature and pressure is feasible

Full Scale-Full Flow Testing

• Phase 2– Full scale-full flow testing of BWR-4 and BWR-5 jet

pump assemblies• Tests to be conducted up to 320F and ~350 psia• Objectives

D fi t t t i l j t



– Define worst case prototypical jet pump response to all three FIV phenomena and show that it can be readily repeated

– Open facility to vendors to test effectiveness of potential FIV mitigation devices in suppressing all three FIV phenomena• Turbulent flow pressure fluctuations• Pump vane passing pressure fluctuations• Slip joint leakage flow instability

Recent BWRVIP Jet Pump Survey

• BWRVIP has requested plants with evidence of degradation to collect and submit operational data, inspection results and repair/maintenance histories since implementation of BWRVIP-41

• Operational parameters include:

– Loop M-ratios by cycle

– Core Plate Delta-P vs flow history and histograms by cycle



– Core flow histograms by cycle

– Rated power/flow

– Recirculation loop flow mismatch by cycle

– Jet pump pair flow mismatch by cycle

– Periods of single loop operation

– Fuel types

BWRVIP Jet Pump Degradation Survey

• Repair and maintenance activities include:

– Jet pump cleaning

– Jet pump beam replacements

– SJ clamp, aux wedge and labyrinth seal installations

• Degradation parameters include:

Wedge movement



– Wedge movement

– Wedge wear

– Set screw gaps

– Other observed degradation

• Intent is to assess relationships between plant operation, repair/maintenance activities and observed jet pump degradation

– Goal is to identify precursors to degradation

Summary

• Jet pump degradation is continuing but varies within the BWR fleet

• BWRVIP-41, R2 provides jet pump inspection guidance to manage jet pump degradation

• BWRVIP-41 has evolved to incorporate industry



operational experience

• BWRVIP has initiated a comprehensive research program to better understand the factors leading to jet pump degradation, develop methods for assessing susceptibility to such degradation and demonstrate mitigation techniques

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