1. Westinghouse Perspective on New Reactor Sumps
Presented by: Timothy S. Andreychek
Westinghouse Electric Company
Phone:
Date: March 12, 2009

2. Long-Term Sump Performance
Three Areas of Concerns
Upstream (in front of and at recirculation screens)
Debris Sources
Insulation
Protective Coatings (Paints)
Chemical Precipitates
Latent Containment Debris
Debris Transport to and Collection on Screens
Head Loss across Debris Bed / Screens
Downstream Ex-Vessel
Wear and abrasion
Blockage of component flow paths
Downstream In-Vessel
Reduction / Blockage of Flow into Core
Precipitation of Debris on Fuel Cladding
Each have been addressed in and for the AP1000 Design

3. Upstream Concerns AP1000 Design provides for:
Limited debris generation
Metal reflective insulation (MRI) used on components subjected to direct jet impingement loads
Other insulation inside containment and outside the zone of influence is jacketed or not submerged
Reduction in debris transport to screens
Natural recirculation flows are low
No containment spray
High flood-up levels - enhanced potential for debris settle-out
Protective overhangs over Containment Recirculation Screens
Reduction in materials contributing to chemical precipitates
Stainless Steel metal reflective insulation (MRI)
Elimination / control of aluminum inside containment
Advanced Recirculation Screen Design

4. AP1000 Debris Sources
Only two potential post-LOCA debris sources for AP1000
Latent containment debris
Dirt, dust, lint and other miscellaneous materials inside containment at initiation of a LOCA
Amount limited/controlled by plant cleanliness program
Post-accident chemical effects
Minimized by design
Used WCAP NP-A, Revision 1, “Evaluation of Post-Accident Chemical Effects in Containment Sump Fluids to Support GSI-191,” to evaluate generation of chemical precipitates
Impact of these debris sources tested
Head loss across the screens
Head loss at core inlet
Sufficiency of AP1000 latent debris amounts under discussion with NRC

5. AP1000 Recirculation Screens
AP1000 advanced screen
Provides for large surface areas
Can collect debris with negligible impact on head loss across screen
Used for both
Containment Recirculation screens
In-containment Refueling Water Tank (IRWST) screens

6. Recirculation Screen Testing
Head loss tests investigated:
Spectrum of debris inventories
Debris staging
Chemical effects and flow rates
Debris loading / flows:
Scaled from AP1000 design
Based on screen frontal area
Testing demonstrated:
Screen design successfully performs its design functions
Insufficient debris in the AP1000 to form a contiguous debris bed on the screens
Essentially no increase in head losses observed
AP1000 Screen Test
Operating Plant Screen Test

7. Downstream Ex-Vessel Concerns
Addressed in Analyses
Potential for wear, abrasion and blockage evaluated
WCAP P-A, Revision 1, “Evaluation of Downstream Sump Debris Effects in Support of GSI‑191,” applied to:
Passive containment cooling liquid recirculation flow paths (safety case)
RHR circulation (non-safety case)
Both flow paths determined to not be adversely impacted by debris in the recirculating liquid

8. Downstream In-Vessel Concerns
Head Loss Testing at Core Inlet:
Test loop same as used for PWR Owners Group
Bounding flow rate scaled to a single AP1000 fuel assembly
Latent debris loading conditions bound those expected following a LOCA for the AP1000
Chemical precipitates exceeded those calculated for AP1000
Tests demonstrated:
Essentially no head loss for debris loads tested
Fibrous latent debris could increase by order of magnitude before significant head loss

9. Downstream Issues Resolution
Support the PWROG topical WCAP NP and its approach
Timely approval of this topical will support addressing concerns
For operating plants
For new-build plants
Analysis of AP1000 shows that
Post-accident chemical precipitate deposit on fuel does not challenge long-term core cooling
ADS Stage 4
Effectively moves water through the core
Limits chemical precipitate deposition on fuel cladding

10. Impediments to Resolution
Need uniform, consistent and justifiable criteria to apply, for each plant to measure against
Need to reach agreement on amount and makeup of latent debris applicable to AP1000
Need to reach agreement on
Level of detail requested for DCD
Appears more detail requested than is provided for other safety analysis and safety features
Amount and scope of requested ITAACs
ITAACs do not apply to operating programs / conditions

11. Overcoming the Impediments
Continue to work with the NRC to define an acceptance criteria
Address NRC RAIs
Use plant walkdown data to resolve latent debris amount / makeup
Improve level of communication / understanding
Conduct a Design Centered focus meeting
Define and agree on an acceptable closure path consistent with the industry (operating plants) direction
Push for rapid turn around of questions / answers on both sides

12. Role of ITACC in Resolution
NRC suggested ITAACs to verify key assumptions associated with design and operational features (insulation, coatings, latent debris) in containment
Westinghouse has proposed several ITAACs to verify key aspects of “as-built” plant, including
Use of Metal Reflective Insulation (MRI) on Class 1 components
Screen type, areas and location
Size, location and use of protective stainless steel plates over recirculation screens
Ex-core detectors are enclosed in stainless steel housing
Westinghouse has not proposed an ITAAC on latent debris
ITAAC not for operating programs or conditions

13. Level of Detail for Inspections
Recirculation screens are required to be inspected regularly by AP1000 Technical Specifications
Specified in AP1000 DCD LCO 3.5.6, SR
Plant containment cleanliness program will ensure that latent debris is limited to values consistent with AP1000 testing
Required in AP1000 COL item

14. Summary AP1000 design features address post-accident sump performance
NRC-approved PWR evaluation methods used to evaluate
Ex-vessel flow paths
Chemical precipitate loading on recirculation screens and core
In-vessel (currently under NRC review)
Debris capture on grids
Chemical precipitate deposition on fuel cladding
Impediments to closure identified
Need uniform, consistent and justifiable criteria to apply, for each plant can measure against
Need agreement on:
Level of detail requested for DCD
Amount and scope of requested ITAACs
Westinghouse is actively working with NRC to address the impediments