Westinghouse Perspective on New Reactor Sumps

1. Westinghouse Perspective on New Reactor Sumps Presented by: Timothy S. Andreychek Westinghouse Electric Company Phone: 412-374-6246 E-mail: andreyts@westinghouse.com 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 chemicalprecipitates • 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-16530-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 AP1000 Screen Test • 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 Operating Plant Screen Test

7. Downstream Ex-Vessel Concerns • Addressed in Analyses • Potential for wear, abrasion and blockage evaluated • WCAP-16406-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. 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 Downstream In-Vessel Concerns

9. Downstream Issues Resolution • Support the PWROG topical WCAP-16793-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 3.5.6.8 • Plant containment cleanliness program will ensure that latent debris is limited to values consistent with AP1000 testing • Required in AP1000 COL item 6.3.8.1

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