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

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

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

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

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

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

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

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

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

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

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

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

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

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