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Westinghouse Perspective on New Reactor Sumps

Presented by: Timothy S. AndreychekWestinghouse Electric Company

Phone: 412-374-6246E-mail: andreyts@westinghouse.com

Date: March 12, 2009

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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

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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

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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

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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

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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

Figure 5 AP1000 Screen Tests Show That There Is Insufficient Debris to Form a Continuous Debris Bed

Figure 6 Operating Plant Screen Test With High Debris

Load Results In Much Higher Head Losses

AP1000 Screen Test

Operating Plant Screen Test

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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

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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

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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

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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

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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

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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

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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

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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