PWR Owners Group Post-Accident Chemical Effects Work

1. PWR Owners GroupPost-Accident Chemical Effects Work NEI Chemistry Meeting, January 26, 2012

2. Chemical Effects • Issue: • Chemical interactions between materials in the containment sump and cooling water additives may affect performance of the sump strainers. • The key effect is generation of precipitates that may increase head-loss across the fiber beds. • PWR Owners Group Approach to Resolution: • Testing has been conducted to; • Identify key interactions, and, • Elucidate the factors that control these interactions, and, • Develop generically applicable tools to evaluate post-accident chemical effects at plants. • PWR Owners Group work does not preclude plants from performing their own plant-specific post-accident chemistry effects work

3. ICET Program ICET Program: Integrated Chemical Effects Test • Program conducted by NRC, EPRI and PWR Owners Group • Purpose: Assess if chemical products would form • Approach: Integrated testing using typical plant materials at bounding material loadings and sump chemistries (3 buffers used at bounding pH values) • Five distinct sets of conditions tested • Buffer agents; sodium hydroxide, trisodium phosphate, sodium tetraborate (for ice condenser containments) • Material included; aluminum, copper, concrete, calcium silicate, fiberglass, zinc (galvanized material) • ICET Program demonstrated • Chemical products would form over time • Dominant chemical products included • Aluminum • Sodium, and, • Calcium • Also demonstrated potential for passivation over time

4. PWROG Program – WCAP-16530-NP-A • Performed to augment ICET Program Results • Included materials not included in ICET program; mineral wool, min-k • Objective was to support replacement sump screen testing by developing: • Testing and developmentment of a generic Chemical Model • Predict bounding quantity and types of precipitates • Use plant conditions as a function of time (i.e. pH, coolant volume, mass of debris sources) • Recipes and a Particulate Generator to produce three “worst case” (maximize head loss) particulates: • Aluminum Oxyhydroxide • Sodium Aluminum Silicate • Calcium Phosphate • Reviewed and approved by NRC with limits and conditions • Used by: • Licensees to perform screen testing • PWR Owners Group to perform fuel debris head loss testing

5. Refinement of Chemical Model Inputs – WCAP-16785-NP • Program evaluated plant-specific inputs for incorporation in the WCAP-16530-NP chemical model spreadsheet • Program results: • Confirmed that; • Silicate inhibits corrosion of aluminum • Phosphate inhibits corrosion of aluminum • Sodium aluminum silicate should continue to be treated as insoluble in current buffer agents • Calcium phosphate should continue to be treated as insoluble in trisodium phosphate buffered solutions • Demonstrated; • For plants using trisodium phosphate buffer, a reduced aluminum release rate was supported by data • Solubility limits of aluminum oxyhydroxide as a function of temperature • Not submitted for NRC Safety Evaluation • Available for participating licensees to use

6. Alternate Buffer EvaluationWCAP-16596-NP • Objective: • Evaluate candidate buffering agents as potential alternatives to trisodium phosphate (TSP) or sodium hydroxide (NaOH) • For high-calcium plants • Changing from TSP to sodium tetraborate (NaTB) buffer would reduce the total precipitate formation by more than 40 percent • No new types of precipitates would form at a target pH of 8.0 or less, irrespective of the calcium loading • Note submitted for NRC Safety Evaluation • Available for participating licensees to use • Approach used by at least one PWR

7. Proposed Work – Increase Fiber Limit for Fuel • Proposed Objective: • Provide data to support the use of lower flow rates in fuel assembly post-LOCA debris testing when chemical surrogates are added • Show that chemical product production does not occur until after hot leg switch-over • If chemical surrogate addition cannot be delayed until the time of hot leg switch-over in for some plants justify the use of; • Less chemical surrogate, and, • A surrogate that causes less pressure drop • To be reviewed for approval by PWR Owners Group first week of February, 2012 • Will be available for participating licensees to use

8. Proposed Work - Effect of Water Chemistry on Head Loss • Proposed Objective: • Evaluate impact of water chemistry on the maximum head loss values in fuel assembly (FA) testing • Basis: • New data that indicates differences in water type could cause non-prototypic test results resulting in overly conservative fiber limits. • Goal is to increase fiber limits to at least; • 20 g fiber/FA for plants with an available driving head of 14 psid • 50 g/FA for plants with an available driving head of 18 psid • 35 g fiber/FA for plants that can maintain sump temperatures greater than or equal to 130°F and have an available driving head of 12 psid. • To be reviewed for approval by PWR Owners Group first week of February, 2012 • Will be available for participating licensees to use

9. Summary • PWR Owners Group has undertaken post-accident chemical effects work to address GSI-191 • The work is applicable to and may be used by all PWRs • The PWR Owners Group work does not preclude individual plants from pursuing a different post-accident chemical effects strategy

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