PWR Owners Group

Post-Accident Chemical Effects Work

NEI Chemistry Meeting, January 26, 2012

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 NEI Chemistry Meeting, January 26, 2012

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 NEI Chemistry Meeting, January 26, 2012

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 NEI Chemistry Meeting, January 26, 2012

Refinement of Chemical Model Inputs –

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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 Slide 5 NEI Chemistry Meeting, January 26, 2012

Alternate Buffer Evaluation WCAP-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 Slide 6 NEI Chemistry Meeting, January 26, 2012

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 Slide 7 NEI Chemistry Meeting, January 26, 2012

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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 Slide 8 NEI Chemistry Meeting, January 26, 2012

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 Slide 9 NEI Chemistry Meeting, January 26, 2012

Are there questions?