PWROG Post-Accident Chemical Effects Work

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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 –
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
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 nonprototypic 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?
NEI Chemistry Meeting, January 26, 2012
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