ML113350563

Licensee Presentation from 12/1/11 Meeting Via Conference Call to Discuss Risk-Informed GSI-191,Assessment of Debris Accumulation on Pressurized Water Reactor Sump Performance

ML113350563
Person / Time
Site:	South Texas
Issue date:	12/01/2011
From:	South Texas, ALION Science & Technology Corp, Univ of New Mexico
To:	Balwant Singal Plant Licensing Branch IV
Singal, B K, NRR/DORL, 301-415-301
References
TAC ME5358, TAC ME5359
Download: ML113350563 (25)

Text

CHEMICAL EFFECTS IMPLICATIONS OF WCAP-16530-NP FOR SOUTH TEXAS PROJECT December 1, 2011

Discussion Overview Conservatism in chemical effects - WCAP-16530-NP Corrosion/release Precipitation Reduction of conservatism Casa Grande Hypotheses of chemical effects occurrences without conservatisms Objectives of new chemical effects testing Preliminary testing ideas Conclusion Areas for requested input 2

Corrosion/precipitation scenario Step 1 Metal Corrosion/Release Step 2 Saturation/Precipitation Step 3 Transport Spray Immersion Aluminum Free metal ions released from solids and dissolved in water OH-Al+3 Saturation limit exceeded suspended solids form Transport to sump or past strainer to core Sump Screen Step 4 Head Loss Collection on fiber Al(OH)3 (amorphous) 3

Conservatism: Corrosion/release Corrosion rates were determined in studies of relatively short duration Over longer time, base metal corrodes but oxide layer forms at surface, limiting release of corrosion products into solution Passivation of surface by silicon and phosphate Contribution of soluble aluminum from un-submerged (sprayed) sources vs submerged sources Results in conservative estimate of soluble metal concentration 4

Corrosion/precipitation scenario Spray Immersion Aluminum OH-Al+3 Formation of oxide layer on surface Localized higher concentration of aluminum in boundary layer causes surface precipitation, preventing supersaturation of aluminum in solution Release of free ions into solution is reduced 5

Aluminum release into solution in ICET 0

50 100 150 200 250 300 350 400 450 0

5 10 15 20 25 30 Time (Day)

Concentration (mg/L)

Unfiltered Aluminum Filtered Aluminum ICET Test 1 6

Al(OH)3 solubility vs. Al concentration 7

0 10 20 30 40 50 60 70 80 0

5 10 15 20 25 30 Aluminum concentration (mg/L)

Time (days)

Test 5 unfiltered Test 5 filtered Aluminum release:

Experimental vs. Estimated 8

Introduce this amount into strainer test in batches near time = 0 WCAP

WCAP 16530 vs ICET 9

0.01 0.1 1

10 100 0

2 4

6 8

10 12 Corrosion Rate (mg/m2-min) pH ICET #2 ICET #3 (max)

ICET #4 (max)

ICET #1 ICET #5 WCAP-16530-NP Equation 6.2 at 140 F All ICET tests were done at 140 F

Passivation of Al corrosion in ICET Tests 10 ICET Test pH Al (mg/L)

Si (mg/L) 1 9.3-9.5 360 7

2 7.1-7.4 BD 45 3

7.3-8.1 BD 45 4

9.5-9.9 BD 82 5

8.2-8.5 50 4

• BD is below instrument detection limit

• Approximate concentrations at day 30 of testing

Soluble aluminum contribution:

Sprayed vs Submerged sources Literature Sprayed aluminum corrosion rate higher than submerged aluminum Experimental Contribution of soluble aluminum from sprayed sources is negligible Net Effect Corrosion rate may be higher but low contribution from sprayed aluminum to soluble aluminum concentration ICET Test Submerged Sprayed 1

-98.6 0.7 2

-0.9 0.4 3

0.6 0.4 4

0 0.6 5

-11.2 0.4 11 Mass change (g) in aluminum coupons after 30-day ICET tests

Conservatism: Precipitation WCAP 16530 estimates precipitate formed NaAlSi3O8 and/or AlOOH Another possible form:

Al(OH)3 Molecular weight of precipitate determines quantity STP WCAP calculation predicts 83 kg of Al in solution 650 kg of NaAlSi3O8 and 36 kg of AlOOH OR 237 kg of Al(OH)3 Quantity of precipitate is used to predict head loss Over or under estimation of actual head loss 12

Conservatism: Precipitation Amorphous phase precipitate Occurs in solution Transported to screen Assumed by WCAP-16530-NP Greater head loss ?

Mineral phase precipitate Occurs on surfaces Not transported Occurred during VUEZ chemical effects tests Less head loss ?

13

Amorphous vs crystalline phases 14 0.01 0.1 1

10 100 1000 0

100 200 300 400 500 600 700 800 Aluminum concentration, mg/L Time, hr Aluminum concentration required to precipitate crystalline product, AlOOH (Boehmite)

Measured aluminum concentration in VUEZ testing Aluminum concentration required to precipitate amorphous product, Al(OH)3

Casa Grande:

Limiting excessive conservatism 15 Risk assessment philosophy Stochastic analysis and uncertainty quantification Allows for educated reduction of previously demonstrated conservatism

Hypothesis of Chemical Effects at STP during a LOCA - Corrosion/Release The release of aluminum into solution resulting from corrosion is less than predicted by WCAP-16530-NP Passivation effects Formation of oxide layer Aluminum exposed to spray releases less metal into solution than submerged aluminum 16

Hypothesis of Chemical Effects at STP during a LOCA - Precipitation Calcium phosphate precipitation will be minimal Crystalline aluminum precipitate will occur in fiber bed or on surfaces in the containment pool and not in the bulk solution Amorphous aluminum precipitation may occur in bulk solution when passed through heat exchanger Precipitation will be less due to less corrosion products in solution 17

Hypothesis of Chemical Effects at STP during a LOCA - Overall Little or no impact of chemical effects on the STP plant Reduced release of aluminum into solution, thus smaller quantity of precipitation Crystalline precipitation onto the fiber bed with possibility of amorphous precipitation in solution due to heat exchanger exposure 18

Objectives for new chemical effects tests Determine the significance of chemical effects on the resolution of GSI-191 at the STP plant without excessive conservatisms Generate data that can be used to develop a model of system of equations that will provide input to Casa Grande Equations predicting concentrations of Al, Si, Ca, and PO4 in solution as a function of pH, temperature, pool volume, spray duration and quantities of materials in containment Equation predicting incremental increase in head loss as a function of soluble Al, Si, Ca, and PO4 concentrations, pH and temperature 19

Thermodynamic/Kinetic Modeling Relative importance of various parameters Integrated Chemical Effects Tests with a Head Loss Loop Corrosion/dissolution/release rates Solubility limits Precipitate characteristics Effect of fiber bed dissolution on HL Effect of precipitate formation on HL Existing knowledge base on chemical effects Benchtop/

Autoclave Testing Corrosion rates Dissolution rates Release rates Solubility limits Precipitate Calculator (Type and Quantity)

High Temperature Vertical Loop Head Loss Tests Head loss given variations in:

Fiber quantity Particulate quantity Precipitate quantity NUREG/CR-6224 Head Loss Correlation Head Loss Calculator CASA Grande Path to reach objectives 20

Preliminary testing ideas ICET Tank Tests 30-day test integrated corrosion/head loss tests Blank Test Examine fiber bed dissolution and associated headless in buffered/borated water only Medium break LOCA Large break LOCA Shorter term test Effects using NaTB as buffering agent at STP Examine contribution from spray metals under different spray conditions Force precipitation for identification purposes Will allow for more accurate head loss correlation Batch Tests Clarify the composition of precipitates that form Impact of variable concentrations of silicon Flow rate effects on formation of aluminum oxide scale 21

Experimental Apparatus ICET Tank 250 gallons Racks and capacity for all materials present in STP containment Recirculation loop to provide required turbulence and mixing in tank RWST chemistry at the STP plant would be simulated in the tank 22

Modifications to ICET Tank Head loss loop, using pre-formed fiber debris beds Heat exchanger loop Scaling parameters to STP Ratio of materials (aluminum, etc) to pool volume Recirculation time through screen / hydraulic residence time Water velocity through fiber bed Hold up time at lower temperature before re-introduction into pool Declining temperature profile similar to LOCA Flow variations to simulate plant evolutions 23

Conclusion 24 Casa Grande is a tool for reducing conservatism Will include chemical effects Overall hypothesis for non-conservative scenarios Little or no impact of chemical effects on the STP plant Testing to prove hypotheses 30-day testing Short term test Batch tests Modified ICET tank

Areas for discussion Use of pre-formed fiber beds Orientation of fiber bed: vertical or non-vertical Use of multiple beds in parallel Use of two beds in series with an intermediate heat exchanger 25