Chemical Effects Head-Loss Research In Support of Generic Safety Issue 191 (NUREG/CR-6913)
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Manuscript Completed: October 2006
Date Published: December 2006
J.H. Park, K. Kasza, B. Fisher, J. Oras, K. Natesan, and W.J. Shack
Argonne National Laboratory
Argonne, IL 60439
Paulette A. Torres, NRC Project Manager
Division of Fuel, Engineering and Radiological Research
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555
NRC Job Code N6100
This summary report describes studies conducted at Argonne National Laboratory on the potential for chemical effects on head loss across sump screens. Three different buffering solutions were used for these tests: trisodium phosphate (TSP), sodium hydroxide, and sodium tetraborate. These pH control agents used following a LOCA at a nuclear power plant show various degrees of interaction with the insulating materials Cal-Sil and NUKON. Results for Cal–Sil dissolution tests in TSP solutions, settling rate tests of calcium phosphate precipitates, and benchmark tests in chemically inactive environments are also presented. The dissolution tests were intended to identify important environmental variables governing both calcium dissolution and subsequent calcium phosphate formation over a range of simulated sump pool conditions. The results from the dissolution testing were used to inform both the head loss and settling test series. The objective of the head loss tests was to assess the head loss produced by debris beds created by Cal–Sil, fibrous debris, and calcium phosphate precipitates. The effects of both the relative arrival time of the precipitates and insulation debris and the calcium phosphate formation process were specifically evaluated. The debris loadings, test loop flow rates, and test temperature were chosen to be reasonably representative of those expected in plants with updated sump screen configurations, although the approach velocity of 0.1 ft/s used for most of the tests is 3–10 times that expected in plants with large screens . Other variables were selected with the intent to reasonably bound the head loss variability due to arrival time and calcium phosphate formation uncertainty. Settling tests were conducted to measure the settling rates of calcium phosphate precipitates (formed by adding dissolved Ca to boric acid and TSP solutions) in water columns having no bulk directional flow.
For PWRs where NaOH and sodium tetraborate are used to control sump pH and fiberglass insulation is prevalent, relatively high concentrations of soluble aluminum can be expected. Tests in which the dissolved aluminum (Al) resulted from aluminum nitrate additions were used to investigate potential chemical effects that may lead to high head loss. Dissolved Al concentrations of 100 ppm were shown to lead to large pressure drops for the screen area to sump volume ratio and fiber debris bed studied. No chemical effects on head loss were observed in sodium tetraborate buffered solutions even for environments with high ratios of submerged Al area to sump volume. However, in tests with much higher concentrations of dissolved Al than expected in plants, large pressure drops did occur. Interaction with NUKON/Cal–Sil debris mixtures produced much lower head losses than observed in corresponding tests with TSP, although tests were not performed over the full range of Cal–Sil that might be of interest.