GSI-191 PWR Sump Screen Blockage Chemical Effects Tests: Thermodynamic Simulations (NUREG/CR-6912)
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Publication Information
Manuscript Completed: November 2006
Date Published: December 2006
Prepared by
J. McMurry, V. Jain, X. He, D. Pickett
R. Pabalan, Y.-M. Pan
Center for Nuclear Waste Regulatory Analyses
Southwest Research Institute
6220 Culebra Road
San Antonio, TX 78238-5166
B.P. Jain, NRC Project Manager
Prepared for
Division of Fuel, Engineering and Radiological Research
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Codes N6121 and N6278
Abstract
This report summarizes chemical modeling studies and experiments performed to support the
resolution of GSI–191. Along with entrained debris components, the formation of secondary
precipitates and gels have the potential to impede the performance of Emergency Core Cooling
System pumps, Containment Spray System pumps, or other components downstream of the
sump strainer after a loss-of-coolant accident (LOCA). The purpose of this study was to
examine the use of chemical modeling software as a tool in predicting whether secondary
precipitates would be likely to form in specific post-LOCA chemical environments. Within the
limits of the available thermodynamic data for the model, the software also identified which
solids would be expected to form and their quantities, and it indicated how the containment
water chemistry was affected by these reactions. Several existing, widely available chemical
modeling programs—EQ3/6 (Lawrence Livermore National Laboratory, 1995), OLI Systems
StreamAnalyzer (OLI Systems, Inc., 2005), The Geochemist's Workbench® REACT (RockWare,
Inc., 2004), and PHREEQC (U.S. Geological Survey, 2003)—and their accompanying
thermodynamic database files were evaluated to simulate the potential formation of precipitates
under post-LOCA conditions. Detailed simulations were performed for five representative post-
LOCA environments, in which alkaline or neutral borated containment waters interacted with
metals, concrete, and insulation materials at 60 °C [140 °F] for times up to 720 hours. The
modeled conditions corresponded to the Integrated Chemical Effects Test (ICET) experiments
conducted at the University of New Mexico, and results of the experiments were used to
benchmark and calibrate the simulations. The input water compositions for the simulations
were estimated from specified initial containment water compositions, previously derived
corrosion rates for the metals of interest, and dissolution rates from new experiments involving
insulation materials and concrete. The modeling programs EQ3/6 and PHREEQC were used to
perform blind predictions of the experiment results. Analytical data and qualitative observations
of precipitation (or lack of it) from the ICET experiments were used to refine the conceptual
model. Revised dissolution rates were obtained from additional experiments at the Center for
Nuclear Waste Regulatory Analyses, after which informed simulations were performed using
StreamAnalyzer and PHREEQC. A more detailed simulation considered the gradual changes in
chemistry of the solution water over time, based on kinetic reaction rates with the reactive
materials and ongoing equilibration (precipitation) with oversaturated secondary phases.
The study determined that the most important requirements for developing more accurate
chemical effects simulations were (i) a realistic estimate of starting water compositions and
dissolution rates, and (ii) the availability of an adequate set of thermodynamic data, particularly
for amorphous or metastable solids that would be expected to form under the simulated
conditions. The study concluded that the codes as tested were broadly useful in assessing
whether precipitation of secondary solid phases was likely under the specified conditions and
the quantity of material that was predicted to form. In applying chemical modeling software to
other plant-specific sets of conditions, the effectiveness of the simulations and confidence in
their predictions would be considerably improved by a more complete characterization of
source-term materials and release rates for the conditions of interest, and by development of an
appropriate thermodynamic database for modeling purposes that includes more realistic
amorphous or metastable solids for the conditions of interest.
