Corrosion Rate Measurements and Chemical Speciation of Corrosion Products Using Thermodynamic Modeling of Debris Components to Support GSI-191 (NUREG/CR-6873)

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Publication Information

Manuscript Completed: April 2005
Date Published: April 2005

Prepared by:
V. Jain, X. He, Y.-M. Pan
Southwest Research Institute
Center for Nuclear Waste Regulatory Analyses
6220 Culebra Road
San Antonio, Texas 78228-0510

B.P. Jain, NRC Project Manager

Prepared for:
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code N6061

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Abstract

This report documents thermodynamic simulations conducted to determine whether post loss-of-coolant-accident (LOCA) debris generation and consequent sump screen head loss in a pressurized water reactor containment can be affected by chemical interactions between the emergency core cooling system/containment spray water and exposed materials. Based on the measured corrosion rates, estimated exposed surface area, and exposure time, the thermodynamics simulations indicated that the formation of dominant solid phases was controlled by the presence of Nukon^® low-density fiber insulation, aluminum, and concrete. The predicted dominant solid phases consisted of potentially amorphous silicate phases such as sodium aluminum silicate (NaAlSi₃O₈), calcium magnesium silicate [Ca₂Mg₅Si₈O₂₂(OH)₂], calcium silicate (CaSiO₃), and silica (SiO₂). The results were based on the solid phases included in the thermodynamic simulation program database. The formation of actual solid phases may be different depending on the reaction kinetics. Although some constituents decreased proportionally with increasing time, the solid NaAlSi3O8 phase continued to be a dominant solid phase at all times. The formation of NaAlSi₃O₈ in the presence of alkaline solutions could lead to gel formation, which could result in clogging of containment area sump pump suction strainers. Thermodynamic simulations indicate that in alkaline simulated containment water at pH 10 there is no significant difference in corrosion product formation as high-temperature and pressure conditions during the initial stages of a LOCA event approach steady-state atmospheric pressure conditions. This report provides insight to and is useful in understanding the evolution of solution chemistry and the formation of solid phases in integrated chemical effects tests at the University of New Mexico.