Abstract
Borated water leakage through spent fuel pools (SFPs) at pressurized water reactors is a concern because it could cause corrosion of reinforcement steel in the concrete structure, compromise the integrity of the structure, or cause unmonitored releases of contaminated water to the environment. Experimental data indicate that pH is a critical parameter that determines the corrosion susceptibility of rebar in borated water and the degree of concrete degradation by boric acid leaching. In this study, reactive transport modeling of concrete leaching by borated water was performed to provide information on the solution pH in the concrete crack or matrix and the degree of concrete degradation at different locations of an SFP concrete structure exposed to borated water. Simulations up to 100 years were performed using different boric acid concentrations, crack apertures, and solution flow rates. Concrete cylinders were immersed in boric acid solutions for several months and the mineralogical changes and boric acid penetration in the concrete cylinder were evaluated as a function of time. The depths of concrete leaching by boric acid solution derived from the reactive transport simulations were compared with the measured boric acid penetration depth.
Highlights
Spent fuel pools (SFPs) at pressurized water reactors are seismically qualified concrete structures that have stainless steel liners and contain borated water, maintain spent fuel temperatures, and provide radiation shielding
Experimental data indicate that pH is a critical parameter that determines the corrosion susceptibility of rebar in borated water and the degree of concrete degradation by boric acid leaching
Reactive transport modeling of concrete leaching by borated water was performed to provide information on the solution pH in the concrete crack or matrix and the degree of concrete degradation at different locations of an SFP concrete structure exposed to borated water
Summary
Spent fuel pools (SFPs) at pressurized water reactors are seismically qualified concrete structures that have stainless steel liners and contain borated water, maintain spent fuel temperatures, and provide radiation shielding. Borated water that leaks through the SFP liner initially will be acidic, but as it diffuses into the concrete pores or flows through the concrete joints or cracks, it will react chemically with the cement matrix and the solution pH will increase. In the absence of information on crack lengths in an actual SFP concrete structure, a 1-m crack length was assumed in the 2-D simulations in order to calculate the solution volume exiting the crack at various half-apertures and inlet flow rate. The calculated flow rate of boric acid solution exiting the crack in Simulations 4, 5, and 6 is more than three times that estimated to be leaking from the Salem Fuel Handling Building. Additional model results for the 2-D simulations include solution pH in the concrete crack and specific discharge at the crack outlet (volume of solution flowing per unit time through a unit cross-sectional area of the crack)
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