Adsorption and Desorption Behavior of Selected 10 CFR Part 61 Radionuclides From Ion Exchange Resin by Waters of Different Chemical Composition (NUREG/CR-6647)

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Publication Information

Manuscript Completed: May 2000
Date Published: July 2000

Prepared by:
D.E. Robertson, SJi. Pratt, C.W. Thomas

Pacific Northwest National Laboratory
Richland, WA 99352

P.R. Reed, NRC Project Manager

Prepared for:
Division of Risk Analysis and Applications
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code W6677

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Abstract

Two sets of laboratory experiments were conducted to determine the sorption and desorption behavior of a selected group of long-lived radionuclides on nuclear grade ion exchange resin in contact with several types of groundwater. The first experiment used a slightly modified version of ASTM Method D 4319-83, "Distribution Ratios by the Short-Term Batch Method" to determine Kd values for 13 radionuclides (¹⁴C, ³⁶Cl, ⁶⁰Co, ⁶³Ni, ⁹⁰Sr, ⁹⁹Tc, ¹²⁹I, ¹³⁷Cs, and isotopes of Th, U, Np, Pu, and Am) on EPICORE AC-32 mixed-bed ion exchange resin in contact with three different water types; 1) Chalk River groundwater (pH 6.6), 2) Hanford groundwater (pH 7.9), and 3) Soap Lake water (pH 10.1). These measurements gave high Kd values (10⁴ to 10⁵) for the Hanford and Chalk River groundwaters, and much lower Kd values for the Soap Lake water. The relatively high dissolved salt content and high alkalinity of the Soap Lake water either saturated the resin or provided high concentrations of competing ions for the adsorption sites on the resin. The second experiment involved determining the leaching rate and magnitude for nine radionuclides (¹⁴C, ³⁶C1, ⁶³Ni, WTc, ¹²⁹I, and isotopes of U, Np, Pu, and Am) previously sorbed onto the same type of EPICORE AC-32 ion exchange resin. A slightly modified version of the INEEL leaching method described in NUREG/CR5224 was used to determine equilibrium desorption coefficients (1/Kd) of radionuclides leached from the resin by two different water types; 1) Hanford groundwater (pH 7.9), and 2) a "cement water" (pH 12.1) prepared by equilibrating Hanford groundwater with Portland cement. The desorption coefficients were very small (mainly in the range of 10^-5 to 10^-7), indicating that the radionuclides were very tightly sorbed to the resin and not easily leached during contact with the test groundwater samples. The measurements from these two experiments have provided LLW site performance assessment modelers with empirical data to more effectively estimate the retention fraction, or conversely, the release fraction of radionuclides on ion exchange resin during contact with infiltrating groundwater types.