Modeling of Radionuclide Transport in Freshwater Systems Associated with Nuclear Power Plants (NUREG/CR-7231)

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Publication Information

Manuscript Completed: November 2016
Date Published: April 2017

Prepared by:
S. B. Yabusaki, B. A. Napier,
W. A. Perkins, M. C. Richmond, C. L. Rakowski,
S. F. Snyder, and L. F. Hibler

Pacific Northwest National Laboratory
Richland, Washington 99352

Mark Fuhrmann, Project Manager

NRC Job Code V6366

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

The potential consequences of radionuclides that have been directly released into a surface water body, as happened in the 2011 Fukushima Daiichi nuclear power plant accident, are not well understood, especially for the lake and river settings where most U.S. nuclear power plant reactors are sited. Accordingly, hypothetical scoping analyses have been performed to better understand how radionuclide transport in freshwater systems might be affected by the interaction of radionuclide-specific decay and sorption with hydrologic and sediment conditions.

Eight radionuclides, ¹³⁷Cs, ¹³⁴Cs, ¹³1I, ⁹⁰Sr, ³H, ¹⁰⁶Ru, ¹²⁵Sb, and ¹⁴⁴Ce, were selected for these analyses based on a methodology that estimated the partitioning of the reactor core inventory to water as a function of reactor type, mass of uranium fuel, and fuel burnup. Transport simulations for each radionuclide were based on the release of a 10-day pulse of 1,000 m³ of water with 1 Bq of activity into small lake, small river, and large river settings. The small lake setting was based on a reservoir impounded by a dam on a river that provided a large water volume but limited transport, which led to high concentrations at early times. The small river setting examined relatively low flow and slow average velocity conditions, which resulted in less dilution (i.e., higher concentrations) and longer transit times for the 10-day radioactive release. The large river scenario examined conditions where relatively high flow resulted in lower concentrations but faster downriver transport.

Bathymetric data and hydraulic parameters were adapted and modified from actual lake and river systems. Consistent with the scoping level of analysis, steady-state hydraulics were used with the rivers simulated in two dimensions (depth-averaged) and the lake in three dimensions. Modeled transport processes included advection, mixing/dispersion, decay, sediment transport, and sediment-radionuclide interaction (i.e., adsorption/desorption); modeled features included the impact of tributaries, dams, and impoundments.