PNNL

Abstract

The U.S. Department of Energy must approve a performance assessment (PA) to support the design, construction, approval, and closure of disposal facilities for immobilized low-activity waste (ILAW) currently stored in underground tanks at Hanford, Washington. A critical component of the PA is to provide quantitative estimates of radionuclide release rates from the engineered portion of the disposal facilities. Computer simulations are essential for this purpose because impacts on groundwater resources must be projected to periods of 10,000 years and longer. The computer code selected for simulating the radionuclide release rates is the Subsurface Transport Over Reactive Multiphases (STORM) simulator. The STORM simulator solves coupled conservation equations for component mass and energy that describe subsurface flow over aqueous and gas phases through variably saturated geologic media. The resulting flow fields are used to sequentially solve conservation equations for reactive aqueous phase transport through variably saturated geologic media. These conservation equations for component mass, energy, and solute mass are partial differential equations that mathematically describe flow and transport through porous media. The STORM simulator solves the governing-conservation equations and constitutive functions using numerical techniques for nonlinear systems. The partial differential equations governing thermal and fluid flow processes are solved by the integral volume finite difference method. These governing equations are solved simultaneously using Newton-Raphson iteration. The partial differential equations governing reactive solute transport are solved using either an operator split technique where geochemical reactions and solute transport are solved separately, or a fully coupled technique where these equations are solved simultaneously. The STORM simulator is written in the FORTRAN 77 language, following American National Standards Institute (ANSI) standards. The simulator utilizes a variable source code configuration that allows tailoring of the execution memory and speed to the specific problem by editing text parameter files and recompiling the code. Execution of the STORM simulator is controlled through a text input file. This input file uses a structured format of associated groups of input data. Input data files and results are also presented for model verification and example simulations. Appendix A to this report presents examples of the STORM Version 3.0 input data format for each of the groups. The STORM simulator may be compiled to run on any number of multiple, parallel processors. Calls to the Message Passing Interface (MPI) libraries have been written directly into the FORTRAN 77 code. Scripts for compiling and running on systems using the Linux operating system are provided in Chapter 6 of this report.