Tracking contamination
from reservation to river

(page 3 of 3)

A code for 3D viewing underground

"The advantage of PETSc is that it leaves to the application scientists like us a lot of time to work on the application rather than the parallelization," Lichtner says. "It does a lot of the work for you."

Originally developed as two separate codes &ndash PFLOW for multiphase flow and PTRAN for reactive transport &ndash PFLOTRAN can now run both elements together, coupled or uncoupled, using continuum-scale mass and energy conservation equations to make accurate predictions of contaminant transport.

PFLOTRAN helps modelers generalize many geochemical flow and transport problems. Although originally designed for work on radionuclide transport, it can model reactive flow in other systems.

"The code handles flows &ndash supercritical flows, CO2 phase, water, brine," Hammond says.

It has already been used to model carbon sequestration &ndash cleaning up power plant emissions by storing carbon dioxide deep underground as carbonate minerals or as gas dissolved in ground water.

"The same chemistry algorithms we use at Hanford, we can also use to describe the CO2-brine interaction and the minerals in the formation when you're modeling injection of CO2 underground," Hammond says.

"Any investment in the CO2 work benefits the waste problem and helps us develop new process models for legacy waste issues."

Stepping up to petascale

The improved and parallelized code is very stable, and with SciDAC's 2006 investment in the project, PFLOTRAN can now be used on petascale computers &ndash capable of a quadrillion calculations or more per second. The researchers will try it out with a 2009 Innovative and Novel Computational Impact on Theory and Experiment (INCITE) award of 10.5 million processor hours on Oak Ridge National Laboratory's Cray XTs and half a million on PNNL's HP Chinook. The University of Illinois also is collaborating.

Approaching flow problems with top supercomputers has changed things, Hammond says. "INCITE (has been) phenomenal. It's allowed us to simulate a lot of science that wouldn't have been possible without it. It's opened doors to new science."

Using the parallelization strengths of PETSc's code elements and getting priority runs on open-science computers has moved simulating the site toward real-world impact. As the model gets more and more reliable, it can help inform better approaches to manage the Hanford site's cleanup.

"We'll get the information to DOE managers," Lichtner says, "and then they can decide if a particular remediation strategy is cost effective or would itself cause more pollution."

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