In the Lab

• By Jeff Wilson
• Jul 01, 2001

New Research Software with Explosive Possibilities

A new computer program created by Dr. Jamie A. D. Connolly, Swiss Federal Institute of Technology and a Penn State alumnus, allows researchers to analyze the products released from arc volcanoes and rock sources. With the program, users can model the way specific mixtures of rocks behave in a subduction zone and determine where carbon dioxide and water are emitted.

Estimates of carbon dioxide components given off at arc volcanoes are generally high. The ability of this program to determine the amount of carbon dioxide emitted at specific volcanoes could be instrumental in generating a more accurate assessment of global warming.

"Models have a tendency to treat all subduction zones the same," said Dr. Derrill Kerrick, professor of geosciences at Penn State. "The question is, how efficient is the return of carbon dioxide to the atmosphere at various subduction zones?"

A subduction zone occurs when two of Earth's tectonic plates converge, and one slips underneath the other. Carbon dioxide and water escape with the magma as arc volcanoes are formed. More carbon dioxide appears to be subducted than emitted from arc volcanoes, which implies that a significant amount of carbon dioxide either is released before reaching the depth at which arc magmas are generated or is subducted to deeper depths, according to researchers in the journal Nature.

The carbon dioxide comes from the mantle, where it is dissolved in the rocks that melt to form the magma. As the magma rises, the pressure acting on it decreases and eventually the gases become saturated and exsolve (the opposite of dissolve) into gas bubbles. The first to exsolve is carbon dioxide, then later water vapor and sulfur dioxide come out. None of the common minerals in magmatic rocks contain carbon, so when the magma cools down and solidifies, carbon is one of the remaining elements. If there is enough oxygen around, it will combine with the carbon to form carbon dioxide.

Scientists have analyzed subducted serpentinites (rocks consisting of serpentine-group minerals) and marine sediments and plan to discuss metabasalts, all types of carbon-containing rocks involved with subduction. They are finding that most of the carbon dioxide in marine sediments does not escape back to the atmosphere during subduction. The clay-rich marls completely lose their carbon dioxide at the highest temperatures in the subduction zone range, releasing less at lower temperatures.

Marine sediments are important in carbon dioxide studies, because the sediments consist of the calcium carbonate shell bodies of marine organisms. The organisms remove carbon dioxide from the ocean near the surface and bring it to the ocean bottom. The carbon dioxide cannot return to the atmosphere until sedimentary rocks formed by these marine organisms are heated in the subduction of a tectonic plate.

Carbon dioxide is abundant in volcanic gases, though not enough to significantly contribute to the greenhouse effect. Volcanoes contribute about 110 million tons of carbon dioxide per year, while human activities contribute about 10 billion tons per year. Still, with new technology researchers will be able to gauge the carbon dioxide emitted from volcanoes more accurately, giving them a more precise estimation of the extent of global warming.

For more information, contact A'ndrea Elyse Messer at aem1@psu.edu, Vicki Fong at vfong@psu.edu or Swiss Federal Institute of Technology at www.ethz.ch/ or www.epfl.ch/.

Lending a Robotic Hand in Nuclear Waste Clean-up

Researchers studying the movements of radioactive contaminants through the earth are receiving help in the form of a robotic crawler, designed to enter radioactive areas and gauge contamination levels and developed by scientists at the Pacific Northwest National Laboratory. It can travel through small spaces and rough terrain and is proving crucial to entering areas unsafe for scientists. Pacific Northwest's robotic crawler is just one kind of robotic technology being used on radioactive waste from former nuclear research, development, production and testing sites.

By researching the effects of radioactive waste and the byproducts of plutonium production, Pacific Northwest is assisting the U.S. Department of Energy (DOE) in its efforts to deal with contaminants left by Cold War nuclear armament efforts. The DOE must treat over 270 underground storage tanks containing almost 100 million gallons of radioactive waste. The tanks' contents and design differ from site to site and tank to tank. Waste types in the tanks include liquids, saltcake and sludges. Some tanks also contain miscellaneous debris, such as pipes and chunks of concrete.

In order to be effective, tank waste retrieval devices must fit through small tank openings (risers) and maneuver around internal structures. Retrieval processes must minimize worker exposure and the addition of materials that increase the volume of waste requiring future treatment and disposal.

New tank waste retrieval technologies are highly effective when combined into systems. At the Gunite and Associated Tanks at the Oak Ridge National Laboratory, a set of technologies is removing radioactive liquid and sludge and preparing the tanks for closure. The integrated system used at Oak Ridge consists of a robotic crawler, robotic arm and a waste dislodging and conveyance tool. This system has so far succeeded where earlier sluicing efforts had failed to fully clean tanks. It has also accelerated the schedule, eliminated the costs of continued tank maintenance and reduced downstream costs by minimizing the volume of water added.

The integrated system's in-tank robotic crawler fits through the tank dome and unfolds on the tank floor. It then deploys, positions specialized tools and pushes waste to locations accessible by the robotic arm and waste removal tool. The robotic arm overcomes restricted access problems through risers and around internal structures. It safely positions measuring instruments and retrieval tools, while minimizing worker exposure. The waste dislodging and conveyance tool is easier to manipulate within the tank to remove tank heels and also minimizes water additions for conveying waste.

Using newly developed robotics and advanced mixing and mobilization approaches, highly radioactive tank waste is now being efficiently removed. These innovative approaches reduce the need for additional liquids, thereby minimizing the waste burden requiring subsequent treatment and disposal.

For more information, visit www.pnl.gov or apps.em.doe.gov/ost/.

This article originally appeared in the July 2001 issue of Environmental Protection, Vol. 12, No. 7, p. 55.

This article originally appeared in the 07/01/2001 issue of Environmental Protection.