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[Sandia Lab News]

Vol. 53, No. 5        March 9, 2001
[Sandia National Laboratories]

Albuquerque, New Mexico 87185-0165    ||   Livermore, California 94550-0969
Tonopah, Nevada; Nevada Test Site; Amarillo, Texas

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Arsenic trapping; CTH code upgrade; Explosive Destruction System

Arsenic-trappers could allay national sticker shock of new EPA standard

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By John German

Sandians who have used Labs supercomputers to custom-design chemicals with žypaper-like arsenic-trapping properties plan to test the new materials in a city water-purification demonstration plant being built on Albuquerque's West Side.

Successful trials of the materials, called Specific Anion Nanoengineered Sorbents (SANS) by their Sandia developers, could have major national implications as thousands of communities and other water providers tally up the costs of complying with a controversial new Environmental Protection Agency (EPA) mandate that reduces the maximum allowable amount of arsenic in drinking water from 50 to 10 parts per billion.

About 3,200 of the nation's 74,000 water systems supply drinking water with arsenic levels that exceed the new limit, according to EPA estimates. Almost half of Albuquerque's wells will fail to meet the new standard. "In essence the ruling says Albuquerque can't use half its wells after 2005 without additional treatment," says Dave Teter of Geochemistry Dept. 6118.

The national price tag for complying with the EPA ruling might be in the tens of billions of dollars. Albuquerque's compliance could cost $150 million, the City estimates.

Water sans arsenic

Inorganic arsenic occurs naturally in some groundwater, seeping out of rock and soils that neighbor the aquifer. Ingesting arsenic over long periods of time can cause cancer of the skin, bladder, liver, kidney, prostate, and other organs and has been linked to a variety of other cardiovascular and neurological illnesses, although scientific data linking low-level, chronic arsenic ingestion to health effects is limited.

The Sandia developers -- Dave, Pat Brady, and Jim Krumhansl (all 6118) -- think the new arsenic-getting SANS could reduce the sticker shock of complying with the new EPA standard for cities served by water treatment plants, rural communities, and homes, schools, and apartment complexes served by single wells.

They also have proposed using the getters to purify arsenic-laden well water in Bangladesh that is poisoning millions of people there (Lab News, April 7, 2000).

Materials selective for arsenic

"We've zeroed in on five classes of materials that are affordable and obtainable and peculiarly selective for arsenic," says Dave.

Most mineral getters have negatively charged surfaces, so they repel similarly charged anions. The SANS selectively attract anions such as arsenate (a toxic arsenic-containing compound) dissolved in water to positively charged sites on the SANS' surfaces and then grab hold.

"It's like a guest who eats the cashews out of a nut bowl," says Pat.

To create the materials, the research team selected mineral families with known affinities for anions, then used Labs supercomputers to rapidly simulate the arsenic-

trapping aptitudes of thousands of combinations and variations of the minerals.

"We knew which classes of materials should be highly selective for arsenic at the atomic level," says Pat, "so we asked ourselves what is peculiar or common about those materials. Then we tried to find or make other materials with similar properties."

Because there are nearly infinite variations of chemical species, phases, and surface chemistries, the researchers let the computer sort out the very best performers.

"We got some big hits on materials that had never been considered before," says Dave. "We expected good results, but not this good."

They ruled out those minerals that are difficult or expensive to obtain or produce, that would become saturated too quickly, or that would result in a hazardous byproduct.

"A prerequisite for us was that the solution be at least as simple, safe, and efficient as, and more affordable than, the current technology," he says.

They verified the computers' results in a lab, pumping arsenic-contaminated water through the powdered materials, then measuring the arsenic content of the outžow.

For proprietary reasons, Dave can't yet divulge what materials the team found, but they generally are nontoxic mixed metal oxides with high molecular surface areas.

At water treatment plants, groundwater could be pumped through columns containing the powdered materials. Arsenic content in the outžow would be reduced to undetectable levels. After perhaps years of use, the nonhazardous arsenic-saturated getters could be disposed of in a standard landfill.

Sandia's relationship with the City of Albuquerque's subcontractor on the new treatment plant, CH2M-Hill, has helped the research team understand the practical needs of municipalities, especially the need for a simple, affordable, available treatment technology.

"Technology has no impact if it isn't used," says Dave.

Needle in a haystack

He estimates that some of the SANS could be supplied for as little as $200 to $300 a ton, compared to the $4,000 a ton for conventional iron hydroxides used in typical water treatment plants. (Iron hydroxides, adopted for water purification around the turn of last century, sweep out many contaminants simultaneously but don't selectively remove arsenic.)

"Municipalities filter out dirt, silt, and sewage, but pulling out stuff at the parts-per-billion range cheaply is new," says Pat. "This is harder than finding a needle in a haystack."

The SANS could be adapted for use with smaller water systems, even down to the individual well or household scale, says Dave.

Albuquerque's Arsenic Removal Demonstration Plant should be operational by next summer, according to City Water Resources Manager John Stomp. The plant will process more than 2 million gallons of water a day using a microfiltration/iron coagulation process, but the facility will reserve space to test developmental technologies such as the SANS.

"We're very interested in working with Sandia to look at emerging technologies that are cheap and easy to dispose of," says Stomp.

In addition, the same research methodology used to identify the SANS for arsenic removal -- computer modeling followed by experimental verification -- has been used to design getters for removing other contaminants as well, says Dave.

"We are now able to predict the outcome of sorption processes at the atomic scale and chemically modify inexpensive natural materials to selectively sorb anions," he says.

"Arsenic is the focus right now, but EPA is looking at restricting concentrations of many more micropollutants in the future," he says.

Future custom-designed getters could be used to purify drinking water as well as industrial waste water, process streams, and other efžuents, he says.

The SANS team includes Dave, Pat, Jim, Buddy Anderson (6118), May Nyman, Steve Thoma (both 6233), Joe Chwirka (CH2M-Hill), Nadim Khandaker (OCETA), and Bruce Thomson (University of New Mexico).

The SANS work is part of a larger Water Initiative managed by the Energy and Critical Infrastructure SBU and led by a team of Sandians from centers 6100, 6200, 6800, 5300, and 5800. The initiative seeks technical solutions to key water issues -- vulnerability of and threats to water-distribution infrastructures, socio-geopolitical stresses relating to water scarcity, and economic concerns associated with supplying drinkable water. Watch for more about the Water Initiative in future issues of the Lab News. -- John German

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Sandia's Explosive Destruction System destroys sarin bomblets at Rocky Mountain Arsenal

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By Nancy Garcia

Sandia's Explosive Destruction System successfully destroyed six sarin-filled bomblets recovered at the Rocky Mountain Arsenal in Colorado.

The self-contained unit, designed and built by Sandia, safely neutralized the last of the nerve agent-containing bomblets (each about the size of a grapefruit) on Feb. 10. The six bomblets were found in October during Superfund cleanup of the site, which is also a wildlife refuge. They had been designed for a 1950s-era missile called "Honest John," and were never used.

"The highlights were the first successful destruction and the sixth successful destruction," says John Rosenow (8118), a field test engineer who has traveled with the system since September 1999. "There was a lot of concern by local citizens. After the first shot Jan. 28, the public seemed much happier."

As the first couple of cars approached the arsenal at 6:30 the morning of the last shot, the drivers saw a bright žash from a power line that had broken in the minus 18-degree weather. The operation "hardly missed a beat" despite this unforeseen happenstance, which was fixed within two hours, John says.

Once the operation was successfully completed, "we were ecstatic," says Al McDonald (8118), whose staff led the EDS design. "Here was a way for Sandia to be involved in a national problem and work with the Army to get it up and running. It made everybody very glad and happy to contribute to a solution." The US is committed to dispose of all chemical munitions by 2007.

The EDS (Lab News, Aug. 27, 1999) was developed by Sandia for the Army's Non-Stockpile Chemical Materiel Program. It is designed to safely dispose of old munitions deemed too unstable to transport. The system can be pulled by trailer to sites where these munitions are recovered. The munitions are placed within an air-tight chamber, where their metal shells are opened with an explosive charge. The contents are then neutralized with caustic chemicals. An alternative disposal method, open burn/open detonation, involves packing explosives around the munition to incinerate the contents. However, the lack of containment has posed concerns for the public.

"You don't want to be breaking anybody's window, even if you do burn everything that's there," says Tim Shepodd (8722), EDS lead chemist.

As an extra reassurance, at the Rocky Mountain Arsenal the trailer carrying the EDS was placed within a large building equipped with an air filter, Tim says. Also, the process is closely monitored through sampling. "We never open the door until we see that both the liquid and atmosphere are completely neutralized."

Acting program manager John Didlake calls the Denver operation a defining moment. "We built up a bunch of confidence," he says, "with the public, the EPA, and the Army."

When the bomblets were found, the EDS had been undergoing field testing at the United Kingdom's Defence Evaluation and Research Agency in Porton Down, England. The tests, spread over 13 months, primarily involved destroying WW I and WW II-era munitions containing phosgene gas or mustard. In anticipation of the Colorado project, one test also included destruction of a 1.3-pound bottle of sarin fabricated for this purpose.

John Rosenow says he really enjoyed working with the British crew, two of whom came to Colorado for the bomblet destruction. Both the British safety officer and the lead crew operator helped train the Army crew that handled the operation (which was pre-approved by a 25-person safety team).

"They felt like they were the cavalry, they had trained for this," John Didlake says.

The current system will undergo more operational testing at Aberdeen Proving Ground in Maryland. Meanwhile, Sandia is building two more systems of the same size (a three-foot-long chamber, pulled on a 30-foot trailer), as well as a third with larger capacity.

Rick Moehrle (8118), acting lead engineer on the new system, says the next models will incorporate some design improvements, such as a trailer layout that provides more space for workers to move about and an electric motor-rotary agitation system to mix the chemicals.

From New Mexico, Jerry Stožeth of Explosives Applications Dept. 15322 has led the development of the explosive munition opening system. The system includes a metal shield to suppress fragments within the reusable containment chamber, shaped charges to cut open the item being destroyed, and a firing system to detonate the charges. -- Nancy Garcia

Labs set to release new version of popular CTH shock code to customers

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By Chris Burroughs

The latest version of the widely used Sandia-developed shock wave physics computer code called CTH, which simulates high-speed impact and penetration phenomena involving a variety of materials, will soon be available to some 250 customers nationwide.

"This new version is really exciting because it offers a computational capability never before available in this type of code, an adaptive mesh refinement model [AMR]," says Paul Taylor, head of the CTH project in Computational Physics/ Simulations Frameworks Dept. 9232.

"AMR, developed for CTH by team member Dave Crawford [9232], gives the software the ability to increase resolution and accuracy in those regions of a simulation where it is needed and reduce resolution in those regions where it is not. For example, in the simulation of a projectile penetrating a target material, greater resolution can be achieved in the region surrounding the impact interface between the two materials where large distortions and high strain rates are occurring."

Interest in the soon-to-be-released version of the software is particularly high among customers like DOE and the Department of Defense (DoD), which use the software for studying weapons effects, armor/anti-armor interactions, warhead design, high-explosive initiation physics, and weapons safety issues. Major users include the national laboratories, the Army, Navy, and Air Force laboratories, and their subcontractors. At Sandia the code is used in national missile defense, hazardous material dispersal by explosive detonation, weapon components design, and reactive materials research.

For armor/anti-armor design -- which is of interest to the DoD -- the software allows users to determine which types of bullets or projectiles can best penetrate armor. It also provides information about how to design an improved penetration protection mechanism.

The medical community is also paying attention to Sandia's CTH software. Paul currently has a small collaborative research effort underway with the University of New Mexico School of Medicine, which is interested in using the shock physics code to better understand brain injury caused by physical trauma, such as a person's head hitting a car windshield. Using the magnetic resonance image (MRI) of an individual's head to construct a CTH model, simulations can be performed showing how shock waves travel through the head and cause damage to the brain.

The software breaks down the penetration simulation into millions of grid-like "cells." As the modeled projectile (such as a copper ball impacting a steel plate) impacts and penetrates the target, progressively smaller blocks of cells are placed around the projectile, each showing in detail the deformation and breakup of the ball and target plate.

CTH with the AMR enhancement also offers the ability to analyze problems involving sophisticated materials with greater accuracy. With the addition of new material models, it can simulate a wider variety of materials, including metals, ceramics, plastics, composites, high explosives, rocket propellants, and gases (e.g., air).

Sandia developed the early precursor to CTH in the 1970s for one-dimensional problems, expanding it to simulate problems in two and three dimensions in the 1980s.

"The widespread popularity that CTH has today as the shock wave physics computer code of choice began in a competition with Los Alamos National Laboratory in the early 1990s," Paul recalls. "DoD wanted a code that could deal with problems such as armor/anti-armor design, weapons effects, and munitions design. The Los Alamos code was called MESA and ours was CTH. Both codes had comparable characteristics, but DoD selected ours."

The Labs began licensing the shock wave physics code in the early 1990s to DOE, DoD, their contractors, and some private US companies with interests in shock physics. An updated version of the software, which is export-controlled, is distributed to customers about every 18 months. Currently 259 licenses have been issued.

DoD, DOE, and their contractors receive licenses for a small distribution fee to use the software. Commercial companies can purchase licenses for $25,000. The updated software will be distributed on CDs at a cost of $400 for each noncommercial, licensed customer.

One of the important aspects of CTH development is validation of code predictions using actual physical testing. Data gathered in a variety of experiments are compared to CTH models.

"In cases where we are studying situations in which the materials are well- characterized, the code predictions and the actual experiments are very close," Paul says. "The fidelity of the simulations is very good. In fact, CTH is used in many programs to simulate events that are either too costly or dangerous to conduct in full-scale tests. Other researchers use the code to reduce the amount of experimental testing that would otherwise be required."

Paul offers CTH classes several times a year so that customers can fully understand how to use the software and have a full grasp of its capabilities. Users from all over the country come to Sandia to take the classes. Department team members help Paul with the classes, which are broken down into theory and lab segments held over a three-day period.

Paul says one of the most appealing aspects of CTH for users is that it can run on almost any computer platform. The code runs on most Unix and Linux-based workstations and personal computers running Windows NT or 2000.

For users who have access to parallel-architecture computers, CTH can run in parallel mode. This feature permits running large three-dimensional simulations using many processors or nodes to break the problem up into smaller pieces, each of which is solved in parallel with neighboring pieces of the problem.

CTH simulations, conducted in parallel mode on Sandia's teražops computer, tend to be the largest problems the code handles. Last December a CTH simulation was performed by Marlin Kipp (9232) on the teražops computer for a problem containing more than 260 million cells, using 1,024 nodes (2,048 processors) and requiring over 60 hours of computer CPU time.

"CTH problems scale very well with the number of processors allocated for the job," says Paul. "The only limitation to the size of a problem that can be treated using CTH appears to be the availability of processors to complete the computing task." -- Chris Burroughs

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Last modified: March 13, 2001

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