QASPR: Making sure the nation’s nuclear weapons offer effective, credible deterrence
It may sound strange to say that nuclear weapons must survive radiation. But as part of Sandia’s role in ensuring the nation’s stockpile is safe, secure, and effective as a deterrent, it must make sure crucial parts can function if they’re hit by radiation, especially a type called fast neutrons.
Sandia is responsible for non-nuclear components in all US weapons systems and for overall system engineering and integration: pulling together thousands of components into a weapon. It qualifies systems — ensuring their safety and effectiveness — through computer simulations and testing at unique facilities that mimic radiation environments a weapon could face during deployment or an accident.
Sandia developed a new way to do that after the Energy Department shut down its facility for creating fast neutrons, the Sandia Pulsed Reactor (SPR), when security concerns over its highly enriched uranium increased after 9/11.
The Labs created a science-based project called QASPR, Qualification Alternative to Sandia Pulsed Reactor. QASPR combines computing modeling and simulation, experiments, and technology development, and draws on expertise throughout Sandia, from materials science to transistor fabrication to sophisticated computer science. The idea is to create better radiation-hardened microelectronics for high-voltage transistors, part of a nuclear weapon’s safety electronics, and to offer a way to qualify the electronics without SPR.
Sandia does more modeling and experimental work than ever before to qualify components to survive fast neutrons produced by a nuclear burst, either from an enemy weapon or one of our own exploding nearby, says QASPR project manager Len Lorence (1341).
Both modeling, experimental work vital
“It’s very important both in the modeling and the experimental worlds that you not only get the right result but you get it for the right reason,” Len says. “It’s very important to understand the physics of what’s going on.”
Experiments don’t simply validate computer models. They are key to developing models in the first place. QASPR didn’t have the models it needed when it began in 2005. But researchers had time to work on them because the next reentry system that needed the tools and expertise for qualification was still years away.
QASPR focuses on how transistors that provide gain, which are crucial in some circuits, react to fast neutron radiation and what happens to its gain in less than a second — an eternity in nuclear weapons work. Transistor gain is the amplification of current passing through the device.
Neutron damage can cause gain to plummet. Designers can compensate for that in their circuit designs, but used SPR to check whether their designs operated correctly.
QASPR uses unique facilities for studies
QASPR does similar studies at Sandia’s Annular Core Research Reactor (ACRR), its Ion Beam Laboratory and two non-Sandia facilities. Each provides unique tests and complementary data that improve computer models.
One of the outside facilities is a fast-burst reactor similar to SPR and the second facility tests response to gamma radiation. ACRR, a long-pulse reactor, creates high levels of damage, although its long pulse makes it less ideal. Still, it provides a calibration point, which simplifies modeling and lets researchers concentrate on phenomena associated with rapid changes in transistor gain. The Ion Beam Laboratory acts as a surrogate for neutron radiation because ions can impart the same kind of neutron displacement damage as neutrons. It combines high damage levels like ACRR with short pulses in one facility. However, it only can irradiate a transistor or a few transistors together, rather than a circuit or component like the larger ACRR can.
QASPR also is creating better radiation-hardened microelectronics in Sandia’s Microsystems & Engineering Science Applications (MESA) fabrication complex. Some of those transistors are based on compound semiconductors, known as III-V for combining elements from the periodic table’s columns III and V. Such compound semiconductor transistors are much more resistant to neutron radiation.
QASPR turns in success story even in early years
Researchers spent QASPR’s early years combining modeling and experiments to understand the basic mechanisms of the silicon commercial-off-the-shelf components then in use and studying III-V devices. The III-V technology has matured to the point it has been chosen for current and future reentry system lifetime extension and alteration programs, Len says. The improved technology, along with more robust modeling and experiments, mitigates risk from the loss of SPR.
“It was a success story for QASPR,” Len says. “We are able to provide information that ended up affecting the design for the future stockpile modernization effort.”
Researchers are interested in the design phase because “we can catch things earlier, we can help guide the design, and ultimately do better qualification,” he says.
QASPR’s computer modeling is hierarchal, beginning with studies of materials inside transistors, using fundamental physics modeling and quantum mechanical tools to understand how radiation damage occurs and evolves. Then researchers create a model of how transistor gain changes during and after radiation exposure, using a Sandia-created transistor model code, Charon. Radiation exposure is modeled with a Sandia code, NuGET. Next, the analog circuit level aggregates transistors and devices such as resistors and capacitors as well as ever-changing voltages — a complex world where some devices respond to gamma radiation but not neutrons. Researchers use another Sandia code, Xyce, to model circuit behavior under radiation.
“The hierarchical approach is very powerful, since it allows traceability from a high-level circuit response all the way down to the most fundamental atomistic material level,” Len says.
Thus, QASPR offers important information. “At the circuit level we can be very impactful, so much so that we can help the system qualification process, which was our goal,” Len says.
Three programs fund QASPR. Advanced Simulation and Computing funds modeling, the Nuclear Survivability Engineering Campaign supports much of the experimental work, and the Readiness in Technical Base and Facilities program provides support through MESA, focusing on new radiation-hardened technologies.
QASPR and similar efforts to blend experiment and modeling will be needed as long as nuclear weapon electronics continue to evolve, Len says.
“It’s hard to put in the stockpile the exact same thing that was originally put in the stockpile. At some point it’s not possible, not cost-effective,” he says.
-- Sue Major Holmes
More California gas stations can provide H2 than previously thought, study finds
by Mike Janes
A study by Sandia researchers concludes that a number of gas stations in California can safely store and dispense hydrogen, suggesting a broader network of hydrogen fueling stations may be within reach.
The report examined 70 commercial gasoline stations and sought to determine which, if any, could integrate hydrogen fuel, based on the National Fire Protection Association (NFPA) hydrogen technologies code published in 2011.
The study determined that 14 of the 70 gas stations could readily accept hydrogen fuel and that 17 more possibly could accept hydrogen with property expansions. Under previous NFPA code requirements from 2005, none of the existing gasoline stations could readily accept hydrogen.
The current code, known as NFPA 2, provides fundamental safeguards for the generation, installation, storage, piping, use, and handling of hydrogen in compressed gas or cryogenic (low temperature) liquid form.
This work is aligned with Hydrogen Fueling Infrastructure Research and Station Technology (H2FIRST), a new project established by DOE’s Office of Energy Efficiency and Renewable Energy.
Science, risk-informed analysis accelerate deployment
The development of meaningful, science-based fire codes and determinations such as those found in the report will help accelerate the deployment of hydrogen systems, says Daniel Dedrick (8367), hydrogen program manager. “This work shows that we can reduce uncertainty and avoid overly conservative restrictions to commercial hydrogen fuel installations by focusing on scientific, risk-informed approaches.
“It turns out that the number of fueling stations able to carry hydrogen can be quantified,” Daniel adds. “We now know that we can build more hydrogen fueling stations if we examine the safety issues within a sound, technical framework that focuses on the real behaviors of hydrogen.”
Sandia’s hydrogen safety, codes, and standards program is a diverse portfolio of activities funded by DOE’s Fuel Cell Technologies Office to provide the technical basis for developing and revising safety codes and standards for hydrogen infrastructure, including the NFPA 2 code.
The study focuses on California, which has more hydrogen fueling stations than any other state. A key factor in the codes that Sandia examined was the separation distances required for fueling infrastructure, including fuel dispensers, air intakes, and tanks and storage equipment. The code defines required distances between such components and public streets, parking, on-site convenience stores, and perimeter lines around the site.
All fueling facilities are susceptible to fire due to the presence of flammable liquids and gases, says Daniel. According to the NFPA, more than 5,000 fires and explosions a year occurred at conventional gasoline stations from 2004-2008. “Whether you are filling your car with gasoline, compressed natural gas, or hydrogen fuel, the fueling facility first of all must be designed and operated with safety in mind,” he says.
“If you have a hydrogen leak at a fueling station, for example, and in the event that the hydrogen ignites, we need to understand how that flame is going to behave in order to maintain and control it within a typical fueling station,” says Chris San Marchi (8252), manager of Sandia’s hydrogen and metallurgy science group. A scientific understanding of how such flames and other potential hazards behave is necessary to properly determine and mitigate safety risks, he says.
“We’re comfortable with the risks of natural gas in our homes and under our streets,” Chris points out. “We want to be just as confident of the safety of hydrogen in our fuel tanks and on our street corners.”
Sandia researchers at the Combustion Research Facility for years have studied and modeled the intricate workings of the combustion engine and, more recently, hydrogen behavior and its effects on materials and engine components, Chris says. The knowledge gained by Sandia’s work on the physical behavior of hydrogen and risks associated with hydrogen fuels provided the scientific basis to revise the separation distances in the NFPA 2 code for hydrogen installations.
As safe as or safer than gasoline stations
Under the previous code, virtually no hydrogen fuel cell stations could be sited at existing stations. The reason, says Chris, is simple: Those codes were developed via an “expert opinion-based process” and not the risk-informed process developed by Sandia researchers and now used in the code. The previous code was developed for flammable gases in an industrial setting, which carries different risks compared to hydrogen fuel at a fueling station.
“The distances set forth in the code, therefore, were much larger than we now know they need to be,” Chris says. The risk metric used to develop the new NFPA code, he adds, was that the stations accepting hydrogen fuel needed to be proven as safe as or safer than gasoline-only stations.
Some gas stations still may not be able to accept hydrogen under the new code because gas station lot sizes vary greatly, and many smaller sites — particularly those in dense, urban areas — cannot be properly configured, he says.
“Certain smaller gas stations, especially those in cities, have unusual shapes that aren’t going to accommodate the right separation distances,” Chris says. For example, he says, the required distance between a high-pressure tank carrying hydrogen and the property boundary would be too great for a “skinny” station or a wedge-shaped lot. While larger lots naturally work better in the current environment, Chris says, there are opportunities to develop risk mitigations that could allow even wider deployment of hydrogen fueling stations.
Enhancing performance-based parts of hydrogen code
One of Sandia’s next objectives is to work with all parties to look more closely at the underutilized performance-based parts of the NFPA 2 code, rather than the prescriptive-based elements that focus on rigid distance requirements.
“While the prescriptive sections of the code are typically implemented, there are also sections of the code that allow for the use of more risk analysis to optimize the fueling facility,” Chris says. If station developers and others take a more performance-based approach, he says, more existing fueling facilities will be able to integrate hydrogen systems and support the developing fuel-cell electric vehicle market.
Sandia is also in the process of developing a risk-informed approach for shortening the separation distances for liquid hydrogen storage at fueling stations, as current efforts only examined separation distances for gaseous hydrogen. Liquid hydrogen is attractive because it takes up less space than gaseous hydrogen and allows fueling stations to accommodate larger numbers of fuel-cell electric vehicles. However, there are additional issues associated with the low temperatures required for liquid systems installed on small properties.
“We need to do more experimental and modeling work to understand and evaluate the science and physics of liquid hydrogen,” says Chris. “By evaluating the risks quantitatively, we believe we can shorten the separation distances required in the code for liquid hydrogen just as we did with gaseous hydrogen. That could then lead to even more fueling stations that can accept hydrogen and support the continued growth of the fuel-cell electric vehicle market.”
-- Mike Janes
An ‘apatite’ for radionuclides: Permeable reactive barriers may be deployed at Fukushima
A technology developed at Sandia to protect groundwater in sites that have been contaminated with radionuclides is being evaluated for use at the Fukushima site in Japan to prevent radioactive strontium from reaching the ocean.
Under a program funded by Tokyo Electric Power Co. (TEPCO), Sandia, Pacific Northwest National Laboratory (PNNL), and Savannah River National Laboratory will provide recommendations for permeable reactive barrier design, implementation, and monitoring at the Fukushima site in an effort to prevent contamination of groundwater.
Barrier technology at Hanford
The same technology, a calcium apatite-based permeable barrier has been in use at the DOE Hanford site for eight years, says its inventor, Sandia chemical engineer Robert Moore (6915). The Hanford barrier is sequestering mobile strontium-90 that threatens the Columbia River, a major source of water for three states.
Hanford, a decommissioned World War II-era nuclear production complex in southeastern Washington State, is contaminated from materials left over from reactor operations and decommissioning activities.
Jim Szecsody, a geochemist at PNNL, says PNNL contacted Robert in 2003 about his patented technology, wondering if it could work at Hanford.
“Before the barrier could be used, we had to figure out how to pump a solution to precipitate apatite without ‘flushing’ the mobile strontium-90 and making it more mobile,” Szecsody says.
A collaboration between Sandia and PNNL tested the calcium apatite barrier using small and then scaled-up lab experiments that looked at reaction rates and pumping rates, intended to customize the geochemistry and delivery for the Hanford site, using some of the calcium available in the subsurface sediments and less injected calcium, which resulted in less flushing of the strontium-90.
“In some ways, it’s like growing crops. You need to know what’s there before you can figure out what nutrients you need to add,” Szecsody says.
The customized barrier was then field-tested by Fluor, the prime contractor for cleanup of the Central Plateau at the Hanford Site. From 2005 to 2011 the barrier was placed along a 300-foot-long section of Columbia River shoreline in Washington state.
The results were impressive: After six years, monitoring wells placed between the barrier and the Columbia River indicated that the barrier sequestered more than 95 percent of the strontium, preventing it from traveling into the river.
The initial work was so successful that CH2M HILL Plateau Remediation Company began expansion of the barrier in 2012 to protect 2,500 feet of Columbia River shoreline, and additional barriers are being considered at Hanford.
How the barriers work
Robert says the barrier can be formed in a few ways, depending on the specific types of contamination and the characteristics of the soil. One way is by pumping an aqueous solution containing a calcium citrate compound and sodium phosphate into the ground.
As groundwater passes through the barrier, nano-size apatite crystals bind to contaminants and immobilize them, allowing groundwater to flow through the barrier, eliminating the need for groundwater treatment, Robert says.
“The indigenous soil bacteria biodegrade the calcium citrate compound, leaving calcium apatite, an insoluble and stable mineral which can immobilize contaminants,” Robert says.
The barrier approach shows several positive advantages over alternative technologies:
- The solution flows into areas with highest soil porosity, so more apatite forms in areas with more groundwater, where greater protection would be needed.
- Leaving the contaminants fixed underground eliminates the costly process of removing contaminated soil and disposing of it as hazardous waste.
- Once in place underground, the barrier requires no ongoing maintenance, eliminating operational expenses for equipment such as ion exchange and filters, though it can be monitored with optional equipment.
- Because there is less contamination exposed above ground, workers are not exposed to contaminants as they would be using conventional trenching and backfilling with a reactive media.
“The barriers work well in locations where conventional solutions are not feasible or are excessively expensive, such as deep underground and under large obstacles such as buried waste tanks and piping systems where conventional construction techniques are not possible,” says Robert.
For example, one such chemical reactive barrier is a 2,300-foot-wide chemically reduced barrier for chromate remediation at the Hanford 100D area. This technology was developed at PNNL and then upscaled to full-scale field tests. After 15 years, this 100D reactive barrier is still 80 percent to 90 percent effective. This barrier technology was then implemented at sites in other states.
Other types of remediation methods are expensive, can only be used in certain locations, and expose workers to contaminated soils and construction hazards. One commonly used current method involves excavating a trench perpendicular to the contaminated groundwater flow-path and then backfilling with the reactive media. Another method is high-pressure injection to force the reactive media into the soil. Both methods are disruptive and, in some instances, have actually altered the site geohydrology, resulting in a portion or all of the contaminated groundwater flowing around the barrier instead of through it.
Immobilizing contamination from Hanford’s tank farms
Sandia has signed a Government Use agreement with CH2M HILL to allow Washington River Protection Solutions (WRPS), a contractor charged with cleanup of Hanford’s tank farms, to use a tin(II) apatite barrier to help prevent the radionuclide technetium, a highly mobile radionuclide with a long half-life, from travelling into the environment.
The Hanford site has 177 underground storage tanks in its “tank farm,” many of which date back to World War II. Because many of the tanks have outlived their anticipated design life, some are leaking.
Some tanks are being grouted to prevent the movement of materials out of the tanks. Unfortunately, the grouting doesn’t prevent technetium from moving out of the tanks since few things bind to technetium.
“Technetium is a difficult problem to solve. It’s a long-term dose driver at the Hanford site because it has long half-life. It’s a challenge because technetium binds to nothing we’ve tried, except this barrier,” says Robert.
Robert says a stannous-treated tin(II)apatite barrier, which is particularly effective for technetium, might be used.
“With some research to determine soil pH, amounts of free calcium, and soil porosity, the same technology could be used in areas around Hanford’s tank farms to contain radionuclides from tank leaks,” Robert says.
So far, the results are promising.
“In tests performed recently by WRPS the a stannous-treated tin(II)apatite bound the technetium into the apatite crystal lattice immobilizing the radionuclide even when subjected to leach testing,” says WRPS senior scientist Jim Duncan.
Other potential uses
Barriers can also be used with a wide variety of radionuclides and heavy metals.
“The method could be used prophylactically to protect groundwater during drilling, hydraulic fracturing operations, or other excavation activities where the potential exists for groundwater contamination,” says Robert.
Thousands of sites throughout the world are contaminated with radionuclides, heavy metals, and natural contaminants that threaten groundwater, surface water, and food supplies.
A 2012 report from the US Geological Survey says approximately 50 percent of the population relies on groundwater as their primary drinking water supply. It is therefore of vital importance to keep contaminants out of groundwater.
One unanswered question is the longevity of the barrier; research is ongoing to assess how long contamination remains in the bound form.
“So far, the results indicate that the contaminants will remain sequestered for a long time,” says Robert.
The work was funded under Sandia’s Laboratory Directed Research & Development (LDRD) program.-- Stephanie Holinka