By Will Keener
Filling up the family car with gasoline, we take some things for granted. The official labels that reveal the octane rating of the gas, inspection stickers, the location of the pumps relative to streets, buildings, tanks. Unseen codes and standards envelop the filling station to provide customers with an administrative layer of safety most of us rarely consider.
For the hydrogen station of the future, similar codes and standards are being developed today, and Sandia is playing a key role.
Within DOE, these standards are one of several elements of the hydrogen economy being addressed by the national laboratories system, says Chris Moen, manager of Sandia/California’s Thermal/Fluid Science and Engineering Dept. 8757.
“In the safety, codes, and standards program element there is a harmonization element and R&D part. We are responsible for the R&D part, which I think is the fun stuff,” says Chris.
Within the complex, the National Renewable Energy Lab is addressing domestic safety standards, and Los Alamos is working on international standards. “These areas require a lot of consensus building,” says Chris. “At Sandia, we are trying to provide technical information to support the codes and standards organizations.”
Ultimately the goal is to have a set of acceptable domestic standards that are harmonized with international standards as much as possible.
Sandia is addressing the science and technology that goes into understanding unintended releases of hydrogen in the cases of large high-pressure (momentum-driven) or small (buoyancy-dominated) releases. The Labs also have an eye on the development of sensors for leak detection and other mitigation strategies. This year, Sandia will pursue codes and standards research with a budget of about $1.5 million.
“We are trying to work with the people who are writing the codes and standards so they have good information,” says Chris. Some industrial standards already exist for hydrogen. “If you want to build a refinery, there are codes and standards that tell you how far to situate a tank from other buildings and things like that,” says Chris. But there are no agreed-upon standards and codes for general public interaction with hydrogen on a daily basis, as will be likely in the envisioned hydrogen economy of the future.
Stakeholders for Sandia’s research are code and standards development organizations, which are working to write technically sound code. Other stakeholders are original equipment manufacturers (OEMs) and the energy companies, which tend to look at the standards as enabling product commercialization. Within DOE’s FreedomCAR and Fuels initiative — to develop pollution- and petroleum-free vehicles — technical teams have been established with industry advisors. “Everything we do gets scrutinized by the OEMs and energy companies, so that we get good feedback about what’s important to them,” says Chris.
Sandia researchers started in 2003 with studies of unintended releases of momentum-driven gas, or jet-type releases. Experiments at 2,500 and 6,000 psi at the SRI burn site east of Livermore, Calif., were conducted under contract to measure the jet characteristics. “One of high-priority items for us was what separation distances are needed for siting equipment at refueling stations,” says Chris. “There was a lack of information for hydrogen in jets, where there may be a fire hazard.”
Sandia worked with the International Code Council as experiments were conducted. Labs researchers also talked to the National Fire Protection Association and presented the data to it.
The next effort involves a transition to small-scale releases, like hairline cracks, O-rings, fittings, and fixtures. These leaks create gases that are not momentum-dominated but buoyant, says Chris. Sandia will do these experiments at the Combustion Research Facility (CRF), with Bob Schefer (8367) as principal investigator. Bill Houf (8757) will generate engineering models based on the data. The engineering models are used to rapidly quantify the consequences of unintended releases.
Sandia is also contributing to future standards by analyzing how metallic materials interact with hydrogen. Generally, molecular hydrogen dissociates on a metal surface and diffuses into the material, affecting the properties. Often, these effects include making metal more brittle and reducing its strength.
Sandia has created a technical reference on these compatibility issues based on the Labs’ 40 years of experience in storing hydrogen in metal containers. The reference also uses other peer-reviewed published literature. Staff metallurgists Brian Somerday and Chris San Marchi (both 8772) are writing the reference guide. They are describing compatibility issues for various grades of steel and other materials in a web document, http://www.ca.sandia.gov/matlsTechRef, available to groups writing the codes involving structural design for hydrogen use. “Everything we learned about hydrogen compatibility in Defense Programs can apply to this project,” says Chris.
Sandia has worked with the American Society of Mechanical Engineers to develop codes for pressure vessels for different material classes and effects, as well as with CSA. “We want to understand how hydrogen works with other materials,” says Chris.
Sandia can do even more, given the opportunity. One area where the Labs can contribute is in materials testing where no information currently exists. Pressures of 10,000 to 15,000 psi are expected in hydrogen refueling; this means pressurized atomic hydrogen will be reacting with the container metals. “We have some unique equipment here we are using in Defense Programs that we also use to develop data for the codes and standards project,” says Chris. “We can test static crack growth at pressures up to 30,000 psi to understand some of these interactions.” Testing at pressure and with cyclic loads is another option Sandia researchers could explore. -- Will Keener
By Will Keener
Sandia doesn’t write codes and standards for the coming hydrogen economy, but if Carmen Mendez has anything to say about it, the Labs will help make those codes better. She and her colleagues will do it using a systematic risk assessment process to address the challenges posed by the new fuel.
“We need to develop a scientific basis for hydrogen risk quantification and use a risk-informed strategy to provide recommendations to code writers,” says Carmen (6861). “We are trying to demonstrate to the codes and standards community that risk-informed decisions can be made.”
“Part of the challenge for us is to get something that the codes and standards writers will treat as realistic,” says Mark Allen, manager of Sandia’s Risk and Reliability Dept. 6861. “It must be a practical alternative if we want our risk approach to influence designs. The codes and standards community doesn’t have to listen, but they will if we have technical answers to their questions.”
“We hypothesize what can cause an accident at the scale of a hydrogen refueling station, but we need to identify the risk drivers,” says Chris Moen (8775), co-manager of the hydrogen codes and standards project at Sandia. “We can identify, quantify, and prioritize the risk drivers using the risk assessment approach. Then we can also address the mitigation strategies for those most likely events.”
“When people go to a gas station, they normally don’t think about the risks,” says Carmen. “However, others have thought of those risks and have put safety measures in effect to protect product users. We want hydrogen to be at least as safe as fueling products that are available now. We want to get to that level with hydrogen refueling. But, instead of doing it as we go along learning from experience, we are trying to understand how to reduce risks before they occur.”
Carmen, who joined Sandia last fall, receives input from an industrial working group, formed by representatives from energy companies and auto manufacturers that provide guidance to DOE on matters of technical interest. Additional industry experts have been brought together to help think through the assumptions being made in creating a risk approach, provide data, and ultimately put the assessment into practice.
The first steps involve studying failure modes (with information provided by industry), understanding the behaviors of the users, and gathering data on the materials and components involved. Data gathering is done in a variety of ways, including comparisons with other available products, such as compressed natural gas, liquefied natural gas, propane, and butane. Because there is not always enough scientific literature on these products, other means are used. “There is always some uncertainty in risk assessment, so we use expert judgment and other quantification alternatives,” says Carmen.
Another source is data from Sandia’s experimental element of the codes and standards project (see “Setting the standards for hydrogen” on page one). “It really comes down to looking at everything that’s available,” says Carmen. -- By Will Keener
A new Integrated Stockpile Evaluation (ISE) program rolling out in May involves multiple cross-disciplinary Sandia teams working together to better ensure the safety, security, and reliability of the country’s nuclear weapons stockpile. The approach will integrate several different weapons evaluation activities into one lean, more cost-effective evaluation program.
“We have many individuals and teams working very hard to design and develop the future evaluation program,” says Dave Corbett, director of Stockpile Resource Center 2900 and chair of the ISE Director Steering Committee. “Teams are working on individual elements of the program — all striving to examine every aspect of current ways of evaluating the stockpile and then redesigning the program to meet the needs for future stockpile evaluation.”
The teams consist of representatives from across the nuclear weapons program, including systems, components, surveillance, assessment, and engineering science organizations.
Every year the three nuclear weapons laboratories assess the state of the stockpile, and the laboratory directors report their conclusions from this assessment to the Secretary of Energy. ISE will help strengthen confidence in this assessment.
The new program is an important Nuclear Weapon Strategic Management Unit (NWSMU) transformation initiative, one that Steve Rottler, VP of Weapon Engineering and Product Realization, calls essential.
“The transformation of stockpile evaluation is imperative, as is the transformation of the stockpile itself,” Steve says. “The current approach used for stockpile evaluation is no longer sustainable technically or financially.”
He adds, “Many studies and assessments have recommended improvements in our stockpile evaluation approach. One example is the 150-Day Study, which was published in January 2001. Through the Integrated Stockpile Evaluation effort, we have revalidated and updated the drivers for change in this area, and now it is time to act — with the goal of achieving a rapid transformation of the way that we evaluate the stockpile.”
The transformation of stockpile evaluation will address the current stockpile and the Life Extension Programs and be extendable to accommodate future stockpile characteristics.
Evaluation to evolve over life cycle
In the past, the core part of stockpile evaluation was pulling 11 random weapons from each of the nine enduring stockpile systems and testing them both at Sandia’s Weapons Evaluation Test Laboratory (WETL) at the Pantex Plant near Amarillo and in the flight test program performed jointly with the Department of Defense. The purpose of this testing was often described as “detecting defects.”
The transformed approach to stockpile evaluation recognizes the need for evaluation to evolve over the weapon system life cycle. Early on, the focus is on detecting unanticipated design or production defects. However, once enough data is accumulated to provide reasonable confidence that any remaining defects are very small in number, the focus of the program can be shifted to look for trends, aging, and degradation.
Most weapons in the current stockpile range from between 15 to 40 years old and are ready for a more focused evaluation program to fill knowledge gaps, quantify margins, and monitor for aging.
Sheryl Hingorani, manager of Integrated Stockpile Evaluation Dept. 2901 and head of the ISE implementation program, says that revising Sandia’s sampling rationale is the most significant initial change.
High confidence in previous results
“We have high confidence that we have found most of the prominent defects in the existing weapons systems through the previous years of testing,” Sheryl says. “The new approach will be driven by a strong technical requirements basis, where the data needs drive the sample requirements. We call this a ‘bottoms-up approach.’ And, we will be developing science-based tools, such as modern computational models and simulation, and new diagnostics for fundamental characterization of aging to gain a predictive understanding of the state of health of the stockpile.”
Sheryl anticipates that ISE will allow Sandia to gain more knowledge from each stockpile sample, allowing a decrease in the overall quantity of field return samples required. It will also improve cost effectiveness. This should be a result of integrated policies and processes, unambiguous roles and responsibilities, strong technical requirements for the evaluation programs, improved data analysis and information systems, efficient communications, and targeted research and development efforts.
There’s one other plus of ISE, says Dave. Staff working in Sandia’s nuclear weapons program will be challenged by many aspects of the new ISE program.
“It will create new technically challenging opportunities for our staff, particularly in areas of component evaluation and in developing new tools and capabilities for monitoring performance trends and the effects of aging,” Dave says. “We are already creating new and expanded capabilities, including the addition of new test equipment at WETL. “
He adds, “The transformation of stockpile evaluation extends beyond Sandia and involves partnerships with our sister labs and the plants. We will continue to be challenged over the next several years to fully transform the program with support needed from across the complex. Expanded efforts to change current processes, requirements, and supporting infrastructure will be needed to achieve transformation.”