By Bill Murphy
On Sept. 24 Sandia President and Labs Director Tom Hunter signed the W76-1 Final Weapon Development Report providing Sandia’s certification of the W76-1 warhead. Pictured with Tom (seated in the center) at the signing ceremony are, from left, Steven Barnhart (2132), Kathleen Diegert (0413), Robert Paulsen (2011), and Mark Rosenthal (2130).
The lab directors’ signatures marked the culmination of a process that began in 1998 with a joint NNSA and US Navy feasibility and cost study. The certification represents a key accomplishment in NNSA’s Life Extension Program, or LEP, which is designed to extend the life of warheads in the nation’s nuclear stockpile.
With the lab directors’ signatures, and with acceptance of the W76-1 by primary customers NNSA and the US Navy, the updated warhead will be deployed over the next several years, replacing first-generation W76 weapons.
It’s hard to overstate the significance of the W76-1 milestone, as Tom made clear in his recent all-hands meeting.
“For the first time since 1989,” Tom noted, “we certified a weapon system for the stockpile,” which allows it to go into full-scale production.
“This is a first in many years for the laboratory,” Tom said, “and it is also a very important commendation on the work of hundreds of people who worked across the laboratory to make this possible and one for which the laboratory has received a lot of recognition.”
Huge for Sandia
As weapon system integrator for the W76-1, Sandia is the design agency for the nonnuclear components of the weapon. Design efforts include systems engineering, requirements management, arming, fuzing and firing system (AF&F), instrumented and high-fidelity Joint Test Assemblies (JTAs), system components, system qualification, handling gear, trainers, and production support.
“This was huge for Sandia,” says Mark Rosenthal (2130), senior manager for Navy Strategic Weapon Systems, who has been involved in the W76-1 LEP effort since its inception. “We changed out the whole arming, fuzing, and firing [AF&F] system. This wasn’t a department accomplishment or a division accomplishment. This was a lab accomplishment.”
In fact, as Mark notes, the accomplishment reaches well beyond Sandia, reflecting the close cooperation among the labs, with Lockheed Martin Space Systems Company, and with a host of DoD partners and suppliers within the nuclear weapons complex. In addition, says Mark, “Sandia was fortunate to have engaged knowledgeable NNSA and Navy customers that set clear expectations and provided the necessary guidance to successfully execute the LEP.”
The W76-1 effort, Mark notes, called for effectively reinventing the weapon’s AF&F system, which not only controls the detonation of the warhead, but incorporates features that ensure it can only be fired under very strictly defined conditions. The AF&F system includes critical components that ensure the safety of the weapon as well as providing the detonation function at the correct fuzing height.
Sandia brings more than 40 years of experience providing the Navy and NNSA with integrated AF&F designs, says Mark, adding that the W76-1 incorporates everything the Labs has learned about AF&F systems during that time. (The arming and fuzing subsystem of the AF&F is a Navy responsibility and the firing subsystem along with its nuclear safety critical components is an NNSA responsibility. The integrated design provides packaging and performance enhancements.)
Though the W76-1 is emphatically not a new weapon system, the scope of the LEP effort was very demanding. The original W76 design, as a product of the 1970s, is built around technology of that era. The LEP program brings W76 technology into the 21st century.
Exceeding Navy requirements
“We haven’t done a project of this size in 20 years,” Mark says. And while the scope was wide-reaching, the efficiencies attained in the project set a new standard. “We designed and qualified the arming and fuzing subsystem for 30 percent of the cost of what we did for the W88,” Mark says, exceeding a 50 percent requirement and almost meeting the 25 percent goal set by the Navy at the inception of the project.
No new W76 warheads have been manufactured since the late 1980s, which, with the passage of time, has loomed as a growing concern for the Navy. With no new weapon designs on the horizon, Navy leadership determined that it needed to extend the useful life of its W76 weapons to coincide with the life-cycle of the delivery system, the Trident II (D5) missile and the Ohio-class ballistic missile submarines.
The W76-1 LEP delivers on that need. The updated weapon, while incorporating modern safety enhancements, extends the service life of the weapon from 20 to 60 years.
In replacing 1970s technology, Mark notes that several of the Labs’ unique capabilities were brought to bear.
“MESA played a big part in this,” he says. “It played a significant role in delivering rad-hardened ASICs.” (Mark is referring to the role Sandia’s Microelectronics Development Laboratory and Microsystems and Engineering Sciences Applications played in delivering radiation-hardened application-specific integrated circuits to the LEP effort.)
Strategic reentry systems like the W76-1 must survive hostile radiation environments. Sandia provides unique radiation effects expertise for developing rad-hardened technology and qualifying performance in severe radiation environments. The W76-1 capitalized on these capabilities to design the AF&F and used advanced computational tools and experimental facilities like the Annular Core Research Reactor to assess the performance in hostile radiation environments.
Physical simulation and computational simulation
The W76-1 drew on the rapid evolution over the past decade or so of NNSA’s computing capabilities.
“A significant amount of the qualification was accomplished with modeling and simulation,” says Mark. “The system was also certified by Los Alamos [National Laboratory] in the absence of underground nuclear tests.” For sake of comparison, Mark points out that five underground weapon effects tests simulating hostile radiation environments were conducted on the W88 weapon system in the 1980s.
Qualification also relied heavily on unique Sandia test facilities for simulating the environments that the W76-1 will encounter during its deployment, mission, or in an abnormal or accident environment. A number of these facilities, like the Light Initiated High Explosive and the Blast Tube, had to be reconstituted, since they were last used on the W88 program. It is noteworthy that the W76-1 was the last weapon to qualify with the Sandia Pulsed Reactor III before its decommissioning and the first system to use the new Thermal Test Complex. Extensive planning and coordination ensured that tests provided necessary data for validating computer codes. Compared to previous weapon systems, physical simulation combined with computational simulation significantly increased the W76-1 technical basis for performance qualification.
Assert, challenge, conclude
In the certification process for the W76-1, Sandia applied a critical approach Labs Director Tom Hunter has come to favor in the annual stockpile surveillance process — “assert, challenge, and conclude.”
In this process, project engineers assert that a particular requirement has been met; a Weapon Assessment Team from the Surety Assessment Center, with no vested stake in the design, examines the assertion. If and where the team finds insufficient evidence, it challenges the assertion. The process wraps up with a conclusion that either endorses the original assertion or directs that the issues raised in the challenge are properly addressed.
Even with certification, the W76-1 LEP is far from over: The challenge now moves to the production arena.
“I tell everyone production is hard, because you want the first unit to look exactly like the last unit,” Mark says. “That’s not a trivial challenge with systems of this complexity, and for most of these components, we haven’t done production in a while.”
Mark says the lessons learned in the W76-1 LEP will serve Sandia well as it continues its role as stewards of the nation’s strategic nuclear deterrent.
“We’ve laid the foundation for the B61 Life Extension Program project,” Mark says, “and that could be a more complex program even than the W76 effort was.” -- Bill Murphy
By Neal Singer
Most scientists believe that staph infections causing inflammation or worse are produced by a large community of bacterial cells signaling each other to emit toxins and biodegradatory enzymes. The signaling process is called “quorum sensing” because many bacteria — a quorum — are thought to be present to start the process.
Jeff Brinker sits next to a cell-suspension wheel that contains bacteria suspended in media. (Photo by Randy Montoya)
Contrary to this opinion, in the Nov. 22 Nature Chemical Biology journal, a research group led by Jeff Brinker (1004) has determined that the very first stage of staph infection — a bacteria’s switch from a harmless to a virulent form — can occur in a single cell independent from the behavior of other cells around it.
“The good news is that by inhibiting the single cell’s signaling molecules with a small protein, we were able to suppress any genetic reprogramming into the bacterium’s more virulent form,” says Jeff. “Our work clearly showed the strategy worked.”
While staph are often harmless bacteria that commonly live in and on the body, the Brinker group’s nonantibiotic approach may make it easier to treat staphylococci strains that have mutated to become drug resistant like the methicillin-resistant Staphylococcus aureus MRSA, control of which is a formidable problem in modern hospitals.
In the course of their experiments, the Brinker team achieved several interesting firsts.
First, they isolated Staphylococcus aureus bacteria in individual nanoscale compartments self-assembled by silica and lipids. Isolation of an individual bacterium previously had been achieved only computationally, leaving open questions of how a physically and chemically isolated bacterium would actually behave.
Second, the team demonstrated that it was the release of signaling peptides from a single cell — not a group — that acted as a trigger to reprogram that same cell so that it released toxins.
The finding challenges a generally accepted but unproven biological hypothesis that it takes a number of cells, called a quorum, to produce enough peptides to stimulate bacterial transformations. So settled is this belief that the process is referred to in technical literature as “quorum sensing.”
But the term may prove a misnomer, the result of observations made in cell cultures rather than in the body, says Jeff. Because signaling molecules diffuse away in liquid, a culture of cells would naturally require many bacteria corralled together to produce enough signaling bacteria to begin reprogramming. The situation is otherwise in nature, where even a single cell may be sufficiently isolated that its own manufactured peptides would remain in its vicinity.
“Also, it’s hard to believe that one cell’s evolution could be based on what a whole bunch of cells do,” says Jeff. “When we instead consider that an individual cell will do what’s best for it, we can more clearly understand the benefits of that cell’s behavior.”
For example, by reprogramming itself to produce toxins or enzymes, a bacterium can break out of its confinement to access external nutrients and survive longer, the Brinker group showed.
This aspect of the research has drawn favorable comment from researchers in the field.
In an email, University of Illinois professor of microbiology and immunology Mike Federle wrote to Jeff, “I am often asked when and where during the infection process quorum sensing starts. I often suggest that shortly after colonization, small numbers of cells may signal to initiate virulence factor expression, but this hypothesis is not always received well since many assume large groups need to be involved.
“Thank you for providing evidence this is not just a theoretical possibility.”
Also at the University of Illinois, Professor Linda Kenney emailed, “. . . that the term quorum sensing is actually not an accurate description of [bacterial] behavior . . . [is] likely to have significant impact on the field as well as enhance our understanding of how biofilms [the relevant bacterial lifestyle in most infections] form.”
Third, and equally startling, the Brinker group demonstrated that merely by introducing an inexpensive, very low-density lipoprotein (VLDL) to bind to the messenger peptide, they could stop the single cell from reprogramming itself.
One aspect of experimental rigor was the team’s ability to organize living cells into a nanostructured matrix. “We’ve already done this with yeast,” says Jeff. “We just extended the process to bacteria.”
By compartmentalizing the bacteria individually, the Brinker group had set the stage to determine whether a single bacterium could reprogram itself without a quorum present.
A key question was whether a cell could distinguish between peptides emitted by itself from those sent by other cells. If the specific signaling peptides were chemically the same, what would it matter which bacterium emitted it?
It turned out, says Jeff, “Peptides could bond to surface receptors on their own [generating] cell. So a single cell’s peptide molecules could activate its own genes into an expression that makes staphs virulent.”
One indication that the experiment had isolated the actual cause of the transformation was that when the number of peptides produced by a cell ultimately came to exceed the number of VLDL molecules in solution the stalled quorum-sensing procedure started up again.
The researchers also demonstrated that if more signaling molecules were added to the mix, the cell’s transformation occurred more rapidly.
A green fluorescent protein inserted in the cell’s DNA showed, in its operation, that proteins were being manufactured by the cell itself when the transformation was permitted to occur.
Among the problems remaining for researchers is to find a mechanism to locate bacteria in the body starting to reprogram and deliver the antidote in time.
The problem could be solved, suggests Jeff, by the insertion of VLDL-bearing nanospheres (another Brinker-group creation) into the bloodstream, linked to a ‘searcher’ molecule designed to find and link to suspect peptides or cells that produce them.
“Inhibiting this species-specific signaling molecule from turning on the virulence wouldn’t inhibit other bacteria,” Jeff says.
Targeting is important because the human gut contains many useful bacteria. These are often decimated by conventional antibiotics but would be spared by the Brinker group’s method.
Extending implications of the work to bacterial pathogenicity in general, Jeff says, “Our results imply that shortly after bacteria colonize the gut, respiratory tract, or other enclosed spaces, small groups of cells or even individual cells initiate an expression of virulence through use of these signaling molecules. So therapies aimed at inhibiting this behavior are promising strategies for eradication of infection at its outset.”
Jeff, a Sandia Fellow and distinguished professor of chemical engineering and molecular genetics and microbiology at UNM, performed this work with Eric Carnes and DeAnna Lopez at the UNM Department of Chemical and Nuclear Engineering (DeAnna is now a Sandia technologist), Graham Timmins at the UNM College of Pharmacy, Niles Donegan and Ambrose Cheung at Dartmouth Medical School, and Hattie Gresham at the New Mexico Veterans Administration Health Care System.
The Sandia work is supported by the DOE Basic Energy Science/Division of Materials Science and Engineering and Sandia’s Laboratory Directed Research and Development (LDRD) program. Other project work is supported by the Air Force Office of Scientific Research, the National Science Foundation, the Defense Threat Reduction Agency, and the National Institutes of Health. -- Neal Singer
The Environmental Restoration Project at Sandia completed construction of an alternative evapotranspirative cover at the Mixed Waste Landfill (MWL) in September. The 2.6-acre site is located in Tech Area 3 in the west-central part of Kirtland Air Force Base.The protective cover consists of four engineered layers, including three layers of compacted soil and a biointrusion rock barrier that will keep burrowing animals out of the former disposal areas. Together, these four layers and the native plants will control water infiltration, thus isolating the wastes from the accessible environment. Because the cover is constructed without rigid layers, it can accommodate differential subsidence, or settling, without undue impairment of its performance.
Mike Mitchell, (6765, left) and Don Schofield (4133) inspect the evapotranspirative cover of the Mixed Waste Landfill. (Photo by Randy Montoya)
The MWL was established in 1959 as a disposal area for low-level radioactive waste generated by Sandia's research facilities. Low-level radioactive waste and minor amounts of hazardous waste were disposed in the MWL from 1959 through 1988. Approximately 100,000 cubic feet of waste containing about 6,300 curies of activity (in 1989) were disposed of in the landfill. Over time, the radioactive materials in the landfill decay and become less hazardous.
The MWL has been monitored since 1969 and actively studied since 1991. An extensive investigation effort provided the technical foundation for the determination that the landfill is not expected to contaminate groundwater and does not represent an unacceptable risk to human health and the environment. After the extensive investigation, public meetings, and a public hearing, the New Mexico Environment Department (NMED) secretary issued the final order in 2005 selecting an evapotranspirative cover with a biointrusion rock barrier as the selected remedy. After a review of competitive bids, Sandia awarded the construction contract to a local small business. Cover construction was completed on schedule, near budget, and without any safety incidents.
The NMED regulates the corrective action to the MWL as well as the implementation of institutional controls and long-term monitoring and maintenance. Sandia and DOE continue to provide quarterly progress reports to the NMED. In addition, the final order requires compilation of a report that reevaluates the feasibility of excavation and analyzes the continued effectiveness of the selected remedy every five years. Construction of the MWL alternative cover will be documented in the
Corrective Measures Implementation Report that will be submitted to the NMED for approval.
According to NNSA Sandia Site Office Federal Project Director Joe Estrada, “If it had not been for the personal perseverance of the project team, this mission would have withered. Now that the remedy is in place the team is looking forward to sharing lessons learned from the project.”
The implementation of the selected remedy at the MWL is a critical step forward for the site. More than a decade of work and many personnel contributed to the success of the project. Although the cover is now constructed, monitoring work continues at the MWL.“The groundwater, soil gas, and the cover will be monitored long-term to ensure performance and the protection of human health and the environment,” says ER project task leader Mike Mitchell (6765). . -- Stephanie Holinka