Program to update W76 warhead is biggest weapon project in 20 years

In late September, when Labs Director Tom Hunter signed the W76-1 Final Weapon Development Report, it represented Sandia’s certification of the US Navy’s strategic warhead. Los Alamos National Laboratory (LANL) Director Michael Anastasio also signed the report along with a yield certification letter, denoting LANL certification of the W76-1.

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.”