The U.S. is successfully maintaining its nuclear arsenal with the use of powerful computer models and by carrying out sophisticated laboratory scale tests, according to a weapons expert who spent years helping to guide the effort.
Especially important are experiments using research facilities like LLNL’s National Ignition Facility, which can generate temperatures like those found in nuclear explosions, the expert said.
“We know how to indefinitely sustain the modern (nuclear weapons) stockpile without having to do nuclear testing,” said Bruce Goodwin, formerly the principal associate director in charge of LLNL’s nuclear weapons program.
Goodwin today is a senior fellow at LLNL’s Center for Global Security Research, a think tank aimed at providing back-and-forth communications between the technical community and political and military policymakers in Washington, D.C.
He spoke two weeks ago at a meeting of the Valley Study Group, reviewing the history of nuclear weapons development, with particular emphasis on miniaturization, in the years since World War II.
In doing so, he gave credit to Tom Ramos, LLNL physicist-turned-historian, who has spent the better part of the past decade compiling first a classified and then an unclassified history of LLNL’s nuclear weapons program.
Ramos’s unclassified history is now being reviewed by Cornell University Press for publication in book form within a year or two. Goodwin said he made extensive use of a prepublication text in developing his talk.
Started at Los Alamos
The U.S. nuclear weapons program famously was based on scientific and technical work done and orchestrated from a top-secret World War II site in northern New Mexico, in the tiny town of Los Alamos.
The fission bombs designed there, based on energy released when very heavy atomic nuclei are split, brought the war with Japan to an abrupt end in 1945.
Edward Teller, who would later help found LLNL, spent the war years contemplating ways to generate thermonuclear explosions, which would exploit energy released when very light atomic nuclei are fused.
Soon after the War, he suggested a way to increase the explosive power of a fission bomb by introducing a small amount of fusion fuel.
The method, called boosting, could either make a bomb more powerful or reduce the size needed to achieve a required explosive yield, Goodwin said.
In 1951, Teller and Hungarian mathematician Stanislaw Ulam published a classified seminal paper detailing the design of a far more powerful thermonuclear or hydrogen bomb, which would use the output of a fission bomb to ignite fusion fuel.
Teller is a highly controversial figure in weapons program history. Some historians have given Ulam the lion’s share of credit for the success of the design, which was tested the following year. Goodwin, however, credits Teller with the central idea, called radiation coupling, and assigns Ulam a supporting role.
Part of the controversy surrounding Teller was his advocacy of a second weapons laboratory, which was eventually established at Livermore. A number of powerful figures in Washington opposed a second lab, as did many at Los Alamos.
The call for a second laboratory was motivated in large part by the Soviet Union’s espionage-aided success in detonating its first atomic bomb much earlier than U.S. intelligence had forecast.
After then-President Harry Truman decided in favor of a second laboratory, Los Alamos accelerated its effort to design a hydrogen bomb. It carried out a proof-of-principal detonation in the Pacific in the Ivy Mike test in November 1952.
It was hardly a deliverable weapon, weighing more than 80 tons and required a separate refrigeration system, Goodwin said. “I don’t call it a weapon unless you think you can deliver a weapon via ocean liner,” he joked.
Although the new laboratory at Livermore had been open for two months when the Ivy Mike test took place, some news media gave Livermore credit for Los Alamos’s success.
At that time, Atomic Energy Commission classification rules forbade any discussion of thermonuclear weapons research, so Livermore was denied permission to correct the public record to give Los Alamos due credit.
The slight, however unintended, added to the resentment felt in New Mexico toward the second laboratory.
‘Technical Genius’ Follows Failures
In an environment of intense technical competition and resentment, then, the young Livermore laboratory was in danger of being shut down, particularly after its initial nuclear tests failed, Goodwin said.
The failed tests were based on designs generated by Edward Teller, trying out ideas he had formulated during his Los Alamos days.
With today’s knowledge and computer modeling capabilities, it is clear that some of the designs were a “really bad idea” and never could have worked, Goodwin said.
At the time, the failures raised doubts about Livermore’s capabilities and bolstered a campaign in Washington to close the new laboratory.
Fortunately for the laboratory’s future, three brilliant young scientists were then given responsibility “and their technical genius basically saved this laboratory,” Goodwin said.
They were Johnny Foster, Harold Brown and Herb York. York was already in charge of the Livermore laboratory under Lawrence’s overall direction. The two others were future directors.
The starting point for a turnaround was a revolutionary design by Foster, who “came up with an entirely new way of doing an atomic bomb.”
Foster’s design was of the first (fission) stage of a thermonuclear weapon, the stage whose energy ignites the second (fusion) stage. Foster’s design was light enough that it could literally be hand-carried to the top of a tower in Nevada, where it was tested successfully, Goodwin said.
Teller’s Surprise Promise
In 1956, the Navy organized a now-famous conference to learn whether and how thermonuclear warheads could be carried by submarines, which would be all but invulnerable to surprise attack.
The explosive yield was defined by the Navy based on the accuracy it expected from thousand-mile missiles. The missiles envisioned at the time were huge, heavy and liquid fueled, an exceptionally dangerous configuration to take to sea.
Comparing its technology to that available in 1955, Los Alamos offered a warhead that would be sixfold lighter and available by 1965. Teller, representing Livermore, then surprised everyone by promising a warhead would be thirtyfold lighter and available by 1963.
Not surprisingly, the Navy chose the Livermore design. Second (fusion) stage innovations by Harold Brown and Herb York, coupled with Foster’s lightweight first stage design, led to warheads that could be carried by compact, solid fueled Polaris missiles. These could be carried safely by submarines, invulnerable to attack beneath the vast oceans.
The first of the Polaris submarines, the George Washington, was deployed in 1960, well ahead of the schedule anticipated by Teller.
It was a breakthrough system, both in its technology and in its effect on national security. Having an invulnerable deterrent gave President John F. Kennedy the confidence to stand up to the Soviets during the 1961 Berlin crisis, according to his national security advisor, McGeorge Bundy.
Further miniaturization of nuclear weapons was driven particularly by innovations at LLNL, Goodwin said.
In fact, in order to keep the two-laboratory concept alive and promote competitive innovation in the nuclear weapons program, the Atomic Energy Commission soon assigned the W76 warhead to Los Alamos to force them to learn Livermore’s miniaturization technologies.
The importance of having two competing laboratories is generally accepted within the weapons program, but specific examples are often hard to cite because the details of weapons development are protected.
Goodwin was able to describe one case that came about following a series of nuclear weapons accidents including B-52 bomber crashes in Greenland and Spain in the 1960s and an Arkansas Titan missile silo explosion in 1980.
Although none of these produced a nuclear explosion, all were dangerous and in some cases radioactive material was spread over a wide area.
To reduce the risk of future accidents, the Air Force then asked Livermore and Los Alamos to create safer forms of the high explosive that initiates the nuclear process.
Los Alamos developed a better “insensitive high explosive,” as the product was called – an explosive that would not detonate in a hot fire, a high-speed crash or when shot repeatedly with high velocity bullets.
On the other hand, Goodwin said, this high explosive proved ineffective when tested in Los Alamos’s nuclear weapons designs. It would only work with designs that were based on the Foster technology invented at Livermore in the 1950s.
The outcome was the successful mating of technologies from the two laboratories and the ability to deploy intrinsically safe nuclear weapons.
“Without two labs, that would not have happened,” Goodwin said.
A Reliable Nuclear Arsenal
As principal associate director, Goodwin was in charge of the Laboratory’s weapons program as it made the transition from the era when nuclear weapon designs could be tested in full-scale field experiments to the present “stockpile stewardship” era.
Today, all U.S. nuclear weapons are much older than was anticipated when they were designed, but Goodwin is confident that they are being maintained reliably by weapons program scientists and engineers who have access to experimental facilities that have advanced greatly since the end of nuclear testing and the advent of the Stockpile Stewardship program.
By analogy with careful bridge designers, Goodwin said, those responsible for maintaining nuclear weapons do not need to carry out full-scale tests to know that the weapons are reliable.
A bridge designer does not test a bridge to failure, he said. Instead, the designer builds parts with safety factors that make the bridge significantly stronger than needed against the simultaneous occurrence of all known risks, from windstorms to earthquakes to corrosion to traffic overloading.
Comparable precautions make today’s nuclear stockpile reliable and safe, he said. Key issues for thermonuclear weapons are the efficiency of the first (fission) stage and the fraction of first stage that reaches the second (fusion) stage.
Goodwin believes LLNL has confirmed the second factor once and for all and is coming close to confirming the first.
He looks forward to continued progress using the National Ignition Facility, including the long-anticipated demonstration of ignition – as a step toward this confirmation.