Scientific American: the media told how nuclear weapons are made in the United States
Everyone has become so used to nuclear weapons that they began to forget about them, writes Scientific American. Meanwhile, it still plays an important deterrent role. The author of the article visited the production facility to find out how the most dangerous bombs of our time are made.
A bowling ball-sized sphere is inserted into every American nuclear warhead. It is made of perhaps the most unusual chemical element that can only be found on our planet. This sphere is called the "plutonium core" and represents the core of a nuclear bomb. Charges from a conventional explosive are installed around the plutonium core: after the explosion of these warheads, detonation occurs, resulting in compression of the plutonium sphere and a fission reaction is triggered. Further, due to radiation, the material heats up around the core. It is the fission reaction that triggers the processes that make this weapon called nuclear.
In the design of the first nuclear bombs, such as those dropped by the United States on Japan during World War II, everything ended at the stage of fission of plutonium or uranium, followed by the release of deadly energy. However, in modern nuclear warheads, the plutonium fission reaction triggers a second, more powerful thermonuclear reaction, resulting in the synthesis of hydrogen atoms and even more energy is released. However, since the late 1980s, plutonium cores have largely been out of production in the United States.
However, the situation is changing now. Currently, the United States is updating its nuclear arsenal, upgrading old weapons and creating new ones. In particular, missile weapons are being upgraded. In addition, new types of weapons are being developed, adjustments are being made to existing products and new plutonium cores. To improve the cores, the US National Nuclear Safety Administration (NNSA) has adopted a rather controversial plan providing for the annual production of fifty new plutonium cores at a facility in Savannah River, South Carolina, and thirty more cores at the Los Alamos National Laboratory in New Mexico (by the way, in the very laboratory where the world's first atomic bomb was created). The plutonium cores created at Savannah River are designed for the W87-1 warhead, which will be used in a new intercontinental ballistic missile codenamed Sentinel ("Sentinel"). After that, cores will be made for other designs of nuclear warheads.
Some people think that there is no need to do all this: There are disagreements on the issue of the production of plutonium cores, because the creation of such products is an expensive pleasure, moreover, it also involves potential risks. In addition, the cores that are stored in our warehouses may well serve us well for some time. In general, plutonium physics is a complicated thing, so no one knows exactly when the previously made plutonium cores will expire. The technology of their manufacture and the principles of operation are a state secret in the United States. But now, in June 2023, the leadership of Los Alamos decided for the first time in many years to invite a group of journalists to take a tour of this closed facility.
We were there at the very time when the Los Alamos National Laboratory and the National Nuclear Safety Administration of the United States began to agitate with all their might in favor of resuming work on plutonium cores: to do this, they will have to win over American taxpayers and attract about 2,500 new employees to work. These works are partly fraught with a high degree of risk, they require experience that our country has largely lost since the end of the cold war — at that time it seemed to many that all countries of the world were moving towards disarmament, it seemed to many that the skills needed to resume nuclear weapons programs, they are unlikely to be useful ever. However, everything turned out exactly the opposite: and now we see how China is rapidly increasing its nuclear arsenal, and Russia, which is at war with Ukraine, boasts of missile tests and modernization of its own nuclear weapons. The United States is doing the same thing. The current world order seems more fragile than ever; now nuclear weapons have once again received increased attention — and this threatens us with the fact that an arms race will re-emerge in the twenty-first century. And as a result, we will have to live in a fragile, fragile world that can be preserved (or maybe not) only with the help of nuclear weapons.
Most of the work on the production of plutonium in Los Alamos is carried out in the PF-4 building, located south of the city, in the Tech Area 55 laboratory complex ("Technical Area 55"). This is one of the most protected units of the laboratory. Before the tour, we were told to carefully examine our hands, forearms and ankles for abrasions and scratches, because all these skin lesions can be exposed to radioactive contamination. Anyone who had at least some abrasions on their skin was obliged to put a patch on them. Indoors, this request is duplicated by a sign that instructs everyone who enters to "protect skin damage."
On the territory of the complex, we plunge into the atmosphere of friendliness. However, at the same time, people here are very serious and focused. Visitors are greeted by a bright wooden signboard fixed outside the building. And so we enter. We are greeted by guards, they are armed with long-barreled weapons. The entrance is somewhat similar to a checkpoint somewhere on transport - when we pass through it into the building, we are closely watched by security. Phones, cameras, recording devices, as well as objects made of metal, nylon and polyester were seized from us. From now on and throughout our stay, we will be accompanied by a security service.
After passing the initial inspection, we enter a special airlock: in it, on both sides of the capsule room, there are yellow-painted doors. At the same time, both doors cannot be opened at the same time — this measure is provided so that no potential radioactive pollutants enter the PF-4 housing at all. So, we pass, the alarm is silent. We wear protective clothing designed to protect us from radiation pollution. Along the way, I note that the red robes are intended for visitors who do not have access to work inside the laboratory building, and the yellow ones are for employees. We also put disposable shoe covers on top of our shoes (the guards get shoe covers with a camouflage pattern). In addition, we should all wear protective glasses, and attach a dosimeter to the damage to the forehead — it will measure radiation activity, reacting to invisible streams of particles. On the day of our tour, all work on plutonium was suspended, this was done so that no information about the technology of manufacturing plutonium cores would leak out.
The element with atomic number 94 — that is, plutonium — is rare. A small amount of plutonium is generated by dying stars when they take their last hot breaths. However, this star-produced substance had almost disappeared before the appearance of the Earth. However, our planet was able to create a small amount of its own plutonium: in the territory of present-day Gabon in Africa, algae have been accumulating natural uranium for thousands of years, that is, a kind of natural reactor worked there, so to speak, which produced four tons of plutonium. However, all this material has since fallen apart too. According to the ratio of uranium isotopes that have survived to the present day, scientists have concluded that there are natural nuclear reactions.
The plutonium used in nuclear weapons is man-made. So, in 1940, the charged particle accelerator at the University of California at Berkeley bombarded the isotope of uranium (92 protons in its nucleus) with deuterium nuclei (one proton and one neutron in the deuterium nucleus). As a result, scientists managed to obtain neptunium (93 protons in the nucleus), and it, in turn, easily disintegrated into plutonium, which has 94 protons in the nucleus — this is how one of the most effective components used in nuclear weapons was obtained. Note that it is easier and cheaper for us to produce the necessary amount of weapons—grade plutonium than enriched uranium, the second chemical element used in nuclear weapons besides plutonium to maintain a chain reaction of fission (namely, with its help, as is known, it is possible to achieve the necessary pressure and temperature at which a thermonuclear reaction is launched in the second stage a thermonuclear bomb).
Plutonium has been produced in reactors for several decades. In fact, so much has been produced that new facilities in Savannah River and Los Alamos no longer require any additional quantities of it - the current stock can be repurposed, breathing new life into it.
However, it is not at all easy to do this, since plutonium itself is a rather complex element. Joseph Martz, an employee of the Department of Materials Science and Technology at Los Alamos National Laboratory, has been studying this complex issue throughout his scientific career. Martz began working with plutonium in college in a special so-called "glove compartment" that protects the laboratory assistant from radiation. Joseph remembered for the rest of his life the moment when his hands touched the element with atomic number 94: a sample of plutonium weighing one kilogram was warm — it was felt even through thick gloves, while the glass was also heated. "I remember being a little scared,— says Martz. "I was taken aback, I even flinched."
However, over time, fear was replaced by interest in this metal. And there was something to be surprised at: under some conditions, plutonium is malleable, and under others it is fragile. Plutonium melts at a temperature of about 650 ° C. In the liquid state, it is the most viscous of all the elements: it drips very, very slowly. If you heat plutonium in a solid state, then in some cases this metal will expand, and in others it will shrink. When interacting with air, plutonium quickly changes its color — from silvery metallic to some kind of tarnished with iridescent streaks. Being in a solid state, plutonium expands like water, and its length and density change for no particular reason. And, of course, the most famous quirk of plutonium is that it is subject to radioactive decay, as a result of which this metal disappears.
It is precisely because of this property that plutonium is so dangerous. Inhaled particles of this metal disintegrate, releasing alpha particles (helium nuclei) and thereby destroying the body. The isotope plutonium-238, which is used as a source of heat and energy, but not in warheads, has its own oddities. "If you spill it on the lab floor, it will move arbitrarily," says Martz. The fact is that the force of the radioactive decay of the plutonium atom is such that it causes it to move quickly across the floor. "He can scurry anywhere," the scientist adds.
The strangeness of plutonium is due to the peculiarities of its electronic configuration. Plutonium is located in the part of the periodic table where the "5f subshell" begins to fill. This characteristic determines the behavior of plutonium, since f-electrons are located in narrow energy zones that overlap, which allows electrons to easily slip between the zones. And when this happens, Martz continues, "the behavior of these f-electrons changes dramatically." For example, if you change the temperature, some electrons will bind to neighboring atoms, forming "very complex configurations," says Martz. It follows from this that plutonium can exist in solid form in six different phases, each of which has its own crystal structure and very strange behavior.
And it took scientists decades to discover all these properties. "Today we know about the complexity and unusual properties of plutonium. However, this was not known to the scientists who participated in the Manhattan project," says Martz. For many years, these classified physicists, in fact, had no material for research at all, because in those days plutonium was obtained with great difficulty. "Almost everything was limited to theorizing. No plutonium. Chalk, blackboard, notebooks — these are, perhaps, the only improvised tools of scientists of that time," explains Alan Carr, chief specialist in the field of history from Los Alamos. The first gram of plutonium was obtained in the hills of Los Alamos in April 1944 - this substance already stumped scientists at that time. When experts received information about its properties, for example, about density, they had to observe a large variability. In the end, scientists managed to create the first hemispheres of metallic plutonium — prototypes of today's plutonium cores, the same ones — the size of a golf ball. However, when the scientists came to the laboratory the next day, intending to conduct an experiment, it suddenly turned out that the hemispheres had cracked because their properties and sizes had changed. "Everyone's mouths literally opened in amazement," says Martz.
A breakthrough in solving this mystery emerged later, in 1944, when an employee involved in the Manhattan project suggested that an alloy of plutonium with some other element could stabilize plutonium in the desired phase. However, the problem was that the scientists did not know which element to take. As stated in one of the historical documents discovered by Martz, the specialists had to use the most primitive scientific method of searching for such a substance: "We need to try everything we find in the laboratory cabinet," that's what the scientists wrote then. Eventually, gallium was found to be suitable. It is still used in plutonium cores.
Sometimes the intense joy caused by these first scientific discoveries overshadowed the main purpose of the work — the need to create a deadly superweapon. In 1945, the United States dropped a uranium bomb on Hiroshima, and then a plutonium bomb (in fact, a plutonium core around which explosives were attached), which destroyed Nagasaki. As a result, tens of thousands of people died during the bombings, and even more people died from their consequences in the future. As physicist Isidor Isaac Rabi, a former participant in the Manhattan Project, wrote with dismay and fear in his 2005 book American Prometheus, weapons of mass destruction were "the apogee of all three previous centuries of physics development."
Shortly after World War II, the production of plutonium cores was moved to a facility outside Boulder, Colorado. It was called Rocky Flats. Thousands of plutonium cores were created at this plant every year — a similar level of productivity was made possible, apparently, due to violations of environmental standards. As a result, in 1989, representatives of the federal authorities descended on the plant, and subsequently the plant was closed. "At that time, the voice of the public was not taken into account," says Bob Webster, deputy director of armaments from Los Alamos. Shortly thereafter, as a result of the announced moratorium on testing and the signed agreement, the US nuclear weapons complex underwent another phase shift. Scientists and engineers have always tested weapons in the simplest way — by conducting explosions. In case of successful tests, this product was finally accepted for production.
However, in 1992, President George H. W. Bush declared a moratorium on nuclear testing. Sig Hecker, then director of the Los Alamos National Laboratory and now a professor at Stanford University, heard this statement from the US president while in Washington, DC. "I went back to Los Alamos and told my colleagues, 'Listen up, everyone! The world has just changed radically,” recalls Hecker. From now on, it will no longer be possible to maintain our nuclear potential through nuclear tests, now we will have to rely only on physical calculations. However, this task turned out to be especially difficult in the case of plutonium cores produced several decades ago. Since plutonium was synthesized for the first time in the world only 80 years ago, experts, of course, did not have the opportunity to study exactly how its properties would change over a longer period of time.
The question of changes in the properties of the plutonium core as a result of aging of this metal remains a matter of debate, but something can already be said for sure: as the atoms of plutonium from which the core is made disintegrate, the decay products damage the crystal structure of the remaining metal, creating voids and defects in it. As a result of the decay, the core is contaminated with helium, americium, uranium and neptunium, among others. In fifty years, about 0.2 liters of helium will accumulate in one kilogram of plutonium. As the physical properties of the plutonium core change, its performance and safety under different storage conditions, including storage in containers, are questioned. Pavel Podvig, a senior researcher at the United Nations Institute for Disarmament Research (UNIDIR) and a researcher working within the framework of the Program on Science and Global Security (PSGS) at Princeton University, questioned the validity of the modernization of plutonium cores. The scientist admits: "At some point it will be safer to make new cores, rather than maintain the old weapons arsenal."
Scientists still do not know the shelf life of plutonium cores. In 2007, the JASON group (a research group of American scientists advising the US government on science and technology issues, mostly confidential), for the first time predicted that plutonium cores would last several decades longer than previously thought, and therefore no programs for their production should be adopted. However, in 2019, scientists from the JASON group changed their point of view, stating the following: "We call for the restoration of production of plutonium cores as soon as possible. At the same time, a targeted program should be adopted to study the process of studying the properties of plutonium as a result of aging of this metal." As studies conducted by the National Nuclear Safety Administration of the United States (NNSA) have shown, plutonium cores will last at least another 150 years, but deterioration in their quality characteristics can unexpectedly lead to defects. And it is quite possible that scientists will never be able to find out for sure how these defects can affect the core and how all this will affect its detonation ability, because the point of possessing nuclear weapons is never to use them.
In the meantime, it turns out that the resumption of production of plutonium cores in the United States is becoming a difficult task. Production in Los Alamos is at least a year behind schedule, and in Savannah River it is about five years behind schedule.
The Defense Nuclear Facilities Safety Board (DNFSB) and other critics have said that the PF-4 production building is not sufficiently resistant to earthquakes, which, as geologists have now learned, may well occur in the Los Alamos area. According to representatives of the DNFSB, which was expressed during last year's hearings, strong tremors and fires caused by them can lead to radioactive contamination with plutonium. Inside the PF-4 building, our tour group came across a poster dedicated to the Seismic Stability Analysis of Structures, Equipment and Risk Assessment (SAFER) used in the laboratory; according to this program, the building itself and the equipment installed inside were modernized. In 2022, the DNFSB considered this upgrade insufficient.
However, some representatives of the laboratory itself disagree with this opinion. Matt Johnson, who is responsible for the production of plutonium cores, also disagrees with him. Matt leads us through the PF-4 building. "If there's an earthquake, I'd like to be here myself," Matt says, looking at a poster dedicated to SAFER. However, other security issues have emerged recently. So, in May, the US National Nuclear Safety Administration (NNSA) published an investigation into four incidents that took place in 2021: the first incident was a safety violation, the second was an accident that resulted in contamination of the skin of three workers, and two other incidents were flooding, as a result of which water got for fissile materials. The NNSA issued its verdict: the private contractor that runs the Los Alamos National Laboratory violated safety rules, regulations, as well as management rules and quality assurance rules.
Bob Webster, who is participating in our tour — he is wearing a yellow lab coat, which all employees are required to wear — claims that the laboratory management and its employees take safety issues very seriously. However, according to Webster, certain problems will still arise. "At the lowest level, we're always going to run into some rough edges," Webster says. According to him, even if everything was going perfectly, then in this case we would still increase the security requirements — this is so that employees do not lose their vigilance. However, Webster continues, the requirements are already so high: "If the same radiation was detected somewhere in the premises, which comes from, for example, Fiesta dishes, then work would be stopped, and these rooms would be blocked."
There is one common feature for all rooms at the plutonium core production facility: a large number of glove boxes are installed everywhere in them — special containers equipped with radiation protection and designed to work with plutonium inside them. Long gloves are hermetically attached to the holes made in the glass surface of the boxes, so by sticking his hands into these gloves, the laboratory technician can touch the plutonium samples without any threat to health. The gloves themselves have a date stamped on them — this is so that employees do not forget when they should be replaced. Each of the employees wears two pairs of gloves. The glass windows of the box are bordered by some kind of metal similar to the notorious plutonium, which has the color of tarnished silver - this metal edging has smooth rounded corners that can be easily cleaned, radiation practically does not penetrate through this metal.
During the tour, we were strictly forbidden to put our notebooks on any surfaces in order to avoid potential contamination. And if, suddenly, someone drops their notebook, then the specialist responsible for radiological control must check each of the pages of the notebook with a special device before returning it. By the way, throughout the tour, this man tirelessly watched us and every time we left any room, he scanned our hands and feet with a special device in order to detect radioactive contamination.
But back to the glove boxes: in some places their windows were covered with aluminum foil — this is so that we could not see any classified materials placed there. In addition to these boxes, there is something resembling a cart in each of the rooms — it is designed to transport plutonium. In some rooms, radioactive waste has already been placed in special packaging and is waiting to be sent to storage. At the same time, information about the radiation dose is written on the floor, which can be obtained by standing next to these packaged waste. In general, we are constantly being made to understand that we are in a dangerous place.
Specialists who work with plutonium cores face these risks every day. Here are the procedures they should do: first, remove the plutonium ingot and clean it of existing defects. After that, it is necessary to divide the plutonium into pieces. Then these pieces must be combined into a single whole. Next to the place where these manipulations are carried out, we saw for the first time an employee of the fair sex who is engaged in the assembly of plutonium cores; we do not publish her first and last name for security reasons. She assembled her first plutonium core in 2013 (from 2007 to 2013, the laboratory produced only 31 cores). Today, it takes her from 30 minutes to an hour to assemble the core. "Everything is by touch," she says. She likes this job, part of which takes place in a glove box two stories high. "You feel safe in the glove box," she says.
After she or one of the other workers completes the assembly of the plutonium core, the microstructure of this product is examined and the standard tolerances are carefully checked to confirm that the core meets the specifications. If the product receives the "go—ahead" (in this case, it is stamped in the shape of a diamond), then it is sent to the Pantex nuclear weapons plant in Texas - there it will be inserted into a nuclear warhead. In the coming years, if everything goes according to plan, this process will be repeated here at least thirty times a year.
All these works on the production of plutonium cores, laced with solid investments, are carried out in the hope that the cores will never be used for their intended purpose at all. The United States, like all other nuclear powers, is stockpiling weapons for the sole purpose of carefully following a policy of deterrence. The point of this policy is as follows: the very fact that we have equivalent or even more powerful weapons will prevent other nuclear Powers from using their nuclear arsenals. In a deterrence strategy, the true purpose of plutonium cores is not to be used, but to be preserved as a threat. But for this strategy to work, our country must be potentially ready to carry out this threat.
And so we leave the PF-4 building — at the exit, permanently installed devices once again scan our arms and legs for radiation contamination. After that, in the airlock, a special device, so to speak, "sniffs" the body of each of us, trying to detect at least some traces of polluting materials emitting alpha, beta and gamma particles on it — I note, despite the fact that contamination is unlikely, we still sigh with It is a relief when we are finally allowed to go out.
And so we have returned to our former ordinary life and now we can easily shake off the memories of plutonium cores. After the Cold War, many Americans have already managed to get used to the very fact of the existence of nuclear weapons. "At some point, they began to treat him so calmly that they even somehow began to forget about him," says Sarah Robey, a specialist in the history of nuclear energy from the University of Idaho. And even the fear that a person who touched plutonium felt seemed to have dulled over time. However, now the heavy tread of the atomic age is being heard again, and we will all have to somehow deal with the growing fears generated by atomic weapons.
Author of the article: Sarah Scholes