Of all the problems facing the nuclear weapons program and nuclear weapons complex over the past several decades, few, if any, have been as vexing as pit production. A "pit" is a hollow plutonium shell that is imploded, creating an explosion that triggers the rest of the weapon. The Rocky Flats Plant (CO) manufactured pits on a large scale during the Cold War until production halted in 1989. It took until FY2007 for the United States to produce even a small quantity, 11 pits per year (ppy), for the stockpile. Yet the Department of Defense (DOD) calls for a capacity to produce 30 ppy by 2021 as an interim goal and 50 to 80 ppy by around 2030. At issue is how to reach the higher capacity. This report is intended primarily for Members and staff with a direct interest in pit issues, including Members who will be making decisions on pit projects that could total several billion dollars. Since the issues are complicated, this report contains technical and regulatory details that are needed to understand the advantages, drawbacks, and uncertainties of various options. It may also be of value for Members and staff with an interest in nuclear weapons, stockpile stewardship, and nuclear policy more broadly. This report begins with a description of plutonium, pits, and pit factory problems. It next considers several pit production options. It notes studies that could provide information to assist Congress in choosing among options, and concludes with several observations. There are several Appendixes, including a list of abbreviations. The pit issue is important because of the relationship between pit production infrastructure and national goals, as shown in Figure 1 . National goals include minimizing the risk of nuclear war and, for the longer term, "the peace and security of a world without nuclear weapons," as President Obama declared in his 2009 Prague speech. The Nuclear Posture Review sets out policy objectives, such as "preventing nuclear proliferation," "reducing the role of U.S. nuclear weapons in U.S. national security strategy," "maintaining strategic deterrence and stability at reduced nuclear force levels," "strengthening regional deterrence," and "sustaining a safe, secure, and effective nuclear arsenal." Various strategies, such as deterrence, counterproliferation, and arms control, seek to implement policy. In turn, delivery systems, such as heavy bombers and long-range ballistic missiles, are one means of implementing strategy. Nuclear weapons (a term used in this report to refer to nuclear bombs and warheads) arm delivery systems. The Nuclear Posture Review declares, "The United States will not develop new nuclear warheads." Accordingly, the United States will retain the weapons in its arsenal for the foreseeable future. Yet weapons deteriorate over time. Extending the service life of existing weapons requires replacing or modifying some components. While "life extension programs" (LEPs) for some weapons can use existing pits, DOD and the Department of Energy (DOE) state that LEPs for other weapons will require newly manufactured pits. The current infrastructure cannot produce pits at the capacity DOD requires, and many efforts stretching back to the late 1980s to produce pits have been canceled or have otherwise foundered. A concern is that if a type of nuclear weapon could no longer perform satisfactorily, an inability to make new pits in the quantities required so the weapons could be replaced could lead to that weapon type being removed from service. That, in turn, would leave missiles and bombers without those weapons, which would undermine strategies, the policies they seek to implement, and the ability to attain national goals. This section begins by discussing plutonium, pits, pit production, programs to extend the service life of nuclear weapons, and production capacity required. It next turns to current plutonium facilities and provides a brief history of unsuccessful efforts to build a facility to produce pits on a scale larger than about 10 per year. It concludes by presenting important regulatory terms. Plutonium is a radioactive metal that is 1.75 times more dense than lead. It has several undesirable characteristics, and is difficult to work with. According to Siegfried Hecker, a plutonium metallurgist and a former director of Los Alamos National Laboratory (LANL), Plutonium is an element at odds with itself—with little provocation, it can change its density by as much as 25 percent; it can be as brittle as glass or as malleable as aluminum; it expands when it solidifies; and its freshly-machined silvery surface will tarnish in minutes, producing nearly every color in the rainbow. To make matters even more complex, plutonium ages from the outside in and from the inside out. It reacts vigorously with its environment—particularly with oxygen, hydrogen, and water—thereby, degrading its properties from the surface to the interior over time. In addition, plutonium's continuous radioactive decay causes self-irradiation damage that can fundamentally change its properties over time. To make plutonium more stable, it is typically alloyed with other materials, such as gallium. Handling and safeguarding plutonium poses significant risks. Plutonium is hazardous: if minute particles are inhaled and lodge in the lungs, their radiation (in the form of alpha particles) can cause lung cancer. In addition, terrorists might be able to build an improvised nuclear device if they were to obtain enough plutonium, so facilities holding more than a small quantity of certain plutonium isotopes require extremely high security. Plutonium does not occur in nature except in trace amounts. It is manufactured by exposing uranium fuel rods to neutrons in nuclear reactors, and then using chemical processes to separate it from other elements in the fuel rods. The result is a mix of plutonium isotopes. The isotope desired for nuclear weapons is plutonium-239, which fissions readily when struck by slow or fast neutrons. Weapons-grade plutonium (WGPu) consists mainly of plutonium-239 and a small fraction of other plutonium isotopes. (Note: When an isotope of plutonium is mentioned, such as plutonium-239, it is abbreviated using its chemical symbol, e.g., Pu-239.) A pit is the trigger for detonating a thermonuclear weapon, or hydrogen bomb. It is a hollow shell of plutonium and other materials surrounded by chemical explosives. When the explosives detonate, they create an inward-moving pressure wave (an implosion wave) that compresses the plutonium enough to make it supercritical. It undergoes a runaway fission chain reaction, that is, an explosion. Various means are used to augment the explosion. This part of the weapon is called the primary stage. The weapon is designed so that energy from the primary stage explosion implodes the weapon's secondary stage, in which nuclear fission and fusion release most of the weapon's total explosive force. While some pits in older weapons were made of uranium and plutonium ("composite pits"), modern pits use only plutonium because much less of that material is required to generate a given explosive force, permitting nuclear weapons to be smaller and lighter. Reducing the size and weight of weapons was important during the Cold War to maximize the number of weapons that could be fitted on a missile and to maximize the explosive force of a weapon of given weight. All nuclear weapons in the current U.S. nuclear stockpile were designed and tested during the Cold War; all but a handful were built during that time. Because plutonium decays radioactively, there was concern that pits could deteriorate in ways that would cause them to fail. However, several studies have projected increased pit life. In 2003, pit life was thought to be 45-60 years; a 2007 study placed life for most pits at over 100 years; and a 2012 Livermore study placed the figure at 150 years. A 2013 Los Alamos study raised uncertainties on the latter claim: Since 2006, plutonium aging work has continued at a low level. That research does not indicate any [e]ffects that would preclude the possibility of pit reuse. However, additional studies that had been planned were never undertaken, leaving some aging questions unanswered for the range of plutonium alloys in the stockpile, and for the potential applications of pit reuse now under consideration. Penrose Albright, then Director of Lawrence Livermore National Laboratory, testified in 2013, And there has been a pretty concerted effort at both Los Alamos and at Livermore over the last decade or more that has been looking at plutonium aging, and we actually have samples that we keep in our laboratory—and Los Alamos does the same—that are 40, 50, 60 years old that so far show no—that support the conclusions that the last decade of study has implied, which is that these pits are good for many, many more decades to come. Longer pit life means that a stockpile of given size can be maintained with a lower pit production rate and opens the possibility of reusing retired pits. Pits must be made to exacting standards in order to function as designed. This requires precision in fabricating them and in supporting tasks. As plutonium decays, it produces other elements, such as americium. That radioactive element increases the radiation dose to workers and is an impurity to weapons-grade plutonium. Plutonium scrap, such as from old pits or from faulty castings, may pick up other impurities. Accordingly, plutonium must be purified for use in new pits. This may involve nitric acid processing, high-temperature processing, electrorefining, and other processes. Such processes result in a substantial stream of waste contaminated with radioactive material, acid, and other harmful substances. This waste must be processed and disposed of; waste processing requires a substantial infrastructure. Pits are fabricated as "hemishells" (half-pits) that are welded together. Rocky Flats Plant made pits using a wrought process, in which sheets of plutonium were run through rollers to attain the desired thickness, then punched into a die.