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GAO-24-106740 1 (2024-02-29)

handle is hein.gao/gaopyo0001 and id is 1 raw text is: U.S. GOVERNMENT ACCOUNTABILITY OFFICE 441 G St. N.W. Washington, DC 20548 February 29, 2024 The Honorable Mike Rogers Chairman The Honorable Adam Smith Ranking Member Committee on Armed Services House of Representatives Nuclear Weapons: Information on the National Nuclear Security Administration's Research Plan for Plutonium and Pit Aging The radioactive element plutonium is a strategic material in the nation's nuclear weapon stockpile that was first made and isolated in 1940. Plutonium is used in pits, which are the central core of all nuclear weapons in the stockpile; pits are compressed or imploded with high explosives to create a nuclear explosion. Because the U.S. has not produced significant numbers of pits since 1989, most pits in the stockpile are at least 30 years old. The U.S. is reestablishing production facilities to manufacture new plutonium pits. However, as we have previously reported, the full pit production capability currently planned will not be achieved as expected by 2030.1 Production delays will create an increased reliance on existing plutonium pits in the stockpile for years to come. Moreover, since 1992, the U.S. has observed a unilateral moratorium on nuclear explosive testing. As a result, pit performance must be assessed in other ways. Scientists and other weapons experts have identified concerns that radioactive decay of plutonium in a pit, called aging, over many years may degrade a weapon's performance. For example, plutonium decay releases helium as a byproduct, which forms bubbles within the plutonium metal that can affect plutonium strength and change the way a pit compresses, among other things. Other byproducts from plutonium's radioactive decay can also affect the way a pit compresses. The concern about such changes in plutonium is that, over time, they could lead to an unacceptable yield reduction in a weapon's first stage, the primary. A plutonium pit in a weapon's primary, when imploded, must produce a sufficient yield to initiate a nuclear weapon's second stage, referred to as the secondary, to achieve the weapon's intended yield performance.2 GAO, Nuclear Weapons: NNSA Does Not Have a Comprehensive Schedule or Cost Estimate for Pit Production Capability, GAO-23-104661 (Washington, D.C.: Jan. 12, 2023). 2Most nuclear weapon systems in the U.S. stockpile are two-stage weapons. The first stage (primary) consists of a hollow pit typically made of plutonium and other materials, surrounded by explosive material. The second stage (secondary) may consist of uranium, lithium, and other materials. The primary and the secondary together, housed within a radiation case, are referred to as the weapon's explosive package. When detonated, these nuclear components produce the weapon's explosive energy, or yield. GAO-24-106740 Plutonium Pit Aging Page 1

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