[简答题]

All U. S. nuclear weapons production facilities are presently closed down, and if the various agreements are adhered to, those facilities will never be required except for one critical capability. All modern nuclear weapons use uranium (铀), plutonium (钚), and tritium (氚). Uranium and plutonium have very long half-lives, and there is large surplus of these materials.
Tritium, however, has a relatively short half-life of about 12.6 years, so about 5 percent of the amount on hand must be replaced each year to maintain the current inventory. (46) Because of the large retirement of nuclear weapons by the United States in compliance with early agreements and national policy, tritium from retired weapons has been used to make up that lost through natural decay. (47) However, in about 10 to 15 years, depending on future negotiations, the United States will need a guaranteed supply of tritium to maintain its stockpile at whatever level is agreed on.
In anticipation

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