In a hole in the center of this system is placed a subcritical sphere of fissionable material.

在这个系统的中心圆洞中放置一枚次临界的球形可裂变物质。

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The reaction is slowed by a combination of depletion of the fissionable material and expansion of the core.

由于裂变物质的耗尽以及由于核心的膨胀，才使反应减慢下来。

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The ingenuity of our scientists will provide special safe conditions under which such a bank of fissionable material can be made essentially immune to surprise seizure.

我们科学家的这种独创性将供应特殊的安全的条件，在裂变物质储藏所能够从本质上获得免疫的就被奇袭没收。

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It is fissionable material and small tactical warheads that are in danger of being stolen or sold, not the well-guarded strategic systems.

CENTERFORSECURITYPOLICY: Center for Security Policy | Bear over the Barrel��: Putin��s Threats re: U.S. Missile Defenses are Strategically Hollow, Economically Unaffordable

Second, although Russian strategic warheads are well-guarded, large numbers of small tactical nuclear warheads and huge amounts of fissionable material usable for bombs are not, and these create a serious stockpile security problem.

CENTERFORSECURITYPOLICY: Center For Security Policy