The chaos in Pakistan has prompted worry about the security of that country’s nuclear arsenal. Will its estimated 50 to 100 nuclear warheads remain in safe hands? But even without that concern, we should ask, and worry about, another pertinent question: how safe and reliable are Pakistan’s nukes? The same question should be asked about North Korean nuclear weapons, of which there are probably less than ten.

Why worry? One answer comes from what we know about our own nuclear arsenal. The Congressional Research Service recently produced a study of ongoing efforts to insure that U.S. nuclear weapons remain safe and reliable. It takes note of a 1983 government report that pointed out that nuclear warheads “contain thousands of parts that deteriorate at different rates. Some parts and materials have well-known limits on service life, while the service life of other parts may be unknown or revealed only by multiple inspections of a warhead type over time.”

Among other things, the report continued, “certain chemically reactive materials” — including uranium, plutonium, high explosives, and plastics — “are inherently required in nuclear weapons.” Both plutonium and uranium “are subject to corrosion” and “[p]lastic-bonded high explosives and other plastics tend to decompose over extended periods of time. . . . portions of materials can dissociate into simpler substances. Vapors given off by one material can migrate to another region of the weapon and react chemically there. . . . Materials in the warhead electrical systems . . . can produce effluents that can migrate to regions in the nuclear explosive portion of the weapon. . . . The characteristics of high explosives can change with time. . . . Vital electrical components can change in character.”

This alarming picture was countered in a 1987 government report, which noted that progress in nuclear engineering had dealt with many of these problems, which in any case may have been overstated.

Whether that is true or not is irrelevant. For our purposes, the point is that the United States is by any standard a wealthy country. In comparison with Pakistan and North Korea it is off the charts. We have had the resources to deal with whatever problems have cropped up inside our warheads and we devote enormous resources, including assigning a huge number of well-compensated scientists and engineers, to this task.

Do Pakistan and North Korea? The answer, of course, is no; these countries are basket cases. To maintain their warheads both nations do what the United States last did in 1992: test them by setting them off underground. North Korea’s first such test late last year was a partial dud: it did not explode but only fizzled. Pakistan last tested a device in 1998.

But testing only ensures reliability; that is, the assurance that when you press the button the device will explode. Safety, the assurance that when you don’t press the button the device will not leak or fizzle or explode, is something else.