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tutes a nuclear test.  If other nations chose to apply a

less restrictive definition than does the United States,

they could conduct very low-yield tests in which the

nuclear energy released was less than, for example, a

four-pound equivalent of high explosives--what the United

States refers to as hydronuclear testing.  Hydronuclear

tests can offer significant advantage to other nuclear

weapons states by helping them to improve their under-

standing of fundamental nuclear weapons physics; develop

new weapons concepts; ascertain existing weapons' reliabil-

ity; and exercise the skills of scientists, engineers, and

technicians.

Very low-yield tests would almost certainly go unde-

tected.  But, even if such tests were exposed by some

means, the nation conducting the tests could simply argue

that they are legal under the treaty.  And that nation

would have the historical CTBT negotiating record on its

side.  Drafts of the CTBT before the Clinton administra-

tion allowed for low-yield "permitted experiments."

Despite the fact that the CTBT does not define what

constitutes a nuclear test, the Clinton administration

adopted a formal, unilateral U.S. interpretation that the

test ban outlaws any tests or experiments unless they are

"zero yield."  This interpretation prevents the United

States from conducting hydronuclear experiments, which had

previously been used to assess the safety of U.S. nuclear

weapons and have played an important role in maintaining

U.S. nuclear weapons expertise and test readiness.16

Simulations cannot substitute for such low-level experi-

ments.17

In summary, the verification regime of the CTBT

increases international capabilities to detect nuclear

tests at yields higher than 1 kiloton nonevasively con-

ducted, and up to 70 kilotons evasively conducted.  This

means that militarily significant testing can be conducted

with little or no risk of detection by either the IMS sys-

tem or the current supplemental capabilities of U.S. tech-

nical means.  The verification problems associated with

the CTBT are complicated by the fact that the treaty

includes no definition of what constitutes a nuclear test.

President Clinton's Safeguards Are Insufficient

The Clinton administration recognized that the CTBT

would diminish confidence in the safety and reliability of

U.S. nuclear weapons and that the CTBT has serious verifi-