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A blast in the Nevada desert

AN underground nuclear blast last week in Nevada should help give new momentum to two arms control treaties that have languished for more than a decade. It should also stimulate discussions on reducing the allowable yield of nuclear tests, with an eye toward a comprehensive test ban. Last week's shot and another scheduled for Sept. 14 in the Soviet Union are designed to demonstrate ways to verify compliance with the Threshold Test Ban Treaty of 1974 and the Peaceful Nuclear Explosions pact of 1976. The agreements place a 150-kiloton cap on the explosive yield of underground nuclear devices. Both lie unratified by the US Senate, largely because of the verification issue. Although the United States and the Soviet Union have adhered to the treaties anyway, they have been working on new verification protocols. But the talks have gotten hung up on monitoring technology. Hence an agreement signed at the May summit to conduct the joint verification experiment (JVE).

The JVE represents the first nuclear tests conducted with a scientific team from each country on the other's site. Studying the results from two measuring techniques should help settle the question of whether seismic methods or more intrusive ones are needed to verify compliance. The Soviets have long maintained that a network of instruments similar to those that measure earthquakes is adequate to verify the 1974 and '76 treaties, and even a comprehensive test ban. Such networks need not be placed right at a test site. Many US scientists agree that this technique would be effective. But the official US position insists on an on-site method that requires drilling a shaft next to the one containing the nuclear device. The shaft would hold cabling for yield-measurement equipment.

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The test will also help determine if the more intrusive method can be used without compromising the security of weapons testing programs. And the JVE should help broaden contacts between the two nations' defense establishments.

In the draft protocols, the US and the Soviets would use on-site methods, but they disagree on how frequently. The US wants to monitor all tests above 50 kilotons; if no test exceeds 50 kilotons, then the two largest tests each year would be measured. The Soviets would limit measurements to two a year on tests exceeding 50 kilotons. Negotiators are expected to meet in October to review JVE data and attempt to narrow their differences.

We hope they narrow those differences. But ratifying a pair of yellowing treaties does not constitute progress in arms control. True progress will come when each side applies what it learns from the JVE to the challenge of a comprehensive test ban.