Soviets visit Nevada nuclear-test site.

Soviets visit Nevada nuclear-test site

A delegation of 20 Soviet nuclear testing experts spent this week at the Nevada facility where the United States tests its nuclear weapons. The visit was part of a bilateral effort to develop on-site systems that monitor compliance with limits on testing. This event follows a similar visit earlier this month to the Soviet testing site in Kazakhstan by a group of experts from the U.S. government.

The Soviet team is touring the facility and learning the testing procedures at the site, according to the U.S. Arms Control and Disarmament Agency in Washington, D.C. Accompanying the Soviets are many of the U.S. officials who visited the Soviet testing site.

The exchanges are aimed at removing obstacles to the ratification of the Threshold Test Ban Treaty and the Peaceful Nuclear Explosions Treaty. The treaties, which limit nuclear test yields to 150 kilotons of TNT, were signed by the Soviet Union and the United States in the mid-1970s. Although both sides have pledged to honor the agreements, neither has ratified them. In the United States, ratification requires the consent of two-thirds of the Senate.

Standing in the way of ratification has been the issue of verification: The two parties have yet to agree on a system that will ensure compliance with the testing limits. The United States has traditionally preferred a hydrodynamic system called CORRTEX for measuring the yield of an explosion, while the Soviets have favored seismic monitoring (SN: 10/26/85, p.268).

CORRTEX, which stands for Continuous Reflectometry for Radius versus Time Experiment, relies on a cable that can be placed in the same hole that contains the explosives or in a nearby hole. As shock waves from the explosion pass through the cable, they affect an electrical pulse that travels along the cable. The changes in this pulse enable scientists to estimate the yield of the explosion. Alternatively, seismic techniques use meters that measure the ground-shaking caused by the explosion. These meters can be placed up to thousands of kilometers away from the blast.

There is debate over which system gives a more accurate estimate of the yield of nuclear explosions.

During the visits this month, the delegations are preparing for future joint verification experiments to be held at the testing sites in Nevada and Kazakhstan. The experiments will allow each side to demonstrate its preferred technique to measure nuclear explosions of yields near 150 kilotons. The schedule for these experiments will be discussed at the second round of nuclear testing talks that begins in Geneva Feb. 15.