Accident-Prone -- And

By GEORGE J. CHURCH

The W-79 is an artillery shell, the W-88 rides atop missiles that would be fired from submarines and the W-69 is the business end of missiles designed to be launched from bombers at ground targets. Despite the diversity of their delivery systems, these three weapons, which together make up about 10% of the total U.S. inventory of nuclear warheads, share a frightening characteristic: all are, or have been, subject to safety problems that some experts fear just might cause them to explode accidentally.

Almost certainly, an unintentional blast would detonate only the chemical explosives that, if fired deliberately, would compress the warhead's plutonium cores and touch off an unstoppable atomic chain reaction. Some experts see a slim chance of a nuclear explosion in the case of the W-79 artillery shell, but the far more likely result would be a chemical blast that could release deadly radioactive plutonium or uranium from the cores. The safety problems, disclosed last week by the Washington Post, were promptly confirmed in public congressional hearings. The difficulties seem sure to complicate immensely a review under way of how many and what kind of nuclear weapons the U.S. should deploy in the light of easing cold-war tensions and prospective arms-control deals with the Soviets.

The story begins in 1988, when scientists at the Lawrence Livermore National Laboratory near San Francisco set some new, supersophisticated computers to simulating the effects of nuclear blasts. One unexpected conclusion: the chemical explosives in a W-79 artillery shell could be detonated if the shell were struck in a single sensitive spot, perhaps by a stray bullet. One military official told the Washington Post, "For a while, we were also worried that these things might go off if they fell off the back of a truck." More than 300 of the shells were reportedly shipped to the U.S. from West Germany, the Netherlands and South Korea, where they had been deployed, then repaired and sent back. Nebraska Democrat J. James Exon, who chaired Senate Armed Services Subcommittee hearings last week, accepts Pentagon assurances that the shells are now entirely safe, but the Pentagon and State Department nevertheless are bracing themselves for an outcry from overseas.

The W-79 problem prompted computer studies of other warheads, which led to questions about the safety of a far more important weapon, the brand-new W-88 warhead carried by D-5 missiles fired by Trident II submarines. The D-5 is one of the principal weapons that would be launched at the Soviet Union in a nuclear war. Some scientists contend that the design of the third stage places too much rocket fuel too close to the warheads. Conceivably the fuel could ignite and detonate chemical explosives in the warhead while the missile was being handled in port, producing a potentially heavy leakage of cancer-causing plutonium dust near Trident bases in Washington State and Georgia. Other experts furiously dispute these findings, which will be examined by a panel of three scientists appointed by Congress with Pentagon acquiescence.

The panel will also look into a hot dispute about the SRAM-A (for Short- Range Attack Missile), another weapon that would be launched in a nuclear war against the U.S.S.R.: it is carried by bombers on airborne alert and designed to knock out Soviet radar installations, defensive missiles and airfields. The fear is that a fire aboard a bomber could ignite the missile's volatile fuel, which in turn could detonate some of the chemical explosives in its W-69 warhead.

At last week's Senate hearings, directors of three nuclear-weapons laboratories, including Livermore, unanimously argued that the SRAM should be ( taken off the bombers flying on alert, put into storage and made removable only at a base commander's order. John Tuck, Under Secretary of the Department of Energy, which builds nuclear weapons and shares responsibility with the Pentagon for their safety, told the subcommittee, "I think that's the direction we're going." Pentagon spokesman Pete Williams, however, insisted that the Air Force would keep the warheads on "alert" status, at least until the safety study is completed. But the Pentagon may have trouble maintaining that stand in the face of public pressure; Secretary of Defense Dick Cheney scheduled a weekend meeting with weapons-laboratory scientists and Energy Secretary James Watkins to consider what to do. SRAM-A is scheduled to be replaced eventually by a longer-range missile, SRAM-II. However, the problems with the older weapon might keep NATO from approving a future tactical version for use in Europe, the SRAM-T, even though it may be safer. One congressional source predicts that "there will never be a SRAM-T."

"The common thread in the three systems," says Exon, "is the problem of previous-generation high explosives." All three weapons carry them, rather than a less volatile Insensitive High Explosive, which is heavier and thus decreases the range of a missile or artillery shell. By presidential order IHE nonetheless has been used in all new weapons built since 1985 -- with, however, at least one exception. Even after that date, defense planners decided not to switch to IHE in the Trident W-88 warhead. That is a design trade-off that the Pentagon may soon bitterly regret.

With reporting by Bruce van Voorst/Washington