The Bush administration is pursuing a dangerous myth, the myth of a usable nuclear weapon. The administration wants new nuclear weapons that can destroy so-called hard and deeply buried targets (HDBTs) — bunkers about 1,000 feet underground — in “rogue” nations without causing substantial collateral damage. The nuclear weapons envisioned by the administration, however, could cause widespread devastation if used, threatening civilian populations and U.S. forces. Moreover, developing these weapons could set back U.S. nonproliferation goals and encourage a new arms race in tactical nuclear weapons.

The administration is considering two alternatives for the HDBT mission. The first is the so-called Robust Nuclear Earth Penetrator. The RNEP would be based on existing B61 and B83 bombs that have been in the U.S. arsenal for a number of years, and have yields in the sub-kiloton to megaton range.

The second is a new class of low-yield nuclear warheads that have an explosive yield of less than 5 kilotons. In 1993, Congress placed a prohibition on “research and development” that could lead to the production of a new low-yield nuclear weapon. The administration now seeks to eliminate this prohibition. The administration’s Nuclear Posture Review calls for exploring new nuclear weapons “concepts” to be able to attack HDBTs with reduced collateral damage. According to the administration, the Congressional restriction on research of low-yield nuclear weapons “impedes this effort.” [IMGCAP(1)]

A bunker-busting nuclear weapon, however, could be expected to produce widespread collateral damage. To be a bunker buster, the weapon design must protect the warhead and associated electronics while it tunnels into the ground. This severely limits the missile to smaller impact velocities, which, in turn, severely limits how far down it can go. In fact, limits on material strengths make 50 feet about the maximum depth to which a missile could penetrate into dry, rocky soil while maintaining its integrity until the warhead detonates.

Yet, even a low-yield nuclear weapon of 0.1 kiloton, according to Princeton University physicist Robert Nelson, must penetrate about 230 feet underground for the explosion to be fully contained. Based on the experience of U.S. underground tests at the Nevada test site, a 5-kiloton explosive has to be buried at least 650 feet to be fully contained. A 100-kiloton explosive must be at least 1,300 feet deep.

Collateral damage resulting from the use of a “low-yield” 1-kiloton warhead, a weapon one-thirteenth the size of the atomic bomb dropped over Hiroshima, would be considerable. At a depth of 20-50 feet, a 1-kiloton warhead would eject more than 1 million cubic feet of radioactive debris from a crater bigger than a football field.

As the war with Iraq shows, Saddam Hussein built his bunker complexes inside or near Baghdad. Leaders of other “rogue states” can be expected to construct their command and control centers inside or near their capital cities too. Even if a low-yield weapon was used to attack an HDBT in or near a city, it would devastate the area. There would be major collateral damage because the ejected radioactive debris would create a lethal gamma-radiation field over a large area.

For the shock of a nuclear explosion to reach a hardened target at 1,000 feet, a much larger warhead would be required, like the B61 and B83 bombs being considered for the RNEP. But the B61 and B83 bombs would dig a much larger crater and create a substantially larger amount of radioactive debris and collateral damage.

U.S. forces might be endangered by the use of a nuclear bunker-busting weapon if on-the-ground spotting was required for precision strikes using nuclear bunker busters. Damage assessment or the recovery evidence would be very difficult and dangerous to our troops. This is not a theoretical consideration. Had the administration used a nuclear weapon to destroy Hussein’s command bunker, the task of identifying remains would have been infinitely more complicated.

There are simpler solutions to the HDBT problem. The intelligence community estimates more than 10,000 potential HDBTs exist worldwide, but only a few hundred of these have stronger concrete re-enforcement, are buried at great depths, or are in tunnels. The Pentagon has conventional weapons capable of putting buried targets out of action directly or by blocking entrances and exits. Conventional bunker busters could meet the challenge of threatening the several hundred most hardened and deep targets in question. Conventional bunker busters would not place civilian populations or our forces at undue risk and harm, and would keep the barrier between nuclear and conventional weapons high and wide.

Finally, the serious international implications of the administration’s pursuit of new nuclear weapons designs must be kept in mind. A new arms race in supposedly low-yield and “usable” nuclear weapons could result if other nuclear nations follow in the path of the United States. This new tactical nuclear arms race should be stopped before it starts. The barrier between nuclear and conventional weapons must be kept high and wide.

Sen. Daniel Akaka (D-Hawaii) is ranking member of the Armed Services subcommittee on readiness and management support.