Hideaways for Nuclear Waste

By Frederic Golden

Salt domes are considered as crypts for radioactive debris

They are great underground mountains of salt, some of them six miles deep and three miles across. They were formed tens of millions of years ago--some even before the age of the dinosaurs--by the evaporation of ancient saline seas. Layer upon layer of sediment piled atop the dried-up ocean beds. Gradually, columns of the lighter salt were forced upward by the pressure, like putty squeezed through the fingers of a slowly clenching fist. In the U.S. alone, there are more than 500 such salt domes, all of them in or around the Gulf of Mexico.

For centuries the domes have served as a source of cheap table salt. In Louisiana, salt miners have carved out huge underground caverns. The domes act as traps for oil and natural gas, which collect in neighboring rock in cracks and fissures created by the upthrust of the salt.

In 1901, drilling around a dome near Beaumont, Texas, produced a gusher of unprecedented size. It was called Spindletop and gave birth to the modern petroleum industry. Since then, salt domes in the Gulf States have helped point the way to more than 6 billion bbl. of oil.

Today those riches have dwindled, but salt domes may again be pressed into service, this time as a solution to one of the country's hottest energy problems: getting rid of nuclear wastes, which can stay dangerously radioactive for 10,000 years. Some scientists suggest storing this debris deep inside salt domes.

The proposal is highly controversial, and residents of dome areas are already up in arms. In Louisiana, a group calling itself Citizens Against Radioactive Storage has been formed. During the last session of Congress, Louisiana Senator J. Bennett Johnston introduced a bill that would have blocked the use of salt domes by calling for storage in shallow beds, where, in case of leakage, the material would be more easily retrievable. Vows Louisiana Governor David Treen: "Unless it could be demonstrated that storing nuclear waste in salt domes is absolutely safe, I would oppose it."

Lately, popular fears have been stirred by a rash of mishaps involving salt domes. Last June methane gas exploded at a salt mine on Belle Isle, La., killing three miners and injuring 17 others. In November an oil-drilling rig accidentally punctured a salt-mine shaft under Jefferson Island, La., sending much of a 1.5-sq.-mi. lake gurgling down into the dome. The most frightening accidents have involved still another use of salt domes: as cheap, convenient storage tanks for crude-oil and natural-gas products. Last fall hundreds of people had to flee Mont Belvieu, Texas (pop. 2,700), which sits atop the largest such hydrocarbon reserve in the U.S., after gases began leaking from it.

These accidents have not altered scientific interest in the domes as nuclear-age crypts. Scientists point out that domes appear geologically stable. They do not have ground water circulating through them to carry off radioactive material. (If such water were present, the soluble salt would long ago have been washed away.) Even if the salt were cracked by heat from radioactive materials, the rupture would tend to close itself, a self-healing characteristic of salt not found in, say, granitic or volcanic rock masses, which are also being investigated as radioactive refuse sites. Says Physicist Neal Carter of the Battelle Memorial Institute in Columbus, Ohio, which is studying the problem of nuclear-waste disposal: "We've concluded that salt domes are fully capable of containing radioactivity."

Containment is certainly needed. Nuclear wastes have been piling up from years of military, medical and power-plant operations. At present, most of it is temporarily--and perhaps dangerously --stored in huge steel-and-concrete tanks. No decision has yet been made on any of the various types of geological storage dumps under study. Carter explains that unlike the oil or gases kept in the ground under pressure at places like Mont Belvieu, solid nuclear wastes could not trickle through the salt. In fact, he and his colleagues already have some preliminary ideas about how the debris should be buried. Vertical shafts, he explains, would be sunk in solid salt to a depth of about 2,000 ft. Horizontal tunnels would fan out from the bottom of the shafts. The wastes, packaged in corrosion-resistant containers, would be buried beneath the tunnel floors. Then the entire mine would be refilled with salt and sealed.

The chief danger: long after all record of the radioactive crypts has vanished, someone may accidentally intrude into the dome. --By Frederic Golden.

Reported by David S. Jackson/Chicago and Robert C. Wurmstedt/Baton Rouge

With reporting by David S. Jackson/Chicago, Robert C. Wurmstedt/Baton Rouge

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