Experimental System on Sunken Sub May Pose Radiation Threat

While a handful of nuclear submarines have been lost at sea with little impact on the environment reported, one expert said Saturday that the Soviet submarine that sank Friday in the Norwegian Sea may bring “a new ballpark� of potential danger because of the experimental cooling system of the two reactors in its power plant.

John Holdren, professor of energy and resources at UC Berkeley, said that the metallic sodium used to cool the reactors reacts violently when exposed to water.

“I personally would be very worried about having a sodium-cooled reactor on the bottom,� he said. “I have the feeling that this radioactivity is going to get out; the question is how fast.

“This thing may be a new ballpark because of the sodium.�

Despite assurances by the Soviets that the reactors were shut down before the vessel sank, Holdren and other physicists said that their nuclear cores still have the potential for a “violent reaction� with seawater that could, in the worst case, send a radioactive “bubble� bursting to the surface.

The seven known past sinkings of nuclear-powered U.S. or Soviet submarines all involved water-cooled reactors that experts said would not be harmed--and might even be made less dangerous--by the effects of seawater. The sodium coolant, however, is very reactive with either air or water, experts said.

Sodium, a liquid metal, allows for a much more compact and efficient reactor but is harder to control, Holdren said. There are several land-based commercial sodium reactors in France and the Soviet Union, he said, but they are still regarded as experimental.

The United States considered using sodium-cooled reactors when it started building a nuclear navy but rejected the idea as too risky, several experts said.

The extent of possible environmental damage in the current incident depends on whether the reactors were involved with the fire when the vessel surfaced; if that was the case, radiation may have been spewed into the atmosphere or could have escaped as the submarine sank, defense and nuclear specialists said. But if the reactors stayed intact, a radiation release is much less likely.

Experts said that several factors make the spread of radioactivity less likely in the ocean than on land. Submarine reactors are about 10% the size of commercial land-based ones, and the double hulls and heavy shielding on most boats serve as tombs to contain any radioactivity. The U.S. Navy has been considering getting rid of old nuclear submarines by removing their fuel cores and scuttling them.

Ocean currents, moreover, are weaker than wind, and the remoteness of the deep sea floor makes contamination less likely.

With few exceptions, like squid, most sea creatures in the food chain inhabit relatively shallow waters.

Sunken Subs Monitored

“There’s a lot of water there to dilute the radioactivity,� said Frank Von Hippel, a physicist at Princeton.

The two U.S. nuclear subs that have sunk at sea have been monitored and only low levels of radiation have been found, said Thomas Cochran, a physicist at the Natural Resources Defense Council.

“You’ve got a lot of containment around the reactors and thick walls,� he said. “I don’t see how anything could get out.�

But experts cautioned against writing off risk completely.

“You’re talking about mounting nuclear reactors inside of a small metal tube; the potential for accidents is great,� said Steven Miller, director of defense studies at the Massachusetts Institute of Technology.

He said it is generally agreed that the Soviets have less strict safety standards than the United States.

UC Berkeley’s Holdren said the sodium adds a new dimension, particularly with the ocean’s pressure on the boat’s hull making some water seepage likely.

“It seems to me very difficult to have a sodium reactor sink without leaking,� Holdren said. “ . . . You’re basically in big trouble.�