Rising against the majestic Cascade Mountains is a great plume of steam that has become a symbol of the spreading national controversy over poisonous nuclear wastes.

Day in and day out, the steam flows from the tower that cools the heat of the nation's largest nuclear plant at Trojan, 42 miles northwest of Portland. The Plume can be seen 60 miles in any direction. The cooling tower itself is 499 feet high, making it the tallest in the world.

Trojan inherits its name from a munitions factory that made explosives during both world wars. At no time in either war did the factory spark the kind of explosive political protests that are now echoing through the site.

A bomb that exploded outside Trojan's gates last fall blew out the windows in the $2 million Visitors Center run by Portland General Electric Co., which owns the Trojan nuclear generator. Twice last year, antinuclear protestors stormed the gates to block technicians from the plant; 82 protesters were arrested the first time and 122 the second.

Now comes an issue that promises to heighten the tensions: what to do with first load of spend radioactive fuel that's about to be discharged from the Trojan plant. This question goes far beyond the borders of Oregon and to the heart of the nationwide debate over nuclear power.

The debate centered five years ago on questions of safety. Some of them have been largely resolved and many critics have been silenced by the fact that nuclear accidents are few and far between.

Between the nuclear waste question is different. Everybody understands garbage and this garbage contains the elements strontium and cesium. Both emit gamma rays, which can penetrate lead. Both stay radioactive for generations, meaning they'll still be generating gamma rays 1,000 years from now.

"These wastes remain potentially lethal for hundreds of thousands of years," said Dr. Terry R. Lash of the Natural Resources Defense Council. "As a consequence of their extraordinary toxicity and longevity, radioactive wastes will require isolation from the biosphere for periods of time unparalleled in human history."

Last year, Oregon passed a law banning the "permanent" disposal of radioactive waste in the state. Michigan enacted a similar law two years ago. Earlier this year, California passed a law banning the construction of new nuclear plants until a national solution to radioactive waste is proposed. Wisconsin is considering similar legislation and 10 other states were exploring it.

So strong are the campaigns against nuclear power over the waste issue that the Carter administration is about to mount a counter-attack. This week, the Department of Energy is expected to announce what promises to be the first comprehensive plan to dispose of radioactive wastes since the dawn of the Atomic Age in 1945.

The first part of the plan will be to take care of the spent fuel that's building up in places like the Trojan plant in Oregon. What to do with these radioactive wastes is what Deputy Energy Secretary John F. O'Leary calls the "most difficult institutional" energy question facing the nation.

"The old Atomic Energy Commission took the view right up to its dying day that this thing could wait," O'Leary said recently. "They were insensitive to the fact that this was a bleeding wound and bleeding wounds can't wait."

The nation's 68 commercial nuclear power plants have accumulated 5,000 tons of spent fuel, all of its spiked with radioactive poisons like strontium 90 and cesium 137.

That doesn't include the 2 million tons of radioactive clothing and medicines discarded and buried the last 25 years at places like Maxey Flats, Ky., and Shefield, Ill. It doesn't include the 100 million gallons of hot waste generated by the nuclear weapons program and stored in giant steel tanks on military reservations at Hanford, Wash., and Savannah River, S.C.

Most crucial is the buildup of commercial nuclear wastes. It varies with size, but a nuclear plant in the United States can generate as much as 32 tons of spent radioactive fuel every year. There are 138 nuclear plants being built in the United States. The Department of Energy estimates there will be 360 nuclear plants licensed to produce power by the year 2000.

Nuclear waste is an inevitable phenomenon. Once uranium undergoes fission, it produces isotopes like strontium, cesium and plutonium, whose gradual accumulation begins to block the chain reaction that produces power and heat. When that happens, usually in little more than a year, the spent fuel must be replaced with fresh fuel to keep the chain reaction going.

The 5,000 tons of spent fuel in existence today will be 10,000 tons in five years, experts estimate. By the year 2000, they say, there will be more than 100,000 tons of spent fuel in the United States.

"The waste problem refuses to solve itself," says Tony Roisman of the Natural Resources Defense Council, the main adversary of nuclear power in the United States. "When the wastes start backing up and the toilets of the nuclear reactors begin to overflow . . . what is the solution? Is there a solution."

Sometime late this month, the 1.2 million kilowatt Trojan plant will be shut down to allow technicians to burrow tools into the plant's nuclear core. Operating the tools remotely, the technicians will remove 64 cylinders containing the spent fuel of more than a year's fission.

The spent fuel cylinders will be taken from the reactor vessel and moved to a huge room alongside the reactor that is separated from it by a thick concrete wall. The 12-foot-long cylinders, each weighing 1,600 pounds, will be lowered into a pool lined with eight feet of concrete and quarter-inch steel plate and filled with 400,000 gallons of water.

For a few days, the pool will glow a pale blue with Cerenkov radiation, named for the Soviet physicist who found that nuclear radiation produces the underwater glow because passing through water it travels faster than light. So quickly does the spent fuel decay that the blue glow disappears in a few days.

The fresh fuel to replace the spent fuel at Trojan is already being stacked near the "swimming pool" that will take the spent fuel. The long cylinders have been arriving at unpredictable hours, for fear that protestors would try to stop the shipments if they knew when they were coming.

"We don't want to talk about that," said Trojan Chief Engineer William (Skip) Orser, when asked when the shipments will be completed.

To hear engineers like Orser tell it, the spent fuel can be safely kept in pools like the one at Trojan for decades. It's true, they say, that a spent fuel storage pool in Florida once leaked irradiated water but that's why the Trojan pool is lined with stainless steel, to prevent such leaks.

It's also true, they add, that the heat radiated into the pool from the spent fuel could warm the water close to the boiling point. But the pool will be cooled to 140 degrees by water pumped in from the nearby Columbia River and recycled. Two pumps will be used at all times, in case one fails.

There is a remote chance so many spent fuel cylinders could be placed in the pool that they'd trigger a chain reaction, but that's why the Nuclear Regulatory Commission won't permit overcrowded pools. Boric acid is flushed into the pool to absorb neutrons that could trigger a one-in-a-million chance of a chain reaction.

"If somebody fell in the pool," says Orser, "the biggest peoblem would be cleaning the boric acid off him when he got back out of the pool."

Many Oregon residents don't share Orser's optimism. A woman in nearby Willamina turned off her electricity and has kept if off ever since she heard that the spent fuel would be kept at Trojan. A petition by Portland General Electric to expand the spent fuel pool in the years ahead has produced so much protest that hearings held by the NRC on the request are now in their third month and are expected to go for another three months.

This pool is "two hundred fifty feet from the Columbia River, the most important river in this part of the world," said David McCoy, one of three protestors filing court challenges to expansion of the spent fuel pool."If we have an earthquake there and get a nice, sizable radioactive release to the environment, I think it could be pretty extraordinary."

Protesters were religious in their zeal against indefinite storage of the fuel anywhere near their homes. People spoke of the peril to their great-grandchildren; even to their parents in California who might be forced to drink water from the Columbian River someday. State politicians spoke of being duped into believing the wastes would leave Oregon when they granted a license in 1971 for the Trojan plant to operate.

Pressure is mounting for a federal solution to the issue but the history of federal nuclear waste disposal is not a happy one. As long ago as 1957, the National Academy of Sciences suggested the Atomic Energy Commission consider the disposal of nuclear waste in abandoned salt mines. Nine years later, the academy made its suggestion a "recommendation."

The ABC, which is no longer in existence, selected an abandoned salt mine near Lyons, Kan., as a test for waste disposal, figuring salt mines are so dry there would be no danger of liquid leaching out wastes buried in them. In as little as three years, geologists found the Lyons mine to be dangerously close to old oil deposits. They also discovered well water leaking perilously close to the salt, and the mine was never used.

At about the same time the salt mine was abandoned in 1972, two private schemes to dispose of nuclear waste in storage tanks were turning sour. One General Electric project outside Morris, Ill., was stopped before it was finished because GE lost an estimated $300 million on it. A project of the Nuclear Fuel Service (NES) Corp. outside Buffalo operated for six years before stopping in 1972 because it was a money loser. The state of New York estimates it will cost $560 million to decommission the NFS facility.

When the Department of Energy was formed last year and took federal title to the waste disposal program, it found a shambles. Schemes like burying wastes under the sea were being financed. So were projects to shoot waste to the sun.

Now, DOE is poised to announce a fresh start on a disposal program. Burial in salt is still an option, but more likely candidates are permanent burial in hard rock like granite and basalt far below the ground.

Unlikely to be approved is an old plan to bury the wastes at the Nevada Test Site, where underground nuclear weapons tests have been conducted for almost 20 years. What if a future test generates a small earthquake? Would it dislodge buried wastes? Suppose a weapons test vents radiation to the atmosphere? Would a repository have to be evacuated?

Energy officials are convinced there are answers to the questions of permanent disposal of nuclear waste. The trouble is, time is running out.

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