Failed Nuclear Plant Remains a Pioneer : Technology: Colorado facility’s helium gas-cooled design was unique. Now the plant is a test case on how to safely decommission an atomic reactor.

Marty Deniston helped build the Ft. St. Vrain nuclear power plant. He helped run the reactor when it got to full power. Now, he’ll have to supervise its dismantling.

“It makes me sick,” said Deniston, the 48-year-old supervisor of plant operations. “One of the biggest disappointments in my life was the day we had to shut down, and I had to give the order.”

The plant, designed to generate up to 330 megawatts of power--enough to supply a third of Denver’s needs--now has barely enough juice left to power three 100-watt light bulbs.

The reactor once operated at about 1,400 degrees Fahrenheit. Now it percolates along at about 150 degrees, waiting for the day when the remaining fuel is removed.

The plant was shut down Aug. 18, 1989, to repair a stuck control rod. Then, unrelated steam line cracking was discovered that would have cost millions of dollars to repair. Public Service Co. decided to cease nuclear operations.

Ft. St. Vrain was the nation’s first high-temperature, gas-cooled commercial reactor, using helium instead of water to cool its core and transfer heat to steam generators to power turbines that make electricity.

But during its troubled 10-year life, the plant operated at an average 14.6% of capacity and rarely approached 100% capacity.

A decommissioning plan requires federal approval, and PSC also is seeking permission to turn the plant into a natural gas-powered commercial power plant and an experimental solar power facility. The converted plant would generate about 335 megawatts by 1995.

The cost of converting Ft. St. Vrain is estimated at $340 million, including $124 million in defueling and decommissioning costs for the nuclear side of the plant.

Construction of the 11-story reactor building began in September, 1968. Initial criticality, the point at which a reactor becomes self-sustaining, was achieved in January, 1974. PSC’s investment in the plant eventually reached $240 million.

The plant was unique in the nation’s nuclear power industry for its reliance on pressurized helium, not water, as a primary coolant.

Unfortunately, it was ahead of its time. While the reactor technology was sound, according to Deniston, problems cropped up in the cooling system.

Bearings used in the helium compressors allowed water into the cooling system, contaminating the reactor and forcing PSC to shut down the plant and clean out the reactor.

As little as a thimbleful of water could force a shutdown. In 1984, equipment problems forced the plant’s closure for 22 months.

A switch to magnetic bearings has solved the problems that plagued the plant, Deniston said. But while Ft. St. Vrain was struggling, the bottom fell out of the nuclear power industry.

The federal government passed strict rules governing plants and the handling and disposal of nuclear wastes. Plans for 10 other gas-cooled plants that would have supported the fuel supplier were canceled. The cost of making fuel only for Ft. St. Vrain escalated.

Now Ft. St. Vrain is pioneering another process, the decommissioning of nuclear reactors. “It’s a learning experience for everybody,” Deniston said.

He said the biggest questions revolve around how much equipment can be dismantled without it being considered part of the decommissioning process, and what safety studies are required now that the plant has shut down.

Joe Gilliland, spokesman for the Nuclear Regulatory Commission in Arlington, Tex., said the agency has guidelines requiring plants to have sufficient resources to pay for safe dismantling and radiation limits that require a reactor site to be returned essentially to background radiation levels.

But rules are vague about how much of the plant can be taken apart without decommissioning approval from the NRC. He said the process at Ft. St. Vrain will help other plants, such as Shoreham on Long Island, N.Y.

Disposal of radioactive waste from Ft. St. Vrain remains a problem. Idaho has blocked waste from Ft. St. Vrain from going to a federal site near Idaho Falls.

A truck loaded with spent nuclear fuel sits outside Ft. St. Vrain, waiting for the day the Idaho dispute is resolved.

But engineers have begun taking the plant apart while awaiting permission for full decommissioning.

Twelve of 37 nuclear core refueling regions have been removed and are stored next to the roof of the reactor. A temporary storage site is being built next to the reactor building to house the rest of the fuel, until a permanent resting place can be found.

In a nearby “hot” service facility, workers using robot arms are cutting up control rod drives for shipment to low level radioactive waste storage sites.

One worker, a volunteer firefighter, won an award for suggesting that hydraulic shears used to open wrecked cars could be used to take apart pieces of the reactor.

If decommissioning is approved by the NRC, plant officials hope to complete removal of the fuel from the plant by July, 1992, and begin decommissioning the following month.

Workers then will remove the roof of the reactor vessel, which towers nine stories and measures 49 feet across, fill it with water to keep radiation levels low, and use wire rope saws to take it apart.

Deniston said the condition of the nation’s nuclear power industry pains him. He moved to the nuclear power industry 20 years ago.

“I was real excited about the prospects for nuclear power at the time,” he said. “Nuclear power was in its heyday.”

He progressed from equipment operator to assistant reactor operator, to reactor operator, shift supervisor and eventually became supervisor of plant operations.

At its height, the plant had more than 500 workers. The work force now is at 250, and will be down to 40 when the plant is decommissioned.

Still, Deniston remains convinced nuclear power will return, and he thinks Ft. St. Vrain paved the way.

Instead of 330-megawatt monoliths, however, he foresees the day when there will be 100-megawatt, prefabricated reactors popping up all over the country.