paraphrased by Melissa Lovin
In Yucca Mountain, Nevada nuclear waste is one of the hottest topics of conversation. This beautiful desert region 100 miles north of Las Vegas is currently being prepared to become the most radioactive place on earth. The government will be digging a network of tunnels to be loaded with radioactive waste from the nations 100 or so nuclear reactors which supply approximately 20% of the country's electricity.
This radioactive waste was never planned on. The first nuclear engineers saw the "spent fuel" that came out of nuclear reactors as potentially more valuable than the slightly enriched uranium dioxide "fresh fuel" that went in. Nuclear reactors do more than make steam to spin the electric generators. A portion of the uranium fuel undergoes a transformation, with the yield, a myriad of radioactive elements. Plutonium-239 is by far the most dangerous and can be separated to create fuel for other types of power reactors and nuclear weapons.
The thermal efficiency of the reactor decreases as the concentration of these radioactive by-product elements increases. Every two to three years each reactor must be shut down and 1/3 of the 100 metric ton fuel load replaced. The "spent fuel" coming out of the reactor is so dangerous that it must first be stored under water for a period of time. The original plan was to then remove the waste to a reprocessing site that would separate and recycle the useful elements.
Although this was technically possible, it was extremely expensive to operate. The federal government then decided to bury the waste in a deep hole presumably in the middle of nowhere. It was then to be monitored and determined safe over a period of time. If the fuel was still unwanted after a period of years, then the waste would be abandoned. The cost of this project upon completion in 2071, would be as much as $50 billion.
After much controversy the site was chosen as Yucca Mountain which is located near the above ground nuclear weapons testing site.
If it is constructed, the repository will hold up to 3 billion curies of radiation. In comparison the nuclear accident at Three Mile Island released 15 curies, mostly as short-lived radioactive iodine. A great portion of the radiation contained at Yucca Mountain will be emitted from plutonium, which has a half-life of more than 20,000 years.
The DOE's strategy for containing the radiation during this process has been described as "very carefully". According to Daniel R. Wilkins, assistant general manager of the repository, " Our estimate is that the first packages will fail in 10,000 years. After that , we're relying on the mountain to contain the waste." The waste is to be contained in casks made of steel and highly corrosion-resistant inner lining which hold 21 or 44 "reactor fuel assemblies". Some of these assemblies contain enough plutonium to build a bomb. The risk for explosion, however, is slight according to experts, because the plutonium is encased in fuel pellets within the assemblies. The greatest concerns center on the presence of water.
The presence of water on Yucca Mountain is noticeably absent, as it overlooks the Amargasso Desert. The waste will be packed into casks at a processing center to be constructed at a later date. Then the casks will be deposited into the tunnels dug into a formation of welded tuff about 600 ft and 900 ft. thick which will be cut using a boring machine the size of several train engines.
To date the construction crews have dug a 5 mile, 25 ft. diameter exploratory tunnel, two ramps to the surface and several side alcoves. Department of Energy scientists are hopeful that, following successful testing in these alcoves, they will have sufficient information to convince the Nuclear Regulatory Committee (NRC) to issue a construction permit. This permit will allow the actual construction of the tunnels to begin. An operating license could also be issued as a result of the testing, and will allow them to begin accepting the nuclear wastes which are now being stored at the nation's 100 or so power plants.
The State of Nevada, however, claims that the data collected thus far tells quite a different story. They say that the mountain has been shown to leak.
"Originally we thought there would be very slow (water) infiltration. New evidence suggests there are some fractures that will allow flows from the surface to the repository and from the repository down," says Wilkins. The water table is almost 900 ft. below the waste emplacement tunnels, and the terrain is stable. Most agree that the water tables could not rise high enough to reach the casks. Water trickling from the top of the mountain seem to cause little alarm, however, there are some concerns about water evaporating from the rock into the tunnels.
According to Steven Frishman, a geologist and the technical policy coordinator from the state of Nevada Nuclear Waste Project Office the repository is being dug in tuff that is filled with microscopic pores and fracture spaces. Almost 80% of the pore space in the rock has surface water that is moving through the fractures, trapped inside.
The importance of the water does not concern Department Of Energy scientists. They contend that heat given off by the casks will increase the temperature of the rock surfaces surrounding the drifts high enough to keep moisture away, therefore, the casks will stay dry and corrosion free for thousands of years. The Scientists plan to prove this by conducting a series of increasingly larger and larger rock heating experiments.
The largest of these experiments called the Drift-Scale Test is being conducted inside a 156-ft. section of welded tuff that has sealed from the adjoining tunnel. Electric heaters are being used to slowly heat 13,000 cubic yards of surrounding rock to temperatures well above the boiling point. The heaters have been running for 3000 hours. In four years the test will be completed. Power will be shut off halfway through the test, and the rock will begin cooling to ambient temperatures.
" The Drift-Scale Test will be the largest test of its type done thus far in the world,"says Department Of Energy geophysicist Robert Yasek. We hope to refine computer models that predict the long-term effects of heart generation from the thermal, mechanical, hydrological and chemical data collected, continued Yasek. Before granting an operating license for the repository, the NRC would look closely at this source of key information.
The NRC doesn't need to wait four years, according to Frishman. The information gathered so far reveals the critical, overlooked flaw in the repository's basic design. "The air temperature inside the sealed alcove was 262 degrees F and the rock was 252 degrees F. Yet, the relative humidity was 11%. It should be virtually zero," added Frishman.
The presence of humidity is positive proof that as heat pushes moisture away from the surface of the tunnel walls, it is also drawing moist air in from water filled pores in the mountains, says Frishman. This isn't necessarily a problem if the tunnel walls remain at temperatures above the boiling point. The trouble will occur hundreds of years from now, he says, after the mine has been sealed but while its contents are still lethally radioactive. Frishman believes that with the humidity rising in the tunnels to nearly 100% the deterioration of the casks will accelerate and eventually cause them all to fail, and spill their radioactive contents.
The problems that have been encountered will not kill the project, says DOE. In a recent meeting with an independent presidential advisory panel on Yucca Mountain, it has begun to paint a darker picture. The Department Of Energy presented information showing how leakage of radioactive material would enter the ground water below the repository, then work back to the surface, in effect exposing humans, food, and water supplies to radiation.
Frishman said, "It's not just some local farmers who will be exposed to this radiation. There are about 2500 acres of alfalfa planted in the basin. It is used as feed for cows that produce 32,000 gallons of milk every day. And, it's all shipped to Los Angeles." Now, a deep hole in the middle of nowhere seems a lot closer to home.