Bruce H. Breslow, executive director of the Nevada Agency for Nuclear Projects, responds to what he sees as “a number of apprehensions” in Lehr’s column. His letter can be found here.
President Barack Obama has proposed a budget that would eliminate funding for the nearly completed Yucca Mountain storage facility for spent nuclear fuel. Proponents vow not to abandon the plan, and they have strong scientific reasons to support it.
Yucca Mountain was selected as the nation’s first repository for high-level nuclear waste because of its many natural barriers preventing the escape of radioactive particles. These include the mountain’s surface soils, its overall physical shape, the thick rock layers above and below the levels used for storage, and the very impermeable materials located below the area’s deep water table.
In addition to these natural barriers, many redundant systems would be engineered into the storage facility to ensure individuals living near the site—which is 11 miles from the nearest residence—would receive no more than an insignificant one additional millirem of radiation per year.
Negligible Radiation Addition
A millirem is a measurement of radiation dose absorbed by the human body. The average American receives 360 millirems per year from a variety of natural sources, such as rocks and soil, radon gas emitted from the Earth’s crust, and cosmic rays from outer space. Some locations in the United States yield twice that annual dose to residents.
Manmade sources such as medical and dental procedures, television sets, and computer screens also transmit radiation. A typical chest x-ray results in 10 millirems of radiation, and three hours of watching television each day amounts to one millirem per year. Smoking one-and-a-half packs of cigarettes a day results in an additional 1,300 millirem each year.
Engineered Safety
To keep the radiation contribution from Yucca Mountain to a paltry single millirem per year, scientists and engineers have devised the engineered barrier system. It includes containment tunnels 1,000 feet below Yucca Mountain’s surface and titanium drip shields to prevent rock or water from falling on the highly fortified waste containers. The containers are double-shelled and corrosion-resistant to eliminate the possibility of rupture.
The waste itself is solid, making the escape of radioactive particles into the natural environment even more unlikely. The robust waste packages, which are to be partly surrounded by crushed volcanic rock, are expected to resist corrosion in the environment inside Yucca Mountain for hundreds of thousands of years because of these combined natural and manmade barriers.
Projected Future
When designing systems intended to last longer than recorded human history, scientists and engineers must consider the possibility that one or more barriers, natural or engineered, may not perform as expected, which is why the facility will contain many redundant features. Projecting what will happen to this first-of-a-kind facility over thousands of years is indeed a daunting task—one that already has consumed 30 years of planning and experimentation.
The Nuclear Regulatory Commission requires the U.S. Department of Energy to use a computer model—the Total System Performance Assessment—to project how the Yucca Mountain repository will perform over time under normal conditions and during special events such as earthquakes and volcanic eruptions. Using huge amounts of data and computer power, scientists believe they can calculate how well and how long the repository can keep the nuclear materials isolated from the environment while the radiation levels of the waste naturally decline over hundreds of thousands of years.
The scientists predict exposure will not exceed one millirem per year as far out as 720,000 years, which is certainly a comfort to us all.
Jay Lehr, Ph.D. ([email protected]) is science director of The Heartland Institute.
