Lesson 1: Reading Lesson

Yucca Mountain Scientific Studies

Throughout history, people have used science to solve problems. In fact, we can define science as using what we know to figure out better ways of doing things. The more we know, the better we can address difficult problems.

Cooling towers at a nuclear power plant.

Since the beginning of the nuclear age, nuclear waste from weapons programs and energy production has been a difficult problem to resolve. It stays highly radioactive for thousands and thousands of years, so we need to figure out what to do with it so it will not harm people or the environment.

Since the 1950s, scientists have been working to solve the problem of nuclear waste. They have looked at many different options such as shooting it into outer space, putting it into the ocean floor, or burying it in polar ice caps. After much study, the international scientific community has decided the most feasible and safest way to dispose of nuclear waste is to put it deep underground in a facility called a “repository.”

Once nuclear waste is isolated deep underground, the rock and soil will shield its radiation. This, however, presents some new problems

Where is a suitable place for an underground repository?
How will a repository impact people and the environment?
How can we prevent water from getting to the waste in an underground repository, corroding the nuclear waste, and carrying radionuclides into the environment?
How would different natural processes (such as erosion, earthquakes, or volcanoes) affect the repository’s safety?
How can we assure the repository will protect people and the environment for thousands of years in the future?

Scientists throughout the world have been working to solve these problems. In the United States, experts began by evaluating many potential sites for a repository. Considering a wide range of geologic criteria, they kept narrowing down the number of sites for further study, going from nine to five, from five to three, and eventually from three to one – Yucca Mountain, Nevada. At this point, scientists considered Yucca Mountain a good site for a repository due to its dry desert climate, remoteness, stable geology, deep water table, and closed water basin with no surface or subsurface connections to lakes, rivers, or oceans.

In 1982, scientists for the U.S. Department of Energy began to study Yucca Mountain in greater detail in a program called site characterization.

^Back to top

Site Characterization Studies

Scientists collect data on past earthquake activity in the Yucca Mountain vicinity.

Yucca Mountain and its surrounding areas are one of the most thoroughly studied sites in the world. For more than 25 years, hundreds of scientists in numerous disciplines performed thousands of studies there. The goal of these studies has been to understand:

Drill rig used to collect rock samples on the Yucca Mountain Project.

the natural system at and around Yucca Mountain
how a repository would affect people and the environment

The first scientific studies at Yucca Mountain involved geologists mapping the geologic and hydrologic features of the area to identify the rock types, faults, and stratigraphy.

Experts drilled over 450 boreholes in the Yucca Mountain region and collected over 22,000 meters of rock samples. Scientists performed thousands of tests on the rock samples to learn about the rock’s properties, such as its mineral content, porosity, and strength. Other studies involved drilling into the mountain to measure water infiltration into the rock and to measure chemical constituents in the water.

Other scientists performed climate studies. These studies were aimed at determining the past climate conditions in the Yucca Mountain area. This is important for projecting if future climates could produce more rainfall, which could affect the amount of water that infiltrates Yucca Mountain.

As the site characterization studies progressed, scientists focused more and more on the processes that could affect a repository’s safety, which include:

The physical characteristics of the different rock layers (e.g., porosity, mineral content, fractures), from the surface of the mountain to below the water table
The amount of water that enters the mountain, how it moves through the rock, and how much water could eventually enter into the tunnels where the waste would be emplaced
The physical and chemical environment in the potential emplacement tunnels and how changes to this environment could affect the durability of the waste containers and other repository systems
The physical and chemical properties of spent nuclear fuel and high-level radioactive waste, how their radioactivity would decay (lessen) over time, and how (and how fast) the materials could dissolve if water eventually reached them in a repository
How radionuclides could move through the repository to the rock underneath, down through the rock to the water table, and away from the repository with the groundwater
How any escaping radionuclides could affect people and the environment
How future earthquakes and volcanic activity could possibly disrupt the repository and the effects on people and the environment

The Exploratory Studies Facility

While performing site characterization studies at Yucca Mountain, scientists needed access to the rock at the repository level. So, in 1994, the Department of Energy began excavating a tunnel under the mountain called the Exploratory Studies Facility. It was completed in 1997. The Exploratory Studies Facility is a U-shaped tunnel over 8 kilometers long. It reaches the depth of the potential repository about 300 meters below the crest of Yucca Mountain and about 300 meters above the water table.

Project scientist connects power to electrical heaters used to simulate the heat that would exist from waste packages in a repository.

Cutaway diagram showing theYucca Mountain emplacement tunnel concept.

Within the Exploratory Studies Facility are several small underground test rooms called alcoves, seven smaller excavations known as niches, and one longer tunnel known as the cross-drift. Scientists have used all of these underground facilities to conduct a multitude of tests directly on the type of rock found within Yucca Mountain and especially rocks found at the repository level.

Nuclear waste is thermally hot, so one experiment involved placing heaters into an underground alcove to simulate the heat that would exist in the emplacement tunnels. For four years, scientists heated over 20,000 cubic meters of rock to 200 degrees Celsius. All the while, more than three thousand sensors measured how water, the air, and the rock reacted to the heat. In 2002, the heaters were turned off and the rock was allowed to cool down naturally. For four additional years (a total test time of eight years), scientists will monitor the rock and gather data about how heat effects Yucca Mountain.

Engineering and Design

Based on years of scientific study, engineers designed a repository that would work specifically with Yucca Mountain's natural environment. The goal of the design is to continually isolate nuclear waste and protect people and the environment for hundreds of thousands of years.

The repository design includes a series of emplacement tunnels excavated deep underground in solid rock. The layout and attributes of these tunnels are engineered to manage the heat that would be generated by the waste. To provide assurance that the waste remains isolated in the repository, engineers plan to complement Yucca Mountain’s natural features with engineered features. The engineered features include waste containers (called waste packages), drip shields to keep moisture off the waste packages, and tunnel inverts to support the waste packages in the tunnels. Eventually the repository will be sealed. The seals are also part of the engineered system.

The metallic engineered features are designed to keep water away from the waste and to prevent radionuclides from escaping into the environment. They will be made of special corrosion-resistant materials. To select the materials, experts had to factor in the long-term effects of such conditions as heat, humidity, and water chemistry. They methodically tested and selected materials that could withstand the environment in the emplacement tunnels.

In addition, materials were chosen to endure the stress and wear of handling, emplacement, and possible retrieval of radioactive waste, and for the ability to withstand the high heat that the waste generates.

Top left - Diagram of the key comonents of a waste package for disposal of the spent nuclear fuel inside Yucca Mountain.

Top Right - Diagram showing how waste packages would be placed inside the emplacement tunnels.

Left - This metal test sample has maintained its mirror finish even after almost 60 years of exposure to a marine environment. It is the predecessor to an even more corrosion resistant metal, (Alloy 22), that was selected for construction of the waste package outer barrier.

Environmental Studies

Project scientist holding reptile from the Yucca Mountain area.

Since 1982, scientists have conducted extensive environmental studies at Yucca Mountain. The purpose of these studies is to eliminate or reduce potential impacts of Yucca Mountain Project activities to the land, air, water, plants, animals, and cultural resources.

The environmental studies involved

Identifying native plant species and mapping their distribution in the Yucca Mountain region
Identifying native vertebrate species and their populations in the Yucca Mountain region. These studies included surveying populations of a variety of mammals, reptiles, and birds
Identifying the most common groups of invertebrate populations (insects, spiders, and scorpions) in the Yucca Mountain region
Identifying the effects of Yucca Mountain Project activities on native flora and fauna. This included studies of how heat generated by the waste in a repository could affect soils, plants, and animals
Conducting archaeological surveys to assure that Project activities do not adversely impact areas containing cultural resources such as Native American ruins or sacred sites

	One of many man-made, flaked, stone tools found in the Yucca Mountain area.
Project scientist measuring a desert tortoise found in the Yucca Mountain area.

Analogue Studies

An analogue study area at Pena Blanca, near Chihuahua Mexico.

The real world offers many examples of the kinds of climatic, geologic, and hydrologic processes that could affect the repository. Researchers call these examples analogues. For years, Project scientists have worked with scientists in other organizations and countries to study dozens of analogue sites throughout the world to gain a better understanding of the long-term processes that are potentially relevant to Yucca Mountain.

For example, an important analogue site is a natural uranium deposit at Peña Blanca,near Chihuahua Mexico, where the climate and type of rock are very similar to those at Yucca Mountain. The studies at this site have focused on the underground migration of naturally occurring radionuclides over millions of years. In these studies, scientists have observed that the radionuclides from the uranium deposit migrated only a few meters along major fractures in the rock. Scientists representing the U.S. Nuclear Regulatory Commission, the U.S.

Department of Energy, the Mexican and French governments, and other international organizations worked together to learn important lessons from analogous natural systems. International collaboration on natural systems, engineered systems, and repository programs continues today.

World map showing some of the analogue sites for the natural system at Yucca Mountain.

Assessing Future Repository Safety

Scientists use computer modeling to evaluate the repository’s ability to protect people and the environment for tens of thousands of years in the future.

Using data from the site characterization studies, experts have developed hundreds of computer models that simulate the different geologic, hydrologic, physical, and chemical processes of the repository. These models are used to analyze how the different parts of the repository work, and how they influence each other’s behavior over time.

Experts have incorporated the results of the computer models into more comprehensive computer simulations called process models for analyzing primary repository processes, which include

Chart shows several aspects of Total System Performance Assessment.

Climate change
Water infiltration into the mountain
Water movement above the repository level
Water seepage in the repository tunnels
The tunnel environment
The effects on the engineered features (e.g., waste packages and drip shields)
The effects on the waste itself
The transport of radionuclides through the rock below the repository
The transport of radionuclides in the groundwater
The potential effects on people and the environment

In addition, process models are used to examine how different damaging events such as earthquakes or volcanoes could affect repository safety.

Experts use the data and results from the individual process models in one large computer simulation of the entire repository system. This simulation, called the Total System Performance Assessment, shows how all the repository’s parts will work together over tens of thousands of years. Scientists also use this simulation to see how different events and processes could affect the entire repository system.

Using the Total System Performance Assessment, experts identify which aspects of the repository are most important to safety and how to improve the entire system. Every time they run the simulation, they add more up-to-date data, which helps them to define new scientific tests to improve the simulation even more. Adding more up-to-date information also helps engineers refine and improve the repository design.

Future Scientific Investigations

Project scientist collecting plant material as part of the reclamation program.

Scientific studies at Yucca Mountain will continue to support efforts to license and construct a repository. If the repository is eventually built, the U.S. Department of Energy will continue scientific studies during the entire time the repository is operational.

Federal law requires the department to monitor the repository until sufficient data has been collected to confirm that the repository can be safely closed. The repository design will allow future generations to decide whether to close the repository or continue monitoring it for up to 300 years. There will also be a monitoring program after the repository is closed and sealed.

The monitoring program will focus on processes that are most important to repository safety (e.g., seepage and corrosion). Monitoring activities will include testing the repository environment (rock properties, chemistry, etc.) and verifying the data with the results predicted by computer models.

Science and Technology Program

In 2003, the Department of Energy formed a new organization called the Science and Technology Program. Scientists within this program investigate, evaluate, and develop new technologies to improve the waste isolation processes at Yucca Mountain. Specifically, the program explores advancements in technology that could enhance the safety of the repository, reduce the costs of the waste management system, and/or accelerate the repository schedule.

Innovations from the Studies at Yucca Mountain

The years of scientific study at Yucca Mountain have produced many new scientific innovations and insights that contribute to the advance ment of science and society as a whole.

Some of these innovations include

Prototype robot transmits video signals as it travels down the tunnel. Similar equipment could be used to view the tunnel environment after waste placement.

Increased understanding of the geologic processes that have created the current landscape of the Yucca Mountain region
Increased scientific understanding of past climates
Unprecedented collection of geologic data on a specific area (Southern Nevada)
Increased scientific understanding of how groundwater moves in unsaturated rock and of how rocks and water interact
Better scientific methods for testing rock and groundwater
Increased scientific understanding of how rocks conduct heat and of the processes that result when heat is introduced into a natural system
Increased scientific understanding of how water can affect and transport radioactive particles
Better methods for testing corrosion resistant materials and new methods for modeling corrosion over thousands of years
Advancements in modeling natural systems over vast lengths of time

The science at Yucca Mountain is likely to have an impact on your life. The cost of electricity, environmental quality, the state of scientific knowledge, and the future potential for jobs will all be affected by scientific developments at Yucca Mountain.