The Exploratory Studies Facility

The U.S. Department of Energy’s Exploratory Studies Facility is an underground laboratory at Yucca Mountain that allows scientists and engineers access to the rock that is being studied for a potential repository.

This underground laboratory consists of an eight-kilometer (five-mile) main tunnel with several research areas, or alcoves, connected to it. Construction of the facility began in 1993 and the main tunnel was completed in 1997.

In October 1998, miners and scientists completed work on a project called the Enhanced Characterization of the Repository Block (ECRB). The ECRB study involved excavating a 2.7-kilometer (1.7-mile) cross-drift tunnel that starts from the north portion of the Exploratory Studies Facility near the first curve and crosses the mountain from northeast to southwest.

Inside the cross-drift tunnel, scientists study properties of the rock and the behavior of water near the potential repository area. Data is collected to verify models and predictions about the geology and hydrology surrounding the cross-drift tunnel.

The purpose of studies at Yucca Mountain is to determine whether the site is suitable for a high-level radioactive waste and spent nuclear fuel repository. These studies, collectively called site characterization, are divided into three types of scientific investigations:

• Surface-based testing, which includes analyzing rock, soil samples, and water movement;
• Underground testing, which includes examining rock at deep levels; and
• Laboratory analyses, which encompass analyzing liquid and gas from rock samples collected from surface-based and underground test activities.

As portions of the underground laboratory were completed, scientists and engineers on the Yucca Mountain Site Characterization Project began working in the alcoves built as deep as 300 meters (1,000 feet) underground. Working underground allows them to observe the actual conditions within the rock they are studying.

Representing many different fields of expertise, these scientists and engineers conduct tests to better understand the complex geology and hydrology of Yucca Mountain. The variety of data gathered helps them assess the geologic, hydrologic, geoengineering, and geochemical properties of the different layers of rock deposits that make up the area being studied.

The tests also provide data for potential repository design and construction. For instance, scientists are assessing the strength and response of the rock to the tunnel excavation. This allows them to understand how the rock would perform in an actual repository. Two major ramps from the surface, a north ramp and south ramp, now lead to the underground facilities. The ramps’ diameter, 7.6 meters (25 feet), allows for adequate ventilation and safe passageway for personnel and vehicles. Additionally, it provides flexibility in construction and operation of the facility. Eventually, the facility would encompass 28 hectares (69 acres) of surface buildings and facilities as well as about 10 kilometers (6.2 miles) of underground ramps and tunnels.