U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3093

July 2012

The U.S. Geological Survey’s TRIGA® Reactor

The U.S. Geological Survey (USGS) operates a lowenriched uranium-fueled, pool-type 

reactor located at the Federal Center in 

Denver, Colorado (fig. 1). The mission 

of the Geological Survey TRIGA®

Reactor (GSTR) is to support USGS 

science by providing information on 

geologic, plant, and animal specimens 

to advance methods and techniques 

unique to nuclear reactors. The reactor 

facility is supported by programs 

across the USGS and is organizationally under the Associate Director for 

Energy and Minerals, and Environmental Health. The GSTR is the only 

facility in the United States capable 

of performing automated delayed 

neutron analyses for detecting fissile 

and fissionable isotopes. Samples from 

around the world are submitted to the 

USGS for analysis using the reactor 

facility. Qualitative and quantitative 

elemental analyses, spatial elemental 

analyses, and geochronology are 

performed. Few research reactor facilities in the United States are equipped 

to handle the large number of samples 

processed at the GSTR. Historically, 

more than 450,000 sample irradiations 

have been performed at the USGS 

facility. Providing impartial scientific 

information to resource managers, 

planners, and other interested parties 

throughout the world is an integral part 

of the research effort of the USGS. 

Figure 1. Cerenkov radiation or “blue glow” 

from operation of the TRIGA® reactor.

Figure 2. TRIGA® reactor control console.

The USGS TRIGA® reactor has been 

in operation since the late 1960s in support 

of nuclear-based research for the USGS and 

a number of universities across the Nation. 

It is the only research reactor of its type in 

the Department of the Interior and the only 

research reactor within a 350-mile radius of 

Denver, Colo. The reactor design is similar to 

research and training reactors at universities 

throughout the United States (see control 

console in figure 2). The reactor provides an 

intense neutron source for experiments and is 

capable of continuous steady-state operation 

at 1,000 kilowatts (thermal). Also, it may 

be pulsed to a peak power of approximately 

1,600 megawatts. Services include, but are 

not limited to, neutron irradiations for argon 

isotopic dating, neutron activation analysis, 

uranium and thorium analysis by delayed 

neutron counting, radioisotope production, 

gamma spectrometry, and fission track 

experiments. 

What the GSTR Can Do 

Routine operations at the GSTR involve 

the irradiation of samples to produce changes 

in the sample specimens (see sample package 

in figure 3). This change or “transmutation” 

of the original elements in the sample is 

accomplished when neutrons from the reactor 

strike the sample and change its nuclear 

composition. This technique, where the 

specimen is “activated” and then analyzed to 

determine its elemental composition, is called 

neutron activation analysis (NAA). Most 

elements can be detected at a level of a few 

nanograms or less. An advantage of NAA is 

that the samples can be analyzed without any 

Figure 3. Sample package before assembly.

Figure 4. Sample transport containers.

chemical processing before or after the activation. This composition information is useful 

in determining geological sources and origins 

of mineral deposits. The reactor is also used to 

produce nuclear changes in rock and mineral 

samples to determine their ages. Elemental 

analyses using other methods often result in 

data of less precision and (or) less accuracy. 

The GSTR provides high-quality data on rock 

and mineral elemental composition using 

state-of-the-art techniques while providing 

the research tools needed to develop new 

and improved analytical techniques (see 

figure 4 for a sample container setup at the 

GSTR). 
Safety

The TRIGA® reactor has many safety 

features, primarily through the inherent 

design of the reactor, that prevent overheating 

or a “core meltdown.” Numerous radiation 

monitors with automatic alarms are located 

throughout the facility. The control system 

provides warnings against unsafe operations 

by monitoring power levels, temperatures, 

and other important properties of the reactor. 

An automatic reactor shutdown will occur in 

a fraction of a second if any operational limit 

is exceeded. A reactor bay air-monitoring 

system detects airborne contamination and 

immediately isolates the reactor space if 

necessary. This isolation system will then 

provide absolute filtering of all reactor space 

air to prevent the release of contaminants to 

the environment. The safety of operations 

is checked annually by the U.S. Nuclear 

Regulatory Commission. 

Collaboration

The reactor staff provides guidance to 

researchers from across the country on the 

feasibility and design of proposed experiments, including preliminary irradiations and 

assistance with counting equipment. The staff 

also provides radiation safety management 

and nationwide assistance to USGS projects 

that involve radioisotopes. A Memorandum 

of Understanding (MOU) exists between the 

USGS and the Colorado School of Mines, 

and the collaborative research benefits both 

organizations in academic and basic research 

efforts.

Examples of Research Projects 

That Use the Reactor Facility

Coral Reefs and Dust 

(Neutron Activation Analyses)

Off the coast of Jamaica, USGS 

scientists studied an array of coral reefs to 

determine the source of reddish-brown soil 

that is affecting reef ecology. The soil is 

believed to be endangering the continued 

growth and development of the reefs. Reefs 

are important sources of food and protect 

tropical shorelines from storms. Through 

neutron activation analysis at the reactor 

facility, the soil was “fingerprinted” as a 

combination of volcanic ash originating from 

the Lesser Antilles island arc and airborne 

dust from Africa (Muhs and Budahn, 2009). 

Dust from Africa is also a dominant parent 

material for soils in the Florida Keys, the 

Bahamas, and Barbados (Muhs and others, 

2007). For the first time, climatic teleconnections could be established using neutron 

activation analyses.

2011 Japanese Earthquake 

and Radioactive Fallout 

(Gamma Spectrometry)

The Fukushima reactor accident in 

March 2011 dispersed radioactive materials 

into the atmosphere. Smoke from the reactor 

traveled around the world, depositing radioactive material as it spread (fig. 5). The GSTR 

analyzed hundreds of water and filter samples 

to help determine the type and amount of 

fission products deposited across the United 

States (Wetherbee, DeBey, and others, 2012; 

Wetherbee, Gay, and others, 2012).

Understanding Volcanic Eruptions 

(Argon Geochronology)

Geologists at the USGS Cascades Volcano Observatory (Vancouver, Washington) 

have used the reactor to understand volcanic 

systems and to develop detailed eruptive 

histories of active volcanoes in the Western 

United States, Alaska, and Hawaii. One of 

these research projects is in the Three Sisters 

volcanic field west of Bend, Oregon. This area 

includes three stratovolcanoes surrounded 

by lava flows (fig. 6), several of which have 

erupted in the last 4,000 years. Using argon 

geochronology, scientists concluded that two 

of the Three Sisters volcanoes formed simultaneously in a narrow time interval between 

48,000 and 15,000 years ago, while the third 

was determined to be substantially older. This 

research suggests that the stratovolcanoes 

are less likely to erupt in the near term, but 

the surrounding lava flows have been more 

active recently and, therefore, pose the greater 

hazard to people and property (Fierstein and 

others, 2011). 

Future Science at GSTR

Continuing improvements in the 

neutron profile characterization of the GSTR 

provide greater precision in geochronology 

measurements for numerous laboratories. The 

Colorado School of Mines, in cooperation 

with the GSTR, plans to install a neutron 

radiography instrument in 2012. The instrument will be the only neutron radiography 

system within a 450-mile radius of Denver, 

Colo., and will be able to facilitate new types 

of analytical research. 

References Cited

Fierstein, Judy, Hildreth, Wes, and Calvert, A.T., 

2011, Eruptive history of South Sister, Oregon 

Cascades: Journal of Volcanology and Geothermal Research, v. 207, nos. 3–4, p. 145–179. 

Muhs, D.R., and Budahn, J.R., 2009, Geochemical evidence for African dust and volcanic 

ash inputs to terra rossa soils on carbonate 

reef terraces, northern Jamaica, West Indies: 

Quaternary International, v. 196, nos. 1–2, 

p. 13–35. 

Muhs, D.R., Budahn, J.R., Prospero, J.M., and 

Carey, S.N., 2007, Geochemical evidence for 

African dust inputs to soils of western Atlantic 

islands—Barbados, the Bahamas, and Florida: 

Journal of Geophysical Research, v. 112, 26 p.

Wetherbee, G.A., DeBey, T.M., Nilles, M.A., 

Lehmann, C.M.B., and Gay, D.A., 2012, 

Fission products in National Atmospheric 

Deposition Program—Wet deposition samples 

prior to and following the Fukushima Dai-Ichi 

Nuclear Power Plant incident, March 8–

April 5, 2011: U.S. Geological Survey OpenFile Report 2011–1277, 27 p. 

Wetherbee, G.A., Gay, D.A., DeBey, T.M., 

Lehmann, C.M.B., and Nilles, M.A., 2012, 

Wet deposition of fission-product isotopes to 

North America from the Fukushima Dai-Ichi 

incident, March 2011: Environmental Science 

& Technology, v. 46, no. 5, p. 2574–2582.

Figure 5. Smoke coming from the Fukushima 

nuclear plant following the accident in 

March 2011 (from DigitalGlobal®).

Figure 6. Aerial view of Three Sisters 

volcanoes in Oregon.

For more information contact:

Tim DeBey (tdebey@usgs.gov) or 

Brycen Roy (broy@usgs.gov)

(303) 236–4724

http://geology.cr.usgs.gov/facilities/gstr/

U.S. Geological Survey

Energy and Minerals, and 

Environmental Health

Box 25046, MS 974

Denver Federal Center

Lakewood, CO 80225

This fact sheet is available online at 

http://pubs.usgs.gov/fs/2012/3093/

Timothy M. DeBey, GSTR Staff, EMEH, USGS

Brycen R. Roy, GSTR Staff, EMEH, USGS

Sally R. Brady, Staff Scientist, EMEH, USGS