TRIGA

TRIGA (Training, Research, Isotopes, General Atomics) is a class of nuclear research reactor designed and manufactured by General Atomics. The design team for TRIGA, which included Edward Teller, was led by the physicist Freeman Dyson. Multiple variants of the reactor have been built, with a total of 66 having been installed across 24 different countries. The reactors have constant thermal power outputs ranging from 0.1-16 MW and can be pulsed to 22,000 MW.

## Contents

* 1 Design
* 2 History
* 3 Inherent Safety via Warm Neutrons
* 4 List of all TRIGA Nuclear reactors built around the world
* 5 See also
* 6 Notes
* 7 References
* 8 External links

## Design

TRIGA is a swimming pool reactor that can be installed without a containment building, and is designed for research and testing use by scientific institutions and universities for purposes such as undergraduate and graduate education, private commercial research, non-destructive testing and isotope production.

The TRIGA reactor uses uranium zirconium hydride (UZrH) fuel, which has a large, prompt negative fuel temperature coefficient of reactivity, meaning that as the temperature of the core increases, the reactivity rapidly decreases. Because of this unique feature, it has been safely pulsed at a power of up to 22,000 megawatts.[1] The hydrogen in the fuel is bound in the uranium zirconium hydride crystal structure with a vibrational energy of 0.14eV.[2] These levels fill when the fuel is hot, and transfer energy to thermal neutrons making them more energetic and, therefore, less likely to cause a fission. TRIGA was originally designed to be fueled with highly enriched uranium, but in 1978 the US Department of Energy launched its Reduced Enrichment for Research Test Reactors program, which promoted reactor conversion to low-enriched uranium fuel.[3][4]

## History

A TRIGA Mark II taken into use at Helsinki University of Technology in 1962 by the Finnish President Urho Kekkonen.

The concept of the TRIGA reactor was invented in the summer of 1956 when the president of the newly founded company General Atomics, Frederic de Hoffmann, invited a group 30–40 nuclear scientists (many of them alumni of the Manhattan Project) to consider what types of reactors would be commercially promising. The exploratory work focused on three concepts: a "Ship Reactor" (to propel merchant ships), a "Test Reactor" (for experimentally irradiating parts of nuclear power reactors), and a "Safe Reactor" (which eventually became TRIGA). During June-September the scientists worked out designs for the three reactors, and at the end of the summer de Hoffmann chose TRIGA for commercial development.[5]

The "Safe reactor" working group was led by Edward Teller, who proposed that General Atomics should break into the market by developing a reactor that was much safer than its competitors. In Teller's words the reactor should be safe "even in the hands of a young graduate student"[6], or in the words of Freeman Dyson "even in the hands of an idiot clever enough to by-pass the entire control system and blow out the control rods with dynamite."[5] The working group comprised ten physicists, chemists, and engineers, including Freeman Dyson (who worked on the mathematical theory) and Massoud T. Simnad (who developed the fuel chemistry). At the end of the summer the preliminary design was handed over to a smaller team of General Atomics scientists, Ted Taylor, Stan Koutz, and Andrew McReynolds, for detailed development. The prototype for the TRIGA nuclear reactor (TRIGA Mark I) was commissioned on 3 May 1958 on the General Atomics campus in San Diego and operated until shut down in 1997. It has been designated as a nuclear historic landmark by the American Nuclear Society.

Mark II, Mark III, and other variants of the TRIGA design have subsequently been produced, and a total of 33 TRIGA reactors have been installed at locations across the United States. Those that remain operational continue to be upgraded or modernized.[7] A further 33 reactors have been installed in other countries. Many of these installations were prompted by US President Eisenhower's 1953 Atoms for Peace policy, which sought to extend access to nuclear physics to countries in the American sphere of influence. Consequently, TRIGA reactors can be found in a total of 24 countries, including Austria, Bangladesh, Brazil, Congo, Colombia, United Kingdom, Finland, Germany, Taiwan, Japan, South Korea, Italy, Indonesia, Malaysia, Mexico, Morocco, Philippines, Puerto Rico, Romania, Slovenia, Thailand, Turkey, and Vietnam.

TRIGA International, a joint venture between General Atomics and Compagnie pour l'étude et la réalisation de combustibles atomiques (fr)—then a subsidiary of AREVA of France—was established in 1996. Since then, all TRIGA fuel assemblies have been manufactured at CERCA's plant in Romans-sur-Isère, France.

Some of the main competitors to General Atomics in the supply of research reactors are Korea Atomic Energy Research Institute (KAERI) of South Korea and INVAP of Argentina.

The TRIGA Power System (TPS) is a proposed small power plant and heat source, based upon the TRIGA reactor and its unique uranium zirconium hydride fuel, with a thermal power output of 64 MW producing 16 MW of electricity.[8][9]

## Inherent Safety via Warm Neutrons

Edward Teller's goal was an "inherently safe" reactor, meaning that even if all the control rods are abruptly withdrawn, the reactor will settle to a stable state before it is damaged by the heat. To achieve this it needs to have a large negative temperature coefficient, i.e. the amount of reactivity should decrease quickly as the reactor gets hotter.

Most nuclear reactors exhibit a negative temperature coefficient to some extent. As fuel temperature rises, thermal expansion reduces the fuel density, lowering reactivity. In addition, the neutron absorption of U-238 (the non-fissile uranium isotope) increases with temperature due to Doppler broadening, increasing neutron capture and thereby reducing the number of neutrons available to sustain the fission chain reaction.

The TRIGA design additionally makes use of effects related to the energy of thermal neutrons.[10] Like most reactors, TRIGA is a thermal-neutron reactor in which fast neutrons produced by fission are slowed by a neutron moderator until they reach thermal equilibrium with the surrounding material. The U-235 fission cross section is much larger for low-energy neutrons than for higher-energy ones. As the temperature of the moderator increases, the average energy of thermal neutrons also increases, reducing the probability that they will induce fission and increasing the likelihood that they will escape from the fuel (the "leakage effect") and be absorbed elsewhere. An even larger negative coefficient can be obtained by incorporating neutron absorbers such as erbium into the fuel[11], which preferentially absorb higher-energy thermal neutrons.

The challenge of exploiting the leakage effect was to ensure that the temperature of the neutrons tracks the temperature of the reactor. In general the thermal energy of the neutrons will always correspond closely to the temperature of the moderator. But in a conventional reactor the moderator is separate from the fuel; for example a light-water reactor uses water next to the fuel rods as a neutron moderator. If there is a power surge in such a reactor, the fuel rods can heat up and melt long before the water starts to heat up. Therefore, the TRIGA designers set out to make a "homogeneous reactor", where the fissionable material and the moderator are combined in a homogeneous mixture.[10]

Several candidate materials were investigated as potential moderators that could be combined with uranium fuel, including beryllium, beryllium oxide, graphite, lithium hydride, sodium hydride, and zirconium hydride (ZrHx). Zirconium hydride was ultimately selected because of its low chemical reactivity, low toxicity, good thermal conductivity, and low cost. However, little was known in 1956 about the metallurgy or neutronics of ZrH, so extensive experimental and theoretical work was needed.[12]

The TRIGA fuel consists of a homogeneous alloy of uranium-zirconium hydride. The zirconium matrix can hold a large number of hydrogen atoms (with a H/Zr ratio around 1.6[13]), and the hydrogen is a good moderator. Water surrounding the fuel provides additional moderation and cooling. Because the uranium is dispersed inside the zirconium hydride matrix, the temperature of the hydrogen and hence the thermal neutrons instantly track the rest of the fuel. Using standard TRIGA fuel, 50% of the temperature coefficient of the reactor is due to the thermal spectrum of the neutrons.[11]

## List of all TRIGA Nuclear reactors built around the world

Country | City | Name | Type | Status | Thermal Power [kW] | Operation Date | Closure Date | Owner and Operator | Notes

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Austria  | Vienna  | TRIGA II VIENNA  | TRIGA Mark II  | Operational  | 250  | 1962-03-07  |  | Atominstitute / Institute of Atomic and Subatomic Physics |
Bangladesh  | Savar, Dhaka  | BTRR, BAEC TRIGA Research Reactor  | TRIGA Mark II  | Operational  | 3000[14] | 1986-09-14  |  | Atomic Energy Research Establishment (Bangladesh)  |
Brazil  | Belo Horizonte  | TRIGA IPR-R1  | TRIGA Mark I  | Operational  | 100  | 1960-11-06  |  | CDTN - Centro de Desenvolvimento de Tecnologia Nuclear  | *The expansion to 250 KW is in the licensing process, for which a new refrigeration system has been installed.
Colombia  | Bogota  | IAN-R1  | TRIGA CONV  | Operational  | 30  | 1965-01-20  |  |  |
Congo, DR of  | Kinshasa  | TRICO I  | TRIGA Mark I  | Permanent Shutdown  | 50  | 1959-06-06  | 1970  | CREN-K University of Kinshasa  |
TRICO II  | TRIGA Mark II  | Extended Shutdown  | 1  | 1972-03-24  |  | CREN-K University of Kinshasa  | extended shut down since 2004 [18]
Finland  | Espoo  | FIR-1  | TRIGA Mark II  | Under Decommissioning  | 250  | 1962-03-27  | 2015  | VTT Technical Research Centre of Finland  |
Germany  | Frankfurt am Main  | FRF-2  | TRIGA Conv  | Decommissioned  | 1  | 1977-10-01  |  |  |
Heidelberg  | TRIGA HD I  | TRIGA Mark I  | Decommissioned  | 250  | 1966-08-01  |  |  |
Hannover  | FRH  | TRIGA Mark I  | Decommissioned  | 250  | 1973-01-31  |  |  |
Heidelberg  | TRIGA HD II  | TRIGA Mark I  | Decommissioned  | 250  | 1978-02-28  |  |  |
Mainz  | FRMZ  | TRIGA Mark II  | Operational  | 100  | 1965-08-03  |  | Johannes Gutenberg-Universität Mainz  |
Munich  | FRN  | TRIGA Mark III  | Under Decommissioning  | 1  | 1972-08-23  |  |  |
Indonesia  | Bandung  | TRIGA Mark II, Bandung  | TRIGA Mark II  | Operational  | 2000  | 1964-10-19  |  |  | 2MW installed 1997
Sleman  | KARTINI-PSTA  | TRIGA Mark II  | Operational  | 100  | 1979-01-25  |  |  |
Italy  | Rome  | TRIGA RC-1  | TRIGA Mark II  | Operational  | 1  | 1960-06-11  |  |  |
Pavia  | LENA, TRIGA II PAVIA  | TRIGA Mark II  | Operational  | 250  | 1965-11-15  |  |  |
Japan  | Tōkai, Ibaraki  | NSRR  | TRIGA Acpr  | Operational  | 300  | 1975-06-30  |  |  |
Yokosuka  | TRIGA-II Rikkyo  | TRIGA Mark II  | Under Decommissioning  | 100  | 1961-12-08  |  |  |
Tokyo  | Musashi Reactor  | TRIGA Mark II  | Under Decommissioning  | 100  | 1963-01-30  |  |  |
Korea, Republic of  | Seoul  | KRR-1  | TRIGA Mark II  | Decommissioned  | 250  | 1962-03-19  |  | KAERI  | Research Reactor,100 kW, built 1962 (Decommissioned)[52]
Seoul  | KRR-2  | TRIGA Mark III  | Decommissioned  | 2  | 1972-04-10  |  | KAERI  | Research Reactor, 2MW, BUILT 1972 (Decommissioned)[53]
Malaysia  | Kajang, Selangor  | TRIGA Puspati (RTP)  | TRIGA Mark II  | Operational  | 1  | 1982-06-28  |  | Malaysian Nuclear Agency |
Mexico  | La Marquesa Ocoyoacac  | TRIGA Mark III  | TRIGA Mark III  | Operational  | 1  | 1968-11-08  |  | National Institute for Nuclear Research  |
Morocco  | Rabat  | MA-R1  | TRIGA Mark II  | Operational  | 2  | 2007-05-02  |  |  |
Philippines  | Quezon City  | PRR-1  | Subcrit (TRIGA-converted)  | Operational  | 0  |  |  |  | 3 MW TRIGA-converted reactor, Quezon City. Managed by the Philippine Nuclear Research Institute (formerly Philippine Atomic Energy Commission). 1st criticality in August 1963, reactor conversion in March 1984, criticality after conversion in April 1988, shut down since 1988 for pool repairs, on extended shutdown at present.
Puerto Rico  |  | Mayagüez - TRIGA reactor (dismantled)  |  | Dismantled  |  |  |  |  |
Romania  | Pitesti  | TRIGA II Pitesti - SS Core  | TRIGA Dual Core  | Operational  | 14000  | 1980-02-02  |  |  |
TRIGA II Pitesti - Pulsed  | TRIGA Dual Core  | Operational  | 500  | 1980-02-02  |  |  |
Slovenia  | Ljubljana  | TRIGA- MARK II LJUBLJANA  | TRIGA Mark II  | Operational  | 250  | 1966-05-31  |  | Jožef Stefan Institute  | (web page link) [51]
Taiwan  | Hsinchu City  | THOR  | TRIGA Conv  | Operational  |  | 1961-04-13  |  |  | [56]
Thailand  | Bangkok  | TRR-1/M1  | TRIGA Mark III  | Operational  |  | 1977-11-07  |  | Thailand Institute of Nuclear Technology (TINT)  | Thai Research Reactor 1/Modification 1, Installed 1962, modified 1975–77.
Turkey  | Istanbul  | ITU-TRR  | TRIGA Mark II  | Operational  | 250  | 1979-03-11  |  | Istanbul Technical University  | Institute of Energy
United Kingdom  | Billingham  | ICI TRIGA Reactor  | TRIGA Mark I  | Decommissioned  | 250  | 1971-08-01  | 1988  | ICI Physics and Radioisotopes Dept of ICI R&D (later to become Tracerco)  |
USA  | Urbana, IL  | LOPRA Univ. Illinois  | TRIGA  | Decommissioned  | 10  | 1971-12-28  |  |  |
San Ramon, CA  | ARRR  | TRIGA CONV  | Operational  | 250  | 1964-07-09  |  |  |
Pullman, WA  | WSUR Washington State Univ.  | TRIGA CONV  | Operational  | 1000  | 1961-03-07  |  |  |
Madison, WI  | UWNR Univ. Wisconsin  | TRIGA CONV  | Operational  | 1000  | 1961-03-26  |  |  |
College Station, TX  | NSCR Texas A&M Univ.  | TRIGA CONV  | Operational  | 1000  | 1962-01-01  |  |  |
Mayagüez, Puerto Rico  | TRIGA Puerto Rico Nuclear Center  | TRIGA CONV  | Decommissioned  | 2000  | 1972-01-19  |  |  |
State College, PA  | PSBR Penn St. Unv.  | TRIGA Mark CONV  | Operational  | 1000  | 1955-08-15  |  |  |
Silver Spring, MD  | DORF TRIGA Mark F  | TRIGA Mark F  | Decommissioned  | 250  | 1961-09-01  |  |  |
Bethesda, MD  | AFRRI TRIGA  | TRIGA Mark F  | Operational  | 1000  | 1962-01-01  |  |  |
Hawthorne, CA  | TRIGA Mark F, Northrop  | TRIGA Mark F  | Decommissioned  | 1000  | 1963-01-01  |  |  |
Omaha, NE  | Veterans Affairs RR  | TRIGA Mark I  | Decommissioned  | 20  | 1959-06-26  |  |  |
Salt Lake City, UT  | TRIGA Univ. Utah  | TRIGA Mark I  | Operational  | 100  | 1975-10-25  |  |  |
Tucson, AZ  | Univ. Arizona TRIGA  | TRIGA Mark I  | Decommissioned  | 100  | 1958-12-06  |  |  |
San Diego, CA  | GA-TRIGA I  | TRIGA Mark I  | Under Decommissioning  | 250  | 1958-05-03  |  |  |
San Diego, CA  | GA-TRIGA F  | TRIGA Mark I  | Under Decommissioning  | 250  | 1960-07-01  |  |  |
Portland, OR  | RRR Reed College  | TRIGA Mark I  | Operational  | 250  | 1968-07-02  |  |  |
Irvine, CA  | UC Irvine TRIGA  | TRIGA Mark I  | Operational  | 250  | 1969-11-25  |  |  |
Austin, TX  | UT TRIGA Univ. Texas  | TRIGA Mark I  | Decommissioned  | 250  | 1963-01-01  |  |  |
East Lansing, MI  | TRIGA Mark I Michigan State Univ.  | TRIGA Mark I  | Decommissioned  | 250  | 1969-03-21  |  |  |
Midland, MI  | Dow TRIGA  | TRIGA Mark I  | Operational  | 300  | 1967-07-06  |  |  |
Richland, WA  | NRF, Neutron Rad Facility  | TRIGA Mark I  | Under Decommissioning  | 1000  | 1977-03-01  |  |  |
Denver  | GSTR US Geological Survey  | TRIGA Mark I  | Operational  | 1000  | 1969-02-26  |  |  |
San Diego, CA  | TRIGA Mark II  | TRIGA Mark II  | Decommissioned  | 50  | 1959-12-11  |  |  |
Manhattan, KS  | KSU TRIGA Mark II  | TRIGA Mark II  | Operational  | 250  | 1962-10-16  |  |  |
Idaho Falls, ID  | NRAD  | TRIGA Mark II  | Operational  | 250  | 1977-10-12  |  |  |
Ithaca, NY  | TRIGA Cornell Univ  | TRIGA Mark II  | Decommissioned  | 500  | 1962-01-01  |  |  |
Corvallis, OR  | OSTR, Oregon State Univ.  | TRIGA Mark II  | Operational  | 1100  | 1967-03-08  |  |  |
Austin, TX  | TRIGA II Univ. Texas  | TRIGA Mark II  | Operational  | 1100  | 1992-03-12  |  |  |
Urbana, IL  | University of Illinois Advanced TRIGA  | TRIGA Mark II  | Decommissioned  | 1500  | 1960-08-16  | 1998  | Grainger College of Engineering - Nuclear, Plasma & Radiological Engineering  | [15]
Sacramento, CA  | UC Davis/McClellan TRIGA  | TRIGA Mark II  | Operational  | 2000  | 1990-01-20  |  |  |
Berkeley, CA  | BRR UC Berkeley  | TRIGA Mark III  | Decommissioned  | 1000  | 1966-08-10  |  |  |
San Diego, CA  | GA-TRIGA III  | TRIGA Mark III  | Decommissioned  | 2000  | 1966-01-01  |  |  |
College Park, MD  | MUTR Univ. Maryland  | TRIGA MODIFIED  | Operational  | 250  | 1960-12-01  |  |  |
Albuquerque, NM  | ACRR Annular Core RR  | TRIGA MODIFIED  | Operational  | 2400  | 1967-06-01  |  |  |
Vietnam  | Da Lat  | Dalat Research Reactor  | TRIGA Mark II  | Operational  | 500  | 1963-02-26  |  |  | (supplied by USA 1963, shut down 1975, reactivated by USSR 1984)

## See also

* List of commercial nuclear reactors
* List of nuclear research reactors
* Hydrogen-moderated self-regulating nuclear power module

## Notes

1. ↑ TRIGA Nuclear Reactors General Atomics
2. ↑ TRIGA Nuclear Reactors General Atomics
3. ↑ Argonne National Laboratory. "RERTR Radiological Threat Reduction Program". http://www.rertr.anl.gov/.
4. ↑ "Global Threat Reduction Initiative - Strategic Plan January 2009". https://www.nrc.gov/docs/ML0907/ML090790171.pdf.
5. ↑ 5.0 5.1 Dyson, Freeman (April 15, 1981). "Chapter 9: Little Red Schoolhouse". Disturbing The Universe. Basic Books.
6. ↑ Teller, Edward; Shoolery, Judith L. (2002). Memoirs: a twentieth-century journey in science and politics. Oxford: Perseus Press. p. 423. ISBN 9780738207780.
7. ↑ "New Console Installed at U's Triga Reactor". 29 October 2020. https://www.civil.utah.edu/2020/10/29/new-console-installed-at-the-us-triga-reactor/#:~:text=Faculty within the Department of Civil and Environmental,in mid-October 2020, the TRIGA’s console was replaced.
8. ↑ "UxC: Small Modular Reactor Market Outlook". https://www.uxc.com/p/product/archive/smo.
9. ↑ Triga Power System: A Passive Safe Co-Generation Unit for Electric Power and Low Temperature Heat, Small Reactors for Low Temperature Heat Applications, IAEA-TECDOC-463 (International Atomic Energy Agency, Vienna, 1988) pp. 45-55
10. ↑ 10.0 10.1 US patent 3127325, issued 1963-03-31
11. ↑ 11.0 11.1 US patent 4186050, issued 1980-01-29
12. ↑ IAEA Technical Reports Series 482: History, Development and Future of TRIGA Research Reactors (PDF) (Technical report). IAEA. July 2016. Retrieved 2026-03-08.
13. ↑ Simnad, Massoud T. (February 1980). "The U-ZrHx Alloy: Its properties and use in TRIGA fuel. Report E-117-833.". General Atomic Company. https://www.nrc.gov/docs/ML2005/ML20052A506.pdf.
14. ↑ "Centre for Research Reactor". https://baec.gov.bd/site/page/daf16a6d-1d39-41d6-87d9-50eadf14d2b4/-.
15. ↑ Mumm, Susan (2015-09-14). "Former TRIGA Reactor gains ANS National Historic Landmark status". University of Illinois Urbana-Champaign. https://npre.illinois.edu/news/stories/former-triga-reactor-gains-ans-national-historic-landmark-status.

## References

* Edward Teller (2001). Memoirs: A Twentieth-Century Journey in Science and Politics. Perseus Publishing. https://archive.org/details/memoirstwentieth0000tell.

## External links

* General Atomics official TRIGA website

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