In the early 1950ies, the U.S. company General Atomics (GA) located in San Diego, California, developed a small research reactor which

• would be inherently safe

• is operationally flexible and relatively inexpensive

• allowed a large variety of experiments

• used low enriched uranium

At the First Geneva Conference on Peaceful Uses of Atomic Energy in 1955, the first TRIGA-type reactor (Training, Research, Isotope Production General Atomic) was presented to the public. During the following decades, approximately 60 TRIGA reactors were constructed all over the world. Three basic TRIGA models have been produced:

• Mark-I: underground pool without beam tubes

• Mark-II: above ground tank with several beam tubes

• Mark-III: above ground oval tank with movable core

A short description of the three TRIGA reactor types and a list of all worldwide TRIGA reactors that were put into operation (some of them already decommissioned) is given in Appendix 1.