Back view of the reactor. Thai Research Reactor 1/Modification 1 (TRR-1/M1). The TRR-1/M1 is of the type TRIGA Mark III, built by General Atomics, and began operation in 1962 after being commissioned in 1961 as a 1MW reactor. The TRR-1/M1 underwent its modification during 1975-1977, at which point it began operation as a 2MW reactor. TRR-1/M1 is the only nuclear reactor in Thailand