Encyclopedia
Reactor
"Reactor" means any apparatus, except for nuclear weapons or other nuclear explosive devices, in which a self-sustaining fission chain reaction occurs. The phrase "designed or used primarily for the production of plutonium or uranium-233" does not apply to breeder reactors that do not produce nuclear materials for use in nuclear explosive devices, nor to reactors that are primarily used for the production of plutonium-238.
Source: Agreement between the Government of the Russian Federation and the Government of the United States of America on cooperation in the peaceful uses of atomic energy