Act ( 42 U.S.C. 2215 note)), including a portable nuclear reactor, that has an electricity generating capacity of not more than 20 megawatts of electricity and not more than 100 megawatts of thermal energy. (2) Natural disaster The term natural disaster has the meaning given the term major disaster in section 102 of the Robert T. Stafford Disaster Relief and Emergency Assistance Act ( 42 U.S.C. 5122 ).