Beginning in the late 1950s, the U.S. met this challenge by developing nuclear batteries known as radioisotope thermoelectric generators (RTGs) and producing plutonium-238 (Pu-238) as their fuel, ...

Japan’s plutonium stockpiles in Britain and France totaled 21.8 tons and 15.4 tons, respectively, as of December 2020. Britain shut down its only M OX plant in 2011, which means it can no longer ...