Uranium-238
Supplement
The more abundant isotope of uranium, which does not readily undergo fission but can be converted into plutonium.
Mentioned in 3 videos
Videos Mentioning Uranium-238

The Man Who Accidentally Killed The Most People In History
Veritasium
The more common isotope of uranium, which decays into lead 206. Clair Patterson used its decay rate to measure the age of the Earth.

The Man Who Gave us the Power To Destroy Ourselves (Oppenheimer)
Veritasium
The more abundant isotope of uranium, which does not readily undergo fission but can be converted into plutonium.

Is Nuclear Energy Green?
Sabine Hossenfelder
The more abundant isotope of uranium, which can be transmuted into plutonium in fast breeder reactors.