Spurred by a pledge of $50 million from Warren E. Buffett, the billionaire investor and philanthropist, the board of the International Atomic Energy Agency voted Friday to set up a global nuclear fuel bank that aspiring nations can turn to for reactor fuel instead of making it themselves.

The goal is to reduce the risks of weapons proliferation by providing an alternative to the production of nuclear fuel, which countries can use to power either bombs or reactors. The built-in ambiguity explains the world’s jitters over plants in Iran and North Korea for purifying uranium.

The new bank is seen as creating a global mechanism to aid the lighting of cities and to hinder the means of destroying them.

“I’ve never been $50 million lighter and felt better,” Mr. Buffett said in an interview on Friday. He called the fuel bank an investment in a safer world.