The Atomic Energy Commission is authorized to purchase or otherwise acquire from the Community special nuclear material or any interest therein from reactors constructed under the joint program in accordance with the terms of an agreement for cooperation entered into pursuant to the provisions of section 2153 of this title: Provided, That neither plutonium nor uranium 233 nor any interest therein shall be acquired under this section in excess of the total quantities authorized by law. The Commission is authorized to acquire from the Community pursuant to this section up to four thousand one hundred kilograms of plutonium for use only for peaceful purposes.