18 CFR 6.4: Termination by implied surrender.

If any licensee holding a license subject to the provisions of section 10(i) of the Act shall cause or suffer essential project property to be removed or destroyed, or become unfit for use, without replacement, or shall abandon, or shall discontinue good faith operation of the project for a period of three years, the Commission will deem it to be the intent of the licensee to surrender the license; and not less than 90 days after public notice may in its discretion terminate the license.