10 CFR §76.66

1. (a)Except as provided in § 76.55, each certificate or approval issued pursuant to this part expires at the end of the day, in the month and year stated in the certificate or approval.
2. (b)The Corporation shall notify the Commission promptly, in writing under § 76.5, when the Corporation decides to terminate operation at either of the gaseous diffusion plants and other activities authorized under the certificate.
3. (c)If the Corporation does not submit a renewal application under § 76.36, the Corporation shall, on or before the expiration date specified in the existing certificate, terminate operation of the gaseous diffusion plants.