10 CFR §51.21

All licensing and regulatory actions subject to this subpart require an environmental assessment except those identified in § 51.20(b) as requiring an environmental impact statement, those covered by categorical exclusions identified in § 51.22(a) through (d), and those identified in § 51.22(e) as other actions not requiring environmental review. As provided in § 51.22, the Commission may, in special circumstances, prepare an environmental assessment on an action that could be covered by a categorical exclusion.