Sentence:  Upon the expiration of a period deemed adequate for demonstration purposes for each plant , but not to exceed such twelve <WSD>year</WSD> period , the Secretary shall proceed as promptly as practicable to dispose of any plants so constructed by sale to the highest bidder , or as may otherwise be directed by Act of Congress . 
Meaning of the word marked with <WSD> tags:  a period of time containing 365 (or 366) days