Sentence:  Upon the expiration of a period deemed adequate for demonstration purposes for each plant , but not to exceed such <WSD>twelve</WSD> year 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:  denoting a quantity consisting of 12 items or units