UNITED STATES 
SECURITIES AND EXCHANGE COMMISSION 
Washington, D.C. 20549

SCHEDULE 13G
Under the Securities Exchange Act of 1934 
(Amendment No. ___________)*

USEC Inc.
(Name of Issuer)

Common 
(Title of Class of Securities)

90333E108
(CUSIP Number)

December 31, 2004
(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to 
which this Schedule is filed: 
[X ]    Rule 13d-1(b)
[  ]    Rule 13d-1(c)
[  ]    Rule 13d-1(d)

*The remainder of this cover page shall be filled out for a 
reporting person's initial filing on this form with respect to 
the subject class of securities, and for any subsequent 
amendment containing information which would alter the 
disclosures provided in a prior cover page. 

The information required in the remainder of this cover page 
shall not be deemed to be "filed" for the purpose of Section 18 
of the Securities Exchange Act of 1934 ("Act") or otherwise 
subject to the liabilities of that section of the Act but shall 
be subject to all other provisions of the Act (however, see the 
Notes). 

CUSIP No.  90333E108

1.      Names of Reporting Persons. 
I.R.S. Identification Nos. of above persons (entities 
only). 
Donald Smith & Co., Inc.
13-2807845              

2.      Check the Appropriate Box if a Member of a Group (See 
Instructions)           

(a)              
(b)  [X]                

3.      SEC Use Only  
.........................................................               

4.      Citizenship or Place of Organization 
A Delaware Corporation  

Number of           5.  Sole Voting Power    7,783,500 shares 
Shares 
Beneficially            6.      Shared Voting Power       0 
Owned by 
Each Reporting          7.      Sole Dispositive Power 8,462,000 shares
Person With                             
8.      Shared Dispositive Power   0

9.Aggregate Amount Beneficially Owned by Each Reporting Person
8,462,000 shares              

10.     Check if the Aggregate Amount in Row (9) Excludes Certain 
Shares (See Instructions)       

11.     Percent of Class Represented by Amount in Row (9)  9.99%                 
12.     Type of Reporting Person (See Instructions)       IA            

Item 1.                 

(a)     Name of Issuer:  USEC, Inc.
(b)     Address of Issuer's Principal Executive Offices
2 Democracy Center
6903 Rockledge Dr.
Bethesda, MD 20817
Item 2.                 

(a)     Name of Person Filing: Donald Smith & Co.,Inc.  

(b)     Address of Principal Business Office:
152 West 57th Street
New York, NY 10019      

(c)     Citizenship:    A Delaware Corporation  

(d)     Title of Class of Securities: Common

(e)       CUSIP Number: 90333E108

Item 3. This statement is filed pursuant to Section 240.13d-1(b), 
and the person filing is an investment advisor registered 
in accordance with Section 240.13d-1(b)(1)(ii)(E);

Item 4. Ownership.              
Provide the following information regarding the aggregate number and 
percentage of the class of securities of the issuer identified in Item 1.       

(a)     Amount beneficially owned:      SEE ITEM 9 OF COVER PAGE        

(b)     Percent of class:               SEE ITEM 11 OF COVER PAGE       

(c)     Number of shares as to which the person has:    
(i)     SOLE POWER TO VOTE:             SEE ITEM 5 OF COVER PAGE 
(ii)    SHARED POWER TO VOTE:           SEE ITEM 6 OF COVER PAGE 
(iii)   SOLE POWER TO DISPOSE:  SEE ITEM 7 OF COVER PAGE 
(iv)    SHARED POWER TO DISPOSE:        SEE ITEM 8 OF COVER PAGE 

Item 5. Ownership of Five Percent or Less is NOT APPLICABLE                     

Item 6. Ownership of More than Five Percent on Behalf of Another Person:                
All securities reported in this schedule are owned by 
advisory clients of Donald Smith & Co., Inc., no one of 
which, to the knowledge of Donald Smith & Co., Inc. owns 
more than 5% of the class.              

Item 7. Identification and Classification of the Subsidiary Which Acquired 
the Security Being Reported on By the Parent Holding Company            
NOT APPLICABLE          

Item 8. Identification and Classification of Members of the Group               
NOT APPLICABLE                  

Item 9. Notice of Dissolution of Group          
NOT APPLICABLE                  

Item 10.        Certification           

(a)      
By signing below I certify that, to the best of my knowledge and 
belief, the securities referred to above were acquired and are held 
in the ordinary course of business and were not acquired and are not 
held for the purpose of or with the effect of changing or 
influencing the control of the issuer of the securities and were not 
acquired and are not held in connection with or as a participant in 
any transaction having that purpose or effect.  

SIGNATURE
After reasonable inquiry and to the best of my knowledge and belief, I 
certify that the information set forth in this statement is true, complete 
and correct. 

February 9, 2005 
Date 

Donald G. Smith___________ 
Signature

President_________________ 
Title