Exhibit 10.3

STANDSTILL AGREEMENT

This STANDSTILL AGREEMENT (“Standstill Agreement”), dated as of June 30, 2011,
is entered into by and among Toshiba America Nuclear Energy Corporation
(“TANE”), Babcock & Wilcox Investment Company (“B&W”) (each an “Investor” and
together, the “Investors”) and USEC Inc. (“USEC”) (each a “Party” and
collectively hereinafter referred to as the Parties”).

WHEREAS, as of May 25, 2010, Toshiba Corporation (“Toshiba”), B&W and USEC
entered into that certain Securities Purchase Agreement (the “Agreement”);

WHEREAS, as of August 10, 2010, Toshiba assigned all of its rights in the
Agreement to TANE;

WHEREAS, pursuant to Section 5.2(e) of the Agreement, the obligations of each
Investor to consummate the transactions contemplated by the Agreement at the
Second Closing are subject to the fulfillment or waiver by such Investor on or
before the Second Closing of the condition that USEC shall have entered into the
Conditional Commitment with DOE;

WHEREAS, pursuant to Section 10.2(a) of the Agreement, if the Second Closing has
not occurred on or before June 30, 2011, each Investor (as to such Investor’s
obligations under the Agreement) or USEC may terminate the Agreement;

WHEREAS, the Second Closing has not occurred on or before June 30, 2011; and

WHEREAS, the Parties desire to enter into this Standstill Agreement in order to
provide USEC with an additional limited period of time to finalize and enter
into the Conditional Commitment.

NOW, THEREFORE, in consideration of the foregoing and of the mutual covenants
contained herein, the Parties hereby agree as follows:

 

  1. Except as expressly set forth herein, each Party reserves all of its rights
under the Agreement, pursuant to the terms thereof, at law and otherwise.
Nothing in this Standstill Agreement shall constitute or be considered a waiver
of any of the rights of any Party or part of a course of dealing or course of
conduct, or otherwise be construed to limit in any respect the rights of any
Party to exercise any of its rights or remedies under the Agreement or otherwise
(except as expressly provided in paragraph 2 hereof).

 

  2. Each Party hereby agrees not to exercise its right to terminate the
Agreement under Section 10.2(a) thereof prior to August 15, 2011.

 

  3. USEC acknowledges and confirms that (a) each Investor has fulfilled all of
its obligations under Section 7.2(a) of the Agreement through the date hereof,
and (b) the failure of the Second Closing to occur on or prior to the date
hereof has not been caused by or been the result of either Investor’s failure to
fulfill any obligation under the Agreement.

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  4. Nothing in this Standstill Agreement shall relieve any Party of any
obligation under the Agreement.

 

  5. Capitalized terms used herein but not otherwise defined herein shall have
the meanings ascribed thereto in the Agreement.

 

  6. This Standstill Agreement may be executed in any number of counterparts and
signatures may be delivered by facsimile or in electronic format (i.e., “PDF”),
each of which may be executed by less than all Parties, each which shall be
enforceable against the Parties actually executing such counterparts, and all of
which together shall constitute one instrument.

 

  7. This Standstill Agreement shall be governed in all respects by the laws of
the State of New York without regard to choice of laws or conflict of laws
provisions that would require the application of the laws of any other
jurisdiction.

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IN WITNESS WHEREOF, the Parties have executed this Standstill Agreement through
their duly authorized representatives as of the date first written above.

 

TOSHIBA AMERICA NUCLEAR ENERGY CORPORATION     BABCOCK & WILCOX INVESTMENT
COMPANY By:   /s/ Akio Shioiri     By:   /s/ Mary Pat Salomone Name:   Akio
Shioiri     Name:   Mary Pat Salomone Title:   President & CEO     Title:  
Senior Vice President & COO

 

USEC Inc. By:   /s/ John C. Barpoulis Name:   John C. Barpoulis Title:   Senior
Vice President & CFO

[Signature Page to Standstill Agreement]