Document:

<PAGE>
                                                                   EXHIBIT 10.79

                           AMENDMENT AGREEMENT NO. 2

      AMENDMENT AGREEMENT ("Amendment") dated as of February 1, 2005 to the
Revolving Credit Agreement dated as of September 27, 2002, as amended to date
(as the same may be further amended, supplemented or modified from time to time
in accordance with its terms, the "Credit Agreement") by and among UNITED STATES
ENRICHMENT CORPORATION, a Delaware corporation (the "Borrower"), the lenders
party thereto (the "Lenders") and JPMORGAN CHASE BANK, N.A. (formerly known as
JPMorgan Chase Bank) as Administrative and Collateral Agent (the "Agent"),
Merrill Lynch Capital, as Syndication Agent, GMAC Commercial Finance LLC
(formerly known as GMAC Business Credit, LLC), as Documentation Agent and
Congress Financial Corporation, as Managing Agent. All capitalized terms used
herein and not otherwise defined shall have the meaning assigned to such terms
in the Credit Agreement.

      WHEREAS, the Borrower, Lenders and the Agent entered into the Credit
Agreement and other Financing Documents, including the Security Agreement;

      WHEREAS, the Credit Agreement and Guarantee of Holdings restrict the
incurrence of Liens on assets of the Borrower or Holdings;

      WHEREAS, the Company and Holdings are parties to (x) Memoranda of
Agreement entered into as of December 10, 2004 pursuant to which the Department
of Energy ("DOE") will deliver to the Company certain feed material and (y) a
Security Agreement dated as of February 2, 2005 ("DOE Security Agreement")
pursuant to which the Company and Holdings will grant to the DOE a security
interest in such feed material and the proceeds thereof; and

      WHEREAS, the Borrower and Holdings have requested that the Required
Lenders amend the provisions of Section 6.02 of the Credit Agreement and the
Holdings' Guarantee for the purpose of allowing a Lien in favor of the DOE on
feed material delivered to the Company by the DOE.

      NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the parties hereto agree as
follows:

      SECTION 1. AMENDMENT TO CREDIT AGREEMENT

      1.1   Section 6.02 of the Credit Agreement is hereby amended by striking
the word "and" at the end of 6.02(g), striking the period at the end of 6.02(h)
and adding in its place "; and" and adding the following subsection (i):

            "(i) Liens created by the Security Agreement dated as of February 2,
      2005 as in effect on its effective date made by the Borrower and Holdings
      in favor of the Department of Energy covering natural uranium feed
      material, the accounts arising from the sale thereof, all contracts and
      agreements for the sale thereof, books and records related thereto and all
      proceeds thereof (none of which for the purposes of this Agreement shall
      constitute Eligible Inventory or Eligible Receivables) (collectively, the
      "DOE Collateral"), provided that such material is maintained in
      specifically designated cylinders and physically separated from Eligible
      Inventory and the accounts arising from the sale of such material are
      maintained by separate written or electronic records identifying the Lien
      of the Department of Energy."
<PAGE>
      SECTION 2. AMENDMENT TO GUARANTEE OF HOLDINGS

      2.1   Section 5 of the Holdings Guarantee is hereby amended by adding the
following unnumbered sentence at the end of such Section:

            "Notwithstanding anything to the contrary contained in this Section
      5, the Guarantor may enter into the Security Agreement dated as of
      February 2, 2005 made by the Guarantor and the Borrower in favor of the
      Department of Energy and grant a Lien on the assets described therein,
      provided that such Lien complies with Section 6.02(g) of the Credit
      Agreement."

      SECTION 3. AMENDMENT TO SECURITY AGREEMENT

      3.1   Section 2.1 Pledge and Grant of Security Interest is hereby amended
                        -------------------------------------
by adding the following sentence at the end of the last paragraph thereof:

            "In addition, in no event shall the Collateral include, and no
      Pledgor shall be deemed to have granted a security interest in, the DOE
      Collateral."

      SECTION 4. CONDITIONS PRECEDENT

      4.1   All representations and warranties contained in this Amendment or
otherwise made in writing to the Agent in connection herewith shall be true and
correct.

      4.2   No unwaived event has occurred and is continuing which constitutes
an Event of Default under the Credit Amendment or would constitute such an Event
of Default but for the requirement that notice be given or time elapse or both.

      4.3   The Agent shall have received counterparts of this Amendment duly
executed by the Borrower, Holdings and Required Lenders.

      4.4   The Agent shall have received a fully executed copy of the DOE
Security Agreement in form and substance reasonably satisfactory to it.

      SECTION 5. MISCELLANEOUS

      5.1   The Borrower reaffirms and restates the representations and
warranties set forth in Article IV of the Credit Agreement and all such
representations and warranties shall be true and correct on the date hereof with
the same force and effect as if made on such date (except insofar as such
representations and warranties relate expressly to an earlier date). Each of the
Borrower and Holdings represents and warrants (which representations and
warranties shall survive the execution and delivery hereof) to the Agent that:

            (a)   It has the power and authority to execute, deliver and carry
      out the terms and provisions of this Amendment and the transactions
      contemplated hereby and has taken or caused to be taken all necessary
      action to authorize the execution, delivery and performance of this
      Amendment and the transactions contemplated hereby;

            (b)   No consent of any other person, and no action of, or filing
      with any governmental or public body or authority is required to
      authorize, or is otherwise required in connection with the execution,
      delivery and performance of this Amendment;

            (c)   This Amendment has been duly executed and delivered on behalf
      of each such party by a duly authorized officer, and constitutes its
      legal, valid and binding obligation enforceable in accordance with its
      terms, subject to bankruptcy, reorganization, insolvency, moratorium and
      other similar laws affecting the enforcement of creditors' rights
      generally and the exercise of judicial discretion in accordance with
      general principles of equity;
<PAGE>
            (d)   The execution, delivery and performance of this Amendment will
      not violate any law, statute or regulation, or any order or decree of any
      court or governmental instrumentality, or conflict with, or result in the
      breach of, or constitute a default under any contractual obligation of
      each.

      5.2   All references to the Credit Agreement in the Credit Agreement, the
Financing Documents and the other documents and instruments delivered pursuant
to or in connection therewith shall mean the Credit Agreement as amended hereby
and as such may in the future be amended, restated, supplemented or modified
from time to time;

      5.3   Except as expressly set forth in this Amendment, the terms,
provisions and conditions of the Credit Agreement and other Financing Documents
are unchanged, and said agreements shall remain in full force and effect and are
hereby confirmed and ratified;

      5.4   This Amendment may be executed by the parties hereto individually or
in combination, in one or more counterparts, each of which shall be an original
and all of which shall constitute one and the same agreement;

      5.5   The Required Lenders hereby authorize the Agent to file Uniform
Commercial Code amendments removing from the Collateral description assets which
are subject to the Lien of the DOE.

      5.6   Delivery of an executed counterpart of a signature page by
telecopier shall be effective as delivery of a manually executed counterpart;
and

      5.7   This Amendment shall be governed by, and construed and interpreted
in accordance with, the internal laws of the State of New York and shall become
effective upon execution thereof by the Borrower, the Agent and the Required
Lenders.
<PAGE>
      IN WITNESS WHEREOF, the Borrower, the Agent and the Required Lenders have
caused this Amendment to be duly executed by their respective officers as of the
date and year first above written.

                              UNITED STATES ENRICHMENT CORPORATION, as Borrower

                              By:        /s/ Ellen C. Wolf
                                  ----------------------------------------
                                  Name:  Ellen C. Wolf
                                  Title: Sr VP and CFO

                              JPMORGAN CHASE BANK, N.A. (formerly known as
                              JPMorgan Chase Bank), individually and as
                              Administrative and Collateral Agent and Lead
                              Arranger

                              By:        /s/ James M. Barbato
                                  ----------------------------------------
                                  Name:  James M. Barbato
                                  Title: Vice President

                              MERRILL LYNCH CAPITAL, a division of Merrill Lynch
                              Business Financial Services, Inc., as Syndication
                              Agent and Lender

                              By:        /s/ Mark Gertzof
                                  ----------------------------------------
                                  Name:  Mark Gertzof
                                  Title: Director

                              GMAC COMMERCIAL FINANCE LLC, as Documentation
                              Agent and Lender

                              By:         /s/ Thomas Maiale
                                   ----------------------------------------
                                   Name:  Thomas Maiale
                                   Title: Director
<PAGE>
                             CONGRESS FINANCIAL CORPORATION, as Managing Agent
                             and Lender

                             By:          /s/ Jason Searle
                                   ----------------------------------------
                                   Name:  Jason Searle
                                   Title: Assistant VP

                             SIEMENS FINANCIAL SERVICES, INC., as Lender

                             By:          /s/ Michael Coiley
                                   ----------------------------------------
                                   Name:  Michael Coiley
                                   Title: Senior Vice President

                             SOVEREIGN BANK, as Lender

                             By:          /s/ Eric Ritter
                                   ----------------------------------------
                                   Name:  Eric Ritter
                                   Title: AVP

Acknowledged:

USEC INC., as Guarantor

By:      /s/ Ellen C. Wolf
      ------------------------------
      Name:  Ellen C. Wolf
      Title: Sr VP and CFO<PAGE>
                                                                   EXHIBIT 10.80

                           AMENDMENT AGREEMENT NO. 3
                           -------------------------

      AMENDMENT AGREEMENT NO. 3 ("Amendment") dated as of April 26, 2005 to (i)
the Revolving Credit Agreement dated as of September 27, 2002, as amended to
date (as the same may be further amended, supplemented or modified from time to
time in accordance with its terms, the "Credit Agreement") by and among UNITED
STATES ENRICHMENT CORPORATION, a Delaware corporation (the "Borrower"), the
lenders party thereto (the "Lenders") and JPMORGAN CHASE BANK, N.A. (formerly
known as JPMorgan Chase Bank), as Administrative and Collateral Agent (the
"Agent"), MERRILL LYNCH CAPITAL, as Syndication Agent, GMAC COMMERCIAL FINANCE
LLC (formerly known as GMAC Business Credit, LLC), as Documentation Agent and
WACHOVIA BANK, N.A. (successor by merger to Congress Financial Corporation), as
Managing Agent and (ii) the Guarantee dated as of September 27, 2002, as amended
to date (as the same may be further amended, supplemented or modified from time
to time in accordance with its terms, the "Holdings Guarantee"), executed by
USEC, Inc., a Delaware corporation ("Holdings"), in favor of the Agent for the
Lenders, the Agent as an issuer of Letters of Credit and certain other persons
more fully described in the preamble to the Guarantee. All capitalized terms
used herein and not otherwise defined shall have the meaning assigned to such
terms in the Credit Agreement.

      WHEREAS, the Borrower, Lenders and the Agent entered into the Credit
Agreement and other Financing Documents, including the Holdings Guarantee;

      WHEREAS, the Credit Agreement permits the Borrower to make Permitted
Investments, but the Holdings Guarantee does not permit Holdings to make
Permitted Investments nor does the Credit Agreement permit the Borrower to make
Restricted Payments to Holdings for the purpose of making Permitted Investments;

      WHEREAS, the categories of Permitted Investments does not permit
investments in auction rate securities;

      WHEREAS, the Credit Agreement contains restrictions on the redemption of
Indebtedness; and

      WHEREAS, the Borrower has requested that the Required Lenders amend the
definition of Permitted Investments to allow investments in certain auction rate
securities, amend the provisions of Section 6.06 of the Credit Agreement to
modify the restrictions on redemptions of Indebtedness and for the purpose of
allowing Restricted Payments to be made to Holdings for the purpose of making
Permitted Investments and to amend the Holdings Guarantee to permit the making
by Holdings of Permitted Investments.

      NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the parties hereto agree as
follows:

      SECTION 1. AMENDMENTS TO CREDIT AGREEMENT
<PAGE>
      1.1   The definition of "Permitted Investments" in Article I of the Credit
Agreement is hereby amended by striking the word "and" at the end of
subparagraph (e), striking the period at the end of subparagraph (f) and adding
in its place "; and" and adding the following subparagraph (g):

            "(g) AAA rated asset backed auction rate securities which are
      repriced at least every 35 days."

      1.2   Section 6.06 of the Credit Agreement is hereby amended by (x)
striking the words "$25,000,000 in any fiscal year and" contained in subsection
(c) and (y) striking the word "; and" in the last line of subsection (e),
substituting a comma, striking the period at the end subsection (f),
substituting the word "and" and adding the following subsection (g):

            "(g) the Borrower may transfer funds to Holdings to permit Holdings
      to make Permitted Investments."

      SECTION 2. AMENDMENT TO HOLDINGS GUARANTEE

      2.1   Section 5 of the Holdings Guarantee is hereby amended by amending in
its entirety the final sentence at the end of such Section to read as follows:

      "Notwithstanding anything to the contrary contained in this Section 5, the
      Guarantor may (i) enter into the Security Agreement dated as of February
      2, 2005 made by the Guarantor and the Borrower in favor of the Department
      of Energy and grant a Lien on the assets described therein, provided that
      such Lien complies with Section 6.02(g) of the Credit Agreement and (ii)
      make Permitted Investments, provided the Guarantor has granted a Lien on
      all such Investments in favor of the Agent as required by the Security
      Agreement."

      SECTION 3. CONDITIONS PRECEDENT

      3.1   All representations and warranties contained in this Amendment or
otherwise made in writing to the Agent in connection herewith shall be true and
correct.

      3.2   No unwaived event has occurred and is continuing which constitutes
an Event of Default under the Credit Amendment or would constitute such an Event
of Default but for the requirement that notice be given or time elapse or both.

      3.3   The Agent shall have received counterparts of this Amendment duly
executed by the Borrower, Holdings, the other Guarantors and Required Lenders.

         SECTION 4.        MISCELLANEOUS

      4.1   The Borrower reaffirms and restates the representations and
warranties set forth in Article IV of the Credit Agreement and all such
representations and warranties shall be true and correct on the date hereof with
the same force and effect as if made on such date (except insofar as such
representations and warranties relate expressly to an earlier date). The
foregoing representations and warranties shall be subject to, and interpreted in
conjunction with, the terms of the Waiver Agreement dated as of April 7, 2005
among the Borrower, Holdings, the Lenders and the Agent. Each of the Borrower,
Holdings and the other Guarantors represents and warrants (which representations
and warranties shall survive the execution and delivery hereof) to the Agent
that:

            (a)   It has the power and authority to execute, deliver and carry
      out the terms and provisions of this Amendment and the transactions
      contemplated hereby and has taken or caused to be taken all necessary
      action to authorize the execution, delivery and performance of this
      Amendment and the transactions contemplated hereby;
<PAGE>
            (b)   No consent of any other person, and no action of, or filing
      with any governmental or public body or authority is required to
      authorize, or is otherwise required in connection with the execution,
      delivery and performance of this Amendment;

            (c)   This Amendment has been duly executed and delivered on behalf
      of each such party by a duly authorized officer, and constitutes its
      legal, valid and binding obligation enforceable in accordance with its
      terms, subject to bankruptcy, reorganization, insolvency, moratorium and
      other similar laws affecting the enforcement of creditors' rights
      generally and the exercise of judicial discretion in accordance with
      general principles of equity;

            (d)   The execution, delivery and performance of this Amendment will
      not violate any law, statute or regulation, or any order or decree of any
      court or governmental instrumentality, or conflict with, or result in the
      breach of, or constitute a default under any contractual obligation of
      each.

      4.2   All references to the Credit Agreement in the Credit Agreement, the
Financing Documents and the other documents and instruments delivered pursuant
to or in connection therewith shall mean the Credit Agreement as amended hereby
and as such may in the future be amended, restated, supplemented or modified
from time to time;

      4.3   Except as expressly set forth in this Amendment, the terms,
provisions and conditions of the Credit Agreement and other Financing Documents
are unchanged, and said agreements shall remain in full force and effect and are
hereby confirmed and ratified;

      4.4   This Amendment may be executed by the parties hereto individually or
in combination, in one or more counterparts, each of which shall be an original
and all of which shall constitute one and the same agreement;

      4.5   Delivery of an executed counterpart of a signature page by
telecopier shall be effective as delivery of a manually executed counterpart;
and

      4.6   This Amendment shall be governed by, and construed and interpreted
in accordance with, the internal laws of the State of New York and shall become
effective upon execution thereof by the Borrower, the Agent and the Required
Lenders.

                  [Remainder of Page Left Intentionally Blank]
<PAGE>
IN WITNESS WHEREOF, the Borrower, the Agent and the Required Lenders have caused
this Amendment to be duly executed by their respective officers as of the date
and year first above written.

                         UNITED STATES ENRICHMENT CORPORATION,
                         as Borrower

                         By:     /s/ Ellen C. Wolf
                             ---------------------------------
                                 Name:  Ellen C. Wolf
                                 Title: Sr VP and CFO

                         USEC INC., as Guarantor

                         By:     /s/ Ellen C. Wolf
                             ---------------------------------
                                 Name:  Ellen C. Wolf
                                 Title: Sr VP and CFO

                         JPMORGAN CHASE BANK, N.A. (formerly known as
                         JPMorgan Chase Bank) individually and as Administrative
                         and Collateral Agent and Lead Arranger

                         By:     James M. Barbato
                             ---------------------------------
                                 Name:  James M. Barbato
                                 Title: Vice President

                         MERRILL LYNCH CAPITAL, a division of Merrill Lynch
                         Business Financial Services, Inc., as Syndication Agent
                         and Lender

                         By:     /s/ Barry W. Dubin
                             ---------------------------------
                                 Name:  Barry W. Dubin
                                 Title: Assistant Vice President

                         GMAC COMMERCIAL FINANCE LLC, as
                         Documentation
                         Agent and Lender

                         By:     /s/ Thomas Maiale
                             ---------------------------------
                                 Name:  Thomas Maiale
                                 Title: Director
<PAGE>
                         WACHOVIA BANK, N.A. (successor by merger to
                         Congress Financial Corporation), as Managing Agent and
                         Lender

                         By:   /s/ Jason Searle
                             ----------------------------
                                   Name:  Jason Searle
                                   Title: Associate

                         SIEMENS FINANCIAL SERVICES, INC., as Lender

                         By:   /s/ Frank Amodio
                             ----------------------------
                                   Name:  Frank Amodio
                                   Title: Vice President - Credit

                         SOVEREIGN BANK, as Lender

                         By:  /s/ Eric Ritter
                             ----------------------------
                                  Name: Eric Ritter
                                  Title:AVP

Acknowledged:

NAC HOLDING INC., as Guarantor

By:   /s/ Michael R. Clarke
     ----------------------------
     Name:  Michael R. Clarke
     Title: Treasurer

NAC INTERNATIONAL INC., as Guarantor

By:   /s/ Michael R. Clarke
     ----------------------------
     Name:  Michael R. Clarke
     Title: Treasurer

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