<PAGE>

                                                                Exhibit 10(dd)

                       FIRST AMENDMENT TO CREDIT AGREEMENT

    Agreement is made as of this 9th day of December, 1997 among STARMET 
CORPORATION, a Massachusetts corporation (f/k/a Nuclear Metals, Inc.) 
("StarMet"), STARMET POWDERS, LLC, a Delaware limited liability corporation 
("Powders"), STARMET AEROCAST, LLC, a Delaware limited liability corporation 
("AeroCast"),  STARMET COMCAST, LLC, a Delaware limited liability corporation 
("ComCast"), STARMET NMI CORPORATION, a Massachusetts corporation ("NMI"), 
STARMET CMI CORPORATION, a Delaware corporation (f/k/a Carolina Metals, Inc.) 
("CMI"), STARMET HOLDINGS CORPORATION, a Massachusetts corporation 
("Holdings"), NMI FOREIGN SALES CORPORATION, a U.S. Virgin Islands 
corporation ("FSC", and together with StarMet, Powders, AeroCast, ComCast, 
NMI, CMI and Holdings, the "Borrowers") and STATE STREET BANK AND TRUST 
COMPANY, a Massachusetts chartered trust company ("Bank").

    WHEREAS, the Borrowers and the Bank are parties to an Amended and 
Restated Credit Agreement dated as of October 1, 1997 (the "Credit 
Agreement"); and

    WHEREAS, the parties have agreed to certain modifications;

    NOW THEREFORE, the parties agree as follows:

    1.   Section 1.01.  Section 1.01 of the Credit Agreement is hereby 
amended by deleting the reference to $6,500,000 in the third line and 
$6,050,000 in the last line and replacing both references with $8,050,000.

    2.   Section 1.02(a).  Section 1.02(a) of the Credit Agreement is hereby 
amended by:

    (a)  deleting the reference to $6,550,000 in the seventh line and 
replacing it with $8,050,000; and

    (b)  deleting the proviso at the end of Section 1.02(a) and substituting 
therefor the following:

    provided that (i) up to January 10, 1998, the aggregate of all Advances
    outstanding shall not exceed $8,050,000 less the maximum aggregate
    liability of the borrowers under any outstanding letters of credit issued
    prior to the date hereof or pursuant to this Credit Agreement and (ii) from
    and after January 10, 1998 up to the Maturity Date, the aggregate of all
    Advances outstanding shall not exceed $6,550,000 less the maximum aggregate
    liability of the Borrowers under any outstanding letters of credit issued
    prior to the date hereof or pursuant to this Credit Agreement (the "Maximum
    Credit").

                                      -1-

<PAGE>

    3.   Section 1.02(b).  Section 1.02(b) of the Credit Agreement is hereby 
amended by adding the following at the end:

    "As provided in Section 1.02(a), the Revolving Credit shall reduce from
    $8,050,000 to $6,550,000 on January 10, 1998 and any amount in excess of
    $6,550,000 shall be paid on or before January 10, 1998".

    4.   Section 1.02(c).  Section 1.02(c) of the Credit Agreement is hereby 
amended by deleting the first sentence in Section 1.02(c) its entirety and 
substituting therefor the following:

    "Amounts owed to Bank with respect to Advances made by Bank shall be
    evidenced by Bank's books and records and may, at the request of the Bank,
    be further evidenced by one or more revolving credit notes (collectively,
    the "Revolving Credit Note").  As of the date of this First Amendment, the
    Advances are evidenced by an Amended and Restated Revolving Credit Note
    dated as of March 31, 1995 (as amended and restated October 1, 1997) in the
    principal amount of $6,550,000 (the "Original Note") and an Additional
    Revolving Credit Note dated as of the date of this First Amendment in the
    principal amount of $1,500,000 (the "Additional Note").  All Advances shall
    be deemed made pursuant to the Original Note up to the maximum principal
    amount thereof and thereafter pursuant to the Additional Note.  Any
    repayments of principal shall be applied first to the Additional Note, then
    to the Original Note".

    5.   Effectiveness; Conditions to Effectiveness.  This First Amendment to 
Credit Agreement shall become effective upon (a) execution of this First 
Amendment by the Borrowers and the Bank, (b) execution by the Borrowers of 
the Additional Revolving Credit Note substantially in the form of Exhibit A 
attached hereto, and (c) receipt by the Bank of evidence satisfactory to the 
Bank that the Borrowers are authorized to execute this First Amendment.

    6.   Miscellaneous.

         (a)  The Borrowers hereby confirm to the Bank that the representations
    and warranties of the Borrowers set forth in Article II of the Credit
    Agreement are true and correct as of the date hereof, as if set forth
    herein in full.

         (b)  There is no Event of Default, and no condition which, with the
    passage of time or giving of notice or both, would constitute an Event of
    Default under the Credit Agreement.

         (c)  Except as set forth above, the Credit Agreement remains in full
    force and effect.

                                      -2-

<PAGE>

         IN WITNESS WHEREOF, the parties have executed this First Amendment to
Credit Agreement under seal as of the date first above written.

                                  STARMET CORPORATION



                                  By: /s/ James M. Spiezio
                                     --------------------------
                                       Name: James M. Spiezio
                                       Title: VP Finance


                                  STARMET POWDERS, LLC



                                  By: /s/ James M. Spiezio
                                     ----------------------------
                                       Name: James M. Spiezio
                                       Title: Treasurer


                                  STARMET AEROCAST, LLC


                                  By: /s/ James M. Spiezio
                                     ----------------------------
                                       Name: James M. Spiezio
                                       Title: Treasurer


                                  STARMET COMCAST, LLC


                                  By: /s/ James M. Spiezio
                                     ----------------------------
                                       Name: James M. Spiezio
                                       Title: Treasurer


                                  STARMET NMI CORPORATION



                                  By: /s/ James M. Spiezio
                                     ----------------------------
                                       Name: James M. Spiezio
                                       Title: Treasurer

                                      -3-

<PAGE>

                                  STARMET CMI CORPORATION



                                  By: /s/ James M. Spiezio
                                      ------------------------------
                                       Name: James M. Spiezio
                                       Title: Treasurer



                                  STARMET HOLDINGS CORPORATION



                                  By: /s/ James M. Spiezio
                                      ------------------------------
                                       Name: James M. Spiezio
                                       Title: Treasurer



                                  NMI FOREIGN SALES CORPORATION



                                  By: /s/ James M. Spiezio
                                      ------------------------------
                                       Name: James M. Spiezio
                                       Title: Treasurer



                                  STATE STREET BANK AND TRUST 
                                  COMPANY



                                  By: /s/ William R. Dewey IV
                                      ------------------------------
                                       Name: William R. Dewey IV
                                       Title: Vice President


                                      -4-

<PAGE>

                                  EXHIBIT A
                                       
                       ADDITIONAL REVOLVING CREDIT NOTE
                                       
                                       
$1,500,000                                                 December 9, 1997

    FOR VALUE RECEIVED, the undersigned, STARMET CORPORATION, STARMET 
POWDERS, LLC, STARMET AEROCAST, LLC, STARMET COMCAST, LLC, STARMET NMI 
CORPORATION, STARMET CMI CORPORATION, STARMET HOLDINGS CORPORATION, NMI 
FOREIGN SALES CORPORATION (the "Borrowers"), hereby jointly and severally, 
promise to pay to the order of STATE STREET BANK AND TRUST COMPANY, a 
Massachusetts trust company ("Bank"), in lawful money of the United States of 
America in immediately available funds at its office at 225 Franklin Street, 
Boston, Massachusetts 02110 the principal sum of ONE MILLION FIVE HUNDRED 
THOUSAND DOLLARS ($1,500,000) or such lesser sum as may from time to time be 
outstanding under the terms of the Credit Agreement between the Borrowers and 
Bank of even date herewith, as amended, modified, supplemented and/or 
restated from time to time (the "Credit Agreement').

    The Borrowers promise to pay interest on the unpaid principal balance at 
the rates and at the times provided in the Credit Agreement.  This Note may 
be prepaid only in accordance with the terms of the Credit Agreement.

    This Note will become due and payable on January 10, 1998 and earlier 
upon the occurrence of an Event of Default (as defined in the Credit 
Agreement).  The Borrowers agree to pay all reasonable legal fees and other 
costs of collection of this Note.

    No delay or omission on the part of the holder in exercising any right 
hereunder shall operate as a waiver of such right, nor shall any waiver on 
one occasion be deemed to be an amendment or waiver of any such right with 
respect to any future occasion.  The Borrowers hereby waive presentment, 
demand, protest and notice of every kind and assents to any one or more 
indulgences, to any substitution, exchange or release of collateral (if at 
any time there be available collateral to the holder of this Note) and to the 
addition or release of any other party or persons primarily or secondarily 
liable.
 
                                      -5-

<PAGE>

    This Note shall be governed and construed under the laws of the 
Commonwealth of Massachusetts and shall be deemed to be under seal.

                                  STARMET CORPORATION

WITNESS:


/s/ Rebecca Perry                      By: /s/ James M. Spiezio
-----------------------                   -------------------------
                                          Name: James M. Spiezio
                                          Title: VP Finance


                                  STARMET POWDERS, LLC


WITNESS:


/s/ Rebecca Perry                      By: /s/ James M. Spiezio
-----------------------                   -------------------------
                                          Name: James M. Spiezio
                                          Title: Treasurer


                                  STARMET AEROCAST, LLC


WITNESS:


/s/ Rebecca Perry                      By: /s/ James M. Spiezio
-----------------------                   -------------------------
                                          Name: James M. Spiezio
                                          Title: Treasurer


                                  STARMET COMCAST, LLC

WITNESS:


/s/ Rebecca Perry                      By: /s/ James M. Spiezio
-----------------------                   -------------------------
                                          Name: James M. Spiezio
                                          Title: Treasurer


                                      -6-

<PAGE>

                                  STARMET NMI CORPORATION

WITNESS:


/s/ Rebecca Perry                     By: /s/ James M. Spiezio
----------------------------             -----------------------------
                                          Name: James M. Spiezio
                                          Title: Treasurer


                                  STARMET CMI CORPORATION

WITNESS:


/s/ Rebecca Perry                     By: /s/ James M. Spiezio
----------------------------             -----------------------------
                                          Name: James M. Spiezio
                                          Title: Treasurer


                                  STARMET HOLDINGS CORPORATION

WITNESS:


/s/ Rebecca Perry                     By: /s/ James M. Spiezio
----------------------------             -----------------------------
                                          Name: James M. Spiezio
                                          Title: Treasurer


                                  NMI FOREIGN SALES CORPORATION

WITNESS:


/s/ Rebecca Perry                     By: /s/ James M. Spiezio
----------------------------             -----------------------------
                                          Name: James M. Spiezio
                                          Title: Treasurer


                                      -7-