PERFORMANCE GUARANTY

Exhibit 10.3

PERFORMANCE GUARANTY

This Performance Guaranty (“Guaranty”) is made and given as of the 11th day of December 2007, by EnergySolutions, LLC, a Utah limited liability company (“Guarantor”), in favor of Exelon Generation Company, LLC, a Pennsylvania limited liability company (“Beneficiary”).

RECITALS

WHEREAS, ZionSolutions, LLC, a Delaware limited liability company and an Affiliate of Guarantor (“Counterparty”), has entered into that certain Asset Sale Agreement, dated the date hereof (the “Asset Sale Agreement”), pursuant to which Beneficiary has agreed to sell, assign, transfer, convey and deliver to Counterparty the Zion Assets and transfer the Assumed Liabilities to Counterparty, and Counterparty has agreed to purchase, assume and accept from Beneficiary the Zion Assets and to assume, agree to pay, perform and discharge when due the Assumed Liabilities,  all in accordance with the Asset Sale Agreement, and the parties have undertaken certain duties, responsibilities and obligations as set forth in the Asset Sale Agreement;

WHEREAS, upon the Closing, Counterparty will be entering into that certain Lease Agreement (the “Lease Agreement”) pursuant to which Beneficiary will lease the Premises and Counterparty will pay Rent for such lease in accordance with the Lease Agreement, and the parties will undertake certain duties, responsibilities and obligations as set forth in the Lease Agreement;

WHEREAS, upon the Closing, Counterparty and Beneficiary will be entering into that certain Put Option Agreement (the “Put Option Agreement”), pursuant to which Beneficiary will grant the Put Option to Counterparty subject to the terms and conditions set forth in the Put Option Agreement;

WHEREAS, upon the Closing, Counterparty and Beneficiary will be entering into that certain Assignment and Assumption Agreement  (the “Assignment and Assumption Agreement”), pursuant to which Counterparty will assume and accept from Beneficiary the Zion Assets and will assume all Assumed Liabilities as provided in the Asset Sale Agreement;

WHEREAS, Guarantor has agreed to guarantee obligations of Counterparty under the Asset Sale Agreement, the Lease Agreement, the Put Option Agreement and the Assignment and Assumption Agreement (together, the “Guaranteed Agreements”); and

WHEREAS, Guarantor has executed and delivered this Guaranty as an inducement for Beneficiary to enter into the Asset Sale Agreement, and it is a condition to the obligations of Beneficiary under the Asset Sale Agreement that this Guaranty remain in full force and effect; and

WHEREAS, Guarantor will benefit from the transactions contemplated by the Asset Sale Agreement.

NOW, THEREFORE, Guarantor agrees as follows:

1.                                      Definitions.  Capitalized terms used but not otherwise defined herein shall have the meanings ascribed to such terms in the Guaranteed Agreements.

2.                                      Guaranty.  As an inducement to Beneficiary, for and in consideration of Beneficiary entering into the Asset Sale Agreement, Guarantor hereby absolutely, unconditionally, and irrevocably guarantees to Beneficiary and its successors, endorsees and permitted assigns, as primary obligor and not merely as a surety, the full and prompt payment and performance, when due, by Counterparty of all of its present and future obligations that are required to be paid or performed in accordance with the Guaranteed Agreements  (collectively, the “Guaranteed Obligations”).  The Guaranteed Obligations shall include, without limitation, all reasonable costs and expenses (including reasonable attorneys’ fees and disbursements), if any, incurred in enforcing Beneficiary’s rights under this Guaranty, but only to the extent that Beneficiary is successful in enforcing its legal rights under this Guaranty.  This is a guaranty of payment and performance and not of collection.

3.                                      Guaranty Absolute.   The liability of Guarantor under this Guaranty shall be absolute, unconditional and irrevocable, and nothing whatever except actual full payment and performance of the Guaranteed Obligations (and all other debts, obligations and liabilities of Guarantor under this Guaranty) shall operate to discharge Guarantor’s liability hereunder.  Without limiting the generality of the foregoing, Guarantor’s liability hereunder shall not be discharged, released or affected, in whole or in part, by:

3.1.                            The occurrence or continuance of any event of bankruptcy, reorganization or insolvency with respect to Counterparty or Guarantor, or any disallowance of all or any portion of any claim by Beneficiary, its successors or assigns in connection with any such proceeding or in the event that all or any part of any payment is recovered from Beneficiary as a preference payment or fraudulent transfer under the United States Bankruptcy Code or any applicable law, or the dissolution, liquidation or winding up of Guarantor or Counterparty;

3.2.                            Any amendment, supplement, reformation, waiver or other modification of the Guaranteed Agreements, unless such amendment, supplement, reformation, waiver or other modification materially increases the liability of Guarantor with respect to the Guaranteed Obligations and Guarantor has not given its consent thereto if such consent is required under the applicable Guaranteed Agreements;

3.3.                            The exercise, non-exercise or delay in exercising, by Beneficiary or any other Person, of any right under this Guaranty or the Guaranteed Agreements;

3.4.                            Any extension, renewal, settlement, compromise or waiver concerning the Guaranteed Obligations or any change in time, manner or place of payment of, or in

any other terms of, all or any of the Guaranteed Obligations or any other amendment or waiver of, or any consent to depart from, the Guaranteed Agreements or any other agreement, document or instrument relating thereto; provided, however, Guarantor’s obligations with respect to the Guaranteed Obligations shall be credited to the extent that that any such settlement or compromise reduces the Guaranteed Obligations;

3.5.                            Any assignment or other transfer of rights under this Guaranty by Beneficiary, or any permitted assignment or other transfer of the Guaranteed Agreements, including any assignment as security for financing purposes;

3.6.                            Any merger or consolidation into or with any other entity, or other change in the corporate existence or cessation of existence of, Counterparty or Guarantor;

3.7.                            Any change in ownership or control of Guarantor or Counterparty;

3.8.                            Any sale, transfer or other disposition by Guarantor of any direct or indirect interest it may have in Counterparty;

3.9.                            The inaccuracy or breach, or alleged inaccuracy or breach, of any of the representations and warranties of Counterparty or Beneficiary under the Guaranteed Agreements;

3.10.                     The failure to create, preserve, validate, perfect or protect any security interest, collateral or other guaranty granted to, or in favor of, any Person;

3.11.                     The existence of, or any substitution, modification, exchange, release, settlement or compromise of, any security or collateral for or guaranty of any of the Guaranteed Obligations or failure to apply such security or collateral or failure to enforce such guaranty;

3.12.                     The existence of any claim, set-off, or other rights which Guarantor or any Affiliate thereof may have at any time against Beneficiary, any Affiliate thereof or any other Person;

3.13.                     The genuineness, validity, regularity, or enforceability, in whole or in part, of this Guaranty, the Guaranteed Agreements, or any other agreement, document or instrument related to the transactions contemplated hereby or thereby or the absence of any action to enforce the same, or any provision of law purporting to prohibit payment or performance by Counterparty of the Guaranteed Obligations;

3.14.                     The absence of any notice to, or knowledge by, Guarantor of the existence or occurrence of any of the matters or events set forth in the foregoing clauses; and

3.15.                     Except as provided herein, any other circumstances which might otherwise constitute a defense to, or discharge of, Guarantor or Counterparty in respect of the Guaranteed Obligations or a legal or equitable discharge of Counterparty in respect thereof, including, a discharge as a result of any bankruptcy or similar law.

4.                                      Waiver.  In addition to waiving any defenses to which Section 3.1 through Section 3.15 hereof may refer:

4.1.                            Guarantor hereby irrevocably, unconditionally and expressly waives, and agrees that it shall not at any time insist upon, plead or in any manner whatsoever claim or take the benefit or advantage of, any appraisal, valuation, stay, extension, marshaling of assets or redemption laws, or exemption, whether now or at any time hereafter in force, which may delay, prevent or otherwise affect the performance by Guarantor of its obligations under, or the enforcement by Beneficiary of, this Guaranty;

4.2.                            Guarantor hereby irrevocably, unconditionally and expressly waives all notices, diligence, presentment and demand of every kind (whether for nonperformance, nonpayment or protest or of acceptance, maturity, extension of time, change in nature or form of the Guaranteed Obligations, acceptance of security, release of security, composition or agreement arrived at as to the amount of, or the terms of, the Guaranteed Obligations, notice of adverse change in Counterparty’s financial condition, or any other fact which might materially increase the risk to Guarantor hereunder) with respect to the Guaranteed Obligations which are not specifically required to be given by Beneficiary to Guarantor in the Guaranteed Agreements, and any other demands whatsoever which are not specifically required to be given by Beneficiary to Guarantor in the Guaranteed Agreements, and waives the benefit of all provisions of law which are in conflict with the terms of this Guaranty; provided, however, Beneficiary agrees that all demands under this Guaranty shall be in writing and shall specify in what manner and what amount Counterparty has failed to pay or perform and an explanation of why such payment is due, with a specific statement that Beneficiary is calling upon Guarantor to pay or perform under this Guaranty.  Any payment demand shall also include the bank account and wire transfer information to which the funds should be wire transferred;

4.3.                            The Guarantor hereby irrevocably, unconditionally and expressly waives promptness, diligence, notice of acceptance and any other notice with respect to any of the Guaranteed Obligations and the delivery, acceptance, performance, default or enforcement of this Guaranty and any requirement that Beneficiary protect, secure or perfect any security interest or exhaust any right or first proceed against Counterparty or any other Person or any other security or guaranty;

4.4.                            Guarantor irrevocably, unconditionally and expressly waives (i) any right it may have to bring a case or proceeding against Counterparty by reason of Guarantor’s performance under this Guaranty or with respect to any other obligation of Counterparty to Guarantor, under any state or federal bankruptcy, insolvency,

reorganization, moratorium or similar laws for the relief of debtors or otherwise; (ii) any subrogation to the rights of Beneficiary against Counterparty and any other claim against Counterparty which arises as a result of payments made by Guarantor pursuant to this Guaranty, until the Guaranteed Obligations have been paid and performed in full and such payments are not subject to any right of recovery; (iii) any setoffs or counterclaims against Beneficiary, Counterparty or any other Person which would otherwise impair Beneficiary’s rights against Guarantor hereunder; and (iv) any right of reimbursement or contribution from Counterparty.  If any amount shall be paid to the Guarantor on account of such subrogation rights at any time prior to when the Guaranteed Obligations have been paid and performed in full, such amount shall be held in trust for the benefit of Beneficiary and shall forthwith be paid to Beneficiary to be applied to the Guaranteed Obligations; and