Summary of Significant Accounting Policies	12 Months Ended
Dec. 31, 2012
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Operations USEC Inc. ("USEC") is a global energy company and is a leading supplier of low enriched uranium ("LEU") for commercial nuclear power plants. LEU consists of two components: separative work units ("SWU") and uranium. SWU is a standard unit of measurement that represents the effort required to transform a given amount of natural uranium into two components: LEU having a higher percentage of U235 and depleted uranium having a lower percentage of U235. The SWU contained in LEU is calculated using an industry standard formula based on the physics of enrichment. The amount of enrichment deemed to be contained in LEU under this formula is commonly referred to as its SWU component and the quantity of natural uranium used in the production of LEU under this formula is referred to as its uranium component. Utility customers typically provide uranium to USEC as part of their enrichment contracts, and USEC delivers LEU to the customers and charges for the SWU component. USEC has historically produced or acquired LEU from two principal sources. USEC has produced about half of its supply of LEU at the Paducah GDP in Paducah, Kentucky, and USEC has acquired the other portion under a contract with Russia (the "Russian Contract") under the 20-year Megatons to Megawatts program. Under the Russian Contract, USEC purchases the SWU component of LEU derived from dismantled nuclear weapons from the former Soviet Union for use as fuel in commercial nuclear power plants. The current arrangement under which USEC is continuing enrichment at the Paducah GDP expires in 2013 and USEC expects to complete its purchases under the Russian Contract in 2013. Commencing in 2013, USEC will continue to acquire Russian LEU under the terms of a new 10-year commercial agreement with Russia (the "Russian Supply Agreement"). Purchase quantities under the Russian Supply Agreement will be about half the level under the Megatons to Megawatts program unless the parties exercise a mutual option to increase such purchases. Additional details are provided in Note 18 under "Purchase of Separative Work Units from Russia." In addition, USEC performs contract services through its subsidiary NAC International Inc. ("NAC") and for the U.S. Department of Energy ("DOE") and DOE contractors at the Paducah gaseous diffusion plant ("GDP") in Paducah, Kentucky and the site of the former Portsmouth GDP in Piketon, Ohio. On March 15, 2013, USEC sold NAC to a subsidiary of Hitachi Zosen Corporation. Refer to Note 20 for details. Basis of Presentation The consolidated financial statements include the accounts of USEC Inc., its principal subsidiary, United States Enrichment Corporation, and its other subsidiaries including NAC. American Centrifuge Manufacturing, LLC, a joint company established by USEC (through its subsidiary American Centrifuge Holdings, LLC) and Babcock & Wilcox Technical Services Group, Inc., is also included in the consolidated financial statements. All material intercompany transactions are eliminated. Liquidity Risks and Uncertainties USEC's accompanying consolidated financial statements have been prepared assuming that USEC will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business for the 12- month period following the date of these consolidated financial statements. USEC reported a net loss of $1.2 billion in the year ended December 31, 2012 and a net loss of $491.1 million in the year ended December 31, 2011. These net losses were primarily the result of expenses related to the development of the American Centrifuge project, including the expense of previously capitalized amounts during both periods and related tax valuation allowances. USEC's cash from operating activities was $142.9 million for the year ended December 31, 2012. USEC expects that its cash balance, internally generated cash from its LEU operations and services provided by its contract services segment, and available borrowings under its revolving credit facility will provide sufficient cash to meet its obligations as they become due for at least 12 months from the date of the accompanying financial statements, assuming the renewal or replacement of its revolving credit facility past September 2013. On March 14, 2013, USEC amended its credit facility, among other things, to extend the expiration date of the credit facility from May 31, 2013 to September 30, 2013. USEC repaid its existing term loan in connection with the amendment. USEC's credit facility is available to finance working capital needs and general corporate purposes. USEC believes it is reasonable to expect an extension or replacement for the facility by September 2013. USEC's credit facility needs at that time will depend on USEC's working capital needs, which in part depend on the timing of USEC's transition of enrichment at the Paducah gaseous diffusion plant, and USEC may need a substantially smaller credit facility in the future. USEC's credit facility would also likely be replaced as part of any potential restructuring (discussed below). In addition, if USEC were unable to renew or replace its credit facility beyond September 2013, USEC would seek to work with customers to effect further order movements to provide sufficient liquidity and working capital. Although USEC expects to have adequate liquidity to meet its obligations during 2013, in light of the significant transition of USEC's business and the uncertainties and challenges facing USEC and in order to improve USEC's credit profile and its ability to successfully finance and deploy the American Centrifuge project and to maximize USEC's participation in such project, USEC is engaged with its advisors and certain stakeholders on alternatives for a possible restructuring of its balance sheet. USEC continues to believe that the deployment of the American Centrifuge project represents USEC's clearest path to a long-term, direct source of domestic enrichment production, and therefore the long-term viability of USEC's LEU business and USEC believes that a restructuring could improve the likelihood of success in the deployment of the American Centrifuge project. Although USEC has no assurance regarding its ability to pursue or complete a restructuring, a restructuring could result in significant changes to the Company's capital structure and adjustments to its balance sheet, including the creation of a new entity for accounting purposes, which would have a material impact on USEC's financial statements, including the going concern assumption on which they have been prepared. In addition, on May 8, 2012, USEC received a notice from the New York Stock Exchange ("NYSE") that the average closing price of its common stock was below the NYSE's continued listing criteria relating to minimum share price. A delisting of USEC's common stock by the NYSE and the failure of its common stock to be listed on another national exchange could cause significant adverse consequences. A fundamental change is triggered under the terms of USEC's convertible notes if USEC's shares of common stock are not listed for trading on any of the NYSE, the American Stock Exchange, the NASDAQ Global Market or the NASDAQ Global Select Market, and the holders of the notes can require USEC to repurchase the notes at par for cash. The occurrence of a fundamental change under the convertible notes that permits the holders of the convertible notes to require a repurchase for cash is also an event of default under USEC's credit facility. USEC intends to seek shareholder approval for a reverse stock split at its next annual meeting of stockholders to seek to regain compliance with the minimum share price condition. As long as USEC's stockholders' equity remains less than $50 million, the NYSE could also take actions to delist USEC's common stock if USEC's average market capitalization is less than $50 million over a 30 trading-day period. If USEC were to fall below this continued listing requirement, USEC would seek to submit a plan to return to compliance, subject to the NYSE's acceptance of such plan and acceptable progress in regaining compliance. See Note 18, "NYSE Listing Notice" for additional information. USEC plans to engage in further discussions with the Pension Benefit Guaranty Corporation ("PBGC") regarding the impact of its de-lease of the Portsmouth gaseous diffusion plant and related transition of employees on its defined benefit plan funding obligations. USEC could also face a liability related to a future decision to discontinue activities at the Paducah gaseous diffusion plant. See note 18, "Potential ERISA Section 4062(e) Liability" for additional information. USEC could also demobilize the American Centrifuge project if additional funding for the research, development and demonstration ("RD&D") program is not obtained or if it determines that there is no longer a viable path to commercialization of the American Centrifuge Plant ("ACP") or could also take actions to restructure the project that could result in changes in its anticipated ownership of or role in the project. See Note 18, "American Centrifuge Plant" for additional information. The above noted actions, as well as actions that may be taken by vendors, customers, creditors and other third parties in response to its actions or based on their view of its financial strength and future business prospects, could give rise to events that individually, or in the aggregate, impose significant demands on USEC's liquidity. Cash and Cash Equivalents Cash and cash equivalents include temporary cash investments with original maturities of three months or less. Inventories USEC holds uranium at the Paducah GDP in the form of natural uranium and as the uranium component of LEU. USEC holds SWU as the SWU component of LEU. USEC may also hold title to the uranium and SWU components of LEU at fabricators to meet book transfer requests by customers. Fabricators process LEU into fuel for use in nuclear reactors. Under inventory optimization arrangements between USEC and domestic fabricators, fabricators order bulk quantities of LEU from USEC based on scheduled or anticipated orders from utility customers for deliveries in future periods. As delivery obligations under actual customer orders arise, USEC satisfies these obligations by arranging for the transfer to the customer of title to the specified quantity of LEU at the fabricator. USEC's balances of SWU and uranium vary over time based on the timing and size of the fabricator's LEU orders from USEC. Balances can be positive or negative at the discretion of the fabricator. Fabricators have other inventory supplies and, where a fabricator has elected to order less material from USEC than USEC is required to deliver to its customers at the fabricator, the fabricator will use these other inventories to satisfy USEC's customer order obligations on USEC's behalf. In such cases, the transfer of title of LEU from USEC to the customer results in quantities of SWU and uranium owed by USEC to the fabricator. These obligations are presented in current liabilities, comprising most of the balance of inventories owed to customers and suppliers. The amounts of SWU and uranium owed to fabricators are satisfied as future bulk deliveries of LEU are made. Inventories of SWU and uranium are valued at the lower of cost or market. Market is based on the terms of long-term contracts with customers, and, for uranium not under contract, market is based primarily on published price indicators at the balance sheet date. SWU and uranium inventory costs are determined using the monthly moving average cost method. SWU costs are based on production costs and Russian purchase costs. Production costs at the Paducah GDP consist principally of electric power, labor and benefits, materials, depreciation and amortization and maintenance and repairs. The cost of the SWU component of LEU purchased from Russia is recorded at acquisition cost plus related shipping costs. Underfeeding is a mode of operation that uses or feeds less uranium but requires more SWU in the enrichment process, which requires more electric power. The quantity of uranium that is earned or added to uranium inventory from underfeeding is accounted for as a byproduct of the enrichment process. Production costs are allocated to the uranium earned based on the net realizable value of the uranium, and the remainder of production costs is allocated to SWU inventory costs. Deferred Income Taxes USEC follows the asset and liability approach to account for deferred income taxes. Deferred tax assets and liabilities are recognized for the anticipated future tax consequences of temporary differences between the balance sheet carrying amounts of assets and liabilities and their respective tax bases. Deferred income taxes are based on income tax rates in effect for the years in which temporary differences are expected to reverse. The effect on deferred income taxes of a change in income tax rates is recognized in income when the change in rates is enacted in the law. A valuation allowance is provided if it is more likely than not that some or all of the deferred tax assets may not be realized. USEC revised its 2011 consolidated financial statements to correct the presentation of the provision for income taxes. The revision reduced the provision for income taxes, net loss and retained deficit by $49.6 million ($.41 per basic and diluted share) and increased other comprehensive loss and accumulated other comprehensive loss by $49.6 million. The revision had no impact on cash flows, comprehensive loss or total stockholders' equity. USEC has determined that the revision is not material to the 2011 consolidated financial statements. Property, Plant and Equipment Construction work in progress is recorded at acquisition or construction cost. Upon being placed into service, costs are transferred to leasehold improvements or machinery and equipment at which time depreciation and amortization commences. Maintenance and repair costs are charged to production costs or cost of sales as incurred. USEC leases the Paducah GDP located in Paducah, Kentucky and portions of the former Portsmouth GDP located in Piketon, Ohio from DOE. Leasehold improvements and machinery and equipment are recorded at acquisition cost and depreciated on a straight line basis over the shorter of the useful life of the assets or the expected productive life of the plant. As a result of discussions with DOE and USEC's belief that it would be difficult to continue enrichment activities at the Paducah GDP through the expiration of the existing lease term, USEC began depreciating leasehold improvements, machinery and equipment at the Paducah GDP on an accelerated straight line basis prospectively starting in the fourth quarter of 2012. Based on internal analysis that provided management's view of the most likely scenarios, USEC did not foresee that the lease term would continue beyond 2014 and determined to depreciate its existing assets over this timeframe unless facts and circumstances affecting the expected term of the lease change. Beginning with the start of the fourth quarter of 2011, all American Centrifuge project costs incurred have been expensed. Based on USEC's internal analysis concluded as part of its annual assessment, all previously capitalized costs related to the American Centrifuge project were expensed as of December 31, 2012. Capitalization of expenditures related to the American Centrifuge project has ceased until commercial deployment resumes. Additional details related are provided below in "Advanced Technology Costs." Advanced Technology Costs Historically, costs relating to the American Centrifuge technology were either charged to expense or capitalized based on the nature of the activities and estimates and judgments involving the completion of project milestones. Costs relating to the demonstration of American Centrifuge technology were charged to expense as incurred and costs relating to the construction and deployment of the ACP were capitalized. Instead of moving forward with a conditional commitment for a loan guarantee for the American Centrifuge project through the DOE Loan Guarantee Program, in the fall of 2011, DOE proposed a two-year cost share RD&D program for the American Centrifuge project. As a result of the shift in focus of the American Centrifuge project, beginning in the fourth quarter of 2011, USEC began spending on the American Centrifuge technology at reduced levels with activities concentrating on development and demonstration. As a result, beginning with the fourth quarter of 2011, all project costs incurred have been expensed, including interest expense that previously would have been capitalized. Refer to Note 4, "Property, Plant and Equipment" and Note 18, "Commitments and Contingencies" for further details. Long-Lived Assets USEC evaluates the carrying value of long-lived assets by performing impairment tests on an annual basis or whenever adverse conditions or changes in circumstances indicate a possible impairment loss. Impairment tests are based on a comparison of estimated undiscounted future cash flows to the carrying values of long-lived assets. If impairment is indicated, the asset carrying value is reduced to fair market value or, if fair market value is not readily available, the asset is reduced to a value determined by applying a discount rate to expected cash flows. Based on USEC's internal analysis concluded as part of its annual assessment, all previously capitalized costs related to the American Centrifuge project were expensed as of December 31, 2012. Although USEC continues to make progress in the deployment of the ACP, including the effective execution of the RD&D program during 2012, and is planning to update its DOE loan guarantee application during 2013, the expense of previously capitalized costs is based on USEC's assessment of its ability to recover the full amount of this prior capital investment. In light of the significant remaining capital needed to deploy the ACP and USEC's view of its anticipated cash flow from operations available to finance the ACP given USEC's other anticipated cash needs during that period, USEC anticipates that its ultimate share of the ownership of the ACP will likely be reduced, which affects its likelihood of recovering this past investment. USEC is also currently developing a revised cost estimate and schedule for the project and several factors are putting pressure on the economics of the ACP, including delays in deployment and related carrying costs and other cost pressures as well as uncertainty regarding financing. This expense of previously capitalized costs does not affect any future capital investment in the ACP. USEC would anticipate that capitalization of amounts related to the ACP would resume if and when commercial plant deployment resumes. Goodwill USEC's long-term assets include goodwill resulting from USEC's acquisition of NAC in 2004. USEC evaluates the carrying value of goodwill by performing an impairment test on an annual basis or whenever events or changes in circumstances indicate that its carrying amount may not be recoverable. The goodwill testing utilizes a two-step process, where the carrying value of the reporting unit is compared to its fair value. If the carrying value is less than the fair value, no impairment exists and the second step is not performed. However, if the carrying value is greater than the fair value, the second step is performed. An impairment charge would be recognized for the amount that the carrying value of the goodwill exceeds its fair value. In an impairment test, the fair value of the reporting unit is estimated using the net present value of projected future cash flows. In lieu of this method of estimating the fair value, USEC determined that there was no impairment as of December 31, 2012 based on indications of interest it had received from independent parties to purchase NAC for prices higher than the carrying value. In January 2013, USEC determined that it would seek to sell NAC and, on March 15, 2013, USEC sold NAC to a subsidiary of Hitachi Zosen Corporation. Refer to Note 20 for details. Financial Instruments and Fair Value Measurement Accounting standards define fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities required or permitted to be recorded at fair value, consideration is given to the principal or most advantageous market and assumptions that market participants would use when pricing the asset or liability. Pursuant to accounting standards, USEC's credit facility term loan and convertible debt are recorded at face value and the fair value is disclosed. The estimated fair value of the term loan is based on the change in market value of an index of loans of similar credit quality based on published credit ratings. The estimated fair value of the convertible notes is based on the trading price as of the balance sheet date. Financing costs are generally deferred and amortized over the life of the instrument. Pursuant to accounting standards, USEC's convertible preferred stock was initially recorded at fair value on a recurring basis. The preferred stock is classified as a liability since it is convertible for a variable number of shares of common stock based on a fixed monetary value known at the issuance date. Since the preferred stock is classified as a liability, the proceeds were first allocated to the liability instrument's full fair value, and no residual proceeds remained to be assigned to the warrants. Upfront costs and fees related to the investment were expensed in 2010 and classified as preferred stock issuance costs. The issuance costs were expensed in the period of issuance, rather than deferred and amortized, since the preferred stock is classified as a liability and was initially recorded at fair value. Dividends paid-in-kind either issued or payable are classified as interest. As of December 31, 2012, the convertible preferred stock can be converted at the holder's option and is classified as a current liability at the redemption value. If a share issuance limitation were to exist at the time of share conversion or sale, any preferred stock shares subject to the share issuance limitation would be subject to optional or mandatory redemption for, at USEC's option, cash or SWU consideration. However, USEC's ability to redeem may be limited by Delaware law, and if not limited may result in mandatory prepayment of USEC's credit facility. The balance sheet carrying amounts for cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities, and payables under the Russian Contract approximate fair value because of the short-term nature of the instruments. Lease Turnover Costs and Asset Retirement Obligations Property, plant and equipment assets related to the Paducah GDP are not subject to an asset retirement obligation. At the end of the lease, ownership of plant and equipment that USEC leaves at the GDP transfers to DOE, and responsibility for decontamination and decommissioning of the GDP remains with DOE. USEC estimates and accrues lease turnover costs. The balance of expected costs is being accrued over the expected productive life of the plant. Costs of returning the GDP to DOE in acceptable condition include removing nuclear material as required and removing USEC-generated waste. Liabilities for lease turnover costs are based on current-dollar cost estimates and are not discounted. USEC also leases facilities in Piketon, Ohio from DOE for the ACP. Pursuant to contract, DOE has obtained title to certain equipment used in the RD&D program. Other than equipment transferred to DOE (collectively "DOE Transferred Property"), USEC owns all capital improvements and, unless otherwise consented to by DOE, must remove them by the conclusion of the lease term. At the conclusion of the lease, USEC is obligated to return these leased facilities to DOE in a condition that meets NRC requirements and in the same condition as the facilities were in when they were leased to USEC (other than due to normal wear and tear). In the event USEC returns the facilities in Piketon Ohio prior to completing installation of 1 million SWU of capacity, DOE retains title to and responsibility for disposition of the DOE Transferred Property. Decontamination and decommissioning requirements for the ACP create an asset retirement obligation. As construction of the ACP takes place, the present value of the related asset retirement obligation (the initially determined fair value of the future obligation) is recognized as a long-term liability. An equivalent amount is recognized as part of the capitalized asset cost during the construction period. Upon commencement of commercial operations, the asset cost will be depreciated over the shorter of the asset life or the expected lease period. USEC has not recognized any changes to the capitalized asset cost related to the asset retirement obligation since the latter half of 2009, when USEC significantly reduced machine manufacturing and construction activities due to project funding uncertainty. The long-term liability for the asset retirement obligation is accreted, or increased, for the passage of time and the estimate also is revised for any changes in long-term inflation rate assumptions. The accretion, based on a time value of money calculation, is charged to cost of sales in the LEU segment. At the end of 2010, USEC reassessed the long-term liability and determined that the current fair value of the obligation was accrued at a sufficient amount based on construction progress and no further increase would be made until additional commercial plant deployment resumed. During each reporting period, USEC reassesses and revises the estimate of the asset retirement obligation based on construction progress, cost evaluation of future decommissioning expectations, and other judgmental considerations which impact the amount recorded in both construction work in progress and other long-term liabilities. Significant increases in asset retirement obligations and related capitalized asset costs would result when ACP construction is fully underway as part of any commercial plant deployment and plant operations. Environmental Compliance Costs Environmental compliance costs relating to operations are accrued and charged to inventory costs as incurred. Estimated environmental compliance costs are accrued where environmental assessments indicate that storage, treatment or disposal of wastes is probable and costs can be reasonably estimated. Liabilities for waste are based on current-dollar cost estimates and are not discounted. Concentrations of Credit Risk Credit risk could result from the possibility of a customer failing to perform or pay according to the terms of a contract. Extension of credit is based on an evaluation of each customer's financial condition. USEC regularly monitors credit risk exposure and takes steps to mitigate the likelihood of such exposure resulting in a loss. SWU and Uranium Revenue Revenue is derived from sales of the SWU component of LEU, from sales of both the SWU and uranium components of LEU, and from sales of uranium. Revenue is recognized at the time LEU or uranium is delivered under the terms of contracts with domestic and international electric utility customers. Some customers take title and delivery of LEU at the Paducah GDP, and revenue is recognized when delivery of LEU to the customer is complete. Most customers take title and delivery of LEU at fuel fabricators. USEC ships LEU to nuclear fuel fabricators for scheduled or anticipated orders from utility customers. Based on customer orders, USEC arranges for the transfer of title of LEU from USEC to the customer for the specified quantity of LEU at the fuel fabricator. Revenue is recognized when delivery of LEU to the customer occurs at the fuel fabricator. In a number of sales transactions, title to uranium or LEU is transferred to the customer and USEC receives payment under normal credit terms without physically delivering the uranium or LEU to the customer. This may occur because the terms of the agreement require USEC to hold the uranium to which the customer has title, or because the customer encounters brief delays in taking delivery of LEU at USEC's facilities. In such cases, recognition of revenue does not occur at the time title to uranium or LEU transfers to the customer but instead is deferred until LEU to which the customer has title is physically delivered. Certain customers make advance payments to be applied against future orders. Advances from customers are reported as deferred revenue, and revenue is recognized as product is delivered or services are provided. Contract Services Revenue USEC performs services and earns revenue from contract work through its subsidiary NAC (prior to its sale effective March 15, 2013) and from limited contract work for DOE and DOE contractors at the Paducah GDP and the Portsmouth site. Revenue from NAC sales related to fixed-price contracts is recognized as services are provided based on milestones or events defined in the work scope. Revenue is recorded on time-and-materials contracts as the work is performed based on agreed-upon hourly rates and allowable costs. U.S. government contract revenue includes billings for fees and reimbursements for allowable costs that are determined in accordance with the terms of the underlying contracts. Revenue is recognized as work is performed and as fees are earned. Allowable costs include direct costs as well as allocations of indirect plant and corporate overhead costs determined in accordance with government cost accounting standards. Amounts representing contract change orders or final billing rates based on incurred costs are accrued and included in revenue when they can be reliably estimated and realization is probable. Allowable costs are subject to audit by the Defense Contract Audit Agency ("DCAA"), or such other entity that DOE authorizes to conduct the audit. The final settlement of amounts submitted by USEC for reimbursement is subject to acceptance by DOE. Revenue resulting from final billing rates is recognized upon completion of the government audits and notice by DOE authorizing final billing. DOE historically has not approved USEC's provisional billing rates and has not completed audits of USEC's incurred cost submissions and authorized final payments in a timely manner. Additional details are provided in Note 5. There is the potential for additional revenue to be recognized, based on the outcome of DOE reviews and audits, as the result of the release of previously established receivable related reserves. However, because these periods have not been audited, uncertainty exists and USEC has not yet recognized this additional revenue. DOE funded a portion of the now-completed work at Portsmouth through an arrangement whereby DOE transferred uranium to USEC which USEC immediately sold. USEC completed six competitive sales of uranium between the fourth quarter of 2009 and the first quarter of 2011. USEC's receipt of the uranium was not considered a purchase by USEC and no revenue or cost of sales was recorded upon its sale. This is because USEC had no significant risks or rewards of ownership and no potential profit or loss related to the uranium sale. The value of the contract work is based on the cash proceeds from the uranium sales less USEC's selling and handling costs. The net cash proceeds from the uranium sales were recorded as advances from customers and are to be applied, at the direction of DOE, (a) as revenue is recognized in USEC's contract services segment as services are provided or (b) to existing receivables balances due from DOE in USEC's contract services segment. As of December 31, 2012, the remaining balance of $20.5 million is included in other long-term liabilities pending resolution of long-term receivables from DOE described in Note 5. Stock-Based Compensation USEC has stock-based compensation plans available to grant restricted stock, restricted stock units, non-qualified stock options, performance awards and other stock-based awards to key employees and non-employee directors. Stock-based compensation cost is measured at the grant date, based on the fair value of the award, and is recognized over the requisite service period, which is either immediate recognition if the employee is eligible to retire, or on a straight-line basis until the earlier of either the date of retirement eligibility or the end of the vesting period. Use of Estimates The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect reported amounts presented and disclosed in the consolidated financial statements. Significant estimates and judgments include, but are not limited to, pension and postretirement health and life benefit costs and obligations, accounting treatment for expenditures on the American Centrifuge project, plant lease turnover costs, the tax bases of assets and liabilities, the future recoverability of deferred tax assets, and determination of the valuation allowance for deferred tax assets. Actual results may differ from such estimates, and estimates may change if the underlying conditions or assumptions change. New Accounting Standards In May 2011, the Financial Accounting Standards Board ("FASB") amended its guidance on fair value measurements and related disclosures. The amendments represent the converged guidance of the FASB and the International Accounting Standards Board and provide a consistent definition of fair value and common requirements for measurement and disclosure of fair value between generally accepted accounting principles in the U.S. ("GAAP") and International Financial Reporting Standards ("IFRS"). The new amendments also change some fair value measurement principles and enhance disclosure requirements related to activities in Level 3 of the fair value hierarchy. The new provisions are effective for fiscal years and interim periods beginning after December 15, 2011 and are applied prospectively. The implementation of the amended guidance in the first quarter of 2012 did not have an effect on USEC's results of operations, cash flows or financial position. In June and December 2011, the FASB issued guidance on the presentation of comprehensive income. The new guidance requires companies to present the components of net income and other comprehensive income either in a single statement below net income or in a separate statement of comprehensive income immediately following the income statement. The provisions of this new guidance are effective for fiscal years and interim periods beginning after December 15, 2011 and are applied retrospectively for all periods presented. The implementation of the new guidance in USEC's financial statements beginning in the first quarter of 2012 did not have an effect on USEC's results of operations, cash flows or financial position. In September 2011, the FASB amended its guidance on testing goodwill for impairment. Under the revised guidance, companies testing goodwill for impairment have the option of first performing a qualitative assessment to determine whether further quantitative assessments are warranted. In assessing qualitative factors, companies are to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount as a basis for determining whether it is necessary to perform the two-step goodwill impairment test prescribed in the existing guidance. The provisions of this new guidance are effective for fiscal years and interim periods beginning after December 15, 2011. USEC's adoption of the new guidance did not have a material effect on its results of operations, cash flows or financial position. USEC's goodwill resulted from the acquisition of NAC in 2004. As of December 31, 2012, USEC determined that there was no impairment based on indications of interest it had received from independent parties to purchase NAC for prices higher than the carrying value. In January 2013, USEC determined that it would seek to sell NAC and on March 15, 2013, USEC sold NAC as detailed in Note 20.

1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Nature of Operations

USEC Inc. ("USEC") is a global energy company and is a leading supplier of low enriched uranium ("LEU") for commercial nuclear power plants. LEU consists of two components: separative work units ("SWU") and uranium. SWU is a standard unit of measurement that represents the effort required to transform a given amount of natural uranium into two components: LEU having a higher percentage of U235 and depleted uranium having a lower percentage of U235. The SWU contained in LEU is calculated using an industry standard formula based on the physics of enrichment. The amount of enrichment deemed to be contained in LEU under this formula is commonly referred to as its SWU component and the quantity of natural uranium used in the production of LEU under this formula is referred to as its uranium component. Utility customers typically provide uranium to USEC as part of their enrichment contracts, and USEC delivers LEU to the customers and charges for the SWU component.

USEC has historically produced or acquired LEU from two principal sources. USEC has produced about half of its supply of LEU at the Paducah GDP in Paducah, Kentucky, and USEC has acquired the other portion under a contract with Russia (the "Russian Contract") under the 20-year Megatons to Megawatts program. Under the Russian Contract, USEC purchases the SWU component of LEU derived from dismantled nuclear weapons from the former Soviet Union for use as fuel in commercial nuclear power plants. The current arrangement under which USEC is continuing enrichment at the Paducah GDP expires in 2013 and USEC expects to complete its purchases under the Russian Contract in 2013. Commencing in 2013, USEC will continue to acquire Russian LEU under the terms of a new 10-year commercial agreement with Russia (the "Russian Supply Agreement"). Purchase quantities under the Russian Supply Agreement will be about half the level under the Megatons to Megawatts program unless the parties exercise a mutual option to increase such purchases. Additional details are provided in Note 18 under "Purchase of Separative Work Units from Russia."

In addition, USEC performs contract services through its subsidiary NAC International Inc. ("NAC") and for the U.S. Department of Energy ("DOE") and DOE contractors at the Paducah gaseous diffusion plant ("GDP") in Paducah, Kentucky and the site of the former Portsmouth GDP in Piketon, Ohio. On March 15, 2013, USEC sold NAC to a subsidiary of Hitachi Zosen Corporation. Refer to Note 20 for details.

Basis of Presentation

The consolidated financial statements include the accounts of USEC Inc., its principal subsidiary, United States Enrichment Corporation, and its other subsidiaries including NAC. American Centrifuge Manufacturing, LLC, a joint company established by USEC (through its subsidiary American Centrifuge Holdings, LLC) and Babcock & Wilcox Technical Services Group, Inc., is also included in the consolidated financial statements. All material intercompany transactions are eliminated.

Liquidity Risks and Uncertainties

USEC's accompanying consolidated financial statements have been prepared assuming that USEC will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business for the 12- month period following the date of these consolidated financial statements.

USEC reported a net loss of $1.2 billion in the year ended December 31, 2012 and a net loss of $491.1 million in the year ended December 31, 2011. These net losses were primarily the result of expenses related to the development of the American Centrifuge project, including the expense of previously capitalized amounts during both periods and related tax valuation allowances. USEC's cash from operating activities was $142.9 million for the year ended December 31, 2012. USEC expects that its cash balance, internally generated cash from its LEU operations and services provided by its contract services segment, and available borrowings under its revolving credit facility will provide sufficient cash to meet its obligations as they become due for at least 12 months from the date of the accompanying financial statements, assuming the renewal or replacement of its revolving credit facility past September 2013. On March 14, 2013, USEC amended its credit facility, among other things, to extend the expiration date of the credit facility from May 31, 2013 to September 30, 2013. USEC repaid its existing term loan in connection with the amendment. USEC's credit facility is available to finance working capital needs and general corporate purposes. USEC believes it is reasonable to expect an extension or replacement for the facility by September 2013. USEC's credit facility needs at that time will depend on USEC's working capital needs, which in part depend on the timing of USEC's transition of enrichment at the Paducah gaseous diffusion plant, and USEC may need a substantially smaller credit facility in the future. USEC's credit facility would also likely be replaced as part of any potential restructuring (discussed below). In addition, if USEC were unable to renew or replace its credit facility beyond September 2013, USEC would seek to work with customers to effect further order movements to provide sufficient liquidity and working capital.

Although USEC expects to have adequate liquidity to meet its obligations during 2013, in light of the significant transition of USEC's business and the uncertainties and challenges facing USEC and in order to improve USEC's credit profile and its ability to successfully finance and deploy the American Centrifuge project and to maximize USEC's participation in such project, USEC is engaged with its advisors and certain stakeholders on alternatives for a possible restructuring of its balance sheet. USEC continues to believe that the deployment of the American Centrifuge project represents USEC's clearest path to a long-term, direct source of domestic enrichment production, and therefore the long-term viability of USEC's LEU business and USEC believes that a restructuring could improve the likelihood of success in the deployment of the American Centrifuge project. Although USEC has no assurance regarding its ability to pursue or complete a restructuring, a restructuring could result in significant changes to the Company's capital structure and adjustments to its balance sheet, including the creation of a new entity for accounting purposes, which would have a material impact on USEC's financial statements, including the going concern assumption on which they have been prepared.

In addition, on May 8, 2012, USEC received a notice from the New York Stock Exchange ("NYSE") that the average closing price of its common stock was below the NYSE's continued listing criteria relating to minimum share price. A delisting of USEC's common stock by the NYSE and the failure of its common stock to be listed on another national exchange could cause significant adverse consequences. A fundamental change is triggered under the terms of USEC's convertible notes if USEC's shares of common stock are not listed for trading on any of the NYSE, the American Stock Exchange, the NASDAQ Global Market or the NASDAQ Global Select Market, and the holders of the notes can require USEC to repurchase the notes at par for cash. The occurrence of a fundamental change under the convertible notes that permits the holders of the convertible notes to require a repurchase for cash is also an event of default under USEC's credit facility. USEC intends to seek shareholder approval for a reverse stock split at its next annual meeting of stockholders to seek to regain compliance with the minimum share price condition. As long as USEC's stockholders' equity remains less than $50 million, the NYSE could also take actions to delist USEC's common stock if USEC's average market capitalization is less than $50 million over a 30 trading-day period. If USEC were to fall below this continued listing requirement, USEC would seek to submit a plan to return to compliance, subject to the NYSE's acceptance of such plan and acceptable progress in regaining compliance. See Note 18, "NYSE Listing Notice" for additional information.

USEC plans to engage in further discussions with the Pension Benefit Guaranty Corporation ("PBGC") regarding the impact of its de-lease of the Portsmouth gaseous diffusion plant and related transition of employees on its defined benefit plan funding obligations. USEC could also face a liability related to a future decision to discontinue activities at the Paducah gaseous diffusion plant. See note 18, "Potential ERISA Section 4062(e) Liability" for additional information.

USEC could also demobilize the American Centrifuge project if additional funding for the research, development and demonstration ("RD&D") program is not obtained or if it determines that there is no longer a viable path to commercialization of the American Centrifuge Plant ("ACP") or could also take actions to restructure the project that could result in changes in its anticipated ownership of or role in the project. See Note 18, "American Centrifuge Plant" for additional information.

The above noted actions, as well as actions that may be taken by vendors, customers, creditors and other third parties in response to its actions or based on their view of its financial strength and future business prospects, could give rise to events that individually, or in the aggregate, impose significant demands on USEC's liquidity.

Cash and Cash Equivalents

Cash and cash equivalents include temporary cash investments with original maturities of three months or less.

Inventories

USEC holds uranium at the Paducah GDP in the form of natural uranium and as the uranium component of LEU. USEC holds SWU as the SWU component of LEU. USEC may also hold title to the uranium and SWU components of LEU at fabricators to meet book transfer requests by customers. Fabricators process LEU into fuel for use in nuclear reactors. Under inventory optimization arrangements between USEC and domestic fabricators, fabricators order bulk quantities of LEU from USEC based on scheduled or anticipated orders from utility customers for deliveries in future periods. As delivery obligations under actual customer orders arise, USEC satisfies these obligations by arranging for the transfer to the customer of title to the specified quantity of LEU at the fabricator. USEC's balances of SWU and uranium vary over time based on the timing and size of the fabricator's LEU orders from USEC. Balances can be positive or negative at the discretion of the fabricator. Fabricators have other inventory supplies and, where a fabricator has elected to order less material from USEC than USEC is required to deliver to its customers at the fabricator, the fabricator will use these other inventories to satisfy USEC's customer order obligations on USEC's behalf. In such cases, the transfer of title of LEU from USEC to the customer results in quantities of SWU and uranium owed by USEC to the fabricator. These obligations are presented in current liabilities, comprising most of the balance of inventories owed to customers and suppliers. The amounts of SWU and uranium owed to fabricators are satisfied as future bulk deliveries of LEU are made.

Inventories of SWU and uranium are valued at the lower of cost or market. Market is based on the terms of long-term contracts with customers, and, for uranium not under contract, market is based primarily on published price indicators at the balance sheet date. SWU and uranium inventory costs are determined using the monthly moving average cost method.

SWU costs are based on production costs and Russian purchase costs. Production costs at the Paducah GDP consist principally of electric power, labor and benefits, materials, depreciation and amortization and maintenance and repairs. The cost of the SWU component of LEU purchased from Russia is recorded at acquisition cost plus related shipping costs.

Underfeeding is a mode of operation that uses or feeds less uranium but requires more SWU in the enrichment process, which requires more electric power. The quantity of uranium that is earned or added to uranium inventory from underfeeding is accounted for as a byproduct of the enrichment process. Production costs are allocated to the uranium earned based on the net realizable value of the uranium, and the remainder of production costs is allocated to SWU inventory costs.

Deferred Income Taxes

USEC follows the asset and liability approach to account for deferred income taxes. Deferred tax assets and liabilities are recognized for the anticipated future tax consequences of temporary differences between the balance sheet carrying amounts of assets and liabilities and their respective tax bases. Deferred income taxes are based on income tax rates in effect for the years in which temporary differences are expected to reverse. The effect on deferred income taxes of a change in income tax rates is recognized in income when the change in rates is enacted in the law. A valuation allowance is provided if it is more likely than not that some or all of the deferred tax assets may not be realized.

USEC revised its 2011 consolidated financial statements to correct the presentation of the provision for income taxes. The revision reduced the provision for income taxes, net loss and retained deficit by $49.6 million ($.41 per basic and diluted share) and increased other comprehensive loss and accumulated other comprehensive loss by $49.6 million. The revision had no impact on cash flows, comprehensive loss or total stockholders' equity. USEC has determined that the revision is not material to the 2011 consolidated financial statements.

Property, Plant and Equipment

Construction work in progress is recorded at acquisition or construction cost. Upon being placed into service, costs are transferred to leasehold improvements or machinery and equipment at which time depreciation and amortization commences. Maintenance and repair costs are charged to production costs or cost of sales as incurred.

USEC leases the Paducah GDP located in Paducah, Kentucky and portions of the former Portsmouth GDP located in Piketon, Ohio from DOE. Leasehold improvements and machinery and equipment are recorded at acquisition cost and depreciated on a straight line basis over the shorter of the useful life of the assets or the expected productive life of the plant. As a result of discussions with DOE and USEC's belief that it would be difficult to continue enrichment activities at the Paducah GDP through the expiration of the existing lease term, USEC began depreciating leasehold improvements, machinery and equipment at the Paducah GDP on an accelerated straight line basis prospectively starting in the fourth quarter of 2012. Based on internal analysis that provided management's view of the most likely scenarios, USEC did not foresee that the lease term would continue beyond 2014 and determined to depreciate its existing assets over this timeframe unless facts and circumstances affecting the expected term of the lease change.

Beginning with the start of the fourth quarter of 2011, all American Centrifuge project costs incurred have been expensed. Based on USEC's internal analysis concluded as part of its annual assessment, all previously capitalized costs related to the American Centrifuge project were expensed as of December 31, 2012. Capitalization of expenditures related to the American Centrifuge project has ceased until commercial deployment resumes. Additional details related are provided below in "Advanced Technology Costs."

Advanced Technology Costs

Historically, costs relating to the American Centrifuge technology were either charged to expense or capitalized based on the nature of the activities and estimates and judgments involving the completion of project milestones. Costs relating to the demonstration of American Centrifuge technology were charged to expense as incurred and costs relating to the construction and deployment of the ACP were capitalized.

Instead of moving forward with a conditional commitment for a loan guarantee for the American Centrifuge project through the DOE Loan Guarantee Program, in the fall of 2011, DOE proposed a two-year cost share RD&D program for the American Centrifuge project. As a result of the shift in focus of the American Centrifuge project, beginning in the fourth quarter of 2011, USEC began spending on the American Centrifuge technology at reduced levels with activities concentrating on development and demonstration. As a result, beginning with the fourth quarter of 2011, all project costs incurred have been expensed, including interest expense that previously would have been capitalized. Refer to Note 4, "Property, Plant and Equipment" and Note 18, "Commitments and Contingencies" for further details.

Long-Lived Assets

USEC evaluates the carrying value of long-lived assets by performing impairment tests on an annual basis or whenever adverse conditions or changes in circumstances indicate a possible impairment loss. Impairment tests are based on a comparison of estimated undiscounted future cash flows to the carrying values of long-lived assets. If impairment is indicated, the asset carrying value is reduced to fair market value or, if fair market value is not readily available, the asset is reduced to a value determined by applying a discount rate to expected cash flows.

Based on USEC's internal analysis concluded as part of its annual assessment, all previously capitalized costs related to the American Centrifuge project were expensed as of December 31, 2012. Although USEC continues to make progress in the deployment of the ACP, including the effective execution of the RD&D program during 2012, and is planning to update its DOE loan guarantee application during 2013, the expense of previously capitalized costs is based on USEC's assessment of its ability to recover the full amount of this prior capital investment. In light of the significant remaining capital needed to deploy the ACP and USEC's view of its anticipated cash flow from operations available to finance the ACP given USEC's other anticipated cash needs during that period, USEC anticipates that its ultimate share of the ownership of the ACP will likely be reduced, which affects its likelihood of recovering this past investment. USEC is also currently developing a revised cost estimate and schedule for the project and several factors are putting pressure on the economics of the ACP, including delays in deployment and related carrying costs and other cost pressures as well as uncertainty regarding financing. This expense of previously capitalized costs does not affect any future capital investment in the ACP. USEC would anticipate that capitalization of amounts related to the ACP would resume if and when commercial plant deployment resumes.

Goodwill

USEC's long-term assets include goodwill resulting from USEC's acquisition of NAC in 2004. USEC evaluates the carrying value of goodwill by performing an impairment test on an annual basis or whenever events or changes in circumstances indicate that its carrying amount may not be recoverable. The goodwill testing utilizes a two-step process, where the carrying value of the reporting unit is compared to its fair value. If the carrying value is less than the fair value, no impairment exists and the second step is not performed. However, if the carrying value is greater than the fair value, the second step is performed. An impairment charge would be recognized for the amount that the carrying value of the goodwill exceeds its fair value. In an impairment test, the fair value of the reporting unit is estimated using the net present value of projected future cash flows. In lieu of this method of estimating the fair value, USEC determined that there was no impairment as of December 31, 2012 based on indications of interest it had received from independent parties to purchase NAC for prices higher than the carrying value. In January 2013, USEC determined that it would seek to sell NAC and, on March 15, 2013, USEC sold NAC to a subsidiary of Hitachi Zosen Corporation. Refer to Note 20 for details.

Financial Instruments and Fair Value Measurement

Accounting standards define fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities required or permitted to be recorded at fair value, consideration is given to the principal or most advantageous market and assumptions that market participants would use when pricing the asset or liability.

Pursuant to accounting standards, USEC's credit facility term loan and convertible debt are recorded at face value and the fair value is disclosed. The estimated fair value of the term loan is based on the change in market value of an index of loans of similar credit quality based on published credit ratings. The estimated fair value of the convertible notes is based on the trading price as of the balance sheet date. Financing costs are generally deferred and amortized over the life of the instrument.

Pursuant to accounting standards, USEC's convertible preferred stock was initially recorded at fair value on a recurring basis. The preferred stock is classified as a liability since it is convertible for a variable number of shares of common stock based on a fixed monetary value known at the issuance date. Since the preferred stock is classified as a liability, the proceeds were first allocated to the liability instrument's full fair value, and no residual proceeds remained to be assigned to the warrants. Upfront costs and fees related to the investment were expensed in 2010 and classified as preferred stock issuance costs. The issuance costs were expensed in the period of issuance, rather than deferred and amortized, since the preferred stock is classified as a liability and was initially recorded at fair value. Dividends paid-in-kind either issued or payable are classified as interest.

As of December 31, 2012, the convertible preferred stock can be converted at the holder's option and is classified as a current liability at the redemption value. If a share issuance limitation were to exist at the time of share conversion or sale, any preferred stock shares subject to the share issuance limitation would be subject to optional or mandatory redemption for, at USEC's option, cash or SWU consideration. However, USEC's ability to redeem may be limited by Delaware law, and if not limited may result in mandatory prepayment of USEC's credit facility.

The balance sheet carrying amounts for cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities, and payables under the Russian Contract approximate fair value because of the short-term nature of the instruments.

Lease Turnover Costs and Asset Retirement Obligations

Property, plant and equipment assets related to the Paducah GDP are not subject to an asset retirement obligation. At the end of the lease, ownership of plant and equipment that USEC leaves at the GDP transfers to DOE, and responsibility for decontamination and decommissioning of the GDP remains with DOE. USEC estimates and accrues lease turnover costs. The balance of expected costs is being accrued over the expected productive life of the plant. Costs of returning the GDP to DOE in acceptable condition include removing nuclear material as required and removing USEC-generated waste. Liabilities for lease turnover costs are based on current-dollar cost estimates and are not discounted.

USEC also leases facilities in Piketon, Ohio from DOE for the ACP. Pursuant to contract, DOE has obtained title to certain equipment used in the RD&D program. Other than equipment transferred to DOE (collectively "DOE Transferred Property"), USEC owns all capital improvements and, unless otherwise consented to by DOE, must remove them by the conclusion of the lease term. At the conclusion of the lease, USEC is obligated to return these leased facilities to DOE in a condition that meets NRC requirements and in the same condition as the facilities were in when they were leased to USEC (other than due to normal wear and tear). In the event USEC returns the facilities in Piketon Ohio prior to completing installation of 1 million SWU of capacity, DOE retains title to and responsibility for disposition of the DOE Transferred Property.

Decontamination and decommissioning requirements for the ACP create an asset retirement obligation. As construction of the ACP takes place, the present value of the related asset retirement obligation (the initially determined fair value of the future obligation) is recognized as a long-term liability. An equivalent amount is recognized as part of the capitalized asset cost during the construction period. Upon commencement of commercial operations, the asset cost will be depreciated over the shorter of the asset life or the expected lease period.

USEC has not recognized any changes to the capitalized asset cost related to the asset retirement obligation since the latter half of 2009, when USEC significantly reduced machine manufacturing and construction activities due to project funding uncertainty.

The long-term liability for the asset retirement obligation is accreted, or increased, for the passage of time and the estimate also is revised for any changes in long-term inflation rate assumptions. The accretion, based on a time value of money calculation, is charged to cost of sales in the LEU segment. At the end of 2010, USEC reassessed the long-term liability and determined that the current fair value of the obligation was accrued at a sufficient amount based on construction progress and no further increase would be made until additional commercial plant deployment resumed.

During each reporting period, USEC reassesses and revises the estimate of the asset retirement obligation based on construction progress, cost evaluation of future decommissioning expectations, and other judgmental considerations which impact the amount recorded in both construction work in progress and other long-term liabilities. Significant increases in asset retirement obligations and related capitalized asset costs would result when ACP construction is fully underway as part of any commercial plant deployment and plant operations.

Environmental Compliance Costs

Environmental compliance costs relating to operations are accrued and charged to inventory costs as incurred. Estimated environmental compliance costs are accrued where environmental assessments indicate that storage, treatment or disposal of wastes is probable and costs can be reasonably estimated. Liabilities for waste are based on current-dollar cost estimates and are not discounted.

Concentrations of Credit Risk

Credit risk could result from the possibility of a customer failing to perform or pay according to the terms of a contract. Extension of credit is based on an evaluation of each customer's financial condition. USEC regularly monitors credit risk exposure and takes steps to mitigate the likelihood of such exposure resulting in a loss.

SWU and Uranium Revenue

Revenue is derived from sales of the SWU component of LEU, from sales of both the SWU and uranium components of LEU, and from sales of uranium. Revenue is recognized at the time LEU or uranium is delivered under the terms of contracts with domestic and international electric utility customers. Some customers take title and delivery of LEU at the Paducah GDP, and revenue is recognized when delivery of LEU to the customer is complete. Most customers take title and delivery of LEU at fuel fabricators. USEC ships LEU to nuclear fuel fabricators for scheduled or anticipated orders from utility customers. Based on customer orders, USEC arranges for the transfer of title of LEU from USEC to the customer for the specified quantity of LEU at the fuel fabricator. Revenue is recognized when delivery of LEU to the customer occurs at the fuel fabricator.

In a number of sales transactions, title to uranium or LEU is transferred to the customer and USEC receives payment under normal credit terms without physically delivering the uranium or LEU to the customer. This may occur because the terms of the agreement require USEC to hold the uranium to which the customer has title, or because the customer encounters brief delays in taking delivery of LEU at USEC's facilities. In such cases, recognition of revenue does not occur at the time title to uranium or LEU transfers to the customer but instead is deferred until LEU to which the customer has title is physically delivered. Certain customers make advance payments to be applied against future orders. Advances from customers are reported as deferred revenue, and revenue is recognized as product is delivered or services are provided.

Contract Services Revenue

USEC performs services and earns revenue from contract work through its subsidiary NAC (prior to its sale effective March 15, 2013) and from limited contract work for DOE and DOE contractors at the Paducah GDP and the Portsmouth site. Revenue from NAC sales related to fixed-price contracts is recognized as services are provided based on milestones or events defined in the work scope. Revenue is recorded on time-and-materials contracts as the work is performed based on agreed-upon hourly rates and allowable costs. U.S. government contract revenue includes billings for fees and reimbursements for allowable costs that are determined in accordance with the terms of the underlying contracts. Revenue is recognized as work is performed and as fees are earned. Allowable costs include direct costs as well as allocations of indirect plant and corporate overhead costs determined in accordance with government cost accounting standards. Amounts representing contract change orders or final billing rates based on incurred costs are accrued and included in revenue when they can be reliably estimated and realization is probable. Allowable costs are subject to audit by the Defense Contract Audit Agency ("DCAA"), or such other entity that DOE authorizes to conduct the audit. The final settlement of amounts submitted by USEC for reimbursement is subject to acceptance by DOE. Revenue resulting from final billing rates is recognized upon completion of the government audits and notice by DOE authorizing final billing. DOE historically has not approved USEC's provisional billing rates and has not completed audits of USEC's incurred cost submissions and authorized final payments in a timely manner. Additional details are provided in Note 5. There is the potential for additional revenue to be recognized, based on the outcome of DOE reviews and audits, as the result of the release of previously established receivable related reserves. However, because these periods have not been audited, uncertainty exists and USEC has not yet recognized this additional revenue.

DOE funded a portion of the now-completed work at Portsmouth through an arrangement whereby DOE transferred uranium to USEC which USEC immediately sold. USEC completed six competitive sales of uranium between the fourth quarter of 2009 and the first quarter of 2011. USEC's receipt of the uranium was not considered a purchase by USEC and no revenue or cost of sales was recorded upon its sale. This is because USEC had no significant risks or rewards of ownership and no potential profit or loss related to the uranium sale. The value of the contract work is based on the cash proceeds from the uranium sales less USEC's selling and handling costs. The net cash proceeds from the uranium sales were recorded as advances from customers and are to be applied, at the direction of DOE, (a) as revenue is recognized in USEC's contract services segment as services are provided or (b) to existing receivables balances due from DOE in USEC's contract services segment. As of December 31, 2012, the remaining balance of $20.5 million is included in other long-term liabilities pending resolution of long-term receivables from DOE described in Note 5.

Stock-Based Compensation

USEC has stock-based compensation plans available to grant restricted stock, restricted stock units, non-qualified stock options, performance awards and other stock-based awards to key employees and non-employee directors. Stock-based compensation cost is measured at the grant date, based on the fair value of the award, and is recognized over the requisite service period, which is either immediate recognition if the employee is eligible to retire, or on a straight-line basis until the earlier of either the date of retirement eligibility or the end of the vesting period.

Use of Estimates

The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect reported amounts presented and disclosed in the consolidated financial statements. Significant estimates and judgments include, but are not limited to, pension and postretirement health and life benefit costs and obligations, accounting treatment for expenditures on the American Centrifuge project, plant lease turnover costs, the tax bases of assets and liabilities, the future recoverability of deferred tax assets, and determination of the valuation allowance for deferred tax assets. Actual results may differ from such estimates, and estimates may change if the underlying conditions or assumptions change.

New Accounting Standards

In May 2011, the Financial Accounting Standards Board ("FASB") amended its guidance on fair value measurements and related disclosures. The amendments represent the converged guidance of the FASB and the International Accounting Standards Board and provide a consistent definition of fair value and common requirements for measurement and disclosure of fair value between generally accepted accounting principles in the U.S. ("GAAP") and International Financial Reporting Standards ("IFRS"). The new amendments also change some fair value measurement principles and enhance disclosure requirements related to activities in Level 3 of the fair value hierarchy. The new provisions are effective for fiscal years and interim periods beginning after December 15, 2011 and are applied prospectively. The implementation of the amended guidance in the first quarter of 2012 did not have an effect on USEC's results of operations, cash flows or financial position.

In June and December 2011, the FASB issued guidance on the presentation of comprehensive income. The new guidance requires companies to present the components of net income and other comprehensive income either in a single statement below net income or in a separate statement of comprehensive income immediately following the income statement. The provisions of this new guidance are effective for fiscal years and interim periods beginning after December 15, 2011 and are applied retrospectively for all periods presented. The implementation of the new guidance in USEC's financial statements beginning in the first quarter of 2012 did not have an effect on USEC's results of operations, cash flows or financial position.

In September 2011, the FASB amended its guidance on testing goodwill for impairment. Under the revised guidance, companies testing goodwill for impairment have the option of first performing a qualitative assessment to determine whether further quantitative assessments are warranted. In assessing qualitative factors, companies are to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount as a basis for determining whether it is necessary to perform the two-step goodwill impairment test prescribed in the existing guidance. The provisions of this new guidance are effective for fiscal years and interim periods beginning after December 15, 2011. USEC's adoption of the new guidance did not have a material effect on its results of operations, cash flows or financial position. USEC's goodwill resulted from the acquisition of NAC in 2004. As of December 31, 2012, USEC determined that there was no impairment based on indications of interest it had received from independent parties to purchase NAC for prices higher than the carrying value. In January 2013, USEC determined that it would seek to sell NAC and on March 15, 2013, USEC sold NAC as detailed in Note 20.