Phoenix Feasibility Study 2023

Gryphon Underground ("UG") Pre-Feasibility Study Update (2023): Provides Denison with additional source of low-cost production to deploy Phoenix cash flows (1) 61.9M lbs U3O8 C$864M estimated Base-case @ 1.7% U308 | after-tax NPV (100% basis) 8% Indicated Mineral Resources (1,643,000 tonnes, 100% basis) Moderate grade allows low-cost conventional UG mining approach Plus... 1.9M lbs U₂O8 Inferred mineral resources (73,000 tonnes @ 1.2% U308, 100% basis) (see note 3, 4) 37.6% estimated Base-case after-tax IRR (see note 3, 4) US$12.75 / lbs U3O8 average Cash Operating Costs | (C$17.27/lb U308) c$737M estimated Initial CAPEX (100% basis) 2023 PFS Update Scope limited to cost update and minor schedule optimization US$25.47 /lbs U₂Og average All-in Cost(2) (C$34.50/lb U308) Lenison PHOTO: View inside the SX circuit at Denison's 22.5% owned McClean Lake mill, which is assumed to toll mill production from the Gryphon UG operation NOTES: (1) See the Wheeler River Technical Report titled "NI 43-101 Technical Report on the Wheeler River Project, Athabasca Basin, Saskatchewan, Canada" dated June 23, 2023. (2) All-in cost is estimated on a pre-tax basis and includes all project operating costs, capital costs post-FID, and decommissioning costs divided by the estimated number of pounds U₂Og to be produced. (3) NPV and IRR are calculated based on assessed "high-case" uranium price, to the start of pre-production activities for the Gryphon operation. (4) Indicative post-tax results were prepared on a combined basis with the Phoenix deposit for Denison's then 90% ownership interest, see slide 12 for details. 16

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