Preliminary Opinion of the Water Supply and Yield Analysis

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STATE ENGINEER’S OFFICE

PRELIMINARY OPINION OF THE

NATRIUM DEMONSTRATION REACTOR

WATER SUPPLY AND WATER YIELD ANALYSIS,

LINCOLN COUNTY, WYOMING

NOVEMBER 2024

The State Engineer’s Office/Surface Water Division completed a comprehensive review of the Water Supply and Yield Analysis Report submitted by Wright Water Engineers, Inc. on behalf of US SFR Owner, LLC for the proposed Natrium Demonstration Reactor Project in Lincoln County, Wyoming.

The Project is currently estimated to use a total of 5,950 acre-feet of water per year, which is equivalent to a continuous diversion of 8.21 cfs. Wright Water Engineers, Inc. conservatively based the Water Supply and Yield Analysis Report on an annual water demand of 6,323 acre-feet of water per year, which is equivalent to continuous diversion of 8.73 cfs. 6,323 acre-feet of water per year is the maximum amount allowed under the agreement between TerraPower, LLC (on behalf of US SFR Owner, LLC) and PacifiCorp, Inc. for use of water from Lake Viva Naughton Reservoir. The projected life of the Project is 60 years including construction, operations, and decommissioning. US SFR Owner, LLC proposes providing the water supply for the Project through the following mechanisms:

The primary water supply for the Project is proposed to be from Lake Viva Naughton Reservoir, under Permit Nos. 6418R and 7476R, through agreement with PacifiCorp, Inc., the owner of the Reservoir. These two permits combined allow for storage of up to 45,465 acre-feet of water in the Reservoir for Industrial – steam power plant purposes. Water from Lake Viva Naughton Reservoir will be released into the Hams Fork River and then pumped from the River and delivered through a 7-mile pipeline system known as the Cooling Water Intake System, which currently has a 20 cfs design capacity.
During the construction phase, dewatering activities will displace up to 120 acre-feet of groundwater. Some of this water will be used onsite for uses such as, but not limited to, dust suppression and compaction. Any of this water not needed for construction purposes will be discharged to North Fork Little Muddy Creek. Any use of this water will be permitted through the State Engineer’s Office and any discharge of water from the Project will be permitted, as required, under the WYPDES Program.
The remainder of the water needed during the construction phase, approximately 25.3 million gallons, will be supplied from the Hams Fork River under existing municipal water rights. This water will be diverted through the Kemmerer-Diamondville Water Treatment Plant and will be trucked to the site.
US SFR Owner, LLC is also in the process of contracting for 6,323 acre-feet of water per year stored in Fontenelle Reservoir. If the contract is approved, it is anticipated that water from Fontenelle Reservoir will be pumped from the Green River through an intake structure located below the Reservoir and conveyed through an approximately 34-mile pipeline to the Project.

The Project will not use groundwater as a source of cooling or potable water, or for other plant needs during the operations or decommissioning phases. The primary water supply for all phases of the Project is surface water.

The Report states that US SFR Owner, LLC is able and willing to accommodate shortages in water supply and adjust operations, as needed.

Based upon the submitted Water Supply and Water Yield Analysis Report, it is the preliminary opinion of the State Engineer’s Office that a sufficient quantity of water for the Project has been adequately demonstrated.

The Natrium Demonstration Reactor Water Supply and Yield Analysis Report (November 2024) and the State Engineer’s Preliminary Opinion (November 2024) in its entirety, are available on the State Engineer’s Office website @ https://seo.wyo.gov/home/news-press-releases

Pursuant to W.S. 35-12-108, the State Engineer’s Office will accept written comments on the Preliminary Opinion through midnight, December 30, 2024. Comments can be submitted to: State Engineer’s Office/Surface Water Division, 122 West 25th Street, Herschler Building, 2W, Cheyenne, WY 82002; or to [email protected]

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