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Long Mott Energy, LLC – Long Mott Generating Station Xe-100 Power Reactor Application

Rendering of Long Mott Generating Station Xe-100 Power Reactor

Who:  

Long Mott Energy, LLC

What:  

Application for a construction permit for an advanced power reactor

When:  

March 31, 2025 (date of application submittal) 

Where:  

Calhoun County, Texas

Website:  

https://x-energy.com/reactors/xe-100

Dashboard:  

Long Mott Generating Station Xe-100 Dashboard

On this page:

Project Overview

The staff of the U.S. Nuclear Regulatory Commission (NRC) is currently engaged in review activities for the construction permit application from Long Mott Energy, LLC (LME), for the Xe-100 power reactor to be located in Calhoun County, Texas. The Xe-100 project is supported by the U.S. Department of Energy’s Advanced Reactor Demonstration program and would be used to demonstrate the X Energy Xe-100 reactor technology.

Plant Characteristics

Description

Reactor Type

High-Temperature Gas-Cooled Reactor (HTGR)

Containment Type

Functional Containment: Uranium Oxy carbide (UCO) fuel kernel, TRIstructural ISOtropic (TRISO) particle fuel layers, Fuel matrix, Helium pressure boundary, (see SECY-18-0096 for a description of functional containment)

Power Level

4-Module plant with 800 MWth/320 MWe

Fuel

Graphite Pebbles with TRISO Particle fuel

Balance of Plant

Shared steam powered conversion system (Rankine Cycle)

Key Milestones

Milestones

Completion Date
Actual - A
Target - T

Application Tendered

03/31/2025

Acceptance Review

Acceptance Review Start

04/01/2025 – A

Docketing Decision Letter
Issued/Acceptance Review Complete

05/12/2025 – A

Review Schedule Established/Schedule Letter Issued to Applicant

06/10/2025 – A

Safety Review

Draft Safety Evaluation — Safety Evaluation (SE) sections drafted, and information gaps identified.

February 2026 – T

*Advanced Safety Evaluation — All SE sections available for Advisory Committee on Reactor Safeguards review.

August 2026 – T

Final Safety Evaluation — Final SE issued.

November 2026 – T

Environmental Review

**Develop Initial Environmental Assessment (EA) Inputs  — Draft EA sections and appendices developed, open items identified, audit plan and information needs issued, and site audit conducted.

September 2025 – T

Revise Environmental Assessment — Initial EA sections updated; site audit completed, and information needs resolved.  Applicant submittals completed. Appendices completed and EA prepared.

October 2025 – T

Finalize Environmental Assessment and Related Activities — Legal review and management approvals of EA/FONSI conducted; EA correspondence prepared.

February 2026 – T

Issue Environmental Assessment and Finding of No Significant Impact — EA/FONSI concurrence completed; publication and issuance activities completed (including all related correspondence).

June 2026 – T

Hearing

TBD

Construction Permit Decision

TBD

* The review team will begin interacting with the Advisory Committee on Reactor Safeguards (ACRS) as soon as portions of the safety evaluation are approved by NRC staff managers. The ACRS may write a letter to the staff commenting on the evaluation.
** The NRC staff has made a decision to first prepare an Environmental Assessment to document its review of the environmental impacts associated with the proposed Long Mott Generating Station. In accordance with the National Environmental Policy Act, at the conclusion of this process, a determination will be made regarding whether to prepare a Finding of No Significant Impact (FONSI) or an Environmental Impact Statement (EIS). If a FONSI cannot be reached the NRC will commence preparing an EIS and this schedule may be subject to change.

Contacts

Contacts for Long Mott Generating Station Xe-100 Power Reactor

Safety Project Manager

Adrian Muñiz
301-415-4093

Environmental Project Manager

Joe O’Hara
301-415-6854

Public Affairs Officer

Scott Burnell
301-415-8204

Page Last Reviewed/Updated Monday, September 29, 2025

Page Last Reviewed/Updated Monday, September 29, 2025