Last Energy PWR-5 Project is advancing through construction at Texas A&M-RELLIS as the developer prepares for initial nuclear testing. The 5MW pilot reactor forms part of a US Department of Energy programme for advanced nuclear technology. Construction began in January 2026, with the project now approaching a critical regulatory and operational milestone.
Last Energy secured more than $100 million through an oversubscribed Series C financing round in December 2025. Astera Institute led the funding, which included several other technology and investment firms.
The financing exceeds the estimated $35 million needed for the pilot programme. It also supports development and commercialisation of Last Energy’s larger PWR-20 reactor.
Last Energy PWR-5 Project advances construction
The Last Energy PWR-5 Project uses a 5MW version of the company’s PWR-20 design. The pilot reactor will demonstrate low-power nuclear operation before progressing toward electricity generation.
The project sits within the Texas A&M-RELLIS Energy Proving Grounds in Bryan, Texas. The campus provides research, testing and workforce development facilities for emerging energy technologies.
Construction has progressed since groundbreaking in January. Last Energy reported completed reactor pits, installed components and substantial progress on the reactor building.
The company is also using factory-fabricated components for the reactor. Those components can reach the site ready for installation, supporting a more standardized construction process.
In May 2026, the Department of Energy approved the project’s Preliminary Documented Safety Analysis. That approval established an important safety basis for continued development.
Last Energy subsequently advanced its final Documented Safety Analysis for DOE review. The approval remains necessary before the reactor can proceed to initial criticality.
The project’s initial testing will operate under strict limits. A DOE environmental determination caps Phase 1 at 100kW thermal power and fewer than 1,000 operating hours.
The initial phase also will not export electricity to the grid. Later programme phases would move toward the PWR-5 design point and electricity generation.
Last Energy PWR-5 Project targets criticality milestone
Last Energy expects to receive final DOE authorization before conducting the first criticality test. Company officials said in September that the milestone could arrive within months.
Criticality will demonstrate that the reactor can sustain a controlled nuclear chain reaction. The milestone would provide an important validation of Last Energy’s reactor technology.
The PWR-5 directly supports development of the company’s commercial PWR-20 reactor. That commercial design targets approximately 20MW of electrical output for industrial customers.
Last Energy aims to deploy standardized nuclear plants for customers requiring reliable electricity. Data centers and other energy-intensive industries form important target markets.
The company’s approach uses established pressurized-water reactor principles. It combines those principles with modular manufacturing and a steel containment concept.
Meanwhile, Texas is attracting several advanced nuclear developments because electricity demand continues to rise. Artificial intelligence infrastructure and data centers are strengthening demand for dependable generation.
That market also includes larger projects pursuing commercial grid connections. The Port of Victoria Project’s $6 billion-plus gas-to-nuclear development plans up to five BWRX-300 reactors alongside gas generation.
The comparison highlights two different approaches to Texas nuclear construction. Last Energy is demonstrating a smaller factory-oriented reactor, while the Port of Victoria development targets utility-scale generation.
Last Energy’s PWR-5 therefore represents more than a pilot facility. Its construction and testing could influence how smaller nuclear systems progress toward commercial deployment.
The immediate objective remains obtaining final DOE authorization and completing initial criticality. Success would move the project from construction demonstration toward operational validation.
Loan Secured
Nuclear startup Last Energy has secured $100 million in Series C to fund its small nuclear reactor project in Texas. The move comes at a time when demand for power to run artificial intelligence systems drives renewed interest in nuclear energy. The company’s funding round was led by Astera Institute and included participation from Galaxy Interactive.
It also involved Gigafund and Woori Technology. Last is developing a 20 MW micro reactor and aims to reduce production costs by incorporating off-the-shelf parts. These parts will be integrated into the common components. The company is part of a growing segment of businesses designing next-generation nuclear systems to address increasing electricity consumption.
The funding amount exceeds the $35 million Last Energy needs to complete a smaller 5-megawatt version. The smaller version is to be showcased as part of a U.S. Energy Department pilot program. “This financing fully capitalizes our DOE pilot project and positions us to transition swiftly into commercialization of our production power plants, ´ Chief Executive Officer Bret Kugelmass noted. SMR projects are taking shape across the U.S. which is seen through other projects such as the Palisades nuclear plant SMR project.
Outlook on Last Energy’s small nuclear reactor project
The implementation of the small nuclear reactor project by Last Energy marks its entrance into the market as a nuclear start up. However, they are not the only ones as numerous startups have raised funds in recent months. For instance, Google-backed X-energy raised $700 million last month. On the other hand, Antares raised $96 million two weeks ago.
In August, Aalo Atomics raised $100 million to build its prototype reactor. Though they are new entrants, Last has an idea in mind that will propel them ahead of the rest. They aim to use an old reactor design developed by the government decades ago.
The new funding will fully fund the pilot project and help the company start delivering its first commercial products, Kugelmass said. Last Energy hopes to turn on the pilot reactor next year, with its 20-megawatt commercial-scale unit entering production in 2028.
Operation on the Startup Reactor Project
Last Energy’s small nuclear reactor is not designed to be serviced during its lifetime. Instead, Last Energy is permanently encasing each core in 1,000 tons of steel. The reactors will arrive on site fueled with six years’ worth of uranium. Apart from electrical and control connections, there are no other penetrations that break the steel wall. Heat from the fission reactions will warm the steel. On the other hand, water flowing through pipes on the outside will harvest that heat to spin a steam turbine. When the reactor’s time is up, Last Energy will leave it on site, with the steel chamber serving as the waste cask, eliminating the need for separate disposal.
Project Fact Sheet
Name: Last Energy PWR-5 pilot reactor.
Location: Texas A&M-RELLIS, Bryan, Texas, United States.
Type: Advanced nuclear microreactor pilot.
Developer: Last Energy.
Pilot capacity: 5MW design output.
Commercial reactor: PWR-20.
Commercial capacity: Approximately 20MW.
Technology: Pressurized-water reactor.
Funding: More than $100 million Series C.
Pilot funding requirement: Approximately $35 million.
Construction start: January 2026.
Current status: Construction substantially advanced.
Safety milestone: DOE approved the Preliminary Documented Safety Analysis.
Next milestone: Final DOE authorization for initial criticality.
Phase 1 thermal limit: 100kW.
Pilot purpose: Demonstrate safe low-power nuclear operation.
Phase 1 operating duration: Fewer than 1,000 hours.
Phase 1 grid export: None.
Commercial purpose: Develop standardized 20MW nuclear plants.
Target customers: Data centers and industrial power users.
Construction model: Factory-fabricated and modular components.
Site: Texas A&M-RELLIS Energy Proving Grounds.
Project Team
Developer: Last Energy.
Pilot host: Texas A&M University System.
Project site: Texas A&M-RELLIS.
Federal programme authority: US Department of Energy.
Lead Series C investor: Astera Institute.
Series C investors:
- JAM Fund.
- Gigafund
- The Haskell Company.
- AE Ventures.
- Galaxy Interactive.
- Woori Technology.
- Ultranative.
Reactor technology developer: Last Energy.
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