Senior Mechanical Engineer, Numenor (Reactor)

About Valar Atomics At Valar Atomics, we're redefining what's possible in energy. Our mission is to make clean, high-temperature nuclear power scalable—unlocking abundant energy for industry, hydrogen, and next-generation manufacturing. We are a team of builders, engineers, and operators who believe nuclear energy should be fast to deploy, factory-made, and built for the real world. Our first pilot plant in Orangeville, Utah will demonstrate how advanced nuclear systems and fuel fabrication can power the future. Joining Valar Atomics means becoming part of a company where autonomy, ownership, and impact exist at every level. The Team The Numenor team is building Valar’s next reactor, the flagship program that will define how we deliver nuclear power at scale. This dedicated team owns the entire plant, from the reactor core and helium systems to cooling, plant modules, and the Citadel, uniting mechanical, systems, safety, IC&E, quality, and supply chain under one mission. The work starts with bringing the first unit to life and ends with a production line that delivers reactors faster with every build. What this team builds will power the critical infrastructure of the future. The Role Valar Atomics seeks a Senior Mechanical Engineer for the reactor program. This role will own the design, build, and test of mechanical subsystems within the reactor plant, including the reactor, control rods, helium pressure boundary, helium services, HVAC, and Citadel. You will take hardware from concept through build, test, and commissioning on the first unit, then help drive it into repeatable, scaled production. The role demands someone who is hands-on and hardware-first, while bringing the rigor and discipline required to ensure the design basis is met. Key Responsibilities Design and Analysis Own the mechanical design of assigned subsystems, from requirements and concept through detailed design and design freeze. Perform and review stress, thermal, and fluid analyses (FEA and CFD) to validate margins, materials, and code compliance. Develop 3D CAD models, assemblies, and drawings, applying GD&T and tolerance analysis. Present designs at design reviews and drive actions to closure. Build, Test and Commissioning Take designs to hardware through procurement specifications, vendor management, factory build, and assembly. Plan and execute component and integrated testing with the V&V team, and support commissioning through first operation. Design for manufacture and repeatability, so each unit builds faster than the last. Collaboration and Leadership Work closely with systems engineering, safety, IC&E, quality, and supply chain so the plant design stays integrated. Mentor junior engineers and contribute to design standards, documentation, and configuration management. Lead root cause investigations and drive corrective actions on hardware issues. Basic Qualifications Bachelor’s degree in Mechanical Engineering or a related field. 5+ years of mechanical engineering on complex hardware, such as pressure systems, heat transfer equipment, mechanisms, or large structures. Proven track record taking hardware from design through build and test. Strong base in stress analysis, thermal design, materials, and pressure vessel and piping codes. Proficiency in CAD (SolidWorks, Creo, NX, or similar) and engineering drawing standards. Preferred Skills and Experience Master’s degree in Mechanical Engineering or a related field. Experience with high-temperature, high-pressure systems, such as pressure vessels, heat exchangers, and piping. First-of-a-kind hardware experience in aerospace, power generation, oil and gas, or defense. Helium or other gas systems, including sealing, leak tightness, and rotating equipment. Precision mechanisms and actuators, plus the qualification testing that goes with them. Working knowledge of ASME pressure vessel and piping codes (Section VIII, B31.3). Design for manufacture and scaling from prototype to series production. Nuclear industry experience: commercial, defense, or national laboratory. A plus, not a prerequisite. What We Offer Competitive base salary Equity ownership in a rapidly growing advanced energy company Comprehensive medical benefits Unlimited PTO Free daily lunch and dinner provided onsite Generous PPE stipend High-impact startup environment with significant ownership and autonomy Opportunities for rapid career growth and internal advancement Direct collaboration with experienced operators, engineers, and industry leaders The opportunity to help build and scale transformative energy technology from the ground up Equal Employment Opportunity Statement Valar Atomics is an equal opportunity employer. We consider all qualified applicants without regard to race, color, religion, sex, gender identity, sexual orientation, national origin, age, disability, veteran status, or any other protected status under applicable law. We are committed to providing a workplace free of discrimination and harassment and will provide reasonable accommodation as required by law. Applicants must be legally authorized to work in the United States as a U.S. citizen or lawful permanent resident (green card holder). Salary $140,000 — $180,000 USD