Staff Mechanical Engineer, Numenor (Reactor)

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 Staff Mechanical Engineer for the reactor program. This role will serve as the technical owner for major mechanical systems within the reactor plant, such as the reactor, control rods, helium pressure boundary, helium services, HVAC, and Citadel. You will set the design direction for your systems, take them from concept through build, test, and commissioning on the first unit, and drive them into repeatable, scaled production.

The role demands someone who can operate with hands-on technical authority and a hardware-first mentality, while maintaining the integrity, rigor, and control required to ensure the design basis is met.

Key Responsibilities

Technical Leadership

• Own the mechanical design basis for assigned systems, including requirements, interfaces, margins, materials, and code selection.
• Make technical calls on design acceptability for your systems and escalate tradeoffs that affect the broader plant.
• Lead design reviews and drive systems through gate decisions from concept to design freeze.
• Perform and review stress, thermal, and fluid analyses (FEA and CFD), and set the analysis approach for the team working on your systems.

Build, Test and Commissioning

• Take designs to hardware through procurement specifications, vendor selection and management, factory build, and assembly.
• Define test and qualification plans with the V&V team, and support integrated testing and commissioning through first operation.
• Design for manufacture and repeatability, so each unit builds faster than the last.

Collaboration and Mentorship

• Work closely with systems engineering, safety, IC&E, quality, and supply chain so the plant design stays integrated.
• Mentor senior and junior engineers, review their designs, and raise the technical bar across the mechanical team.
• Lead root cause investigations on complex hardware issues and set mechanical design standards and best practices.

Basic Qualifications

• Bachelor's degree in Mechanical Engineering or a related field.
• 8+ years of mechanical engineering on complex hardware, such as pressure systems, heat transfer equipment, mechanisms, or large structures.
• Experience as the technical owner of a major system, setting margins and making design decisions.
• Led mechanical scope on hardware from concept through build, test, and commissioning.
• 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.
• PE license (Mechanical): a plus.

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