About Radiant

Radiant is an El Segundo, CA-based startup building the world’s first mass-produced, portable nuclear microreactors. The company’s first reactor, Kaleidos, is a 1-megawatt, fail-safe microreactor that can be transported anywhere power is needed and run for up to 5 years without refueling. Portable nuclear power with rapid-deploy capability can replace similar-sized diesel generators and provide critical asset support for hospitals, data centers, remote sites, and military bases. Radiant’s unique, practical approach to nuclear development leverages modern software engineering to rapidly deliver safe, factory-built microreactors that use existing, well-qualified materials. Founded in 2020, Radiant is on track to test its first reactor at the Idaho National Laboratory this summer, with initial customer deliveries beginning in 2028.

About the Role

Radiant is seeking a highly motivated Senior Build Engineer to lead the assembly, integration, and build execution of high-performance turbomachinery systems for our portable nuclear microreactor. This is a hands-on engineering role requiring strong mechanical fundamentals, precision assembly experience, and the ability to independently solve complex hardware challenges.

You will take ownership of prototype and first-article turbomachinery builds, working closely with design, manufacturing, and test teams to translate engineering designs into functional, test-ready hardware. This role will be instrumental in developing assembly processes, resolving integration challenges, and improving hardware reliability and build repeatability as we advance toward production.

Responsibilities & Duties:

Turbomachinery Build & Integration

• Lead hands-on assembly, integration, and troubleshooting of complex turbomachinery hardware, including compressors, turbines, rotors, electric motors, bearings, seals, and housings.

• Own precision assembly operations, including rotor stacking, bearing installation, balancing, alignment, and mechanical fit-up.

• Interpret engineering drawings, GD&T, tolerance stack-ups, and mechanical specifications to ensure proper assembly and hardware functionality.

• Identify and resolve assembly challenges involving tight tolerances, component interfaces, alignment, and mechanical interference.

• Drive first-article build execution, ensuring hardware meets engineering requirements and is ready for testing and validation.

Build Process Development & Tooling

• Develop, implement, and refine assembly processes, work instructions, alignment procedures, and torque specifications for complex rotating machinery.

• Design and develop custom assembly tooling, fixtures, and work-holding solutions to improve build efficiency, precision, and repeatability.

• Evaluate assembly methods, identify process improvements, and establish best practices for transitioning prototype builds toward repeatable production processes.

• Maintain detailed build documentation, including as-built configurations, inspection results, nonconformances, and lessons learned.

Technical Problem-Solving & Cross-Functional Collaboration

• Partner closely with design, manufacturing, and test engineers to resolve hardware integration challenges and improve design for manufacturability and assembly.

• Lead root cause investigations and corrective actions for assembly defects, mechanical failures, and hardware nonconformances.

• Provide technical feedback on component design, tolerances, material selection, and assembly interfaces to improve hardware performance and reliability.

• Support hardware testing, including pre-test inspections, post-test teardown, failure investigations, and implementation of design or process improvements.

• Provide technical guidance and mentorship to junior engineers and technicians, establishing high standards for precision assembly, workmanship, and build quality.

Required Qualifications & Skills

• Bachelor's degree in Mechanical Engineering, Aerospace Engineering, or a related engineering discipline.

• 5+ years of relevant experience in mechanical assembly, hardware integration, manufacturing, or build engineering involving complex mechanical systems.

• Demonstrated hands-on experience assembling, integrating, and troubleshooting precision mechanical hardware.

• Strong understanding of GD&T, tolerance stack-ups, mechanical fits, fasteners, torque requirements, and alignment principles.

• Proficiency in reading and interpreting complex engineering drawings, assembly documentation, and 3D CAD models.

• Experience developing assembly procedures, troubleshooting hardware issues, and improving build processes.

• Strong mechanical aptitude and first-principles problem-solving skills, with the ability to independently resolve complex technical challenges.

• Ability to work effectively across design, manufacturing, and test engineering teams in a fast-paced hardware development environment.

Desired Qualifications & Skills

• Direct experience with turbomachinery, gas turbines, compressors, high-speed rotating equipment, or power generation systems.

• Experience with precision rotor assembly, dynamic balancing, bearing installation, shaft alignment, and high-speed rotating machinery.

• Familiarity with precision measurement and inspection techniques, including dial indicators, micrometers, bore gauges, and other metrology equipment.

• Experience designing or developing custom assembly fixtures, tooling, and mechanical ground support equipment.

• Familiarity with rotor dynamics, thermal growth, bearing preload, interference fits, and mechanical clearances.

• Experience supporting first-article builds, prototype development, hardware testing, and design iteration.

• Experience transitioning complex hardware from engineering development to repeatable production processes.

• Prior nuclear industry experience is not required.

Additional Requirements

• Must be willing to work extended hours and occasional weekends to support critical build and test schedules.

• Must work 100% onsite at Radiant's El Segundo headquarters.

Benefits and Perks

• Stock: Substantial incentive stock plan for all full-time employees.

• Medical: 100% up to base silver level plan for employee + 50% dependents, offers up to Platinum plans.

• One Medical: Sponsored memberships for employees and their dependents.

• Vision: 100% top tier plan coverage + 50% for dependents.

• Dental: 100% top tier plan coverage, orthodontia extra, 50% for dependents.

• Voluntary life, accident, hospital, critical illness, commuter and FSA/HSA are offered as employee contributed benefits.

• 8-weeks of paid parental leave for all parents. Additional paid pregnancy leave for CA employees.

• Daily catered lunch. Free snacks and drinks.

• Flexible PTO policy. Remote workday allocation.

• Company and team-bonding events, happy hours and in-person camaraderie.

• Beautiful El Segundo headquarters close to the Pacific Ocean.

Total Compensation and Benefits
Radiant compensates people for impact and invests in those who continue to raise the bar. Radiant’s new hire compensation package includes base salary, substantial equity grants, and comprehensive health benefits. Total compensation and level are determined through a rigorous evaluation of interview performance, experience, education, and qualifications, and are designed to support continued growth as scope, responsibility, and impact expand at Radiant.

The best of today’s advanced reactor builders don’t wait for job postings. They join the winning team. If that’s you, contact us directly for immediate opportunities: [email protected].

We are an equal opportunity employer and all qualified applicants will receive consideration for employment without regard to race, color, religion, sex, sexual orientation, gender identity or expression, pregnancy, age, national origin, disability status, genetic information, protected veteran status, or any other characteristic protected by law.

This position involves access to technology that is subject to U.S. export controls. Any job offer made will be contingent upon the applicant’s capacity to serve in compliance with U.S. export controls.