Senior Build Engineer, Turbomachinery

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 turbo machinery 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 turbo machinery 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:

Turbo machinery Build & Integration Lead hands-on assembly, integration, and troubleshooting of complex turbo machinery 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…