Prototype Build Engineer Jobs (NOW HIRING)

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.

We are seeking for a Build Engineer to help bring high-speed rotating hardware from design into reality. This is a hands-on role ideal for new graduates or early-career engineers who want to learn by building, assembling, and integrating complex turbomachinery systems. You will work closely with design, test, and manufacturing teams, helping prepare hardware for first-article testing and system validation. 

This is a fantastic opportunity to gain real-world experience with high-speed, high-temperature rotating machinery while making a direct impact on a first-of-its-kind nuclear microreactor program. 

Responsibilities & Duties:

• Responsible for assembly and integration of prototype and first-article turbomachinery. hardware, including compressors, turbines, rotors, electric motors, bearings, seals, and housings. 

• Develop precise assembly instructions, alignment procedures, and torque specifications.

• Support rotor stacking, bearing installation, balancing, and alignment operations. 

• Document assembly activities, as-built observations, and lessons learned. 

• Help develop and maintain build tools, fixtures, and work-holding solutions. 

• Support creation of work instructions and standard operating procedures for assembly processes. 

• Provide feedback to design and manufacturing teams to improve hardware assembly and integration. 

• Work closely with design engineers, test engineers, and technicians to prepare hardware for testing and validation. 

• Participate in troubleshooting assembly issues and contribute to iterative improvements.

• Receive mentorship from senior build engineers while gradually taking on more responsibility. 

• Gain experience with high-speed rotating machinery, tight tolerances, and precision assembly. 

• Learn industry best practices for turbomachinery build, integration, and first-article readiness.

• Develop problem-solving skills and hands-on engineering judgment in a fast-paced startup environment.

Required Qualification & Skills:

• Bachelor’s degree in Mechanical Engineering or a related field (or expected graduation within 6 months).

• Strong interest in hands-on mechanical assembly, rotating machinery, or turbomachinery systems. 

• Basic understanding of GD&T, fits, torque, and alignment principles.

• Comfort reading and interpreting mechanical drawings and CAD models. 

• Willingness to learn, take initiative, and work safely with precision hardware. 

Desired Qualifications & Skills:

• Prior hands-on experience from internships, co-ops, class projects, or design competitions (SAE, Formula SAE, robotics, etc.). 

• Familiarity with mechanical assembly, rotor balancing, or bearing handling. 

• Interest in turbomachinery, power generation, or high-speed rotating systems. 

• Excited to work in a fast-paced, innovative startup environment. 

• Prior nuclear experience is not required. 

Additional Requirements:

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

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

• 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: recruiting@radiantnuclear.com.
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.

Unfortunately, we are unable to provide visa sponsorship at this time.

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.

Compensation Range: $74K - $130K