Senior Reactor Engineer

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 Senior Reactor Engineer to lead the testing and verification of critical components, mechanisms, and subsystems within the Kaleidos microreactor. You will work closely with nuclear, mechanical, thermal, controls, and test engineering teams to ensure reactor hardware meets its functional, performance, and safety requirements.

This role combines hands‑on test engineering with direct involvement in reactor design and development. You will own testing activities from requirements definition and test planning through execution, data analysis, and technical review. Your work will focus on core-related hardware, reactivity control mechanisms, instrumentation, and other reactor subsystems, using test results to inform design decisions and improve hardware performance.

The ideal candidate brings strong engineering fundamentals, practical testing experience, and sound technical judgment. You should be comfortable developing and reviewing test procedures, evaluating hardware performance, collaborating with reactor operations, and driving complex engineering problems through resolution.

Responsibilities & Duties

• Lead testing and verification of reactor components, mechanisms, and subsystems, including core assemblies, reactivity control mechanisms, instrumentation, and associated hardware.

• Own test activities from requirements definition and planning through execution, data analysis, and documentation.

• Develop test plans, procedures, instrumentation requirements, and acceptance criteria to verify hardware performance against design and safety requirements.

• Collaborate with nuclear, mechanical, thermal, and controls engineers to develop test strategies, evaluate designs, and resolve technical challenges.

• Perform engineering analyses and compare experimental results against analytical predictions and design assumptions.

• Review and technically approve test procedures, verification reports, and engineering documentation within assigned authority.

• Support reactor operations, commissioning, and integrated testing through procedure reviews, readiness assessments, and technical evaluations.

• Investigate hardware failures and test anomalies, identify root causes, and work with design teams to implement corrective actions.

• Translate test findings into design improvements while maintaining rigorous requirements traceability, documentation, and configuration control.

Required Qualifications & Skills

• Bachelor's degree in nuclear engineering, mechanical engineering, or a related technical discipline from an accredited institution.

• 5+ years of relevant experience in reactor engineering, hardware testing, design verification, or complex hardware development.

• Demonstrated experience developing and executing component or subsystem tests, including planning, instrumentation, data analysis, and performance evaluation.

• Strong engineering fundamentals in mechanical systems, heat transfer, materials, instrumentation, and component performance.

• Understanding of reactor operating principles, safety functions, and component-level performance requirements.

• Experience developing technical procedures, establishing acceptance criteria, and evaluating results against engineering requirements.

• Experience troubleshooting hardware failures, conducting root cause investigations, and implementing design improvements.

• Ability to interpret engineering drawings, specifications, and technical requirements while independently owning multidisciplinary engineering projects.

Preferred Qualifications & Skills

• Master's degree or Ph.D. in nuclear engineering, mechanical engineering, or a related technical discipline.

• Experience with reactor components, core assemblies, reactivity control mechanisms, instrumentation, or safety-critical hardware.

• Experience with high-temperature gas-cooled reactors, microreactors, advanced reactors, or first-of-a-kind nuclear systems.

• Familiarity with reactor physics, thermal-hydraulics, nuclear safety, and reactor operations.

• Experience supporting reactor testing, commissioning, startup, or operational readiness.

• Experience with test instrumentation, data acquisition systems, and testing under demanding thermal, mechanical, or environmental conditions.

• Proficiency with Python, MATLAB, or similar engineering tools for test automation and analysis.

• Familiarity with DOE authorization processes, NRC licensing, nuclear industry standards, or nuclear quality assurance requirements.

Additional Requirements

• Must be mission driven and willing to support extended hours when needed.

• 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-week 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.
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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.