Senior Reactor Engineer

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.

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.

• 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.

• 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…