Nuclear Engineer

Position: Staff Nuclear 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 Staff Nuclear Engineer to provide technical expertise across the nuclear design and analysis of Kaleidos.

You will work across core physics, neutron and radiation transport, shielding, activation and dose, thermal-hydraulics, safety analysis, instrumentation and controls, reactor operations, and regulatory evaluations to solve multidisciplinary reactor design challenges.

This role combines deep hands-on analysis with technical ownership across major nuclear engineering work streams. You will lead complex projects from requirements definition and early design trades through model development, analysis, verification and validation, testing, and regulatory documentation. You will help establish analytical methods and technical standards, mentor engineers, and serve as a key technical interface between nuclear analysis and the broader reactor engineering organization.

The ideal candidate brings deep technical judgment, strong engineering fundamentals, and the ability to translate complex nuclear analysis into practical reactor design decisions. You should be comfortable operating with significant technical autonomy, working across disciplines, and driving difficult engineering problems through closure.

Responsibilities & Duties Provide technical leadership across reactor physics, core performance, shielding, dose and activation, thermal-hydraulics, safety analysis, I&C, and reactor operations.

Own complex nuclear engineering projects from requirements capture and design iteration through model development, analysis, technical review, and final documentation.

Perform and guide analyses of criticality, reactivity control, shutdown margin, power distribution, depletion, temperature feedback, radiation transport, dose, activation, and shielding performance.

Develop, review, and improve high-fidelity neutron and radiation transport models used to support reactor design, safety, testing, and regulatory evaluations.

Translate analytical results into actionable requirements and design decisions affecting the core, shielding, control systems, instrumentation, fluid systems, structures, and surrounding hardware.

Lead multidisciplinary technical trades and evaluate the interaction between nuclear performance, thermal behavior, mechanical design, controls, operations, manufacturability, and safety.

Establish and improve rigorous practices for model verification and validation, peer review, configuration control, uncertainty evaluation, and technical documentation.

Ensure analytical assumptions, limitations, uncertainties, margins, and conclusions are clearly documented and technically defensible.

Develop analytical methods, workflows, and tools that improve the accuracy, efficiency, and scalability of Radiant’s nuclear engineering capability.

Collaborate with reactor systems, thermal, mechanical, electrical, test, operations, safety,…