Staff Nuclear Engineer at Radiant in El Segundo, CA

Job description

About Radiant Radiant is an El Segundo, CA-based startup building the world’s first mass-produced, portable nuclear microreactors. Rising energy demand is straining the U.S. grid and driving up utility costs, emissions, and interconnection backlogs. Radiant decentralizes energy, producing power close to where it’s used. Its first reactor, Kaleidos, is a factory-built, 1-megawatt, fail-safe microreactor that can be transported by land, sea, or air and runs up to 5 years without refueling. Deployed locally without a decade-long build or permitting fight, Kaleidos provides independent power for critical infrastructure like military bases, data centers, hospitals, and remote sites. Founded in 2020, Radiant is under contract to deliver power to the U.S. Army, Air Force, Navy, and has pre-order agreements with Equinix, with deployments 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 workstreams. 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, and regulatory teams to resolve multidisciplinary design challenges. • Work with the regulatory organization to translate applicable nuclear standards and requirements into analysis plans, design criteria, calculat