Lead 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 Lead Nuclear Engineer to provide technical and people leadership within the nuclear design and analysis organization supporting Kaleidos. You will lead an interdisciplinary team working across core physics, neutron and radiation transport, shielding, activation and dose, thermal-hydraulics, safety analysis, instrumentation and controls, reactor operations, and regulatory evaluations. This role combines hands-on technical leadership with team and project ownership. You will guide nuclear engineering work from requirements definition and early design trades through analysis, verification and validation, testing, and regulatory documentation. You will also own team priorities, schedules, resource planning, hiring, and execution against key program milestones. The ideal candidate brings deep technical judgment, strong engineering fundamentals, and the ability to translate complex nuclear analysis into practical design decisions. You should be comfortable leading in a fast-moving, interdisciplinary environment while developing engineers and driving difficult technical problems through closure. Responsibilities & Duties • Lead an interdisciplinary team working across reactor physics, core performance, shielding, dose and activation, thermal-hydraulics, safety analysis, I&C, and reactor operations. • Hire, manage, and develop a high-performing team of nuclear engineers through clear expectations, technical guidance, actionable feedback, and regular coaching. • Establish team priorities, project plans, schedules, resource needs, budgets, and clear ownership for nuclear engineering deliverables. • Own nuclear engineering projects from requirements capture and design iteration through model development, analysis, technical review, and final documentation. • Guide analyses of criticality, reactivity control, shutdown margin, power distribution, depletion, temperature feedback, radiation transport, dose, activation, and shielding performance. • Translate analytical results into actionable requirements and design decisions affecting the core, shielding, control systems, instrumentation, fluid systems, structures, and surrounding hardware. • Establish 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. • 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, calculation packages, and verification activities. • Support reactor testing and startup by defining analysis needs, instrumentation requirements, acceptance criteria, and methods for comparing predicted and measured performance. • Identify technical and programmatic risks, develop practical mitigation plans, and drive complex nuclear engin