Lead 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 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 engineering problems through closure. - Communicate technical status, risks, decisions, and recommendations clearly to engineering teams and company leadership. Required Qualifications & Skills - Bachelor’s degree in nuclear engineering or a related technical discipline from an accredited institution. - 5+ years of relevant nuclear engineering experience across reactor design, analysis, testing, licensing, safety, or operations. - 1+ year of experience managing direct reports. - Demonstrated experience leading complex nuclear engineering projects involving multiple technical disciplines and stakeholders. - Deep knowledge of neutron transport theory, Monte Carlo simulation methods, nuclear data, and statistical convergence. - Professional experience developing and applying MCNP, OpenMC, or comparable neutron and radiation transport models. - Strong understanding of reactor physics concepts, including criticality, reactivity coefficients, depletion, power distribution, shutdown margin, neutron and gamma transport, and uncertainty analysis. - Experience translating analytical results into reactor design decisions, technical requirements, safety conclusions, or regulatory documentation. - Familiarity with model verification and validation, configuration control, peer review, and nuclear software quality practices. - Strong written and verbal communication skills, including the ability to explain complex analyses, assumptions, uncertainties, and technical conclusions to multidisciplinary teams. Preferred Qualifications & Skills - Master’s degree or Ph.D. in nuclear engineering or a related technical discipline. Subject-matter expertise in safety analysis, shielding, radiation dose and activation, instrumentation and controls, reactor operations, thermal-hydraulics, or radioactive-material transportation. - Experience with high-temperature gas-cooled reactors, microreactors, advanced reactors, or first-of-a-kind nuclear systems. - Experience with SCAL