Nuclear Engineer

Position: Staff Nuclear Engineer
About Radiant Radiant is an El Segundo, CA-based company building the world's only mass-produced, transportable nuclear microreactors. The U.S. grid is under growing strain, with power demand accelerating, driving higher utility costs, rising carbon emissions, and interconnection backlogs. Radiant has a solution, transportable, on-site power. Our first reactor, Kaleidos, is 1 megawatt: small enough to be factory-built, transported by land, sea, or air, and deployed wherever power is needed.

1 MW can power 1000 homes for five years. Ship it back and we refuel for a 20 year operating life. We made energy a product that can be used for critical infrastructure like military bases, data centers, hospitals, and remote sites, as well as the commercial main street businesses that keep America running. Founded in 2020, Radiant is under contract to deliver power to the U.S. Army, Navy and Air Force and has signed 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 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, 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.

Provide technical mentorship and review for engineers across nuclear design and analysis activities.

Identify technical risks, develop practical mitigation strategies, and drive complex…