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 driven Senior Thermal Modeling & Analysis Engineer to own high-fidelity CFD and thermal modeling for the Kaleidos microreactor. You will analyze heat generation and transport, high-temperature gas flow, and thermal interactions across reactor systems, cooling systems, shielding, and surrounding hardware under steady-state, transient, and off-normal conditions.

Your work will directly influence system architecture, component design, material selection, operating limits, test planning, and safety margins. You will work across mechanical, fluid systems, nuclear, structures, controls, and test engineering to develop validated analytical tools that support the commercialization of the first mass-produced nuclear reactor.

Responsibilities & Duties:

• Own thermal and CFD analyses from problem definition through model development, execution, validation, documentation, and design recommendation.

• Model turbulent gas flow, conduction, convection, radiation, conjugate heat transfer, and coupled multiphysics behavior across Kaleidos systems.

• Evaluate steady-state, transient, and off-normal operating conditions to identify hotspots, thermal gradients, heat loads, flow distribution, pressure losses, and system margins.

• Define modeling assumptions, boundary conditions, material properties, and appropriate fidelity based on the engineering decision being supported.

• Translate analytical results into actionable design recommendations and collaborate with engineering teams through design iteration.

• Establish and implement simulation best practices, including convergence assessment, mesh and time-step independence, sensitivity studies, uncertainty evaluation, and model verification.

• Correlate analytical models with test data and update modeling assumptions based on measured system behavior.

• Build automated, reproducible workflows for parametric studies, design exploration, post-processing, and simulation efficiency.

• Develop and validate reduced-order models that support system-level analysis and rapid design iteration.

• Clearly communicate assumptions, limitations, risks, margins, and recommendations to cross-functional teams.

Required Qualifications & Skills:

• Bachelor’s degree in mechanical, aerospace, nuclear engineering, physics, or a related field.

• 5+ years of relevant thermal, CFD, or thermal-fluid analysis experience.

• Extensive experience with STAR-CCM+, Ansys Fluent, or comparable CFD software.

• Strong foundation in heat transfer, fluid mechanics, turbulence modeling, and numerical methods.

• Experience performing steady-state and transient thermal-fluid analyses.

• Experience with model verification, sensitivity studies, and validation or test correlation.

• Ability to prepare and simplify CAD geometry for analysis using Siemens NX or comparable software.

• Experience using Python or another scripting language to automate simulation and post-processing workflows.

• Demonstrated ability to translate analytical results into engineering decisions and communicate effectively across disciplines.

Desired Qualifications & Skills:

• Experience modeling high-temperature gas systems, nuclear reactors, propulsion systems, turbomachinery, or other complex energy systems.

• Experience with thermal FEA and coupled fluid-thermal-structural analysis.

• Experience modeling radiative heat transfer, including surface-to-surface or participating-media radiation.

• Familiarity with nuclear heat generation, decay heat, neutronics coupling, or radiation transport.

• Experience developing reduced-order or system-level thermal-fluid models.

• Experience with high-performance computing, optimization, or large parametric simulation campaigns.

• Driven, self-motivated, and capable of owning technically ambiguous problems end to end.

Additional Requirements

• Willing to support extended hours when needed to meet critical program milestones.

• Must work 100% onsite at El Segundo HQ.

Benefits and Perks

• Stock: Substantial incentive stock plan for all full-time employees.

• Medical: 100% up to base silver level plan for employee + 50% dependents, offers up to Platinum plans.

• One Medical: Sponsored memberships for employees and their dependents.

• Vision: 100% top tier plan coverage + 50% for dependents.

• Dental: 100% top tier plan coverage, orthodontia extra, 50% for dependents.

• Voluntary life, accident, hospital, critical illness, commuter and FSA/HSA are offered as employee contributed benefits.

• 8-weeks of paid parental leave for all parents. Additional paid pregnancy leave for CA employees.

• Daily catered lunch. Free snacks and drinks.

• Flexible PTO policy. Remote workday allocation.

• Company and team-bonding events, happy hours and in-person camaraderie.

• Beautiful El Segundo headquarters close to the Pacific Ocean.

Total Compensation and Benefits
Radiant compensates people for impact and invests in those who continue to raise the bar. Radiant’s new hire compensation package includes base salary, substantial equity grants, and comprehensive health benefits. Total compensation and level are determined through a rigorous evaluation of interview performance, experience, education, and qualifications, and are designed to support continued growth as scope, responsibility, and impact expand at Radiant.

The best of today’s advanced reactor builders don’t wait for job postings. They join the winning team. If that’s you, contact us directly for immediate opportunities: [email protected].

We are an equal opportunity employer and all qualified applicants will receive consideration for employment without regard to race, color, religion, sex, sexual orientation, gender identity or expression, pregnancy, age, national origin, disability status, genetic information, protected veteran status, or any other characteristic protected by law.

This position involves access to technology that is subject to U.S. export controls. Any job offer made will be contingent upon the applicant’s capacity to serve in compliance with U.S. export controls.