Senior Thermal 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 driven Senior Thermal Engineer with expertise in CFD and thermal FEA modeling. You will design, develop and implement simulations for the Kaleidos microreactor to ensure high fidelity, reliability, and safety of our systems. You’ll work on cutting edge technical problems for a high temperature gas reactor that inform decisions across reactor systems, cooling systems, shielding, and more. You will have an opportunity to work in an interdisciplinary environment and drive milestones forward to unlock commercialization of the first mass‑produced nuclear reactor. Responsibilities & Duties Own and execute thermal CFD analysis to evaluate design and performance of Kaleidos reactor systems. Develop and implement solutions to model turbulent flow, heat transfer, and multi‑physics interactions. Identify and implement CFD simulation best practices. Build automated workflows to expand simulation capabilities, accuracy, and efficiencies. Collaborate across teams and disciplines to support design of reduced order analysis methods. Required Qualifications & Skills Bachelor’s degree in engineering, physics, or similar field from an accredited institution. 5+ years of relevant industry experience. 5+ years experience with STAR‑CCM+, Ansys Fluent, or other commercial CFD code. Proficiency with CAD software (Siemens NX). Mastery of finite element and computational fluid dynamics modeling principles and methods. Experience communicating and distilling information with cross‑functional teams. Desired Qualifications & Skills Experience with radiation heat transport modeling. Knowledge of nuclear reactor design. Driven, self‑motivated, and takes ownership of work end to end. Additional Requirements Must be willing to work extended hours and weekends as necessary to accomplish our mission. 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: View email address on click.appcast.io. 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. Unfortunately, we are unable to provide visa sponsorship at this time. 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. #J-18808-Ljbffr