Principal Mechanical Design Engineer, Turbomachinery

About RadiantRadiant 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 RoleRadiant is seeking a Principal Mechanical Design Engineer, Turbomachinery to serve as the Responsible Engineer for the turbomachinery within our nuclear-driven power generation system. This role owns the mechanical design, integrity, and performance of the core rotating assembly at the heart of our 1MW closed-loop Brayton cycle.You will define and drive the mechanical architecture of high-speed rotating hardware operating at extreme temperatures, pressures, and rotational speeds. As a deeply technical individual contributor, you will set direction for rotor dynamics, structures, bearings, seals, and system integration while working closely with electrical, thermal, and manufacturing teams.This is a hands-on, high-ownership role focused on technical excellence, sound engineering judgment, and delivering reliable, production-ready turbomachinery.Responsibilities & Duties:Technical Ownership & System ArchitectureServe as Responsible Engineer for the turbomachinery mechanical system.Own the mechanical architecture and design strategy for high-speed rotating assemblies.Lead rotor dynamics, structural integrity, and life analysis for rotating components and assemblies.Define and flow down requirements from system-level constraints including thermal, structural, and operational environments.Make key technical decisions on rotor layout, shafting, bearings, seals, materials, and clearances.Ensure designs meet performance, reliability, safety, and regulatory requirements.Establish and uphold standards for mechanical design rigor, analysis quality, and documentation.Mechanical Design & AnalysisLead detailed design of turbomachinery components including rotors, shafts, housings, and support structures.Test and validate turbomachinery, driving model correlation, risk reduction, and performance verification.Perform and review structural and thermal analysis to ensure integrity under high-speed and high-temperature operation.Define tolerances, fits, stack-ups, and alignment strategies for precision rotating assemblies.Partner with electrical engineering on alternator integration, including electromagnetic and structural coupling.Cross-Functional IntegrationPartner closely with turbomachinery aero, motor design, thermal, manufacturing, and test teams.Ensure seamless integration between turbine, compressor, and alternator subsystems.Drive clear interface definitions across mechanical, electrical, and thermal boundaries.Collaborate with manufacturing to ensure designs are producible, inspectable, and scalable.Engage with suppliers on technically critical components and design decisions.Prototyping, Testing & ValidationSupport assembly, integration, and test of turbomachinery hardware.Define validation strategies including spin testing, thermal testing, and system-level operation.Lead root cause analysis and drive design iteration for test failures or performance gaps.Remain hands-on in hardware bring-up, troubleshooting, and refinement.Technical InfluenceAct as a subject matter expert in turbomachinery mechanical design and rotating systems.Provide technical guidance and design reviews across the team without direct people management responsibility.Influence engineering direction through deep expertise, data-driven decisions, and strong judgment.Contribute to technical roadmap, risk identification, and mitigation strategies.Required Qualifications & Skills:B.S. in Mechanical Engineering or related field.10+ years of experience designing high-speed rotating machinery (turbines, compressors, or similar systems).Deep expertise in structural analysis and mechanical design of turbomachinery.Experience with bearings, seals, and high-speed shafting design.Expert-level proficiency with analysis tools (e.g., ANSYS) and advanced use of NX and Teamcenter for complex design, simulation, and product lifecycle management.Strong understanding of tolerancing, GD&T, and precision mechanical assembly.Experience owning hardware through design, build, and test cycles.Hands-on experience with assembly, integration, and troubleshooting of turbomachinery.Strong system-level thinking and mechanical intuition.Excellent engineering judgment and decision-making capability.Ability to influence without authority across cross-functional teams.Clear communicator capable of articulating complex technical concepts.High ownership mindset and accountability for hardware outcomes.Ability to operate effectively in a fast-paced, first-of-a-kind development environment.Desired Qualifications & Skills:Experience with closed-loop Brayton cycle systems or similar energy systems.Familiarity with high-temperature materials and extreme environment design.Experience integrating mechanical systems with high-speed electric machines.Prior experience as a Responsible Engineer for complex hardware.Experience scaling hardware from prototype to production.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 PerksStock: 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.Nuclear Engineering Certificate Program: 100% covered educational program with Penn State University, for eligible employees, to rapidly upscale into nuclear.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 BenefitsRadiant compensates people for impact and invests in those who continue to raise the bar. Radiant’s full-time 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 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.Compensation Range: $200,500 - $314,475LocationEl Segundo, CAEmployment TypeFull timeLocation TypeOn-siteDepartmentEngineeringMechanical EngineeringCompensation$200,500 – $314,475 • Offers Equity