Senior Mechanical Engineer, Fluid Systems

About Radiant Radiant is an El Segundo, CA-based startup building the world’s first mass-produced, portable nuclear microreactors. Rising energy demand is straining the U.S. grid and driving up utility costs, emissions, and interconnection backlogs. Radiant decentralizes energy, producing power close to where it’s used. Its first reactor, Kaleidos, is a factory-built, 1-megawatt, fail-safe microreactor that can be transported by land, sea, or air and runs up to 5 years without refueling.

Deployed locally without a decade-long build or permitting fight, Kaleidos provides independent power for critical infrastructure like military bases, data centers, hospitals, and remote sites. Founded in 2020, Radiant is under contract to deliver power to the U.S. Army, Air Force, Navy, and has pre-order agreements with Equinix, with deployments beginning in 2028.About the Role Radiant is seeking a highly motivated Senior Mechanical Engineer to own critical Kaleidos fluid systems from preliminary design through build and production.

These systems include the primary loop subsystems and power conversion loop, serving to convert heat from the reactor core into electrical power. You will be responsible for the following: trade studies, component selection, thermal hydraulic analysis, piping design, vendor selection, assembly, and testing. You will have an instrumental impact of fueling the first new commercial reactor design in over 50 years by 2026.  

Responsibilities & Duties:

Own end-to-end engineering of fluid systems and components, including compressors, valves, and heat exchangers.  Perform complex thermal and fluids analysis to drive design decisions, verify system performance, and ensure structural integrity using first-principle hand calculations and finite element tools.  Perform trade studies to optimize system and meet program requirements.   Develop and execute manufacturing/assembly instructions and test plans.    Create and manage a Bill-Of-Materials (BOM).   

Find and develop suppliers for all components.   Own subassembly design, manufacturing, and test schedules.  Own risk analysis (FMEA) for subsystems.  Collect requirements, provide expertise and feedback to engineers in other functional areas via clear, constructive communication.

  
Required Qualifications & Skills :

Bachelor’s degree from an accredited institution in Mechanical, Materials, Aeronautical, Civil or Structural Engineering.

  
Experience with fluid system architecture design.  5+ years of experience in designing, building, and testing fluids systems.   Proficient knowledge in fluid dynamics and thermodynamics.  Proficient knowledge of heat exchanger design and analysis methods.  Desired

Qualifications & Skills : Professional Engineer (PE) Mechanical license.

Knowledge of thermodynamic power cycles.  Prior experience with designing piping system for thermal growth using hand calculations and FEA tools.

  Experience with process piping design and testing codes, such as ASME B31.3 and ASME PCC-2.  Prior experience with fluid system modeling via Matlab/Python.   Experienced in design for manufacturability and ramping up hardware build in a production environment.  Experienced in designing and operating test stands.   Takes extreme ownership of work and a high degree of responsibility.   Excellent communication across multidisciplinary teams.  

Prior nuclear experience in not required for this role. 

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…