Mechanical Engineer – Heat Exchangers

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 failsafe microreactor that can be transported anywhere power is needed and run for up to five years without the need to refuel. 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 utilizes modern software engineering to rapidly achieve safe, factory-built microreactors that leverage existing, well-qualified materials. Founded in 2020, Radiant is on track to test its first reactor next year at the Idaho National Laboratory, with initial customer deliveries beginning in 2028.

Mechanical Engineer – Heat Exchangers

Radiant is seeking a highly motivated Mechanical Engineer with a deep understanding of heat exchanger and fluid sytems design to join our engineering team. This role focuses on developing and optimizing heat exchangers across a range of thermal systems, balancing high-performance heat transfer with design for manufacturability (DFM), cost-efficiency, and reliability. The ideal candidate will have hands-on experience with both thermal-fluid analysis and practical mechanical design, and will work cross-functionally with manufacturing, supply chain, and the secondary cooling loop development teams. 

Responsibilities and Duties:   

• Design various types of heat exchangers (e.g., shell-and-tube, plate-fin, air-cooled, printed circuit) for the Kaleidos secondary cooling loop based on system requirements, from concept through prototyping and production. 
• Develop detailed CAD models and manufacturing drawings using Siemens NX. 
• Conduct thermal-fluid simulations (e.g., using ANSYS Fluent, COMSOL, or proprietary tools) to predict heat transfer and pressure drop characteristics, while optimizing fluid paths, fin geometry, and flow distribution for high performance and efficiency. 
• Integrate DFM principles early in the design process to minimize cost, reduce complexity, and ensure scalability. 
• Engage with vendors and suppliers to evaluate component feasibility and cost effectiveness. 
• Ensure designs meet applicable codes, standards (e.g. ASME Section VIII), and regulatory requirements. 
• Participate in design reviews and technical discussions. 

Required Qualifications and Skills:  

• Bachelor’s or master’s degree in mechanical engineering or a related field. 
• 3+ years of experience in heat exchanger or fluid component design in a high-performance hardware environment. 
• Strong mechanical design skills and CAD proficiency (e.g., NX, SolidWorks, or equivalent). 
• Proficiency with thermal, fluid, and/or structural analysis tools (e.g. STAR-CCM, ANSYS, or similar). 
• Demonstrated experience applying DFM principles in a product development environment. 
• Excellent communication and technical documentation skills. 

Desired Qualifications and Skills:   

• Prior experience with supercritical CO2 applications. 
• Experience designing recuperators or compact heat exchangers in nuclear, aerospace, or high-temperature process industries. 
• Familiarity with high-temperature alloys and fabrication techniques such as diffusion bonding and welding. 
• Working knowledge of ASME codes relevant to heat exchangers and nuclear components. 
• Experience with design for manufacturability (DFM) and working directly with vendors on prototype development. 
• Basic programming knowledge (e.g. Python, C++, or equivalent).

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. 

Total Compensation and Benefits

Radiant's new hire compensation package includes base salary, substantial equity grants, and comprehensive benefits. Total compensation and level are determined through a holistic evaluation of your interview performance, experience, education, and qualifications. 

Benefits and Perks for Eligible Employees:

• 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.

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.