Radiant is an El-Segundo, CA-based clean energy startup building a nuclear microreactor. A climate-friendly alternative to diesel generators, Radiant's Kaleidos 1MW microreactor will be the world's first portable, zero-emissions power source that works anywhere. We plan to test our development reactor by 2026 and if successful, it will be the first new commercial reactor design to achieve a fueled test in over 50 years. Radiant's goal is to bring one of the world's first factory-constructed microreactors to market. Our microreactor can bring power to remote parts of the world and provide backup power for life-saving applications in hospitals or disaster-relief scenarios.

Fluid Systems Engineer – Heat Exchangers

Radiant is seeking a highly motivated Fluid Systems Engineer to own the design and development of the heat exchangers in the Kaleidos power generation cooling loop. You will develop critical hardware at the heart of the supercritical CO2 heat engine while considering for long-term production requirements related to hardware performance, reliability, mass, cost, and manufacturability. The ideal candidate is experienced in building early concept hardware through production, and is excited about our vision to build Earth’s mass-produced nuclear reactors and provide portable clean power to remote areas globally.

Responsibilities and Duties:

• Perform conceptual and detailed design of heat exchangers for the Kaleidos secondary cooling loop, including shell-and-tube, finned tube, and printed circuit heat exchanger (PCHE) technologies.
• Perform thermal and fluid flow modeling to evaluate heat exchanger performance under a variety of operating scenarios.
• Work with structural and materials teams to select appropriate alloys and manufacturing processes compatible with high-temperature and irradiated environments.
• Support FEA and CFD simulations to validate design assumptions and optimize geometry.
• Collaborate with fabrication partners to develop prototypes and guide manufacturing trials.
• Ensure designs meet applicable codes, standards (e.g. ASME Section III), and regulatory requirements.
• Participate in design reviews and contribute to safety case development and risk assessments.
• Document design processes, specifications, and performance metrics in a traceable and auditable manner.

Required Qualifications and Skills:

• B.S. in Mechanical Engineering, Aerospace Engineering, Nuclear Engineering, or related discipline.
• 3+ years of experience in heat exchanger design or thermal systems in a high-performance hardware environment.
• Proficiency with thermal/fluid analysis tools (e.g. STAR-CCM, ANSYS, or similar).
• Familiarity with high-temperature alloys and fabrication techniques such as diffusion bonding and welding.
• Strong mechanical design skills and CAD proficiency (e.g., NX, SolidWorks, or equivalent).
• Excellent communication and technical documentation skills.
• Basic programming knowledge (e.g. Python, C++, or equivalent)

Desired Qualifications and Skills:

• Experience designing recuperators or compact heat exchangers in nuclear, aerospace, or high-temperature process industries.
• 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.

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.

Employee Benefits for Eligible Employees:

• Stock: Substantial incentive stock plan for all full time, salaried 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 are offered as employee contributed benefits.
• Free snacks and drinks onsite.
• Flexible PTO policy.

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.