Senior Nuclear Thermal-Hydraulics Engineer

Radiant is an El Segundo CA-based startup building the worlds first mass-produced portable nuclear microreactors. The companys 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. Radiants 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 Senior Nuclear Thermal-Hydraulics Engineer to lead thermal-hydraulics and coupled physics analysis for the Kaleidos microreactor. You will own the modeling that determines how heat coolant and reactor core behavior interact under normal and accident conditions work that directly informs core design cooling systems and safety case development for the first mass-produced nuclear reactor. This role is suited to engineers with reactor-specific thermal-hydraulics or coupled multiphysics experience who want to apply that depth to a fast-moving factory-built reactor program.

Responsibilities & Duties

• Own and execute thermal-hydraulics analysis to evaluate design and safety performance of Kaleidos reactor systems under normal and accident conditions.

• Develop and apply coupled physics models integrating thermal-hydraulics with neutronics and/or structural response.

• Identify and implement best practices for reactor thermal-hydraulics and systems-code analysis.

• Build automated workflows to expand simulation capabilities accuracy and efficiency.

• Collaborate across reactor physics mechanical and safety teams to support licensing and design trade studies.

Required Qualifications & Skills

• Bachelors degree in nuclear engineering mechanical engineering physics or similar field from an accredited institution.

• 5 years of relevant industry or national laboratory experience.

• Experience with thermal-hydraulics analysis and/or reactor systems codes (e.g. RELAP5 TRACE CTF/COBRA-TF SAM TRANSFORM).

• Experience with high-temperature (500F) heat transfer analysis involving conduction convection and radiation.

• Experience communicating and distilling technical information with cross-functional teams.

Desired Qualifications & Skills

• Experience with coupled multiphysics modeling (e.g. MOOSE BISON MARMOT) or neutronics coupling.

• Experience with commercial CFD/FEA tools (STAR-CCM Ansys Fluent) and CAD (Siemens NX).

• Prior experience at a national laboratory reactor vendor or advanced reactor developer.

• 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.

• 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. Radiants 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 todays advanced reactor builders dont wait for job postings. They join the winning team. If thats you contact us directly for immediate opportunities: .

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.

This position involves access to technology that is subject to U.S. export controls. Any job offer made will be contingent upon the applicants capacity to serve in compliance with U.S. export controls.

Required Experience:

Senior IC