About Radiant

Radiant 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 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

Bachelor's 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 (500°F+) 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.

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 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.