Senior Nuclear Engineer El Segundo, California,

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.

Radiant is seeking a driven Senior Nuclear Engineer to join our team! You will own modeling methods and reactor physics calculations of neutronics parameters such as reactivity, kinetics parameters, and energy deposition distributions used within our cutting‑edge custom‑made Digital Twin simulation software. You’ll be responsible for assessing conservatism and verifying assumptions within the modeling methods and documenting all results. Because these methods are pivotal in the safety analysis, you will play a key role in the commercialization of the first mass‑produced nuclear reactor.

• Own modeling methods of core neutronics and reactor physics calculations supporting Radiant’s transient safety analyses.
• Perform calculations of energy deposition distributions, reactivity coefficients, kinetics parameters, and control blade worths to input into Digital Twin models.
• Verify assumptions and assess conservatism of neutronics models.
• Document methods for both technical and non‑technical audiences.
• Assist in Verification & Validation (V&V) efforts for the Digital Twin.
• Review and support other nuclear analyses across the company in reactor physics, shielding, and radiation detection.

• Bachelor’s degree in nuclear engineering or a similar field from an accredited institution.
• 4+ years of experience with Monte Carlo nuclear engineering software such as OpenMC, MCNP, Serpent, SCALE, etc.
• Experience documenting analysis methods and assumptions.
• Strong programming skills in any language, preferably Python.

• Knowledge and experience in reactor kinetics.
• Basic knowledge of thermal hydraulic principles.
• Experience communicating and distilling information with cross‑functional teams.
• Driven, self‑motivated, and takes ownership of work end to end.

• Must be willing to work extended hours and weekends as necessary to accomplish our mission.
• Must work 100% onsite at El Segundo HQ.

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.

• Stock:
  Substantial incentive stock plan for all full‑time employees.
• Medical: 100% premium coverage for base Silver level plan for employee + 50% premium coverage for dependents. Platinum plans available.
• One Medical:
  Sponsored memberships for eligible employees and their 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.