About Radiant

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, 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. Radiant’s 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 Staff Nuclear Engineer to provide technical expertise across the nuclear design and analysis of Kaleidos. You will work across core physics, neutron and radiation transport, shielding, activation and dose, thermal-hydraulics, safety analysis, instrumentation and controls, reactor operations, and regulatory evaluations to solve multidisciplinary reactor design challenges.

This role combines deep hands-on analysis with technical ownership across major nuclear engineering workstreams. You will lead complex projects from requirements definition and early design trades through model development, analysis, verification and validation, testing, and regulatory documentation. You will help establish analytical methods and technical standards, mentor engineers, and serve as a key technical interface between nuclear analysis and the broader reactor engineering organization.

The ideal candidate brings deep technical judgment, strong engineering fundamentals, and the ability to translate complex nuclear analysis into practical reactor design decisions. You should be comfortable operating with significant technical autonomy, working across disciplines, and driving difficult engineering problems through closure.

Responsibilities & Duties

• Provide technical leadership across reactor physics, core performance, shielding, dose and activation, thermal-hydraulics, safety analysis, I&C, and reactor operations.

• Own complex nuclear engineering projects from requirements capture and design iteration through model development, analysis, technical review, and final documentation.

• Perform and guide analyses of criticality, reactivity control, shutdown margin, power distribution, depletion, temperature feedback, radiation transport, dose, activation, and shielding performance.

• Develop, review, and improve high-fidelity neutron and radiation transport models used to support reactor design, safety, testing, and regulatory evaluations.

• Translate analytical results into actionable requirements and design decisions affecting the core, shielding, control systems, instrumentation, fluid systems, structures, and surrounding hardware.

• Lead multidisciplinary technical trades and evaluate the interaction between nuclear performance, thermal behavior, mechanical design, controls, operations, manufacturability, and safety.

• Establish and improve rigorous practices for model verification and validation, peer review, configuration control, uncertainty evaluation, and technical documentation.

• Ensure analytical assumptions, limitations, uncertainties, margins, and conclusions are clearly documented and technically defensible.

• Develop analytical methods, workflows, and tools that improve the accuracy, efficiency, and scalability of Radiant’s nuclear engineering capability.

• Collaborate with reactor systems, thermal, mechanical, electrical, test, operations, safety, and regulatory teams to resolve multidisciplinary design challenges.

• Work with the regulatory organization to translate applicable nuclear standards and requirements into analysis plans, design criteria, calculation packages, and verification activities.

• Support reactor testing and startup by defining analysis needs, instrumentation requirements, acceptance criteria, and methods for comparing predicted and measured performance.

• Provide technical mentorship and review for engineers across nuclear design and analysis activities.

• Identify technical risks, develop practical mitigation strategies, and drive complex nuclear engineering problems through closure.

• Communicate technical status, risks, decisions, and recommendations clearly to engineering teams and company leadership.

Required Qualifications & Skills

• Bachelor’s degree in nuclear engineering or a related technical discipline from an accredited institution.

• 8+ years of relevant nuclear engineering experience across reactor design, analysis, testing, licensing, safety, or operations.

• Demonstrated experience owning complex nuclear engineering projects involving multiple technical disciplines and stakeholders.

• Deep knowledge of neutron transport theory, Monte Carlo simulation methods, nuclear data, and statistical convergence.

• Professional experience developing and applying MCNP, OpenMC, or comparable neutron and radiation transport models.

• Strong understanding of reactor physics concepts, including criticality, reactivity coefficients, depletion, power distribution, shutdown margin, neutron and gamma transport, and uncertainty analysis.

• Experience translating analytical results into reactor design decisions, technical requirements, safety conclusions, or regulatory documentation.

• Experience developing or reviewing technically rigorous analysis methodologies, models, calculation packages, or engineering standards.

• Familiarity with model verification and validation, configuration control, peer review, and nuclear software quality practices.

• Demonstrated ability to operate independently on technically complex problems and drive work from definition through technical closure.

• Strong written and verbal communication skills, including the ability to explain complex analyses, assumptions, uncertainties, and technical conclusions to multidisciplinary teams.

Preferred Qualifications & Skills

• Master’s degree or Ph.D. in nuclear engineering or a related technical discipline.

• Subject-matter expertise in safety analysis, shielding, radiation dose and activation, instrumentation and controls, reactor operations, thermal-hydraulics, or radioactive-material transportation.

• Experience with high-temperature gas-cooled reactors, microreactors, advanced reactors, or first-of-a-kind nuclear systems.

• Experience with SCALE, Serpent, Shift, Griffin, MOOSE-based applications, or similar nuclear analysis tools.

• Proficiency with Python or another language used for simulation automation, model generation, and analysis post-processing.

• Experience with coupled neutronics and thermal-hydraulics or other multiphysics analyses.

• Familiarity with DOE authorization processes, NRC licensing, nuclear industry codes and standards, or regulatory safety analysis.

• Experience supporting reactor testing, commissioning, startup, or operational readiness.

• Experience developing analytical methods, technical standards, or nuclear engineering capabilities within a growing engineering organization.

• Demonstrated experience mentoring engineers and providing technical review across complex engineering programs.

Additional Requirements

• Must be mission driven and willing to support extended hours when needed.

• Must work 100% onsite at Radiant’s El Segundo headquarters.

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.

• 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. Radiant’s 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 today’s advanced reactor builders don’t wait for job postings. They join the winning team. If that’s you, contact us directly for immediate opportunities: [email protected].

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 applicant’s capacity to serve in compliance with U.S. export controls.