Staff Nuclear 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.

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 Radiants 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

• Bachelors 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

• Masters 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 Radiants El Segundo headquarters.

• 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:

Staff IC