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 Senior Safety Analysis Engineer to lead reactor safety analyses supporting the design, testing, and deployment of Kaleidos. You will evaluate reactor behavior during normal, transient, and accident conditions, assess safety margins, and develop technically defensible analyses that inform reactor design decisions and regulatory evaluations.

This role combines reactor systems and thermal-hydraulic analysis with fuel performance, source term development, and radiological consequence assessments. You will own complex analytical work from methodology development and model execution through uncertainty evaluation, technical review, and documentation, working closely with nuclear design, thermal, mechanical, materials, testing, and regulatory teams.

The ideal candidate brings strong reactor safety fundamentals, hands-on modeling experience, and sound engineering judgment. You should be comfortable identifying dominant physical phenomena, evaluating analytical uncertainties, and translating complex results into practical design and safety decisions.

Responsibilities & Duties

• Lead deterministic reactor safety analyses covering anticipated operational occurrences, transients, and postulated accident scenarios.

• Develop and apply system-level thermal-hydraulic and transient models to evaluate reactor response, operating limits, and safety margins.

• Perform source term and radiological consequence analyses, including fuel performance, fission product release and transport, and dose evaluations.

• Evaluate uncertainties in reactor physics, power distributions, fuel behavior, and thermal-hydraulic models and their impact on safety conclusions.

• Apply sensitivity studies, bounding assumptions, and phenomena-ranking methods to develop technically defensible analysis approaches.

• Collaborate with nuclear, mechanical, thermal, materials, and controls teams to establish analysis inputs, evaluate design alternatives, and resolve safety-related technical challenges.

• Partner with testing and materials teams to identify data gaps, establish validation requirements, and correlate analytical predictions with experimental results.

• Develop and improve safety analysis methods, models, and tools, including verification and validation, configuration control, and uncertainty quantification.

• Prepare and technically review calculation packages, safety analysis reports, and regulatory documentation supporting reactor design and licensing activities.

• Work with regulatory and safety teams to establish safety requirements, support technical submissions, and resolve technical issues through closure.

Required Qualifications & Skills

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

• 5+ years of relevant experience in reactor safety analysis, thermal-hydraulics, nuclear systems modeling, or related engineering disciplines.

• Experience developing and applying reactor systems or safety analysis codes such as RELAP5-3D, TRACE, SAM, MELCOR, or equivalent tools.

• Strong understanding of reactor thermal-hydraulics, transient behavior, heat transfer, and deterministic safety analysis.

• Knowledge of reactor physics, fuel performance, fission product behavior, and radiological safety principles.

• Experience developing or evaluating source terms, radiological consequences, or other safety-related performance calculations.

• Experience evaluating modeling assumptions, uncertainty, sensitivity, and conservatism in engineering analyses.

• Demonstrated ability to independently own complex analytical projects and translate results into design requirements, safety conclusions, and technical documentation.

• Strong written and verbal communication skills, including experience preparing rigorous calculation packages, technical reports, or safety-related engineering documentation.

Preferred Qualifications & Skills

• Master's degree or Ph.D. in nuclear engineering, mechanical engineering, or a related technical discipline.

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

• Experience with TRISO fuel performance, irradiation behavior, fuel failure mechanisms, and fission product release and transport.

• Familiarity with source term, dose consequence, or fuel performance tools such as ORIGEN, MACCS, PARFUME, or BISON.

• Experience with reactor physics and neutronics tools such as MCNP, OpenMC, Serpent, or SCALE.

• Familiarity with probabilistic risk assessment (PRA), licensing basis event selection, and risk-informed safety methodologies.

• Experience with safety analysis code verification and validation, uncertainty quantification, and nuclear quality assurance practices.

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

• Experience supporting reactor testing, safety basis development, regulatory submissions, or technical engagement with regulators.

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.