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El Segundo, California, United States
Onsite
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
We are seeking a Reactor Systems Engineer to support the technical integration of a first-of-a-kind reactor. With no operating predecessor to copy and no mature supply chain, you will help ensure that design decisions across nuclear physics, thermal-hydraulics, controls, structures, materials, fuel, and licensing come together into a reactor that works safely and is delivered to customers on time.
This role is hands-on technically — you'll dig into thermal models, component specs, and subsystem designs — while also building the collaboration and communication skills needed to work across engineering disciplines. You'll work closely with senior systems engineers and discipline leads to learn how a fast-moving nuclear hardware program stays coherent. Writing is a core part of the job: specifications, decision memos, and system descriptions are how our team stays aligned.
Responsibilities & Duties
Support translation between reactor physics, thermal-hydraulics, materials, controls, mechanical design, manufacturing, and regulatory teams, helping surface assumptions and tensions that appear at team boundaries.
Help maintain libraries of P&IDs, sensors, and subsystem specifications to support alignment from design and analysis through reactor operations.
Assist in identifying cross-cutting risks early and help drive them toward resolution.
Work with safety analysis and licensing teams to help keep design decisions, safety cases, and regulatory submissions consistent.
Support development of design basis, safety classification, and technical specification documentation.
Support component and subsystem testing efforts, including help with test plans, data collection, and feeding results back into design.
Help maintain the technical baseline (requirements, configuration, change control, risk registers, and documentation) using lightweight processes scaled to a fast-moving startup.
Communicate clearly with engineers and leadership; contribute to technical documentation for regulators and customers under guidance from senior staff.
Required Qualifications & Skills
BS in nuclear, mechanical, aerospace, systems, or a related engineering discipline.
3–5 years of full-time professional engineering experience, with some exposure to systems engineering, integration, or cross-disciplinary technical work on complex hardware.
Ability to work effectively across multiple engineering disciplines.
Developing experience collaborating on cross-functional technical efforts.
Strong written and verbal communication skills, including the ability to produce clear technical documents.
Good organizational skills: able to track open items and follow through on assigned work.
Ability to apply first-principles thinking and contribute sound judgment amid ambiguity and incomplete data.
Exposure to highly regulated or high-consequence industries (e.g., nuclear, aerospace, defense, advanced energy, medical devices, semiconductor equipment) preferred.
Desired Qualifications & Skills
Experience in first-of-a-kind or early-stage hardware programs, even in a supporting capacity.
Familiarity with nuclear reactor design, safety, or regulatory frameworks (e.g., 10 CFR 50/52/53, NQA-1, GDCs, defense in depth) a plus but not required.
Startup or small-team experience, or strong interest in working in that kind of environment.
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.
Eligibility to work in the U.S. and ability to meet export control requirements.
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: recruiting@radiantnuclear.com.
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.
