Staff Reactor Systems Engineer

Radiant is an El Segundo, CA-based company building the world's only mass-produced, transportable nuclear microreactors. The U.S. grid is under growing strain, with power demand accelerating, driving higher utility costs, rising carbon emissions, and interconnection backlogs. Radiant has a solution, transportable, on-site power. Our first reactor, Kaleidos, is 1 megawatt: small enough to be factory-built, transported by land, sea, or air, and deployed wherever power is needed. 1 MW can power 1000 homes for five years. Ship it back and we refuel for a 20 year operating life. We made energy a product that can be used for critical infrastructure like military bases, data centers, hospitals, and remote sites, as well as the commercial main street businesses that keep America running. Founded in 2020, Radiant is under contract to deliver power to the U.S. Army, Navy and Air Force and has signed pre-order agreements with Equinix, with deployments beginning in 2028.

About the Role
We are seeking a Staff Reactor Systems Engineer to own the technical integration of a first-of-a-kind reactor. With no operating predecessor to copy and no mature supply chain, you will be the person who holds the whole machine together, making sure hundreds of design decisions across nuclear physics, thermal-hydraulics, controls, structures, materials, fuel, and licensing add up to a reactor that works safely and is delivered to customers on time.
You will be the technical authority for how the pieces of Kaleidos fit together: translating top-level product and safety requirements into subsystem requirements, owning interfaces, and making sure the integrated system performs, is safe, and can be built, tested, and deployed repeatably.
As a staff-level engineer, you will work across every engineering discipline, resolve the hardest cross-system tradeoffs, and set the systems engineering practices the team uses as Kaleidos moves from first-of-a-kind builds to scaled production. You will be instrumental in unlocking commercialization of the first mass-produced nuclear reactor.
Responsibilities & Duties

• Own the Kaleidos system architecture and serve as technical authority for integrated system performance, safety, and reliability.

• Define and manage system budgets (e.g., thermal, mass, power, reactivity, and volume) and allocate margins across subsystems.

• Own interface definitions and interface control documents between subsystems, including reactor core, primary loop, power conversion loop, shielding, controls, and structures.

• Maintain the technical baseline (requirements, configuration, change control, risk registers, and documentation) using lightweight processes scaled to a fast-moving startup.

• Identify cross-cutting risks early and drive them to resolution before they become safety or schedule problems.

• Define the verification and validation strategy and partner with Test Engineering to turn requirements into test plans, success criteria, and acceptance tests.

• Correlate analysis and test results against system requirements, and drive resolution of discrepancies.

• Support safety-basis and licensing or regulatory documentation as needed.

• Mentor engineers across the organization in systems thinking, requirements quality, and interface discipline.

• Communicate system status, risks, and tradeoffs clearly to engineering and program leadership.

Required Qualifications & Skills

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

• 10+ years of professional engineering experience, including meaningful time in systems engineering, integration, testing, engineering operations, or technical leadership on complex hardware.

• Demonstrated experience owning requirements and interfaces for a complex system from concept through build, test, and operation.

• Experience leading system-level trade studies and making sound decisions with incomplete information.

• Strong working knowledge across several relevant disciplines, such as thermal-fluids, mechanical, structural, power systems, or controls.

• Experience with verification and validation, and with hazard and risk analysis methods (e.g., FMEA, FTA).

• Demonstrated technical leadership across multidisciplinary teams without relying on formal authority.

• Strong written and verbal communication, including producing clear technical documents and presenting to varied audiences.

Desired Qualifications & Skills

• Knowledge of nuclear reactor design, reactor safety, or nuclear regulatory frameworks.

• Experience with high-temperature systems, thermodynamic power cycles, or power generation systems.

• Experience with configuration management and change control for hardware programs.

• Experience transitioning hardware from development builds to repeatable production.

• Startup or fast-paced hardware development experience.

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.

• Nuclear Engineering Certificate Program: 100% covered educational program with Penn State University, for eligible employees, to rapidly upscale into nuclear.

• 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 full-time 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.