Senior Reactor Systems Engineer

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.

About the Role

We are seeking a Senior 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.

This position goes beyond traditional systems engineering. You will be hands-on technically, deep enough to challenge a thermal model or a pump spec, while serving as the connective tissue of the engineering organization. You will lead through credibility rather than title, aligning people who don't report to you and keeping a fast-moving program coherent. Writing is a core part of the job: specifications, decision memos, and system descriptions are how our team stays aligned.

Responsibilities & Duties

• Translate between reactor physics, thermal-hydraulics, materials, controls, mechanical design, manufacturing, and regulatory teams, surfacing assumptions and tensions that only appear at the boundaries.
• Own libraries of P&IDs, sensors, and subsystem specifications to ensure alignment from design and analysis through reactor operations.
• Identify cross-cutting risks early and drive them to resolution before they become safety or schedule problems.
• Work with safety analysis and licensing teams to keep design decisions, safety cases, and regulatory submissions consistent, and evaluate design changes for their safety and licensing implications.
• Support development of the design basis, safety classification, and technical specifications for regulatory engagement and operator training.
• Support the path from component and subsystem prototypes to integrated testing and commissioning, defining test plans and success criteria and feeding results back into the design.
• Maintain the technical baseline (requirements, configuration, change control, risk registers, and documentation) using lightweight processes scaled to a fast-moving startup.
• Communicate clearly to engineers, leadership, regulators, and customers.

Required Qualifications & Skills

• BS in nuclear, mechanical, aerospace, systems, or a related engineering discipline.
• 6+ years of full-time professional engineering experience, including meaningful time in systems engineering, integration, or technical leadership on complex hardware.
• Demonstrated ability to work effectively across multiple engineering disciplines.
• Track record of leading cross-functional technical efforts without direct authority.
• Strong written and verbal communication, including producing clear technical documents and presenting to varied audiences.
• Excellent organizational and administrative skills: you keep complicated work moving, track open items, and follow through.
• Ability to apply first-principles thinking and make sound decisions amid ambiguity, incomplete data, and changing requirements.
• Background in highly regulated or high-consequence industries (e.g., nuclear, aerospace, defense, advanced energy, medical devices, semiconductor equipment).

Desired Qualifications & Skills

• Experience on first-of-a-kind or early-stage hardware programs, ideally from prototype through qualification.
• Familiarity with nuclear reactor design, safety, and regulatory frameworks (e.g., 10 CFR 50/52/53, NQA-1, GDCs, defense in depth).
• Startup or small-team experience where you built the process rather than just followed it.

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.

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.