Nuclear Engineer, Core Physics

Radiant; El Segundo, Northern (CA, KY); Hybrid; USD 180,000 - 250,000; Full time

Benefits offered by this job

Stock options

Comprehensive medical plan

One Medical membership

Vision plan

Dental plan

Flexible PTO (on-site and remote)

Job summary

Radiant is seeking a Nuclear Engineer, Core Physics for the 2026 demonstration in El Segundo, CA. The role centers on designing and implementing nuclear-specific testing operations and ensuring safety and objective alignment across test campaigns.

You will work with nuclear engineers to define success criteria and collaborate with systems engineers to implement procedures, training, and control room interfaces. This onsite position demands deep reactor-operations knowledge.

Qualifications

• Bachelor’s degree in nuclear engineering or equivalent.
• 2+ years of reactor operations experience.
• Experience with radiation transport methods (MCNP/OpenMC/Serpent).
• Knowledge of thermal-hydraulic fundamentals.

Responsibilities

• Collect testing requirements, objectives, and success criteria from nuclear engineers.
• Develop procedures that satisfy test requirements within Kaleidos’ operational bounds.
• Perform reactor physics calculations (neutronic and transient analyses) to verify testing.
• Document procedures and support operator training and control room GUI development.

Skills

Reactor operations

Radiation transport methods

Thermal hydraulics

Education

Bachelor's degree in nuclear engineering or equivalent

Tools

MCNP/OpenMC/Serpent

Job description

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 a seeking a Nuclear Engineer, Core Physics responsible for designing and implementing nuclear-specific testing operations at our 2026 demonstration. You will be responsible for the design of a large portion of the test campaign, which includes providing analysis to verify that the proposed testing is both safe and meets the test’s objectives. This position will work closely with nuclear engineers to establish test success criteria and systems / operations engineers to implement written procedures.

Responsibilities & Duties:

• Collect testing requirements, objectives, and success criteria from nuclear engineers.

• Develop procedures that satisfy test requirements within the operational bounds of Kaleidos.

• Perform various reactor physics calculations (neutronic and transient analyses) to verify proposed testing sequence addresses all requirements.

• Document testing procedures and support operator training and control room GUI development.

Required Qualifications & Skills:

• Bachelor’s degree in nuclear engineering or equivalent degree from an accredited institution.

• 2+ years of experience with reactor operations.

• Experience with radiation transport methods, including with codes such as MCNP/OpenMC/Serpent.

• Knowledge of thermal hydraulic fundamentals.

Desired Qualifications & Skills:

• 4+ years of experience with reactor operations.

• Direct experience as a reactor operator of an existing nuclear reactor.

• Hands-on experience in developing technical procedures, human factors engineering, or operational interface design.

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.

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.

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.