Principal Software Engineer - Simulation

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 failsafe microreactor that can be transported anywhere power is needed and run for up to five years without the need to refuel. 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 utilizes modern software engineering to rapidly achieve safe, factory-built microreactors that leverage existing, well-qualified materials. Founded in 2020, Radiant is on track to test its first reactor next year at the Idaho National Laboratory, with initial customer deliveries beginning in 2028.

About the Role

Radiant is seeking an experienced Lead Software Engineer for Simulation to mentor and lead the engineering team responsible for reactor physics modeling, thermal-hydraulics simulations, and Digital Twin development. In this role, you will serve as the technical lead for a high-performing team while maintaining technical depth, ensuring our simulation infrastructure enables Radiant to design, test, and validate reactor systems—accelerating our path to commercialization.

Responsibilities and Duties

• Lead technical architecture and implementation for simulation systems across thermal, hydraulic, and nuclear reactor physics models.


• Mentor and provide technical guidance to simulation engineers developing reactor and subsystem physics models.


• Design and scale software infrastructure to support Digital Twin simulation, visualization, and data processing capabilities.


• Define and own the technical roadmap for thermal and safety analysis simulation. Develop and execute strategies for model tuning as models and frameworks evolve.


• Drive technical excellence by establishing best practices for simulation software development, code quality, and testing standards.


• Collaborate cross-functionally with Hardware, Nuclear, and Electrical engineering teams to accelerate software-in-the-loop and hardware-in-the-loop testing capabilities.


• Own delivery of mission-critical internal simulation products while ensuring sustainable development practices and technical debt management.


• Contribute to team growth through technical mentorship and promoting a high-performance engineering culture.

Required Qualifications

• 8+ years of professional software engineering experience with significant depth in simulation, scientific computing, or physics-based modeling.


• Deep technical expertise in programming languages such as Python, Rust, C#, or C/C++, with demonstrated ability to drive architectural decisions.


• Experience providing technical leadership and mentorship to engineering teams.


• Strong background in simulation tools, physics-based modeling, numerical methods, or computational science with proven ability to guide technical strategy.


• Expertise with numerical solvers, visualization frameworks, and automated testing approaches for scientific software.


• Strong foundation in software engineering best practices, including version control, code review, and CI/CD pipelines.


• Proven ability to balance hands-on technical contributions with technical leadership and mentorship.


• Bachelor's degree in physics, mechanical engineering, computer science, or a similar field, or equivalent experience

Preferred Qualifications

• Advanced degree (Master's or Ph.D.) in physics, mechanical engineering, computer science, or a similar field.


• Experience as a technical lead on simulation or computational modeling, parallel computing, or high-performance computing projects.


• Background with modern simulation frameworks, finite element analysis, or computational fluid dynamics tools.


• Track record of successful cross-functional collaboration with Hardware, Nuclear, and Electrical engineering teams.


• Strong communication skills with the ability to translate technical complexity for diverse audiences.


• Experience with Machine Learning, Deep Learning, AI, or other probabilistic modeling techniques.

Work Environment

• Must work 100% onsite at El Segundo HQ.


• Must be willing to work extended hours and weekends as necessary to accomplish our mission.

Total Compensation and Benefits

Radiant's new hire compensation package includes base salary, substantial equity grants, and comprehensive benefits. Total compensation and level are determined through a holistic evaluation of your interview performance, experience, education, and qualifications.

Benefits and Perks for Eligible Employees:

• Stock: Substantial incentive stock plan for all full-time employees.


• Medical: 100% premium coverage for base Silver level plan for employee + 50% premium coverage for dependents. Platinum plans available.


• One Medical: Sponsored memberships for eligible employees and their dependents.


• Vision: 100% premium coverage for top tier plan + 50% for dependents.


• Dental: 100% premium coverage for top tier plan (including orthodontia) + 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.

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.

Unfortunately, we are unable to provide visa sponsorship at this time.

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.