Senior Simulation 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.

Radiant is seeking a Simulation Engineer to design tests, collect data, and validate our in-house reactor simulation capability. You will collect evidence showing where our models can be trusted, quantify the approximations, and demonstrate where a different model is needed. Your work will directly support the regulatory approval process and improve our ability to optimize next-generation reactor performance.

You will join the simulation software engineering team and serve as its link to the real world. Working closely with our materials lab and materials team, you will design experiments, build digital representations of them in our simulation environment, and use the results to anchor the models to physical reality. This is a highly autonomous individual contributor role for someone who is hands-on, rigorous, and comfortable making technical judgment calls in an early-stage environment.

• Build and maintain a verification program for our simulation tools, including manufactured solutions and automated regression testing.

• Compare simulation results against commercial and proprietary software on shared problems, and investigate and document the cause of any differences.

• Validate the models against data from existing reactors, Radiant’s reactors, and experiments you design.

• Partner with the materials lab and materials team to design experiments that, taken together, comprehensively cover the scenarios the simulation must predict.

• Create digital representations of those experiments in the simulation environment to anchor the model to reality.

• Run convergence studies and use them to assess the correctness and validity of results.

• Quantify and propagate uncertainty from measurement, material properties, numerical error, and model form, and report results with defensible confidence bounds.

• Recognize when the simulation is missing physics or components needed to represent reality, and recommend which models to add.

• When simulation and measurements disagree, determine whether the model needs refinement or is the wrong model for the scenario, and guide developers on the fix.

• Produce V&V documentation that meets rigorous quality assurance and regulatory standards.

• Bachelor’s degree in mechanical, nuclear, aerospace, or materials engineering, applied mathematics, or a related field. An advanced degree is preferred.

• Hands-on V&V experience, through industry work or graduate research, including manufactured solutions, code-to-code comparison, convergence analysis, and validation against experimental data.

• Working knowledge of materials behavior and testing, enough to design meaningful experiments with a materials team and interpret their data.

• Experience with design of experiments, including planning test matrices that efficiently cover a broad range of conditions.

• Competence in data science and uncertainty quantification (statistics, sensitivity analysis, calibration).

• Software competence: comfortable reading and modifying simulation code, scripting analyses, and working with version control and CI.

• Experience with MATLAB and/or Python.

• Strong communicator who can present findings to developers, program leadership, and external reviewers, including when a model is not ready to be trusted.

• Experience with C++.

• Experience with commercial simulation tools such as STAR-CCM+ and Abaqus.

• Experience with CAD, particularly NX.

• Experience in nuclear or other safety-critical, regulated domains.

• Familiarity with NQA-1, ASME V&V standards, or similar quality frameworks.

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

• Must work 100% onsite at El Segundo headquarters.

• 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.