Senior Test Engineer, Mechanical/Fluids

About Radiant 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. We are seeking a Senior Test Engineer to drive test operations for the development, qualification, and acceptance of our nuclear microreactor technology, with a primary focus on fluid and mechanical systems. This role offers a rare opportunity to bridge engineering, operations, and human factors in a highly technical and fast-paced environment. You will collaborate with a multidisciplinary team to translate complex hardware and software designs into clear, executable test operations, with encompassing test procedures that will efficiently and safely execute test, commissioning, and operational activities. As part of a small, passionate, and accomplished team of test engineers, you will help drive test operations to meet Radiant’s requirements in a fast-paced production environment. You will directly contribute to test operations by assisting with test planning and execution, risk identification and mitigation, hardware integration for test campaigns, post-test inspections, data review, and hardware performance analysis. This position goes beyond traditional systems engineering - you will also gain hands-on experience as a test conductor and test director, directly influencing the development of operational software, procedures, and test ground support equipment. Responsibilities & Duties: Test Strategy, Planning & Technical Ownership Own and lead the test strategy across development, qualification, and production acceptance phases. Define test objectives, plans, success criteria, instrumentation strategies, and data requirements for hardware and systems. Serve as the technical authority for test methods, measurement quality, and data integrity. Translate analytical predictions and design requirements into targeted test campaigns that validate assumptions and retire risk. Balance test coverage, technical risk, schedule, and hardware availability to enable rapid iteration while maintaining safety and rigor. Test Execution & Data Analysis Serve as Test Conductor/Test Director, ensuring procedures reflect real-world execution. Plan and execute fluid, mechanical, and thermal tests on Kaleidos hardware, from component level to full system development, qualification, and acceptance. Partner with design engineers to develop test methods and fixtures for fluid, mechanical, and electrical hardware. Integrate hardware into test setups: plumbing, instrumentation, data acquisition, and controls. Author and maintain test procedures meeting DOE/NRC-aligned documentation standards, with strict formatting, clarity, and usability. Identify risks and hazards (e.g., FMECA, keep-out zones) and define mitigations for pressurized and high-energy tests. Analyze test data, compare results to analytical predictions, and support root cause investigations. Specify and source test components and help qualify suppliers for fabrication. Drive continuous improvement in test processes and data quality. Support one-off test campaigns in a fast-moving environment where requirements are still being defined. Required Qualifications & Skills: 5+ years of full-time professional experience in engineering problem-solving, including system design, analysis, or testing. Bachelor’s degree from an accredited institution in mechanical, manufacturing, or other related engineering discipline. Ability to apply first principles thinking to solve problems and make decisions in uncertain or ambiguous situations. Background in highly regulated industries (e.g., nuclear, aerospace, aviation, maritime). Demonstrated ability to lead projects and work independently. Strong technical fundamentals in fluids and thermodynamics. Strong written and verbal communication skills. Flexible and adaptable mindset - self-driven with the ability to seek out requirements with minimal direction. Desired Qualifications & Skills: Prior experience working in a fast-paced test environments (e.g., rocket engine testing, turbopump testing, component level testing), with familiarity in safety protocols, and high-reliability operations, high pressure gases, safety engineering (FMECAs, Keep-out Zone). Experience in regulated or high-reliability environments (nuclear, aerospace, aviation, maritime). Experience overseeing proof and leak testing, guiding technicians, and activating test skids/stands. Experience with high pressure gases, pressure safety and stored energy. Experience designing, fabricating, or operating fluid systems; ability to read P&IDs and drawings. Knowledge of instrumentation: pressure transducers, flow meters, thermocouples, RTDs, accelerometers. Experience with thermal, material, and mechanical test fixtures. Experience with DAQ, PLCs, and analysis tools (e.g., Beckhoff, Python, MATLAB). Familiarity with ASME B31.3, B31.1, and BPVC Sections III/VIII. Experience with leak detection methods (helium, pressure decay). Proficiency with Ion, Epsilon3, NX CAD, Teamcenter. 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. 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: recruiting@radiantnuclear.com . 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.