Senior Test Engineer, Mechanical/Fluids

About RadiantRadiant 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.We are seeking a SeniorTest Engineer to drive mission-critical test operations for the development, qualification, and acceptance our groundbreaking nuclear microreactor technology. 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:Perform testing as a Test Conductor/Test Director to gain firsthand experience, ensuring procedures align with real-world execution.Partner with design engineers to develop innovative test methods for complex mechanisms and structures.Support testing and iterative improvements of fluid, electrical, and structural hardware of the Kaleidos reactor through development, qualification, and acceptance testing.Identify and develop appropriate suppliers for component sourcing and fabrication.Drive initiatives for continuous improvement in test processes and data delivery quality.Support one-off test campaigns in a fast paced, minimum-requirements environment to drive hardware risk reduction.Ensure compliance with DOE and NRC standards, maintaining strict formatting, clarity, and usability in procedural documentation.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 as an operator in 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 designing, fabricating, or operating fluid systems.Knowledge of instrumentation including pressure transducers, thermocouples, resistance temperature detectors, and accelerometers.Ability to read and interpret engineering standards, technical requirements, and engineering drawings (ASME 31.3, 31.1, and ASME Boiler Code Section III/VIII).Hands-on experience in developing technical procedures.Experience reviewing test data and hardware performance analysis.Prior operations experience with hands-on work designing and commissioning test ground support equipment (test fixtures, fluid systems, electrical systems).Proficiency with Ion, Epsilon3, NX CAD, Teamcenter.Experience with Beckhoff PLC Controllers.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 PerksStock: 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 BenefitsRadiant 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. If that’s you, contact us directly for immediate opportunities: View email address on click.appcast.io 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.Compensation Range: $133.5K - $184.8KLocationEl Segundo, CAEmployment TypeFull timeLocation TypeOn-siteDepartmentEngineeringProduction & ManufacturingCompensation$133.5K – $184.8K • Offers Equity