Test Engineer, Mechanical​/Fluids

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.We are seeking a Test 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:

2+ 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…