Principal Nuclear Engineer

About this role

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.

ABOUT THE ROLE

Radiant is seeking a Principal Nuclear Engineer to lead the interdisciplinary nuclear engineering work supporting Kaleidos. This role combines people leadership with hands-on technical ownership across core physics, neutron and radiation transport, shielding, activation and dose, thermal-hydraulics, safety analysis, instrumentation and controls, operations, and regulatory evaluations.

You will guide work from requirements and early design trades through analysis, verification and validation, testing, and regulatory documentation. The ideal candidate brings deep expertise in neutron transport and Monte Carlo methods, along with the judgment to translate complex analysis into practical reactor design and operational decisions.

RESPONSIBILITIES & DUTIES

- Lead an interdisciplinary team working across reactor physics, core performance, shielding, dose and activation, thermal-hydraulics, safety analysis, I&C, and operations.

- Establish technical priorities, project plans, resource needs, and clear ownership across the nuclear engineering organization.

- Serve as a technical authority for neutron and radiation transport and Monte Carlo simulation methods.

- Own nuclear engineering projects from requirements capture and design iteration through model development, analysis, technical review, and final documentation.

- Guide analyses of criticality, reactivity control, shutdown margin, power distribution, depletion, temperature feedback, radiation transport, dose, activation, and shielding performance.

- Translate analytical results into actionable requirements and design decisions affecting the core, shielding, control systems, instrumentation, fluid systems, and structures.

- Establish technically rigorous practices for model verification and validation, peer review, configuration control, uncertainty evaluation, and documentation.

- Collaborate with reactor systems, thermal, mechanical, electrical, test, operations, safety, and regulatory teams to resolve multidisciplinary design challenges.

- Translate nuclear standards and regulatory requirements into analysis plans, design criteria, calculation packages, and verification activities.

- Support reactor testing and startup by defining analysis needs, instrumentation requirements, acceptance criteria, and methods for comparing predicted and measured performance.

- Identify technical risks, drive complex problems through closure, and communicate decisions and recommendations to engineering teams and company leadership.

- Mentor engineers through technical guidance, actionable feedback, and regular coaching.

REQUIRED QUALIFICATIONS & SKILLS

- Bachelor’s degree in nuclear engineering or a related technical discipline from an accredited institution.

- 9+ years of relevant nuclear engineering experience across reactor design, analysis, testing, licensing, safety, or operations.

- Demonstrated experience leading complex nuclear engineering projects and multidisciplinary technical teams.

- Experience hiring, managing, mentoring, or technically leading nuclear engineers.

- Deep knowledge of neutron transport theory, Monte Carlo simulation methods, nuclear data, and statistical convergence.

- Professional experience developing and applying MCNP, OpenMC, or comparable neutron and radiation transport models.

- Strong understanding of criticality, reactivity coefficients, depletion, power distribution, shutdown margin, radiation transport, and uncertainty analysis.

- Experience translating analysis into reactor design decisions, technical requirements, safety conclusions, or regulatory documentation.

- Familiarity with model verification and validation, configuration control, peer review, and nuclear software quality practices.

- Strong written and verbal communication skills, including the ability to explain complex analyses, assumptions, uncertainties, and technical conclusions.

PREFERRED QUALIFICATIONS & SKILLS

- Master’s degree or Ph.D. in nuclear engineering or a related discipline.

- Experience with high-temperature gas-cooled reactors, microreactors, advanced reactors, or first-of-a-kind nuclear systems.

- Experience with SCALE, Serpent, Shift, Griffin, MOOSE-based applications, or similar analysis tools.

- Proficiency with Python or another language used for simulation automation and data post-processing.

- Experience with coupled neutronics and thermal-hydraulics or other multiphysics analyses.

- Familiarity with DOE authorization, NRC licensing, nuclear codes and standards, or regulatory safety analysis.

- Experience supporting reactor testing, commissioning, startup, or operational readiness.

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

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