Senior Neutronics Engineer - Isotope Production

We are searching for a Senior Neutronics Engineer to join our engineering team, focusing on developing and executing neutronics analyses for an isotope production reactor.

About the role

The Senior Neutronics Engineer will perform analyses to support core design, fuel cycle, target performance, shielding, and sensitivity/uncertainty quantification across the reactor lifecycle and isotope production facility. This role requires close collaboration with thermal hydraulics, mechanical design, materials, isotope processing, operations, safety, and licensing teams. The engineer will translate system and production objectives into analysis requirements, develop computational models and methods, and produce technically sound, traceable, and defensible results.

Areas of analysis include criticality, depletion, isotope production, target optimization, shielding, activation, source term, and sensitivity/uncertainty analysis. The isotope division is a small but growing team, so the candidate must be capable of operating in a highly iterative and independent environment.

Responsibilities

• Perform reactor core design and optimization using Monte Carlo and, where appropriate, deterministic neutron transport methods.
• Develop and execute models using codes such as MCNP, Serpent, and SCALE.
• Perform core lifecycle and fuel management analyses, including depletion, burnup, reactivity evolution, power distributions, fuel utilization, and operating cycle optimization.
• Evaluate core physics parameters, including excess reactivity, control element worth, shutdown margin, reactivity coefficients, kinetics parameters, and criticality safety margins.
• Design and optimize irradiation targets to meet isotope yield, specific activity, radionuclidic purity, heat limits, and production schedule objectives.
• Perform depletion, activation, decay, and transmutation analyses for fuel, targets, structural materials, experimental hardware, and reactor components.
• Develop neutron and photon source terms for shielding, activation, decay heat, dose, and isotope processing evaluations.
• Perform shielding analyses using variance reduction techniques.
• Apply sensitivity and uncertainty methods using tools such as TSUNAMI and SAMPLER to quantify nuclear data, modeling, and manufacturing uncertainties.
• Establish appropriate biases and uncertainties to determine design margins.
• Develop, qualify, and maintain computational methods, analysis procedures, cross-section libraries, and reference models.
• Perform verification and validation using critical experiments, shielding benchmarks, depletion benchmarks, operating data, and applicable international benchmark programs.
• Support the design and evaluation of startup testing, physics measurements, irradiation experiments, and reactor surveillance activities.
• Couple neutronics results with thermal hydraulic, mechanical, isotope processing, and safety analyses.
• Perform design space exploration and optimization across competing objectives such as isotope production, fuel utilization, power peaking, irradiation damage, cycle length, and safety margin.
• Develop repeatable analysis workflows using modern software development practices, including configuration control, automated testing, code review, and reproducible data processing.
• Provide timely technical feedback to rapidly iterating multidisciplinary design teams.
• Document assumptions, methods, results, uncertainties, and limitations in clear technical reports.
• Support design reviews, safety evaluations, licensing activities, and responses to regulatory questions.

Requirements

• Bachelor’s, Master’s, or PhD in a technical field, such as nuclear engineering, with experience in reactor design and analysis (Master’s or PhD may be preferable).
• Fluency with Python.
• Proficiency with high-performance computing systems.
• Proficiency with MCNP, SERPENT, or SCALE (TRITON, KENO, SAMPLER, TSUNAMI, MAVRIC) is highly recommended.

Qualifications

• Hands-on experience with irradiation experiments at a research and test reactor is a plus.
• Experience with methods for light water/research and test reactor analysis.
• Highly skilled with Monte Carlo tools such as MCNP, Serpent, SCALE, or OpenMC.
• Experience with or eagerness to develop expertise in sensitivity and uncertainty analyses.
• Familiarity with shielding calculations and variance reduction methods.
• Interest in irradiation target design and isotope yield optimization.
• Able to develop and qualify computational methods using benchmarks, experiments, and independent verification.
• Comfortable working across neutronics, thermal hydraulics, materials, mechanical design, operations, safety, and licensing disciplines.
• Proficient in scientific programming and analysis automation, preferably using Python or a comparable language.
• Attentive to model configuration, software quality assurance, traceability, and reproducibility.
• Able to identify important assumptions and communicate the effects of uncertainty on engineering decisions.
• Excellent technical writer who communicates assumptions, methods, limitations, and conclusions clearly.
• Able to present technical content and results effectively to both specialist and multidisciplinary audiences.

Skills

• Passionate about applying nuclear technology to isotope production.
• Knowledgeable about reactor physics and radiation transport methods.
• Willing and able to learn quickly and take ownership of technically challenging work.
• Comfortable in a fast-paced, highly iterative development environment.
• Willing to propose creative, technically rigorous solutions rather than relying solely on established approaches.
• A startup person: You aren't driven by titles or hierarchy and prefer efficiency to excess process.
• Self-motivated with enthusiasm for the team and a sense of passion beyond clocking in and out.
• A team-player who works collaboratively without focusing on personal credit or blame.
• An excellent communicator, both technically and interpersonally.
• Creative in solving open-ended problems that may change day-by-day.
• Detail-oriented, with a focus on excellence, consistency, and quality.

Benefits

• Flexible time off.
• Equity and bonuses.
• Competitive pay.
• 401(k) with employer contribution.
• Health insurance with employer contribution.
• HSA and FSA options.
• Flexible work hours.
• Wellness credits.

Pay

Salary: $130,000–$220,000.

Schedule

• Remote employees are required to travel to headquarters (Santa Clara, CA) twice per quarter annually for team meetings, off-sites, and other company events.
• For the first two weeks of onboarding, employees must be in person at headquarters in Santa Clara, CA.

This position may involve access to information subject to U.S. export control laws. Only applicants who meet the definition of a U.S. person under applicable laws may be eligible.