Thermohydraulics Safety Analysis Engineer

Deep Fission is a nuclear technology company pioneering the development of a revolutionary deep borehole pressurized water reactor. We recently completed a private placement financing and Alternative Public Offering and are now operating as a public company while maintaining our startup agility and innovation focus. With strategic partnerships in place, strong private and public investment, and active engagement with the U.S. Nuclear Regulatory Commission (NRC), we are executing our next phase of growth as we advance our groundbreaking nuclear technology toward commercial deployment. 

Job Summary

We are looking for a Thermal-Hydraulic Engineer with 2–5 years of experience to join our T/H Group as a hands-on technical contributor. You will own the development and maintenance of reactor system models, execute steady-state and transient analyses, support code validation and benchmarking activities, and contribute directly to the documentation and analysis packages that underpin our NRC licensing program.

This is not a support role. You will be expected to produce analysis work independently, coordinate across engineering disciplines, and grow your scope as the program matures. You will work alongside experienced nuclear safety and licensing engineers who will provide technical guidance, but the expectation is that you bring enough foundational depth to execute real work from day one.

Key Responsibilities

• Thermal-Hydraulic Analysis
  • Develop, run, and interpret steady-state and transient system-level T/H simulations using codes such as RELAP5, RELAP5-3D, TRACE, RETRAN, or MOOSE.
  • Perform design-basis analyses including non-LOCA transients, loss-of-flow, station blackout (SBO), and reactivity-initiated accidents (RIA), with mentorship available for less familiar event types.
  • Build and maintain reactor system nodalization models; perform steady-state benchmarking against design data and code-to-code comparisons.
  • Conduct sensitivity studies and post-process simulation results using Python, MATLAB, or equivalent scripting tools.
• Code Validation & Quality Assurance
  • Support V&V activities for T/H system codes in accordance with applicable regulatory requirements and NQA-1 quality assurance standards.
  • Develop and maintain analysis procedures, calculation packages, and QA documentation consistent with licensing-grade standards.
  • Assist in the development and application of Deep Fission’s safety analysis methodology, including licensing basis event identification and acceptance criteria.
• Licensing & Documentation
  • Prepare clear, well-organized technical analysis reports and calculation packages suitable for internal design reviews and NRC licensing submittals.
  • Support preparation of safety analysis report (SAR) sections and responses to NRC Requests for Additional Information (RAIs) under the direction of senior staff.
  • Contribute to licensing basis documentation as the design and safety basis evolves through the regulatory process.
• Coordination & Collaboration
  • Coordinate with reactor physics, systems engineering, mechanical design, and licensing teams to maintain technical alignment across the design and safety basis.
  • Participate in design reviews, safety review committee activities, and in-person technical workshops.
  • Support nuclear safety culture and contribute to technical discussions in both internal and regulatory forums as your experience and confidence grow.

Required Skills & Experience

• 2–5 years of professional or research experience in nuclear or mechanical engineering, applying thermal-hydraulic analysis methods in a nuclear, research, or closely related technical environment.
• Bachelor’s degree in Nuclear Engineering, Mechanical Engineering, or a closely related technical field.
• Demonstrated hands-on experience — professional or research — with at least one T/H system code applicable to light water reactor analysis: RELAP5, RELAP5-3D, TRACE, RETRAN, or MOOSE.
• Working knowledge of reactor system nodalization, steady-state benchmarking, and transient simulation for LWR applications.
• Familiarity with NRC regulatory requirements for nuclear safety analysis (e.g., 10 CFR Part 50); direct professional experience is preferred but academic exposure is acceptable.
• Working awareness of nuclear quality assurance principles (e.g., 10 CFR 50 Appendix B, NQA-1) as applied to engineering calculations and technical documentation.
• Ability to produce clear, well-organized technical documentation; some experience contributing to licensing-grade calculations or NRC submittals is a plus.
• Comfortable working independently and across disciplines in a virtual and hybrid team environment.
• Must be a U.S. person eligible to meet DOE Export Control requirements under 10 CFR 810.
• Ability to travel up to 20%

Desired Skills & Experience

• Master’s degree or Ph.D. in Nuclear Engineering or Mechanical Engineering.
• Experience contributing to a safety analysis or T/H methodology program at a reactor vendor, national laboratory, utility, or nuclear engineering consultancy.
• Exposure to NRC licensing submittals — topical reports, RAI responses, or ACRS interactions — in any capacity.
• Familiarity with uncertainty quantification methods (e.g., CSAU, ASTRUM, or statistical analysis approaches) for best-estimate T/H analyses.
• Familiarity with advanced reactor designs, SMRs, or novel reactor concepts (e.g., underground siting, microreactors, Generation IV designs); exposure to 10 CFR Part 53 or emerging 10 CFR Part 57 licensing pathways is a meaningful plus.
• Proficiency with Python or MATLAB for scripting, post-processing, and model automation.
• Exposure to AI-enabled engineering platforms or modern simulation toolchains.

Key Competencies

• Technical Depth – Working understanding of thermal-hydraulic phenomena in light water reactor systems, including two-phase flow, critical heat flux, natural circulation, and reactor transient behavior; willingness to develop deeper expertise in safety analysis methods.
• Licensing Acumen – Ability to learn and apply regulatory requirements to engineering analysis and documentation; prior exposure to NRC-regulated environments is preferred.
• Curiosity & Initiative – Eagerness to understand the broader design and licensing context, ask good questions, and grow into expanded responsibility over time as the program matures.
• Adaptability/Resilience – Ability to thrive in an early-stage, resource-constrained environment, adjusting priorities and scope as the project evolves.
• Organizational – Experience functioning within structured engineering programs with multiple engineering disciplines, subcontractors, and regulatory stakeholders.
• Communication – Demonstrated ability to clearly convey complex technical concepts in written reports and verbal presentations to both internal teams and external regulators.

Our Commitment: 

Deep Fission is an equal opportunity employer committed to building a diverse and inclusive workplace. We welcome applicants from all backgrounds who share our passion for advancing clean nuclear energy and creating a sustainable future. We do not discriminate on the basis of race, color, creed, religion, ancestry, age, sex, marital status, national origin, disability, veteran status, or any other characteristic protected by applicable law.