Principal Engineer, Safety Methods This role supports the development, enhancement, and deployment of plant-scale thermal-hydraulic analysis methods and models for the Natrium reactor. Reporting to the Manager, Plant Thermal Hydraulics Methods, the principal engineer supports the creation, improvement and qualification of advanced system-level modeling approaches that enable accurate, robust prediction of plant behavior across operational and transient scenarios. The position requires expertise in system-level thermal-hydraulics, thermal-fluids behavior, and the formulation of computational methods and closure models that represent complex reactor phenomena. Responsibilities • Develop plant-scale thermal-hydraulic analysis methods, including modeling strategies, numerical approaches, and closure models. • Perform steady-state and transient system-level analyses to characterize model behavior, assess method performance, and define method fidelity requirements. • Develop and maintain method qualification plans, including numerical verification, applicability envelopes, and performance characterization. • Formulate and integrate closure models and correlations (e.g., heat transfer, pressure drop, mixing, component-level physics) into existing analysis frameworks. • Identify modeling gaps and drive method enhancement priorities using Phenomena Identification and Ranking Table (PIRT), sensitivity studies, and multi-physics needs. • Develop automated workflows and tools for model setup, execution, post-processing, and repeatable method application. • Collaborate with test engineering to define data needs that inform method development (not for validation purposes, but to guide model formulation and closure development). • Document modeling methodologies, assumptions, method applicability, and numerical performance for design processes and licensing-support activities. • Work across disciplines to ensure thermal-hydraulic methods integrate effectively with plant design, safety analysis, and coupled simulation workflows. • Apply and improve TerraPower's SQA and NQA-1 modeling practices, ensuring traceability, configuration control, and reproducibility of methods. • Mentor junior engineers in numerical method development, system modeling, and modern computational analysis practices. Key Qualifications and Skills • Degree in Mechanical, Nuclear, Chemical Engineering, or similar field, with 12+ years of experience in system-level thermal-hydraulic modeling and method development for nuclear or complex energy systems. • Demonstrated experience in developing or improving analysis methods, including numerical scheme development, closure model formulation, and stability/accuracy optimization strategies. • Experience performing system-level thermal-hydraulic analyses using tools such as RELAP5-3D, GOTHIC, SAS, or equivalent, with the ability to extend or tailor modeling approaches within these frameworks. • Strong foundation in thermal-fluids and reactor system behavior, including complex thermal-hydraulic phenomena relevant to advanced reactor designs. • Experience in sensitivity analyses and model gap identification that support method development priorities. • Familiarity with scientific programming and workflow automation (e.g., Python, MATLAB). • Familiarity with NQA-1 quality assurance for modeling workflows, including documented methodologies, configuration control, and model traceability. • Strong analytical thinking, clear technical communication, and the ability to support multiple method development efforts in parallel. This position is subject to qualification requirements in accordance with ANSI/ANS 3.1. Candidates must meet the minimum education and experience criteria applicable to the role, including relevant nuclear industry experience where required. Verification of data will be part of the hiring process. Job Functions: Job Functions are physical actions and/or working conditions associated with the position. These functions may also constitute essential functions for the job which the employee must be able to fulfill, with or without accommodation. Information provided below is to help describe the job so that the applicant has a reasonable understanding of the job duties/expectations. An applicant's ability to perform and/or tolerate these actions and conditions will be discussed and workplace accommodations may be made on a case-by-case basis following an individualized assessment of the applicant and other considerations, including but not limited to any governing safety standards. • Motor Abilities: Sitting for extended periods, bending/stooping, grasping/gripping, fine motor control (hands) • Physical exertion and/or requirements: Minimal, with ability to safely lift up to 25 pounds. • Repetitive work: Prolonged • Special Senses: Visual and audio focused work • Work Conditions: Stairs, typing/keyboard, standard and/or sitting working environment of >8 hours/day • Travel required 0-10% TerraPower's technology is controlled for export by various agencies of the U.S. Government. TerraPower must evaluate applicants who are foreign nationals (other than asylees, refugees, or lawful permanent residents) in accordance with U.S. Government export control requirements. To facilitate TerraPower's export control reviews, you will be asked as part of the application process to identify whether you are a U.S. Citizen or national, asylee, refugee, or lawful permanent resident of the United States. Government export authorization approval times vary. Based on the business needs for a particular position, TerraPower may not consider a foreign national from a country if it is impracticable to obtain timely Government export approval. Job details Salary Range: $168,316 - $252,475 Any salary offered within the posted salary band is based on market data and commensurate with the selected candidate's qualifications and experience. This range is specific to Washington State. Benefits: • Competitive Compensation • Salary, eligible to participate in discretionary short-term incentive payments • Comprehensive Medical and Wellness Benefits • Medical • Vision • Dental • Life and Disability • Gender Affirmation Benefits • Parental Leave • 401k Plan • Generous Paid Time Off (PTO) • 21 days of annually accrued PTO • Generous Holiday Schedule • 10 paid holidays • Relocation Assistance • Professional and Educational Support Opportunities TerraPower Career and Benefits information: https://www.terrapower.com/contact-us/careers/