Mechanical Engineer – High-Temperature Stress Analysis

ZettaJoule is a nuclear technology startup developing High-Temperature Gas-cooled Reactors (HTGRs) for clean energy and industrial heat. The Mechanical Engineer will perform structural analysis and code qualification of high-temperature metallic reactor components, develop ASME-compliant design methodologies and calculation packages, and support pressure equipment design, materials evaluation, vendor oversight, and regulatory compliance.

Responsibilities:

• Perform elevated-temperature stress analysis of HTGR Class A metallic components — reactor vessel, core support structures, heat exchangers, and hot gas ducting — to demonstrate compliance with ASME Section III, Division 5 (Subsection HB, Subpart B)
• Evaluate primary and secondary stress limits, strain accumulation (ratcheting), creep-fatigue damage, and creep buckling using Division 5 elastic, simplified inelastic, viscoplastic, and full inelastic design-by-analysis methods
• Develop nonlinear finite element models (thermal-structural, plasticity, and creep) and the supporting methodologies, and document results in calculation packages and ASME Design Reports
• Work with Thermal Hydraulics and Systems Engineering to define design loadings, service levels, and thermal transients, and support development of the ASME Design Specifications for high-temperature components
• Apply material allowables, isochronous stress-strain curves, and creep-fatigue interaction data in collaboration with Materials Engineering, and identify data gaps that require additional testing or code cases
• Evaluate weldments, bolted and flanged joints, and structural discontinuities under time-dependent loading, including weld strength reduction factors and local strain concentrations
• Track and contribute to ASME Section III Division 5 code cases and technical positions, and support ZettaJoule’s engagement with code committees and regulators
• Manage analysis vendors and perform independent review and verification of calculations, including qualification of FEA software and models under a nuclear quality assurance program (10 CFR 50 Appendix B / NQA-1)
• Perform design and analysis of non-nuclear pressure vessels and heat exchangers, such as balance-of-plant, process heat, and helium/gas handling equipment, in accordance with ASME Section VIII, Division 1 (design by rule) and Division 2 (design by analysis, Part 5)
• Prepare and review Section VIII design specifications, calculations, and U-1/U-2 manufacturer’s data report inputs, and work with fabricators and the Authorized Inspector to resolve design and Code compliance questions
• Determine the appropriate Code of construction (Section III Division 5 or Section VIII) for each component based on function, safety classification, and regulatory requirements, and document the basis for that decision
• Coordinate with Systems Engineering, Design, Materials, and Licensing teams to ensure structural analyses support the plant design basis and regulatory strategy

Requirements:

• BS in Mechanical Engineering, Nuclear Engineering, or a related field required
• Minimum 8 years of experience in stress analysis of pressure-retaining components, including direct experience with elevated-temperature design (HTGR, sodium fast reactor, molten salt, or similar advanced reactor, or high-temperature power/process equipment)
• Demonstrated experience applying ASME Section III design-by-analysis rules, with working knowledge of Division 5 Subsection HB, Subpart B (HBB-T) for creep, creep-fatigue, and ratcheting evaluation
• Proficiency in nonlinear finite element analysis (ANSYS, Abaqus, or equivalent) including plasticity, creep, and coupled thermal-structural modeling
• Experience preparing formal calculation packages and stress reports under a nuclear quality assurance program
• U.S. citizenship or U.S. permanent resident status is required
• advanced degree preferred
• Direct participation in ASME Boiler & Pressure Vessel Code committees or working groups (Section III Division 5)
• Experience with unified viscoplastic constitutive models or Division 5 inelastic analysis methods for alloys such as 316H, Alloy 800H, or Alloy 617
• Professional Engineer (PE) license
• Experience with ASME Code certification, including Design Specification and Design Report review by an Authorized Inspection Agency
• Experience automating analysis and Code post-processing using Python or APDL scripting