Senior Principal Mechanical Engineer

Location: Assystem, Sunderland, England, United Kingdom

Assystem is a global leader committed to accelerating the energy transition with over 7,750 employees across 12 countries, leveraging 55+ years of experience in regulated sectors to deliver top‑notch engineering, project management, and digital solutions.

Join the Fusion and Modular Nuclear (FMN) Business Unit as a Senior Principal Mechanical Engineer and contribute to cutting‑edge projects that help make net‑zero power generation a reality.

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• Lead and support the development of designs for Personnel Airlocks, Main Equipment Access Hatch, Fuel Transfer Channel, Piping Penetrations, Electrical Penetrations, Specialist Nuclear Doors.
  
• Conduct DFMEA to identify and mitigate potential failure modes early.
  
• Perform HAZID to assess and document risks across the system.
  
• Complete and maintain Human Factors Checklists.
  
• Update and manage the project’s Risk Register.
  
• Design Package Production in line with requirements, ensuring alignment with specifications and standards.
  
• Manage interfaces between engineering teams, suppliers and stakeholders for cooling water systems integration.
  
• Prepare Technical Specifications for procurement, fabrication, and installation of cooling water system components.
  
• Collaborate with cross‑functional teams, including new and existing FTEs and secondees across engineering and project functions.
  

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• Multi‑Disciplinary Team Leadership – experience managing diverse engineering teams.
  
• Steam Cycle Modelling Oversight – defining modelling outcomes and accurate implementation.
  
• Project Budget & Lifecycle Planning – budgeting and planning for full design lifecycles.
  
• Cooling Water Equipment Expertise – designing and optimizing cooling water systems.
  
• Regulatory & Compliance Knowledge – proficiency in ONR, Environment Agency, and HSE regulations.
  
• Requirements Capture – gathering and defining technical requirements.
  
• Systems Engineering Awareness – integrated design principles.
  
• Subcontractor Management – overseeing and coordinating subcontractors.
  
• Chartered Engineer (CEng) – professional accreditation.
  
• Security Clearance Eligibility – capability to obtain SC clearance.
  
• Excellent communication skills, written and oral.
  
• Strong leadership skills.
  
• Focus on delivering quality output to time and budget.
  
• Act with integrity and instill it in others.
  
• Appreciation of wider technical issues beyond own discipline.
  
• Ability to work independently with initiative and self‑motivation.
  
• Confidence in multi‑party, multi‑national environment.
  
• Availability to travel to Assystem offices and customer sites within the UK.
  
• Capable of undertaking work packages supporting major UK & international nuclear clients.
  

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• Over 55 years in nuclear engineering.
  
• Ranked among the top 3 largest nuclear engineering companies.
  
• Attractive social benefits, including Employee Committee and holiday bonuses.
  
• Ongoing training with numerous career opportunities.
  
• 70% of managers promoted internally.
  
• Hybrid work: 1–2 days remote per week.
  

We are committed to equal treatment of candidates and promote all forms of diversity within our company. We believe that diverse backgrounds and perspectives are essential for innovative solutions.

Applicants will be required to meet security clearance residency criteria for a minimum SC level.