Full-Time

Senior Principal Mechanical Engineer

ASSYSTEM

ASSYSTEM

5,001-10,000 employees

Engineering services for design, construction, commissioning

No salary listed

Derby, UK

Hybrid

Hybrid role: 1-2 days remote per week.

Category
Mechanical Engineering (2)
,
Requirements
  • FEED to Detailed Design Experience – Proven expertise in leading projects from Front-End Engineering Design through to execution.
  • Multi-Disciplinary Team Leadership – Skilled in managing and coordinating diverse engineering teams.
  • Steam Cycle Modelling Oversight – Ability to define modelling outcomes and ensure accurate implementation.
  • Project Budget & Lifecycle Planning – Experienced in budgeting and planning for full design lifycles.
  • Cooling Water Equipment Expertise – Strong track record in designing and optimizing cooling water systems.
  • Regulatory & Compliance Knowledge – Well-versed in ONR, Environment Agency, and HSE regulations.
  • Requirements Capture Experience – Skilled in gathering and defining technical requirements.
  • Systems Engineering Awareness – Strong understanding of integrated design principles.
  • Subcontractor Management – Experienced in overseeing and coordinating subcontractors.
  • Chartered Engineer (CEng) – Professional accreditation in a relevant discipline.
  • Security Clearance Eligibility – Capable of obtaining SC clearance for secure projects.
Responsibilities
  • Leadership of the Engineering Activities of the Cooling Water Team – Lead and mentor a team of engineers, driving technical excellence, innovation, and collaboration to deliver critical cooling water systems for the Small Modular Reactor program.
  • Development of Safety and Functional Requirements – Define and establish rigorous safety and performance criteria, ensuring compliance with industry regulations and best practices to support safe and reliable reactor operation.
  • Design Package Production in Line with Requirements – Oversee the creation of comprehensive design packages, ensuring alignment with project specifications, technical standards, and operational needs.
  • Management of Interfaces – Coordinate effectively between engineering teams, suppliers, and stakeholders to ensure seamless integration of cooling water systems with other reactor components.
  • Preparation of Technical Specifications – Develop clear, detailed technical specifications to guide procurement, fabrication, and installation of key cooling water system components.
  • Maintain Equipment Lists and Schedules – Track, update, and manage critical equipment inventories and project schedules to ensure timely delivery and smooth execution of engineering activities.
  • Management of Risk and Opportunity – Proactively identify potential risks and opportunities, implementing strategies to mitigate challenges and optimize system performance, cost-effectiveness, and overall project success.
Desired Qualifications
  • Ability to travel to Assystem offices and customer sites within the United Kingdom.
  • Experience working in a multi-national environment.

Assystem provides engineering services for complex projects, covering design, construction, supervision, commissioning, and operation, with a strong focus on the nuclear and energy sectors. Its approach combines multidisciplinary engineering teams and project-management capabilities to move projects from initial concept through to operation. The company differentiates itself through a long track record, strategic acquisitions (including Alphatem in 1995 and Mactech Energy Group in 2025) and an early public offering in 2013, which have expanded its capabilities and market reach in the energy and nuclear fields. Its goal is to be a leading, reliable partner for clients by delivering end-to-end engineering services and helping them meet safety, performance, and regulatory requirements across the project lifecycle.

Company Size

5,001-10,000

Company Stage

IPO

Headquarters

Paris, France

Founded

1966

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Simplify's Take

What believers are saying

  • Q1 2026 nuclear revenue grew 8% to 81% of €165.8M total with organic 2.2% rise.
  • Acquired L&T Infrastructure Engineering in 2024 boosting India energy market share.
  • Secured UK government frameworks supporting Rolls-Royce SMR's three-reactor contract.

What critics are saying

  • Expleo erodes non-nuclear margins with 15,000 employees and €1.1B scale since 2019 split.
  • Currency drops in pound, rupee, riyal cut international revenue 7.1% in Q1 2026.
  • Framatome and Orano integrate services internally, capturing Assystem's nuclear revenue stream.

What makes ASSYSTEM unique

  • Assystem ranks top 3 worldwide in nuclear engineering since 1966.
  • Provides end-to-end lifecycle services for EPR reactors in Flamanville, Taishan, and Olkiluoto.
  • Partners with Dassault SystΓ¨mes on PLM and Virtual Twins for SMR projects.

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Benefits

Health Insurance

Dental Insurance

Vision Insurance

Unlimited Paid Time Off

Flexible Work Hours

Remote Work Options

Paid Vacation

Paid Holidays

Hybrid Work Options

401(k) Retirement Plan

Wellness Program

Mental Health Support

Gym Membership

Professional Development Budget

Conference Attendance Budget

Stock Options

Company Equity

Phone/Internet Stipend

Home Office Stipend

Relocation Assistance

Childcare Support

Meal Benefits

Parental Leave

Family Planning Benefits

Fertility Treatment Support

Company News

Bdaily
Jan 30th, 2025
Assystem expands UK footprint with takeover

A global nuclear engineering firm has strengthened its UK presence with the acquisition of a specialist construction company. Paris-headquartered Assystem has… | North East | Construction | Engineering | International | Energy | Mergers & Acquisitions | Commercial Partnerships | Manufacturing & Construction |

Assystem
Jan 17th, 2024
Assystem acquires KEOPS Automation, engineering specialist in automated systems and data enhancement

Assystem, an international engineering, digital services and project management company, has acquired 100% of the shares of KEOPS Automation, a French company specializing in the integration of industrial operating platforms and the enhancement of their data (industrial OT and IT, automated systems, supervision systems, BI applied to manufacturing).

Global Construction Review
Jan 5th, 2024
France’s Assystem acquires India’s L&T Infrastructure Engineering - Global Construction Review

France-headquartered engineer and project manager Assystem has acquired India’s L&T Infrastructure Engineering, a subsidiary of the Larsen & Toubro group.

Tech.eu
Feb 11th, 2022
Germany’s SQS acquired by Assystem Technologies for over Β£280 million

German company Software Quality Systems (SQS), a provider digital quality assurance services,…