Full-Time

Principal Mechanical Engineer

ASSYSTEM

ASSYSTEM

5,001-10,000 employees

Engineering services for design, construction, commissioning

No salary listed

Warrington, UK

Hybrid

Hybrid work: 1-2 days remote per week.

UK Top Secret Clearance Required

Category
Mechanical Engineering

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Requirements
  • Strong previous experience in highly regulated industries like nuclear, thermal power generation, or oil and gas.
  • Expertise in thermal power systems and equipment, from steam turbines to pumps, with a keen understanding of nuclear power plant operations.
  • Proficiency in optioneering and conducting studies to evaluate viable options, backed by a track record of crafting compelling ALARP and BAT arguments.
  • Experience in mentoring and developing junior staff, along with a proven history of leadership in managing small teams.
  • Exceptional communication skills for seamless interaction with internal and external stakeholders.
  • Familiarity with ASME, European, and UK codes and standards, coupled with a deep understanding of Product Safety Legislation.
  • Appreciation for requirements management and systems engineering principles.
  • Results-oriented with the ability to work both independently and collaboratively, coupled with strong organizational skills.
  • British National with eligibility for obtaining and maintaining full UK security clearance.
  • UK security clearance criteria and eligibility for full security clearance
Responsibilities
  • Spearheading the delivery of cutting-edge power station systems.
  • Taking charge of optioneering studies to pinpoint the ultimate solution that perfectly aligns with client objectives.
  • Leading a dynamic team in crafting and refining essential design documents, from Process Flow Diagrams to Equipment Datasheets, ensuring precision and excellence at every step.
  • Directing the development of Design Description Documents and Requirement Specifications, driving innovation and efficiency in every design aspect.
  • Seamlessly integrating developed systems into the broader plant infrastructure for optimal performance and functionality.
  • Serving as the technical guru for designated scopes, guaranteeing top-notch expertise and oversight.
  • Chairing exhilarating Design Reviews and leading HAZID/HAZOP studies with diverse, multidisciplinary teams to ensure safety and excellence in every project facet.
  • Enforcing strict adherence to company statutory H&S Policies and regulations, while ensuring unwavering compliance with project and Quality Management System standards.

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 Jobs

Simplify's Take

What believers are saying

  • H1 2026 revenue reached €328.5 million, with 2.5% organic growth.
  • Assystem won Rolls-Royce SMR momentum, plus GBE-N, MoD, and FRAM roles.
  • Cotentin's 120 hires support Aval du Futur, targeting 10,000 jobs by 2028.

What critics are saying

  • International revenue fell 7.1% in Q1 2026, hurt by India, Saudi Arabia, and currencies.
  • Eighty-one percent nuclear concentration exposes Assystem to French and UK program slippage.
  • Wylfa SMR or Aval du Futur delays would damage backlog, hiring, and margins.

What makes ASSYSTEM unique

  • Nuclear made 81% of H1 2026 revenue, anchoring Assystem's specialization.
  • June 24, 2026 CPS2 Tier 1 status embedded Assystem in UK nuclear procurement.
  • Mactech's 2025 acquisition and 2026 Cotentin hiring deepened nuclear delivery capacity.

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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

Yahoo Finance
Jul 23rd, 2026
Assystem's H1 revenue rises 2.5% organically to $371.2M on nuclear growth

Assystem reported consolidated revenue of €328.5 million for the first half of 2026, representing organic growth of 2.5% despite a 1.9% negative currency effect. The French engineering group's nuclear activities drove performance with 8.0% organic growth, accounting for 81% of total revenue. Revenue in France rose 4.2% organically to €201.1 million, led by strong momentum in nuclear new-builds and fuel cycle activities. International operations generated €127.4 million, remaining stable organically despite currency headwinds from the pound sterling, Indian rupee, and Saudi riyal. The UK showed robust growth in civil nuclear engineering and defence. However, business volumes declined in the Middle East, Central Asia region and India due to project endings and slower contract phasing. Assystem confirmed its full-year 2026 targets.

Yahoo Finance
Apr 23rd, 2026
Assystem posts $187.4M Q1 revenue with 2.2% organic growth driven by nuclear sector

Assystem, an international engineering group, reported first-quarter 2026 consolidated revenue of €165.8 million, representing 2.2% organic growth driven by strong nuclear sector performance of 8.0%. Nuclear activities accounted for 81% of total revenue, up from 76% in the prior year. French operations grew 4.4% to €102.6 million, driven by momentum in fuel cycle activities, new-builds and digitalisation. International revenue declined 7.1% to €63.2 million, primarily due to a 6.0% negative currency effect from the pound sterling, Indian rupee and Saudi riyal. The UK showed robust growth in civil nuclear engineering and defence. Assystem secured key positions on government frameworks and its client Rolls-Royce SMR signed a contract with Great British Energy for three small modular reactors.

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.