Assystem is an international company with one mission: accelerate the energy transition around the world.

Every day, our 6,500 switchers located in 12 countries (Europe, Middle East, Pacific Asia & Africa) connect their six thousand billion neurons to tackle the task of the century: switching to low-carbon energy.

We are a collective committed to the actors who are making the energy switch. Sharing our knowledge, expertise and values allows us to innovate and think differently about the energy transition.

Drawing on more than 55 years’ experience in highly regulated sectors subject to strict security and safety requirements, we provide our customers with engineering and project management services, as well as digital services and solutions to optimize the performance of complex infrastructure projects throughout their life cycle. The Group is currently ranked second in the world for nuclear engineering.

To ensure a viable, efficient, and reliable energy future for all

Job Description

We are currently looking for a Senior Mechanical Engineer to join Assystem working within Defence infrastructure. The work is varied and can cover aspects such as the design of new equipment, as well as the justification of existing equipment across a range of systems, as such there is no generic set of duties for the position. 

Typical duties would include, but not limited to:

  • To provide technical support across a portfolio of consultancy projects.
  • To carry out engineering justification of existing equipment and new-build
  • To ensure equipment is safe and fit for purpose. To support Engineering Substantiation and Validation activities across equipment and infrastructure.
  • To develop engineering designs through a gated design process.
  • To compile and to author technical documentation that will meet the stringent needs of the customer.
  • To carry out engineering activities from home, from our office as well as from the customer’s site.
  • Adhere to Assystem quality system Work to budgets for assigned tasks If required, assist in proposal writing and other related bidding activities

My profile


BEng Mechanical Engineering (or other relevant degree)


  • Excellent communication skills, written and oral
  • Strong leadership skills
  • Focus on delivering quality on time and to budget
  • Appreciation of wider technical issues beyond own discipline
  • Able to lead small projects, including oversight of an engineering team
  • Self-leading and able to work autonomously

Skills, Qualifications and Experience

Essential Experience:

  • Process / piping system design experience covering the full design life cycle from requirements definition, optioneering, concept, detailed and design for manufacture. 
  • Requirements management and verification experience, preferably working within a Model Based Systems Engineering (MBSE) process.
  • Experience in design engineering substantiation in a highly regulated industry
  • Proven capability to deliver work in area of expertise
  • Ability to define budgets/work programmes for complete project lifecycles e.g. requirements capture, concept design, detailed design, manufacture, site installation.
  • Managing internal and external clients / stakeholders to meet expectations and requirements
  • Production of high quality design documentation

Desirable Experience:

  • Engineering support to manufacture and installation
  • Evaluating, delivering and managing complex engineering systems
  • Producing and checking technical documentation e.g. equipment specifications, system descriptions, P&IDs, plant arrangements, piping arrangements, BOMs/ equipment lists
  • Equipment selection e.g. rotating equipment (pumps, compressors etc.), valves / actuators, pressure vessels, heat exchangers
  • Producing and checking supporting calculations e.g.  pipe head loss, NPSH, pipe support calculations, heat loss / balance calculations, pipe stress analysis, surge analysis (water hammer),  compressible fluid design
  • Experience of Piping Solutions in a marine environment including galvanic corrosion and materials selection
  • Instrumentation specification and selection
  • Development of control philosophies
  • Nuclear industry experience
  • Experience of on-site assessments and surveys
  • Experience of current EU regulations e.g. PED, CDM, Machinery Directive
  • Draughting software – AutoCad, Inventor
  • MathCad software
  • Pipestress software e.g. Caesar II
  • 1D CFD software e.g. Fluid flow, Flowmaster
  • CEng or working towards CEng
  • Support junior engineers in their development

Security Clearance:

Due to the nature of work to be undertaken applicants will be required to meet certain residency criteria in order to attain a minimum level of UK security clearance if not already security cleared to a minimum SC level. 


We are committed to equal treatment of candidates and promote, as well as foster all forms of diversity within our company. We believe that bringing together people with different backgrounds and perspectives is essential for creating innovative and impactful solutions. Skills, talent, and our people’s ability to dare are the only things that matter !. Bring your unique contributions and help us shape the future.

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