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ASSYSTEM

Engineering services for design, construction, commissioning

Thermohydraulics Engineer - SOFIA

Full-Time
€36k - €50k/yr
Mid
Bachelor's
Courbevoie, France
In Person
Mechanical EngineeringThermal & Fluids Engineering

About the job

Requirements
  • A diploma from an engineering school or a Bac+5 degree in nuclear engineering, energy engineering, thermohydraulics, numerical simulation, or an equivalent discipline.
  • Confirmed experience on projects involving pressurized water reactors (REP/EPR), nuclear simulators, or scientific computation codes.
  • Knowledge of one or more of the following environments: SOFIA, CHORYS, ORCHID, or CATHARE.
  • Proficiency in validation, testing, anomaly handling, and analysis of simulation results.
  • Strong nuclear-safety culture and quality-assurance knowledge.
  • Strong analytical, synthesis, technical-writing, and collaboration skills when working with technical experts.
Responsibilities
  • Act as the reference for EPR FA3 operation and simulator exploitation, development, and validation.
  • Analyze EPR FA3 configuration changes and assess their impacts on the simulator.
  • Translate configuration changes into simulator-model and parameter modifications.
  • Define, prepare, and execute operating scenarios representing normal, incident, and accident situations.
  • Verify and validate simulated behavior against technical and operational requirements.
  • Participate in analyzing and resolving anomalies detected during tests or validation campaigns.
  • Contribute to functional testing, qualification, and validation of modifications.
  • Support users and participate in simulator training activities.
  • Develop, adapt, and maintain thermohydraulic simulation models.
  • Analyze REP/EPR transients and interpret the results from a physical perspective.
  • Participate in scientific software development, debugging, and model-improvement activities.
  • Design and execute functional, validation, and regression-testing campaigns.
  • Identify, analyze, and correct behavioral discrepancies between different configurations.
  • Maintain traceability of completed developments, corrections, and validations.
  • Produce associated technical deliverables and contribute project lessons learned.

About the company

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

  • H1 2026 revenue grew 2.5% organically; nuclear grew 8.0%.
  • France delivered 4.2% organic growth on new-builds, fuel cycle, and digitalisation.
  • UK momentum accelerated after April 2026 SMR, CPS2, and MoD framework wins.

What critics are saying

  • Nuclear concentration leaves Assystem exposed if French EPR2 schedules slip beyond 2027.
  • H1 2026 international revenue fell from currency hits and project endings in India.
  • Rolls-Royce SMR still needs FID, regulatory clearance, and site decisions before revenue scales.

What makes ASSYSTEM unique

  • Assystem derived 81% of H1 2026 revenue from nuclear engineering.
  • April 2026 UK wins placed Assystem on CPS2 and MoD delivery frameworks.
  • January 2025 Mactech Energy Group deepened Assystem's UK nuclear construction capabilities.

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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

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.