Senior Multiphysics Modeler
Commonwealth Fusion Systems
Devens, MA, USA
Posted on Nov 13, 2025
About Commonwealth Fusion Systems:
Commonwealth Fusion Systems is on a mission to deliver the urgent transition to fusion energy.
Combining decades of research, top talent, and new technologies, we’re designing and building commercially viable fusion power plants. And working with policymakers and suppliers to build the energy industry of the future.
We’re in the best position to make it happen. Since 2018, we’ve raised nearly $3 billion in capital, making us the largest and leading private fusion company in the world.
Now we’re looking for more thinkers, doers, builders, and makers to join us. People who’ll bring new perspectives, solve tough problems, and thrive as part of a team.
If that’s you and this role fits, we want to hear from you.
Join the power movement as a Senior Multiphysics Modeler
The Senior Multiphysics Modeler will work closely with the CFS tritium program and process engineering team to develop a fuel cycle model for the world's first fusion power plant, ARC, located in Chesterfield County, Virginia.
The senior multiphysics modeler will develop simulation toolkits and workflows that integrate first-principles multiphysics simulations with industrial process models to support technology development and subsystem integration for key fuel cycle systems, supported by the CFS fuel team to understand system requirements.
Designing and deploying a fusion fuel cycle is an integral part of building power plants. This position will build the tools to optimize the fuel cycle design for the world's first power plant by becoming CFS’s expert in this important tool. The senior modeler will collaborate with an interdisciplinary team of engineers and scientists, and report to the Director of the Fueling and Tritium Systems.
Applicants must have a degree in a relevant engineering or science discipline as well as experience in process modeling and programming. Applicants must have a demonstrated ability to apply a first principles approach in solving complex engineering problems and experience conducting cost-benefit to evaluate the economics of proposed solutions. Applicants must have demonstrated success working on engineering projects in multi-disciplinary teams generating effective solutions to complex problems.
What you'll do:
- Lead the development of an integrated power plant fuel cycle model
- Develop models for unit operations of key systems
- Develop simulation tools to enable targeted R&D for key fuel cycle technologies
- Own the fuel cycle simulation tools and models
- Validate models and identify key R&D requirements to enable validation where there are currently gaps in the literature
- Collaborate cross-functionally with both internal and external experts to ensure fuel cycle models are feasible, economic and state-of-the-art
- Develop processes and layouts for fueling subsystem blocks that are communicated through standard engineering documents
- Generate detailed work plans and define milestones, integrated with R&D, to deliver validated models
- Provide guidance to colleagues for use of developed modeling tools and outputs
- Identify emerging trends and opportunities and influence CFSs’s fuel cycle modeling strategy
What we're looking for:
- Master’s degree or similar experience with 7+ years in chemical engineering, mechanical engineering, physics, materials science, physical chemistry or similar
- 5+ years experience modeling process systems
- 5+ years experience in computer programming
- Knowledge of transport phenomena and chemical processes in gasses
- Experience building integrated process models
- Process engineering and systems integration
- Experience managing large data sets
- Understanding of scalable simulations
- Track record in version control
- Data reduction and results analysis
Bonus points for:
- Experience with Python and/or Matlab
- Experience with multiphysics tools such as Comsol
- Exposure to process simulators like HYSYS
- Use of engineering management tools
- Confluence/JIRA and remote collaboration tools
- Fusion energy experience
- Chemical engineering
- Atom and molecular mass transport
Must-have requirements:
- Ability to occasionally lift up to 50 lbs
- Perform activities such as sitting, typing, standing, stooping, or climbing for extended periods of time
- Dedication to safety to mitigate industrial hazards that may include heat, cold, noise, fumes, strong magnets, lead (Pb), high voltage, and cryogenics
- Willingness to travel or work required nights/weekends/on-call occasionally
#LI-Hybrid
At CFS, we excel in fast-paced environments, driven by our values of integrity, execution, impact, and self-critique. As we grow, we’re eager to bring on mission-driven folks who offer diverse perspectives and fresh ways to tackle challenges.
We value diversity deeply and are proud to be an equal opportunity employer by choice. We consider all qualified applicants equally, regardless of race, color, national origin, ancestry, citizenship status, protected veteran status, religion, physical or mental disability, marital status, sex, sexual orientation, gender identity or expression, age, or any other basis protected by law.
This role requires compliance with U.S. laws concerning the export of controlled or protected technologies or information (collectively, “Export Control Laws"). Any offer of employment will be contingent on the need for compliance with such Export Control Laws.
Salary range for this full-time position + equity + benefits. The actual salary will depend on level, location, qualifications, and experience. The range displayed on each job posting reflects new hire salaries for the position across all US locations. Benefits include:
• Competitive compensation with equity
• 12.5 Company-wide Holidays
• Flexible vacation days
• 10 sick days
• Generous parental leave policy
• Health, dental, and vision insurance
• 401(k) with employer matching
• Professional growth opportunities
• Team-building activities