The Paul Scherrer Institute PSI is the largest research institute for natural and engineering sciences within Switzerland. We perform cutting-edge research in the fields of future technologies, energy and climate, health innovation and fundamentals of nature. By performing fundamental and applied research, we work on sustainable solutions for major challenges facing society, science and economy. PSI is committed to the training of future generations. Therefore, about one quarter of our staff are post-docs, post-graduates or apprentices. Altogether, PSI employs 2300 people. 

The Laboratory for Reactor Physics and Thermal-hydraulics LRT conducts computational and experimental research with a focus on the safety of nuclear reactors, with an emphasis on Light Water Reactors LWRs and specifically the Swiss nuclear power plants. The modelling and simulation of postulated design basis scenarios for PWRs such as loss-of-coolant accidents LOCA and the further development, verification and validation of associated simulation methodologies are of primary interest. In this context, we are looking for a

PhD Student in the Development of Models for Droplet Behaviour in PWRs

Your tasks

  • PhD research on the development of advanced closure models for droplet breakup on wet and dry spacer grids of pressurised water reactors 
  • Development, implementation, testing and validation of a mechanistic droplet breakup model for wet spacer grids 
  • Development of physics-based correlations for droplet size distributions in PWR fuel assemblies during reflood 
  • Implementation and testing of droplet behaviour models in the US-NRC’s system thermal-hydraulics code TRACE 
  • Sensitivity and uncertainty analysis of the newly implemented models 
  • Preparation of technical reports and publication of scientific results at international conferences and in peer-reviewed journals 
  • Participation in teaching activities in coordination with thesis advisor

Your profile

  • Master’s degree or equivalent in nuclear or mechanical engineering, physics and/or applied mathematics 
  • Solid background in nuclear engineering, including in particular two-phase thermal hydraulics 
  • Experience using system and/or subchannel thermal-hydraulics code and CFD simulation codes, ideally the systems code TRACE 
  • Programming experience in FORTRAN and scripting languages such as Python 
  • Familiarity with uncertainty quantification and sensitivity analysis methodologies (e.g., BEPU, CSAU) is an asset 
  • Fluent spoken and written English, proficiency in German is beneficial

We offer

Our institution is based on an interdisciplinary, innovative and dynamic collaboration. You will profit from systematic training on the job, in addition to personal development possibilities and our pronounced vocational training culture. If you wish to optimally combine work and family life or other personal interests, we are able to support you with our modern employment conditions and the on-site infrastructure.

For further information, please contact Dr Omar Al-Yahia, phone +41 56 310 27 84. 

Please submit your application online by 30 June 2026 (including list of publications and addresses of referees) for the position as a PhD Student (Index-Nr. 4103-27812).

Paul Scherrer Institute, Human Resources Management, Mariusz Prus, 5232 Villigen PSI, Switzerland

Apply now