Senior Core Physics and Radiation Protection Engineer

Thorizon is a European developer of next-generation small modular reactors (SMRs) based on molten salt technology. The company builds compact, modular nuclear reactors designed to deliver reliable baseload power and high-temperature industrial heat for sectors such as manufacturing, data centers, and energy-intensive industry. Spun off from NRG, the Netherlands' national nuclear research institute, Thorizon is commercializing molten salt reactor technology that was developed over decades of quiet research. The company aims to begin reactor construction in the early 2030s, with designs optimized for series production and flexible deployment close to end users. Thorizon's mission centers on providing clean, affordable, and safe nuclear energy without compromise. A defining feature of its technology is the use of existing nuclear waste as fuel, dramatically improving fuel efficiency and reducing the long-term waste burden of nuclear power. The company's patented cartridge system divides the reactor core into smaller, factory-produced modules, enabling off-site manufacturing, faster construction timelines, and true modular scalability. Operating at low pressure, the reactors offer an intrinsically safer profile compared to conventional nuclear designs. Thorizon has secured investment and signed a memorandum of understanding with partners including EPZ and NRG PALLAS, as well as provincial authorities, to build Europe's first commercial molten salt reactor in the Netherlands. The company has also received recognition for innovation, winning the ASML Emerging Innovator Award. By working with partners across engineering, fuel production, operations, and financing, Thorizon is positioned to scale its reactor technology to meet the growing demand for clean, dispatchable energy.

Your mission

Are you passionate about core physics, radiation protection and criticality? Are you motivated to apply your expertise and know-how to the ongoing design studies for the Thorizon One reactor? Are you passionate about designing cutting-edge neutronics systems and solving complex engineering challenges? Do you get energized when working on innovative solutions?  
 
You will be a major contributor of the core physics, radiation protection, and criticality expertise center, whose primary missions are, on the one hand, to provide comprehensive support and expertise in this area to the system design teams in charge of the fuel cycle, the reactor design and safety studies and, on the other hand, to define, execute, and adapt where needed the validation program using experiments carried out through shared initiatives, designed to ultimately prove that the innovations in our solution are feasible within the performance, cost, and time constraints of our project. 
 
Within this general framework you will develop methods and tools to perform core physics, radiation protection and criticality studies, possibly in collaboration with external specialists, perform high quality studies with the appropriate computational tools, and validate the computational tools.  
 
In your role, you can carry out an analysis to meet any core physics, radiation protection and criticality needs for Thorizon projects (Pioneer nuclear demonstrator design, FOAK/NOAK design), including budget, planning, tools selection, calculations, report issuance. You interact easily with other areas of expertise (such as nuclear safety, thermal-hydraulics, chemistry and mechanics). 
 
Your level of expertise allows you to prioritize based on the importance of the needs, and as an expert, you have the power to recommend any necessary actions for the project related to your area of expertise. 
Furthermore, you participate in external networks, including international initiatives, to stay at the forefront of industry developments.  
 
In this environment, you get the unique opportunity to put your knowledge to the best use, develop your ideas, and explore various aspects of thermal-hydraulics engineering. 
 
This role is based in Amsterdam, Netherlands or in Lyon, France. 

In this role you will:

• Set up an effective core physics computational train, using both probabilistic(MCNP, SERPENT for example)and deterministic approaches(APOLLO3, SCALE for example), as well asprovidingnumerical/physicalinsights and practical approachestoestablishappropriatecouplingwiththermal-hydraulicsfor effective transient analyses.
• Set up core radiation protection or criticality models for simulation of shutdown, storage,handlingand transport
• Set up andmaintainscientific computing environments on Linux, including installing and configuring scientific software, libraries, and data analysis tools.
• Automate the studies and their pre- and post-processing. 
• Contribute to definition and justification of the safety case.
• Contribute to orestablisheffectiveexchangewith other codes and results from other disciplines, such as thermal-hydraulics, salt compositionchemistryand structural mechanics.
• Participate in specifying, selecting, and managing external contractors and suppliers that support the project.
• Guide junior colleagues in the samediscipline, andshare your knowledge with your teammates.
• Create transparency on development progress,identifyissues andchallenges,andpropose solutions that will help team problem-solving and designiteration.
• Implement a learning loop and ensure lessons learned are systematicallyintegrated in way of working and the design itself.
• Contribute to the definition, execution, and adaptationwhere neededofthe validation programusingexperiments, designed toultimately provethat the innovations in our solution arefeasiblewithin the performance, cost, and time constraints of our project. This program includes thequalificationof thecore physics, radiationprotectionand criticalityComputational Tools to be used for design and safety, applying national (e.g., ASNR guide 28) or international (IAEA in particular) approaches.
• Participate in meetings with regulators with the aim of defending in-house positions and contribute tomaintainingan active dialogue with regulators (in particular ASNR, ANVS and FANC).
• Be involved in various international initiatives (IAEA, Euratom…) dedicated toyourdiscipline.
• Stay updated on industry trends and advancements in approaches, methodologies,Computational Tools incore physics, radiationprotectionand criticality.
• Report tothe Core Physicslead, andworkin different project teams.

About you:

• You have a master’sdegreeor a PhDin science or engineering, experience in the nuclear field ismandatory.
• You have minimum 8 years of proven experience in core physics,radiation protectionandcriticalitysimulations and analyses. A PhD is regardedasworkexperience, ifthe subject of study is relevant to the job position.
• You have experience withmultidisciplinarycode couplingfrom the fundamental data tothereal worldapplicationand (simulation) experiencein other disciplines is regarded a plus.
• You know the MSR specificities related tocore-physics,radiationprotectionand criticality.
• You haveproficiencyin Linux(Ubuntu, CentOS, Fedora, etc.) with strong command-line skills and knowledge of shell scripting.
• You have experience with scientific computing toolslike Python, R, MATLAB, SciPy, NumPy, or similar libraries.
• You have a good knowledge ofnational orinternational (IAEA, NRC, ASNR or other) standards on scientific computing tool qualification.
• You have strong organizational and multitasking abilities, with drive for quality and accuracy.
• You get inspired by an organisation with a large variety of people, with different experiences and background.
• You are eager to learn and like challenges.
• You are creative and innovative: You rethink issues to find practical solutions to difficultproblemsand youdemonstrateagility by minimizing complexity. You have a pragmatic and constructive mindset.
• You have a good sense of judgement: you think strategically (in your field andtaking into accountall the dimensions of the project), and you know how to prioritise your actions according to the key issues at stake.
• You have excellent communication skills: you listen before you react, you are concise, you treat people with respect, you keep calm in stressful situations, you have excellent writing skills. You are an excellent communicator in English, and preferably also French or Dutch, both spoken and written. 
• You create impact: your productions are models for your colleagues.