The urgency for decarbonization of the energy grid is ever increasing and fossil energy sources must be replaced by sustainable sources of energy to prevent detrimental levels of global warming. Renewable energy sources wind and solar show potential and contribute to decarbonization but are intermitted and require storage solutions that are exposed to further constrictions and costs. Nuclear fusion is regarded as the most promising new energy source since scientists first learned about it and in theory poses the ideal properties to meet the needs of the world's future energy system. Despite fusion’s potential as the ideal energy source for innovating and decarbonizing the energy system, the reality is that 70 years of research and development have not yet resulted in fusion energy on the grid. Overpromises by fusion scientists since the seventies have resulted in scepticism and cynicism towards fusion development with the longstanding quip that “Fusion energy is thirty years away…and always will be”. Nevertheless, 2021 saw many important breakthroughs and achievements in fusion research which resulted in it being titled “The best year in the history of fusion development” and led to revived optimism and claims that fusion development is moving from the lab to the grid and commercialization is closer than ever before.

In order to truly understand the process of commercializing fusion energy, the barriers need to be known and understood so that these can be addressed specifically, and the process can be accelerated. Adding to that is, that there are also numerous different technical approaches to fusion, each with their own characteristics. However, currently comprehensive knowledge of these barriers is missing. Information is highly scattered as it is focusses on specific topics of fusion development, mostly the scientific or technical barriers. Adding to that is that most information is on separate technologies or specific experiments. As a result, there is a severe lack of knowledge: it is unknown what all the barriers towards commercialization are, how these barriers differ in severity and how they differ amongst the numerous fusion technologies. In an attempt to tackle this knowledge gap and enable a better understanding of the fusion development, the objective of this research was to develop a comprehensive list of barriers and subsequently study and assess this list for the different approaches to fusion with the intention of increasing the understanding of the pathway for commercialization of fusion energy.

Before starting this endeavour, a conceptual analysis was performed to define the concepts “barrier” and “commercialization”. Using these definitions an extensive literature study was performed, alongside 23 semi-structured interviews with almost all the leading fusion institutes and companies. Using predefined selection criteria to deal with the vast amounts of information, a list of fifteen relevant barriers was identified. The barriers described in literature were complemented and extended by empirical experiences and practical examples obtained in the interviews, resulting in a manageable but comprehensive list of fusion barriers towards commercialization, including several barriers that have received very little attention to date.

In an attempt to gain further insight into these barriers and research how these are different for the various approaches to fusion, a methodology was developed to assess the barriers in a standardized way. Based on the principles of the Y-factor method developed by (Chappin et al., 2020), a customized framework was developed for the commercialization of fusion energy technologies. Each barrier was concisely described and subsequently the identified barriers were organized into five categories: Technology, Operation, Cost & Financing, Governance and Engineering. The framework assesses the barriers on a tripartite scale, scoring a value of 0 indicating no barrier, 1; indicating a potential barrier and 2; indicating a significant barrier. For every barrier the scoring criteria were detailed to allow for accurate scoring.

The five most developed and pursued technical approaches to fusion (Tokamak, Spherical Tokamak, Stellarator, Field Reversed Configuration and Inertial Confinement Fusion) were assessed using the designed framework. This was done by three sperate expert interviews. These respondents were selected because they all had high expertise of both fusion energy and experience within the fusion industry and hence contribute to the validity of the research. Analysis of the results lead to numerous interesting findings

• Barriers generally apply to all technologies: Although the difference between the fusion technologies were identified and acknowledged by the various respondents, this did not result in notable differences in the scoring of these technologies. Instead, most barriers apply in a similar severity for all technologies.

• Experts disagree on fundamental barriers: Two of the respondents disagreed strongly on the scoring of several barriers, such as “Plasma physics”, “Radiation shielding” and “Energy production”. The fact that these respondents both have a PHD in plasma physics, demonstrates the uncertainty of fusion development and underlines the complexity and difficulty of predicting the pathway of fusion technologies. In this particular case the differences mostly originated from the reasoning of the respondents; one argued more from a theoretical point of view while the other purely looked at results to date, exposing that the framework can be interpreted differently by different respondents.

• Barriers have a strong time element: The abovementioned disagreements can be partially explained by time. The application of the framework exposed that nearly all barriers are characterized by a strong time dependency and that the barrier value is heavily dependent on the timeframe it is evaluated in. Fusion technology is still under development and while an active effort was made to describe the scoring criteria as closely as possible during the synthesis of the framework, the time dependency and the interpretability that comes with it could not be eliminated

• Hierarchy within barriers: The application of the framework also exposed a certain degree of hierarchy within the barriers and found that there was an order of urgency within the barrier categories. A clear and logical pathway could be observed; firstly the “Technology” barriers must be resolved, afterwards the category of “Operation” barriers become most urgent and finally the “Engineering” category. This was substantiated by the scores as these categories received the highest scores. The remaining categories “Governance” and “Cost & Financing” are present throughout the entire innovation pathway.

All in all, the research has three main contributions. The first contribution is the identification of a comprehensive list of fifteen barriers that is validated by experts, can be used to assess all fusion technologies and captures the complete commercialization pathway. Secondly, the developed framework is the first tool that can be used to uniformly assess these barriers and compare them amongst different technologies. Finally, application of the framework increased understanding of the time-dependency and hierarchy of the barriers. Despite the limited value of the quantitative output, the qualitative findings have certainly increased understanding of the barriers and complexity of fusion energy development and showed that the use of the method can enable insightful discussions.

It should be noted that in spite of continuous attempts at safeguarding the validity of the research, there are a number of limitations that should be taken into account when interpreting the research and its results. The development of the scoring criteria is subjective and can be interpreted differently by different respondents, despite the effort to formulate these with a high accuracy and clarity. Simultaneously, because the barrier definitions and scoring criteria are newly designed, these are also constrained by the perception and interpretation of the researcher. Lastly it is important to note that the application of the designed framework was limited to only 3 respondents and the outcomes are therefore based on a small sample size. The overall results of applying and scoring the framework is greatly determined by the individual views and can’t be generalized.