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Meeting Goals and Objectives

The understanding of its short- and long-term behavior in fission environments is crucial not only for the operation and optimization of existing reactors but also for the efficient design and safe deployment of future advanced reactors. It is thus of utmost importance to incorporate in nuclear data libraries accurate evaluations of the interaction of thermal neutrons with graphite used in applications. This is however a complex task as there are challenges in defining the detailed characterizations of the studied material, appropriate modeling, and optimal validation suite. This will only be achieved by the concerted effort of experts of all relevant areas.

The objective of the 1^st Reactor Graphite workshop is precisely to bring together this expertise and define a path forward in the following points:

• Material characterization: Not only there are different types of graphite used in reactor applications, with internal structure ranging from idealized crystalline to highly porous, but also prolonged exposure to neutron radiation affects and changes the material structure. We aim to clearly identify, from the application perspective, what material characteristics need to be described in order to properly model graphite performance.
• Modeling: Once the material characteristics are identified, we aim to investigate the different modeling approaches, and ideally identify preferred ones, from the physics perspective.
• Differential data: Models are only as good as their capability to reproduce experimental data. The workshop should deliberate and define which differential data sets should be used to compare and constrain the models. Also, in case of ambiguity or data gaps, we should define clear recommendations for new experimental measurements.
• Validation: Ultimately, adoption of nuclear data libraries is intrinsically tied with their usability in applications. Therefore, it essential to define which benchmarks or integral tests can and should be used to assess the quality and performance of evaluations. This workshop should provide a set of recommended benchmarks or integral tests to be used to assess and cross-compare different potential candidate evaluations.
• Library recommendation: The final goal of this effort is to produce one single set of recommended thermal neutron scattering law evaluations for reactor graphite to be eventually incorporated in the next ENDF/B release. This recommendation is to be authored by all participants of the ReGra workshop. Due to the complexity of the task, provided there are significant progress in the topics above, the 1^st ReGra workshop can still be considered successful even if a consensus on final library recommendation is not achieved, leaving the final decision for a second future workshop.
• Workshop report: All the discussions, perspectives, approaches, findings and decisions will be thoroughly documented and released in a laboratory report authored by all workshop participants.

Cross Section Evaluation Working Group (CSEWG)
Executive Committee