One of the major achievements of the NEA is the knowledge it has helped generate by organising joint international nuclear safety research projects. These projects, established under the auspices of the NEA, bring together the world’s leading experts, who contribute to maintaining and improving nuclear safety expertise and tools in participating countries. They also contribute to promoting consensus building on approaches to resolve complex safety issues.
In the field of thermal-hydraulics (TH), the NEA has since 2001 run collaborative projects to investigate thermal-hydraulic safety issues for existing pressurised water reactors (PWRs) and new PWR design concepts through experiments such as ETHARINUS and ATLAS3.
The NEA ATLAS3 and NEA ETHARINUS projects on 7-9 November 2023 organised a workshop with around 70 experts from 19 organisations and 13 countries that was hosted by the Spanish Nuclear Safety Council (Consejo de Seguridad Nuclear, or CSN) at Universitat Politècnica de Catalunya, in Barcelona, Spain. The workshop featured a number of sessions that provided an overview of the two projects, detailed presentations of analytical activities for the two projects, plant applications, future opportunities for collaborative research and a wrap-up to highlight the main conclusions and recommendations. The workshop was a good occasion to share experiences and practices among project participants and to discuss the progress made in knowledge, modelling and applications and perspectives.
A key part of activities in nuclear reactor safety technology relates to the need to demonstrate that the computer codes and calculation methods used to assess the safety of nuclear installations are validated for the intended applications. Therefore, the qualification of best-estimate codes, computational simulation models, “best modelling practices” and uncertainty methods must be considered of great importance to ensure the validity of performed best-estimate plus uncertainty (BEPU) analysis. Code validation is important for developing accurate predictive tools for the simulation of different reactor scenarios. This requires separate effect tests (SETs) and integral effect tests (IETs) that represent reactors under steady, transient and accident conditions. Those data need to be generated by means of experimental programs such as ATLAS3 and ETHARINUS.
The code result benchmark exercises provide a way of continuously testing the current TH simulation codes in their predictive capabilities. Project partners and operating agents of both projects have noted the advantage of having a large number of participants involved.
Code results have shown good performance and satisfactory agreement with experimental results, which increases the confidence in current TH codes technologies.
Further nuclear power plant applications, particularly in improving scaling techniques, were also encouraged, now that good and relevant counterpart tests have been conducted in both projects as a result of previous workshops recommendations.
As highlighted in similar joint analytical workshops previously (Barcelona 2003, Pisa 2005, Budapest 2006, Pisa 2010, Paris 2012, Lucca 2016, Barcelona 2019), the experience of having experimental and analytical specialists together in a common conference has been fruitful. They represent good examples of the effective and necessary interaction between codes and experiments for the solution of topical safety issues.
One of the discussions, triggered by recommendations discussed at the January 2023 Joint Nuclear Safety Research Project week, focused on how to implement a more integrated approach to safety research in the thermal-hydraulic area, around sets of experimental platforms for the reactor coolant system (RCS) and containment thermal-hydraulic investigations.
The new SYStem THERmal hydraulics (SYSTHER) joint project proposal is an attempt to create a platform to address thermal-hydraulic nuclear safety priorities for both existing and advanced reactor designs, including small modular reactors. Discussions should continue on how to ensure a more integrated approach in the area, considering other proposals for collaborative research, such as for instance the ATLAS-4 proposal.
To achieve such meaningful tasks, international co-operation is crucial to identify the key R&D needs for the Nuclear TH community.