Summary of 3rd Sino-German symposium on fundamentals of advanced nuclear safety technology

The 3rd "Sino-German Symposium on Fundamentals of Advanced Nuclear Safety Technology (SG-FANS)" took place in Xi’an, China, in 2019. Common fields of interests have been identified on both Chinese and German side, such as code benchmarking, common access to experimental facilities and joint experimental data base for nuclear safety analyses.

Development of AC2 for the simulation of advanced reactor design of Generation 3/3+ and light water cooled SMRs

The transition from Generation 2 to Generation 3/3+ and 4 reactors, as well as the development of small modular reactors (SMR), place new demands on computational programs designed to simulate conditions of normal operation, operational occurrences, design basis accidents and severe accidents. On the one hand, most passive safety systems of advanced and innovative plants operate at low pressures even down to vacuum conditions and the driving forces are low compared to active systems. On the other hand, the containment is no longer just a barrier to retain radioactive material in the event of leakage of the cooling system, but it is an important link in the passive cooling chain. This requires an expansion and improvement of the existing simulation programs for the cooling circuit and containment, as well as the realization of a coupling between these simulation programs. The new AC2 program package combines the proven simulation codes ATHLET/ATHLET-CD and COCOSYS in one software suite to hit this target. The individual components of the suite are continuously extended and validated for their application to novel safety systems. This makes it possible to simulate the entire spectrum of accidents for Generation 3/3+, 4 and light water cooled SMR systems with just one program package. This publication gives an overview of the current state of development of AC2 and its individual modules.

Validation of the AC2 Codes ATHLET and ATHLET-CD

Verification and validation are basic quality assurance elements in code development and essential for code release. Therefore, the codes of AC2 (ATHLET – ATHLET-CD – COCOSYS) are tested on separate effect tests, integral tests as well as plant scenarios to verify and validate the models after new implementation or updates. The verification assures that the models are implemented and working correctly while the validation checks if the models predict the right phenomena and combined with other models and modules. The selected experiments are summarized in GRS's validation matrices, which in turn are based on the CSNI validation matrices derived from OECD/WGAMA task groups as well as current activities on experimental test campaigns. For ATHLET several test series are used to cover a wide range of phenomena which can occur in PWR, BWR and VVER. Additionally, plant transients are considered for German LWR. The ATHLET-CD validation matrix contains experiments covering most phenomena which can occur during a severe accident. But due to the interaction of several effects even in small scale experiments mainly integral experimental campaigns are used for the validation. Over the last decades the validation of the AC2 codeds ATHLET and ATHLET-CD has reached a high degree of fulfilment of GRS's validation matrices over all code versions. Innovative and advanced reactor concepts come with new or newly relevant phenomena, which AC2 needs to provide models for. Extending the validation base of AC2 for these models is one challenge for further code validation efforts besides the on-going update of the validation basis to recent code versions.

Necessary improvements of the GRS simulation chain for the simulation of light-water-cooled SMRs

Small modular reactors (SMRs) are one interesting option for new builds in almost all countries worldwide continuing to use nuclear energy for commercial power generation. For asserting of legitimate nuclear safety and/or security interests German authorities require in this context own and independent expertise for the safety assessments. The Gesellschaft für Anlagen und Reaktorsicherheit (GRS) mbH, which is the main technical support organization in nuclear safety for the German federal government, has among others performed a study on Safety and International development of Small Modular Reactors (GRS-376) to identify essential issues of SMR safety as well as needs for adaption, improvement and validation of nuclear evidence tools developed and applied by GRS. For the light-water-cooled SMRs, which have (at least according to GRS) the best prospects for realization, selected results of this study will be presented.

Lessons learned on probabilistic methodology for precursor analyses

Based on its experience in precursor assessment of operating experience from German NPP and related international activities in the field, GRS has identified areas for enhancing probabilistic methodology. These are related to improving the completeness of PSA models, to insufficiencies in probabilistic assessment approaches, and to enhancements of precursor assessment methods. Three examples from the recent practice in precursor assessments illustrating relevant methodological insights are provided and discussed in more detail. Our experience reinforces the importance of having full scope, current PSA models up to Level 2 PSA and including hazard scenarios for precursor analysis. Our lessons learned include that PSA models should be regularly updated regarding CCF data and inclusion of newly discovered CCF mechanisms or groups. Moreover, precursor classification schemes should be extended to degradations and unavailabilities of the containment function. Finally, PSA and precursor assessments should put more emphasis on the consideration of passive provisions for safety, e. g. by sensitivity cases.

Traumatic pseudoaneurysm of the brachial artery

Detection and treatment of vascular injuries in extremity and pelvic trauma can be challenging. Angiography, while no longer routinely used in asymptomatic patients, is still a primary means of diagnosis. Appropriate patient selection based on physical examination, along with other less invasive imaging modalities, can decrease the need for angiography while still detecting the vast majority of clinically significant injuries. Angiography also plays a definitive therapeutic role in most cases of significant hemorrhage in the pelvis through precise identification and selective embolization of bleeding vessels.