Investigation of Core Thermohydraulics in Fast Reactors—Interwrapper Flow during Natural Circulation

VVUQ of a thermal-hydraulic multi-scale tool on unprotected loss of flow accident in SFR reactor

Within the framework of the French 4th-generation Sodium-cooled Fast Reactor safety assessment, methodology on VVUQ (Verification, Validation, Uncertainty Quantification) is conducted to demonstrate that the CEA's thermal-hydraulic Scientific Computation Tools (SCTs) are effective and operational for design and safety studies purposes on this type of reactor. This VVUQ-based qualification is a regulatory requirement from the French Nuclear Safety Authority (NSA). In this paper, the current practice of VVUQ approach application for a SFR accidental transient is described with regard to the NSA requirements. It constitutes the first practical, progressively improvable approach. As the SCT is qualified for a given version on a given scenario, the transient related to a total unprotected station blackout has been selected. As it is a very complex multi-scale transient, the SCT MATHYS (which is a coupling of the CATHARE2 tool at system scale, TrioMC tool at component scale and TrioCFD tool at local scale) is used. This paper presents the preliminary VVUQ application to the qualification of this tool on this selected transient. In addition, this work underlines some feedback on design and R&D aspects that should be addressed in the future to improve the SCT.

Analysis code development for the direct reactor auxiliary cooling system of the pool-type sodium-cooled fast reactor

Sodium-cooled fast reactor (SFR) is one of the most promising reactors among the six Gen-IV reactor systems due to its significant advantages in close fuel cycle, comprehensive technology foundations and operation experiences. China is designing and constructing a demonstration SFR, in which, to ensure the reactor passive safety, a direct reactor auxiliary cooling system (DRACS) with the inter-wrapper flow is proposed as the decay heat removal system. Xi'an Jiaotong University is in charge of the DRACS analysis code development. The physical models in the DRACS are extracted and the numerical models for each component are established. The Gear method and the SIMPLE method are adopted as the primary solution algorithm. The code is developed and validated by EBR-II and PHENIX benchmarks, the results of which indicate that the code can predict experimental results very well.