Study on dominant aspects of unprotected loss-of-flow to be evaluated in the initiating phase for a sodium-cooled fast reactor

ABSTRACT

SAS4A is presently the worldwide standard computer code for simulation of the initiating phase of the Core Disruptive Accident (CDA) in MOX-fueled Sodium-cooled Fast Reactors (SFR). In order to improve the capability of the computational code, SAS4A, to be applied to the safety assessment for SFRs, detailed investigations of physical phenomena under unprotected loss-of-flow (ULOF) conditions were conducted, and physical models to be developed and improved were identified using the Phenomena Identification and Ranking Table (PIRT) method. A fuel stub motion, in which the residual fuel pellets would move to the core central region after fuel pin disruption, was selected as one of the key phenomena to be simulated properly and a key concept of the fuel stub motion model was presented.

KEYWORDS:

• FBR
• fast reactor
• severe accident
• safety analysis
• CDA
• SAS4A
• ULOF
• ATWS
• CABRI
• PIRT

Acknowledgments

The authors express their sincere gratitude to Ms Keiko Takahashi of NESI Inc., for technical assistance in parametric calculations using the SAS4A code. The authors also would like to thank all the SAS4A specialists of CEA, IRSN and KIT for the contribution of PIRT development and Mr Ikken Sato of JAEA for his helpful advice. The supports by Dr. Yoshitaka Fukano and Dr. Shinya Ishida are also appreciated.

Disclosure statement

No potential conflict of interest was reported by the authors.