Publications

Development and Validation of a Flexible RELAP5-3D-Based Subchannel Analysis Model for Fast Reactor Fuel Assemblies

Matthew Memmott, Jacopo Buongiorno, and Pavel Hejzlar

MIT-ANP-TR-121 (December 2008)

Abstract

The capabilities of the RELAP5-3D code to perform subchannel analyses in sodium-cooled fuel assemblies were evaluated. The motivation was the desire to analyze fuel assemblies with traditional (solid pins) as well as non-traditional (annular pins) geometries. Since no existing subchannel codes can handle the non-traditional geometries, it was decided to develop a new flexible RELAP5-based subchannel model. It is shown that subchannel analysis of sodium cooled fuel assemblies is possible through the use of control variables in the code. Since it is the first time that RELAP5 has been used for this type of analysis, extra care was taken in validating it. First, the code was compared with the SUPERENERGY II code for the case of solid fuel pins in a conventional hexagonal lattice. It was shown that the temperature predictions from the two codes agreed within 2%. Second, the RELAP5 subchannel model was applied to the ORNL 19-pin test, and it was found that the code could predict the measured outlet temperature distribution with a maximum error of ~8%. Finally, using the new RELAP5 model, the geometry of a traditional hexagonal assembly with wire-wrapped fuel was optimized. The results of the optimization are also reported here to provide an example of the model capabilities.