Experimental study on fuel-discharge behavior through in-core coolant channels

Kamiyama, Kenji  ; Saito, Masaki*; Matsuba, Kenichi  ; Isozaki, Mikio; Sato, Ikken ; Konishi, Kensuke ; Zuyev, V. A.*; Kolodeshnikov, A. A.*; Vassiliev, Y. S.*

In core disruptive accidents of sodium cooled fast reactors, fuel discharge from the core region reduces the possibility of severe re-criticality events. In-core coolant channels such as the control-rod guide tube and a concept of the FAIDUS (Fuel Assembly with Inner Duct Structure) provide effective fuel discharge paths if effects of sodium in these paths on molten fuel discharge are limited. Two series of experiments conducted in the present study showed that the discharge path can be entirely voided by the vaporization of a part of the coolant at the initial melt discharge phase, that this is followed by coolant vapor expansion, and that melt penetrates significantly into the voided channel. In conclusion, the effects of the sodium on fuel discharge are limited and therefore in-core coolant channels provide effective fuel discharge paths for reducing neutronic activity.