Investigation of effect of gas release on coolability of locally blocked LMFBR fuel subassemblies.

Abstract

The objective of the present study is to evaluate the temperature rise due to gas release behind local blockage in LMFBR fuel subassemblies.The experiments were conducted using six sets of electrically heated 37-, 61- and 91-pin bundles. The central or edge subchannels of each test section were blocked by a non-heat generating blockage of stainless steel plate. The effect of operational and geometrical con-ditions on the coolability of the blocked bundle were investigated from the test results. The examined factors are gas release rate, sodium flow rate, spacer type and blockage location.The high coolant flow more than 2 m/s in the velocity at the blocked plane, forced the released gas to be accumulated within the recirculation region resulting in marked tempera-ture increase. The dependency of the temperature rise on the gas release rate was classified into two stages; (1) the temperature increases with the gas release rate, (2) after reaching a peak value, the temperature gradually decreases with the gas release rate. From these conclusions empirical correlations were derived to estimate the temperature rise under the condition of blockage with gas release. It was deduced that fission gas release in an LMFBR fuel subassembly with a local blockage has a potential to cause a limited pin-to-pin failure propagation in the recirculation region.