The effect of pressure tube creep on dryout power of an advanced 37-element fuel bundle

A pressure tube (PT) which is loaded with the 12 fuel bundles horizontally allows an independent flow passage of the 380 fuel channels. Most of the aging effects for the CANDU primary heat transport system were originated from the horizontal creep PTs. The creep PT deteriorates the CHF (Critical Heat Flux) of the fuel channel and finally worsens the reactor operating performance and thermal margin. In particular, a standard 37 fuel bundle (37S fuel bundle) has been used in commercial CANDU reactors for over 40 years as a reference fuel bundle. It is known that most CHF of a 37S fuel bundle were occurred at the peripheral region of a central rod because a 37S fuel bundle has a relatively small flow area or high flow resistance at the center subchannels compared to the other subchannels. Hence, it is noted that the configuration of a fuel bundle is one of the important factors affecting the local CHF occurrence. Recently, an advanced 37 fuel bundle which is the 37S fuel bundle with the increases of an inner ring radius was proposed and evaluated the CHF enhancement for the uncrept PT. At this study, the subchannel analyses were carried out to investigate the dryout power characteristics of a 37A fuel bundle for the crept PTs and its results for a 37A fuel bundle in the crept PT were compared with those of 37S fuel bundle. Also, the flow characteristics of the subchannels were investigated. (author)