Steam Dryer Cracking Evaluation

Steam dryer component cracking has recently been of significant interest in BWR plants operating at extended power uprate (EPU).  Structural Integrity (SI) has been working with several plants in addressing this issue.

Scheduled inspection, following operation at EPU levels, uncovered several degraded locations in the outer hood cover plates and internal bracing at one specific plant.  Although dryer cracking itself is not a safety concern, loose parts can be an issue.  Reactor efficiency is also reduced by less effective steam drying performance.  In addition, demonstration of an understanding of the cause for the degradation is important in finding a solution and designing a repair.  Thus, a better understanding and solution is critical for future operation at EPU levels. 

The results of finite element modeling performed prior to EPU operation were not consistent with the extent of observed cracking.  This implies that forcing functions and pressure levels experienced by the steam dryer during EPU operation were not well understood.  Life long exposure to low frequency flow induced vibration was another unaccounted for contributor. 

Structural Integrity has contributed in third party review of various analyses including finite element structural, acoustic modeling to help define the forcing function and performed finite element analyses to better understand the complicated stress state at various key locations.  This work has involved both an understanding of the cracking of the original dryer design and implemented and proposed repairs and modifications to the steam dryer.

For further information contact SI.