An EDF-developed technique for measuring deposit build-up on tube support plates is being assessed for its applicability to steam generators worldwide.

	Video inspection of secondary side leak

Between 2004 and 2006, primary-to-secondary leaks in steam generators caused three forced outages at two 900 MW units in France. In each instance, inspections revealed a circumferential crack in a tube near the tube-free chimney region of the steam generator. Engineers hypothesized that deposit build-up on the tube support plates (see figure) caused tube vibrations that led to high-cycle fatigue and eventual crack initiation.

EDF developed a monitoring technique to determine the level of deposit build-up on the tube support plates. The level of deposit build-up can then be used to determine whether and when further action, such as chemical cleaning, may be warranted.

The EDF technique monitors the response of the steam generator wide-range water level during a routine down-power and compares the results with output from a transient simulation of a steam generator to determine the deposit build-up level. Because plants outside France do not require this routine down-power, the research team’s first step in 2010 has been to determine the type of power transient (magnitude and duration) required for successful implementation of this technique. If the results show that the technique can be applied to other types of power transients, a field-testable version will be developed in 2011 to enable a quantitative assessment and allow for an informed decision regarding its commercial viability.

For more information, contact Rick Rusaw at 704.595.2690, rrusaw@epri.com, or Heather Feldman at 704.595.2735, hfeldman@epri.com.