EPRI is using plant data collected over the past 10-15 years to re-evaluate the technical basis for inspection frequency of many safety-related BWR internal components.

EPRI's Boiling Water Reactor Vessel and Internals Project (BWRVIP) has developed inspection guidelines for many safety-related BWR internal components, including the core shroud, core spray piping, and jet pumps. The guidelines specify inspections of each component at specified intervals to monitor the effect of aging.

The inspection guidelines were based on best available technical information in the 1995-2000 time frame, recognizing that future revisions might be needed to reflect cumulative data from plant inspections. This recognition has proven true. In some cases, the amount of degradation observed has been less than anticipated and the initial inspection guidance appears to have been conservative. In other cases, unexpected degradation has been observed, and more frequent inspections are appropriate.

	BWR core spray system.

To address this issue, BWRVIP initiated an inspection optimization project in 2009 to develop a methodology for revising inspection guidance and ranking component priority. Some of the factors considered in ranking the components were availability of new inspection data, effectiveness of mitigation technologies, nondestructive evaluation technology developments, component structural margin, and time-dependent factors such as neutron fluence and fatigue sensitivity. The evaluation determined that core spray piping should be addressed first, followed by jet pump, core shroud, shroud support and control rod drive components. The results of the prioritization task are reported in BWRVIP-236 (EPRI report 1020730).

The optimization of core spray inspections began in 2010, culminating in a report documenting the technical basis for revising the inspection guidelines. A key input to the report was a utility survey that captured detailed historical results of core spray inspections from 32 BWR plants. Overall, the technical basis report concludes that some inspections (e.g., certain bracket and sparger welds) do not need to be conducted as frequently as required by the current guideline, while other locations (e.g., some 304L piping welds) should be inspected more frequently.

The analysis determined that a strong technical basis exists for reducing the total number of core spray inspections by approximately one-third with no adverse affects on plant safety. The technical basis report will form the basis for a revision to the BWRVIP Core Spray Inspection Guidelines (BWRVIP-18, Revision 1) to be completed later this year.

Optimization of jet pump and core shroud inspections is currently underway. Revised guidance for those inspections is anticipated in 2012.

For more information, contact Bob Carter at 704.595.2519 or bcarter@epri.com.