Additional information
by Nrc Staff United States Nuclear Regulat (Created by)
The U.S. Nuclear Regulatory Commission (NRC) issued Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors (PWRs)," on September 13, 2004, as the primary vehicle for addressing and resolving concerns associated with Generic Safety Issue 191, "Assessment of Debris Accumulation on PWR Sump Performance." Additionally, the NRC staff developed a safety evaluation of industry-developed guidance to provide an accepted method for evaluating PWR sump performance as requested in Generic Letter 2004-02. However, the safety evaluation and the industry guidance document provide little guidance for assessing chemical effects. The licensees are to address chemical effects on a plant-specific basis. Both the NRC and industry have sponsored research to provide additional information and develop some guidance for evaluating chemical effects. The NRC convened an external peer review panel to review the NRC-sponsored research conducted through the end of 2005 and to identify and evaluate additional chemical phenomena and issues that were either unresolved or not considered in the original NRC-sponsored research. A phenomena identification and ranking table (PIRT) exercise was conducted to support this evaluation in an attempt to fully explore the possible chemical effects that may affect emergency core cooling system performance during a hypothetical loss-of-coolant accident (LOCA). The PIRT was not intended to provide a comprehensive set of chemical phenomena within the post-LOCA environment. Rather, these phenomena should be combined with important findings from past research and informed by ongoing research results. It is anticipated that knowledge gained by ongoing and completed research will be considered along with the PIRT recommendations to identify and resolve existing knowledge gaps so that a more accurate chemical effects evaluation can be performed. The PIRT panel identified severa
