United States Nuclear Regulatory Commission - Protecting People and the Environment

Phenomena Identification and Ranking Table Evaluation of Chemical Effects Associated with Generic Safety Issue 191 (NUREG-1918)

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Publication Information

Manuscript Completed: August 2008
Date Published: February 2009

Prepared by:
R.T. Tregoning1, J.A. Apps2, W. Chen3, C.H. Delegard4, R. Litman5,
D.D. MacDonald6

1U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

2Lawrence Berkeley National Laboratory
1 Cyclotron Road
Berkeley, CA 94720

3Dow Chemical Co.
2301 N. Brazosport Blvd.
B-1603
Freeport, TX 77541

4Pacific Northwest National Laboratory
P.O. Box 999
Richland, WA 99352

5Radiochemistry Laboratory Basics
28 Hutchinson Drive
Hampton, NH 03842

6Pennsylvania State University
201 Steidle Building
University Park, PA 16802

J.P. Burke, NRC Project Manager

NRC Job Code N6100

Office of Nuclear Regulatory Research

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Abstract

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 several significant chemical phenomena. These phenomena pertain to the underlying containment pool chemistry; radiological considerations; physical, chemical, and biological debris sources; solid species precipitation; solid species growth and transport; organics and coatings; and downstream effects. Several of these phenomena may be addressed using existing knowledge of chemical effects in combination with an assessment of their implications over the range of existing generic or plant-specific post-LOCA conditions. Other phenomena may require additional study to understand the chemical effects and their relevance before assessing their practical generic or plant-specific implications.

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