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Experimental Measurements of Pressure Drop Across Sump Screen Debris Beds in Support of Generic Safety Issue 191 (NUREG/CR-6917)

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Publication Information
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NUREG/CR-6917

Publication Information

Manuscript Completed: December 2006
Date Published: February 2007

Prepared by
C.W. Enderlin, B.E. Wells, M. White, F. Nigl,
D.R. Rector, T.J. Peters, A.D. Guzman

Pacific Northwest National Laboratory
Richland, WA 99352

W.J. Krotiuk, NRC Project Manager

Prepared for
Division of Risk Assessment and Special Projects
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Code N6106

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Abstract

The U.S. Nuclear Regulatory Commission (NRC) Generic Safety Issue-191 deals with the possibility that, during a loss of coolant accident in a pressurized water reactor, thermal insulation and other materials may be damaged and the debris transported to accumulate on the sump screens of the emergency core cooling system and containment sump. Over time, a debris bed could form, blocking the sump screen, increasing the pressure drop across the sump screen, and reducing the available suction head for the recirculation pumps resulting in the safety margins for pump operations being exceeded.

Pacific Northwest National Laboratory (PNNL) conducted experiments to help the NRC predict the flow through debris beds consisting of fiberglass and calcium silicate particulate. The effects of debris preparation on debris bed formation and pressure drop were evaluated and a metric developed for characterizing the preparation. Testing consisted of forming the debris bed within the test loop and obtaining a steady-state pressure drop at the bed formation velocity. The velocity was then changed incrementally through several cycles—increasing and decreasing—with a steady pressure measurement obtained at each flow set point. The loop temperature was then changed and the velocity variation sequence repeated.

The test setup, data acquisition system, procedures, experimental results, and observations are presented. In situ measurements and photographs show the debris beds contracting and relaxing with the cycling of flow velocity.