Screen Penetration Test Report (NUREG/CR-6885, LA-UR-04-5416)
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Manuscript Completed: September 2005
Date Published: October 2005
C.B. Dale and B.C. Letellier
Los Alamos National Laboratory
Los Alamos, New Mexico 87545
A. Maji, K. Howe, and F. Carles
Department of Civil Engineering
University of New Mexico
Albuquerque, New Mexico 87110
Tsun-Yung Chang, NRC Project Manager
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Code Y6041
The concern raised by Generic Safety Issue (GSI-191), “Assessment of Debris Accumulation on PWR Sump Performance,” is the transport of debris to pressurized-water-reactor (PWR) sump screens following a loss-of-coolant accident (LOCA) and subsequent impact to emergency-core-cooling systems (ECCS) and containment-spray systems during recirculation. This document describes the first in a series of tests being conducted to address the effects of debris downstream of the ECCS sump screens. ECCS intake systems have been designed to screen out large post-LOCA debris materials. However, small-sized debris can penetrate these intake strainers or screens and reach critical components of the high-pressure safety injection system, such as pumps and throttle valves.
This report addresses the propensity of different types of insulation debris [fibrous, particulate, and reflective metallic insulation (RMI)] to penetrate PWR sump screens. The variables under consideration include the size of screen openings; the size, shape, and type of debris; the flow velocity upstream of the screen; and the manner in which the debris reaches the screen (on the floor or in the flow). The test matrix consists of 44 tests using combinations of representative screen-opening sizes of 1/4 in., 1/8 in., and 1/16 in. and debris sizes and shapes. Insulation debris consisting of NUKONTM fiberglass, calcium silicate (CalSil), and stainless-steel RMI was tested individually within a linear hydraulic flume. Approach velocities ranged from 0.2 to 1.0 ft/s. These velocities are representative of containment pool approach velocities at the sump screen for current designs, but modifications in many plants may result in lower approach velocities.
Debris screen penetration depends to some extent on all of the test variables examined: screen size; debris size, shape, and type; flow velocity; and method of introduction (on the floor versus in the flow). The debris type determines the relative importance of the remaining test variables. Under certain conditions, results indicate the potential for significant debris screen penetration. It was observed that a significant amount of particulate CalSil insulation (up to 70% in some cases) can pass through a screen opening of any size. Higher flow velocities cause large CalSil clumps to break up, allowing more CalSil to be transported to and pass through the sump screen. A significant amount of fibrous NUKONTM debris (up to 90% in some cases) arriving at the screen in finely separated fibers can pass through the screens. However, if the NUKONTM debris arrives at the screen in larger, agglomerated pieces, only a small amount (<5%) may pass through the screens. Last, when RMI debris was introduced on the floor, the RMI tended to remain stationary on the floor and not transport to the screen. The result was that <22% of the RMI introduced on the floor passed through the screen for all tests. However, a significant percentage (up to 75%) of the RMI passed through the screen when the RMI was introduced directly into the flow immediately before the test screen.
The results presented are applicable to the determination of the effect of the debris that passes through the sump screen on downstream components, such as high-pressure safety injection system pumps and throttle valves. These effects are being investigated in ongoing research at the University of New Mexico, using debris sizes and shapes that can penetrate the screen, as demonstrated by this testing.