GSI-191: Experimental Studies of Loss-of-Coolant-Accident-Generated Debris Accumulation and Head Loss with Emphasis on the Effects of Calcium Silicate Insulation

ii iii ABSTRACT This report documents experiments conducted to determine the head-loss characteristics associated with calcium silicate insulation debris accumulated on a sump screen. These experiments were performed under the direction of Los Alamos National Laboratory in facilities operated by the Civil Engineering Department of the University of New Mexico. Experiments confirmed that calcium silicate insulation could degenerate into very fine particulates in the containment environment after the occurrence of a loss-of-coolant accident (LOCA), and that debris beds formed by a combination of fine calcium silicate particulates and fibrous insulation on a sump screen can cause substantial head loss across the sump screen. Recommended head-loss parameters to be used in the NUREG/CR-6224 correlation were established with consideration of uncertainties in test parameters and variability in the manufacture of the particular brand of calcium silicate insulation tested. Using these recommended input parameters (e.g., specific surface area and particle density), the NUREG/CR-6224 correlation predicts reasonably well conservative head losses as demonstrated by comparisons with experimental data obtained in this study. Debris accumulation on a simulated (vertical) pressurized-water reactor (PWR) sump screen was examined for several different types of LOCA-generated debris, including shredded fiberglass, crushed calcium silicate insulation, mixtures of NUKON TM and calcium silicate, and crumpled stainless-steel foils from the interior of reflective metal insulation. Results from this research enhance the understanding of head-loss characteristics important to the resolution of Generic Safety Issue 191, " Assessment of Debris Accumulation on PWR Sump Performance. " iv v FOREWORD In the event of a loss-of-coolant accident (LOCA) at a nuclear power plant, thermal insulation and other materials in the vicinity of the pipe break may be dislodged by the impingement of the high-energy steam/water jet. In such instances, some of the debris is eventually transported to the sump screens, where it accumulates and causes a pressure drop (i.e., head loss) across the sump screens. As a result, such debris accumulation could challenge the plant's ability to provide adequate long-term cooling water to the emergency core cooling system (ECCS) and the containment spray system (CSS) pumps. Since the nuclear industry recognized this phenomenon, extensive head loss testing has been conducted both within the United States and internationally. One such study, sponsored by the U.S. Nuclear Regulatory Commission (NRC), was documented in NUREG/CR-6224, " Parametric Study of the Potential for BWR ECCS Strainer Blockage Due to LOCA-Generated Debris, " dated October 1995, for which the NRC …