The effect of electric potential on fibrous debris bypass through a containment sump strainer

Fiberglass is an efficient thermal insulation material in Pressurized Water Reactors (PWRs). However, fibrous debris generated during a Loss-of-Coolant Accident (LOCA) from fiberglass insulation materials may cause a safety issue in the containment sump strainer. This safety issue addressed in the Generic Safety Issue (GSI) 191 by the U.S. Nuclear Regulatory Commission (U.S. NRC) can be categorized into upstream effects, which concern loss of Net Positive Suction Head (NPSH), and in-vessel effects which concern debris bypass through the strainer and transportation into the primary system. PWR power plants in the U.S. have increased the size of their sump strainers, in the attempt to decrease the head loss. However, the quantity of debris bypass through the strainer still remains an issue not fully resolved. It is known that filtration through a porous medium is affected by water chemistry, affecting the double-layer electric potential close to the surface of particles and filter media. In the present study, the effect of water chemistry (pH and ionic strength) and the effect of external electric potential (voltage applied to a strainer) were investigated. NUKON fiberglass was prepared using a high pressure (1800 psi) washer method. Two positive (+ 500 mV and +1000 mV) and two negative (-500 mV and -1000 mV) electric potentials were applied between the strainer and water in the tank. Total mass of debris penetrated through the strainer under different conditions was compared. It was found that debris bypass is influenced by water chemistry and that, an electric potential applied to the strainer may affect the mass of debris penetration.