In pressurized water reactor (PWR) water systems, what component is described as a bed made of small spherical beads used as a filter?

• A. Activated carbon bed
• B. Demineralizer beds
• C. Mechanical strainers
• D. Ion-exchange cartridge

Answer: (B)

Demineralizer beds are packed with small spherical ion-exchange resin beads. As water flows through the bed, dissolved minerals (like calcium, magnesium, sodium, bicarbonate, and sulfate ions) are exchanged with ions attached to the resin (typically hydrogen and hydroxide in a mixed bed). This chemical exchange removes most of the dissolved ions, producing very pure water suitable for the reactor’s systems. The bead bed acts as a filter in the sense that it captures and holds these ions, not by physical straining but by chemical binding and exchange. Over time the resin’s capacity is used up and it’s regenerated with acid (for the cation part) and caustic (for the anion part) to restore its effectiveness. While activated carbon beds filter organics and mechanical strainers remove particulates, the description of a bed of small spherical beads used to remove dissolved ions best matches the demineralizer bed.