Demineralizers and Ion Exchangers Flashcards
Describe the principles of demineralizer operation.
Ion exchange is the reversible exchange of ions used to remove undesirable ions from the liquid and substitute acceptable ions from the solid. When the undesirable ions removed are minerals, such as calcium (Ca++) and
magnesium (Mg++), ion exchange is called demineralization.
Describe the effects of demineralizer operation on water conductivity.
Conductivity is reduced.
State the reason for sampling both the inlet and outlet conductivity of a demineralizer.
Provides the demineralizaton factor (DF) ratio of inlet conductivity to outlet conductivity.
Describe the effect of excessive differential pressure on demineralizer performance.
Higher than normal D/P may indicate the bed is clogged due to buildup of corrosion products and suspended solids, or may indicate high flow through the demineralizer.
Describe how demineralizer differential pressure is used to determine the condition of a demineralizer resin bed.
As corrosion products and suspended solids are accumulated over the service run, the flow resistance, and therefore the D/P, increases.
Describe the reason for demineralizer flow limitations.
Abnormally high flow may reduce the rate of ion exchange due to insufficient time for exchange to take place. Resin beads may be forced through the lower retention element into the demineralizer effluent. High flow can physically break down resin beads into “fines”,
which will also pass through the retention element. Finally, high flow rates can cause channeling of the bed, which decreases mechanical filtration and results in very little exchange occurring.
Describe the effects of channeling in a demineralizer.
Channeling occurs as a result of water finding or forcing a low resistance flow path from inlet to outlet. A direct indication of channeling is a decrease in differential pressure, since the resin bed no longer provides sufficient flow resistance to the influent. These conditions can result in high ion concentrations and conductivity in the demineralizer effluent, as well as high radiation readings.
Describe the reason for demineralizer temperature limitations.
Ion exchange resins are very sensitive to elevated temperatures. Although the inert resin bead structure is stable up to fairly high temperatures (300°F), the active exchange sites are not. The anion resin begins to decompose slowly at about 140°F and the decomposition
becomes rapid above 180°F. The cation resin is stable up to 250°F.
Describe the demineralizer characteristics that can cause a change in boron concentration.
The boron affinity of a resin bed is affected by the temperature of the coolant passed through the bed. At lower temperatures, the borate ion bonding to the exchange site contains three boron atoms. At higher temperatures, the borate ion contains only one boron atom. The result of this characteristic is that at lower temperatures the resins are more efficient at removing boron from the coolant than at higher temperatures. A
saturated resin bed will actually release boron as
temperature is increased.
State the reason for bypassing demineralizers
To protect from high temperatures.
State the reason for using mixed bed demineralizers to process primary water.
1) Mechanically filter solids, crud and other corrosion products. 2) Remove soluble ions from primary water.
3) Control pH of primary water. 4) Reduce conductivity in the system
Describe plant evolutions which can cause crud bursts.
Those characterized by rapid and severe changes in coolant system temperature or pressure. These include
reactor trips, a rapid heatup or cooldown and reactor coolant pump starts. A crud burst can also be induced by chemically shocking theprimary systems.
State the definition of boron saturated as it relates to a demineralizer.
It can absorbed no more boron atoms at its present temperature.o
State the definition of lithium saturated as it relates to a demineralizer.
It can absorbed no more lithium atoms at its present temperature
Describe the effect of temperature on saturated ion exchangers.
Higher temperature flow may actually release ions from the demineralizer.
