Operator Generic Fundamentals
Components - Demineralizers and Ion Exchangers
© Copyright 2017 – Rev 3
Operator Generic Fundamentals
2
Terminal Learning Objective
At the completion of this training session, the trainee will demonstrate
mastery of this topic by passing a written exam with a grade of 80
percent or higher on the following Terminal Learning Objective (TLO):
1. Explain demineralizer operation and its effect on power plant
operations.
© Copyright 2017 – Rev 3
TLO
Operator Generic Fundamentals
3
Enabling Learning Objectives for TLO 1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
State the purpose of a demineralizer.
Describe the principles of demineralizer operation.
Describe the process of demineralizer regeneration.
Describe the following demineralizer conditions to include causes,
hazards, and corrective measures as applicable:
a. Excessive differential pressure
b. Channeling
c. Excessive temperature
d. Breakthrough
e. Leakage
Explain how demineralizer use affects pH.
Describe the decontamination factor and explain how it is
calculated.
Describe plant evolutions that could affect demineralizer operation.
Explain the condition of a saturated demineralizer and the effect
temperature has upon it.
© Copyright 2017 – Rev 3
ELO’s
Operator Generic Fundamentals
4
Demineralizers and Ion Exchangers
Purpose
ELO 1.1 – State the purpose of a demineralizer.
• Demineralizers (ion-exchangers) used in nuclear power plants to:
– Remove ionic impurities
– Filter/remove small particles
– Help control pH of water
• Hold ion exchange resins that remove dissolved impurities from fluids
– Dissolved impurities generate corrosion problems and foul heat
transfer surfaces
– Ion exchange aids in pH control
• Classified into two groups:
– Single-bed ion exchangers
– Mixed-bed ion exchangers
© Copyright 2017 – Rev 3
ELO 1.1
Operator Generic Fundamentals
5
Demineralizers and Ion Exchangers
Purpose
• Demineralizers provide filtration
and ion exchange for
– Purifying water going to
steam generators
– Cleanup of RCS via
letdown/charging
Figure: Typical PWR
© Copyright 2017 – Rev 3
ELO 1.1
Operator Generic Fundamentals
6
Principles of Demineralizer Operation
ELO 1.2 – Describe the principles of demineralizer operation.
• Ion exchange is an exchange of
ions between two electrolytes or
between an electrolyte solution
and a complex solution
• Ionic impurities are removed and
replaced with acceptable
substitutes
Figure: Resin Beads
© Copyright 2017 – Rev 3
ELO 1.2
Operator Generic Fundamentals
7
Ion Exchange
• Small resin beads complete ion
exchange
• Resin beads are porous with
many exchange sites for ion
exchange
• Generally will contain
exchangeable ions that are
harmless such as H+ or OHFigure: Resin Beads
© Copyright 2017 – Rev 3
ELO 1.2
Operator Generic Fundamentals
8
Ion Exchange
Anion Resins
Cation Resins
• Exchange ions with undesirable
negative ions
• Exchange with undesirable
positively charged ions
• OH- or hydroxyl ion is typically
released by an anion resin
• H3O+ or hydronium is typically
released by a cation resin
© Copyright 2017 – Rev 3
ELO 1.2
Operator Generic Fundamentals
9
Reactions
• Sodium chloride will separate in water to form the Na+ and Cl- ions
𝑁𝑎𝐶𝑙
𝐻2 𝑂
𝑁𝑎+ + 𝐶𝑙 −
• Anion resin exchanges negative Cl- for negative OH- ion
• Cation resin exchanges positive H+ for positive Na+
• Exchanges take place because resin has a higher affinity for
undesirable ions than mobile ions it contains
• Ion affinity is selective and resin will give up an ion in favor of one it
has higher affinity for
𝑅− 𝐻 + + 𝑅+ 𝑂𝐻 − + 𝑁𝑎+ + 𝐶𝑙 − → 𝑅− 𝑁𝑎+ + 𝑅+ 𝐶𝑙 − + 𝐻 + +𝑂𝐻 −
𝐻 + + 𝑂𝐻 − ↔ 𝐻2 𝑂
• Hydrogen and hydroxyl ions from the resin react to form water
© Copyright 2017 – Rev 3
ELO 1.2
Operator Generic Fundamentals
10
Resin Regeneration
ELO 1.3 – Describe the process of demineralizer regeneration.
• Contains cation or anion resin
beads
• Generally two single-bed ion
exchangers used in series
– First is a cation bed
– Second is an anion bed
• Impurities are replaced with
– Hydrogen ions from cation
bed
Figure: Single-Bed Demineralizer
– Hydroxyl ions from anion bed
– Combine to form pure water
© Copyright 2017 – Rev 3
ELO 1.3
Operator Generic Fundamentals
11
Regeneration
• Resin bed becomes exhausted and not able to function at peak
performance
– Indicated by increased effluent conductivity
– Resin exchange sites will run out of enough mobile ions
– Impurities in outlet indicate resin exhaustion
• Restore resin bed ability to exchange ions
• Regeneration strips away impurities
• Chemicals used to reverse chemical process refreshing the resin bed
for further use
© Copyright 2017 – Rev 3
ELO 1.3
Operator Generic Fundamentals
12
Single-Bed Regeneration
Three-Step Process
1. Backwash – Water is pumped into the bottom of the ion
exchanger and up through the resin, fluffs resin, and washes out
entrained particles
2. Regeneration – Uses an acid solution for cation units and caustic
solution for anion units
3. Rinsing – Removes any excess regenerating solution
© Copyright 2017 – Rev 3
ELO 1.3
Operator Generic Fundamentals
13
Mixed-Bed Regeneration
Figure: Mixed-Bed Demineralizer Regeneration
© Copyright 2017 – Rev 3
ELO 1.3
Operator Generic Fundamentals
14
Mixed-Bed Regeneration
Mixed-Bed Demineralizer
• Normal operation
Regeneration Sequence
• Backwash
• Regeneration
• Slow rinse
• Vent and partial drain
• Final rinse
© Copyright 2017 – Rev 3
ELO 1.3
Operator Generic Fundamentals
15
External Regeneration
• Some mixed-bed demineralizers are designed to be regenerated
externally
– Resins removed from the vessel, regenerated, and then replaced
• Resin is sluiced with water (sometimes assisted by air pressure)
© Copyright 2017 – Rev 3
ELO 1.3
Operator Generic Fundamentals
16
External Regeneration
• Resins backwashed in cation tank to remove suspended solids and
to separate resins
• Anion resins are then sluiced to an anion tank
• Two batches of separated resins are regenerated by the same
techniques used for single-bed ion exchangers
• Then sluiced into a holding tank where air is used to remix them
© Copyright 2017 – Rev 3
ELO 1.3
Operator Generic Fundamentals
17
Changes in Demineralizer Operation
ELO 1.4 – Describe the following demineralizer conditions to include
causes, hazards, and corrective measures as applicable: excessive
differential pressure, channeling, excessive temperature, breakthrough,
leakage.
• Under normal operations, demineralizers and ion exchangers are
passive components that can process a portion of or total system
flow
• No moving parts and therefore not subject to mechanical failures like
a pump or motor, but internal components can fail or deteriorate and
affect performance
• Susceptible to effects of temperature, flow rate changes, and
chemical saturation
© Copyright 2017 – Rev 3
ELO 1.4
Operator Generic Fundamentals
18
Changes in Demineralizer Operation
• Differential pressure (D/P) across the demineralizer is a valuable tool
in assessing demineralizer operation
• Demineralizer filters suspended solids that cannot pass through the
resin and retention element
Differential Pressure
• More materials removed results in higher resistance to flow or D/P
– Low D/P could indicate demineralizer operating at a reduced
capacity
– High D/P could indicate clogging or the flow rate is too high
© Copyright 2017 – Rev 3
ELO 1.4
Operator Generic Fundamentals
19
High Flow Rate and Channeling
• Abnormally high flow rate could cause several problems
– Lower retention element clearances are designed to hold the
resin under normal conditions
– Resin beads could be forced through retention element
– Resin organic material could break down into small resin fines
– Conductivity could suddenly increase at demineralizer outlet
© Copyright 2017 – Rev 3
ELO 1.4
Operator Generic Fundamentals
20
High Flow Rate and Channeling
• Channels are developed under high flow rates
– Reduces ion exchange effective surface area
– Reduces mechanical filtration
• Creates a path of least resistance for fluid indicated by
– Decrease in differential pressure
– High outlet ion concentration and conductivity
© Copyright 2017 – Rev 3
ELO 1.4
Operator Generic Fundamentals
21
Excessive Temperature
• Exchange resin sites start to break down above 140°F
– Damaged resin smells like dead fish
– High temperatures cause resin to release boron
– Damaged resin increases the concentration of sulfate and
organics in the effluent
– Basic indication
o Contamination of effluent
© Copyright 2017 – Rev 3
ELO 1.4
Operator Generic Fundamentals
22
Breakthrough and Leakage
• Breakthrough – Ionic impurities in outlet indicate resin exhaustion
• Leakage – Small amounts of impurities pass through demineralizer
during normal operation
© Copyright 2017 – Rev 3
ELO 1.4
Operator Generic Fundamentals
23
Changes in Demineralizer Operation
Knowledge Check – NRC Question
A sudden increase in conductivity of water at the outlet of a
demineralizer will result from...
A. increased demineralizer flow rate.
B. reduced demineralizer inlet temperature.
C. reduced demineralizer inlet conductivity.
D. increased demineralizer effluent pressure.
Correct answer is A.
© Copyright 2017 – Rev 3
ELO 1.4
Operator Generic Fundamentals
24
Changes in Demineralizer Operation
Knowledge Check – NRC Question
What is the reason for bypassing a demineralizer due to high
temperature?
A. Resins expand and restrict flow through the demineralizer.
B. Resins decompose and restrict flow through the demineralizer.
C. Resins decompose and create preferential flowpaths through
the demineralizer.
D. Resins decompose and release resin particles into the flow.
Correct answer is D.
© Copyright 2017 – Rev 3
ELO 1.4
Operator Generic Fundamentals
25
Changes in Demineralizer Operation
Knowledge Check – NRC Bank
A condensate demineralizer differential pressure (D/P) gauge indicates
4.0 psid at 50 percent flow rate. Over the next two days, plant power
changes have caused condensate flow rate to vary between 25 percent
and 100 percent. Which one of the following combinations of
condensate flow rate and demineralizer D/P, observed during the power
changes, indicates an increase in the accumulation of corrosion
products in the demineralizer?
A. 100 percent flow, 15.0 psid
B. 75 percent flow, 9.0 psid
C. 60 percent flow, 5.0 psid
D. 25 percent flow, 2.0 psid
© Copyright 2017 – Rev 3
ELO 1.4
Operator Generic Fundamentals
26
Changes in Demineralizer Operation
Knowledge Check – NRC Bank – SOLUTION
To solve this problem, we must apply the pump law that flow rate is proportional
to the square root of the D/P. Therefore, you have to plug in the expected D/Ps
for each flow rate and find out which one exceeds the expected D/P.
At 100 percent flow, the D/P should be:
(100/50)2 × 4 = 16 psid
At 75 percent flow, the D/P should be:
(75/50)2 × 4 = 11.25 psid
At 60 percent flow, the D/P should be:
(60/50)2 × 4 = 5.76 psid
At 25 percent flow, the D/P should be:
(25/50)2 × 4 = 1 psid
Only the 25 percent flow rate has a higher than the expected D/P, and therefore
indicates that there is accumulation of corrosion products.
Correct answer is D.
© Copyright 2017 – Rev 3
ELO 1.4
Operator Generic Fundamentals
27
pH Effects on Demineralizer Use
ELO 1.5 – Explain how pH is affected by demineralizer use.
• Measure of acidity or basicity of
a solution
• Defined as cologarithm of
activity of dissolved hydrogen
ions (H+)
• Hydrogen ion activity coefficients
cannot be measured
experimentally
– based on theoretical
calculations
• pH scale is not an absolute
scale
Figure: pH Scale
© Copyright 2017 – Rev 3
ELO 1.5
Operator Generic Fundamentals
28
pH Effects on Demineralizer Use
• Exchanged mobile ions from resins are H+ and OH-
– Affect pH of fluid undergoing exchange
– Basic solutions will have an excess of OH- ions
– Acidic solutions will contain excess H3O+
• In mixed-bed demineralizers containing both resins, pH effect cancels
• In mixed-bed, a different type of cation resin is used to counteract
canceling effect
• Lithium form cation resin used with anion to form mixed-bed resin
• Mobile Li+ given up does not counteract OH- thereby increasing pH
• pH of solution can be controlled by ion exchange
© Copyright 2017 – Rev 3
ELO 1.5
Operator Generic Fundamentals
29
Decontamination Factor
ELO 1.6 – Describe decontamination factor and how it is calculated.
• Decontamination (demineralization) factor is used for determining
when resin bed is exhausted
• Decontamination factor (DF) is:
– inlet conductivity divided by outlet conductivity
• In some cases actual inlet and outlet conductivities are provided
– Otherwise, you must understand that 100% of the conductivity is
entering the demineralizer
– For example, determine the DF if 95% is being removed
o Inlet is 100%, outlet is 5% (95% being removed)
o DF = Inlet/Outlet; = 100/5 = 20
© Copyright 2017 – Rev 3
ELO 1.6
Operator Generic Fundamentals
30
Example – Decontamination Factor
• What is the DF and percent of
impurities removed for an ion
exchanger with condensate of
20 μmho/cm entering and 0.4
μmho/cm exiting?
𝐷𝑒𝑐𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟 =
𝜇𝑚ℎ𝑜𝑖𝑛
𝜇𝑚ℎ𝑜𝑜𝑢𝑡
𝐷𝑒𝑐𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟 =
20 𝜇𝑚ℎ𝑜𝑖𝑛
0.4 𝜇𝑚ℎ𝑜𝑜𝑢𝑡
𝐷𝑒𝑐𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟 = 50
% 𝑖𝑚𝑝𝑢𝑟𝑖𝑡𝑦 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 =
=
=
𝜇𝑚ℎ𝑜𝑟𝑒𝑚𝑜𝑣𝑒𝑑
× 100
𝜇𝑚ℎ𝑜𝑖𝑛
20 − 0.4 𝜇𝑚ℎ𝑜𝑟𝑒𝑚𝑜𝑣𝑒𝑑
× 100
20 𝜇𝑚ℎ𝑜𝑖𝑛
19.6 𝜇𝑚ℎ𝑜𝑟𝑒𝑚𝑜𝑣𝑒𝑑
× 100
20 𝜇𝑚ℎ𝑜𝑖𝑛
= 0.98 × 100
= 98%
© Copyright 2017 – Rev 3
ELO 1.6
Operator Generic Fundamentals
31
Demonstration – Decontamination Factor
• A demineralizer has been in service for 60 days. When first placed in
service, the decontamination factor was 200. Currently, the inlet and
outlet conductivities are:
– 35 μmho/cm entering
– 0.3 μmho/cm exiting
• What is the decontamination factor now, what percent impurities are
removed, and would you recommend regeneration?
• 35μmho/0.3μmho = 117
• Decontamination Factor = 117
• (35-0.3) μmho removed)/(35 μmho in) =0.99 x 100 percent
• impurities removed = 99 percent
© Copyright 2017 – Rev 3
ELO 1.6
Operator Generic Fundamentals
32
Demonstration – Decontamination Factor
The demineralizer is removing 99 percent of the inlet contaminants.
Although the decontamination factor has decreased to about 55
percent of the original value, it is still effective at removing unwanted
ions. The demineralizer should remain in service. Normally,
demineralizers are replaced or regenerated when the DF is 25 or less.
© Copyright 2017 – Rev 3
ELO 1.6
Operator Generic Fundamentals
33
Decontamination Factor
Knowledge Check – NRC Bank
The decontamination factor for ionic impurities of a demineralizer can
be expressed as...
A. inlet conductivity minus outlet conductivity.
B. outlet conductivity minus inlet conductivity.
C. inlet conductivity divided by outlet conductivity.
D. outlet conductivity divided by inlet conductivity.
Correct answer is C.
© Copyright 2017 – Rev 3
ELO 1.6
Operator Generic Fundamentals
34
Plant Evolutions that Affect
Demineralizer Operation
ELO 1.7 – Describe plant evolutions that could affect demineralizer
operation.
• During plant heatup or cooldown, coolant purification system's inlet
temperature can vary greatly
– May change suspended solids in coolant system and in turn affect
performance of resin bed
• Oil contamination is another potential hazard for demineralizers
© Copyright 2017 – Rev 3
ELO 1.7
Operator Generic Fundamentals
35
Crud Burst
• Crud burst is a release of a large amount of corrosion products in
reactor coolant system
• Operational events cause large amounts of solids to become
suspended within system
• Events that may cause a crud burst:
– Reactor scrams
– Cooldown
– Heatup
– Reactor coolant pump starts/stops
• Evolutions will tax demineralizer with excessive corrosion products,
resulting in increased pressure drop across demineralizer
• Effluent should be monitored during cleanup efforts
© Copyright 2017 – Rev 3
ELO 1.7
Operator Generic Fundamentals
36
Temperature
• Resin beads susceptible to damage at elevated temperatures
• Exchange sites break down around 140°F
• Proper procedures must be followed to ensure resin remains intact
• Damaged resin will give off an odor similar to dead fish
© Copyright 2017 – Rev 3
ELO 1.7
Operator Generic Fundamentals
37
Oily Water
• Oily water is another hazard for demineralizer resin beds
• Oil will affect exchange sites and render the resin ineffective
• Oil will create a film on the resin beads that will block or inhibit resin
exchange sites from performing their intended function since oil is an
organic compound
© Copyright 2017 – Rev 3
ELO 1.7
Operator Generic Fundamentals
38
Plant Evolutions that Affect
Demineralizer Operation
Knowledge Check – NRC Bank
A nuclear power plant was operating at steady-state 100 percent power
when the reactor coolant system experienced a large crud burst. After
20 minutes, the operators began to record parameters for the in-service
reactor coolant purification ion exchanger.
Assuming no additional operator actions, what trend will the recorded
parameters show during the next few hours?
A. Increasing flow rate through the ion exchanger
B. Increasing pressure drop across the ion exchanger
C. Increasing ion exchanger inlet water conductivity
D. Increasing ion exchanger outlet water conductivity
Correct answer is B.
© Copyright 2017 – Rev 3
ELO 1.7
Operator Generic Fundamentals
39
Saturated Demineralizer
ELO 1.8 – Explain the condition of a saturated demineralizer and the
effect temperature has on it.
• A demineralizer is saturated when the resin beads are loaded with
positive or negative ions
– Biases resin so it will have a reduced affinity for certain ions
– Occurs based on exposure of ion exchanger to an
overabundance of either hydroxyl or hydronium ions
• Saturating a resin bed effectively changes the affinity for ions of the
whole bed and can be used to buffer changes in coolant chemistry
© Copyright 2017 – Rev 3
ELO 1.8
Operator Generic Fundamentals
40
Boron Saturation
• During lower temperatures
– Borate ion bonding to the resin exchange sites contains three
boron atoms
• During higher temperatures
– Borate ion bonding to the resin exchange sites contains one atom
• Lower temperature resin will remove more boron and is more efficient
• Lowering the temperature of influent may increase the affinity for a
particular ion such as boron
• If temperature is increased, boron is released due to changed affinity
© Copyright 2017 – Rev 3
ELO 1.8
Operator Generic Fundamentals
41
Lithium-Saturated Demineralizer
• In PWR's, reactor coolant chemistry is maintained slightly basic to
inhibit corrosion
• A pH of approximately 6.8 can be achieved by maintaining a balance
between boron and lithium concentrations
• At beginning of core life, boron concentration is high; to balance pH,
must maintain the lithium concentration high
• Lithium hydroxide added to maintain pH value in alkaline range
• If ion exchanger was not saturated with lithium, it would rapidly
remove Li+ and release H+
© Copyright 2017 – Rev 3
ELO 1.8
Operator Generic Fundamentals
42
Saturated Demineralizer
Knowledge Check – NRC Bank
A nuclear power plant is operating at 70 percent steady-state power
level when the temperature of the reactor coolant letdown passing
through a boron-saturated mixed-bed ion exchanger is decreased by
20°F.
As a result, the boron concentration in the effluent of the ion exchanger
will ____________ because the affinity of the ion exchanger for boron
atoms has __________.
A. decrease; increased
B. decrease; decreased
C. increase; increased
D. increase; decreased
Correct answer is A.
© Copyright 2017 – Rev 3
ELO 1.8
Operator Generic Fundamentals
43
NRC KA to ELO Tie
KA #
KA Statement
RO SRO
ELO
K1.01 Effect of excessive differential pressure on demineralizer performance
2.3
2.5
1.4
K1.02 Effects of channeling in a demineralizer
2.1
2.3
1.4
K1.03 Reason for sampling inlet and outlet of demineralizer
2.2
2.5 1.2, 1.6
K1.04 Reason for demineralizer temperature and flow limits
2.4
2.4
K1.05 Principles of demineralizer operation
2.0
2.2 1.2, 1.5
K1.06 Demineralizer D/P to determine condition of demineralizer resin bed
2.1
2.5 1.4, 1.6
K1.07 Effects of demineralizer operation on water conductivity
2.1
2.2 1.2, 1.5
K1.08 Demineralizer characteristics that can cause a change in boron concentration
3.Z
3.1
1.7
K1.09 Reasons for bypassing demineralizers
2.5
2.7
1.4
K1.10 Reasons for using mixed-bed demineralizers to process primary water
2.1
2.3
1.2
K1.11 Plant evolutions which can cause crud bursts and the effect on demineralizers
2.5
2.8
1.7
K1.12 Definition of "boron saturated" as it relates to a demineralizer
2.7
2.9
1.8
K1.13 Definition of "lithium saturated" as it relates to a demineralizer
2.1
2.1
1.8
K1.14 Effect of temperature on saturated ion exchangers
2.4
2.6
1.8
© Copyright 2017 – Rev 3
1.4
Operator Generic Fundamentals