nuclear ion exchange resin - Purolite.com

ION EXCHANGE RESINS
FOR USE IN NUCLEAR
POWER PLANTS
Original by J.J. Wolff
Revised and Updated
January 2012
Limerick Nuclear Generating Station
Source: US NRC file photo

Special Thanks:
The original author of this paper, Jean-Jacques Wolff, was born on April 23, 1930.
He first studied Chemistry and then Bio-technology. He worked in the sugar and
sweetener field of the food industry prior to joining a growing producer of ion
exchange resins, Duolite, in the early 1960’s. There he progressed quickly to
become Technical Manager.
Following the acquisition of Duolite by Rohm and Haas in June 1984, he decided
to reinforce the technical team of a new fast-growing manufacturer of ion
exchange and adsorbent resins called Purolite International. There he brought
his deep expertise in the Nuclear Industry, mainly to Électricité de France.
Jean-Jacques Wolff was well known and appreciated by his clients all over the
world, especially in Asia. He was an excellent open minded colleague and during
his life developed many new purification processes.
Jean-Jacques Wolff was married and had two sons. He passed away on 25th
November 1992.
The ‘Wolff’ Paper – Apr 2012
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Table of Contents
INTRODUCTION Page 3
SECTION 1: NUCLEAR POWER GENERATION Page 4
A. Nuclear Fission
B. Controlling the reaction
C. Nuclear Industry Water Quality Guidelines
D. System Contaminants
SECTION 2: TYPES OF REACTORS & WATER TREATMENT CIRCUITS Page 8
A. Graphite-Gas Reactor (AGR) Page 8
Graphite-Gas Reactor Treatment Circuits
1. Makeup Water
2. Condensate Polishing
3. Turbo-blowers
4. Spent Fuel Ponds
B. Pressurized Water Reactors (PWR) Page 11
PWR Primary Circuit Treatment
1. Reactor Coolant Purification
a. Outage Clean-up Beds
b. pH Control (CVCS)
c. Outage Activity
2. Deboration
3. Spent Fuel Ponds (SFP)
4. Radwaste Effluent Treatment
PWR Secondary Circuit Treatment Page 19
5. Makeup water Treatment
6. Condensate Polishing
7. Steam Generator Blowdown Treatment
C. Boiling Water Reactors (BWR) Page 24
BWR Circuit Treatment
1. Makeup water Treatment
2. Condensate Polishing
3. Reactor Coolant Purification
4. Spent Fuel Pool Treatment
5. Radwaste Treatment
D. Fast Breeder Reactor (LMFBR) Page 28
SECTION 3: NUCLEAR ION EXCHANGE RESIN Page 29
1. Nuclear Quality Resin
2. Operating Capacity
3. Decontamination Capacity
SECTION 4: REFERENCES Page 33
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1. INTRODUCTION
Nuclear power plants are currently operated in 31 countries with 15 more countries currently
planning the construction of their first nuclear power plants. Nuclear power generation will
continue to grow as a strategic option due to the increasing cost of fossil fuel based energy
and the pressure to reduce greenhouse gases.
Ion exchange resins — in both bead and powder form — are used extensively in all types of
nuclear power plants throughout the world. Ion exchange systems are the most cost
effective and in some cases the only way to produce water with the quality required for
proper plant operation.
Ion exchange plays a vital role in the elimination of soluble chemical components that
contribute to corrosion as well as removing corrosion products and radioactive isotopes from
the different coolant circuits. The objective of controlling these chemistries is to protect the
nuclear generating systems from corrosion, extend the system life and maintain a safe
working environment in and around the plant.
The purpose of this paper is to review the different types of nuclear reactors that are in use
today, and explain in some detail the important role that ion exchange systems (and ion
exchange resins) play in the different nuclear applications.
Worldwide nuclear power plants
Source: Targetmap.com
Note: All Purolite products referred to in this paper are Purolite® unless specifically noted.
The ‘Wolff’ Paper – Apr 2012
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SECTION 1: NUCLEAR POWER GENERATION
A. Nuclear Fission
Nuclear fission is a process in which a nucleus of an atom splits to form free neutrons and
protons while producing a tremendous amount of energy in the form of heat. The atom splits
because it is bombarded by slow moving neutrons that briefly are absorbed by the nucleus
(neutron and proton) and cause it to change. New lighter elements are formed (fission
products) as well as free neutrons. As more neutrons are produced when the atoms split, the
reaction becomes self-sustaining. The new neutrons collide with other nuclei. Isotopes of
Uranium and Plutonium have historically been used because they can sustain this chain
reaction and are called fissionable materials.
Today, nuclear fuel is natural or enriched uranium in the form of UO2 pellets. These pellets
are fitted into sealed sheaths made of steel, zirconium or magnesium alloys called fuel rods.
These fuel rods are arranged into bundles or elements in a very specific geometric manner.
Based on the diameter of the rods, the elements are gathered into vertical or horizontal
columns at an optimal distance apart. This increases the probability of neutrons meeting with
a 235U nucleus, thereby inducing nuclear fission. The neutron flux is the term used for rate of
reaction inside the reactor. The heat emitted during fission in the reactor core is transferred
to a coolant that can be a liquid (water, heavy water or liquid sodium) or a gas (CO2). This
heat is used to boil water and create high pressure steam in a secondary closed system. This
steam is used to drive a steam turbine and generate electricity.
B. Controlling the Reaction
In order to control the reaction, the fuel bundles are typically immersed in materials that act
to moderate (moderator) neutrons or retard (retarder) the production of neutrons. A
moderator is a medium that reduces the speed of fast neutrons to control the nuclear
reaction. These include solid graphite, light water or heavy water. The reactor casing is
made of steel and clad in a thick wall of concrete which provides a shield against radiation.
After the reactor starts up, neutron production progressively increases and slow neutrons
may behave in one of several ways.
1. Enter a 235U nucleus and induce fission, yielding heat and other neutrons
2. Disappear by diffusion through the reactor casing
3. Be reflected by the reactor casing
4. Be absorbed by:
a. Various structural materials
b. Control rods: They are designed to reduce the neutron flux and are made of
materials with a high-neutron-absorbing capacity, such as silver, indium and
cadmium.
c. A neutron absorbent such as boric acid.
d. Poisons manufactured into the fuel assemblies
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The relationship between these processes must be precisely managed to achieve optimal
control of the reactor. When a state of equilibrium is reached the reactor is said to be critical
or that it has diverged.
During the life of the reactor fuel, the concentration of 235U, and therefore the neutron flux
rate, decreases. The accumulation of fission products causes parasitic absorption of neutrons
which further decreases neutron flux. In order to compensate for these effects, control rods
are progressively removed during operation or the concentration of adsorbent in the
moderator is reduced.
If the production of neutrons falls below the critical level that is required to produce energy,
the fuel must be replaced in a refueling outage. This occurs during a scheduled shutdown in
which a portion of the fuel rods are replaced and the remaining rods are rearranged.
Refueling outages are typically carried out every 18 to 24 months for most reactor designs.
Several reactor designs allow operators to change fuel while the facility is still generating
power.
Figure 1:
Source: World Nuclear Association
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C. Nuclear Industry Water Quality Guidelines
Although the nuclear industry does not regulate the type or quality of ion exchangers used in
nuclear plant operations, it does establish guidelines on makeup water, primary chemical
volume control, and shutdown chemistry, as well as secondary chemistry coolant that impacts
condensate polishing, and steam generator blowdown quality. These guidelines strongly drive
the selection and specification of resins by nuclear operations to maintain consistent quality
and cleanliness within circuits.
Individual nuclear power companies set specifications for resins purchased for the different
plants. However, these are generally based on resin manufacturers’ specifications. The level
of impurity on the resins is established by the resin manufacturer or service company based
on achievable post-processing capabilities.
Make-up water chemistry parameters have been referenced by the Institute of Nuclear Power
Operations’ (INPO) Chemistry Guidelines, the World Association of Nuclear Operators
(WANO), and the Electric Power Research Institute (EPRI) Chemistry Guidelines. All
emphasize the importance of maintaining extremely low contaminant concentrations in the
makeup water and minimizing corrosion products and trace impurities from coolant water
and condensate streams. The most critical chemistry parameters listed in the referenced
reports are: Key ionic species such as sodium, fluoride, chloride, sulfate and nitrate ions and
specific conductivity. While the first four ions are common, nitrate is not normally present in
significant concentrations. A specific conductivity limit ≤ 0.08 �S/cm measured at 25°C must
be maintained or conversely, a resistivity value ≥ 12.5 MΩ/cm must be maintained.
D. System Contaminants
During operation, sodium will concentrate in crevices and points of evaporation, resulting in
high sodium alkalinity which contributes to stress corrosion cracking in steam generator tubes
and on turbine components. The sodium specification for nuclear makeup water is normally

thermally or radiolytically in the system, producing chloride and sulfate ions, which
potentially reduce the water pH and lead to intergranular corrosion (IGC) and stress corrosion
cracking. The typical allowable level of sulfate in the steam generator is 1.50 ppb and the
allowable level of chloride is

SECTION 2: TYPES OF REACTORS & TREATMENT OF CIRCUITS
A. The Graphite-Gas Reactor (Figure 2)
The Graphite-Gas Reactor was one of the first types to be introduced and quickly became the
main backbone for the nuclear industry in the United Kingdom. Initial designs were the
Magnox and later the AGR (Advanced Gas Cooled Reactor) system. The AGR design operates
at higher temperatures, which requires certain design modification to accommodate the
elevated temperatures. Today, most of the Magnox designs are no longer in operation, but
there are several AGR designs still in successful commercial operation. All of these operate
with two reactors in a single structure, and use uranium as the fuel.
In the reactor core, the fuel rods are located inside a block of graphite that acts as a
moderator. The coolant is pressurized CO2, which passes through the reactor core removing
heat. This heated CO2 stream is used to produce steam, which drive turbine generators that
generate electricity as part of the overall power plant.
Figure 2: Magnox Reactor Schematic
Source: English Wikipedia.
Today’s highly regulated nuclear power plants are considered to be safe, and produce
relatively low amounts of radioactive waste material. One of the primary advantages seen
with the graphite-gas design is their ability to allow for the online replacement of fuel
elements. However, operating difficulties make Graphite-gas reactors commercially less
attractive to build and have restricted widespread use of this design.
The ‘Wolff’ Paper – Apr 2012
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Graphite-Gas Reactor Treatment Circuits (Figure 3)
Ion exchange is used to treat four circuits in a Graphite-Gas nuclear plant. They are the
makeup water, the returned condensate, the turbo blower and the spent fuel pool.
Figure 3:
1. Makeup water
Almost all AGR units operate their own make up treatment systems. However service
providers are available to support makeup requirements with service trailers. These systems
commonly employ pre-filtration followed by reverse osmosis (RO) technology with a final,
high-purity mixed bed polisher. Nuclear power plants that continue to own and operate their
own makeup water-treatment systems will generally use standard resins that produce
high-quality water but also have good regeneration efficiency.
The following resins configured in the order shown can be used to demineralize the makeup
water for AGR Reactors:
� NRW100 strong acid cation exchanger
� PFA100 weak base anion exchanger
� NRW400 strong base anion exchanger
� NRW3240 for polishing mixed beds
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This combination of resins will produce water with conductivity below 0.1 µS/cm and less
than 10 ppb of Si02. The makeup water recommended purity is specified in Table 1.
Table 1: AGR Makeup Water Specifications
2. Condensate Polishing
Component Specification
Total Dissolved Solids

B. Pressurized Water Reactor (PWR) (Figure 4)
The Pressurized Water Reactor (PWR) is the most widely used nuclear power generation
design and has achieved great success worldwide. The reactor core heats the surrounding
pressurized water (the primary circuit or coolant) and the water circulates to a steam
generator where it transfers its heat to a secondary water system. Steam at approximately
900psig is created and is sent to a steam turbine to generate electricity. The advantage of
this system is that the radioactive sections (the reactor and primary circuit) are separate from
the rest of the power plant. Such separation helps to control and minimize potential
contamination risks.
PWR’s use enriched UO2 (between 2.0 and 4.95 wt. %) in pellet form as fuel. In a 900 MW
power plant, the reactor uses up to 72 tons of uranium per year. These pellets are contained
inside zirconium alloy sheaths (Zircalloy) to form a rod. In a typical design, approximately 200
of these fuel rods are bunched together to form a bundle or element. Depending on its
capacity, a reactor core can contain from 150 to 200 rod bundles which are arranged for
optimum heat generation.
Figure 4: Pressurized Water Reactor
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Source: US Nuclear Regulatory Commission
The coolant running through the reactor core is purified water and is given the term “light
water”. Acting as both a heat transfer fluid and a moderator, it is heated to 290 – 320 o C and
maintained under a pressure of 150 bar (2,200 psi). The neutron flux rate can be controlled
by varying the concentration of boric acid dissolved in this primary circuit water and by
moving the control rods up and down. However, typical operation has the control rods
almost completely withdrawn to maximize fuel burn-up. Large water pumps circulate the
pressurized water through the steam generators, which function as heat exchangers. Certain
PWR reactor designs such as the Candu system use “heavy water”. This is water highly
enriched in the hydrogen isotope deuterium. Deuterium has a proton and a neutron in the
nucleus whereas hydrogen has only a proton. Other than the moderator, the basics of the
Candu reactor are the same as the PWR described herein.
The PWR was originally designed in the United States by Westinghouse’s Bettis Atomic Power
Laboratory for military ships. Westinghouse, Asea Brown Boveri-Combustion Engineering
(ABB-CE), Framatome, Kraftwerk Union, Siemens, and Mitsubishi have typically built this type
of reactor throughout the world. Babcock & Wilcox (B&W) built a PWR design but used
vertical once-through steam generators rather than the U-tube design used by the rest of the
suppliers. Industry consolidation has occurred so that Framatome-Areva-NP, Westinghouse,
Mitsubishi and Toshiba are the key remaining manufacturers. Such reactors, especially the
Westinghouse AP1000 and the Areva EPR designs, are expected to be widely used in the years
to come and will constitute a major portion of the world’s nuclear power generation
programs in the foreseeable future.
PWR Treatment Circuits
The PWR is composed of two entirely separate circuits: Primary (Figure 5) and secondary
(Figure 8).
Primary Circuit Treatment
Ion exchange is used to treat four circuits within the primary circuit in a PWR nuclear plant.
They are the reactor coolant purification system, deboration, spent fuel pool and radwaste
effluent.
The primary circuit water is in direct contact with the reactor fuel. It acts as coolant and
moderator. Impurities from the makeup water and corrosion products that are exposed to
the core become radioactive and thus require special treatment. Primary circuit water
transports heat from the fuel bundles and helps to cool the fuel. This water, although high in
boron and, to a much lower level, lithium, must be clean and free of soluble and suspended
corrosion matter that will collect on the fuel rods. In addition, inorganic salts of sodium,
sulfate, and chloride must be controlled to minimize corrosion in the granular structure of the
fuel rod sheaths and system metal surfaces. Two types of corrosion can occur: Intergranular
Corrosion (IGC) or Stress Corrosion Cracking (SCC). Corrosion byproducts will foul fuel and
contribute to irregular burning known as axial anomalies or Crud Induced Power Shift (CIPS).
The ‘Wolff’ Paper – Apr 2012
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These corrosion byproducts will become activated isotopes that release as crud bursts during
cool down periods of outages. These buildups and releases can potentially damage fuel
sheaths and contribute to fuel leaks and support Crud Induced Localized Corrosion (CILC).
To further minimize colloidal and dissolved impurities, corrosion-resistant materials with
special alloys, such as Zircaloy, Inconel and stainless steel are utilized. It must be noted,
however, that stainless steel is sensitive to the presence of chloride in the water. Today,
special corrosion-resistant stainless metals, such as Alloy690TT and Alloy 80Mod, are being
used to replace current steam generators to minimize source term and extend unit life.
Source term is latent radiation that builds up in the system and must be controlled.
The pH of the primary water is typically maintained between 6.9 and 7.4 at 300°C or coolant
average temperature. This may change depending on materials of construction, water
chemistry and system design. If necessary, it is adjusted up by adding lithium hydroxides.
Lithium can be natural lithium, a mixture of two isotopes (approximately 7% 6 Li + and 93% 7 Li + ),
or purified lithium (99.5% 7 Li + ). Natural lithium is notably less expensive but has the
disadvantage of producing tritium by neutron capture of 6 Li + . Purified 7 Li + is the principal
lithium isotope used in a large majority of PWR’s worldwide.
The pH of the primary water must be maintained at the specified level and adjusted based on
the water temperature. Reactor pH (temperature corrections of 0.2 to 2 units) is adjusted
down by removing lithium. Boric acid is used to slow down neutrons. When a power plant
starts up, the concentration of boric acid is typically 1,500 ppm as B. As the nuclear fuel
activity decreases, the concentration is reduced progressively until low concentrations are
reached by the end of the fuel life cycle. However, the plant may need to increase or decrease
the boric acid concentration in order to adjust the power supply at a given moment. Natural
boron is a combination of B 11 and B 10 . B 10 is a powerful neutron absorbent and changes into
7 Li + via a nuclear reaction known as radiolysis. Thus, the 7 Li + concentration is maintained
within the circuit proportionally to the boric acid concentration.
The ‘Wolff’ Paper – Apr 2012
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Figure 5: PWR - Primary Circuit Treatment
1. Reactor Coolant Purification
The primary circuit coolant water is treated exclusively by the Chemical-Volume-Control
System (CVCS). This system consists of 2 to 4 ion exchange vessels that remove ionic
impurities, control pH by adding lithium or removing lithium, control activity by adding or
removing boron and remove radioactivity. During full power, one vessel loaded with lithiated
cation and borated anion mixed bed resin (Li:B) is operated to control low-level ionic
impurities and temperature-adjusted pH. All anions are borated from boron in the primary
coolant. Some plants are designed with Boron Thermal Regeneration Systems that can add or
remove boron. Near the end of the full power cycle the RFO (Refueling Outage) cleanup bed
will be loaded and may be borated during intermittent operation.
Mixed bed resins used in the CVCS include NRW3460 and NRW3560 (both available in natural
6 Li + and purified 7 Li + forms). If a greater capacity is required to remove Co58, Co60 and Cs137,
the mixed bed can be layered with macroporous strong acid cation NRW160. Some systems
will have a separate cation bed available in the event that additional cation control is
required.
All ion exchange resins used for primary coolant purification have a quality rating and must
meet specific criteria for nuclear purity. If not, there will be a risk of impurity leaching. Studies
have shown that in presence of 3,000 ppm boric acid and 2 ppm lithium, an anionic resin
containing 800 mg chloride per kg of dry resin produces water containing approximately 50
ppb chloride. Therefore, low-chloride anionic resins must be used — that is, with less than
The ‘Wolff’ Paper – Apr 2012
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0.1 % of total active sites with chloride, or approximately 200 mg per kg of dry resin. Special
attention should also be paid to the silica content in anionic resin, as silica found on the
anionic resin is easily displaced by boric acid and can end up leaching into primary coolant.
a. Outage Cleanup Beds
Near the end of a power cycle prior to a scheduled shutdown a mixed bed is loaded with H +
form cation, OH - form anion (H:OH) and layered resins for refueling cleanup. These resins
replace the previous outage bed resins which have been sluiced to a spent resin tank (SRT).
This bed may be operated intermittently prior to end of cycle to remove residual lithium and
borate the anion. This becomes an H:B bed. During the refueling outage (RFO) this bed will
remove corrosion isotopes that are released during the shutdown and forced oxygenation.
This is to minimize personal contamination and dose while work is being done on the primary
system.
Chemical adjustments to the primary system carried out shortly after shutdown are, by design,
intended to force significant levels of radioactivity, both soluble and insoluble, into the
coolant stream. These adjustments include controlling the hydrogen concentration to
maintain a reducing phase followed by the addition of hydrogen peroxide to create an
oxidizing phase. Iron solubility increases in the reducing phase while nickel solubility increases
in the oxidizing phase. The addition of hydrogen peroxide will cause iron to precipitate.
These steps force corrosion and radioisotopes from the reactor surface and crevices of fuel
bundles. Steam generators may or may not be isolated during the cleanup, however if
recirculating coolant pumps (RCP) remain on, more activity will be released from these areas.
Ion exchange beds and filters are designed to reduce radioactive contaminants to EPRI’s
action level of 5.0E-2 µCi/gm before outage activities can begin.
Due to limited flow of one cleanup bed, it is common for the Li:B bed used during full power
to operate with the H:B layered bed in parallel. This literally doubles the cleanup rate. If
pump capacity allows, some plants will have only the layered cleanup bed in service and
double the service flow. The objective of operating at double the flow is to reduce the time
required to reach the required action level. This operation works well when CVCS and cleanup
beds are used only one cycle.
Refueling outage (RFO) beds are CVCS beds used to clean the primary coolant during an
outage. RFO beds are loaded with a special configuration (layering) of resins to reduce both
soluble and insoluble isotopes. For instance, RFO beds typically have 20cf of nuclear mixed
bed NRW3560 loaded on the bottom, 5cf of high capacity, macroporous cation NRW160 in
the middle and 5cf of macroporous anion NRW5010 or NRW5070 to cap the top. The bottom
layer of NRW3560 consists of high-capacity cation (NRW160) and anion resins (NRW600) to
polish the coolant. The middle layer of NRW160 is used to remove soluble metals such as
cobalt, cesium, iron, nickel and other metal ions in the coolant water. The top layer of
NRW5010 or NRW5070 will effectively filter very fine particulates – colloids - that commonly
pass through the cleanup mixed beds. This macroporous anion layer at the top of the bed is
efficient at removing particulates below 0.1 µm in size, which would otherwise plug or bypass
standard operating filters. Use of these macroporous anions will also favorably impact
radwaste cleanup, by lowering the post-filtration dose and allowing smaller effective size
The ‘Wolff’ Paper – Apr 2012
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filters (0.1 µm) to be used during outage activities, reducing the number of filters used, and,
to a limited extent, assisting in the reduction of source term within the primary system.
Currently there is a push to reduce nuclear waste because of lack of storage sites. Resins are
now being used in more than one cycle. Originally the NRW5010 product was considered to
be too fragile and not possible to be loaded on full service bed, but with the development of
the stronger macroporous anion NRW5070, full power beds can be layered and used for
possibly 2 cycle’s without concern of bead failure. Cleanup beds however may not be good
candidates for multiple outages due to the high level and type of loading they encounter.
b. pH control
As mentioned earlier, pH is adjusted upward by adding lithium hydroxide and downward by
removing lithium. Since B 10 absorbs neutrons and changes into 7 Li + there may be an excessive
increase in lithium in the circuit. This concentration is controlled by routing the mixed bed
effluent (primarily Westinghouse systems) into a separate CVCS vessel loaded with strong
acid cation resin NRW160 to remove excess lithium.
c. Outage Activity
When the reactor cavity coolant has reached the specified activity level the reactor coolant
pumps (RCP) are stopped, steam generators isolated and the reactor head is lifted. From this
point the cavity is flooded with water from the reactor or refueling water storage tank (RWST)
and refueling begins. This creates a large pool where fuel bundles are manipulated under
water. Some bundles are moved to a spent fuel pool through a refueling canal and
continually remain submerged. Once the refueling has been completed, the reactor water is
returned to the RWST or released to the radwaste stream for processing before discharge.
The discharged water is termed primary effluent and includes primary circuit let down (water
released from primary system to be replaced with water of a different boron concentration)
and the various liquid waste streams originating from the radioactive sections of the power
plant. These waters contain lithium and boron in addition to a large variety of radioactive
isotopes. The effluents are filtered before being treated by ion exchangers. Usually the resin
train consists of activated carbon, natural zeolite, a strong acid cation exchanger H + form
(NRW160, NRW1100, NRW1000), followed by mixed bed resins (NRW3240 or NRW3260). The
strong acid cation exchanger removes lithium, cobalt, cesium etc. Fluoride and antimony are
generally the difficult species to remove.
2. Deboration
The term deboration is related to ion exchange systems that will remove boron in a controlled
manner. The deboration system removes residual boric acid remaining in the first part of the
waste stream by ion exchange before passing to the radwaste processing system. The system
may consist of an evaporator or a reverse osmosis system which produces a highly
concentrated boron solution. The solution, according to its quality, is either recycled back to
the primary circuit or directed to a treatment system for solid effluent. Permeate containing
boron may be treated with nuclear grade strong base anion exchanger (NRW6000 or
NRW7000).
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The capacity of the anion resin for boron will vary proportionally with the boric acid in the
evaporator effluent or RO permeate. When the boron concentration increases, the anion
resin operating capacity will increase. When boron is about 100 ppm, the operating capacity
of the anion will be about 40 grams of boric acid per liter of resin.
3. Spent Fuel Pool (SFP) Treatment
There are generally three pools in a nuclear power plant: the reactor water cavity (RWC), the
spent fuel pool (SFP) and the reactor water storage tank (RWST). The RWC is the pool created
when the reactor cavity is flooded with water from the RWST. RWC completely covers the
reactor dome and allows for fuel to be moved to and from the reactor while being covered
with water. The RWST tank is used during the entire cycle to refill the RWC during the outage,
the SFP and during an emergency shutdown, and to refill the Cold Leg Accumulators (CLA).
The CLA is a pressure vessel that will discharge, in the event of pressure loss, high borated
water into the cold leg piping feeding the reactor vessel and assists in the shutdown of the
nuclear reaction. The SFP is connected to the RWC by a fuel-transport canal. Fresh fuel is
stored in the SFP prior to an outage and exhausted fuel is stored in the SFP after its useful
service.
Purification of the RWC and the SFP is carried out by a spent fuel pool demineralizer, which
uses a mixed bed of strong acid cation resin and strong base anion resin (NRW3560 or
NRW3670). Peroxide generated by radiation from the exhausted fuel contributes to oxidative
attack on the cation resin, which results in the release of sulfates. Fuel pools with a higher
percentage of spent fuel will have greater issues with this resin degradation than others. The
highly cross-linked macroporous cation resin NRW160 (found in NRW3560 and NRW3540),
gel cation NRW1160 (NRW3660) and NRW1180 tolerate this oxidative condition better than
lower cross linked resins. This allows for a longer service life before sulfates in the pool water
requires resin replacement.
Figure 6: Oxidative stability of Purolite cation resin in a peroxide environment
Maintaining the clarity of both the reactor water and spent fuel pool water is crucial.
Sediments are easily disturbed during fuel movement causing clarity to deteriorate and
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turbidity and radiation levels to increase. Use of the macroporous anion resins NRW5010 or
NRW5070 assist in reducing turbidity and associated radioactivity when layered on top of the
mixed bed resin. Additionally, if fuel bundles are moved from the fuel pool and transported to
dry storage in special storage casks, the SFP demineralizer with an NRW5010 layer on the
mixed bed removes fine particulates that collect on metal surfaces. This significantly reduces
the task of decontaminating casks prior to moving them to storage.
Figure 7: Activity buildup on anions used for RFO cleanup
uSv/h
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
4. Radwaste Effluent Treatment
Cleanup Bed Activity
NRW400 NRW5010
The radwaste system collects all effluents from the power plant, such as active and inactive
blowdown and wash water. Depending on the ionic load, a mixed bed may be used alone
(NRW3240) or in a train consisting of a strong acid cation exchanger (NRW160) followed by
the mixed bed. However, it has been found that a number of radioactive products are present
in colloid form (this is the case with ions in association with Co58 and Ag 110, in particular)
and therefore are not captured by conventional resins. Adding a layer of the macroporous
anion resin NRW5010 or NRW5070 on top of either the strong acid cation bed or the mixed
bed will effectively address this type of contaminant.
The conventional radwaste mixed bed resin may be replaced with the higher-capacity mixed
bed, NRW3560. It should be noted that the resins used for the treatment of wastewater do
not necessarily have to be nuclear quality since this water is to be released into cooling ponds
under the guidelines of the Off-site Dose Calculation Manual (OCDM) following treatment.
They must however be highly regenerated to maximize loading of activity.
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Middle
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Secondary Circuit Treatment
Ion exchange is used to treat three circuits within the secondary circuit in a PWR nuclear plant.
They are the makeup water, returned condensate and steam generator blowdown.
The secondary water circuit generates steam which is fed directly to the turbines and is non –
radioactive. It is possible for it to become radioactive if a leak in the steam generator
develops or a small amount of tritium passes through the steam generator. The system feed
water consists of condensate return, steam generator blowdown and demineralized makeup.
This water must have a high purity. During full power, the makeup water system will
compensate for blowdown losses and any possible leaks.
Figure 8: PWR Secondary Circuit Treatment
5. Makeup Water Treatment
Many makeup water treatment systems have moved to build, own and operate (BOO)
generally consisting of clarification or ultra-filtration (UF), carbon filters, reverse osmosis (RO)
technology, electronic deionization (EDI), followed by polishing using mixed bed ion exchange
systems. This approach allows plants to move away from chemical-based regeneration,
which contributes to plant waste. This approach also minimizes frequent replacement of
service DI trailers. These makeup systems are commonly operated by offsite contract
suppliers.
When resins are used to treat makeup water, they must be highly regenerated and specially
processed to meet tight specifications for chloride, sulfate, sodium, iron and TOC (also known
as “POC” or purgeable organic carbon). Regeneration is generally carried out offsite.
NRW3240 can be used as a polisher in makeup systems. This mixed bed resin is composed of
The ‘Wolff’ Paper – Apr 2012
19

esins that are characterized by high total capacity and selectivity for influent cations such as
sodium, and anions such as silica and chloride. This resin is also easily regenerated to a high
level of conversion with minimal release of impurities.
As a final polishing step before water enters the deionized water storage tank (DWST), a
non-regenerable, high-purity mixed bed resin, such as UltraClean UCW9964 may be used.
For a “less separable” mixed bed, UCW9966 can also be used. The makeup water quality will
achieve 17.9 MΩ, residual silica

closely and when effectiveness decreases, the resins must be replaced. They should be
replaced even if the ionic operating capacity has not been depleted completely. Plants using
ETA-naturalizing amines may require a cation resin that has been specially manufactured and
post treated to minimize foulants that degrade anion kinetics.
Condensate polishing, which removes corrosion products and in-leakage, is accomplished
primarily with deep mixed bed polishers and less frequently with precoat filters. Precoat
filters are vessels that have several filter elements that are coated with a layer of powdered
resins and are typically used where steam condenser water has a relatively low salinity and
when the risk of leakage is considered small. When plants use fresh water for cooling,
deep-bed condensate polishers are operated during startup or upset conditions. When plants
cool with brackish or salt water, the deep beds are operated continuously.
Care is required to ensure that the steam generator receives high-purity water containing
0.02 ppb of Na + , Cl - and SO4 - , as these dissolved solids will concentrate in the steam generator
as steam is produced. A small number of PWR plants regenerate their condensate-polishing
resins. However, the level of purity required from the polishing resin is critical and
regenerating this resin to achieve levels where sodium, chloride and sulfate do not leach is
often difficult to attain. Special efforts must be taken to ensure proper separation of resins,
minimize cross-contamination and minimize residual ions from regeneration remaining in the
resins. These ions are Na + on the strong acid cation and carboxylic groups that may form on
the anion resin (See papers by Auerswald (7) and by Crone (8) ). Polishing systems that are not
regenerated will operate intermittently to extend the resin life. Once these
condensate-polishing resins begin breaking on amine, the condensate-polishing resins must
be replaced. A small number of condensate polishers do operate past the amine break,
however, these plants have extremely high purity secondary systems and no cooling water
leakage.
The following Purolite deep-bed demineralizer resins are recommended for condensate
polishing:
1. Non-regenerable polishers will use the strong acid macroporous cation exchanger
NRW160, or gel NRW 1160, followed by the complimentary mixed bed NRW3560, or
NRW3670. This system has a lead strong acid cation exchange resin which removes
unwanted cations, corrosion products, ammonia, and amines. The H + and OH - polishing
mixed bed captures traces impurities and supports longer unit run times. This system is
capable of operating the lead cation past the amine break and possibly to a sodium
break as long as sodium on the cation (and anion) is low (

4. A non-regenerable mixed bed with 1:1 cation-to-anion ratio by volume addressing
elevated amine chemistries is NRW3561 or 2:1 cation to anion by volume NRW3562.
Items 3 and 4 above generally require the service cycle to stop at the ammonia break
resulting in approximately 2–4 weeks service. If service continues beyond the ammonia
break to a sodium break service time will be greater, approximately 6 weeks, but Na+
leakage to the hot well will also be higher.
Precoat filters (elements) are coated with a mixture of strong acid cation exchanger in H +
form (Microlite PrCH) or an ammonia-form exchanger (Microlite PrCN) and a strong base
anion exchanger in OH - form (Microlite PrAOH). Precoat filters have a relatively limited
capacity for removing soluble salts and thus become rapidly exhausted in the event of a
condenser leak. However, powdered resins have an inherent advantage over bead resins in
that they have less capital cost associated with precoat facilities than a regeneration system.
Furthermore, filtration of corrosion products is more efficient with powdered resins than with
bead resins.
Precoat products are available premixed as mixed bed products, without fiber (Microlite MB)
and with fiber (CG range). If precoats exhaust on pressure drop due to excess corrosion or
crud, precoat with fiber may allow extended runs.
7. Steam Generator Blowdown Treatment
The steam generator blowdown (SGBD) is required to maintain water quality within specified
EPRI Secondary Water Chemistry Guidelines. SGBD is designed to remove and control
dissolved solids in the steam generator, which can build up from 50 to 200 times higher than
those concentrations in the makeup feedwater. The blowdown stream can be routed either
to waste or to a demineralizer. Waste blowdown is sent to radwaste or to cooling lagoons if
no radioactivity is present. Demineralized blowdown is typically returned to the condensate
storage tank (CST), where it contributes to makeup water. Dissolved solids entering steam
generators are primarily amines (MPA, ETA), ammonia, and hydrazine along with low levels of
sodium, sulfate and chloride. Concentrations in the steam generator are low ppm levels for
amines and low ppb or sub ppb levels for inorganic salts. If leakage from the primary circuit
occurs, radioactivity will be removed by the blowdown demineralizer resins, which will then
require disposal as low-level radioactive (Class A) waste or blown down overboard and
quantified per the ODCM.
A blowdown demineralizer system generally consists of two vessels: A strong acid cation
exchange resin in the lead vessel and a mixed bed of strong acid cation and strong base anion
in the second vessel. Blowdown resins require high purity cation and anion resins, both of
which have low levels of sodium and TOC. High-capacity cation resins, generally macroporous
NRW160 or gel NRW1160 with very low sodium (20g/kg), are typically used to control sodium
in the steam generation. Using low-sodium and high-capacity cation resins, the cation bed can
be operated past the amine break as long as there are no leaks, which allows the cation bed
to be operated 3–4 times longer than cation beds operated only to the amine break.
Plants with any kind of condenser leak must operate only to the amine break. Plants that use
ammonia and morpholine have more experience operating past the amine break to a sodium
The ‘Wolff’ Paper – Apr 2012
22

eak compared to plants using ETA. High cross-linked macroporous cations resins operated
in the low sodium form will result in only a slight sodium excursion when the amine break is
reached. However, sodium levels will drop back after a short time and be maintained at low
levels until the sodium break occurs. Low-level sodium released from the lead cation will be
removed by the downstream mixed bed (NRW3560 or NRW3670). The mixed bed following
the cation bed may also be operated past an amine break to a sodium break. However, the
sodium break is much sooner (typically occurring in a matter of weeks) compared to what is
often experienced on the cation bed (several months). For plants with higher ammonia and
amine levels, use of a mixed bed resin with a higher cation capacity may add additional bed
life. NRW3562 has a 2:1 cation-to-anion ratio by volume, which provides approximately 4.2:1
equivalence cation-to-anion.
The ‘Wolff’ Paper – Apr 2012
23

C. Boiling Water Reactor (BWR) (Figure 9)
The Boiler Water Reactor (BWR), originally designed by General Electric and Idaho National
labs, is the second most widely used type of light-water reactor. GE Hitachi Nuclear Energy is
the main current manufacturer of this type of reactor.
The BWR has a single circuit, which is used to supply steam directly to turbines. The drawback
of the system is the presence of radioactivity in the steam. This requires a more robust
protection system for the entire circuit. The fuel used in the BWR is similar to the fuel used
for a PWR but the fuel rods have a larger diameter and the bundles contain only about 50
sheaths.
The moderator and coolant water temperature reaches 286°C at the core. The water is
maintained at a pressure of only 70 bars (1000 psig) where it is transformed into steam.
Consequently, the reactor itself acts as the steam generator.
Similar to the PWR, periodic fuel replacement requires the power plant to be shut down for
two to six weeks, after approximately 18 – 24 months of service.
Figure 9: Boiling Water Reactor Configuration
Source: US Nuclear Regulatory Commission
The ‘Wolff’ Paper – Apr 2012
24

BWR Treatment Circuits (Figure 10)
The Boiling Water Reactor (BWR) reactor serves as a steam generator (9) , which means the
whole circuit is radioactive and the water must be of very high purity. Ion exchange is used
to treat five systems in a BWR nuclear power plant. They are the makeup water, returned
condensate, spent fuel pool, reactor coolant purification and radwaste treatment.
Figure 10: BWR Treatment Circuits
1. Makeup Water Treatment
The specifications for makeup water indicated by General Electric Company are shown in
Table 2.
Table 2: GE Makeup Water Specifications
Component Specification
Conductivity

As in the case of other reactors, regenerable ion exchange resins are typically used to produce
demineralized water that meets the required quality of the plant, while non-regenerable,
highly regenerated mixed beds are used for final polishing. These final polishing mixed bed
resins are re-used in regenerable vessels after they are exhausted.
Many nuclear units rely on service companies to supply makeup water in order to minimize
the handling, storage and use of treatment chemicals and the production of chemical waste
streams onsite.
2. Condensate Polishing
Condensate polishing is one of two methods to control purity of the BWR coolant after
makeup polishing. This polishing is primarily accomplished by using precoat filters only on
freshwater cooled units and deep bed ion exchange vessels for brackish and salt water cooled
units.
Units that rely on low-salinity cooling water commonly use precoat filters with powder resins
(Microlite PrCH, PrAOH, MB and CG range). Although powdered resins have a disadvantage
of rapid exhaustion in the event of a condenser leak, they do present the following
advantages:
� Lower capital cost because regeneration facilities are not required
� Good filtration of corrosion products. For instance, the quantity of suspended
matter in treated condensate is only a few ppb, and will generally be
controlled under 0.8 ppb at the filter outlet, even when startup levels of inlet
impurities (such as iron and copper) may be on the order of several ppm
� Powdered resins are used once and therefore are a minimal risk of
deteriorating chemically, even at relatively high temperatures. It is thus
possible to install the precoat filters after one of the low-pressure heat
exchangers, to improve filtration. Consequently, powder-form resins are very
widely used in BWR power plants in many countries
In brackish and saltwater-cooled systems, resins in bead form used in deep-bed polishers are
primarily high-capacity gel form resins. However, macroporous exchange resins offer
exceptional selectivity for cobalt-60 and iron compared to gel-type resins. Macroporous
anion resins also have a greater affinity for particulate iron compared to gel resins. Mixed
beds with an equivalent cation-to-anion ratio are preferred. Compared to the precoat
polisher, deep-bed polishing systems ensure several hours of operation in the event of a leak
in the cooling condenser.
After the polishing step, condensate is sent directly to the reactor through the makeup line.
Condensate polishing must both demineralize the stream and filter corrosion products, which
are predominately iron.
Note: No chemical condensate conditioning (amines) or reducing chemistry are used in BWR
systems.
The ‘Wolff’ Paper – Apr 2012
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3. Reactor Coolant Purification
The reactor water or coolant purification system is the primary system for cleaning the
reactor coolant. Reactor coolant water becomes charged with radioactive corrosion products
during the power cycle, therefore it becomes necessary to remove impurities prior to a
refueling outage. This is achieved by diverting water through the suppression pool
demineralizer. The suppression pool is a large reservoir located below the reactor that
supplies cooling water for outage activity and in the event the reactor water pumps fail. This
demineralizer is loaded with a mixed bed ion exchange resin in equivalent ratios. Mixed beds
with macroporous type bead resins (NRW3560) layered with a macroporous anion NRW5010
or NRW5070 have proven to be more effective for iron cleanup than gel resins. Cycling of
reactor coolant is stopped when activity drops below 5.0E -2 mRem. Additionally, the
decontamination factor drops to low levels (single digits), which generally occurs when >90 %
of cobalt, copper, iron as well as other elements have been removed. Submersible
demineralizers also increase effectiveness with a similar resin configuration.
Cleanup systems that use only powdered precoat resins have had success using a precoat
mixed resin CG125H which has a blend of macroporous cation resins for removal of metals
such as copper. Microlite precoat products used for RWC demineralizers include MB1:1H and
CG1:1H.
4. Spent Fuel Pool Treatment
The exhausted or spent fuel is stored in large pools of cooling water to remove residual heat.
This coolant becomes loaded with radioactive isotopes, primarily cobalt-60, that are released
from the fuel bundles with low levels of iron. These pools must be treated to control clarity
and remove activity. As noted above, suppression pool demineralizers and/or submersible
demineralizers are used for this cleanup and are loaded with mixed bed resins such as
NRW3560 or NRW3660. Also, topping these beds with NRW5010 or NRW5070 facilitates
cleanup. Powdered resins MB1:1H, CG1:1H and CG125H are also used in the RWC
demineralizers to clarify these fuel pools.
5. Radwaste Treatment
Service water and wasted coolant from BWR operations must be treated to ensure that no
radioactivity is released. Radioactivity originating from the plant is treated with mixed bed
ion exchange resins to reduce activity to a level that is appropriate for release back to the
environment. The mixed bed resin that is most appropriate for this application is NRW3240.
If pretreatment clarification is not employed, the addition of a top layer of the macroporous
anion NRW5010 or NRW5070 will significantly improve the removal of suspended colloids
such as activated iron. Contract companies are often used to provide this waste-treatment
service.
The ‘Wolff’ Paper – Apr 2012
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D. Fast breeder reactor (fast neutrons) (Figure 11)
In a fast breeder reactor or more recently named liquid metal fast breeder reactors (LMFBR),
splitting atoms generates more fissionable material (fissile) than it consumes. LMFBR’s are
able to reduce nuclear fuel requirement by two orders of magnitude compared to an LWR
that uses less than 1% of the U235 in the fuel.
Breeders use mixed oxide fuels (MOX) composed of primarily of U238 and other minor
Actinides (i.e., Plutonium, Americium and Curium). The typical design of the fast breeder
begins with the center of the reactor core coated with impoverished uranium (238U). The
initial fuel, 235U, harnesses the fast neutrons emitted by the impoverished 238U and
becomes 239Pu. The active isotope production rods are replaced approximately every week
and the 239Pu is extracted to be used once more in the same or in another power plant.
The coolant in an LMFBR (commonly liquid sodium) is operated at a temperature of
approximately 600 o C and the reactor is enclosed within a concrete protection shield. The fact
that this temperature can be maintained virtually without any pressure allows the use of
sheaths barely 0.5 mm thick. The liquid metal coolant does not limit the neutron energy from
U235. Unlike a PWR or BWR which uses water as a moderator, the neutrons emitted by the
fission of active nuclei are virtually not slowed down.
Figure 11: Liquid Metal cooled Fast Breeder Reactor
Source: English Wikipedia.
In spite of its advantages, the LMFBR has gained limited interest due to shorter fuel life,
higher operating cost and a plentiful supply of uranium fuel. Government regulations related
to reprocessing Pu239, which is a weapons grade isotope, has limited the number of
operating LMFBR to 20 units worldwide.
To ensure better safety, the primary circuit transfers its heat to a secondary circuit, which also
contains liquid sodium. The steam generator is part of the tertiary circuit. As you can see, an
LMFBR offers limited ion exchange resin opportunities.
The ‘Wolff’ Paper – Apr 2012
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SECTION 3: NUCLEAR ION EXCHANGE RESIN
1. NUCLEAR RESIN QUALITY
Ion exchange resins used in nuclear power plants (Table 3) are quality rated and must meet
nuclear-grade specifications that are established by plant chemical engineers. These quality
specifications establish limits on low levels of residual inorganic and organic constituents
found in the resin that remain after resin manufacturing. Resins designed to treat radwaste
although not requiring the high degree of cleanliness, do require a high degree of conversion
to the regenerated form so that the operating cycle can maximize resin loading.
Table 3: Purolite Resins for Nuclear Circuits
Circuit Type of reactor Ion Exchanger Resin
Condensate Graphite-gas reactors,
PWR
The ‘Wolff’ Paper – Apr 2012
Cation: NRW1100, NRW1160
Anion: NRW6000, NRW7000, NRW5050
MB: Supergel SGC650H,
SupergelSGA550OH
Microlite®: PrCN-PrAOH, CG-MB range
BWR Deep Bed MB: NRW3670
Microlite®: MB1:1H
Turbo-blower Graphite-gas reactors Cation: NRW1000, NRW1100
Anion: NRW4000, NRW6000
MB: NRW3240, NRW3460
Spent fuel pool Graphite-gas reactors Anion: NRW5010, NRW5070
MB: NRW3560, NRW3660, NRW3860
PWR-BWR Anion: NRW5010, NRW5070
MB: NRW3560
Steam generator PWR Cation: NRW160, NRW1160
blowdown
MB: NRW 3560, NRW3660
Primary coolant
purification (CVCS, RCV)
PWR Cation: NRW160, NRW1100
Anion: NRW5010, NRW5070
MB: NRW3560, NRW3460, NRW3562
pH control PWR MB: NRW3560(Li/Li7), NRW3460(Li/Li7)
Refueling Outage (RFO) PWR Cation: NRW1160, NRW160
Anion: NRW5010, NRW5070
MB: NRW3240, NRW3560
Radwaste PWR-BWR Cation: NRW1000, NRW160
Anion: NRW5010, NRW5070
MB: NRW3240
29

2. OPERATING CAPACITY OF RESINS
The operating capacity of nuclear-grade ion exchange resins, whether in bead form or powder
form, is a function of the impurities to be removed from the influent, the amount of ionic
leakage tolerated, the concentration of ions remaining on the resin treating the influent after
regeneration, and the pH of the influent stream. If exchange conditions are favorable (low
velocity), the operating capacity of new nuclear-grade ion exchange resins should be close to
the total capacity. However, given the fixed time of a power generating cycle, resins are
generally sacrificed well before they reach useful exhaustion. This is particularly true with the
CVCS resins because of its relatively light service.
The use of boric acid as a neutron moderator in PWR primary units is an exception to the ion
exchange resin capacity explanation above. Levels of boron will be in the thousands of ppm
therefore the use of boric acid will convert anion resins to the boron form in a short time.
Because of polyborate formation resulting from high concentrations and pH changes in the
anion bed, the concentration of boron on the anion resin will rise in proportion to boron
concentrations in the influent stream. Thus the capacity of an anion exchange resin for boric
acid increases with increased boron concentrations.
Resins used to treat the water in the spent fuel pool will reach the end of life sooner than
resins in other systems because the cation component of the mixed bed will degrade in the
presence of peroxide releasing organo-sulfonic compounds. Energy from fuel will support
radiolysis of water forming peroxide and hydrogen. Organo-sulfonic compounds will foul the
anion resin and leach into the pool where they will subsequently degrade to sulfate. A
sufficient rise in sulfate generally requires this resin to be replaced. Higher cross linked gel
and macroporous cation resins have been employed to extend mixed bed resin life with
limited success. Concentration of fuel volume and temperature of pool water are related to
cation resin life.
Condensate polishing resins are subjected to high linear flow rates. Thus, they are prone to
ionic leakage and kinetic fouling of the anion. Resins used to polish BWR condensate streams
will operate until the conductivity (sodium break) or silica break occurs or the radioactivity
limit on the bed is exceeded. BWR plants will not regenerate their resins so replacement with
new resin is required.
Resins used to polish PWR condensate resins are impacted by multiple chemistries being fed
to the steam generator. The presence of different amines at different concentrations will
quickly load the resin. Ammonia will compete with ions left on the resin, so if the cation resin
has residual sodium generally above 40 ppm, the resin will need to be replaced at the amine
break. If the cation resin has sodium < 20 ppm, it is possible to operate these resins for many
months past the ammonia break. Anion fouling by organo sulfonates or ionic leakage of
sulfate or silica from the anion will generally determine resin replacement or regeneration.
Regeneration of PWR condensate is challenging in order to meet the low ionic sodium and
chloride leakage required; therefore, service companies are often contracted to provide this
service offsite.
Resins used to treat steam generator blowdown encounter the same issues as the condensate
The ‘Wolff’ Paper – Apr 2012
30

esin but at a lower flowrate because of higher concentrations of dissolved solids in the
generator. Additionally, this resin is designed to primarily remove sodium, metals, chlorides
and sulfate. Because of the competition between sodium and ammonia, the resins are
replaced when sodium leakage reaches a design level. Resin life can be as long as two years
for very clean systems, but generally the life expectancy of resins in this service is between six
weeks and six months. However, systems that are susceptible to condenser leaks may be
changed every two weeks. There are a few plants that regenerate their steam generator
blowdown resins. This is generally done for a lead cation resin. When the mixed bed exhausts
both cation and mixed bed resins are replaced.
Makeup resins are regenerable and these resins may last many years depending on influent
water impurities. Service companies supply these resins under contract.
3. DECONTAMINATION CAPACITY
Resin capacity for radioactive isotopes is defined by the decontamination factor (DF), which is
influent radioactivity divided by effluent radioactivity. This capacity depends on the nature
and concentration of radioactivity isotopes being addressed and the density of functional
groups on ion exchange resins used. Table 4 (below) presents relative affinities (ion
selectivity) for cobalt and cesium, compared with lithium and hydrogen, for different degrees
of cross-linking.
Table 4: Ion selectivity for principal soluble cations on varying cross-linked cation resins
DVB% 4% 8% 12% 16%
Li 0.9 0.85 0.81 0.74
H 1.0 1.0 1.0 1.0
Co 2.65 2.8 2.9 3.05
Cs 2.0 2.7 3.2 3.45
Table 4 shows that the affinity for cesium over H + and Li + ions increases with the cross-linking
of the strong acid cation exchange resin, while the affinity for cobalt is slightly lower than
cesium. Therefore, an exchange resin with high DVB (divinyl benzene) cross-linking has higher
removal rates — and therefore a longer cycle for removing cesium (NRW160) — compared to
the mixed beds containing this component (NRW3560 and NRW3540(Li/Li7). High
cross-linked macroporous cation exchange resins have greater porosity, which allows higher
molecular weight divalent ions greater access to the active sites within the bead.
By contrast, highly cross-linked gel-type exchanger resins have a tighter matrix, and thus
insufficient porosity. This results in lower operating capacity. However, certain higher
cross-linked gel resins may have a greater capacity for smaller molecular weight ions, such as
lithium and sodium, compared to comparable cross-linked macroporous resins.
The ‘Wolff’ Paper – Apr 2012
31

Table 5 presents results of tests carried out on coolant purification (primary circuit)
containing lithium and boric acid. The tests compared a mixed bed resin with a gel type strong
acid cation NRW3260 (normal cross-linkage) and a mixed bed resin with a macroporous type
strong acid cation NRW3560 (high cross-linkage). The average influent was Co58 1.0E -3
µCi/cm, Cs137 3.0E -1 µCi/cm.
Table 5: Decontamination Factors (DF)
Bed Volumes
Treated
Mixed bed with
gel type SAC
NRW3260
DF for
Cs 137
11,000 3
DF for
Co 58
The ‘Wolff’ Paper – Apr 2012
Mixed bed with
macroporous type SAC
NRW3560
DF for
Cs 137
DF for
Co 58
33,000 1 61 32 127
Note: The DF are averaged over total treated volume.
The DF increases when the concentration of activity increases in the solution. The DF will vary
noticeably during the cycle and as the influent concentration changes.
32

SECTION 4: REFERENCES
The following references were reviewed:
References
1. EPRI, Fruzzetti, K.P. et al., Pressurized Water Reactor Secondary Water Chemistry
Guidelines, Revision 6, EPRI, Palo Alto, CA: 2004. 1008224
2. WANO, Guidelines for Chemistry at Nuclear Power Plants, WANO GL 2001 – 08, August
2002
3. INPO, Guidelines for Chemistry at Nuclear Power Stations, INPO 88-021, Rev. 02, October
1995.
4. EPRI, Passell, T. O., Effect of Organics on Nuclear Cycles, EPRI TR-100785, Project 2977-08,
July 1992
5. McGaffic V.J., and Bishop W.N., Nuclear Power Plant Water Quality in the 1990s – An INPO
Perspective, ASTM STP 1102, Philadelphia, 1991.
6. OPG’s REVIEW OF TOC AND TOX AS MAKEUP WATER PARAMETERS, Makeup Water
Specifications, October 6, 2005.
7. Auerswald, D.C., “20 Years of Condensate Polishing at San Onofre Nuclear Generation
Station,” IWC 07-61 International Water Conference, Oct. 2007.
8. Crone, L., “Amine form operation of deep bed condensate polishing ion exchange resins”,
IWC 10-02, October 2010
9. “Boiler Water Reactor (BWR) System,” USNRC Technical Training Center Reactor Concept
Manual, 0400.
10. IAEA.org “Current Trends in Nuclear Fuel for Power Reactors”
The ‘Wolff’ Paper – Apr 2012
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