Purolite Ion Exchange Resins for Use in Nuclear Power

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

The ‘Wolff’ Paper – Apr 2012

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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.


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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.


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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 <0.1 ppb (µg/kg), while the level in systems is controlled at ≤ 1.0 ppb (µg/kg).

Silica is also of concern in steam generators. It easily complexes with metals such as aluminum and zinc to form zeolite compounds which will accumulate on heat transfer surfaces and undermine efficient heat transfer. Many nuclear plants have adopted a reactive silica limit for the makeup water of ≤10 ppb, which is consistent with INPO and WANO guidelines (2, 3). This concentration limit provides adequate protection, since the boiler water silica specification is ≤1,000 ppb, but preferably <300 ppb. Boroflex coated fuel racks used to store spent fuel in the spent fuel pool are a significant source of silica and contribute to primary coolant treatment issues particularly at start up after a refueling outage.

Total chloride and sulfate ion concentrations introduced into the systems, if not from system leaks, typically come from the ion exchange resins themselves. These impurities are present as a combination of inorganic (i.e., ionic) chlorides and sulfates and organically bound chloride (OBCl) and sulfate (OBS). The latter, i.e. the organic fraction, is not detected by ion chromatography (IC) in the makeup water since it is not ionized. These compounds degrade


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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 <0.5 ppb. Chloride is sometimes added back into the steam generator to help control caustic buildup (NaOH) in crevices.

Total Organic Carbon (TOC) or Total Organic Hetero-atoms (TOX), where X is typically chlorine, sulphur or nitrogen, come from resins as well as degradation products from chemicals used to treat the primary and secondary coolant systems. To determine concentrations of organically bound chlorine and organically bound sulphur, it is necessary to first analyze samples using IC, followed by a second IC analysis after the sample has been subjected to UV radiation. The latter result represents total chloride and total sulfate, which includes the organically bound portion of these compounds. The concentration of total organic hetero-atoms (TOX) is the sum of all the organically bound atoms.

Transport cask lowered into an unloading pool Source: World Nuclear Association


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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.


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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

Component Specification

Total Dissolved Solids <0.1 ppm

Total Fe and Cu <10 ppb

Chloride <5 ppb

O2 <10 ppb

pH 9.2 to 9.5

SiO2 <10 ppb

2. Condensate Polishing

Because the heat exchanger is built into the reactor and is difficult to reach, it is important to treat 100% of the condensate and eliminate corrosion byproducts and dissolved salts that could result from condenser leaks and makeup water. Morpholine and other special amines, along with ammonia, are used to adjust water pH to the target range of 9.2 to 9.5 to minimize corrosion. Since the system contains a small quantity of makeup water and the opportunity for blowdown is limited, even low levels of impurities in the feed water rapidly become a critical concern.

The condensate-polishing system recommended consists of a strong acid cation gel, NRW1140, to remove ammonia from condensate and a mixed bed, NRW3460, to complete the condensate-purification step. These resins can be regenerated onsite but non-regenerable resins are also available. These include the strong acid cation macroporous NRW160 and the mixed bed NRW3560.

Keep in mind that the condensate flowrate and volume can be considerable. For example, a 500-MW power plant has to treat 4,000 m3/h (17,000 gpm) of condensate.

3. Turbo-blowers

Turbo-blowers are fans designed to keep carbon dioxide circulating through the reactor core to the heat exchangers. Each turbo-blower is driven by a steam pump using plant steam. Each steam turbine has its own condenser and the condensate must be treated with the same main condensate treatment resins described above.

4. Spent Fuel Ponds

Waste fuel is stored under water in spent fuel pools or ponds. This pond water contains radioactive elements, including Cesium 137, which must be removed using mixed bed ion exchange resins. NRW3560, is a mixture of macroporous cation resin (NRW160), which has a high affinity for cesium, and a gel anion (NRW600). NRW3550, which can also be used for this application, is a mixture of the macroporous cation and anion resins (NRW160 and NRW5050).


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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 – 320oC 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).


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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% 6Li+ and 93% 7Li+), or purified lithium (99.5% 7Li+). Natural lithium is notably less expensive but has the disadvantage of producing tritium by neutron capture of 6Li+. Purified 7Li+ 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 B11 and B10. B10 is a powerful neutron absorbent and changes into 7Li+ via a nuclear reaction known as radiolysis. Thus, the 7Li+ concentration is maintained within the circuit proportionally to the boric acid concentration.


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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 6Li+ and purified 7Li+ 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


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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


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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 B10 absorbs neutrons and changes into 7Li+ 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

4. Radwaste Effluent Treatment

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.

Cleanup Bed Activity

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

NRW400 NRW5010

uS

v/h

Top

Middle

Bottom


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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


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resins 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 <2 ppb, residual sodium <0.02 ppb, residual TOC <1.5 ppb. When the final polishing UCW mixed bed is removed from service, it can be used as a regenerable resin elsewhere in the plant, but not returned to final polishing.

When makeup water is from a surface water source, such as lakes, reservoirs or rivers, it may contain colloids, especially colloidal silica. Colloidal silica is difficult to remove by conventional filtration and ion exchange. Once it enters the steam generator, pressure and temperature convert into ionic silica which can form deposits on the steam generator and volatilize and deposit on the steam turbine. NRW5010 effectively removes colloidal silica from water and prevents it from entering the steam generator. If required, this targeted treatment step is best used in a stand-alone vessel following filtration pretreatment and regeneration with caustic.


Treatment of condensate is essential for extending steam generator life. The goal is to remove iron and other corrosion elements in order to prevent deposits in the secondary circuit. In general, secondary chemistry is tightly controlled to maintain measurable iron levels below 0.8 ppb. Polishing resins are operated at high flow velocities up to 122 m/h (50 gpm/ft2). They are expected to remove ions such as sulfate to <0.2 ppb. This is especially true during condenser leaks.

Proper selection of materials of construction is critical in minimizing corrosion in condensers. Special metals such as titanium are typically used, especially in the case of seawater cooling. Condenser manufacturing techniques are sometimes considered to be so complex that the risk of leakage has become theoretically negligible. This too has allowed many plants to minimize condensate polishing operation, however this represents risk.

There are different ways to control secondary corrosion. First, secondary circuits are conditioned with hydrazine to remove trace oxygen. Second, condensate and steam generator water pH is maintained within a range of 8.8 to 10.5. This is done by the use of amines with the more common being ammonia, MPA (methoxy propylamine), and/or ETA (ethanolamine). The use of amines, especially ETA, can significantly reduce the formation and transport of iron-based corrosion products.

Although favorable in reducing corrosion, this amine chemistry approach is suspected of negatively impacting condensate polishing resins by drawing foulants from the cation resin, fouling the anion resin and reducing kinetics. Theoretically ETA displaces (cleans) organo-sulfonates from the cation resin. These, in turn, accumulate on anion resin surfaces, thereby impairing kinetics. When anion resin becomes kinetically impaired, sulfate levels begin to increase in the steam generator. Therefore, anion resin kinetics must be monitored


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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 (<20mg/Kg). The mixed bed will operate past the amine break to a sodium break depending on operating conditions. The run time may be as long as 6 months.

2. Regenerable mixed bed polishing resins are the strong acid cation SGC650 and the strong base anion gel SGA550 or the macroporous anion PFA503OH. This mixed bed only system is also operated past the amine break to a sodium break. Conservative operations will operate only to the amine break.

3. Non-regenerable mixed beds NRW3562 and NRW3672


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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


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break 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.


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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


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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 <0.085 µS/cm

pH 6.8 to 7.2

Fe <0.8 ppb

Na <1.0 ppb

Si02 <5 ppb

Cl <0.20 ppb

SO4 <0.5 ppb

02 <10 ppb

Metals <0.80 ppb


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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.


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.


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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-2mRem. 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.


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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 600oC 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.


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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

Cation: NRW1100, NRW1160 Anion: NRW6000, NRW7000, NRW5050 MB: Supergel ™SGC650H, Supergel™SGA550OH 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 blowdown

PWR Cation: NRW160, NRW1160 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


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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


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resin 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.


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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)

Mixed bed with gel type SAC NRW3260

Mixed bed with macroporous type SAC

NRW3560

Bed Volumes Treated

DF for Cs 137

DF for Co 58

DF for Cs 137

DF for Co 58

11,000 3

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.


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SECTION 4: REFERENCES

References

The following references were reviewed:

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”

Documents

Purolite Ion Exchange Resins for Use in Nuclear Power