Corrosion and Water Chemistry Control in Nuclear Power Plants, Exams of Nursing

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EPRI Chemistry Test/ Chemistry Test EPRI Exam Lesson 5,

6, & 7 with All Questions and Answers

The following are the purpose of:

• Protect the reactor coolant system pressure boundary integrity
• Protect fuel cladding integrity and fuel performance Minimize out-of-core radiation fields
• Minimize corrosion of all secondary plant and auxiliary system components - ANSWER >> Properly Controlled Power Plant Chemistry Program Dense nucleus includes protons (+) and neutrons (0) surrounded by dense cloud of electrons in describe orbits (known as shells) - ANSWER

General Atomic Structure atom that is electrically neutral; aka = amount of protons & electrons - ANSWER >> ion positively charged ions - ANSWER >> Cations negatively charged ions - ANSWER >> Anions atoms with same # of electrons in outermost shell will have similar ______ - ANSWER >> properties atoms want to complete their outermost shell by having how many electrons(in the outermost shell)? - ANSWER >> 8 how many electrons does the first shell of an atom need to be complete? - ANSWER >> 2

measure of number of electrons that an atom can give up to leave a completed outermost shell - ANSWER >> Positive Valence measure of number of electrons that an atom can take in to have a completed outermost shell - ANSWER >> Negative Valence Atoms don't want to give up/take in more than how many electrons? - ANSWER >> 4 What type of chemical bonding transfers electrons? - ANSWER >> Ionic Bond What type of chemical bonding shares electrons? - ANSWER >> Covalent Bond All reactions must be _________; reactants must be accounted for in products - ANSWER >> Balanced What type of chemical reaction is when a substance gains electrons? AKA GER - ANSWER >> Reduction Reaction What type of chemical reaction is when a substance loses electrons? AKA LEO - ANSWER >> Oxidation Reaction GER stands for - ANSWER >> Gains Electrons Reduced LEO stands for - ANSWER >> Loses Electrons Oxidation The agent that supplies electrons is the? - ANSWER >> Reducing Agent The agent that takes away lost electrons is the? - ANSWER >> Oxidizing Agent

What type of chemical reaction can show how electrons transfer into and out of individual reactants/ products? - ANSWER >> Half-Cell Reactions What are the 3 factors that affect reaction rates? - ANSWER >> Temperature, Catalyst, Concentration What happens to the reaction rate if you increase the temperature? - ANSWER >> increases The presence of a catalyst in a chemical reaction increases the rate at which ________ occurs? - ANSWER >> reaction What forms an intermediate product with 1+ of reactants which lowers activation energy for other reactants; intermediate product breaks up and releases uncombined ______ and combined products? - ANSWER

Catalyst Increasing concentration of reactant also results in greater chance of other reactants colliding with ______ reactant - ANSWER >> Original rate of chemical reaction is directly proportional to _________ of its reactants - ANSWER >> Concentration a compound that increases concentration of positively charged hydrogen ions (H+) (and hydronium ions (H30+)) when dissolved in water - ANSWER >> Acids a compound that increases concentration of negatively charged hydroxyl ions when dissolved in water (OH-) - ANSWER >> Bases Acids have a pH balance ______ than 7 - ANSWER >> less

Bases have a pH balance _____ than 7 - ANSWER >> greater measure of acidity or alkalinity of a solution - ANSWER >> pH When pressure is reduced and exposed to the atmosphere what happens to the gases in the solution? - ANSWER >> Escape Affects solubility and can be defined by various gas laws? - ANSWER >> Pressure When _______ of solution is near freezing/ boiling, gases are less soluble? - ANSWER >> Temperature What is an example of temperature affecting gas in solutions? - ANSWER >> leaving a carbonated drink in the sun, causing it to go flat Corrosion products, material design, leaks, make up water impurities, chemical addition impurities, and maintenance activities (such as poor FME or improper use of chemicals) are all sources of? - ANSWER >> Impurities What are problems of impurities? - ANSWER >> Corrosion, fouling, plugging, mechanical binding, and radiation dose Some impurities move with steam in systems but most stay in liquid phase of _________? - ANSWER >> Boiling Process When impurities stay in liquid phase of the boiling process, they concentrate to levels high enough to cause problems like? - ANSWER >> scale, corrosion, flux tilt the inevitable process of metal finding something that will accept is unwanted electrons - ANSWER >> Corrosion

Uniform attack on a metal surface by its environment; corrosion rate is uniform over entire surface of metal - ANSWER >> General Corrosion The following factors influence:

• Increasing Temperature
• Increasing Dissolved Oxygen
• Decreasing pH
• Increasing Flow
• Shocks and Stresses - ANSWER >> General Corrosion Rates As temperature rises, corrosion generally _____ - ANSWER >> increases Increasing dissolved oxygen also increases _______ potential - ANSWER

electrochemical sudden change in pH level can dissolve passive layer or add H+ ions to increase corrosion rate - ANSWER >> Chemical shock temp change that causes metal to expand/ contract causing defects in passive layer - ANSWER >> Thermal shock caused by fluid forces that may remove passive layer - ANSWER >> Hydraulic shock may remove passive layer - ANSWER >> Mechanical shocks/stresses can increase corrosion, remove the protective layer and allow corrosion to proceed - ANSWER >> Shocks and Stresses Can increase general corrosion rate due to the following:

• Transport of oxidants to corroding surface is increased

• Proper formation of a passive metal oxide layer is prevented or oxide film is removed Metal surface is eroded - ANSWER >> Increasing flow The following are ways general corrosion can be _________:
• Controlling Dissolved Oxygen Content
• Maintaining Neutral/ Slightly Basic pH
• Using Corrosion Inhibitors - ANSWER >> minimized The following are a type of ______ corrosion:
• Galvanic Corrosion
• Crevice Corrosion
• Pitting
• Stress Corrosion Cracking (SCC)
• Intergranular Attack
• Microbiologically Influenced Corrosion (MIC)
• Flow Accelerated Corrosion
• Boric Acid Corrosion - ANSWER >> Localized What type of localized corrosion is caused by dissimilar metals placed in electrical contact.? - ANSWER >> Galvanic Corrosion What type of localized corrosion is caused by a difference in the concentration of impurities inside a crack or crevice? - ANSWER >> Crevice Corrosion What type of localized corrosion is a localized electrochemical attack occurring in the vicinity of local irregularities in a metal that form a localized anodic area? - ANSWER >> Pitting What type of localized corrosion is caused by a combination of temperature, stress, corrosive environment, and a susceptible material? - ANSWER >> Stress Corrosion Cracking

What type of localized corrosion occurs when the corrodent attacks the bulk material? - ANSWER >> Transgranular cracking (TGSCC) What type of localized corrosion occurs when the grain boundary is more susceptible; BWRs, conductivity (primarily from chloride and sulfate ions) is a strong factor? - ANSWER >> Intergranular cracking (IGSCC) What type of localized corrosion occurs when a corrodent attacks the grain boundaries without sufficient stress to cause cracking? - ANSWER

Intergranular Attack (IGA)

What type of localized corrosion is a combination of stress, susceptible microstructure, and temperature are sufficient for cracking to occur even in pure water environments with no specific corrodent? - ANSWER

primary water stress corrosion cracking (PWSCC) What type of localized corrosion caused by relatively high flow rate at corroding surface

• typically impacts carbon steel in slightly basic water under reducing conditions
• also turbulent flow conditions increase? - ANSWER >> Flow Accelerated Corrosion (FAC) What type of steel is resistant to boric acid? - ANSWER >> stainless What type of localized corrosion occurs when leaks from primary systems through gaskets, mechanical joints, valve packing, or cracks à significant corrosion can develop; water becomes oxygenated and boric acid can concentrate as water boils off/ evaporates? - ANSWER >> Boric Acid Corrosion

What factors influence galvanic corrosions? - ANSWER >> interface between two dissimilar metals What factors influence crevice corrosions? - ANSWER >> leaking occurring on outside of piping What factors influence pitting? - ANSWER >> stagnant water What factors influence Stress Corrosion Cracking and Intergranular Attack? - ANSWER >> synergistic interaction of temperature, tensile stress, a corrosive environment, and susceptible materials What factors influence Microbiologically Influenced Corrosion (MIC)? - ANSWER >> Untreated water, High purity water, stagnant, low, or intermittent flow conditions (standby and redundant systems) What factors influence Flow Accelerated Corrosion (FAC)? - ANSWER >>

• reducing conditions
• high flow rates
• turbulent flow What factors influence Boric Acid Corrosion? - ANSWER >> water leaks from primary systems through gaskets, mechanical joints, valve packing, or cracks...greatest leakage is wastage: form of uniform corrosion The following are ways which localized corrosion is minimized?
• Preventing ELECTRICAL contact b/w dissimilar metals and minimizing conductivity of electrolyte
• Exercise caution when using dissimilar metals in same system
• Cathodic protection (sacrificial anodes) - ANSWER >> Galvanic Corrosions

The following are ways which localized corrosion is minimized?

• Control dissolved oxygen concentration and water impurities
• Identify/ correct any leaks on pipes - ANSWER >> Crevice Corrosion The following are ways which localized corrosion is minimized?
• Controlling dissolved oxygen concentrations/ water impurities
• maintain FLOW of components (typically occurs when water is stagnant) or place component in service regularly - ANSWER >> Pitting The following are ways which localized corrosion is minimized?
• avoiding stagnant conditions
• eliminating nutrient source(s)
• periodically cleaning systems to remove organic deposits
• using BIOCIDES to kill bacteria - ANSWER >> Microbiologically Influenced Corrosion (MIC) The following are ways which localized corrosion is minimized?
• Increase pH and a small increase in oxygen concentration can lower corrosion product solubility - ANSWER >> Flow Accelerated Corrosion (FAC) The following are ways which localized corrosion is minimized?
• Boric Acid Control programs that ensure all boric acid leakage is identified and problem is documented - ANSWER >> Boric Acid Corrosion Makeup water sources, such as lakes, rivers, or oceans Leaks between system interfaces, such as heat exchangers Foreign material that entered the system during maintenance, such as packaging material, tools, chemicals, or even sweat Degradation of components due to corrosion or wear Different materials used in replacement parts and equipment

Are all _____ of impurities? - ANSWER >> sources Clogging of filters and/or small pipes Fouling of heat exchangers Higher radiation levels, due to activation of the impurities in the reactor core Accumulation of sludge in steam generators Corrosion Are all _____ of impurities? - ANSWER >> problems What method described is used to remove impurities from impurities?

• Removing some of impure water and replacing with pure water
• also known as "blow down" - ANSWER >> Letdown/ Makeup What method described is used to remove impurities from impurities?
• Used to remove solid material from water
• Can be used in form of screens to remove bulk material from water (ex: fish from makeup, or rust from condensate or feedwater)
• sub-micron filtration to remove microscopic particles from system water - ANSWER >> Filtration What method described is used to remove impurities from impurities?
• some impurities dissolve in water and cannot be removed by filters
• many of these impurities carry an ionic change (+ or - )
• exchanges impurities that carry an ionic charge
• typically, a mixture of cation and anion resins are used= mixed beds
• can also remove boron; important to reactivity control
• improper use of an ion exchanger can cause a reactivity event - ANSWER >> Ion Exchange What method described is used to remove impurities from impurities?
• Captures a + ion and replaces with H+ ions (hydronium ions)

• causes pH to go down (become more acidic) - ANSWER >> Cation Resin What method described is used to remove impurities from impurities?
• Removes A Negative ION and replaces with OH- ions (hydroxyl ions)
• causes pH to rise (become more basic) - ANSWER >> Anion Resin What method described is used to remove impurities from impurities?
• balance PH effects
• generally, use a mixture of cation and anion resin in ion exchangers
• removes both anion and cations without having much effect on pH - ANSWER >> Mixed Resin What category of reactor coolant radionuclides: When uranium fission occurs, the atom does not split into two equal fragments. Instead, the two fragments tend to have atomic weights of about 95 and 140 mass units. Occasionally, fission results in three fragments? - ANSWER >> Fission Products What category of reactor coolant radionuclides: As the reactor coolant passes through the high flux of an operating reactor core, the water itself, impurities dissolved in the water, and corrosion products in the water are bombarded by nuclear particles. This particle bombardment causes some stable atoms to become activated. Those newly formed radionuclides are known as activation products? - ANSWER >> Activation Products what are 3 ways fission products enter reactor coolant? - ANSWER >> tramp uranium, diffusion, cladding defects uranium that is either on or very close to surface of fuel pin and is available for fission

• Presence of baseline iodines and noble gas isotopes (krypton/ xenon) - ANSWER >> Tramp uranium fuel cladding is porous and there are spaces b/w atoms which other atoms can migrate - ANSWER >> diffusion quickness of diffusion depends on - ANSWER >> temperature and size of atom fission gases like _______ can diffuse relatively quickly - ANSWER >> xenon/ krypton Fission products in GAP region can escape through cladding defects such as · imperfect welds (end caps welded on pin tubing) · minute cracks (thermal stresses or chemical attack) · larger holes (chemical attack) mechanical damage (hydraulics or intro of FM in RCS) - ANSWER >> Result of Fuel Clad Failure As the reactor coolant passes through the high flux of an operating reactor core, the water itself, impurities dissolved in the water, and corrosion products in the water are bombarded by nuclear particles. This particle bombardment causes some stable atoms to become activated. Those newly formed radionuclides are known as activation products. - ANSWER >> How activation products are produced in RCS Some water molecules undergo __________ (chemical deposition of water molecules by radiation) and are broken down into oxygen and hydrogen
• dissolved gases are impurities that affect reactor water quality

• ionizing radiation from reactor can induce coolant water to break apart into oxygen and hydrogen radicals - ANSWER >> Radiolysis
• There is a minimum hydrogen concentration level need to suppress the radiolysis of water in core
• Over 400 degrees F in RC with a sufficient hydrogen concentration ... hydrogen and oxygen will undergo _______ to make water
• adding hydrogen ... suppresses oxygen levels/ corrosion rate - ANSWER >> Recombination AKA hydrogen-3, is a radionuclide produced by neutron activation and fission in nuclear reactors.....it can be inhaled, digested, and absorbed by human body; typically exists as tritiated water and can migrate anywhere accessible by water in the human body... is a biological concern about? - ANSWER >> Tritium Production
• Ensure primary system boundary integrity
• Ensure fuel-cladding integrity and achievement of design fuel performance
• minimize out-of-core radiation fields to limit exposure to personnel
• limit radioactivity released into environment
• control core reactivity the following are the purpose of? - ANSWER >> controlling primary chemistry What is one of largest concerns in reactor water systems and is controlled to prevent general corrosion and SCC due to large amounts of stainless steel? - ANSWER >> Dissolved oxygen For corrosion to occur, what four conditions must be present? - ANSWER >> oxygen, halide/halogen impurity (chloride, fluoride: attack stainless steel and cause SCC), a susceptible material, and stress

attack stainless steel and cause SCC; controlled by monitoring makeup water - ANSWER >> sulfates can be introduced from cladding corrosion into condenser/ RCS - ANSWER >> zirconium corrosion of structure materials: releases metals _______ into reactor water - ANSWER >> metals (iron, cobalt, copper, zinc) tube leaks in condenser release: - ANSWER >> metal & salt ions (Calcium, Magnesium, Chloride, Sulfate) air in-leakage causes: - ANSWER >> oxygen and carbon dioxide ingress Fission process itself can produce impurities: - ANSWER >> over 30 radionuclides fission/ daughter products (xenon, krypton, iodine, cesium) What process described for controlling primary chemistry?

• purification ion exchangers are cation/anion mixed bed demineralizers Process: · demineralizer bed is made of small spherical insoluble beads (porous plastic coat in ion resin) · insoluble in water, acid and basic solutions · ion resin is used to purify water by replacing the undesirable ions in the water with ions that combine to form pure water (i.e. replace Cl- with OH-, or Na+ with H+) · insoluble materials are mechanically filtered and removed.
• PWR's: used in Chemical volume control systems
• BWR's: used in Reactor water cleanup and condensate systems - ANSWER >> Ion Exchange/ Demineralizers

What process described for controlling primary chemistry? de-gas RCS by charging gas spaces w/nitrogen and vent to gaseous waste system · let down water exchanges dissolved hydrogen for nitrogen, reduces RCS hydrogen gas concentration · tank pressure is kept as low as possible to ensure max reduction in hydrogen (>10psig for pump seals) · Hydrogen is removed for flammability concern when opening system - ANSWER >> PWR: Hydrogen Controls (Shutdown) What process described for controlling primary chemistry? · Hydrogen added to RCS to maintain reducing=minimized General Corrosion & SSC · adjusting volume control tank or makeup tank gas space overpressure in order to maintain RCS hydrogen between 25 and 50 cc/kg · increasing bulk coolant hydrogen above 50 cc/kg improves PWSCC mitigation w/out adverse conditions · correlation between the coolant hydrogen relative to the nickel-nickel oxide transition · operating with elevated (>50 cm3/Kg at STP) or reduced (<25 cm3/Kg at STP) RCS hydrogen to mitigate PWSCC must be tempered against collateral issues including:

• fuel impact
• corrosion product impact
• system limitations - ANSWER >> PWR: Hydrogen Controls (Operation) What process described for controlling primary chemistry?
• Hydrogen is added to the RCS via the feedwater system to maintain reducing conditions
• addition minimizes general corrosion and risks of stress corrosion cracking (SCC) - ANSWER >> BWR: Hydrogen Controls

What process described for controlling primary chemistry? · hydrogen injected into feedwater to achieve eletromechanical potential (ECP: <-230mV) of reactor internal/piping · feedwater concentration= 1.0 & 2.0 ppm - ANSWER >> BWR: Hydrogen Controls (Method 1) What process described for controlling primary chemistry? · Reducing ECP involving HWC w/ Noble Metal Chemical Application (NMCA) · Combines: reduced hydrogen injection concentrations (<0.4ppm) + noble metal treated surfaces on reactor/piping systems · Metal provides catalytic surface for recombination reactions of hydrogen & oxidants at a reduced hydrogen injection rate Hydrogen injection practiced continuously in BWRS w/rates >95% - ANSWER >> BWR: Hydrogen Controls (Method 2) primary system pH ≥ 6.9 during operation to min corrosion release rates & deposition - ANSWER >> PWR What process described for controlling primary chemistry?

• pH maintained by adjusting lithium and boron concentrations
• pHT is maintained as close to constant and as high as practical - ANSWER >> Maintaining pH What process described for controlling primary chemistry? used to mitigate PWSCC of Alloy 600 to reduce plant dose rates Process: · Zinc is injected into the primary systems via letdown or charging systems · Zinc is incorporated into the oxide films of wetted surfaces in an operating PWR · changing the morphology and composition of oxide films changing the corrosion characteristics - ANSWER >> PWR:

Primary Zinc Injection What process described for controlling primary chemistry?

• Zinc injection is used in to reduce radiation exposure and shutdown dose rates. Process:
• Zinc is injected though feedwater system, zinc ion effect is 2-fold · promotes the formation of a more protective corrosion film on stainless steel, especially when reducing conditions are present cobalt and zinc will incorporate into fuel deposits where activation takes place. When the zinc ion concentration exceeds the cobalt concentration, fuel deposits will contain (and release) lower concentrations of activated corrosion products, such as Co-60. Consequently, the reactor water will have reduced Co- 60 concentrations - ANSWER >> BWR: Primary Zinc Injection pH not controlled since operated at neutral pH range - ANSWER >> BWR main turbine, steam generators, feedwater heaters, and turbine condenser are major components in which chemistry must be controlled to:
• Minimize corrosion
• Minimize deposits on steam turbine surfaces
• Minimize sludge buildup in steam generators
• minimize scale deposits on steam generator
• Minimize feedwater oxygen constant which is the purpose of? - ANSWER >> controlling secondary water chemistry

ATTACKS iron in feed water heating system and deposits the ions in steam generators is the purpose for controlling which chemical parameter? - ANSWER >> Dissolved Oxygen Can cause SSC of alloys in SG's and also induce rapid local corrosion is the purpose for controlling which chemical parameter? - ANSWER >> Sodium and Chloride

• Secondary system (condensate & feedwater) is mostly carbon and stainless steel
• carbon steel: Iron corrosion of increases rapidly when pH < 8.8 is the purpose for controlling which chemical parameter? - ANSWER >> pH
• If oxygen, pH, and impurity ingress is not controlled ... corrosion rates in condensate and feedwater system will be high
• Products may be deposited into SG and foul the tubes / support structures
• One ppb = 40 lbs of iron one year in steam generator is the purpose for controlling which chemical parameter? - ANSWER >> Corrosion Products control leaks and addition of oxygen scavengers such as hydrazine/ carbohydrazide to condensate water (form various nitrogen compounds) is how you control which chemical parameter? - ANSWER

Dissolved Oxygen demineralizers is how you control which chemical parameter? - ANSWER >> Sodium and Chloride demineralizers and SG blowdown is how you control which chemical parameter? - ANSWER >> pH

AMINE compounds such as ethanolamine, etc; ammonia also helps is how you control which chemical parameter? - ANSWER >> Corrosion Products what processes are used to control secondary chemistry? - ANSWER >> Ion Exchange/ Filtration/Purification, Steam Generator Blowdown, All Volatile Treatment what processes described is used to control secondary chemistry?

• Components used to perform this process include deep bed Polishers (use resin beads) and precoat demineralizers (used powdered resin=ground up bead resin)
• Both replace harmful ions in the process stream with ions that combine to form water. Both types of ion exchange systems contain both anion and cation resins - ANSWER >> Ion Exchange/ Filtration/Purification what processes described is used to control secondary chemistry?
• used to clean water that is extracted from the steam generators
• steam generator is like a boiling teapot with a constant makeup flow into the pot. The steam leaves at the top and most of the salts and corrosion products stay in the bulk water. If the salts should come out of solution, they will fall to the bottom of the generator
• Steam generator blowdown comes from the bottom of the steam generator and is high in concentrated salts and suspended solids. It is cooled, then processed through a demineralizer
• Impurities are constantly removed and clean water is returned to system - ANSWER >> Steam Generator Blowdown what processes described is used to control secondary chemistry?
• Chemicals must be added to the condensate system to control pH and dissolved oxygen. The chemicals used0 (hydrazine, ammonia, ethanolamine, and other amines) are volatile.

• Volatile compounds are chemicals that are gases at steam generator temperature and pressure
• function of an AVT chemical is to remain homogeneously mixed in the water existing as either a liquid or gas - ANSWER >> All Volatile Treatment The Reactor Coolant System (RCS) and Reactor Water Systems are also subject to impurity ingress and corrosion. Due to the safety significance of these systems, their requirements are incorporated into each plant's Technical Specifications
• The purpose is to limit radiation exposure (dose) to the public during an accident in which secondary system steam or water is released to the environment is the reason for? - ANSWER >> Technical Specification Limits for steam generator tube leakage effect of organisms growing within plant components or being drawn into plant components. NOT a corrosion mechanism, has the potential to significantly impact plant operation. - ANSWER >> Biofouling
• Intake structures are designed with trash screens to prevent larger debris and fish from entering the intake structure.
• Amertap systems are used on most condensers to continuously scrub deposits from the inside of the tubes.
• Operationally, some systems are periodically flushed and/or chlorinated to prevent the accumulation of any biomass.
• Other components are periodically disassembled and cleaned to ensure continued operability.
• Closed cooling systems which contain corrosion inhibitors may be treated with biocides to control biological activity are ways to minimize _____? - ANSWER >> Biofouling