Primary Coolant Chemistry: Fundamental Aspects & Improvements/Optimizations

Transcription

1 Primary Coolant Chemistry: Fundamental Aspects & Improvements/Optimizations 1/ 89

2 Content of presentation > Water chemistry: Fundamental aspects & requirements Material compatibility Control of radiation field Fuel compatibility > Developments in chemistry control program: Siemens designed PWRs (SG with I8 Tubing) versa all other PWRs (SG with I6/69 tubing) Radiation field control: ph/li control strategies; EBA-Chemistry Control of radiolysis / Material Compatibility: Hydrogen addition Zinc chemistry: Radiation field control; Material compatibility 2/ 89

3 Primary coolant chemistry Fundamental aspects & requirements: Material compatibility Control of radiation field Fuel compatibility > Primary Coolant Chemistry:Fundamentals & Developments ( November 28) < 3/ 89

4 Objective of Coolant Chemistry 1 Reactor Pressure Vessel 2 Steam Generator 3 Main Coolant pump 4 Pressurizer 5 Pressurizer release Tank Coolant has a function of: Moderator / neutron reflector Heat transfer from core to SG Requirements to coolant chemistry: Material compatibility Radiation field control Coolant Chemistry functions: Core Reactivity Control Boric acid chemical shim for reactivity control RCS Integrity Reducing conditions (preventing water radiolysis) + Impurity control to prevent stainless steel & I6 PWSCC (I69TT, I8 are immune against PWSSC) Fuel Integrity Limit Li concentration & optimized ph operation to prevent fuel clad corrosion & crud deposition Radiation Field Control Optimized ph operation to minimize corrosion product release, activation & transport For the selection of chemistry the materials, design & operating conditions of RCS, especially the key components should be considered 4/ 89

5 1 Reactor Pressure Vessel 2 Steam Generator 3 Main Coolant pump 4 Pressurizer 5 Pressurizer release Tank Materials Used World wide in Reactor Coolant System Reactor Pressure Vessel Key Components: Steam Generator RCS Materials exposed to coolant have in general high corrosion compatibility: * Components: Austenitic stainless steel * Loop piping: Austenitic stainless steel * Fuel Cladding: Zircaloy, M5, Zirlo * SG Tubing: I 8, I 6 (MA, TT), I 69TT * In small amount: Stellite and Cr-Steels 5/ 89

6 Materials Used Worldwide in Reactor Coolant System Material Combination Alloy Compositions 34SS 38SS 39SS 316SS 321SS 347SS Inconel 6 Inconel 69 Icoloy 8 Inconel 718 Stellite 6 Zircaloy-4 ZIRLO Zr 1%NB Zr 2.5% Nb Cr Ni Fe Mn Co Zr Mo Ti Nb Sn Cu W % 2% 4% 6% 8% 1% 6/ 89 SG Tubing Fuel Cladding Stainless Steel Ref: K. Garbett, IAEA-Seminar Karlsruhe, 26

7 How Coolant Chemistry Fulfills These Objectives? Chemical Additives to Coolant > Coolant alkaline & reducing conditions are achieved by adding Lithium-7 Hydroxid for optimum ph T control Minimizing the Corrosion Product transport / Radiation Field Control Minimizing the Fuel cladding corrosion (Limitation of Li-concentration) Hydrogen to achieve Reducing conditions / suppressing the water radiolysis To influence the corrosion product solubility (to improve Radiation Field Control) > Impurity control to avoid selective type of corrosion by Operating Coolant Purification System, Consumables control (especially during annual outages) > Boric acid is added for neutron absorption as required by core reactivity control during different operating modes 7/ 89

8 Fundamental Aspects of Coolant Chemistry / Alkalinity Optimum ph T -Value for Radiation Field Control > Primary Coolant Chemistry:Fundamentals & Developments ( November 28) < 8/ 89

9 Fundamental Aspects of Coolant Chemistry Metal Release Rate of RCS Materials Metal release rates of different main RCS materials 1.E+2 1.E+1 Stellites Alloy 8 RCS materials are in general corrosion resistant low metal release rates 1.E+ Alloy 69 SS 1.E-1 1.E Test Duration (hours) Stellites Stainless Steel Alloy 69 Alloy 8 Even though, the extreme small amount of released corrosion products (CP) can be deposited and activated in the core; causing: * Radiation field increase in RCS * Increased risk for fuel corrosion 9/ 89 Metal Release Rate (mg.dm-2.mo-1)

10 Fundamental Aspects of Coolant Chemistry Mechanism of Radiation Field Built-up Mechanism of radiation field build-up: 1 st step: CP release from out of core areas (especially from SGs) 2 nd step: Transport with coolant 3 rd step: CP deposition in Core 4 th step: Activation of CPs in Core 5 th step: Re-release of activated CPs into coolant & transport 6 th step: Deposition of activated CPs out of Core area Increase of Radiation Field Reactor pressure vessel In-core activation Incorporation of Co 6, Co 58 in system surfaces Coolant Metal release (Fe, Ni, Co, Cr,...) 58 Co & 6 Co are the main responsible activated CP for Radiation Field (RF). 58 Co & 6 Co sources : 58 Ni (n,p) 58 Co Mainly SG tubing Steam generator 59 Co (n,γ) 6 Co Stellite, SG tubing Radiation field increase by incorporation of 58 Co & 6 Co in the Spinels 58 Co t 1/2 : ~ 7 days dominates RF in early plant life 6 Co t 1/2 : ~ 5.24 years dominates RF later Reactor coolant pump Coolant purification 1/ 89

11 Fundamental Aspects of Coolant Chemistry SG Tubing Material as Corrosion Product Source Element Fe Ni Cr Ni / Fe Ni / Fe+Cr Inconel > >9. >3.6 Chemical Composition Inconel > >6.4 >1.7 SG tubing material with highest surface area is the main source of the corrosion products (CP) in RCS. Based on field experience the CPs are a mixture of * Ni Ferrites * Ni oxide and metallic Ni Incoloy 8 ~ ~.81 ~.53 Their composition depends on SG tubing material: * I 6 / I 69 are Ni based materials more Ni & NiO can be expected * I 8 as Fe based material produces less Ni, NiO containing CPs This fact to be considered for selection of optimum ph T control program 11/ 89

12 Fundamental Aspects of Coolant Chemistry Chemical Composition of RCS Oxide Layers Past assumption: RCS oxide layers consists mainly of Fe 3 O 4 Recent knowledge: RCS oxide layers consists mainly of Ni-Ferrites (Ni x Fe 3-x O 4,Co y Fe 3-y O 4 and Ni x Co y Fe 3-(x+y) O 4 ) The solubility of RCS oxide Spinels depends on Temperature and ph-value Solubility of Magnetite Solubility of Ni-Ferrite 12/ 89

13 Fundamental Aspects of Coolant Chemistry Temperature influence on ph-value For ph T definition it is needed to consider the temperature 7,6 7,5 7,47 7,4 7,3 7,2 In Europe ph T is defined at 3 C; in several other countries it is defined at T averg (plant specific; e.g C) 7,1 7,4 ~ 326 C 7 ~ 292 C 6, Temperatur [ C] 13/ 89 ph

14 Fundamental Aspects of Coolant Chemistry Coolant ph Values as a Function of Temperature Influence of Temperature on ph-value 11 7 LiOH is selected instead of natural LiOH: 1 More Tritium production due to 6 Li (n,α) 3 H Water alone or Water + Boric Acid don t have the ph value, to achieve the solubility minimum of RCS oxide layers, necessary for radiation field control! Addition of alkalizing agent, 7 LiOH, is necessary Temperatur [ C] 14/ 89 ph-wert Pure Water 1 mg/kg B nat 1,4 mg/kg Li 1 mg/kg B nat und 1,4 mg/kg Li

15 Fundamental Aspects of Coolant Chemistry Strategy for ph T Control Nickelferrit Magnetit 6 6,5 7 7,5 8 8,5 ph(3 C) 6 ph T Control Strategy: * Oxide solubility minimum in entire RCS Demand to increase the ph T ( ) * Considering fuel cladding compatibility Lithium concentration / ph T limitation Variation of ph T -chemistry control programs ph 7.1 ph 7.2 ph 7.3 ph 7.4 ph 7.5 ph 7.6 ph 3 C ph 7. ph 6.9 ph 6.8 ph B concentration [ppm] / 89 Li concentration [ppm] Solubility Löslichkeit of von magnetite Magnetit & und Ni-Ferrite Nickelfer ph T -value as Function of Li- & B-concentration Li limitation due to material compatibility considerations

16 Fundamental Aspects of Coolant Chemistry Lithium & Fuel Clad Compatibility Enriched Li concentration in fuel deposits can cause cladding corrosion Isothermal, non-leachable Li Ramasubramanian McDonald Framatome ANP Isothermal, total Li Pecheur Kido Framatome ANP Coolant Li concentration is therefore limited by fuel vendors Field experience: * Most experience with Li: 2 ppm * Sufficient amount of experience up to 3.5 ppm * Few experience with 5-6 ppm / 89 Factor of Li-enhanced corrosion rate Li-content of the oxide layer (ppm)

17 Fundamental Aspects of Coolant Chemistry Solubility of Fe in Ni-Ferrites Optimum ph T for Fe: ~ 7.4 Fe Solubility in Nickel Ferrites ph chemistry refers to a ph defined at 3 C 9 ph(296 C) ph(328 C) Core inlet chemistry ,2 6,4 6,6 6,8 7 7,2 7,4 7,6 7,8 8 ph(t) 17/ 89 solubility of Fe [ppb] Core outlet

18 Fundamental Aspects of Coolant Chemistry Solubility of Ni in Ni-Ferrites Ni solubility higher at core outlet,7 Ni Solubility in Nickel Ferrites ph chemistry refers to a ph defined at 3 C ph(296 C) ph(328 C),6,5,4 Core outlet 7.2 chemistry 7.4 chemistry,3,2 6 6,2 6,4 6,6 6,8 7 7,2 7,4 7,6 7,8 8 ph(t) 18/ 89 solubility of Fe [ppb] Core inlet

19 Fundamental aspects of Coolant chemistry / Hydrogen Addition: Reducing Conditions/ Suppressing of Water Radiolysis > Primary Coolant Chemistry:Fundamentals & Developments ( November 28) < 19/ 89

20 Fundamental Aspects of Coolant Chemistry Hydrogen Addition The objective of hydrogen adding: * Suppressing the water radiolysis * Counteracting the risk of selective type of corrosion, which might be caused by oxidizing species Influences the corrosion product solubility in a positive way with respect to Radiation Field Control 2/ 89

21 Fundamental Aspects of Coolant Chemistry How much Hydrogen is needed to Control Radiolysis [H2O2]/ppm 1.E+2 1.E+1 1.E+ 1.E-1 1.E-2 1.E-3 Plot of H2O2 concentration against H2 concentration for boron 25C 1C 15C 2C 3C [H2]/cc kg-1 1.E+3 Plot of H2O2 concentration against H2 concentration for 18 ppm boron [H2O2]/ppm 1.E+2 1.E+1 1.E+ 1.E-1 1.E-2 1.E-3 ppm Bor 25C 1C 15C 2C 3C [H2]/cc kg-1 18 ppm Bor Necessary hydrogen concentration to suppress the radiolysis: Radiolysis calculations: * At 3 C: >.9 ppm (1 cc) * At: 25 C: >.9 ppm (1 cc) Plant measurements: * NPP Belleville : >.45 ppm (5 cc) * NPP Gösgen: >.43 ppm (4.8 cc) * NPP Obrigheim: ~.5 ppm (5.6 cc) Guide line values: Germany: 2 4 ppm H 2 ( cc) World wide: 25 5 cc H 2 (Selected based on calculations at 25 C) Ref: K. Garbett, IAEA-Seminar Karlsruhe, 26 21/ 89

22 Primary coolant chemistry Improvements and Optimizations: Material compatibility Control of radiation field Fuel compatibility > Primary Coolant Chemistry:Fundamentals & Developments ( November 28) < 22/ 89

23 Improvements & Optimization of Primary Coolant Chemistry Experience in the early days of PWR operation: * Crud transportation SG Reactor Core * Heavy crud build-up on fuel surfaces This resulted in: * High radiation fields on out-of-core surfaces, * Fuel performance compromised, * Even in several PWRs Coolant flow disturbances p problems in reactor core Corrosion products deposit out of core Corrosion products activated in reactor core Corrosion products released from SG tubing World wide need for coolant chemistry improvements to counteract these problems!!! 23/ 89

24 Improvements & Optimization of Primary Coolant Chemistry Siemens designed PWRs SG tubing material: I 8 Element Fe (%) Ni (%) Cr (%) Ni:(Fe+Cr) Coolant chemistry improvements: World wide two main approaches due to used Steam generator tubing materials Inconel > :1 SG Tubing Materials Inconel > :1 W, CE, B&W, FA and MHI designed PWRs SG tubing material: I 6, I 69 Incoloy 8 ~ :1.9 1:2.1 Facts to be considered: Oxide film growth on I 8 does not result in the formation of large quantities of excess nickel Additional aspect: I 8 & I 69 are immune against PWSCC but I 6 not! 24/ 89

25 Primary Coolant Chemistry EPRI Guidelines for W, CE and B&W Designed PWRs (SG Tubing: I 6 /T 69TT) Control Parameter Chloride (ppb) Fluoride (ppb) Sulphate (ppb) Lithium (ppm) Hydrogen cc(stp)/kg Dissolved Oxygen (ppb) Diagnostic Parameter Conductivity (µs/cm, 25 C) ph (25 C) Boron (ppm) Suspended Solids (ppb) Silica (ppb) Zinc (ppb) Ref: Garbett, IAEA Workshop Karlsruhe, 26 Sample Frequency 3/week (typical) 3/week (typical) 1/week 3/week 3/week Defined in Tech.Specs. Sample Frequency 1/day 1/day 1/day 1.week 1/week Defined in zinc addition programme Action Level Plant specific limit >15 >15 Plant specific limit >15 >15 Plant specific limit >15 >15 Defined by ph programme - - <25 <15 >5 <5 >5 - >1 Reason for Analysis Assess consistency with additives Assess consistency with additives As required for reactivity control To establish and trend changes from Plant-specific target <3 ppb As required by plant-specific programme Revision 5 25/ 89

26 Primary Coolant Chemistry EdF Guidelines for Framatome Designed PWRs (SG Tubing: I 6 /T 69TT) Ref: Nordmann, IAEA Workshop, Karlsruhe, 26 26/ 89

27 Primary Coolant Chemistry VGB Guidelines for Siemens Designed PWRs (SG Tubing: I 8) Ref: Odar, etal, Jeju Island, 26 27/ 89

28 Occupational Radiation Exposure per Plant and Year Nuclear industry has been successful in reducing radiation exposures of PWRs within the past decades France USA Japan All Siemens PWRs Siemens pre-convoy PWRs Siemens Convoy PWRs Year 28/ 89 Collective dose per plant and year in man-sv Ref: Guinard et al. Berlin 28 Extremely low radiation exposure (<.5 ManSv/a) experienced in German Pre- Convoy and Convoy PWRs (Stellite free plants)

29 Primary coolant chemistry Improvements and Optimizations: Siemens Designed PWRs (SGs with I 8 tubing material) > Primary Coolant Chemistry:Fundamentals & Developments ( November 28) < 29/ 89

30 Historical Development of Innovations regarding Primary System Design and Primary Coolant Chemistry at German PWRs Improvements 1969 to / / / / to 1985 since 1995 Qualification and Implementation of I-8 SG Material Implementation of 7 Lithium-hydroxide 1-2 ppm Lithium chemistry Implementation of Hydrogen Injection Start of Coordinated Coolant Chemistry Start of Modified Coolant Chemistry Identification of Main Radiation Sources (Reactor Pressure Vessel or Steam Generator?) Qualification of Stellite Replacement Material Implementation of Stellite Replacement Material (In-Core and Out-Of-Core) in New Plants Implementation of Zinc Injection Start of Enriched Boric Acid Application / 89

31 Coolant Chemistry Improvements: Strategy for ph T Control at Siemens Designed PWRs 1-2 ppm Li Chemistry Variation of ph T -chemistry control programs ph 7.3 ph 7.4 ph 7.5 ph 7.6 ph 7.1 ph 7.2 ph 3 C Date ph 7. ph 6.9 ph 6.8 ph B concentration [ppm] ph T -value as Function of Li- & B-concentration 31/ 89 Li concentration [ppm] Li (mg/kg) ph 3 : 6.9 Coordinated Li Chemistry Modified Li Chemistry Li (mg/kg) Date

32 lithium concentration [ppm] 2,5 2 1,5 1,5 ph3 C 8, 7,5 7, 6,5 14 Typical Coolant Chemistry in a German PWR with EBA (32 d cycle) EBA Cycles Non EBA Cycles BOC boron conc. for nat. BA 12 BOC = begin of cycle, nat. BA = natural boric acid EBA = enriched boric acid T = 3 C / 572 F 1 8 Improvements in Coolant Chemistry German ph T Control Program modified chemistry 6, Operation Days Plant A Plant E Plant L Plant Q 6 boron concentration [ppm] coordinated chemistry ph 3 : 6.9 BOC boron conc. for EBA 4 Li [mg/kg] ph 3 : ,5 2 1,5 1,5 2 Li = 2, +,1 ppm ph bei 3 C B [mg/kg] 315 mg B/kg 7,6 7,5 7,4 7,3 7,2 7,1 32/ 89 ph [3 C]

33 Improvement of Material Concept: Replacement of Stellite by Improved Hardfacing Material Siemens Designed pre-convoy and Convoy Plants 1975 to 1985 Areas with Co-Base Alloys Control Rod Drives Reason: Reduction of Co sources (Stellite is the main Co source) Hold Down Plates Alignment for Grid plate Core Barrel Reactor Alignment Control Rod Guide Assembly Irradiation Channel Example: RPV Internals Entire Hardfaced Area Control Rod Drives Former Co-base Alloy Now Co-base Alloy 1.46 m² 1.46 m² Core Area 1.59 m².3 m² Radial Core Stop Support 33/ 89

34 Bq/m³ 4 3,5 3 2,5 2 1,5 1,5 1,E+1 1,E+9 1,E+8 1,E+7 1,E+6 1,E+5 Dose rate improvements Dose Rate [msv/h] Coordinated Chemistry Change ph 7, coord.. to ph 7,4 mod. Coordinated Chemistry 1,E Decrease of coolant 58 Co Stelltei PWRs Modified Chemistry Cycle No. Modified Chemistry Coolant Chemistry in Germany Results of ph T Increase Coreplacem. B/Lichem. Plant I, coord. - none Plant K, mod. - none Plant L, mod % Plant M, coord % Plant N, mod % Plant O, mod % Plant Q, mod % } Co arm PWRs Co-58 Co-6 Load Load [%] Lithium [ppm] 2,5 2 1,5 1,5 14 Specifications: Li: < 2.2 ppm H2: 2-4 ppm Cl: <.1 ppm O2: <.5 ppm 12 Coordinated Chemistry Boron [ppm] 4 Modified Chemistry Increase of ph T resulted in: * Reduction of 58 Co in Coolant * Reduced field radiation 2 Solubility minimum of Spinel oxides Löslichkeit von Magnetit und Nickelferrit Magnetite Nickelferrit Magnetit 6 6,5 7 7,5 8 8,5 ph(3 C) Ni-Ferrite ph T : 6.9 ph T : / 89

35 Li [ppm] Optimization of Primary Coolant Chemistry at Siemens Designed PWRS ph T -Control Using EBA ph T control using Natural and Enriched Boric Acid % B % B % B % B German PWRs ph < 7,4 Li < 2 ppm (see full lines) natural B (2 atom-% B-1) Due to power up-rates and increased core duty EBA is introduced EBA: Option to operate for long time at higher ph T for radiation field control Target ph T : 7.4 ppm B natural B ppm B 3 % B-1 ppm B 5 % B-1 ppm B 8 % B-1 ppm B 1 % B-1

36 Hydrogen Control Band at German PWRs VGB Guideline Revisions 1982: cc DH/kg 27: cc DH/kg Plant DH cycle averages: DH concentration values: 18 4 cc DH/kg Average DH concentration: ~ 3 cc DH/kg 45, 4, Low Duty Plants Medium Duty Plants High Duty Plants 35, 3, 25, 2, 15, 1, 5,, C D F A B G E I K M H L N O P Q Plants 36/ 89 H2 Concentration [cc/kg]

37 1 PWR: Coordinated Chemistry (pht: 7.) 16 PWRs: Modified Chemistry (ph T : 7.4) 8 PWRs: DZO Chemistry 9 PWRs: EBA Chemistry 3 PWRs: DZO + EBA Chemistry Coolant Chemistry Applied Different Core Duties ppm Li strategy Coordinated Chemistry Modified Chemistry (MC) PHWR-Chemistry MC + DZO MC + EBA MC + EBA + DZO Low Duty Plants: Medium Duty Plants: High Duty Plants: Ext. High Duty Pl t HDCI < >15 >2 11 High Duty Plants Obrigheim Stade Borssele Atucha 1 Biblis A Neckarwestheim1 Biblis B Unterweser Gösgen Grafenrheinfeld Grohnde Philippsburg 2 Brokdorf Isar 2 Emsland Trillo Neckarwestheim2 Angra 2 37/ 89

38 Fuel Deposits at German PWRs Visual Inspection Results No visual fuel deposits, not only in low / medium duty plants but also in high duty plants Medium Duty Plant (HDCI: 14) High Duty Plant (HDCI: 326) 38/ 89

39 Primary coolant chemistry Improvements and Optimizations: W, CE, B&W, MHI, FA Designed PWRs (SGs with I 6, I 69 tubing materials) > Primary Coolant Chemistry:Fundamentals & Developments ( November 28) < 39/ 89

40 US PWR Historical Chemistry Trends Hydrogen Management elevated constant ph (7.3/7.4) ultrasonic fuel cleaning elevated constant ph (7.1/7.2) zinc injection modified elevated lithium program EPRI Water Chemistry Guidelines elevated lithium program constant ph Fruzzetti, Jeju Island 26 4/ 89

41 Primary coolant chemistry Improvements and Optimizations: Radiation Field Control Li/pH Control Strategies > Primary Coolant Chemistry:Fundamentals & Developments ( November 28) < 41/ 89

42 Variation of ph T -chemistry control programs Li concentration [ppm] ph 7.1 ph 7.2 ph 7. ph 6.9 ph 6.8 ph Elevated Chemistry Modified Chemistry Coolant Chemistry Improvements: Strategy for ph T Control at US & Other PWRs with I6/I69 SG Tubing ph 7.3 ph 7.4 ph 7.5 ph 7.6 Elevated Modified Chemistry Coordinated Chemistry B concentration [ppm] 6 ph T -value as Function of Li- & B-concentration 4 2 ph 3 C Longer cycles demands higher Li concentrations at BOC, in order to have ph More corrosion resistant fuel cladding materials (Zirlo, M5) enable increase of Li concentration As of 28 field experience exists with up to 6 ppm Li (Comanche Peak PWRs) 42/ 89

43 Coolant Chemistry Improvements: Different Strategies for ph T Control (1) Co-ordinated ph Chemistry ph 7.2 Usually Li concentration is limited to 2 ppm at BOC ph 6.9 Coordinated ph Chemistry ph T : 6.9 and EDF Chemistry 15 1 Boron, mg kg -1 Modified ph Chemistry 15 ph 6.9 ph 7. 1 Boron, mg kg ph 7.4 Due to extended cycle duration (12 m 18m), BOC Boron concentration had to be increased ~12 ppm ~ 18 ppm. Because of still Li limitation of 2.2 ppm, modified chemistry is introduced. Modified ph Chemistry ph T : 7., 7.2 and / 89 Lithium, mg kḡ 1 Lithium, mg kg -1

44 Coolant Chemistry Improvements: Different Strategies for ph T Control (2) Elevated ph Chemistry ph 7.4 Elevated: Li concentration > 2 ppm ph 7. Elevated ph Chemistry ph T : 7., 7.2 and Boron, mg kg -1 5 First introduced in Ringhals Units, followed by Milstone 3 Elevated or Elevated- Constant ph chemistry ph 7.4 Elevated or Elevated-Constant ph Chemistry ph T : 7., 7.2 and ph 7. 1 Boron, mg kg -1 5 Constant ph operation between 7.2 and 7.4 is expected to minimize the core crud deposition, fuel corrosion, radiation fields and AOA 44/ 89 Lithium, mg kg -1 Lithium, mg kg -1

45 Coolant Chemistry Improvements: US PWR Experience with Elevated ph Chemistry Number of US PWRs operating with elevated Li concentrations at BOC is increasing Year 45/ 89 Percentage of Plants Within Range <3. ppm ppm >3.25 ppm Fruzzetti, Berlin 28

46 Coolant Chemistry Improvements: Comanche Peak Demonstration of Elevated ph/li Chemistry Lithium (ppm) ph Lithium Behavior RCS ph MWD/MTU at plant Tav Li control during last 4 cycles ph T control during last 4 cycles MWD/MTU U2C6 U2C7 U2C8 U2C9 U2C6 U2C7 U2C8 U2C9 Dose Rate, Gy/hr EPRI Fuel Reliability Program, WG#1 September 6-7, 26 Objective was to reduce * Radiation fields, * Susceptibility to AOA Results: * No adverse trends either in the area of chemistry or core performance * No indications of AOA * Indications for improved radiation fields * No anomalous shutdown chemistry 7.E-4 6.E-4 5.E-4 4.E-4 3.E-4 2.E-4 1.E-4.E+ SG Tube Bundle dose rates Loop 1 Loop 2 Loop 3 Loop Outage Stevens, Berlin 28 46/ 89

47 Coolant Chemistry Improvements: Ringhals Experience with Elevated ph Chemistry 4 ph increase in Ringhals 2 & 3 resulted in decrease of * 58 Co Shut-down release * SG channel head dose rates SG cold leg channel head dose rates 2 3 Whereas in Ringhals 4 with lower ph the opposite is experienced ph regimes (MC to EOC) in Ringhals Units Co-58 Shut-down release Bengtsson, Berlin 28 47/ 89

48 Primary coolant chemistry Improvements and Optimizations: Material Compatibility: Hydrogen Control Strategies Fruzzetti, Jeju Island 26 Jones, San Francisco 24 Identification of PWSCC in RPV Head penetrations in US PWRs lead to root cause investigation programs. It resulted in: * Reconsidering the hydrogen control strategies. * Encouraging the use of zinc injection > Primary Coolant Chemistry:Fundamentals & Developments ( November 28) < 48/ 89

49 PWSCC Susceptible Alloys in W-PWRs Alloys 6, 182, 82 locations in W-PWRs Li, B and ph T are observed to have almost no influence on PWSCC CGR. But DH!!! Ref: Jones, Intr. Water Chem. Conf. San Francisco, 24 49/ 89

50 Current Industry Operating Hydrogen Ranges Current operating limit is 25-5 cc/kg and EPRI is assessing an increase up to 8 cc/kg RCS Operating Hydrogen Ranges Chemistry Monitoring Data Assessment Ref: Fruzzetti, Berlin Cycle Average RCS Hydrogen Range (cc/kg) 5/ 89 Number of Cycles in Range US International

51 Effect of H 2 on the crack growth rate of Alloy X-75 in 36 o C water NiO H 2 Specs Ni Metal Reference: Andersen, et al., International Conference on Water Chemistry of Nuclear Reactor Systems, Jeju Island Korea, Oct. 26 Effect of Dissolved Hydrogen on the Crack Growth Rate of Alloy X - 75 H 2 operating range Crack Growth Rate (mils/day) Hydrogen Concentration (cc/kg) Temperature & DH dependence of PWSCC Reference: K. Sato, Dissolved H2 Workshop, Tohoku University, Japan July 27 Increased PWSCC CGR at the Ni/NiO phase boundary observed 51/ 89

52 Effect of Dissolved Hydrogen on PWSCC of Alloy 6 Crack Growth Rate and Crack Initiation Rate ml H2/kg H2O (33 C) ,E M67:4 M67:5 8,E-8 6,E-8 4,E-8 2,E-8 M34: ,E+ Hydrogen activity, kpa 52/ 89 Crack initiation time, h Crack growth rate, mm/s Growth Initiation Reference: A. Molander, Dissolved H2 Workshop, Tohoku University, Japan July 27 With increasing DH concentration: * Crack growth rates increase, * Crack initiation time decreases

53 US Approach: Increase of Coolant Hydrogen Concentration Expected improvements by DH increase: Future considerations: * Investigations on adverse effect of DH increase: - Safety issues (Post-LOCA considerations) - Fuel performance - Radiation field control * Stepwise increase of DH Andresen, etal, 13th Intern. Conf. on Optimization of DH in PWR Primary Coolant, Tohoku Univ, Japan, July 27 According to US mind: Increase of DH provides benefit, but lowering might be detrimental below 33 C 53/ 89

54 Japanese Approach: Decrease of Hydrogen Concentration Lab results: PWSCC initiation time delay and lower PWSCC susceptibility is expected by decreasing coolant H 2 concentration Dozaki, 13th Intern. Conf. on Optimization of DH in PWR Primary Coolant, Tohoku Univ, Japan, July 27 Sato, 13th Intern. Conf. on Optimization of DH in PWR Primary Coolant, Tohoku Univ, Japan, July 27 54/ 89

55 Japanese Approach: Field Experience- Additional Benefits for Radiation Control Japanese field experience with decreasing the hydrogen concentration Result of hydrogen decreasing: * NiO with high solubility becomes more stable * Decrease of fuel deposits * Decrease of Ni in fuel deposits (Ni/Fe Ratio) (Less 58 Co during S/D & Less dose) 55/ 89

56 Zinc Chemistry For Dose Rate Reduction Mechanism Dose Rate Reduction Material Compatibility Field Experience > Primary Coolant Chemistry:Fundamentals & Developments ( November 28) < 56/ 89

57 Fundamental Aspects of Coolant Chemistry Discovery of Zinc Influence on Dose Rate Build-up BWR Dose Rate Field Experience Plants with stainless steel condenser tubes Plants with brass condenser tubes 57/ 89

58 Fundamental Aspects of Coolant Chemistry Dose Rate Mitigation by Zinc Chemistry Site preference energies for spinels Mechanism of Zinc Chemistry Spinel Structur Reference: Nawrotsky & Kleppa, J. Inorg. Nucl. Chem., 1967, Vol. 29, p / 89

59 Zinc Chemistry: Dose Rate Reduction in German PWRs PWRs with I8 SG tubing 3 25 Avg. values Outlet: 25 msv/h Inlet: 178 msv/h Zinc injection Field experience at NPP Biblis Unit B: SG-Chanel head Avg. values Outlet: 213 msv/h Inlet: 19 msv/h Zinc injection Year 15 Unit A: SG Chanel head 1 5 Outlet Inlet Biblis B Year 59/ 89 Dose rate [msv/h] Dose rate [msv/h] Outlet Inlet Biblis A

60 Zinc Chemistry: Dose Rate Reduction in US PWRs PWRs with I6 SG tubing NPP Palisades NPP Diablo Canyon Reference: H. Ocken, et al., International Conference Water Chemistry in Nuclear Reactor systems, Chimie 22, Avignon April 22 6/ 89

61 DR SG Channel Heads, Hot Leg [msv/h] Zinc Chemistry NPP Angra-2: Zinc Chemistry from First Day on! Co containing plants full color: 1st Cycle hatched pattern: 3rd Cycle Angra2 3-Loop, coord. 4-Loop, coord. 4-Loop, mod. 3-Loop, mod. Angra 2 pre-konvoi, mod. Due to Zn chemistry from day 1 on, Angra 2 has similar low field radiation like Co free plants!!! Co free plants pre-konvoi, coord. 2,5 msv/h 2 1,5 1,5 Konvoi, mod. Cross-Over Average Contact Dose Rates at German Plants Co containing plants In NPP Angra-2 Zn chemistry was applied from first day of criticality Angra2 4-Loop, coord. 4-Loop, mod. 3-Loop, mod. Angra 2 Pre-Konvoi, coord. Pipe wall thicknesses: Angra 2: 58 mm. Sister plants (4-loop coord and 4-loop mod): 5 mm All other plants: 55 mm Pre-Konvoi, mod. full color: 1. cycle hatched pattern: 2. cycle checkered pattern: 3. cycle Co free plants Konvoi, mod. Konvoi, mod. Konvoi, mod. 61/ 89

62 Zn Influence on dose rate build-up Reference: D.H. Lister, Presentation at EPRI Robust Fuel Program, Feb. 22 mg/m²d Zinc Chemistry Material Compatibility Zn Influence on material compatibility Stellite 6 181CrNi I6/I69 IX-75 Stellite 6 181CrNi I6/I69 IX-75 Corrosion Rate Test conditions: 12 ppm B 2.2 ppm Li 5 ppb Zn (as Zn borate) T = 33 C t = 3.5 months Without Zn With Zn Metal Release Rate Reference:.N. Esposito, et al, 5th Int. Symposium on Environmental. Degradation of Materials in Nuclear Power Systems-Water Reactors, 1991, 62/ 89

63 PWRs with Zinc Application 6 PWR Fleet Injection History Application Worldwide 5 28 U.S., Actual to date: 25 (36%) 4 28 U.S., Actual + Projected by yr-end: 29 (42%) 3 2 Siemens PWRs: 7 on Zn Chemistry (44% of total; or 78% of Stellite-PWRs) Percent of PWRs injecting Number of Units Injecting 28 data is projected for end-of-year based on current information. Ref: Fruzzetti, Berlin 28 63/ 89 Units (#) & Percent Injecting (%)

64 Primary Coolant Chemistry Conclusions (1) > World wide alkaline and reducing coolant chemistry is applied for Adequate control of radiation fields Maintaining high material compatibility and High fuel performance > Even all these coolant chemistry strategies look in general very similar, they differ in detail significantly due to used SG tubing materials SG with I 8: No excess Ni in the fuel crud (Magnetite & Ni-ferrites) Coolant chemistry: Modified Li 2 ppm chemistry (ph T : 7.4); DH: 2-4 ppm Even operating with high duty cores no AOA is experienced No need for elevated Li & DH chemistry Older Siemens PWRs (stellites!): Zn injection for radiation field control 64/ 89

65 SG with I6/69: Excess Ni in the fuel crud; Primary Coolant Chemistry Conclusions (2) Extended cycles (18-24 months), high duty cores caused in several PWRs AOA, high radiation field and/or shut-down chemistry problems (particulate release). Need for elevated Li/pH chemistry (ph T : 7.2 / 7.4) PWSCC sensibility of Nickel base alloys (A 6, 182, 82 and X-75) demands modification of coolant DH content Need either to increase or decrease DH! > Zinc injection is applied world wide in many PWRs with success Dose rate reduction Mitigating PWSCC > Cycle extensions, increasing core duty remains world wide a challenge for coolant chemistry 65/ 89