Out-of-Reactor Test of Corrosion and Hydrogen Pickup in Fuel Cladding Materials in Contact with Nickel Metal

Transcription

1 Out-of-Reactor Test of Corrosion and Hydrogen Pickup in Fuel Cladding Materials in Contact with Nickel Metal Daniel M. Wells (EPRI), Richard Becker (Studsvik), Jiaxin Chen (Studsvik), Clara Anghel (Westinghouse), Dennis Hussey (EPRI), Jayashri Iyer (Westinghouse), and Jacqueline Stevens (AREVA) 18th International Symposium on Zirconium in the Nuclear Industry May 2016 Hilton Head, South Carolina, USA

2 Dissolved Hydrogen and Crack Growth Rate The Primary Pressure Boundary Motivation Rate of PWSCC Crack Growth Rate for Nickel Based Alloys Reduced By Operating at Higher Primary Water Hydrogen Concentration 8.E-07 Current band 7.E-07 6.E C Based on a mean MRP Growth Rate for Alloy 182 (16X peak vs. H 2, = 20.2) CGR, mm/s 5.E-07 4.E-07 3.E-07 2.E C 35 cc/kg H2 60 cc/kg H 2 80 cc/kg H 2 1.E C 0.E H 2 Level, cc/kg 2

3 Zircaloy Corrosion and Hydrogen Pickup Corrosion and Hydrogen Pickup Hydrogen pickup causes embrittlement and potentially failures Dominant source believed to be cladding oxidation, not RCS H 2 Nickel Window Effect Nickel in direct contact with the cladding surface can enhance hydriding (window for hydrogen transport into material) In-reactor and out-of-pile observations Zr-based Alloy Protective Oxide Water Zr 4+ +2O 2- ZrO 2 O 2- Zr-based Guide tubes [ 1 ] Zr Zr 4+ +4e - Zr+2H ZrH 2 Zr+2H Zr(H) e - xh 2H 2 O+4e - 2O 2- +4H 4H xh +(2-x/2)H 2 HPUF (%) = (x/4)(100) Total H2 Pickup (ppm) Nickel SS 410 Cold handling and accident condition regulation (LOCA, RIA, etc.) main concern SS 304 Copper Pressure H 2 (MPa) Assessment of the Effect of Elevated Reactor Coolant Hydrogen on the Performance of PWR Zirconium-Based Alloys. EPRI, Palo Alto, CA:

4 Hydrogen and Corrosion Product Transport The Fuel Crud Motivation - Based on Thermodynamics 3 Nickel Solubility as a Function of ph300 C and Hydrogen (B = ppm, Ni initial input = 0.1 ppb, Fe initial input = 10 ppb) Nickel Solubility (ppb) Nickel Solubility (ppb) ph(300c) = 6.9, H2 = 35 cc/kg ph(300c) = 7.3, H2 = 35 cc/kg ph(300c) = 7.5, H2 = 35 cc/kg ph(300c) = 6.9, H2 = 0 ph(300c) = 7.3, H2 = 0 ph(300c) = 7.5, H2 = Temperature (C) H2 = 0 cc/kg H2 = 15 cc/kg H2 = 25 cc/kg H2 = 35 cc/kg H2 = 60 cc/kg Ni solubility varies significantly with Ni/Fe ratio due to precipitation of NiFe 2 O 4 Hydrogen impacts the trend in at temperature Ni solubility Fe solubility increases with temperature for all conditions evaluated ZnFe 2 O 4 solubility increases with increasing hydrogen Nickel Solubility as a Function of Hydrogen for ph300 C = 7.1 (B = 600 ppm, Ni initial input = 1 ppb, Fe initial input = 10 ppb) Temperature (C) Soluble transport will be impacted by hydrogen 4 3 MULTEQ Version 7.0 (EPRI Product )

5 Elevated Reactor Coolant Hydrogen and Zircaloy Materials Provide a chemical mitigation technique for Primary Water Stress Corrosion Cracking (Alloy 600 weld metals) Only mitigation technique for Bottom Mounted Instrument nozzles FRP, MRP, and Chemistry all collaborating to support implementation FRP/P-TAC Supported Projects Literature Review 1 Autoclave Tests 3 In-reactor tests Cladding Spacer Grid Welds End Plug Welds Plant Demonstrations 1. Analysis of the Effect of Elevated Reactor Coolant Hydrogen on the Performance of PWR Zr-Based Alloys. EPRI, Palo Alto, Ca: Out-of-Reactor Corrosion Tests of Fuel Cladding Materials. EPRI, Palo Alto, CA:

6 The Autoclave Parameters Target Values ph at 300ºC (360 C) using BORIS code ~7.2 (~8.4) Boron, ppm as boric acid 750 Lithium, ppm as lithium hydroxide 2.67 Dissolved hydrogen, cc H 2 /kg H 2 O* 30, 100, 500 Dissolved oxygen, ppb < 1 Exposure temperature, C 360 Pressure, bar *Dissolved hydrogen concentration in cc H 2 /kg H 2 O is calculated at 1 atm and 25 C. Exposure Period Number of Days a 100 5b 100 6

7 Long Term Autoclave Exposure START long term exposure: (as-received and pre-oxidized materials*) Ni-material contact effect testing d 100d 200d 200d 100d 100d Build up experimental facility for the long term exposure Ni window effect testing (nickel platting) 5 exposure periods 2014 Technical Report Public Report *Including the full set of AREVA (M5, Zry-4, Zry-2) and WEC (ZIRLO and Opt ZIRLO ) fuel cladding, spacer and end plug materials 7 3 Out-of-Reactor Corrosion Tests of Fuel Cladding Materials: Corrosion as a Function of Hydrogen Overpressure. EPRI, Palo Alto, CA:

8 Hydrogen Uptake Fuel Cladding Samples 3 Hydrogen Pickup Rate Fuel Cladding Samples 30 cc/kg 100 cc/kg 500 cc/kg 30 cc/kg Hydrogen Pickup Fuel Cladding Samples 730 days exposure, without correction for pre-oxidation Hydrogen pickup rates for various fuel cladding materials were approximately constant (~ 50 ppm/year 150 ppm/year) No correlation between hydrogen pickup rate and dissolved hydrogen could be positively identified Note: Hydrogen content corrected for pre-oxidation hydrogen. Select data are presented, see report for details. 8 3 Out-of-Reactor Corrosion Tests of Fuel Cladding Materials: Corrosion as a Function of Hydrogen Overpressure. EPRI, Palo Alto, CA:

9 Nickel Metal Plating Experiment 3 Exposure time: 100 days exposure Exposure conditions: Targets ph at 300ºC ~7.2 Boron, ppm 750 Lithium, ppm 2.67 Hydrogen, cc/kg 30, 100, 500 Oxygen, ppb <1 Test temperature, C 360 Naturally formed (native) ZrO 2 oxide No coating Zry-4 substrate Zircaloy-4 with natural oxide No etching before Ni coating Etching by Ar ion sputtering before Ni coating 100% Ni directly in contact with Zry-4 or with the ZrO 2. Zry-4 substrate Zry-4 substrate Zry-4 substrate Five of each type in each autoclave = 45 samples. Reference sample ZrO 2 /Zry-4 Zr-oxide with embedded Ni layer (~1 µm thick). Ni/ZrO 2 /Zry-4 Ni layer (~1 µm thick) sputtered after the removal of the native Zroxide. Ni/Zry Out-of-Reactor Corrosion Tests of Fuel Cladding Materials: Corrosion as a Function of Hydrogen Overpressure. EPRI, Palo Alto, CA:

10 Visual/SEM results Ni/Zry-4 samples 3 Uncoated Ni-coated 30 cc H cc H cc H 2 Increasing H 2 level 10 3 Out-of-Reactor Corrosion Tests of Fuel Cladding Materials: Corrosion as a Function of Hydrogen Overpressure. EPRI, Palo Alto, CA:

11 More Representative Ni-Window Effect Testing Will an increased hydrogen uptake (corrosion) be observed with a more realistic contact with nickel metal? Zry-4/Crud contact samples (Subject of Paper) Step 1 Step 2 Step 3 Zry-4 tube section Crud powder P Crud composition (weight fraction %): Type 1 (Ref.) Type 2 Type 3 Ni (m) NiO NiFe 2 O P Zry-4/Nickel alloy 718 coupling specimens 3 Dimple for smearing and contact point Average 120 ± 13N of force used to insert the rod into the holder Zry-4 Nickel Alloy 718 Smeared line 11 3 Out-of-Reactor Corrosion Tests of Fuel Cladding Materials: Corrosion as a Function of Hydrogen Overpressure. EPRI, Palo Alto, CA:

12 Zry-4/Crud contact samples XRD of Crud 0 wt% Ni 15 wt% Ni 60 wt% Ni Peaks for Ni(m) have appeared for the specimens exposed at 100 and 500 cc The ratio between Ni(m)- peaks and NiO/NiFe 2 O 4 - peaks changes at different DH levels. The ratio between Ni(m)-peaks and NiO/NiFe 2 O 4 -peaks changes at different DH levels. Conversion of NiO/NiFe 2 O 4 to Ni metal at higher DH is observed 12

13 Zry-4/Crud Contact Samples Cladding Hydrogen Pickup Results Zry-4/Crud Contact Samples Cross-sectional SEM of Hydrides Zry-4/Crud Contact Samples Hydrogen Pickup Increasing DH Hydrides Increasing Ni The CRUD has been positioned towards the lower part of each of the figures Zry-4/Crud Samples: accelerated hydrogen pickup above 100 cc/kg and 60 weight% nickel metal crud Zry-4/Nickel Alloy 718 Samples: no visually (including microscopic) or profilometricly observable impact Baseline HPU at 30 cc H 2 /kg 13

14 Is this the same Ni window effect? HPU with high Ni CRUD content (arb. unit)? At 100 cc H 2 /kg H 2 O converts NiO / NiFe 2 O 4 to Ni metal At 100 cc H 2 /kg H 2 O and a high Ni content (60 wt%) increases the HPU DH (cc/kg) Primary concern is where the onset of increase HPU occurs 14

15 Dissolved Hydrogen and HPU Risk Most PWRs operate with dissolved hydrogen closer to 40 cc H 2 / kg H 2 O EPRI guidance is cc H 2 / kg H 2 O 4 Regulatory concern related to operation at elevated DH without benchmarking data for corrosion / hydrogen pickup models 5 PWR Cycle Average Hydrogen 6 Most concern for cores with highly crudded reload fuel where crud can redistribute to fresh cladding surfaces at restart Crud from highly boiling plants is known to contain more nickel 4 FRN , Proposed Rules, Performance-Based Emergency Core Cooling System Cladding Acceptance Criteria, March 24, Pressurized Water Reactor Primary Water Chemistry Guideline, Revision 7. EPRI, Palo Alto, CA: EPRI Fuel REliability Database (FRED) - EPRI 15

16 Path to Safe Operation of a PWR with Elevated Reactor Coolant Hydrogen Initial Fuels Plan to Reach Demonstration 1. Literature Review 2. Autoclave Tests 3. In-reactor tests 4. Plant Demonstrations Autoclave testing results No effect on the oxide growth for clean materials No effect on the hydrogen pick up for clean materials But, accelerated hydrogen pickup above 100 cc/kg with a high weight% nickel crud Both AREVA Inc. and Westinghouse have indicated in-reactor tests are not required BUT Plant demonstrations on hold due to limited interest Drivers of elevated hydrogen for mitigation of PWSCC in bottom mounted instrument nozzles unclear Peening may be more viable and cost effective 16

17 Summary and Conclusions A two year program of autoclave experiments was completed to evaluate the impact of dissolved hydrogen concentration on zirconium alloy corrosion and hydrogen pickup Long-term testing of many materials found no impact of dissolved hydrogen on corrosion or hydrogen pickup The nickel-window effect was also tested Significant corrosion and hydrogen pickup in all sputter-coated Zry-4 materials and catastrophic failure at highest dissolve hydrogen concentrations (500 cc H 2 / kg H 2 O) More representative testing of Zry-4 in contact with nickel based alloy spacers and nickel containing crud found less dramatic results Increased hydrogen pickup was observed for Zry-4 in contact with synthetic crud containing 60 wt% nickel metal and exposed to 100 cc H 2 / kg H 2 O dissolved hydrogen Further testing is warranted 17

18 18 Acknowledgments (non-author project contributors) Studsvik Mr. Peter Gillén Mr. Jimmy Karlsson Ms. Johanna Hjorteen Mr. Henrik Zakrisson Mr. Sören Karlsson Mr. Bo Johansson Dr. Daniel Jädernäs Ms. Maria Hövling Mr. Roger Lundström Mr. Henrik Nilsson Mr. Jari Syrjänen Mr. Timo Jokinen Mr. Per Ekberg Mrs. Ann-Sofi Pettersson Ms. Riitta Johansson Mrs. Anna-Maria Alvarez-Holstein Dr. Pia Tejland Mr. Anders Molander Ms. Charlotta Gustafsson Mr. Gunnar Wikmark Dr. Petter Andersson Ms. Lotta Nystrand EPRI Dr. Aylin Kucuk Mr. Jeff Deshon Dr. Bo Cheng Westinghouse Dr. Rita Baranwal Mr. Andrew Atwood Mr. Joe Long AREVA Mr. Larry Lamanna Mr. Damien Kaczorowski Mr. John Riddle Other Organizations Dr. George Sabol Dr. Fredrik Lindberg and Dr. Lyuba Belova (Swerea Kimab) Mr. Niklas Pettersson, KTH Mr. Sven-Erik Bäckman, Mr. Ingvar Bernhardsson (Degerfors Laboratorium)

19 References 1 Assessment of the Effect of Elevated Reactor Coolant Hydrogen on the Performance of PWR Zirconium-Based Alloys. EPRI, Palo Alto, CA: (publicly available) 2 MULTEQ Version 7.0 (EPRI Product ) 3 Out-of-Reactor Corrosion Tests of Fuel Cladding Materials. EPRI, Palo Alto, CA: (publicly available) 4 FRN , Proposed Rules, Performance-Based Emergency Core Cooling System Cladding Acceptance Criteria, March 24, Pressurized Water Reactor Primary Water Chemistry Guideline, Revision 7. EPRI, Palo Alto, CA: EPRI Fuel REliability Database (FRED) - EPRI 19

20 Together Shaping the Future of Electricity 20