WIR SCHAFFEN WISSEN – HEUTE FÜR MORGEN Sousan Abolhassani:: Senior Scientist :: Paul Scherrer Institut Towards an improved understanding of the mechanisms involved in the increased hydrogen uptake and corrosion at high burnups in zirconium based claddings ASTM International, Manchester, 21st May 2019
WIR SCHAFFEN WISSEN – HEUTE FÜR MORGEN Sousan Abolhassani1, Adrienn Baris1, Robin Grabherr1, Jonathan Hawes1, Aaron Colldeweih1, Radovan Vanta1, Renato Restani1, Armin Hermann1, Johannes Bertsch1, Melanie Chollet1, Goutam Kuri1, Matthias Martin1, Stephane Portier1, Holger Wiese1, Herbert Schweikert1, Gerhard Bart1, Katja Ammon2, Guido Ledergerber2, Magnus Limbäck3 1Laboratory for Nuclear Materials, Nuclear Fuels Group, NES, and AHL, NES, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland. 2Kernkraftwerk Leibstadt AG, CH-5325 Leibstadt, Switzerland, 3 Westinghouse Electric Sweden AB, SE-72163 Västerås, Sweden.
The aim of the project • To search for the causes of increased H Uptake at high burnups • The strategy selected: − Step 1: To study a very high burnup cladding (here a 9-cycle BWR) and look at the hints pointing to changes in characteristics. − Step-2: Then extrapolate the changes to lower burnup examples of the same cladding grade under very similar conditions − Step-3: Determine the indicators − Step-4: Check if they are valid in other alloys or other reactors • Evaluate which regime is acting at which stage?
Parameters influencing hydrogen distribution Correlation between oxidation and hydrogen content (example of a BWR) Hydrogen content as a function of oxide thickness 800 100 % 50 % 25 % Hydrogen content (ppm) 15 % HPF LK3/L 6 c LK3/L 7 c 600 LK3/L 9 c LK3/L 5 c LK3/L 3 c 400 LK2/L 7 c LK2/L 6 c LK2/L 3 c LK2/L 6 c new 200 0 0 20 40 60 80 100 120 140 Average oxide thickness (micrometer) Different alloys (LK3/L and LK2/L cladding) behave differently. For identical elevation hydrogen uptake increases with the burnup, the hydrogen pickup fraction (HPF) is not constant and it increases with the high burnup in one alloy and decreases in a second alloy. Data in graph is for mid-span peak burn-up elevation, approx. 2000 mm. [Abolhassani et al. ASTM 17 th , 2013]. Page 4
Outline • i. Study of the 9-cycle Zircaloy-2, LK3/L from KKL (BWR) cladding to look for great changes • ii. Comparison with a low burnup (here 3-cycle) and an intermediate burnup (here 6-cycle) cladding from the same grade material and the same reactor; to verify the validity of indicators • iii. Examination of mechanical and semi-conducting properties of the oxide layers in the case of the two extreme cases • iv. Verification of PWR material to search for general phenomena • v. The use of the data to define the determinant indicators • vi. Correlation with the known parameters • vii. Conclusion
Materials selected for the current study Comp. Sn Fe Cr Ni Nb Fe+Cr(+Ni) C O Si H.T. Specimen ppm ppm ppm LK3/L (Zircaloy-2)* 1.34 0.18 0.11 0.05 0.34 - 1320 70 logA* wt% -14.2 LK3/L (Zircaloy-2) 1.02 0.29 0.19 0.077 0.557 at% Low-tin Zircaloy-4 1.20 0.22 0.107 - - 140 1730 - 504 ° C 0.337 wt% SRA Low-tin Zircaloy-4 - - 0.914 0.356 0.186 0.542 at% Zr-2.5%Nb - 0.07 - - 180 1170 60 500 ° C 2.5 - wt% PRX Zr-2.5%Nb at% The chemical composition of alloys used for the current study, (H.T.: heat treatment, SRA: stress relieve annealed, and PRX: partially recrystallized condition) [13], [17] and [19] 6
Outline • i. Study of the 9-cycle Zircaloy-2, LK3/L from KKL (BWR) cladding to look for great changes • ii. Comparison with a low burnup (here 3-cycle) and an intermediate burnup (here 6-cycle) cladding from the same grade material and the same reactor; to verify the validity of indicators • iii. Examination of mechanical and semi-conducting properties of the oxide layers in the case of the two extreme cases • iv. Verification of PWR material to search for general phenomena • v. The use of the data to define the determinant indicators • vi. Correlation with the known parameters • vii. Conclusion
Step 1 • i. Study a very high burnup cladding to look for great changes (in this case a Zirc-2 with LK3/L grade from KKL after 9 cycles) − a- Observation of macroscopic changes in the cladding from PIE: NDT and DT − b- Observation of microscopic changes in the cladding: from EPMA, TEM, 3D FIB, micropillar compression test, etc.
a- Observation of macroscopic changes in the cladding from PIE: NDT and DT Profilometry A GB108-G6 (272-25167; LK3) Diameter midspan AGB108-G6 (272-25167) DIM0.180 DIM90.270 0 DIM45.225 750 9,8 9,95 DIM135.315 1507 DIMRING 1995 315 45 9,90 3000 9,7 [mm from BEP] 9,85 Diameter [mm] Diameter [mm] 9,6 9,80 9,5 9,5 270 90 9,75 9,70 9,6 9,65 9,7 225 135 9,60 0 500 1000 1500 2000 2500 3000 3500 4000 9,8 180 Position from tip of bottom end plug [mm] Filename: AGB108-G6_272-25167 Profilometrie.opj Filename: AGB108-G6_272-25167 Profilometrie.opj WI43-17.10.2007 WI43-23.07.2007 Results of profilometry of rod AGB108-G6 Azimuthal plot of rod diameter at different elevations. diameter plot at different orientations: 0 ° , 45 ° , 90 ° , 135 ° (corrected for comparison with other data) Page 9
a- Observation of macroscopic changes in the cladding from PIE: NDT and DT a b Comparison of hydrogen content (DT) at different elevations (a) and rod growth (b) from pool side NDT investigations; for LK3/L cladding grade and as a function of number of cycles. As can be observed, the 9 cycle rod shows a rapid rod growth. Ledergerber, G., et al. “Fuel Performance Beyond Design – Exploring the Limits,” Proceedings of 2010 LWR Fuel Performance/Top Fuel/WRFRM, American Nuclear Society, Orlando, FL, Sept 26–29, 2010, Paper 0044
a- Observation of macroscopic changes in the cladding from PIE: NDT and DT a b Comparison of hydrogen content (DT) and rod growth (NDT), (a) as a function of oxide thickness, for LK3/L cladding grade and (b) as a function of burnup for two different cladding grades
a- Observation of macroscopic changes in the cladding from PIE: NDT and DT Correlation between rod average hydrogen concentration in the metal and %age rod growth 1.00 0.80 Rod growth (%) LK3/L rods 0.60 LK2/L rods 0.40 LK3/L 3c a b 0.20 Comparison of hydrogen content (DT) and rod growth (NDT), (a) as a function of 0.00 oxide thickness, for LK3/L cladding grade and (b) as a function of burnup for two 0 200 400 600 800 different cladding grades Hydrogen content in metal (ppm) Calculated volume increase of the rod as function of hydrogen content (all expansion assumed in axial direction)
Step 1 • i. Study a very high burnup cladding to look for great changes (in this case a Zirc-2 with LK3/L grade from KKL after 9 cycles) − a- Observation of macroscopic changes in the cladding from PIE: NDT and DT − b- Observation of microscopic changes in the cladding: from EPMA, TEM, 3D FIB, micropillar compression test, etc.
b- Observation of microscopic changes in the cladding: from EPMA, TEM, 3D FIB… Fe Ni Cr O AGB108-G6-GF: SEM, BSE and EPMA distribution mappings of Cladding at the Metal/Oxide interface; at orientation of (200 0 ). HV 15kV, 200nA, 120 ms/pix (192 x 192 pix.) Large hydrides in the metal side, depleted from Fe and to some extent Ni. A. Baris et al. «Causes of increased corrosion and hydrogen uptake of Zircaloy-2 cladding at high burnups – A comparative study of the chemical composition of a 3 cycle and a 9 cycle cladding»; Proceedings of the TopFuel Conference, 2018.
b- Observation of microscopic changes in the cladding: from EPMA, TEM, 3D FIB, micropillar compression test, … Distribution of hydride precipitates, in the 9-cycle LK3/L observed in the EPMA, with no etching. Hydrides are distributed unevenly and the waterside rim has a higher density of hydrides.
b- Observation of microscopic changes in the cladding: from EPMA, TEM, 3D FIB, micropillar compression test, … Area fraction of hydrides along the 9-cycle LK3/L cladding wall from inner to the outer surface of the tube. The hydride present in the liner is not taken into consideration in this graph.
b- Observation of microscopic changes in the cladding: from EPMA, TEM, 3D FIB … HAADF and Chemi-STEM maps of 9-cycle LK3/L showing the grain boundary segregation in the metal side of the interface [19]. A. Baris et al. «Causes of increased corrosion and hydrogen uptake of Zircaloy-2 cladding at high burnups – A comparative study of the chemical composition of a 3 cycle and a 9 cycle cladding»; Proceedings of the TopFuel Conference, 2018.
3D imaging of the FIB cut layers (example of the metal- oxide region in the cladding) radial crack metal-oxide interface A C B Cracks of the oxide formed in the last cycle, i.e. close to the metal-oxide interface. A, B and C indicates the possible subdivision of the cracks. A. Baris et al. “Chemical and microstructural characterization of a 9 cycle Zircaloy-2 cladding using EPMA and FIB tomography”; Journal of Nuclear Materials, 2018, 504, pp. 144-160. Page 18
3D imaging of the FIB cut layers (example of the metal- oxide region in the cladding) 3D reconstruction of the waterside oxide of the 9 cycle sample. Green objects: cracks, transparent pink object: oxide matrix. A. Baris et al. “Chemical and microstructural characterization of a 9 cycle Zircaloy-2 cladding using EPMA and FIB tomography”; Journal of Nuclear Materials, 2018, 504, pp. 144-160. Page 19
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