Advanced Zirconium Alloy for PWR Application

Transcription

1 Advanced Zirconium Alloy for PWR Application Anand Garde Westinghouse Nuclear Fuel Columbia, South Carolina, 29209, USA 16 th Zr International Symposium Chengdu, China, May 9-13,

2 Outline Advanced Alloy Objectives Composition of X5A and ZIRLO TM Composition Selection Basis for X5A Processing Development & Fabrication Sequence Microstructure and Second Phase Particles Autoclave Test Results Weld Corrosion Resistance Alloy Performance in PWRs A to D Comparison of Corrosion Resistance & H Pickup Conclusions 2

3 Advanced Alloy Objectives Improved Corrosion Resistance Lower Hydrogen Uptake Improved Wear Resistance Improved Creep Resistance Lower Irradiation Growth Stability of Irradiated Microstructure Enhanced PCI Resistance Improved Performance Post-Postulated Accidents Acceptable Weld Corrosion Resistance 3

4 Comparison of Composition of One Alloy Candidate X5A & ZIRLO (Nominal Wt%) Element Sn Nb Fe Cr Oxygen Zr X5A Balance ZIRLO Balance 4

5 Alloying Elements Level Selection Basis for X5A Tin level of 0.5%: a good compromise between good corrosion resistance & adequate mechanical strength Niobium level of 0.3%: a good compromise between improved in-reactor performance & good fabricability (Below Ex-reactor Solubility in Binary) Iron level of 0.35% to improve corrosion resistance & reduce irradiation growth Chromium level of 0.25 to improve weld corrosion resistance 5

6 Processing Variants of X5A Initial High Temperature Process (HTP) Applied to Small Ingots: HTP used for Zircaloy-4 Later Optimized Low Temperature Process (LTP) Applied to Large Commercial Size Ingot: LTP used for ZIRLO Both Variants Irradiated as Part of Lead Test Assemblies (LFAs) in Several PWRs Performance Data for Both Variants Discussed in this Presentation 6

7 Fabrication & Irradiation Sequence of Alloy X5A Variants HTP X5A (called Alloy A then) Made from Small Ingots Fabricated & Irradiated first in 2 PWRs and one Test reactor with Low Tin Zircaloy-4 (OPTIN) & Several Dilute Alloys Alloy Comparison Published in 2002 (ASTM STP 1423): HTP X5A Best Performing in 2002 Testing LTP X5A made from Large Ingot in 2003 & Tubes Irradiated in Many Rectors & Compared to ZIRLO Current Paper Reviews Data for both LTP & HTP X5A 7

8 Microstructure & SPP Size Comparison To Enhance the Creep Resistance of X5A with a relatively lower total alloying elements, the microstructure of as-fabricated clad tube is selected to be partially recrystallized (prxa) The average SPP size for LTP X5A is 90 nm. SPP size of LTP X5A is coarser than that of ZIRLO (less than 80 nm) 8

9 SPP Compositions for Two Alloys For LTP X5A: STEM-EDS Analysis Identified two types of SPP in X5A One type is rich in Nb: Zr-Nb-Fe-Cr particles Other type is Zr-Fe-Cr with some lower level of Nb No Beta niobium particles were detected For HTP X5A Only Zr-Fe-Cr with lower level of Nb, Coarser than LTP For ZIRLO: Beta Niobium & Zr-Nb-Fe particles 9

10 Review of Autoclave Test Results In lithiated water 633 K test, LTP X5A corrosion resistance was comparable to that of Zirlo while that of HTP X5A was significantly inferior In a 700 K Steam test, both versions of X5A have superior corrosion resistance than Zirlo In-PWR corrosion resistance of all 3 alloys are affected by in-pwr SPP evolution 10

11 Weld Corrosion Resistance of LTP X5A Laser Welds of Sheets Test 84-day 132-day Oxide Thickness Measured Region 633 K 700 K after Autoclaving Water Steam Low Ratio of Oxide Base 2.1µm 11.0µm thickness in Weld to Nonweld region Weld 2.8µm 13.8µm LTP X5A has Satisfactory Weld Corrosion Resistance Ratio W/B 11

12 Alloy Performance in PWR A (14x14 Design, 2 year Cycles) Burnup Maximum Fuel Rod Alloy Range, Oxide Range, Growth, % GWd/MTU µm LTP X5A HTP X5A ZIRLO

13 Alloy Performance in PWR B (17x17XL, Annual Cycles) Burnup Maximum Fuel Rod Alloy Range, GWd/MTU Oxide Range, µm Growth, % LTP X5A ZIRLO

14 Irradiation Growth in Test Reactor C Fluence 16 x n/m 2 ( E > 1MeV) Non-Fueled Specimens Alloy, Microstructure Growth, % Non-Aqueous Environment LTP X5A, 0.29 Growth not Impacted by Pellet Stack Interaction or prxa Cladding Hydrogen Uptake Evaluation of Breakaway Growth due to Neutron Damage ZIRLO, SRA ZIRLO, RXA 14

15 HTP X5A, ZIRLO Irradiated in Reactor D 50 Oxide Thickness (µm) HTP X5A ZIRLO Burnup (MWd/KgU) 15

16 Oxide Thickness vs. Burnup Oxide Thickness (µm) LTP X5A - PWR A LTP X5A - PWR B HTP X5A - PWR A HTP X5A - Test Reactor D ZIRLO - PWR A ZIRLO - PWR B ZIRLO - Test Reactor D Burnup (MWd/KgU) 16

17 Oxide Thickness vs. Modified Fuel Duty Index 50 Oxide Thickness (µm) LTP X5A ZIRLO Modified Fuel Duty Index (MFDI) 17

18 Comparison of Corrosion Resistance of X5A and ZIRLO Corrosion Resistance of HTP X5A is Comparable to that of ZIRLO Corrosion Resistance of LTP X5A is 30% Superior to that of ZIRLO - Improvement seen at high burnups and is also confirmed for higher modified fuel duty index 18

19 Comparison of Fuel Rod Irradiation Growth of Alloys Large Scatter in the data Possibly due to variable contribution of Pellet Stack Interaction with Clad It appears that -Growth of HTP X5A is Higher than that of ZIRLO -Growth of LTP X5A May be lower than that of ZIRLO 19

20 Post-Irradiation Cladding H Measurements from Test Reactor D Burnup of Fueled Segments about 44 GWd/MTU Four Specimens Evaluated for each Alloy Hydrogen Pickup of HTP X5A is 35% Lower than that of ZIRLO Impact of X5A Processing on its H pickup yet to be evaluated Segment Clad Alloy HTP X5A ZIRLO Hydrogen Range, ppm

21 Conclusions At a Burnup of about 50 GWd/MTU, Corrosion Resistance of LTP X5A is 30% Lower than that of ZIRLO while that of HTP X5A is Comparable In-PWR Irradiation Growth of LTP X5A is Lower than that of ZIRLO while that of HTP X5A is Comparable In-PWR Hydrogen Pickup of HTP X5A is 35% Lower than that of ZIRLO 21

22 Conclusions (Continued) X5A Weld Corrosion Resistance is Adequate for Potential In-PWR use of X5A Reduction of Fabrication Process Temperatures Improved In-PWR Performance of X5A Available In-PWR Performance Data up to 50 GWd/MTU Demonstrate that LTP X5A is a Promising Candidate Alloy for Future Application. Additional Higher Burnup Data Are Needed to Confirm the Alloy Performance 22

23 SPP in LTP X5A 30 Niobium (weight percent) Zr-Fe-Cr-(Nb) Zr-Nb-Fe-Cr Iron + Chromium (weight percent) 23

24 633 K Water Autoclave Test Results Weight Gain (mg/dm 2 ) LTP X5A HTP X5A ZIRLO Time (days) 24

25 70 ppm Li 633 K Water Test Results Weight Gain (mg/dm 2 ) LTP X5A HTP X5A ZIRLO Time (days) 25

26 700 K Steam Autoclave Test Results Weight Gain (mg/dm 2 ) LTP X5A HTP X5A ZIRLO Time (days) 26