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Nuclear Science User Facilities 140 Irradiation and Post-Irradiation Examination to Investigate Hydrogen- Assisted Anomalous Growth in Zirconium Alloys Paul Murray Idaho National Laboratory paul.murrayinl.gov Zirconium Zr alloy specimens are being irradiated inATR to study the mechanisms of irradiation- induced growth and its dependence on hydrogen H content and neutron fluence.The H produced by corrosion and dissolved in Zr alloys during service in light water reactors LWR can form hydrides and may promote irradiation growth. Differential strain resulting from H-assisted irradiation growth is postulated to be partly responsible for fuel channel bowing observed in boiling water reactors BWR. Project Description The objective of this project is to irradiate 200 specimens of various Zr alloys with various H concentra- tions in ATR up to four different neutron fluence levels.The change in length of the irradiated specimens will be measured to determine the irradiation-induced growth strain and transmission electron microscopy TEM will be performed to study the mechanism of irradiation growth. The knowledge gained from this experiment will be used to select Zr alloys that exhibit small growth strain which will improve the reliability of commercial reactors by minimizing fuel channel distortion caused by irradiation growth. Accomplishments The irradiation is taking place in an inert environment at a temperature of 285C and at four neutron damage levels expressed in terms of displace- ments per atom dpa. Four sets of 50 identical specimens were placed in four separate irradiation capsules identified as A B C and D. Capsule A completed irradiation to 6.7 dpa in January 2013 Capsule B completed irradiation to 12.3 dpa in January 2014 and Capsules C and D are currently being irradiated with a goal of reaching approximately 20 and 30 dpa respectively Figure 1. CapsulesA and B were subsequently transferred to INLs Hot Fuel Examina- tion Facility HFEF for post-irradiation length measurements.Those were completed for CapsuleA in September 2013 and for Capsule B inAugust 2014. An instrument was designed and built at INL to measure the length of irradiated specimens in HFEF using remote manipulators. It was tested and validated using specimens of known length.The geometric Figure 1. Measured growth strain of selected Zr alloys as a function of dpa normalized using the maximum growth strain. This experiment will provide the data needed to select Zr alloys that exhibit small growth strain which will improve the reliability of commercial reactors by minimizing fuel channel distortion caused by irradiation growth.