Smith, Tyler. The influence of second phase precipitates on hydride reorientation in spent nuclear fuel cladding

Principal Investigator
First Name:
Tyler
Last Name:
Smith
Institution:
University of Tennessee-Knoxville
Title:
Graduate Student
Team Members:
Name: Institution: Expertise: Status:
Steven Zinkle University of Tennessee-Knoxville Irradiation-Induced Degradation, Structural Damage Faculty
Experiment Details:
Experiment Title:
The influence of second phase precipitates on hydride reorientation in spent nuclear fuel cladding
Describe the work that you are proposing in detail. Please include as many specifics as possible (e.g., dose, dose rate, ion energy, types of ions, beam line x-ray energy, irradiation temperature, analysis temperature, atmosphere, etc.):
This work proposes to use in-situ heating tensile testing and Differential Scanning Calorimetry (DSC) investigate the influence of second phase precipitates on hydride reorientation in spent nuclear fuel rods from H.B. Robinson, North Anna, and Surry-2 U.S. commercial nuclear power reactors. The cladding specimens from the H.B. Robinson and Surry-2 pressurized water reactors (PWRs) are cold-worked/stress relieved Zircaloy-4 rods that have average burnups of 67 and 36 GWd/MTU and average hydrogen contents of 800 and 300 wppm, respectively. The cladding specimens from the North Anna PWR are recrystallized M5 rods that have an average burnup of 72.9 GWd/MTU and an average hydrogen content of 120 wppm. We have performed post-irradiation hydrogen reorientation treatments (HRT) on these samples using a high pressure/high temperature system that we designed in the 3525 hot cells at ORNL and have sent them to LAMDA for the proposed work. Microstructural characterization results from Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (S/TEM), and optical microscopy revealed a possible influence of second phase precipitates on the ability for a hyrdride to successfully reorient under HRT conditions. DSC has been selected to determine the terminal solid solubility and precipitation temperatures of the hydrogen in the spent nuclear fuel rods. In-situ heating tensile testing has been selected to investigate the hydride reorientation mechanism in real time. These results will be compared with the previously obtained TEM and STEM data for the three irradiated cladding conditions.
Technical Abstract
The objective of this project is to investigate the mechanistic effect of hydride reorientation in spent nuclear fuel cladding. Synergistic effects of irradiation at these conditions in spent nuclear fuel rods from H.B. Robinson, North Anna, and Surry-2 U.S. commercial nuclear power reactors have previously been studied and initial results have indicated a potential influence of irradiated-induced second phase precipitates on the re-precipitation of hydrogen during hydride reorientation. The results indicate a migration of second phase precipitates along reoriented hydrides in post-hydride reorientation samples, however, the magnitude of their influence on hydride reorientation has not explicitly been quantified. To more realistically investigate the mechanism and influences of these precipitates on hydride reorientation behavior, this project requires advanced microanalysis techniques including differential scanning calorimetry (DSC), focused ion beam (FIB), and in-situ heat tensile testing. DSC analysis provides terminal solid solubility and precipitation curves that describe the behavior of the hydrides during hydride reorientation in the presence of second phase precipitates. FIB will be used to perform the final sample thinning for in-situ heat tensile testing. The in-situ heat tensile testing will be utilized to produce live images of the hydrides during hydride reorientation. Data collected will provide key insight into the fundamental mechanism of hydride reorientation in spent nuclear fuel clad specimens that have been exposed to commercial light water reactor conditions. This will directly address issue of degradation in nuclear fuel cladding in the United States during the transportation and post-irradiation storage of nuclear fuel. The Nuclear Regulatory Commission (NRC) regulations on the storage of used nuclear fuel are spelled out in 10 Code of Federal Regulations (CFR) Part 72, in which the licensing of dry storage is being proposed to increase from 20 years to 40 years, and beyond. In this case, understanding the effects of hydrides and hydride reorientation in nuclear fuel cladding (potential embrittlement mechanisms) become increasingly important to formulate the technical basis for continued safe, long-term storage of used nuclear fuel that will accommodate the final used fuel management options. This project is predicted to take no more than 5 months to complete. Data collection from DSC testing is expected to take no more than 1 month. Fabrication of in-situ heat tensile testing samples using FIB techniques is expected to take no more than 1 month. Data collection from in-situ heat tensile testing is expected to take no more than 3 months. Data analysis and reporting will take approximately 4 months from the date of initial data collection.