Sister Rod Destructive Test Results (FY19)

Abstract

This report documents work performed under the Spent Fuel and Waste Disposition, Spent Fuel and Waste Science and Technology program for the US Department of Energy (DOE) Office of Nuclear Energy (NE). This work was performed to fulfill Level 2 Milestone M2SF-19ORO010201026 within work package SF-19OR01020102 and is an update to the work reported in M2SF-19OR010201028 and M3SF-19OR010201027. The document incorporates comments received with respect to the previous reports and incorporates additional test results. As a part of the US Department of Energy (DOE) Office of Nuclear Energy (NE) High Burnup Spent Fuel Data Project, Oak Ridge National Laboratory (ORNL) is performing destructive examinations (DEs) of high burnup (HBU) (>45 gigawatt days per metric ton uranium) spent nuclear fuel (SNF) rods from the North Anna Nuclear Power Station operated by Dominion Energy. The SNF rods, called the "sister rods," are all HBU and include four different kinds of fuel rod cladding: standard Zircaloy-4 (Zirc-4), low-tin Zircaloy-4 (LT Zirc-4), ZIRLO ® , and M5 ®. The DEs are being conducted to obtain a baseline of the HBU rod's condition prior to dry storage and are focused on understanding overall SNF rod strength and durability. Both composite fuel and empty cladding will be tested to derive material properties. While the data generated can be used for multiple purposes, a primary goal for obtaining the post-irradiation examination data and the associated measured mechanical properties is to support SNF dry storage licensing and relicensing activities by (1) addressing identified knowledge gaps and (2) enhancing the technical basis for post-storage transportation, handling, and consolidation activities. This report documents the status of the ORNL Phase I DEs of 8 sister rods and outlines the DE tasks performed and the data collected to date, as guided by the sister rod test plans. The DEs are performed using a phased approach, and the Phase 1 DEs being performed at ORNL include: • full-length rod heat treatments (FHT) of 3 selected sister rods to examine the effects of temperatures reached during dry storage preparation, Sister Rod Destructive Examinations

Sister Rod Destructive Examinations (FY22) Appendix J: Leaching of High Burnup Used Nuclear Fuel in Deionized Water

“…Two UO 2 fuel rods from an Advanced Mark-BW fuel assembly that had been irradiated in a Westinghouse PWR at the North Anna Power Station were selected based on similar burnup and fuel-cladding compositions for the leaching experiments [12]. Of the two samples, one has been heat treated to fuel drying temperatures as described in the sister rod destructive examinations (DE) report [11]. The rod specimens chosen were residues from the CIRFT experiment addressed in the sister rod reports.…”

“…Average measurements of the cladding thickness, pellet thickness, PCI layer, porosity, and HBU rim regions were provided for both samples, as shown in [11] and the gamma scanning, eddy current, and LVDT measurements provided in the nondestructive examination (NDE) report [13]. The PCI layer is visible throughout the perimeter of the fuel pellet, extending in the range of 9-15 µm.…”

Sister Rod Destructive Examinations (FY2021) Appendix J: Leaching of High Burnup Used Nuclear Fuel in De-ionized Water

“…One rod was heat treated to an average temperature of 409.4°C (Table J-1). The heat treatment was part of a separate study to analyze hydride re-orientation in the cladding [11]. Although the presence of hydrides in the cladding is not expected to have an effect on the leaching phenomenon, it has been observed that hydride realignment can reduce cladding strength, allowing water to more easily penetrate into the gaps and grain boundaries in the fuel's periphery.…”

“…Two UO2 fuel rods from an Advanced Mark-BW fuel assembly that had been irradiated in a Westinghouse PWR at the North Anna Power Station were selected based on similar burnup and fuel-cladding compositions for the leaching experiments [12]. Of the two samples, one has been heat treated to fuel drying temperatures as described in the sister rod destructive examinations (DE) report [11]. The rod specimens chosen were residues from the CIRFT experiment addressed in the sister rod reports.…”

“…Average measurements of the cladding thickness, pellet thickness, PCI layer, porosity, and HBU rim regions were provided for both samples, as shown in [11] and the gamma scanning, eddy current, and LVDT measurements provided in the nondestructive examination (NDE) report [13]. The central region (darker area in Figure J-20) appears to be higher in porosity than the surrounding fuel volume; the porosity was lower than that of the burnup rim and is distinguishable.…”