Analytical Report for the Department of Energy Office of Nuclear Energy on the Characterization of High-Burnup Fuel Specimens

Abstract

This report documents the second and final phase of the high-precision radiochemical assay (HP-RCA) of high burnup fuel specimens sampled from select fuel rods that are part of the DOE’s Sister Rod project. Reported here are the final seven of the sixteen high-burnup Zircalloy-clad UO2 fuel specimens analyzed by the Nuclear Analytical Chemical (NAC) Section in the Chemical Sciences Division (CSD) at the U.S. Department of Energy’s (DOE’s) Oak Ridge National Laboratory (ORNL). The analytical protocols and results for the first nine specimens have been previously reported in ORNL/TM 2022-2788, Analytical Report for Nuclear Regulatory Commission High Burnup Fuel Specimens [1]. As previously described, the HP-RCAs were performed using several analytical methodologies developed by the NAC to minimize the total uncertainties of the experimental results. The HP-RCA methodology consists of the following analytical protocols: • Dissolution: High-precision gravimetric hot cell dissolutions. • Separations and analyses via the rapid analysis of post-irradiation debris (RAPID) protocol: High-resolution chemical separations using high-pressure ion chromatography (HPIC). Additionally, prescreens and independent characterizations of fission and activation isotopes and isotopic distributions using the RAPID hyphenated HPIC and inductively coupled plasma–mass spectroscopy (ICP-MS) instrument throughout the fuel sample analyses. • Measurement Protocol 1: Uranium titrations using the Davies-Gray (D-G) uranium titration method. • Measurement Protocol 2: High-precision isotope ratio measurements using multi-collector ICP-MS (MC-ICPMS) or single-detector ICP-MS. • Measurement Protocol 3: Internal ratios using isotope dilution (ID)-MC-ICPMS or ID-RAPID high-precision methodologies to quantify isotopes in the sample with equivalent detector responses (within the uncertainty of the analysis). • Measurement Protocol 4: External calibration using gravimetric procedures to prepare the calibration standards when isotope ratio measurements were not possible. Detail descriptions of these protocols can be found in Reference 1. Results are reported in units of gram analyte per gram uranium (g/g U). These units negate any biases that may exist in the dissolution process, such as buoyancy effects or balance performance, associated with measurements performed in a hot cell that has temperatures approaching 35°C. Elemental uranium makes up the bulk of the fuel and can be measured to a significantly higher degree of accuracy and precision than the other analytes. Using uranium to anchor the measurements of the other analytes keeps their reported total uncertainties (bias and precision) as low as possible.