Re-evaluation of spent nuclear fuel assay data for the Three Mile Island unit 1 reactor and application to code validation

Abstract

Destructive radiochemical assay measurements of spent nuclear fuel rod segments from an assembly irradiated in the Three Mile Island unit 1 (TMI-1) pressurized water reactor have been performed at Oak Ridge National Laboratory (ORNL). Assay data are reported for five samples from two fuel rods of the same assembly. The TMI-1 assembly was a 15 × 15 design with an initial enrichment of 4.013 wt % 235 U, and the measured samples achieved burnups between 45.5 and 54.5 gigawatt days per metric ton of initial uranium (GWd/t). Measurements were performed mainly using inductively coupled plasma mass spectrometry after elemental separation via high performance liquid chromatography. High precision measurements were achieved using isotope dilution techniques for many of the lanthanides, uranium, and plutonium isotopes. Measurements are reported for more than 50 different isotopes and 16 elements. One of the two TMI-1 fuel rods measured in this work had been measured previously by Argonne National Laboratory (ANL), and these data have been widely used to support code and nuclear data validation. The recent measurements performed by ORNL provided an important opportunity to independently cross check results against previous measurements performed at ANL. These measurements serve to improve confidence in the data, to verify reported uncertainties, and to investigate previous anomalies noted in the plutonium measurements. The measured nuclide concentrations are used to validate burnup calculations using the SCALE nuclear systems modeling and simulation code suite. These results show that the new measurements provide reliable benchmark data for computer code validation.

Analysis of new measurements of Calvert Cliffs spent fuel samples using SCALE 6.2

“…More details about the dissolution procedures can be found in Ref. [1]. The weight of the fuel was calculated as the difference between the initial total fuel-clad weight and the post-digestion cladding weight.…”

“…Details of the sample preparation for DA and of the weight measurements can be found in Ref. [1]. For this set of fuel digestions, analysis of the undissolved solids (UDS) was not performed.…”

“…For alpha spectrometry, aliquots were diluted using nitric acid to obtain a satisfactory gross count rate and to keep the amount of solids on a plate to a minimum. Same alpha spectrometry measurement procedures were followed as the ones used for the TMI-1 fuel [1]. The alpha spectrometry analyses were used to determine emitted alpha energy ratios and were used in conjunction with the respective gross alpha analysis to associate alpha activity to the detected alpha energies.…”

“…External calibration curves for each of the fission product isotopes were made using NIST traceable certified standards. Same measurement procedures were followed as the ones used for the TMI-1 fuel [1].…”

“…A large selection of isotopes (51) was considered in this experiment. A similar DA measurement campaign was recently performed at ORNL on 5 spent fuel samples from the Three Mile Island-1 reactor; these measurements were analyzed using SCALE 6.1.3 and documented [1]. In addition to DA for the two CC-1 samples, gamma spectrometry was performed on the fuel rod segment from which these samples were obtained.…”