An analysis of nuclear fuel burnup in the AGR-1 TRISO fuel experiment using gamma spectrometry, mass spectrometry, and computational simulation techniques

Abstract

AGR-1 was the first in a series of experiments designed to test US TRISO fuel under high temperature gascooled reactor irradiation conditions. This experiment was irradiated in the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) and is currently undergoing post-irradiation examination (PIE) at INL and Oak Ridge National Laboratory. One component of the AGR-1 PIE is the experimental evaluation of the burnup of the fuel by two separate techniques. Gamma spectrometry was used to non-destructively evaluate the burnup of all 72 of the TRISO fuel compacts that comprised the AGR-1 experiment. Two methods for evaluating burnup by gamma spectrometry were developed, one based on the Cs-137 activity and the other based on the ratio of Cs-134 and Cs-137 activities. Burnup values determined from both methods compared well with the values predicted from simulations. The highest measured burnup was 20.1 %FIMA (fissions per initial heavy metal atom) for the direct method and 20.0 %FIMA for the ratio method (compared to 19.56% FIMA from simulations). An advantage of the ratio method is that the burnup of the cylindrical fuel compacts can be determined in small (2.5 mm) axial increments and an axial burnup profile can be produced. Destructive chemical analysis by inductively coupled mass spectrometry (ICP-MS) was then performed on selected compacts that were representative of the expected range of fuel burnups in the experiment to compare with the burnup values determined by gamma spectrometry. The compacts analyzed by mass spectrometry had a burnup range of 19.3 % FIMA to 10.7 % FIMA. The mass spectrometry evaluation of burnup for the four compacts agreed well with the gamma spectrometry burnup evaluations and the expected burnup from simulation. For all four compacts analyzed by mass spectrometry, the maximum range in the three experimentally determined values and the predicted value was 6% or less. The results confirm the accuracy of the nondestructive burnup evaluation from gamma spectrometry for TRISO fuel compacts across a burnup range of approximately 10 to 20 % FIMA and also validate the approach used in the physics simulation of the AGR-1 experiment.

AGR-1 Post Irradiation Examination Final Report

“…The gamma scans of the compacts are described briefly in Section 3.2.1.2 and detailed in Harp 2014. Details of the burnup measurements from all of the techniques can be found in Harp et al 2014. Activities derived from gamma spectrometry measurements were converted to burnup via a relationship that was derived from simulations (Sterbentz 2013) and related activity or activity ratio to burnup. Both the direct 137 Cs burnup evaluation and the 134 Cs/ 137 Cs ratio burnup evaluation agreed well with simulations.…”

“…For example, Compact 5-1-2 has a minimum measured local burnup of 15.0% FIMA and a maximum measured local burnup of 17.2% FIMA. The use of this local burnup monitor is best illustrated by Figure 9 in Harp et al 2014. Determination of burnup from mass spectrometry data first involved dissolution of a small number of kernels from each compact examined. The method used to dissolve the actinides and fission products from the kernels for burnup analysis is described in the individual compact reports (Demkowicz et al , 2015b(Demkowicz et al , 2015c(Demkowicz et al , 2015d.…”

“…Regardless of the dissolution method, the burnup was calculated from the resulting mass spectrometry data in the same way. Burnup was calculated using the measured mass of a specific fission product in the fuel, the cumulative fission yield of that specific fission product, and the total mass of actinides present in the sample (Harp et al 2014). This method is sometimes referred to as the "Fission Product Monitor -Residual Heavy Atom" technique (Maeck et al 1973).…”

A summary of the results from the DOE advanced gas reactor (AGR) fuel development and qualification program

“…Flux wire measurements from the experiment also provide information on thermal and fast fluences after the experiment. Burnup has been measured by gamma scanning of compacts and dissolution of a few kernels from particles [18,19].…”

Testing Fast Reactor Fuels in a Thermal Reactor: A Comparison Report

“…The determination of burnup was performed using the measured mass of a specific fission product in the fuel, the cumulative fission yield of that specific fission product, and the total mass of actinides present in the sample. This method is sometimes referred to as the "Fission Product Monitor -Residual Heavy Atom" technique [35,36] and calculates burnup in Fission per Initial heavy Metal Atoms (%FIMA). All fission yields were taken from ENDF/B-VII.1 [37].…”