Fission Product Monitoring of TRISO Coated Fuel for the Advanced Gas Reactor-1 Experiment

Abstract

The US Department of Energy has embarked on a series of tests of TRISO-coated particle reactor fuel intended for use in the Very High Temperature Reactor (VHTR) as part of the Advanced Gas Reactor (AGR) program. The AGR-1 TRISO fuel experiment, currently underway, is the first in a series of eight fuel tests planned for irradiation in the Advanced Test Reactor (ATR) located at the Idaho National Laboratory (INL). The AGR-1 experiment reached a peak compact averaged burn up of 9% FIMA with no known TRISO fuel particle failures in March 2008. The burnup goal for the majority of the fuel compacts is to have a compact averaged burnup greater than 18% FIMA and a minimum compact averaged burnup of 14% FIMA.At the INL the TRISO fuel in the AGR-1 experiment is closely monitored while it is being irradiated in the ATR. The effluent monitoring system used for the AGR-1 fuel is the Fission Product Monitoring System (FPMS). The FPMS is a valuable tool that provides near real-time data indicative of the AGR-1 test fuel performance and incorporates both highpurity germanium (HPGe) gamma-ray spectrometers and sodium iodide [NaI(Tl)] scintillation detector-based gross radiation monitors.To quantify the fuel performance, release-to-birth ratios (R/B's) of radioactive fission gases are computed. The gamma-ray spectra acquired by the AGR-1 FPMS are analyzed and used to determine the released activities of specific fission gases, while a dedicated detector provides near-real time count rate information. Isotopic build up and depletion calculations provide the associated isotopic birth rates. This paper highlights the features of the FPMS, encompassing the equipment, methods and measures that enable the calculation of the release-to-birth ratios. Some preliminary results from the AGR-1 experiment are also presented.

Analysis of Fission Products on the AGR-1 Capsule Components

“…After each irradiation cycle in the ATR, a measurement was performed to determine the fraction of I-135 outside of the fuel. These measurements indicate the release fraction for I-135 is less than 10 -7 (Scates et al 2010, Hartwell et al 2007). Assuming the release of I-135 is similar to the release of other radioiodine isotopes, there is insufficient evidence to suggest a detectable amount of iodine (fractional release approximately 10 -6 ) migrated to the gas exit lines to justify a chemical evaluation of I-127 or I-129.…”

Detection and analysis of particles with failed SiC in AGR-1 fuel compacts

“…Rapid release of gaseous radioisotopes of krypton or xenon was used to monitor for TRISO coating failure in individual particles. Detection of this type of coating failure was an extremely rare event, with no occurrences during the three-year AGR-1 irradiation test of approximately 298,000 particles [Scates, 2010] and only two suspect particles in one of the fourteen safety-tested compacts (a compact tested at 1800°C) [Demkowicz et al, 2015].…”

TRISO-Coated Particle Fuel Performance

“…31 In all cases, the R/B is less than $10 À7 , indicative of release from heavy metal contamination. After 514 effective full power days, the time-averaged peak fuel temperatures ranged between 1120 and 1180 C Value is an estimate of an attribute property, not the mean of a variable property.…”