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.

Evaluation of a Versatile Experimental Salt Irradiation Loop (VESIL) inside the Advanced Test Reactor

“…This includes insoluble fission gases (e.g., Xe, Ar, Kr) but also volatile salt species that can form due to radiolysis among other things (e.g., CsF2). Such a system could leverage the existing AGR experiment infrastructure at ATR, which monitors fission-gas releases from TRISO fuel particles [17]. The fission-gas monitoring system for the AGR is illustrated in Figure 6.…”

“…Illustration of the gas flow monitoring system for the AGR-1 experiment. The capsuled labeled 1 to 5 contain fuel particles and are within the ATR core (taken from [17]).…”

AGR-1, AGR-2 and AGR-3/4 Release-to-Birth Ratio Data Analysis

“…The FPMS detector is capable of detecting individual fuel-particle failures and providing release rates for the 12 gaseous radionuclides, as specified in SPC-1345, "AGR-3/4 Irradiation Test Specification." The summary of FPMS and release-data determination for the AGR-1 experiment is given in Scates (2010). This procedure is also used for all AGR irradiations.…”

“…Actual transport times were calculated from outlet-gas flow rates and the capsule-specific volumes through which samples flow to reach the respective monitoring detector. This conversion formula was derived under the assumption that the equilibrium release conditions were established (Scates 2010). This system provides the fission-gas release rate in individual capsules at 8-hour intervals.…”

Quantity of ¹³⁵I released from the AGR-1, AGR-2, and AGR-3/4 experiments and discovery of ¹³¹I at the FPMS traps during the AGR-3/4 experiment

“…The usual measurement protocol acquires gamma-ray spectra with counting times of eight hours. This gives adequate measurement sensitivity and provides three sets of results each day which are used to compute daily capsule release activity values [3,4,5]. Transport times from each capsule to its respective FPM are estimated using capsule-specific effluent flow rates and transport volumes, the volumes through which the effluent flows between the capsule and the FPM.…”