Results of Tests to Demonstrate a Six-Inch Diameter Coater for Production of TRISO-Coated Particles for Advanced Gas Reactor Experiments

Abstract

The Next Generation Nuclear Plant (NGNP)/Advanced Gas Reactor (AGR) Fuel Development and Qualification Program includes a series of irradiation experiments in Idaho National Laboratory's (INL's) Advanced Test Reactor. TRISOcoated particles for the first AGR experiment, AGR-1, were produced at Oak Ridge National Laboratory (ORNL) in a twoinch diameter coater. A requirement of the NGNP/AGR Program is to produce coated particles for later experiments in coaters more representative of industrial scale. Toward this end, tests have been performed by Babcock and Wilcox (B&W) in a six-inch diameter coater. These tests are expected to lead to successful fabrication of particles for the second AGR experiment, AGR-2.While a thorough study of how coating parameters affect particle properties was not the goal of these tests, the test data obtained provides insight into process parameter/coated particle property relationships. Most relationships for the six-inch diameter coater followed trends found with the ORNL two-inch coater, in spite of differences in coater design and bed hydrodynamics. For example the key coating parameters affecting pyrocarbon anisotropy were coater temperature, coating gas fraction, total gas flow rate and kernel charge size. Anisotropy of the outer pyrolytic carbon (OPyC) layer also strongly correlates with coater differential pressure.In an effort to reduce the total particle fabrication run time, silicon carbide (SiC) was deposited with methyltrichlorosilane (MTS) concentrations up to 3 mol %. Using only hydrogen as the fluidizing gas, the high concentration MTS tests resulted in particles with lower than desired SiC densities. However when hydrogen was partially replaced with argon, high SiC densities were achieved with the high MTS gas fraction.

SiC layer microstructure in AGR-1 and AGR-2 TRISO fuel particles and the influence of its variation on the effective diffusion of key fission products

“…The two fuel lots in AGR-2 consisted of upgraded TRISO fuel particles each from a single batch of coated particles, one made with UCO kernels and one with UO 2 kernels. The TRISO coating process was conducted in a commercial-scale 150-mm-diameter fluidized bed coater and utilized similar SiC deposition conditions as the AGR-1 V3 composite, that is, MTS+H 2 +Ar at a bed temperature of ~1425 o C [14]. The two AGR-2 particle lots are denoted as "AGR-2 UCO" for the UCO kernel particles and "AGR-2 UO 2 " for the UO 2 kernel particles in the remainder of the manuscript.…”

“…Multiple particles from each batch were investigated to obtain a more representative data set for each variant. Discussions of the coating processes, variables, and differences between AGR-1 and AGR-2 coatings can be found in references [11,12], [14].…”

Preparation of Diffusion Couples for Irradiation and High Temperature Testing of Representative TRISO PyC/SiC

“…The SiC layer for the Baseline and PyC Variants were deposited using MTS in Ar + H2 at 1425 ºC to target the fine-grained SiC microstructure obtained during deposition of AGR-1 Variant 3 and AGR-2 UCO TRISO fuel [38,39]. Initial SiC depositions focused on obtaining optimal fluidization conditions.…”

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

“…Table 4, Table 5, and Table 6 provide typical attributes of UCO and UO 2 kernels, TRISO-coated particles, and fuel compacts used for the AGR-2 irradiation. The overall result from the AGR fuel fabrication efforts has been controllable and reproducible fabrication and improved characterization of the fuel forms, all of which contribute to better quality TRISO fuel [8,9,10]. Figure 2compares the standard deviation in coating layer thicknesses from historical German, Japanese, and U.S. fuel with recent results from the AGR program.…”