Monolithic ATF MiniFuel Sample Capsules Ready for HFIR Insertion

Abstract

Several advanced nuclear fuel concepts are being considered throughout the nuclear industry. Implementation of these concepts could increase accident tolerance or enhance performance beyond the capabilities of the UO2-based nuclear fuel currently in use. Qualification and deployment of any new fuel requires rigorous irradiation testing to demonstrate performance under representative normal and offnormal operating conditions. The traditional approach for qualifying new fuels requires exhaustive execution of many integral fuel tests. However, due to the long timeframe for executing these integral tests and the limited number of available materials test reactors, this approach is becoming impractical. To accelerate fuel qualification, Oak Ridge National Laboratory developed the MiniFuel irradiation vehicle for use in conducting accelerated separate effects irradiation testing of a wide range of nuclear fuel materials in the High Flux Isotope Reactor (HFIR). The first MiniFuel irradiations performed in the facility tested sol gel-derived uranium nitride kernels and tristructural isotropic (TRISO)-coated particle fuels. This report describes the preparation and assembly of the first set of monolithic MiniFuel irradiations conducted to support accident-tolerant fuel (ATF) development and accelerated fuel qualification. Two irradiation targets containing a variety of UO2 and U3Si2 disk fuel specimens were fabricated and assembled for irradiation to burnups of 8−10 and 28−40 MWd/kg U. The target irradiation temperature is 450−550°C. Irradiation of U3Si2 will provide new data regarding the irradiation performance of a candidate ATF to complement current ATF-1 integral experiments being performed in the Advanced Test Reactor. UO2 samples were included as a reference so that the results from the MiniFuel experiments can be compared with the extensive UO2 fuel performance database. The monolithic MiniFuel capsules were successfully assembled, welded, and tested per HFIR requirements and are ready for insertion into the reactor. Pictures of the assembly process are included in this report. The experiment is planned for insertion into the HFIR during cycle 487 in April 2020.

Evaluation of BISON's Transient Fission Gas Release Model on High-Burnup UO₂ MiniFuel

“…In addition to higher burnups, FGR at higher fuel temperatures, representative of an LWR fuel centerline temperature, needs to be investigated. In fact, in the previously discussed MiniFuel irradiation tests, the target fuel temperature is around 500°C [2,4] similarly to the fuel temperature at the rim region in LWR normal conditions [11].…”

“…This allows for a decoupling of the fuel temperature from the fission rate, and hence better control of the experimental conditions [1]. Overall, compared to integral fuel tests, MiniFuel tests can potentially provide more detailed information on irradiation-induced mechanisms such as fission gas release in a shorter time and with less fabrication cost and effort than separate effects testing [1][2][3][4].…”

“…In addition to UN kernels and UN TRISO particles, monolithic MiniFuel capsules of UO2 and U3Si2 disks have been fabricated and prepared to be irradiated in HFIR at low irradiation temperature [4]. The target burnup is 8 to 10 MWd/kgU for UO2 and 28 to 40 MWd/kgU for U3Si2, an accident tolerant fuel [4].…”

“…Miniature Fuel (MiniFuel) has recently emerged as a new fuel testing design to provide insight into fuel behavior under accelerated and well-controlled conditions [1][2][3][4][5], similarly to the Halden disk concept [6].…”