**2.2 Ki-Jang Research Reactor—Fuel Assembly Irradiation**

The Ki-Jang Research Reactor is a new isotope production reactor being pursued by the Republic of Korea [2]. This fuel is the first-of-a-kind of U-Mo fuel for commercial utilization; thus, it requires a license to be granted and a qualification of the fuel at scale. Thus, the KJRR-FAI is a full-size prototype designed to test mechanical integrity, geometric stability, acceptable dimensional changes, and assurance that the performances of the fuel meat and fuel element are stable and predictable during irradiation. This testing was conducted in the northeast lobe of the ATR from October 2015 to February 2017 in cycles 158A, 158B, 160A, and 160B [3]. These irradiations successfully demonstrated the KJRR fuel element's reliability in prototypic conditions to a burnup of 83.1% U-235.

The KJRR fuel element is based on the very successful plate-in-box fuel concept used in many research reactors across the world. Coincidently, this type of fuel has its origins in ATR's predecessor, the Materials Testing Reactor (MTR) [4]. The KJRR fuel is of the genre of high-density High Assay Low Enriched Uranium (HALEU) research reactor fuels, enriched to 19.75% 235U/U [3]. The fuel meat is a dispersion fuel consisting of uranium-molybdenum alloy (U-7Mo) (i.e., seven w/o Mo) dispersed in an Al-5Si matrix (i.e., five w/o Si) (**Figure 2**). This dispersion fuel is clad in aluminum alloy Al-6061. There are 21 straight (not curved) fuel plates. The inner 19 fuel plates have a uranium density of 8.0 g-U/cm<sup>3</sup> . The outer two fuel plates have a uranium density of 6.5 g-U/cm<sup>3</sup> . The enrichment zoning is to reduce the radial power peaking in the fuel element (**Figure 3**).

The overall dimensions of the KJRR fuel element are 76.2 76.2 1010 mm. However, the active height of the KJRR-FAI fuel meat is only 60 cm (23.6 inch), which is less than half that of the active height of an ATR fuel element which is 48 in [5]. The KJRR-FAI was irradiated in the ATR northeast flux trap (**Figure 1**).
