Jae-Ho Yang

KAERI’s Development of LWR Accident-Tolerant Fuel

Abstract The Fukushima accident has had a tremendous impact on Japan and the rest of the world in the areas of public health, economy, and nuclear energy policy. Thus, international consensus has been reached that inherent tolerance of nuclear fuel to severe accidents needs to be increased significantly to prevent accidents or to mitigate their consequences. In this respect, several countries have started to develop accident-tolerant fuel (ATF) that can tolerate loss of active cooling for a considerably longer time period than current fuels, while maintaining or improving performance during normal operations and operational transients and also enhancing fuel safety for beyond-design-basis events. The Korea Atomic Energy Research Institute is also developing ATF: surface-coated Zr cladding and metal-ceramic hybrid cladding for the purpose of suppressing hydrogen generation during severe accidents, and microcell UO2 pellets to enhance the retention of highly radioactive and corrosive fission products such as Cs and I, where all UO2 grains are enveloped by thin cell walls that act as chemical traps or physical barriers for the movement of fission products. When the screening of developing fuel materials has been performed through various out-of-pile tests, irradiation tests of the selected materials will be carried out in a research reactor to demonstrate their enhanced accident tolerance.

On the Minimum Thickness of FeCrAl Cladding for Accident-Tolerant Fuel

Abstract The thickness of iron-based accident-tolerant fuel (ATF) cladding is discussed in this technical note because its thickness tends to be reduced from conventional zirconium alloy cladding. Structural stability may be lost if the thickness cannot withstand external pressure. Thus, the minimum allowable thickness of the ATF cladding is studied here from the viewpoint of preventing a cladding collapse. The elastic buckling theory is used to obtain the minimum thickness. The uncertainties of the mechanical properties and dimension tolerances are taken into consideration. The ovality of the cladding is also incorporated. An example calculation is carried out for APMT cladding. It is evaluated that the minimum thickness is 0.45 mm when the safety factor against the buckling is set as 2.0 and 1% of the cladding radius is accommodated for the ovality. A reference guideline of the minimum thickness depending on the mechanical property variation is suggested.