|
|
| Fig. 1: Fukushima Daiichi reactor pre-meltdown. (Courtesy of the Japan Ministry of Land, Infrastructure, Transport and Tourism. Source: Wikimedia Commons) |
Trying to create an accident tolerant nuclear fuel is a task easier said than done, with many different constraints to the process. The benefits of implementing an accident tolerant fuel (ATF) into modern-day light water reactors (LWRs) though are substantial. The ability to negate severe accidents from occurring is an ATFs calling card, something that has plagued the nuclear energy industry for decades. A recurring answer as to why nuclear energy should not be expanded upon is often the safety concerns associated with operating a nuclear power plant. The most recent and notable nuclear disaster in Fukushima, Japan in 2011 stands as the example often used to cite nuclear energys potential hazards (See Fig. 1). [1] Thus, that is why there Is considerable interest in developing an ATF for light water reactors that improves performance, reliability, and safety characteristics during normal operations and potential accident-prone conditions.
The fuel pellets in ATFs are one of the main technological pieces that differentiate accident- tolerant fuel from other fuel types. [1] The goal of ATF pellets is to remain reliable during normal operation and show enhanced retention of fission products during severe incidents. For example, the Fukushima disaster proved that the development of said pellets are needed to reduce the amount of radioactive material into the environment. The KAERI National Laboratory has developed a microcell UO2 pellet with the ability to enhance the retention capability of highly radioactive and corrosive fission products. The retention of highly volatile Cs and I is key due to their hazardousness to public health when released. [1] The key development behind the microcell UO2 pellets is to immobilize the Cs and I by providing chemical traps inside the pellet and reducing their diffusiveness. Inside a microcell UO2 pellet the grains are around 50 μm in size. At this size more than 150 cell walls are located around the diameter of the pellet, blocking the release of fission products. [1] These specific pellets were created by mixing 1 wt% of additive mixtures with ammonium diuranate-UO2 powder and then sintering those two powder mixtures at 1720°C for 4 hours in a dry hydrogen atmosphere. The sintered pellet density and average grain size for the pellets are within the ranges of 96.5% to 96.9% theoretical density and 80 to 87 μm, respectively.
The positives of implementing an accident-tolerant fuel in light water reactors are apparent, but it is not as easy as simply replacing fuel. Various steps are necessary to make ATF viable for use in current operations in LWRs. Continuing to research and develop new ways to improve nuclear energy's safety is paramount if the industry wants to survive into the future.
© Erik Miller. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] Y.-H. Koo et al., "KAERI's Development of LWR Accident-Tolerant Fuel," Nucl. Technol. 186, 295 (2014).
