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India’s PFBR attains criticality at last
Prime Minister Narendra Modi proclaimed it “a proud moment for India” when on April 6 the 500-MWe, sodium-cooled Prototype Fast Breeder Reactor (PFBR) achieved initial criticality. This milestone, which comes some 22 years after the continually delayed PFBR project began, marks India’s entrance into the second stage of its three-stage nuclear program, which has the ultimate goal of supporting the country’s nuclear power program with its significant thorium reserves.
S. Patnaik, B. W. Spencer, E. Roberts, T. M. Besmann, T. W. Knight
Nuclear Science and Engineering | Volume 195 | Number 12 | December 2021 | Pages 1307-1326
Technical Paper | doi.org/10.1080/00295639.2021.1932223
Articles are hosted by Taylor and Francis Online.
A variety of normal operation and accident scenarios can generate thermal stresses large enough to cause cracking in ceramic fuel pellets. Cracking in fuel pellets can lead to reduced heat removal, higher centerline temperatures, and localized stress in the cladding—all which impact fuel performance. It is important to experimentally characterize the thermal and mechanical behaviors in the pellet both before and after cracking, which would help to improve cracking models in fuel performance codes such as BISON. However, in-reactor observation and measurement of cracking are very challenging due to the harsh environment and design of the fuel rods involved. Recently, an experimental pellet-cracking test stand was developed for separate-effects testing of pellet cracking under normal operations and accident temperature conditions using thermal imaging to capture the pellet surface temperatures in order to evaluate the thermal stresses and optical imaging to capture the evolution of cracking in real time. Experiments were performed using depleted uranium dioxide (UO2) pellets, which are useful for collecting valuable data for development and validation of cracking models. A combination of induction and resistance heating was used to create thermal gradients similar to those seen in a reactor environment. Characterization of the pellets was conducted both before and after cracking. The cracking patterns are moderately different from those expected in a typical reactor because of the variations in the thermal conditions and pellet microstructures. However, when the actual conditions of these experiments are reproduced in computational models with sufficient precision, such out-of-pile testing on UO2 pellets provides relevant data for modeling purposes.