Host: The Japan Society of Mechanical Engineers
Name : The 30th International Conference on Nuclear Engineering (ICONE30)
Date : May 21, 2023 - May 26, 2023
In order to economically increase cycle lengths of pressurized water reactor, current regulatory burnup limit of 62 GWd/tU is expected to extend to ~75 GWd/tU. According to the experimental observation in the Halden IFA-650 tests, high burnup fuel seems more susceptible to turn into fine fragments (pulvers) in loss-of-coolant accidents (LOCAs). Due to the cladding ballooning and burst under temperature transients, fuel relocation and dispersal may occur, raising the licensing concerns related to core coolability as described in 10 CFR 50.46. The fuel relocation has been widely observed in various experimental programs and numerically investigated by onedimensional algorithm and three-dimensional simulation. However, there is few effort devoted to numerical investigation on fuel dispersal. This paper proposed a three-dimensional simulation framework with the coupled finite element method and discrete element method for fuel dispersal, in which coarse fuel fragments were modelled with Voronoi cells and the high burnup structure was established through small isolated particles. Besides, a method based on spline projection was used to build the geometry of cladding with burst opening. Three tests (191, 192, 193) conducted in the Studsvik program were chosen to validate the simulation results, in which the predicted dispersed mass of fragments fitted well with the experimental observation, indicating the viability of the simulation framework. Based on the validated simulation results, the mass fraction and filling ratio of fuel fragments along the axial direction were discussed to investigate the effects of burst opening size on fuel dispersal. Finally, the verification against the fuel dispersal model proposed by U.S. Nuclear Regulatory Commission was conducted to verify the high fidelity features of the DEM model in simulating fuel dispersal under LOCA.
