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Undeclared uranium hitches a ride on cobalt exports from Congo, study says
Philippe (left) and Manzuk quantified the amount of uranium that has been exported from the DRC in cobalt shipments or left behind in the environment. (Photo: Joel Hallberg/UW–Madison)
Researchers at the University of Wisconsin–Madison and Princeton University have published a study in Nature Communications that calls attention to a blind spot in nuclear nonproliferation: The Democratic Republic of the Congo (DRC) has exported thousands of metric tons of uranium, and there is no accounting for where it has gone.
In partnership with Lighthouse Reports and the Financial Times, UW–Madison nuclear engineering professor and nuclear security expert Sébastien Philippe and Ryan Manzuk, a geologist and research fellow in Philippe’s group and at Princeton, conducted the study using countrywide mineralization and geochemical data.
Vaclav Tyrpekl, Pascal Piluso, Snejana Bakardjieva, Olivier Dugne
Nuclear Technology | Volume 186 | Number 2 | May 2014 | Pages 229-240
Technical Paper | Reactor Safety | doi.org/10.13182/NT13-63
Articles are hosted by Taylor and Francis Online.
During a severe accident sequence in a pressurized light water reactor, the hot (∼3000 K) molten materials (corium) coming from the degraded reactor core may generate a violent interaction if they come in contact with water. This melt-water interaction, called fuel-coolant interaction (FCI), may damage the structures and threaten the reactor integrity if there is a steam explosion. FCI occurs generally in two phases: a premixing phase, during which the molten corium jet is fragmented into large droplets and mixed with the water, and the explosion phase, during which the vapor film that has developed around the fuel droplets is destabilized and the droplets are finely fragmented. The presented work covers a set of experimental studies describing the morphology and nature of the solidified materials after interaction with water. Debris from experiments performed in the KROTOS (Commissariat à l'Énergie Atomique, Cadarache, France); PREMIX, ECO (Karlsruhe Institute of Technology, Karlsruhe, Germany); and MISTEE (Royal Institute of Technology, Stockholm, Sweden) facilities have been characterized by metallographic, analytical, and microscopic techniques. These post-test analyses are able to provide important information on the solidification path and other main phenomena involved during FCI. It was found that the behavior of metallic and oxide melts differs significantly from the standpoint of debris morphology. Oxide melts that underwent simple coarse fragmentation showed spherical or angular rocklike shape, unlike metallic melts. A statistical analysis was performed on the debris from the KROTOS tests; a data set of particles was described by the circularity, solidity, and porosity. The mechanism of water ingression (Kim and Corradini) inside the melt droplet was observed to be the key mechanism of fine (secondary) fragmentation. The particles participating in fine “thermal” fragmentation have significantly higher porosity, up to ∼30% for prototypic corium in the KROTOS facility. It was calculated that only a part of the premixed melt participates in fine fragmentation, i.e., about one-third of the melt mass for the KROTOS tests using UO2-ZrO2 mixture.
