![]() The experiments provide data for validating computer models that simulate corium-concrete interaction. “We’re often testing unique cooling systems that can be placed in the concrete floors at plants in order to cool core material if it fails the reactor vessel, and this enhances reactor safety.”ĭifferent types of concrete have unique chemical properties that can resist the corium, and can also affect how the corium erodes into concrete. as well as international organizations in countries like France, Japan, and Korea,” said Argonne nuclear engineer Mitch Farmer, who leads the team. Nuclear energy companies often cosponsor the tests to improve safety at their plants. The building is now one of the only places in the national lab system rated strong enough to conduct these types of tests. The walls are three feet thick, built decades ago to contain experiments on fully functioning nuclear reactors the air is heavily filtered and the thick steel doors seal shut. One of the lab’s most secure facilities lets a team of scientists safely conduct these experiments. Atomic Energy Commission’s primary lab for developing reactors for peaceful energy generation. ![]() Next, they examine how the corium interacts with the concrete beneath.Īrgonne does the largest experiments of this type in the world, thanks to its early history as the U.S. Typically, researchers produce a large pool of molten corium via a chemical reaction and then run an electric current through it to mimic the heat produced in the fuel during a meltdown. To make sure that the final concrete barrier can withstand the stress of any failure at a reactor, Argonne nuclear engineers have been conducting tests for decades to simulate the effects of partial and full meltdowns on concrete materials. Experiments at Argonne help us understand what happens to fuel and the concrete beneath in case of a meltdown to improve safety. This cutaway diagram shows the barriers in place to contain the fuel, including the primary containment, reactor vessel, and thick concrete basemat beneath the reactor. Three Mark I boiling water reactors at Fukushima Daiichi experienced at least partial fuel meltdowns after the earthquake and tsunami there on March 11, 2011. If backup generators fail and can’t cool the core-which is what happened at Fukushima-the uranium rods of the core and their cladding can melt together into a substance called “corium.” During a full meltdown, this material may leak through the steel vessel and pour out onto the thick concrete floor below. However, the core continues to generate heat, and has to be continuously cooled. If a disaster, such as a tsunami, knocks out power to a reactor, all reactors have safety systems that shut down the reactor. The first is a layer of metal “cladding” directly around the uranium the second is a thick steel reactor vessel and the third is a sturdy concrete containment building with walls, floors, and ceiling several feet thick. In all modern nuclear reactors, there are three barriers to contain the uranium fuel. ![]() The emergency prompted hundreds of thousands of people in the region to leave their homes amid fears of radiation contamination and a nuclear explosion.Other Argonne scientists consulted for the DOE, lending their expertise in the very scenario that experts believed took place at Fukushima: nuclear fuel eroding the concrete floor beneath the reactor. The plant suffered a triple meltdown after it was hit by a powerful earthquake and ensuing tsunami in March 2011. In February, a remote-controlled robot with tongs removed pebbles of nuclear debris from the Unit 2 reactor but was unable to remove larger chunks, indicating a robot would need to be developed that can break the chunks into smaller pieces. Robotic probes have photographed and detected traces of damaged nuclear fuel in all three reactors that had meltdowns, but the exact location and other details of the melted fuel are largely unknown. The work is carried out remotely from a control room about 500 metres away because of still-high radiation levels inside the reactor building that houses the pool. The whole process occurs underwater to prevent radiation leaks. Workers are remotely operating a crane built underneath a jelly roll-shaped roof cover to raise the fuel from a storage rack in the pool and place it into a protective cask. Removing the fuel in the cooling pools was delayed for five years by mishaps, high radiation and radioactive debris from an explosion that occurred at the time of the reactor meltdown, underscoring the difficulties that remain. The step comes ahead of the real challenge of removing melted fuel from inside the reactors, but details of how that might be done are still largely unknown. ![]()
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