Phébus research reactor

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Phébus is a relatively small research reactor in the French nuclear research center Cadarache , which was used in the 1990s and 2000s to carry out international experiments on core meltdown processes in nuclear power plants.

So far, five experiments have been carried out, which are currently considered final for the project. All experiments were carried out with a real, scaled-down uranium reactor core, with which accident findings were obtained for the actually existing reactor cores of mainly pressurized water reactors . The Phébus core was artificially melted.

An important new finding from the experiments is, for example, that the loss of the so-called core geometry, i.e. the transition of the core shape into a partial melt mass, occurs at significantly lower melting temperatures than previously assumed. It was also found that the very volatile applicable radionuclide 131 iodine by prolonged length of stay in a still-tight containment (containment) Although various structural materials such as paint, or then the also relatively volatile radionuclide 137 cesium in water on the containment floor to molecules binds, which are less volatile and therefore tend not to be released into the environment through a possible leak. This was discovered during the inspection of the containment a few years after the accident at the Three Mile Island nuclear power plant . However, Phébus has now shown that the findings there were too optimistic, mainly due to the time elapsed up to the inspection of the nuclear power plant Three Mile Island reactor ruins: A considerable part of the 131 iodine released into the containment is over the short time in a reactor accident not bound until it decays ( half-life 8 days), so it remains volatile and escapes into the environment through a possible containment leak.

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