Core debris interactions with coolant

Extensive release of ruthenium in case of violent fuel coolant interactions remains controversial [Ex. 2a - 2b] and though possible explanations have been provided to justify why such releases would be minimal, no experimental validation substaining the magnitude of this phenomenon currently exists. Anyway releases caused by melt interaction with water would only produce temporary increases in the containment atmosphere concentration of radioactive aerosol. So long as containment integrity is preserved, such releases are not risk significant. Again, the mass releases can cause difficulties for some filter systems because of water droplets created by the core debris interactions with coolant. 

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The hydrogen gas produced in-vessel can escape to containment, where its combustion can pressurize and heat the containment. Violent in-vessel fuel coolant interactions have the potential to fail the reactor vessel, or even containment, with the accompanying forceful ejection of radionuclides. The melting and downward relocation of core materials in the reactor vessel, if unarrested by the restoration of coolant, can breach the reactor vessel resulting in the discharge of hot core debris, radionuclides, and aerosols into Containment, where they may interact with the containment... 

Case 5 was identical to Case 3 except for the way heat transfer from molten materials was treated during relocation. In Case 3, it was assumed that molten materials would remain intact during relocation from the core to the reactor vessel lower head. This approach minimizes heat loss from the debris so that a relatively rapid thermal attack on the vessel follows. In contrast, it was assumed in Case 5 that molten materials would break up during relocation. This break-up could occur as a result of the pour interacting with vessel structures and with water below the core. However, the break-up of molten materials maximizes debris/coolant heat transfer, which delays the thermal attack on the reactor vessel until the debris has time to reheat. 

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