‘The system kicks in automatically and no operator action is required,’ said Prof. In a reactor’s case, it can rapidly remove heat from the core’s surface and release it through steam. Its strength rests in the fact that supercritical CO2 is able to transport huge amounts of heat in a low-cost, non-toxic and non-flammable way. In theory, the system designed by sCO2-HeRo would stop a meltdown before it begins, opening a window for power plant operators to identify, and address, the potential overheating of the core by, for example, alternative mobile cooling systems. ‘By removing the heat, it prevents a potential core meltdown and buys time to react,’ said Professor Dieter Brillert from the University of Duisburg-Essen in Germany, who is the project coordinator of sCO2-HeRo, an EU-funded project developing the technology. The supercritical CO2 approach effectively removes heat build-up from a core without the requirement of external power sources, meaning it could work if the power is somehow cut, for example, during a natural disaster. They are working towards different ways to eliminate the risk of nuclear meltdowns, with automatic methods such as a heat removal system using so-called supercritical CO2, a state where the chemical has properties of both a gas and a liquid, and the use of molten salt. However, if the threat of a meltdown can be removed, some scientists think we should reconsider tapping into this carbon-free source of energy. Over the last few decades, public fears in some countries have prevented more nuclear power from entering the grid. The core - where the nuclear reactions take place - can’t withstand the rising temperature and begins to melt, allowing radioactive materials to possibly escape into the environment. Finally, using a geometric mesh for the lower plenum and applying the COUPLE code, the results show that the core slumping into the lower plenum and the lower plenum rupture occur at 1750 seconds after the onset of accident, respectively.A nuclear meltdown happens when the reactor's residual power exceeds the heat that can be removed by the cooling systems. The results also demonstrate that the operators have ∼3 h before the fuel rod cladding rupture and ∼2.5 h before the inception of exothermic steam-zirconium reaction.
INSIDE NUCLEAR REACTOR MELTDOWN CODE
Analysis of the scenario by the code shows the production of around 350kg Hydrogen with the maximum rate of about 1kg/s and releasing a large amount of FPs in the order of 10kg.
In the second part the results of Hydrogen production rate, cladding oxide thickness, cladding damage level, release of fission products into the coolant are studied. In the first stage, the study of ECCS and KWU tanks efficiency to keep the reactor core in the safe condition, the calculation of the elapsed time before the reactor core heat up and the estimation of available time for operator’s action to avoid core degradation, are investigated.
INSIDE NUCLEAR REACTOR MELTDOWN PLUS
For each group a corresponding channel is modeled in RELAP5 code plus a bypass channel. Fuel assemblies in the core are grouped into five based on average power peaking factors and are modeled in SCDAP code. The analyses are performed in two stages, before and after the core heat up, without considering operator’s action on the accident management.
In this study, VVER-1000/V446 nuclear reactor modeling using RELAP5/SCDAP3.4 code to investigate the reactor core behavior during severe accident conditions in a LBLOCA scenario along with station-black-out (SBO) is carried out.