China
Africa
Explore chapters and articles related to this topic
Response of a Containment Building to a Reactor LOCA
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
During very severe accidents (which occur very infrequently), the core can melt down into a mixture of molten materials called corium. This corium consists of a combination of melted steel, zirconium, uranium dioxide, and other materials and gases. In liquid metal fast breeder reactors (LMFBRs), liquid sodium is also added to this mix. If an accident is severe enough, the temperature of this molten mass will rise above 2,300°C, and the resulting mixture will melt through the bottom of the pressure vessel and empty onto the containment building floor. If this occurs, the corium can react chemically with the concrete and a number of other by-products can be produced. The results of this reaction are depicted in Figure 34.6, and it is commonly called the corium–concrete reaction. The ensuing set of chemical reactions adds another 4% to 5% to the total amount of energy that is produced during an extremely large LOCA.
Direct Containment Heating
Published in J. T. Rogers, Fission Product Transport Processes in Reactor Accidents, 2020
Molten corium, consisting of oxides and unreacted zirconium and stainless steel, accumulates within the lower plenum of a pressure vessel, with the reactor coolant system at “high” pressure. The containment building may initially contain a mixture of air, steam and hydrogen released from the reactor vessel during core degradation. The vessel fails in the region of the molten material and the corium is forcefully ejected as a molten jet through a breach in the vessel wall into the reactor cavity.
Experimental Simulation of Decay Heat of Corium at the Lava-B Test-Bench
Published in Nuclear Technology, 2023
M. K. Bekmuldin, М. K. Skakov, V. V. Baklanov, А. V. Gradoboev, A. S. Akayev, K. O. Toleubekov
However, despite this, the probability of an accident is nonzero, and under certain circumstances, it may occur. The most severe accidents in NPP reactors are accompanied by the melting of the core and the formation of corium, a melt of a radioactive mixture of uranium oxides, zirconium, oxidized steel, and other structural elements. The discharge of corium under certain conditions outside the reactor plant is a feasible scenario, aggravated by the presence of decay heat in corium. The nuclear fuel contained in the composition of corium continues to be a source of heat, generated due to the decay reactions of 235U nuclear fission products accumulated during the operation of the reactor, which allows the melt to remain in a liquid state for a long time and to melt the reactor structure with its subsequent potential discharge up to the ground and groundwater.[1]
Comparison of Triggered Steam Explosion Behavior According to Corium Injection Mode in TROI Facility from TEXAS-V Code Simulations
Published in Nuclear Technology, 2021
Sang Ho Kim, Seong-Wan Hong, Rae-Joon Park
A molten fuel-coolant interaction (FCI) is one such important phenomenon in a core melt accident. Corium is a mixture material consisting of reactor core materials such as UO2, Zr, ZrO2, and Fe. When molten corium falls to the cooling water, the molten corium mixing with the water can cause a steam explosion due to rapid steam generation in a very short time. Steam explosions can occur in a reactor vessel or reactor cavity. The issue of containment failure caused by an in-vessel steam explosion has been resolved with regard to risk1,2; however, an ex-vessel steam explosion that can be caused by reactor vessel breakage also introduces various concerns, including the structural capacity of the containment of occurrence as well as the probability and consequence of occurrence.
Severe Accident Phenomena: A Comparison Among the NuScale SMR, Other Advanced LWR Designs, and Operating LWRs
Published in Nuclear Technology, 2020
Scott J. Weber, Etienne M. Mullin
The ex-vessel challenges following relocation of debris to containment are managed by attempting to cool the molten corium and limiting the containment pressurization. Cooling the molten corium requires coolant that may already be present in the reactor cavity or can be introduced from external sources. A large basemat surface area promoting corium spreading enables the effective cooling of debris by an overlying layer of coolant. However, even with coolant present, localized failure via melt-through can still occur. Pressure suppression generally takes the form of suppression pools, containment sprays, large isolation condensers, or ice condensers. While these can greatly reduce steam partial pressure in the containment atmosphere, they are ineffective at reducing the partial pressure of NCGs. Venting can reduce the total pressure but may require operator action and can increase the off-site radionuclide release. Even considering all these methods of controlling the accident progression, in a highly unlikely accident in which the primary vessel has failed, it is difficult for the currently operating fleet to completely stabilize ex-vessel corium and depressurize containment, and there is a significant risk of corresponding late containment failure.6