During core meltdown

On the basis of the results of a larger number of experiments, two different types of tellurium behavior during core meltdown can be distinguished ... 

Some results of these calculations are shown in Tables 7.6. and 7.8. Under the assumption of a static system in which the vaporization takes place, in both PWR and BWR cores the control rod materials are the main contributors to the total mass of aerosols formed during core meltdown, followed by fission product cesium and rubidium (not included in the tables), while vaporized constituents originating from the other structural materials represent only a small fraction. In total, about 1% of the PWR core mass is vaporized (including silver from the control rods) in a BWR, the corresponding value is 1.4% (including the contents of the B4C control rods). If the volatilized materials from the control rods are not considered, the... 

Step 1 obtain a short term core meltdown risk level during mid-loop cold shutdown operation which is comparable to the one existing with a water level up to the vessel mating surface mate ... 

The melting down of the reactor core does not only affect the nuclear fuel, but also the core internals, i. e. the core support structures, control rods, BWR fuel assembly shrouds etc. (see Chapters 1 and 2). At the very high temperatures which are experienced during the meltdown process, radionuclides as well as non-radioac-... 

Some attempts were made to obtain more detailed information on the chemical conditions prevailing inside the reactor pressure vessel during the core meltdown phase, in particular on the redox conditions. Post-accident examinations showed that the oxide layers on the steel structural surfaces consisted exclusively of Fe304, with neither FeO nor FeaOs being detected. From these and other results it was concluded that over long periods of the accident sequence the ratio H2 H2O had been somewhat below 1.0. 

Probabilistic safety analysis has shown that the ultimate beyond design basis accident in the ELENA NTEP does not lead to core meltdown. Radioactivity release in the event of a failure of fuel element claddings and a loss of the primary circuit integrity during routine operation has a very low frequency of occurrence (lO ") personnel and the population in the territory near the plant would not be exposed to hazards in excess of the existing standards. 

K. Bracht, "Orienting Analysis on Core Melt Slump During A Core Meltdown Accident," Gesellschaft fur Reaktorsicherheit (GRS) mbH, GRS-A-490 (NRC Translation 1069), May 1982. 

The safety issues of nuclear energy systems are discussed sometimes from the viewpoint of the inherent and passive safety characteristics of the system. The essential safety question concerning FRs is how to avoid radioactive material release to the environment during meltdown of the core. 

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