Radionuclides from core components and structural materials

2 Radionuclides from core components and structural materials 

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- 

Material/ Element Mass (kg) Percent vaporized Condensing form Mass vaporized (kg) 

The materials present inside the reactor pressure vessel and, in particular, their masses depend highly on the type of plant and its particular design. The numbers given in Tables 7.6, 7.7., and 7.9., therefore, are only examples to give an idea of the materials and elements to be considered in this context. 

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 

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