Link to the study - European Parliament - Europa

Policy Department D: Budgetary Affairs
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The effect that usually non-radioactive materials become radioactive by neutron-capturing is called
activation. Activated materials are not only radioactive on their surfaces but the whole material that
was exposed to the neutron flux is more or less homogenously radioactive.
Figure 7 illustrates that activation process for cobalt in steel as an example for the many other
activation processes.
Figure 7: Example: the activation of cobalt in steel and subsequent decay of activated cobalt
Source: Authors
A second mechanism that spreads radioactivity to non-radioactive materials in a nuclear reactor is a
contamination process.
During reactor operation certain fission products such as cesium can leave the fuel rods to a certain
extent (e.g. in a gaseous form through micro fissures in the metal enclosure called cladding, during
cladding failure events), dissolve in the cooling liquid and are removed by filtering and ionexchangers.
Irradiated metal surfaces corrode or are mechanically abrased. Both types, fission
products as well as abrased activated particles from surfaces either dissolve or are suspended in the
cooling liquid and are also removed by filters.
As a result the liquid transferring the heat (normally the cooling water) is contaminated with
dissolved radioactive ions and activated particles. All surfaces with which such contaminated cooling
water gets in contact (pipes, valves, heat exchangers, etc.) can adsorb dissolved and suspended
contamination on their surface and so themselves become more and more contaminated. Normally
the contamination remains on the surface or in the outer oxide layer. A deeper penetration can only
take place in materials with a rough surface (e.g. concrete) or when the base material has surface
defects (e.g. on metal surface with scratches).
Figure 8 illustrates that as a simplified example.
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