Activation of structural and coolant materials

The build-up of strong gamma emitters within the coolant circuit and on reactor components causes maintenance problems. One source of gamma activity in the coolant arises from the decay of Co-58 and Co-60. These are reaction products which result from trace quantities of cobalt and nickel which are dissolved into the coolant from components in the primary coolant circuit, activated in the core and then plated out in various parts of the circuit, 

Helium embrittlement is another structural material damage mechanism. Helium is produced in (n,a ) reactions. Trace quantities of boron and nitrogen in structural materials can make a significant contribution to the helium production. Consideration must also be given to (n,a) reactions in isotopes which are formed as a consequence of irradiation for example Ni-58 (n,y) Ni-59 (n,a) 

Integral measurements of (n,a ) reactions in structural materials have been made by irradiating samples in power reactors and measuring the helium produced. Uncertainties in the amounts of trace quantities of elements such as boron and nitrogen can introduce large 

The types of dosimetry reaction can be divided into fission and non-fission, threshold and non-threshold. The choice of the set of reactions to be used for a particular plication depends on the intensity of the flux, the duration of the irradiation, the type of reactor spectrum (thermal reactor, fast reactor, core, shielding, vessel) and the neutron energy range of importance in the effect being monitored. 

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