Investigation of various crud particles originated from NPP Paks, Hungary

Morphology, elemental composition and radioactivity of solid particles - aggregates of crud originated from NPP Paks were studied by micro- and radioanalytical methods. Solid particles were taken: 1) from the primary coolant during transient operational conditions (reactor shutdown); 2) from the coolant contaminated by fuel debris due to the incident happened at the cleaning tank in April 2003; 3) particles collected from the fuel element surfaces and 4) from some steam generator tubes. Crud particles - aggregates from the primary coolant and from the incidentally contaminated water were studied by autoradiography, SEM - EDX and by alpha spectrometry. Based on the measured transuranium ratios, the burn up of these particles was estimated. Examination of particles originated from the incidentally damaged fuel has shown that particles with high burn up originated from the 'rim' layer were released, too. Application of SEM -EDX methods on corrosion particles taken from the primary coolant and from some steam generator tubes makes it possible to compare them and to find the possible origin of the corrosion particles in the primary coolant - the cleaning of the steam generator tubes performed earlier. By determination of the specific activities of long-lived corrosion products using beta and gamma spectrometry and ICP-MS technique, the residence times of them were estimated. According to these data, the studied particles could be grouped into two classes: 1) particles residing in the zone for longer period and taken by the primary coolant; 2) particles activated in the zone only for shorter period and then deposited on the steam generator tubes. (Author)