Composition of Contamination Layers

Summary

In the framework of the development of decontamination methods, the first studies to be made concern the oxide layers. This paper presents the research carried out in several European countries, on thickness, distribution and characterization of the contaminated layers and penetration depth of each radionuclide.

K.W.Iingen performed studies on composition of contamination layers. These investigations have been performed on samples taken out of the primary circuit of the Lingen reactor (250 MWe BWR shut down in 1977 after nine years of operation).

Activity depth profiles and characteristics of the oxide layers have been determined on the pipe samples:

• after removal of 86 μ m by elecrtrolytic erosion in the primary water pipe samples, the ⁶⁰Co content is equal to the content of the outer part of the pipe;

• the same result is achieved after removal of about 80–90 μm on the condensate pipe.

ENEL CKTN — Milan: developed vigorous decontamination techniques using contaminated samples from the Garigliano reactor (160 MW BWR shut down in 1978 after 15 years of operation. A characterization of the oxide layers (OM, SEM, EMPA) showed the presence of magnetite, nickel ferrite and copper oxide. Radiometric measurement on some specimens of various primary tubing showed surface contamination of about 10⁷ nCi/m² of gamma activity mainly due to ⁶⁰Co and about 10⁴ nCi/m² due to alpha activity.

KRB Gundremmingen studied the development of economic decontamination in the KRB-A nuclar power plant (a 237 MWe BWR shut down in 1977 after 11 years of operation). Even in special areas of very high contamination and frequent damages of the protective paint during plant operation, the penetration did not exceed 7 mm.

CEA/CEN-Cadarache performed studies on metal decontamination by chemical methods. Several experiments have been made with contaminated oxide from electromagnetic filter connected to the primary circuit of the PWR (GAP Cadarache). The best result is obtained with a fluonitric bath after a pre-treatment. The tests mentioned have been carried out on samples from the German BWR ISAR. The specimens have been taken of a non activated ferritic steel component which had been operating for 5 years in the primary cooling circuit. Among the reagents which are available for decontamination, we have chosen sulfuric acid, halogenous and formid acid. An eletrolytic decontamination in two steps (reduction followed by oxidation) is used.

OM: Optical microscopy; SEM: Scanning electron microscopy; EMPA; Electron microprobe analysis.