Comprehensive study of uranium, transuranium and fission products accumulation on stainless steel surfaces II. Sorption studies in dynamic model system

As a result of the breakdown on April 10, 2003 there was a significant contamination by uranium and transuranium (Pu, Am, Cm) nuclides in some technological units (such as reactor pit No. 1, fuel-transfer pond) of the reactor block 2 of the Paks Nuclear Power Plant (PNPP). It is of special importance to know the contamination processes (adsorption-desorption) of uranium and transuranium (TRU) nuclides during the release of the damaged fuel assemblies. In the reactor pit No.1 uranium and TRU nuclides can be present in different chemical forms (molecular, colloidal and/or disperse) in the boric acid coolant. A reliable evaluation of the extent and kinetic of the above contamination phenomena on the constructional materials used in the fuel-transfer pond seemed to be fundamental to perform the safe release work of the damaged fuel, started in October 2006. However, there were only limited pieces of information about the extent, chemical forms and kinetic behaviors of the uranium and transuranium species accumulated on the surface of the main structural materials (stainless steels). Within the frame of a joint project four domestic institutes have been cooperated in order to study the accumulation of uranium and transuranium (Pu, Am, Cm) species of construction materials (such as heat exchanger tube samples and stainless steel can material). The experiments were carried out in a dynamic model system. During the sorption experiments, boric acid coolants provided by the PNPP from pit No.1 of reactor block No.2 were circulated for a period of 30 hours at linear flow rate of 9 m/h. Solution and tube samples obtained in the course of above studies were analyzed by independent (alpha- and gamma-spectrometry, ICP-MS, SEM-EDX, voltammetry and XPS) methods. In the first article our two part paper by the virtue of literary data we gave a view of the main parameters influencing the extent and character of the surface contamination by uranium and transuranium products. In the present (2(nd)) paper we review the contamination-decontamination experiments, carried out on two types of steel sample, as welt as summarize and interpret the measured surface analytical, solution chemical and radiochemical results. During our work we studied the accumulation of uranium and transuranium (Pu, Cm) as well as fission products (Cs) on two types of construction material materials (such as heat exchanger tube samples and stainless steel can material). The experiments were carried out in a dynamic model system. During the sorption experiments, boric acid coolants provided by the PNPP from pit No.1 of reactor block No.2 were circulated for a period of 30 hours at linear flow rate of 9 m/h. Solution and tube samples obtained in the course of above studies were analyzed by independent (alpha- and gamma-spectrometry, ICP-MS, SEM-EDX, voltammetry and XPS) methods.