Improvement of nuclide leaching resistance of paraffin waste form with low density polyethylene.
Low-level liquid borate wastes have been immobilized with paraffin wax using a concentrate waste drying system (CWDS) in Korean nuclear power plants. The possibility for improving chemical durability of paraffin waste form was suggested in this study. A small amount of low density polyethylene (LDPE) was added to increase the leaching resistance of the existing paraffin waste form. The influence of LDPE on the leaching behavior of waste form was investigated by performing leaching test according to ANSI/ANS-16.1 procedure during 325 days. It was observed that the leaching of nuclides immobilized within paraffin waste form made a marked reduction although little content of LDPE was added to waste form. The acceptance criteria of paraffin waste form associated with leachability index (LI) and compressive strength after the leaching test were fully satisfied with the help of LDPE.
Leaching behavior of boric acid and cobalt from paraffin waste forms
Ninety-day leaching test was performed to investigate the leaching characteristics of paraffin waste forms that had been recently generated in large quantities at Korean nuclear power plants(KNPPs). In the case where mixing weight ratio of boric acid to paraffin was 78/22, which was adopted in concentrate waste drying system(CWDS) of KNPPs, the cumulative fraction leached(CFL) of boric acid and cobalt was about 51% and 61%, respectively. The compressive strengths of waste form before and after the leaching test exhibited 666psi(4.53MPa) and 232psi(1.58MPa), respectively. The CFLs of paraffin waste form were well expressed by diffusion-controlled dissolution model such as Gintsling-Brounshtein kinetics. The internal cross-sectional view of specimen after the test demonstrated the applicability of this unreacted shrinking core model to the leaching analysis of paraffin waste form.
Phase formation during mechanical alloying in the Ti–Si system
Abstract Mechanical alloying of Ti–Si powder mixture or TiH 1.924 –Si powder mixture was performed by high-energy ball milling, in which the Ti to Si mole ratio was 1:2. The phase formations in both mixtures during milling were investigated by X-ray diffraction. Mechanical alloying a mixture of elemental powders led to the formation of TiSi 2 equilibrium compound, while when starting from Si + TiH 1.924 , a metastable phase was formed. The metastable phase completely transforms to TiSi 2 when the mechanically alloyed powder is annealed at temperatures above 800 °C. Two different pathways of phase transitions during mechanical alloying are attributed to the existence of hydrogen atoms, i.e., when starting from Si + TiH 1.924 compared to Si + Ti, the kinetics for the formation of the TiSi 2 intermetallic compound slows down. The kinetics related to the different phase transitions depending on the starting powder mixture are discussed.