A Study on Isotopic Scaling Factor Effect with Different Power Histories for Radioactive Waste Storage Drum

Scaling factor has been widely used to quantify difficultly measuring (DTM) radioactive isotopes by using the key (KEY) isotopes which are relatively easily measured such as Co-60, Cs-137, and Ce-144. Still there are lots of uncertainties in scaling factors due to different packaging conditions and chemical waste treatments. Above all, assumed power irradiations of fission products result in significant uncertainties. Cycle-wise calculations are carried out. The assumed cycle-dependent power histories are based on a typical Westinghouse type PWR. In order to apply radioactive waste drum, main isotopes are taken into consideration including activation products(Co-58, Co-60, Fe-55, Nb-94, Ni-59, Ni-63), fission products(H-3, C-14, I-129, Ce-144, Sr- 90, Tc-99, Cs-137), and actinides which emit alpha particles. It is found out that significant change in power histories gives an effect on the scaling factors for a couple of isotopes such as Ce-144, Co-58, and Fe-55. In case of Ce-144, about 8% increases in scaling factors for both key isotopes such as Co-60 and Cs-137. From the results of this study, it is important to follow reactor-wise irradiation histories for estimation scaling factors. Thus, it is also recommended this effect may be included as an uncertainty of scaling factors.