(A) study on the development and application of models for the activities of long-lived fission products at operating PWR

Abstract

It requires estimating difficult-to-measure (DTM) radionuclides, especially PDTM (particularly DTM) radionuclides such as I-129 and Tc-99, in the waste package generated from nuclear power plants (NPPs) prior to shipment to disposal facility. These radionuclides are critical nuclides for the disposal of low and intermediate level waste because they dominate radiation dose through ground water. Therefore, their activities in each waste package should be accurately identified prior to disposal. However, their activities cannot be analyzed by routine measurement techniques used in NPPs because these PDTM radionuclides are non-gamma emitters. Therefore, instead of direct measurement, scaling factor method is typically used to estimate the quantity of the PDTM radionuclides in the waste package. The scaling factor is empirically derived ratio or correlation between a reference gamma emitting radionuclide, which can be easily measured at NPPs, and the non-gamma emitting radionuclide. The scaling factor is typically derived from a set of waste samples analyzed at commercial laboratories for both gamma and DTM radionuclides. However, in general, the concentrations of PDTM radionuclides in low-level waste are too low to be detected by the conventional measurement techniques i.e., photon counting method. When the lower limit of detection rather than the actually analyzed concentration is used for scaling factor, the determination of the scaling factor value is difficult but also the value generally involves a large uncertainty. In addition, the activity of radionuclide in radioactive wastes can be highly overestimated. Therefore, theoretical approaches have been proposed as a means of estimating activity or scaling factor for PDTM radionuclides, especially $^129I$. Also, evaluations of the $^129I$ inventory are generally based on the release of related fission products from the source term such as defective fuel and tramp uranium. However, in these approaches, the ratio ...