The overestimation and underestimation of the radioactivity concentration of difficult-to-measure radionuclides can occur during the implementation of the scaling factor (SF) method because of the uncertainties associated with sampling, radiochemical analysis, and application of SFs. Strict regulations ensure that the SF method as an indirect method does not underestimate the radioactivity of nuclear wastes; however, there are no clear regulatory guidelines regarding the overestimation. This has been leading to the misuse of the SF methodology by stakeholders such as waste disposal licensees and regulatory bodies. Previous studies have reported instances of overestimation in statistical implementation of the SF methodology. The analysis of the two most popular linear models of the SF methodology showed that severe overestimation may occur and radioactivity concentration data must be dealt with care. Since one major source of overestimation is the use of minimum detectable activity (MDA) values as true activity values, a comparative study of instrumental techniques that could reduce the MDAs was also conducted. Thermal ionization mass spectrometry was recommended as a suitable candidate for the trace level analysis of long-lived beta-emitters such as iodine-129. Additionally, the current status of the United States and Korea was reviewed from the perspective of overestimation.

1. Introduction
2. Statistical Models for the Determinationof SF
3. Overestimation of SF in a Simple LinearModel: y = ɑx
4. Overestimation of SF in a Simple LinearRegression Analysis: y = ax + b + ϵ
5. Current Status of the United States andKorea From the Perspective of Overestimationof Radioactivity Concentrationin SF Methodology
6. Overestimation-Preventable InstrumentalTechniques for Trace Level Detection
7. Conclusions
REFERENCES

• Junghwan Park(Korea Atomic Energy Research Institute/Korea Advanced Institute of Science and Technology)
• Tae-Hyeong Kim(Korea Atomic Energy Research Institute)
• Jeongmook Lee(Korea Atomic Energy Research Institute/University of Science & Technology)
• Junhyuck Kim(Korea Atomic Energy Research Institute)
• Jong-Yun Kim(Korea Atomic Energy Research Institute/University of Science & Technology) Corresponding Author
• Sang Ho Lim(Korea Atomic Energy Research Institute/University of Science & Technology) Corresponding Author