Dae-Seok Hong

Development of the Analysis Method for the Radioactivity Concentration Estimation of Soils for a Regulatory Clearance

In this study, for the analysis of a radioactivity concentration of soil, a sampling and an analyzing method were developed. To create homogeneity of the contents for each drum, big particles such as pebbles, rocks and scraps of concrete were removed after pouring the soil into a tray. And then the soil in the tray was mixed thoroughly. A 10 × 10 grid was used to partition the soil into 100 sections. 2 liter of soil was sampled out of 30 randomly pre-selected sections. Only 1 liter of the soil out of 2 liters was used for the γ-spectrometry analysis. The remaining 1 liter of soil was stored for a validation purpose. For a verification of the sampling process, 3 samples were taken from each drum and analyzed. 5 drums were used for the verification. And the results show that this sampling method has about a 9% sampling error. Also, the analysis results of the 865 drums of soil showed that the major nuclides in the soils were Co-60 and Cs-137 while a small amount of Mn-54, Fe-59, I-131, Cs-134 and Eu-152 were detected as γ-emitters. About 73% of the soils had a total radioactivity concentration below 0.1 Bq/g, while the soils with more than 0.4 Bq/g of a radioactivity concentration were only 3%. Based on the guide for the regulatory clearance criteria recommended by the IAEA (International Atomic Energy Agency), about 73% of the soils can be regulatory cleared without any treatment. Also, the remaining soils can be regulatory cleared after a further storage. Only 3% of the soils are considered to be necessary for a decontamination treatment. The results of this study can be applied to the treatment of radioactive soils generated in a large amount during the decommissioning of a nuclear facility.Copyright

Regulatory Clearance of Spent Steel Drums

At KAERI (Korea Atomic Energy Institute), radioactive soil and concrete wastes with extremely low level of activity were regulatory cleared in 2008 and large amount of spent drums remained. After generation, drums having good physical integrity reused for packaging radioactive wastes and about 50 tons of drums unsuitable for reuse were stored as radioactive wastes. Having once been used for packaging regulatory cleared radioactive wastes, these spent drums were determined to be regulatory cleared. Before regulatory clearance, steel drums were radiation monitored, washed with pressurized water two times, compacted and stored at a designated area. Based on radiological dose assessment results using a recycling scenario derived from actual situation, the regulatory clearance of steel drums was permitted by the regulatory body. Treatment of the regulatory cleared drums was then committed to a scrap-metal dealer for recycling. In this study, a process of regulatory clearance for spent steel drums and a modified radiological dose assessment model for staff members of a scrap-metal dealer will be discussed.Copyright

Feasibility Study on the Nuclide Analysis of the Radwaste Drum Using the Spectrum to Dose Conversion Factor

Estimating the radioisotope inventory of a drum based on the measured dose rate information, which is called as the dose to curie (DTC) conversion [1–3], has been known that there could be extremely high uncertainty associated with establishing the radioactivity of gamma emitters in a drum. However, the DTC method is still an effective assay method to calculate the radioisotope inventory because of their simple and easy procedures to be applied. To make the DTC method practical, numerous assumptions have to be made and limitations placed on its use. These assumptions and limitations were related to the dose rate measurement and the relative abundance of gamma emitters in a drum. These two variables were generally obtained from the different detection mechanism. Unfortunately, that expanded the limitation of using the DTC method. The spectrum to dose (STD) conversion factor [4,5] that was calculated from the measure pulse height spectrum of the gamma ray detector could be made obtaining two variables from the drum to be assayed at once. This method could be made estimating the radioisotope inventory of a drum more practical.Copyright

Conditioning Operation by an Encapsulation and Shielding of Spent Sealed Radium Sources

In order to avoid accidents that could result from an improper storage of spent radium sources, it is necessary to condition and store them safely. The program for a safe conditioning of spent radium sources by the IAEA (International Atomic Energy Agency) has been established to assist the developing countries. The main object of this paper is to summarize the technology that was adapted by the IAEA for the conditioning of spent radium sources in the national inventory of Ra-226 sources in member states and the actions performed by the Korean expert team as a part of the IAEA’s project titled as ‘Radium Conditioning in Southeastern Asia’. The whole inventory of the spent radium sources of 8,671.13mCi was safely conditioned by the Korean expert team according to the guidelines under the supervision of the IAEA’s technical officer. The 1,821 sources of spent radium were encapsulated, welded, and conditioned into 18 concrete-shielded drums.Copyright